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
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. 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! 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 )
- 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 . If we’re doing the effort of managing our energy, why not be bold?
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.
 “Design of a micro wind turbine and its economic feasibility study for residential power generation in built-up areas”, Loganthan et al. (2019)
 “Does replacing coal with wood lower CO2 emissions? Dynamic lifecycle analysis of wood bioenergy.”, Sterman et al. (2018)
 “Residential and Commercial Buildings”, IPCC Report, Chapter 6, page 407 (2021)
 “Economic analysis of BIPV systems as a building envelope material for building skins in Europe”, Gholami et al. (2020)