Column by Sune Thorsteinsson,senior officer, Studyline coordinator (Solar energy) and National BIPV-ekspert (IEA PVPS Task 15). Published in Energy Supply, November 2024.
Over the past 13 years, the price of solar cells has dropped by 90 per cent, making them one of the cheapest renewable energy sources and an important part of the green transition. With the initiative ‘Denmark Can Do More II’, the Danish government aims to increase solar cell power ten-fold by as early as 2030, and the EU recently launched an updated Energy Performance Directive (EPBD), requiring solar cells to be mandatory on all buildings in a few years.
At the same time, there is a fairly intense debate about whether solar cells should be placed on buildings or in the open land, with some nuances being lost in the discussions. We want solar cell systems on buildings, but we will inevitably also have them in open land areas—simply so that we can produce enough green power.
Two years ago, I wrote here in Energy Supply that a rapid development has taken place, so that solar cells can now be integrated with conventional roof and façade materials, and with good options for architectural integration. These solutions are even available from Danish companies, which at the moment are experiencing strong growth. Due to market developments, the price of these solutions has also decreased significantly.
Even though there is a political desire for greater incentives to install solar cells on buildings, there are other parts of current legislation—including the Danish building regulations (BR18)—that continue to hinder this. I will try to describe this briefly in the following.
The climate impact of solar cells and its calculation in the building regulations
From 1 January 2023, climate impact requirements have been introduced for new buildings over 1,000 m2, where the total climate impact (CO2 emissions) embedded in the building materials and the building’s operational energy must not exceed 12 kg CO2eq/m2 per year. From 1 July 2025, these requirements have been tightened, so they apply to almost all new heated buildings, where the limits vary between 4 kg and 8 kg CO2eq/m2 per year depending on the building’s use. As the construction sector accounts for a significant part of total CO2 emissions, this requirement is an important tool for reducing the sector’s climate impact.
But it is inappropriate to include solar cells in this calculation, as is currently the case—both traditional roof-mounted solar cells as well as the solar cells integrated into roof and façade materials. Generally, solar cells—today almost exclusively made of monocrystalline silicon—require a lot of energy to produce. So, their climate footprint is mainly derived from the climate footprint of the electricity grid at the place of production. However, despite the high energy consumption for their production, the solar cells recoup this energy in just over a year.
To understand why it is inappropriate to include solar cells in the climate impact calculation in the building regulations, we need to understand some key details. It concerns the stipulated 50-year period of consideration for the building and the chosen method of calculating the solar cells’ contribution to the building’s operational energy.
Solar cells’ CO2 displacement is artificially reduced based on high ambitions for renewable energy
The climate impact calculation in the building regulations sums up the climate impact from all building materials and building components—including entire replacements during the building’s lifespan if the lifespan of the building materials is shorter than the building’s 50-year design lifespan—as well as the climate impact of the building’s operational energy. The operational energy is converted into climate impact measured in CO2 equivalents via emission factors that reflect the climate impact of the expected future electricity mix year by year. The solar cells that are part of the building’s energy frame are included here, and CO2 displacement from these solar cells (both integrated and installed) is offset based on the same method with the expected electricity mix. The total climate impact is then divided by the heated floor area and the design lifespan period of 50 years, and this resulting number must comply with the above requirements for the building’s total climate impact.
The significant amount of energy needed to produce solar cells means that solar cells per square metre have a climate impact 5–15 times higher than commonly used roofing materials, so the embedded CO2 from the solar cells has a significant contribution on the climate impact calculation.
The emission factors, i.e. the figures that convert energy into CO2 equivalents and which seek to reflect the climate impact of the Danish electricity mix, are reduced. In the long term, this will be based on figures determined by the political visions for the expansion of renewable energy, including solar cells. Thus, the factored CO2 displacement from the solar cells becomes marginal, simply because the displacement is calculated as the displacement from an expansion of renewable energy that is greater than the political visions for the expansion of renewable energy. This is happening without factoring in that solar cells constitute a significant part of the reduced climate impact of the electricity mix and are therefore also part of the solution to achieving a lower climate footprint. In other words: A calculation method based on high political ambitions for the expansion of renewable energy makes solar cells have a higher climate load in the building regulations than what is real.
Furthermore, the lifetime of solar cells is set at 30 years, based on a performance guarantee of perhaps 80 per cent after 30 years. That means that two solar cell systems must be included in the building’s design lifespan period of 50 years, based on today’s climate impact of solar cells. The ambitious political visions for the expansion of renewable energy mean that the emission factors have been written down so sharply that the second plant does not displace CO2. This methodology puts significant negative load on the building’s climate impact calculation. Over the past 10–15 years, we have seen that the climate impact from solar cells per square metre has been halved, and that an even stronger development is expected in future due to the technological development towards less silicon consumption. Due to these facts the climate impact of the second solar cell system is lower than the first plant, and the calculation is therefore misleading.
Political visions or actual emissions?
I have made calculations for the impact of solar cells on the climate impact which show that, under the current rules, only the most efficient and the ones with the least climate impact neutrally affect this climate impact using the proposed 2025 emission factors.
So, I ask openly: Should we really let the political visions for the expansion of renewable energy determine whether it is advantageous to install solar cells to meet the energy performance framework for a building?
For the above reasons, the current method for calculating the climate impact of solar cells is not appropriate, and the method used in the building regulations based on the standard EN 15978 is neither appropriate nor fair, and to some extent prevents the expansion of solar cells on buildings, which is in clear contradiction with the political intentions. Solar cells are both part of a building, but also part of the energy system, and therefore you have to include both parts in the calculation rather than simply focusing on the building part.
Solar cells must, of course, be held accountable for their climate impact, and in the EU work is currently being done on Ecodesign requirements that are intended for most solar cells, and which are expected to be a better method to account for the climate impact of solar cells, respecting they are also a part of the energy system.
In conclusion, solar cells should therefore be completely exempted from the climate impact requirement in the building regulations, so that the ambitious goals for the expansion of renewable energy do not cause the climate impact of solar cell systems to become artificially high and thus counteract the good political intentions of having more solar systems on the buildings.
