A Few Thoughts on the Decarbonisation of Construction in Portugal

Decarbonization is a new buzzword. It seems like it is replacing sustainability, a very ample, anthropocentric concept*, coined in 1987. Global and European policies are looking to ‘lower greenhouse gas (GHG) emissions’ by 2030 and 2050 [1]. The ongoing COP26 in Glasgow was the best confirmation. We have seen big words and declarations, many times. In recent history, we have seen multiple events [img 01]. Probably the most influential one was the Roman Club Report in 1972 that clearly indicated the Limits of Growth. Many have heard about the Kyoto Protocol signed in 1997, a treaty that aimed to lower (!) GHG emissions. At the COP26 António Guterres, Secretary-General of the United Nations and former Portuguese Prime Minister, is urging to change the business as usual. Can we decarbonize the Portuguese building stock? How to do that?

*Its definition is focused on human wellbeing and future. As per Our Common Future, sustainable development meets the needs of the present without compromising the ability of future generations to meet their own needs.

Image 01. GHG emission and environmental events

But first, a small disclaimer. greenhouse gas emissions are not the only aspect of the actual crisis. We have only started to work with the most tangible aspect of the planetary crisis. Stockholm Resilience Center has clearly shown the complexity of the crisis and the domains we are crossing. [Image 02]. Climate change, which is closely related to GHG emissions, impacts the other limits, but as we can see in the diagram [Image 01], it is not the most urgent. Biogeochemical flows (pathways by which elements like carbon, phosphorus or compounds like water, flow in the environment) and biodiversity loss are two domains that are beyond the zone safe zone. If they cross the point of no return, we should expect disequilibrium of the system and unknown activities in other domains. Biodiversity loss is connected to the territory we occupy. It is an exponential relation: the level of biodiversity increases exponentially with the surface area of uninterrupted, natural land [1].

That is why we prioritise working within already-occupied areas, especially here in Portugal, where 97% of building stock requires renovation [3], the population rate is virtually not growing [4] (do we need more houses for fewer people?) and centres of major cities are low-populated [5]. Also, denser walkable centres mean less carbon emitted during everyday commuting. Most of the relations between planetary domains are beyond the scope of an engineer, we can only act within our professional responsibilities. Everything is connected.

Image 02. Planetary Boundaries, Stockholm Resilience Center

Decarbonization is a very demanding aspect. We at Dosta Tec are researching and prototyping solutions. We have been meeting industry champions and talking with Portuguese companies, and public authorities to understand what their approach is. Many questions popped up: How to lower the energy intensity of housing when we experience energy poverty? How to renovate for thermal comfort, low-energy consumption and simple maintenance? What kind of low-carbon materials can be used for insulation? Do we have them available in Portugal? Is hemp insulation brought from the Czech Republic still sustainable? Can we replace concrete with cross-laminated timber (CLT)? How will climate change influence thermal comfort and heating needs?

Since the EU imposed ESG (Environmental, Social and Government) certification for large companies, they have been asking for services of minimizing energy intensity, carbon emission, and renewables. Will policies help the transition? Are we not going to stack in carbon tunnel vision [image 03]? Well, this is another trap. Certification systems can help but many of them (like LEED or BREEAM) validate only the project. What if the operation of the building doesn’t reflect the project? Some studies [6] have shown that LEED-certified buildings do not outperform conventional ones.

Image 03. Carbon Tunnel Vision, Jan Konietzko

As engineers, we are trapped between “weak sustainability” and “strong sustainability”. Two handy terms were coined by Robert Solow and John Hartwick [7]. The first is focused on the technical solution and the second on policy-making; the first one is human-centred and the second is bio-centred, the first is business as usual the other is to innovate.  As an engineering and technology company working in the field of architecture and construction, we are answering the clients’ and market’s needs, looking to be at the forefront of changes, trying to push from weak sustainability to strong. It might seem that weak sustainability is inferior to strong. Indeed it is, but it is also complementary, as it gives actual solutions that can be implemented almost immediately, and its prototypes and verifies regulations. Many of them have been already checked on the market and require further work.  

The big issue is: how to decarbonize? In Portugal, we need local and verified knowledge, data, qualified policy-makers, clerks, engineers and architects, construction companies, a whole new collection of materials to replace concrete, steel and glass, and procurement schemes that favour low-carbon design. The challenge seems to be enormous and it might bring innovation and an exciting working environment for the next decade.

Adrian Krezlik


[1] https://www.europarl.europa.eu/legislative-train/theme-a-european-green-deal/package-fit-for-55

[2] Wilson E. O., Half-Earth: Our Planet’s Fight for Life. Liveright, 2016. 

[3] Buildings Performance Institute Europe, 2017, Energy Performance Certificate Factsheet

[4] INE 2020

[5] Almeida M. A. P. de, “Fighting depopulation in Portugal: Local and central government policies in times of crisis,” Portuguese Journal of Social Science, vol. 17, no. 3, (Sep. 2018), pp. 289–309. 

[6] Scofield J. H., “Efficacy of LEED-certification in reducing energy consumption and greenhouse gas emission for large New York City office buildings,” Energy and Buildings, vol. 67, (Dec. 2013), pp. 517–524. https://doi.org/10.1016/j.enbuild.2013.08.032

Buildings & Renewable Energy Sources

There has been much talk going on in the past decades about decarbonisation of the economy. And as if that wasn’t a big enough problem to tackle, this year brought about an energy crisis. Electricity prices are soaring in Europe. In the Iberian market, the price for 1MWh has reached its second highest historical value. Both these issues mean that energy is not a future problem, but it already exists, alive and kicking.

This doesn’t necessarily mean that we will or should stop all our activities as we know them. It requires a combination of evolving our production processes towards restorative and regenerative methods and limiting, compensating and finally eliminating those activities that are economically or environmentally unfeasible.  Evolving our processes is a practice tightly related to Renewable Energy Sources (RES). Why? Because most activities are not bad for the environment on their own, but the energy they use up is. The emissions related to these energy sources are known as “indirect emissions”. For example, burning coal at home releases CO2 directly, but using an electric heater in a town with a coal power plant creates indirect emissions.

Buildings come into the picture because they provide us with space and infrastructure to replace dirty energy with RES and cut down both direct and indirect greenhouse gas emissions. Doing it at across the built environment  is good for many reasons: 

(a) we can implement quicker domestically than a big, clean energy power plant can be built, 

(b) we help reduce high-voltage electric transmission losses (which may reach at almost 3% in Europe), and

(c) we feel good as we’re in direct contact with our contribution to climate change mitigation, as well as saving money. 

In Portugal, distributed generation of electricity (at home and in industrial buildings) accounts for around 1% of all electricity. This may seem low, but it’s growing very, very fast: in only six years, installed distributed generation capacity has grown by 400%. And it’s already a great choice for saving money.

