Does Rooftop Solar Cause More Harm than Good?
- Perspectives
PV Panel Price ($USD / Wp). Panel costs have continued to decline as production ramps up globally.
Data: https://ourworldindata.org/grapher/solar-pv-prices
Whether to embrace rooftop solar has traditionally been a matter of assessing its financial benefits: Will it save money? The continuous decline in the price of solar panels, coupled with tax incentives and regulatory support, is making that an easier ‘yes’ than ever(1). However, today’s building owners contend with a broader spectrum of considerations beyond mere capital and operational expenses. Real estate managers and lenders find themselves balancing internal ESG goals, tenants’ sustainability expectations, and new climate rules from the SEC. How do we ensure that the installation of solar panels is a net positive when scrutinizing emissions and environmental impact?
Embodied Carbon of PV Panels (kg CO2e / Wp) There is a considerable difference between solar panels when it comes to embodied carbon. Check for emissions on the manufacturer’s EPD.
Data: Manufacturer’s published Environmental Product Declarations.
The issue is that making solar panels takes energy, which inevitably results in carbon emissions. Building owners may reasonably wonder if it’s better to skip the up-front pollution from solar panels, especially considering that electricity from the power grid is getting ‘greener’ each year. What if the pollution generated during the manufacturing of panels is actually greater than the amount of pollution it ‘saves’ by making clean energy?
Life Cycle Embodied Carbon of Energy Generation Resources (kg CO2e / kWh)
Data: Pehl, et al. 2017
After reviewing the literature and running our own life cycle assessment, we can report that solar panels are indeed good for Mother Earth. This is because:
- Solar panel production is becoming cleaner. Most panels are currently manufactured in East Asia, where a large share of energy is coal-generated (An & Sun, 2024) (2). However, renewable energy is gaining momentum in China. Government regulations and incentives are fostering increased panel production in Europe and the United States. These regions have cleaner grids, and advancements in technology, such as the development of next-generation photovoltaics like thin-film panels, require less energy input.
- We need more electricity. Our energy sector is decarbonizing, creating an unprecedented demand for capacity. When compared to other options for adding electricity generation, photovoltaics has relatively low embodied carbon. Solar panel systems have an embodied carbon of about 13g CO2e per kWh produced over the life of the panels (Pehl, et al. 2017). This is more than wind power, which has about 4g CO2e per kWh, but dramatically less than building a new hydroelectric plant (97g) or natural gas plant (78g).
- On-site renewables produce energy where it is consumed. This reduces the burden on an already-stressed grid infrastructure. This stands in contrast to utility-scale renewable energy projects that require big grid extension infrastructure investments, which are often the bottleneck for bringing green power online.
PV Panel Embodied Carbon Trade in 2017 (millions of tons CO2e). East Asia the major exporter of solar panels (and embodied carbon).
Data: Wang, et al. 2021
To summarize, rooftop solar panels support climate action goals in almost all cases. When judging the merits of rooftop solar, it’s not fair to weigh the embodied carbon solely against avoided emissions from the energy produced. Instead, it’s essential to evaluate solar panels against the other options we have for generating electricity. In that regard, solar looks very good.
So when planning for rooftop solar, consider the following tips to have the greatest impact on resilience:
- When selecting PV panels, target embodied carbon emissions below 0.35 kg CO2e / Wp as documented by an Environmental Product Declaration (EPD). Bi-facial panels and thin-film technology are best-in-class options with low embodied carbon per kW produced
- Install metering to report any renewable energy exported to the grid separately from energy consumed. This helps comply with emissions reporting standards.
- The time of day that electricity is produced and consumed is fundamental to grid resilience. Smart meters and batteries allow building owners to reduce emissions even further by optimizing grid energy use.
- Finally, evaluate rooftop PV against other uses, such as skylights, plantings, and occupant access. Climate change, biodiversity, urban heat island, and occupant health are interrelated dimensions of resilience.
If you’d like to discuss this article, or your next project, feel free to connect with us at Improvinglife@branchpattern.com.
Footnotes
- There are plenty of ways to evaluate the financial picture, but for projects in the US, tax incentives are making that decision much easier (https://www.energy.gov/eere/solar/federal-solar-tax-credits-businesses). Increasingly, some amount of onsite renewable is required by the energy code. https://www.iccsafe.org/content/net-zero. And a new class of regulations such as NYC Local Law 97 levy penalties against building owner who exceed their emissions budget, adding a whole new financial incentive to reduce electricity use.
- Solar panel production in East Asia results in significant carbon emissions and the environmental stress associated with coal plants. Most of the world’s panels are produced here, presumably due in part to a permissive regulatory environment. This highlights a social justice concern for climate action. For example, see Wang, et al. 2021.
References
An, M., & Sun, X. (2024). Carbon footprints of solar panels in China provinces based on different production and waste treatment scenarios. Journal of Cleaner Production, 435, 140453.
Hannah Ritchie, Pablo Rosado and Max Roser (2023) – “Energy”. Data adapted from International Renewable Energy Agency, Nemet, Farmer and Lafond. Retrieved from https://ourworldindata.org/grapher/solar-pv-prices [online resource]
Pehl, M., Arvesen, A., Humpenöder, F., Popp, A., Hertwich, E. G., & Luderer, G. (2017). Understanding future emissions from low-carbon power systems by integration of life-cycle assessment and integrated energy modelling. Nature Energy, 2(12), 939-945.
Wang, M., Mao, X., Xing, Y., Lu, J., Song, P., Liu, Z., … & Zusman, E. (2021). Breaking down barriers on PV trade will facilitate global carbon mitigation. Nature communications, 12(1), 6820.
