Solar farms and wind developments are two of the most prolific renewable energy technologies currently available. The compatibility of these technologies at a single site is a topic that requires consideration because:
- Many companies at the forefront of the renewable energy industry are engaged in large scale projects for both solar and wind.
- The number of wind and solar installations is likely to increase globally.
- The amount of space available for renewable energy installations is finite.
- There may be logistical advantages to a combined solar/wind site rather than separate sites.
- It has been suggested that a combined solar/wind site may allow for a more stable production of electricity [1] to the grid thereby reducing energy intermittence.
Do combined solar/wind farm sites exist?
There are already examples of combined solar and wind developments – one such example is Ecotricity’s Fen Farm development in Lincolnshire in the UK which claims to be one of the first combined Wind and Sun energy parks in the world.
What are the issues?
One potential complication with regard to co-located wind turbines and solar panels is the issue of ‘shading’ . This is when a shadow is cast over the face of a solar panel – which reduces the amount of light that can be absorbed and converted to electricity.
When large-scale solar farms are built, the rows are generally separated by a distance that ensures they will never cast a shadow over each other in order to prevent shading.
Wind turbines are large structures which can cast a large shadow in their vicinity. The most significant shadow with regard to shading of a solar panel is likely to be due to the tower. However, the moving rotor will also cast an intermittent shadow in the area around the turbine.
When wind developments are assessed for potential Shadow Flicker effects – i.e. an intermittent shadow causing a nuisance to local residents – it is common to consider issues at a distance of 10 rotor diameters from a wind turbine. Therefore, some degree of shading is inevitable at a combined wind/solar installation.
How much of a problem is shading?
Accurately predicting the reduction in performance and revenue from a solar development with partially shaded panels is not straightforward [2]. In general terms, more shading means less performance but the quantified answer will depend on many parameters including:
- How much of the panel area is shaded.
- Under what conditions the shading occurs – for example a small amount of shading in winter when the sun is at its lowest is likely to be less significant than shading in summer under sunnier conditions.
- Whether a clear, defined area is shaded or whether the amount of light falling on the whole panel is reduced by a small amount.
- How the panels are connected to each other and the inverter.
- The amount of electricity generated by the combined site compared to the solar installation by itself.
Is there guidance for this issue?
Studies have been carried out to investigate the issue of solar panel shading by wind turbines, however there does not appear to be any formal guidance. It has been reported that one study showed that the losses caused by shading of solar panels by the wind turbines are low and would not undermine the viability of a combined development [3].
Moving forward
The issues around shading of solar panels by wind turbines will be better understood as more combined sites are developed. However, shadowing of a solar development does affect its output and the consequences of shading at a combined wind/solar development are worthy of further consideration.
References
[1] Optimal day-ahead scheduling of a hybrid electric grid using weather forecasts – Bouaicha, Hamadi
[2] How Shade Affects a Solar Array – Sargosis Solar & Electric – http://sargosis.com/articles/science/how-shade-affects-a-solar-array/
[3] Study Reveals Solar and Wind Power Plants to be a Perfect Combination – Solarpraxis AG – http://www.solarpraxis.de/en/company/news-media/detailview/article/Studie_Solar_und_Windkraftanlagen_ideal_als_Komb/