The first image that comes to mind when thinking about production of heat or electricity is usually a black solar panel on the roof. Solar photovoltaic generation is an excellent choice when thinking about self-managing our energy at home, whether we include a battery bank or not. Even if some parts of the panels’ life cycle have a negative impact on the environment, it remains as a regenerative option. But it’s not the only clean option. We can separate the main domestic RES in the following way:

  • Electricity Production
    • Photovoltaic Cells (PV)
    • Wind Turbine
  • Ambient Heating
    • Biomass & Biogas
    • Passive Solar heating
  • Domestic Hot water Heating
    • Solar Thermal heating
    • Biomass & Biogas
    • Geothermal

Of course, there are more options such as mini-hydroelectric. But let’s stick to the common ones.

We’ve talked about PV. What about wind energy at home? Even if the idea of having a turbine on our roof seems like a disruptive choice, it’s not a very good one. Yes, it’s renewable energy and yes, it’s technically feasible. However, the amount of electricity it provides is extremely low, and producing small turbines has a relatively negative impact on the environment. To quantify: a practical study showed that a small, commercially available wind turbine that can be installed on a rooftop can produce up to 10W of electricity in approximately 3m2[1]. In that same area, a PV panel can generate five times as much. Built-up urban areas can’t really implement this technology in an isolated way, but it may be added to complement a PV system in an area with consistent wind.  Keep in mind, the saying among LCA engineers goes “the bigger the turbine, the greener the electricity”. 

Biomass is slightly more complex. On one hand, the combustion process releases a significant amount of CO2 into the atmosphere. For example, burning wood, which accounts for 18,4% of residential energy use in Portugal, normally releases more of this greenhouse gas than burning coal does, which is surprising to many. However, in terms of climate change mitigation it is considered a clean energy source, as the whole life cycle of the fuel (tree to log to fireplace/furnace) involves a huge amount of carbon capture, which compensates for most of the released carbon at the end of the log’s life. But there are two other issues with this fuel. Firstly, the energy source is not strictly clean: domestic wood burning produces soot, which is very harmful to human health, even if the smoke itself is not a greenhouse gas. Fireplaces and wood stoves may be quaint, but they’re not the best choice when thinking of daily use and overall dependency. Secondly, the proven “net-zero” effect mentioned above is very real, but it has a time lag. Again, it is related to life cycle analysis. Burning a log may be compensated by the growth of a new tree, but studies show this “carbon payback time” ranges between 44 and 104 years after cutting down![2] Other examples of biomass energy sources include agricultural waste and processed wood pellets.

What are the variables to consider when thinking about designing a building that generates electricity and/or heat? Firstly, I should point out that this doesn’t mean isolating from the grid, although it’s possible to do so. “Going solo” is sometimes feasible, but it requires specific conditions and quite some effort. The smarter choice is usually generating a part of electricity or heat, while staying grid-connected. The European grid has adapted to enable houses to conveniently plug into the grid. For example, it’s usually possible to inject excess generated electricity in hours of the day when it is not being used. And you get paid for it.

But coming back to what should be analysed by a building owner or facility manager who wants to access distributed energy resources. The main variables to be considered (I’ve placed examples in the form of questions):

  • Space and building geometry: do the PV panels fit on the roof? Is there room for a solar heating system? 
  • Infrastructure: do existing installations allow for biogas to flow? Is there appropriate ventilation?
  • Cost: is the investment affordable? Can it be financed? Will the utilities pay for excess energy?
  • Site: is the resource available at the site/region? Will constant snow block my PV panels? Is there geothermal energy underground? (the IPCC has a very robust publication on the feasibility of each technology by region [3])
  • Metering: will the energy be measured, for economic and environmental reasons? What metering system will I use?

The variables and questions should spark thought in both the engineers dealing with the installation and the building or house owners that want it. For instance, if we’d like to maximise PV generation in a building, we don’t have to stop at the available space on the roof. We can consider Building Integrated Photovoltaic (BIPV) panels. These are placed on the façade and integrated seamlessly into the structure. Some suppliers even provide choices in colours and shapes, to fit aesthetically into our building. The technology is economically feasible, and available in Europe at average costs of around €450/m2 for facade tiles and €350/m2 for the roof. Compare this to brick ceramic tiles cost at 240€/m2 or roof slates at 130€/m2, add in the electricity generated during the lifetime, and you’ll understand why it’s a great investment, virtually anywhere in Europe [4]. If we’re doing the effort of managing our energy, why not be bold?

Facade of the Copenhagen International School and detail of its blue-green Building-Integrated Photovoltaic (BIPV) panels

 At Dosta Tec, we apply digital tools to model as many RES as we possibly can. The more the alternatives, the more the chances of finding an energy-positive combination. Building energy use has been modelled for some time now, but the combination of these models with simulated heat and electricity generation is a different level of complexity. We love challenges, which is why we explore new technology whenever we possibly can.

Mateo Barbero



[1] “Design of a micro wind turbine and its economic feasibility study for residential power generation in built-up areas”, Loganthan et al. (2019)

[2] “Does replacing coal with wood lower CO2 emissions? Dynamic lifecycle analysis of wood bioenergy.”, Sterman et al. (2018)

[3] “Residential and Commercial Buildings”, IPCC Report, Chapter 6, page 407 (2021)

[4] “Economic analysis of BIPV systems as a building envelope material for building skins in Europe”, Gholami et al. (2020)

Carbon Budget

According to the new policies of the European Union, all the industries will cut their emissions by at least 55% until 2030 and become almost carbon neutral until 2050. Decarbonization is one of the most important goals of the EU and a tool to combat the climate crisis. For several years there has been a discussion on carbon outsourcing [1]

and it comes back when we want to talk about the carbon budget and a building’s carbon budget. The carbon budget is a term that connects anthropogenic GHG emission reduction with the temperature rise. It limits plans ahead, giving a maximal threshold for GHG emissions. It could be called the total carbon budget too, when referred to the sum of emission of all activities or industries. I am introducing here the term Buildings Carbon Budget (BCB), a chunk of the total carbon budget that is related to Architecture, Engineering and Construction. 

The BCB quantifies all carbon used by the industry, starting from sourcing and manufacturing, through design and construction, operation until demolition. Herewith I am going to focus on the whole life cycle of a building, which includes embodied carbon. And this is a game changer from the point of view of carbon outsourcing. It pushes the construction companies to verify products of their suppliers and manufacturers, to review their production technology, use of energy, transport and more. The BCB may seem to be very similar to the Life Cycle Assessment. And in fact it is based on the LCA, although in contrast to the LCA that assesses and measures impact to compare with other solutions, BCB estimates expenditure for a set period of time, establishes thresholds and looks for minimization of CO2 involved in the project. Similarly to cost budgeting known from economics, it could use the same repertoire of tools: incremental budgeting, budget planning, cutting, carbon flow. I will use the LCA as a starting point and therefore I need to explain it in detail. 

