Known unknowns



Historical weather data is typically used to estimate the yield of solar farms and to secure project financing, but as climate change begins to affect all areas of society, past weather data may no longer be a reliable guide. Everoze partner Nastasia Pacau let’s look at how solar power projects can be secured for the future in a changing climate.

Climatic studies have shown that potential solar radiation varies over time both regionally and locally, with many influencing factors. No clear way to predict irradiance far into the future has yet been found, and historical variations have shown a strong correlation with air pollution, meaning that climate change is not the only cause of changes in solar irradiance.

The global temperature increase affects the performance of solar power plants. Solar panels lose when operating temperatures rise by a factor of 0.3 W/C – 0.5 W/C.

According to the likely outcome presented by the Intergovernmental Panel on Climate Change’s Common Socio-Economic Pathway (SSP), the average global temperature would increase by 2 C by 2060 and 3.5 C by 2100. We already have a 1.1 C rise. Although those few degrees may not seem that significant in terms of solar plant performance, they are associated with an increase in the frequency and intensity of heat waves, as has already been observed in recent years.

The production of solar electricity also depends on other factors, such as wind speed and the spectral composition of light related to humidity or aerosols. Many of the variables are uncertain and difficult to predict. Other extreme weather events such as fires, droughts and storms can be expected to occur more frequently thanks to a warming planet. This increases the uncertainty of solar yield forecasts and can lead to greater risk and longer project construction schedules.

We know that climate change affects the production of solar electricity, but since the effects vary from region to region, the impact on solar output cannot be accurately estimated. Since nothing is certain, energy assessments must develop ways to account for the potential impacts of a changing climate.

Customization of assessment

Energy production evaluations often made with the PVsyst software have become more detailed. One of the main inputs to these models is global horizontal irradiance obtained from meteorological models and databases. Other input parameters such as temperature, wind speed and spectral content affect the energy assessment. Since research depends directly on weather conditions, the effects of climate change on solar projects can no longer be ignored.

The current market approach to solar yield forecasting involves evaluating a typical weather year to estimate a solar project’s future performance and output. Because this typical year is based on historical data, it may not always apply to a changing climate.

This risk accelerates the already heated debate about which solar resource database or model is best suited for the task. As a technical advisor, Everoze is often challenged on these topics, as the use of one or the other source directly affects the bottom line and the potential profitability of the project. It can be difficult to judge whether we are too optimistic, too pessimistic or balanced. The results are already different based on data from the last 10 years instead of the last 30 years.

We could adapt our method for one or more SSP scenarios and propose a potential energy production output and performance ratio dependent on the socio-economic pathways chosen. This means adjusting our weather databases and models to account for future levels of radiative forcing, which can be done (and some already do) because these levels of radiative forcing give us the overall change in temperature, radiation, and wind speed.

We could also consider changing the uncertainty factors when estimating the potential solar yield. All this would affect the profit figures, which are so central in project development and financing. Any change in assumptions leads to a change in results and this needs to be studied very carefully.

Waiting for change

So far, we do not have a consensus or a clear solution for accurately assessing the effects of the climate crisis. However, work towards that is necessary, especially for projects lasting decades. In the near future, clearly different numbers will be applied to solar energy projects in terms of radiation, temperature and wind speed, as well as other parameters.

We expect changes in yield and performance ratios, as well as new risks related to project planning, construction and schedules. This means an impact on the assessment of energy production, but also on due diligence and preliminary calendars. As independent technical advisors, we have a responsibility to develop our expertise, develop new services to assess risks related to climate change and disclose unpleasant results. One thing is certain: the solar electricity market is becoming more and more popular and solutions to this topic are emerging. But we need to act as soon as possible and as quickly as possible.

About the author: Nastasia Pacau is an engineer for the French solar team at Everoze. He mainly works in energy production evaluation and technical due diligence. He is also part of the sustainable development team. Pacaut has experience in thermal energy networks and sustainable development, focusing on Spain and France.

David is a passionate writer and researcher who specializes in solar energy. He has a strong background in engineering and environmental science, which gives him a deep understanding of the science behind solar power and its benefits. David writes about the latest developments in solar technology and provides practical advice for homeowners and businesses who are interested in switching to solar.

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