The method to estimate environmental impact of a building we have been following at Dosta Tec so far is described in the ISO norm 14040. It is divided in four parts [fig. 01]: (A) Production and Construction, (B) Operation, (C) End of Life, and (D) Beyond the Building. Different activities are divided into embodied impact and operation impact, and finally, materials can be divided in three groups: cradle-to-gate, cradle-to-grave, and cradle-to-cradle. Let me explain all the components and groups so that the process is as transparent as possible.

Stage A: Production and Construction, embraces all the activities needed for a building to be built. Material sourcing which could be a process that releases a big amount of CO2 if metal ores are

used and the process of getting a pure metal is carbon-expensive; large glazed (flat or curved) surfaces require not only significant amounts of fuel to be produced but also often transport from specialized glass factories. Sometimes thanks to very efficient manufacturing processes, and we are not discussing here the social aspect of that – so-called Social Life Cycle Assessment (S-LCA), in China the production carbon footprint is low, but the question of where does the material come from and how is it transported to the construction site needs to be asked. Sometimes it happens that after burdening a low-carbon product from China with high-carbon transport cost it has still lower embodied-carbon than a local product. 

Stage B is related to the operation of a building, it is related to energy and resources needed for the correct functioning of a building. For example, in commercial buildings in this stage, an important role is played by the facility manager and building integrated systems that monitor the needs of the occupants and can adjust the building’s performance according to their needs. I would like to emphasize that stages A and B are strictly related and it is highly advised that a representative of future occupants participates in the design stage. It helps the design team to make decisions based on the actual needs, and later to pass the information on the best use of the buildings to the future occupants. Today it happens more and more often with BIM 6 level.

Stage C happens when the buildings stop responding to the occupants or market needs, and cannot be reconstructed or renovated more. It is deconstruction and waste processing. This stage seems to be quite outdated since it uses the terms like a waste. Although taking into consideration that most of the buildings in Europe are 30 years or older I recognize that the ideas of circular construction were not introduced yet and many building’s components cannot be recycled or we don’t know how to recycle them.

Finally, Stage D is related to a building afterlife. All the parts of the building are looking for use in another building or to be recycled. Here the topic of Building as Material Banks appears. At all the stages we can set up a yearly or total carbon budget as we set a financial budget. All the activities’ emissions can be measured across their lifecycle. The stages can also be thought of in three groups: cradle-to-gate,  cradle-to-grave, and cradle-to-cradle. The first assesses only the sourcing and production process (i.e. half of Stage A), it is the most common in Environmental Product Declarations (EPD) and is a good tool to compare how the product is manufactured but does not measure the afterlife of the product. If a product is biodegradable it is a great attitude. But typically it gives a false impression while comparing insulation materials such as hemp fibre and XPS. In the cradle-to-gate approach, they might have the same environmental impact, or maybe even XPS has a lower environmental impact, but it does not assess the impact after the afterlife of the product. How many resources are needed to process it or decompose it? Cradle-to-grave (i.e. Stages A to C) assesses the impact of a material that would be processed and disposed of, it means that it will not become a part or raw material for the next cycle of the material nor nutrient. Finally, cradle-to-cradle (i.e. all four stages) defines all the materials that would stay in a closed loop of use. There is no need for sourcing after recovery and recycling. Although it does not mean that there is no carbon footprint in manufacturing or sourcing. It is also important to verify where it is recycled and recovered. Unfortunately, at the present time, the information is not transparent and confirmed yet.

The Buildings Carbon Budget is a measure that helps to meet with the decarbonization of the industry. No doubt it is a difficult task. It is about planning, measuring and integrating all the parties involved in the building lifecycle. Making it a sum of all the activities engages everyone and at the same time helps to avoid a situation when carbon is being outsourced to another stage of a building. By making it a total measure we ensure that every stage and all the parties involved are compromised to stay within carbon limits. The first challenge is to establish actual thresholds for build typologies and locations. In Dosta Tec we are building our internal database when simulating building performance, and embodied energy and carbon to be able to establish a carbon budget for our next projects.

Adrian Krężlik

[1] It is an effect of moving factories and production from Europe to Asia and other places. Companies and factories located in Europe are obliged to meet certain standards, including CO2 emission. Their subcontractors, producing parts, are often located in areas where standards are not high. 

Modelling the effect of windows size


Window position, size, and type are variables that affect both visual and thermal comfort. Typically, for better thermal comfort we look to minimize fenestration rate (area of windows on the facade). That is, reduce the size of windows (thermal transmittance is lower for walls, for example, 25 cm brickwall + 5 cm of insulation is about 0.5 W/m2K while double glazed windows can be 1.5 W/m2K). To achieve good visual comfort, multiple factors are taken into consideration: typically we look for large windows (to achieve a high level of daylight availability through the year and to have a connection to the outdoors – well, who doesn’t love having a view) and controllable shadings to prevent glare [1]. Also, operable windows allow a user to control indoor temperature, change air when needed, and connect to the exterior weather conditions. As seen, there are multiple reasons to have large and small windows. Is there an ultimate best size for the windows, their position, and type? No. We are not looking for that. Although we wanted to learn about relations between the size of windows, energy consumption and daylight conditions for the Lisbon Metropolitan Zone. 

Model setup

As with any scientific study that focuses on simulation, we built a virtual model. Such a virtual model of a building is a 3D design that looks to represent typical characteristics of a building typology in a selected region. In our case, it is a detached house in the rather rural part of the metropolitan zone (it means there is no shade cast by neighbouring buildings, and that the urban island effect modifies the site’s climate data to list the most important reasons). The roof ridge is oriented south-north. Windows can be located on all facades, depending on the visual and thermal needs. The house was divided into four rooms, occupying the south, north, east, and west part and each room has only windows belonging to one of the exterior walls.  It essentially means that to comply with visual comfort standards, the fenestration rate for each zone needs to be higher than 0.  Fenestration rate might be a confusing characteristic, it essentially means how much of the facade is transparent. It excludes grills, frames, aprons, etc.The smallest fenestration rate was 30% and the highest 90%, also no shadings for the windows were provided. 


We ran 276 options for different window configurations to check which one is the best from the point of view of daylight and energy. It turned out that the relation between the average fenestration rate and the total energy consumption is linear: with a higher fenestration rate comes higher energy consumption.


Another step was to compare some of the 276 solutions:

A, all the facades have the fenestration rate equal to 30%

B, the north facade has the fenestration rate equal to 60%, other facades 30%

C, all the facades have the fenestration rate equal to 60%

D, all the facades have the fenestration rate equal to 90%

According to the European Norm EN 17037, a view outdoors to a landscape and clearance of a minimum of 6 meters is required. The norm specifies the size of the smallest window for 1.00×1.25 m. 

Option A is also the least energy-consuming, while option D is the most energy-consuming. 

First off in Lisbon daylight availability does not seem to be a problem. For a well designed, not very deep interior, there is always enough light regardless of the size of the windows [2]. Just have a look at Fig.02, made for a different study but it clearly illustrates the problems, for a test room with a 45% fenestration rate facing east. Rooms as deep as nine meters will receive enough light for everyday activities and a depth of seven meters or less would be good for work. 

Fig 02. Top view of a room

The problem is rather the overexposure, as strategies A and B illustrate quite well. When looking at the energy consumption, option D requires 60% more than option A to maintain occupant comfort. Overglazing the facade in Portugal does not elevate visual comfort nor thermal comfort. For all the typologies the facade should be solid with carefully studied windows equipped with shading.



The following study shows that minimization of window size in Portuguese vernacular and contemporary architecture (look at the projects of Souto de Moura or Aires Mateus) is a characteristic that aligns with daylight availability and thermal comfort. It is important to mention and emphasize that view to the outside provides a visual connection with the surroundings, it supplies residents withinformation about the local environment, weather changes and the time of day. Lack of this information can relieve the fatigue associated with long periods of being indoors.

In Scandinavia the lack of light is omnipresent in architectural design, they have been designing to capture as much daylight as possible. Large windows are not a problem anymore since they can be very energy efficient. The tradeoff between the amount of daylight and thermal performance was a topic. Now it is time to tackle this problem in the south when daylight conditions need to negotiate with thermal comfort in another context. 

Adrian Krężlik


Continue reading “Modelling the effect of windows size”

Cost-Effectiveness: Getting the Most out of Building Renovation

Lately, there’s been much talk of climate change and climate policy. Even though it’s been in the news and in our conversations since at least 1988, two events have arguably sparked more discussions than ever in the past months: the recent IPCC report (officially called the Sixth Assessment of the Intergovernmental Panel on Climate Change) and the European Union’s Recovery Plan.The first is the output of all the work that the world’s leading climate scientists (under the umbrella of the United Nations) put into studying the current and future situations, and through it they have confirmed what many feared: we are far from the emissions reductions goals that are needed to avoid widespread disasters. The latter is the EU’s plan to restart the economy after the crisis induced by the pandemic and take it through a restorative path, assigning resources for decarbonisation measures in virtually every sector. Each EU country will take  the funding and funnel it into their national budget. It represents the action we need to change the course of our carbon-based economy. As we discussed in our last article, Portugal is chipping in through the Plano de Recuperação e Resiliência.

Within these policies, there is a concept that is growing in importance in building renovation: cost-effectiveness. At a general level, it represents the relationship between how expensive a renovation measure is and how good it is at increasing energy efficiency. In other words: for every euro put into a renovation, how much energy saving will it provide. Think of it as return on investment (ROI) for a specific measure. Cost-optimality is achieved when the selected renovation measure maximises the ROI.

Through the Energy Performance of Buildings Directive (EPBD), the EU requires countries to not only take energy efficiency measures in their building stocks, but also 

set cost-optimal minimum energy performance requirements for new buildings, for existing buildings undergoing major renovation, and for the replacement or retrofit of building elements like heating and cooling systems, roofs and walls”.

 In short, it restricts the measures that may be taken to increase energy efficiency for a good cause. It ensures that the money and effort put into the national renovation plans is invested smartly. The methodology that must be used to reach this cost-optimal level is standardised and described in detail, but I’ll keep it a bit simpler in this article for the sake of being practical.

But enough with high-level policy stuff. What are the implications of all this in individual decision-making? When faced with the need to renovate, you will probably (definitely) want to get the most out of your money, even if you already know that the value of your property will certainly rise if it’s more energy-efficient.  At Dosta Tec we have the expertise for providing alternatives for building renovation, and this is how it goes in terms of cost-effectiveness: we look at the performance of some possible (and reasonable) measures that can be taken, scattered across a “investment vs. energy cost” graph, and from it read the cost-effectiveness of each option. Note that the “return” part of our ROI represents the savings in energy use that we enjoy when increasing our house or building’s energy efficiency. The graph below shows an example of this, where we produced 216 alternatives for insulating a house in Lisbon, with different combinations of materials, thickness, and design. The point at the top-left is the “baseline” case in which no renovation is done.

Energy cost during 50 years for each of the 216 alternatives

If we look at two points with the same amount of investment, the point that is lower in the graph represents a more cost-effective solution, since we are getting a larger benefit with the same amount of money. But to avoid drowning in data, we can look at specific clusters of alternatives. For instance, we may want to only see how a specific material performs. The graph below shows Extruded Polystyrene foam (XPS) wall insulation, a popular wall-insulating material. And the graph after that one shows how organic hemp insulation performs under the same conditions.

Three alternatives for extruded polystyrene wall insulation
One alternative for hemp wall insulation

The trendline and its formula are not just us being nerds, they are essential: the steeper the line, the more cost-effective a material is. See how the hemp curve is much steeper? This is because this material provides more savings for each euro spent. However, it also has only one graph point: sometimes there are not many available alternatives to choose from for a specific material. So, in this case, choosing hemp is more cost-effective, but XPS provides more options. Experience has shown us that this wiggle room is valuable, since this digital model represents a real-life renovation project, and in real life we can’t always optimise as we’d like to. It’s important for me to note here that we are now focusing on cost-effectiveness, but real renovation projects may bring things like the life-cycle environmental impact of materials into the decision-making. In this case, XPS has significant global warming potential, while hemp’s is negative (it’s regenerative!).

So which is the cost-optimal alternative? Here is where the EPBD adapts its methodology to the real world. EU member states submitted their detailed studies on cost-optimality for building performance measures in 2015 (both cost and energy use vary greatly across countries). They accepted that “many member states find a cost-optimal range of measures by combining the building envelope and the technical systems rather than an individual optimal point.” This was expected. A single, maximum, isolated point representing the best technology and materials sounds and looks great, but we don’t need a team of engineers to tell us that it might not be always feasible. Cost-optimality is something to strive for, but rarely achieved. This is not negative – on the contrary, it’s a great way of guiding our choices.

Cost-optimality is also strongly affected by tax policy, which as in any area of the economy, affects costs and thus cash flows and payback times. For example, all insulation materials have the same VAT value in Portugal, but this could change in the near future. Looking at all the activities around the New European Bauhaus we can observe a significant interest in biomaterials.

Decision-making in building performance is a complex process as there are multiple variables to optimise for. Cost-efficiency, indoor thermal comfort, environmental impact – they all play a role in the trade-off game that is a renovation project. We all want to invest smartly, have a positive impact on the environment, and live well. The more we understand each concept, the easier it becomes to make the right decisions and join the path towards regenerating the environment.

Mateo Barbero


Recovery and Resilience Plan

The pandemic of COVID-19 has changed the European economy. For several months some of the industries were frozen, many had to shift their business model and offer new services, and digitalization became a fact – not a future plan. As a response to the economic crisis, the European Commission decided to launch ‘the largest stimulus package ever’ – NextGenerationEU. This is not only a recovery plan, but an attempt to transform the economy into digital and green. Each Member State was responsible for preparing a national plan to allocate funds and create a bright scenario for the European Community. In Portugal, it is called the Recovery and Resilience Plan (Plano de Recuperação e Resiliência) and operates an outstanding budget of 16 644 million euros. It is developed in three axes: Resilience, Climatic Transition and Digital Transition. Two out of twenty components are related directly to construction: Housing and Energy Efficiency in Buildings [1]. In this article, I will focus on the domain in which Dosta Tec has the biggest expertise: energy efficiency.

The component Energy Efficiency in Buildings looks to promote decarbonization in the residential sector, favouring urban rehabilitation and increased energy efficiency in buildings, promoting progressive electrification of the sector and the use of more efficient equipment, and combating energy poverty. Among multiple goals to be achieved, the following stand out:

  • reduction of greenhouse gas emissions by reducing very significant energy consumption,
  • reduction of energy bill and dependence,
  • reduction of energy poverty, 
  • improvement of levels of comfort and indoor air quality,
  • promotion of labour productivity, as a result of the increased Environmental Indoor Quality (EIQ) and the mitigation of occupant illness situations,
  • extending the life of buildings and increasing their resilience through the improvement of buildings and their characteristics (renovation),
  • use of materials that can be manufactured in Portugal with the use of intensive and specialized local manpower;

Apart from quite standard goals and conclusions like reducing energy use, it looks to connect knowledge and research from multiple disciplines, such as productivity and comfort. In fact, multiple studies have proved the relation between productivity and EIQ [2] [3]. Although in Portugal, this topic is not well explored[4] nor measured properly. It seems that the component creates a great opportunity to focus on this and other vaguely researched topics. Also, the goals point out the importance of embodied energy and durability. It promotes renovation as a simple way to enhance the energy efficiency of the existing building stock.  Finally, it draws a sharp relation between architecture, the circular economy and local materials. 

Renovation of a façade in Porto, 2021

According to the plan, the investment would focus on the three following actions:

  • Long Term Strategy for Building Renovation (Estratégia de Longo Prazo para a Renovação de Edifícios – ELPRE). A reform approved in the National Energy and Climate Plan (Plano Nacional Energia e Clima 2021-2030) [5] is going to promote the energy-efficient renovations of the Portuguese buildings stock, paying attention to residents’ comfort. The plan includes the Road Map with indicative measures and targets for 2030, 2040 and 2050 developed in seven domains:
    1.  Building renovation: the creation of an adequate financial framework – reorientation of financing lines for the energy renovation of the buildings envelope, revision of the current Energy Efficiency Program in Public Administration (according to EBPD), better environmental performance of buildings,
    2. Development and promotion of smart building envelopes, with a focus on research and technological innovation, 
    3. Strengthening the normative and regulatory framework for energy certification of buildings, which includes, among other measures, the labelling of products and/or services related to the energy renovation of buildings, the use of energy certificates as an access mechanism for financing or other types of benefits, and qualification of the energy class of buildings as an incentive or conditioning factor in the rental market,
    4. Closing gaps in training and professional qualification in the field of performance of buildings, in terms of energy efficiency and resources, 
    5. Actions to combat energy poverty, reduction of energy consumption charges and providing support to the most vulnerable households in the energy renovation of their homes through, through the provision of mechanisms for financing and tax benefits, 
    6. Actions to ensure the information and awareness of citizens and companies, public and private, for the benefits arising from the renovation of buildings through,
    7. Implementation of a set of indicators and mechanisms to monitor ELPRE’s progress and ascertain the respective practical results in the energy performance of the buildings,
  • Resource Efficiency Program in Public Administration 2030 (Programa de Eficiência de Recursos na Administração Pública 2030 – ECO.AP 2030) The  program aims to promote the decarbonization and energy transition of activities carried out by the State, contributing to the goals of reducing GHG emissions, reducing energy consumption by reinforcement of energy efficiency, the incorporation of renewables in the gross final consumption of energy, as well as promoting the efficient management of resources in the Public Administration,
  • National Strategy for Combating Energy Poverty (Estratégia Nacional para o Combate à Pobreza Energética) strengthens the role of the citizen as an active agent in decarbonization and energy transition, fighting energy poverty, creates instruments for the protection of vulnerable citizens and promotes the active involvement of citizens and territorial enhancement.

The investments to be implemented amount to 620 M€ and will allocate the resources in three groups: energy efficiency in residential buildings (300 M€), energy efficiency in central public administration buildings (250 M€), energy efficiency in service buildings (70 M€). Energy efficiency in residential buildings is divided into the following specific tasks:

  • Passive improvements at the level of the envelope, e.g., thermal insulation of walls, thermal insulation of roofs and glazing,
  • Active improvements, eg., HVAC systems for heating and/or cooling and SWH,
  • Energy generation systems and measuring through, e.g., electric energy generation systems from renewable sources, renewable energy community, 
  • Interventions aimed at water efficiency, including the replacement of equipment with more efficient equipment,
  • Interventions that promote biomaterials, recycled materials, natural-based solutions, green facades and roofs and bioclimatic architecture solutions, on urban buildings or their existing autonomous fractions;

Some of the implementations are already functioning, like CasA+, and they clearly reflect the legislation.

Deep Renovation in Olhão, 2020

The Recovery and Resilience Plan draws an interesting scenario for the next years of development of Portugal, importantly next to the Renovation Wave Directive and New European Bauhaus it shows a new way of development of Portuguese architecture: renovation. Some of the activities repeat in different actions, which essentially mean that these aspects are crucial and multifaceted, and funds will be allocated by different rules. With more than 97% of building stock with renovation potential, it sends clear information to the industry: renovate efficiently. 

Adrian Krezlik



[1] Ministério do Planeamento, “Plano de Recuperação e Resiliência,” Lisbon, Version 2.0, Feb. 2021.

[2] Wyon D., “Indoor Environmental Effects on Productivity,” (Jan. 1996).

[3] Heschong L., “Daylighting in Schools An Investigation into the Relationship Between Daylighting and Human Performance Condensed Report,” (1999). https://doi.org/10.13140/RG.2.2.31498.31683

[4] Macedo A. et al., “Characterization of Indoor Environmental Quality in Primary Schools in Maia: A Portuguese Case Study,” Human and Ecological Risk Assessment: An International Journal, vol. 19, no. 1, (Jan. 2013), pp. 126–136. https://doi.org/10.1080/10807039.2012.683751

[5] Council of Ministers Resolution, “Plano Nacional Energia e Clima (PNEC 2030),” 2019.

Lo-Tech Solutions: Solar Water Heaters and their Embodied Carbon

Dr. Harry Zvi Tabor was a British-Israeli physicist who is known for pioneering work in the field of solar energy in Israel. His work isn’t only relevant in the academic world, but had a big impact on the energy use of israeli cities. He developed a solar water heater that is the most common in the country, with 90% of dwellings getting their hot water from his technology (or similar) [1]. Locals know it as the “dud shemesh’’, and it’s the cornerstone of heating energy efficiency in Israel. Of course, other measures have been taken since the ’80s, when the heater was popularised.

The fact that makes this success story especially good is that it’s not based on high-tech research & development, which normally looks to turn expensive, cutting-edge solutions into economically viable alternatives. The solar heating landscape in Israel did, however, sprout from innovation.

90% of Israeli dwellings depend on solar heating devices for their hot water (Miriam Alster/FLASH90)

The ’70s oil crisis pushed an oil-dependent country (which has improved, but is still lagging behind in renewable energy) into a very common problem at the time, and they turned to a resource that is massively available in the country: solar energy. Many homes do have both electric heaters and solar heaters, in case the sun isn’t shining — which is rare for a city like Tel Aviv, with over 300 sunny days during the year, which translate in abundance of solar radiation. We can draw similarities between the current climate emergency and the ’70s oil crisis: both demand an urgent change in energy policy and high innovation in the energy matrix (albeit for different reasons: back then it was a massive surge in costs, now it’s due to rising surface temperatures). We can learn from the way Israel navigated the change when confronted with their black swan.

Solar heaters around the world typically consist of a collector (the flat part) that receives solar radiation and heats up water that circulates through it. The water is then stored in a tank that is coupled to the collector, where it stays warm for as long as the weather allows it to. The collector is not always present in the set up, as is common in less developed areas.

Basic functioning of a Solar Water Heater

This technology is economically feasible (with as little as a three-year payback time [2]). It also pays back the user very quickly when measured only by “embodied energy” — meaning energy used in setting it up is easily paid back in two or three years (this is a good measure as it is independent of energy price). But what is its real environmental cost? As we usually do at Dosta Tec, we resort to emissions through Life Cycle Assessment (LCA) to answer this question. It turns out, the “environmental payback time” is also extremely reasonable. In other words, the yearly energy savings provided by solar water heaters are enough to offset the carbon emissions incurred during mining, manufacturing, and installation — and this happens quite fast too.

As noted in a previous article of ours, embodied carbon is strongly dependent on both a country’s energy mix (the “cleaner” the grid’s sources are, the milder the positive impact a solar heater will have) and the availability of solar heaters in a particular location. The more they travel, the more carbon they embody. Even accounting for these variations (and uncertainties), solar heaters are an exceedingly good idea, way more often than not [3]. Their payback time is so small, that they’re a great choice even when accounting for the installation of back-up electric heaters. In Portugal, the price of a simple solar heater with an efficient heat collector can start at as little as 1000€, with a proven environmental payback time of less than three years [4].

When choosing technology (or making any engineering decision, really) we always compare alternatives. The most robust solutions always come from scanning the available options. In this sense, a study from the University of Liverpool [5] compared technologies that are usually used to increase energy performance in buildings. Solar Thermal (ST, outlined in green in the graph below), is significantly better than, for instance, Solar Photovoltaic. They achieved this by measuring the carbon embodied during the whole life cycle (typically using cradle-to-grave strategy) and dividing by a standardised unit of energy efficiency, known as a Functional Unit (FU). This might sound confusing, but just think of it like this: it costs so much carbon to build and install this technology, and we divide it by how much energy it saves during its lifetime. This way we can compare technologies in a cost/benefit manner. The graph speaks for itself.

Comparing building-efficiency technology by embodied carbon equivalent [5]. GSHP: ground source heat pump | ASHP: air source heat pump | ST: solar thermal | MVHR: mechanical ventilation and heat recovery | SPV: solar photovoltaic | LED: light-emitting diode (lighting)

So, why doesn’t everyone living where the sun shines use them? There are multiple barriers, on several fronts, to implement this technology: legislative, cultural, and organisational. Life cycle assessment studies and the concept of embodied carbon are relatively new to both policy and industry (in the context of the fossil fuel problem). And we sometimes tend to think all innovation must be at the forefront of new technology. Efficient, low-tech solutions often appear when necessity calls, such as an oil crisis, or just general lack of economic resources, as happens in many developing countries. As we keep pushing the boundaries of energy efficiency towards regeneration, we should remember that the energy problem is complex and shouldn’t expect to solve it with a single, high-tech silver bullet. Instead, why not source a portion of our knowledge and practices from simpler highly efficient options? We might just hit the right technology mix and move closer to a real, cost-efficient solution.

Mateo Barbero


— — — — — — — — —

[1] https://www.reuters.com/article/idUS311612153620110318

[2] Soteris Kalogirou, “Thermal performance, economic and environmental life cycle analysis of thermosiphon solar water heaters”, Solar Energy, Volume 83, Issue 1, 2009

[3] Battisti, R., Corrado, A.: Environmental assessment of solar thermal collectors with integrated water storage, in Journal of Cleaner Production 13, p. 1295–1300, 2005

[4] Fernandes, V. et al., “Life cycle assessment of solar thermal systems”, AHS Sustainable Housing Construction 2014

[5] Finnegan S. et al, “The embodied CO2e of sustainable energy technologies used in buildings: A review article”, Energy and Buildings, Volume 181, 2018, Pages 50–61

Materials for Future Buildings

The New European Bauhaus conference (22-23 April 2021) was inaugurated by a speech by the President of the European Commission, Ursula von der Leyen. She outlined an ambitious plan of challenges and changes that await us in the forthcoming years. Her speech probably surprised most of the participants – they were not prepared for such a bold statement. It seems that it’s time for decisive action that can really change the course. There is a lot of work to be done. It’s going to be difficult, but interesting and satisfying.

Von der Leyen put sustainability next to aesthetics and accessibility as a European development direction. Her speech leads us to the welfare state. This time is to take care not only of people but also of Nature.

In her speech, the President emphasises the role of building materials. She recalled that the historic Bauhaus promoted two new materials: steel and concrete. Meanwhile, it is time for us s to build using materials that release less carbon dioxide during production, preferably absorbing carbon. According to von der Leyen, the future belongs to building materials that are based on natural resources such as wood and bamboo. Materials that support the circular economy and decarbonisation.

Such a declaration from one of the most influential politicians and other officials set the direction for the entire Europe and sent a clear signal: we need a shift. 

An important voice in the material challenge, Björn Florman, founder of the Swedish Material Library in May 2020, said in an interview for dezeen:

Before we started to invent plastics made from fossil-based oil, we were already using bioplastics, and many of those plastic materials are the ones being perceived as ‘new’ today. They are not new, they have just been forgotten for 70 years or so.

Heterogeneous and perfect materials were one of Le Corbusier’s obsessions, which is probably why they entered the architect’s primer without any reservations. Today, the movement of searching for and producing new materials is gaining momentum.I’ll present a few projects and designers dealing with this topic.

Materiom is a platform that collects information about the new generation of materials and popularises their production. The collection contains recipes for materials that fit into the regenerative design and are made available on the basis of open knowledge. The creators of the platform emphasise that the production of the material should be available and possible in the kitchen, based on the raw materials available in the immediate vicinity. They remind us that materials can be produced from virtually anything, including agricultural ‘waste’. The materials that we find on the platform are at a low technological readiness level (so-called TRL3 or TRL4) – so far they do not have a fully defined function and we do not know their durability, abrasion, flammability, or actual environmental impact. Some of them are designed as a filament for 3D printers, for example, MS01, consisting of clamshells and alginate, or another made of eggshells and xanthan gum. I don’t know in which direction the platform will go, I’m waiting for more information about materials (durability, carbon footprint, abrasivity) and a critical look at the content, the road from TRL3 to TRL9 is long.


Future Materials Bank is a platform initiated by the Nature Research Department at the Jan van Eyck Academy in Maastricht, in collaboration with the Master’s Degree in New Materials at Central St Martins, London. Together, they look for non-toxic, biodegradable or sustainable alternatives to materials. The platform brings together 45 organisations related to art from Asia, Latin America and Europe, creating the Green Art Lab Alliance. Like the previous library, it’s under development and the materials contained there can’t be used for serial or mass production.

In Portugal, there are engineers and designers that have started working on alternative construction materials. For example, eCO2blocks is a carbon-neutral technology that looks to replace building blocks used in wall construction (today typically made of brick or concrete). A team of three scientists from Coimbra have been participating in programs called Climate Launchpad and Climate KIC to accelerate the introduction of their product to the market. Their material uses industrial waste to create new building materials.

As mentioned in the introduction, bio-materials are the most sought after. This is a very important signal for Portugal, where vernacular architecture could be characterized not only by the diversity of spatial forms but also by its use of materials. It has used both local stones and plant-based materials – principally fibers. Fibers use was closely connected to agriculture. Straw is a by-product of barley, wheat or rye production used for the production of flour. The biodiversity of agriculture has changed but huge amounts of so-called by-products become compost, although they could stay within the biological cradle-2-cradle production of thermal insulation, thatching or finishes. There is a great, undiscovered possibility for cooperation between the food and construction industries. 

Hempcrete blocks

Research on materials has been going on for a long time, but it seems that today, in the era of the climate crisis and subsequent declarations of the European Union (the Circular Economy Directive and the New European Bauhaus), its pace will increase. Architects and investors all around the world are looking for ‘new concrete’ and ‘new steel’. We still do not know about viable substitutes for some of the most frequently used materials such as OSB boards (which are toxic), GFRC panels,  etc. New materials are just waiting to not only be discovered but also used. Most importantly, this time we’re not looking for one magical solution, but for the diversity of alternatives that are connected with the local condition and resources.

Adrian Krężlik

Embodied Carbon of HVAC Systems

We’ve mentioned in previous articles how Life Cycle Assessment (LCA) of buildings is an engineering problem that is becoming more and more relevant. As action for climate change mitigation becomes more urgent, engineers are looking for more sources of energy savings, that is, opportunities for energy efficiency. Heating, Ventilation and Air Conditioning (HVAC) systems are known to be the cause of massive amounts of energy use in buildings, reaching almost 50% of operational use in developed countries [1]. From the perspective of Portugal, it is crucial to understand their impact, since only a small portion (23%) of the households in Portugal counts with a fixed heating equipment and even smaller with air conditioning systems (10%), but in recent years these numbers have shown the tendency of growth [2]. There is no widespread knowledge regarding the embodied carbon of these systems, but early studies are being conducted with more and more detail. It turns out, the impact of their energy use during operation may be very similar to that of their manufacturing and installation, and systematic replacements over a building’s lifetime.

Let’s brush up on the typical life cycle phases of a product (as defined by the European Committee for Standardisation in the ISO 14040 and 14044 standards):

A. Construction

B. Operation

C. End of life

D. Reuse

Not all these energy-using phases need to be considered in every single study on the problem. It may turn overly complex, and some phases may not even be worth accounting for. For instance, end of life of HVAC systems is practically irrelevant carbon-wise, due to the relative ease with which they are disassembled and disposed of. So in this article I will analyse only the cradle-to-grave cycle (without Disassembly nor Reuse).

What constitutes an HVAC system? Any piece of active technology that heats, cools, or moves air into, out of, or within a building. Active means that it consumes power (e.g. burns natural gas or uses electricity). The technology needs power because, as opposed to the flows seen in passive strategies, heat or air are forced to flow in the opposite direction in which they naturally would if the building space were left alone. That is, heating a room that is already warmer than the outdoors during wintertime, or the opposite. Think of it as pushing a big rock up a hill with growing steepness instead of letting it roll down to the bottom. Or more accurately: holding it at a specific point on the hill. These scenarios would require you to exert physical power onto the rock. The specific point of the hill can be thought of as the set point of the HVAC system’s thermostat, and the slope’s steepness as the difference in temperature with the outdoors.

A recent experimental study in six small healthcare centres in Extremadura, Spain, showed that the embodied carbon of their HVAC systems amounted to 2.3 times that of the operation phase considering 15 years lifetime for the HVAC systems [3]. We should note that Badajoz in Extremadura suffers average minimums of 4.5ºC in January and average maximums of 33.7ºC in August (with 438 cooling degree days, and 1372 heating degree days). This means that not only are health centres in continuous operation (thus their HVAC systems practically don’t switch off), but both heating and cooling are essential at different points during the year. It’s safe to say, then, that proportion of embodied-to-operational carbon is alarming. Why? Well, when engineers approach energy efficiency in buildings, they usually look at two things: heat flows across the building envelope and efficiency of the selected HVAC technology. In other words, they seek to reduce the operational use (life cycle Phase B) and do not look into phase A. Mining the materials, transporting, manufacturing, and installing are extremely energy-intensive activities, and prone to using carbon-base fuels (e.g.: petrol used in transport or mining), as proven in the mentioned ratio.

To understand how to tackle this issue, we must dive into the details of the Phase A of HVAC systems. Try the following thought exercise: think of a simple packaged air conditioning unit. Think of all the parts that constitute the cooling system: ducts, mechanical ventilation devices, fittings, air terminal, and the list goes on. And now imagine all the work put into creating those parts and bringing them together. This results in embodied carbon for each part, which may then be added up to the total. The graph below shows the results of a study based on Building Information Modelling (BIM) of Siemens’ office building in Zug, Switzerland [4]. It shows not only how energy-demanding maintenance can be (reflected in the Replacement phase) along the studied 60 years, but also shows that the impact of piping must not be overlooked. When annualising, the embodied carbon is 1.32 kgCO2eq/m2 for Fabrication and 1.70 kgCO2eq/m2 for Replacement. Compare this to 1.25 kgCO2eq/m2 for Operations and you will probably agree on the importance of LCA in HVAC.

Embodied carbon results for an HVAC of an office building in Switzerland [4]

The numbers above tell us that the issue of human thermal comfort is more complicated than we were aware of. The fact that this discussion is barely starting is worrying. On a personal note, I have not seen significant mention of HVACs’ embodied carbon, even as I sat through a specialisation programme in Sustainable Energy Systems that went through Energy in Buildings thoroughly. In Portugal, wood and coal-powered sources of heat are still very common, but modernisation of the economy and the households are leading to adoption of electrified HVAC systems such as heat pumps or simple ACs (in the South). Each piece of HVAC system is different, the technology is ever evolving, and the climate is changing. This means there can be a significant range of values for embodied carbon, depending on numerous variables. In future articles, we’ll look into some of the specifics of each technology. But for now we can agree on one thing: HVAC systems’ embodied carbon is a pressing issue in today’s and tomorrow’s built environment.

Mateo Barbero


[1] S.K. Alghoul: A Comparative Study of Energy Consumption for Residential HVAC Systems Using EnergyPlus (2017)

[2] Vilhena A. et al., O parque habitacional e a sua reabilitação. Análise e evolução 2001–2011, INE (2013)

[3] Justo García-Sanz-Calcedo et al.: Measurement of embodied carbon and energy of HVAC facilities in healthcare centres (2021). Journal of Cleaner Production.

[4] Kiamili, C. et al: Detailed Assessment of Embodied Carbon of HVAC Systems for a New Office Building Based on BIM (2020). Sustainability

PV’s Embodied Carbon

Looking back at 2020, one thing will naturally come up in most people’s mind. The pandemic’s reach is global and very much ongoing, with only a handful of countries now flirting with a“back to normal”. Beyond the ubiquitous health crisis, we are all familiar with the economic implications that it brought about as well (Portugal’s GDP dropped a historical -7.6%, for instance). However, every so often a news outlet somewhere would communicate the rare good piece of news which would circle the world and quickly fade. Most might remember the before-and-after image of air pollution in China’s cities during the country’s lockdown. Or the slump in carbon emissions that took place virtually everywhere. But why is this? Remember the word “carbon” is a concept that standardises and groups all greenhouse gases.

Well, economic activity and energy use are proven to be tightly coupled. And energy use is in turn coupled to carbon emissions [1]. Rarely has a country grown without worsening their emissions due to higher consumption, transport, construction, and more. With economic activity returning after a drastic drop, emissions are expected to surge at historical values. We are all aware of the urgent need to deepen the change from a strictly economic to a broader sustainable development. And the question of decoupling GDP and emissions is more relevant than ever. The answer to this is either to reduce the amount of energy used per unit of activity, or to reduce the amount of carbon emitted per unit of energy used (or even be “energy positive”). Put simpler: use less or use cleaner. Of course, both can be attacked at the same time.

When this problem is brought to building energy use, using less can be understood as having more efficient buildings. And using cleaner, switching to renewable sources of energy such as onsite solar PV systems. But there’s a catch: renovating a façade or installing a PV system (with wiring, batteries, an inverter, and more) are economic activities that bring about energy use and emissions themselves. But this doesn’t mean that they are useless — what we need to look at is their overall effect by quantifying how much carbon their existence brings and avoids in the different phases of their lifetime. In other words, understanding their embodied carbon and comparing them to business as usual, with our environmental goals in mind.

Let’s concentrate on the use cleaner part. Research on carbon that is embodied by different electricity generation technologies is widely available. These studies typically offer a range of values, as each installation carries with it specific mining, manufacturing, transport, and installation/construction needs which use up different amounts of energy (in short, Life Cycle Assessment studies). However, a mid-point estimation can be taken for reasonably accurate comparisons against other technologies.

Take the Portuguese case. The graph below compares 3 scenarios for a typical Portuguese dwelling’s electricity consumption profile of 3293 kWh/year [2]. The first scenario, in yellow, shows what emissions look like with the current portuguese energy mix. That is, considering the grid’s carbon intensity based on the existing power plants and onsite generation (a combination of low-carbon and high-carbon sources [3]). The second, in green, shows what would happen if that dwelling installed PV panels. A typical residential PV installation is considered, replacing 1720 kWh/year of what is taken from the grid [4] (a bit over half of the total of 3293 kWh/year). The third scenario, in red, shows an extreme hypothetical situation in which all electricity is produced in a coal plant in the baseline scenario. This is not true for Portugal, but it is somewhat representative of other countries, such as Poland (with a whopping 74% of electricity coming from coal [5]).

Note onsite PV starts at 3740 kgCO2eq in year 0, as we are accounting for the carbon it embodies during its manufacturing and installation.

What we see is that PV mitigates emissions, no matter the case. When replacing coal, less than 2 years of using 1720 kWh/year of PV-generated electricity already offsets its embodied carbon (see the red line crossing the green line). When comparing to the current Portuguese scenario, carbon flow for the PV implementation proves to be better somewhere around the 7th year. Keep in mind we are being practical and considering a real decision case, so we are not accounting for the embodied carbon of the existing grid infrastructure (as the damage has already been done). So we are being very demanding with PV in this study — even unfair. The embodied carbon of the PV installation is the reason why the green line starts above the red and yellow ones in year 0. Once this is offset, every year is pure mitigation (remember: renewables don’t make carbon “disappear” nor do they absorb it, they just avoid emissions from other dirty sources). And why stop here? Buildings can be low-carbon, but they can even be “energy-positive”. This means they generate more (cleaner) electricity than they consume, which can be injected into the grid and be used up by another building that needs it.

What all this shows is that even by conservative estimations, PV offsets its own negative effects. And this needs to be common knowledge. Almost all technology has negative effects. In fact, virtually all activity implies direct or indirect carbon emissions. This in itself isn’t a valid reason to dismiss technological changes or energy uses, as the whole picture must be analysed. A combination of use less and use cleaner is what engineers and designers should strive for. And why stop there? Let’s start thinking energy positive and start generating more than we consume.

Mateo Barbero


— — — — –

[1] Haberl, Helmut et al. (2020). A systematic review of the evidence on decoupling of GDP, resource use and GHG emissions, part II: Synthesizing the insights. Environmental Research Letters.

[2] https://www.odyssee-mure.eu/publications/efficiency-by-sector/households/electricity-consumption-dwelling.html

[3] https://www.apren.pt/contents/publicationsreportcarditems/boletim-renovaveis-maio-2020.pdf

[4] PV carbon data: Stephen Finnegan, Craig Jones, Steve Sharples, The embodied CO2e of sustainable energy technologies used in buildings: A review article, Energy and Buildings, Volume 181, 2018, Pages 50–61, ISSN 0378–7788

[5] https://www.eia.gov/international/analysis/country/POL