What might be considered one of the greenest energy sources with the highest potential – solar parks – pose new environmental questions, potential threats and untapped benefits.
The construction of solar photovoltaics (PV) is growing at an unprecedented rate globally, expanding by 50% per year over the last decade, reaching almost 100 terawatt-hours (twh) in 2012. The growth is set to continue with the European Photovoltaic Industry Association predicting that solar PV could provide between 7% and 11% of European electricity demand by 2030and the International Energy Association that 690GW capacity will be installed across the world by 2035.
This rise in solar PV is driven by governments, and businesses, chasing targets for low carbon energy. Government support programmes and subsidies have helped the growth of solar PV, including major additions in Germany, Italy, China, US, Japan and India. Generation costs are becoming comparable to retail electricity prices, and in some places solar PV may become competitive to the average wholesale electricity prices.
Solar is already a giant rolling stone. The problem is the scale of land involved, and the change of land use. The energy density – the amount of land required to produce wattage – of PV is relatively low. But, according to the US Department of Energy, to hit the 2035 target of 690 GW capacity of PV, we would need 6,900 to 34,500 sq km.
In environmental terms, building-mounted is the greenest approach, but more complex and costly than ground-mounted systems. Solar PV parks are generally built on brownfield sites or agricultural land, and policies usually dictate that only low-grade agricultural land can be used. Ground-mounted solar panels have been constructed throughout the world, including the UK, US, India, China, Spain, France, Abu Dhabi and Australia. The split between building- and ground-mounted systems varies, for example ground-mounted systems constituted 82% of solar PV capacity in China and around 45% across Europe in 2011.
Climate is a known and powerful factor in changing the nature of soil and the relationship with plants that can grow there. Research carried out so far into both wind farms and solar parks suggests that these types of changes in land-use could result in micro-climate changes.
Work on wind farm sites, for example, has highlighted local effects on temperatures, changed humidity levels through turbulence, higher concentrations of biogenic gas (CO2, methane and nitrous oxide), and changes in patterns of cloud cover and rainfall. It’s clear that PV panels will cause shading and changes to wind flow, and in principle is likely to alter temperature, change the rainfall distribution (which impacts on soil moisture) and the wind flow over the land.
But we just don’t know enough about what happens to the soil, plants and wildlife in areas where ground mounted PV parks are constructed. The phenomenon is still a new one and rapid development is taking place on the basis of ignorance. But the effect the PV panels have on the local climate and what impact this has on the plants and soil is very important.
Soil is the most significant player in storing carbon – containing more than vegetation and the atmosphere combined – and the interaction between soil and plants regulates carbon storage and the release of greenhouse gases. So the expansion of solar parks matter for the carbon cycle, the growth rate of plants, the amount of carbon locked up in the soil, the release of greenhouse gas emissions to the atmosphere and the types of species that can live in the new conditions. Mass use of solar farms over time will increase the areas affected and the scale of the new phenomenon.
Once the effects on the environment are better known we will be able to design the next generation of solar PV parks that move beyond maximum energy production to ways of combining land use.
In the UK, combining solar with grazing livestock is fairly common, but again, we don’t know what the implications are for the animals and the grass they are grazing on. At Piedmont Biofarm in North Carolina they are trialling the use of solar panel arrays installed at height to provide shade to enable the growth of crops that cannot survive in the direct sunlight.
A trial study in southern France has demonstrated that by reducing the density of the solar panels by half, it was still possible to grow lettuces on the land underneath them. If the ‘new climate’ created by a solar park is not conducive to crop growth, there may be ways to change the solar PV park, to innovate, to promote better conditions through less intensive clustering of the solar arrays, supporting systems of irrigation, or trials of different types of crop.
Next generation solar PV parks could have a particularly important role to play in hot regions where both food and energy are scarce. For example, in the rural communities of Tanzania access to electricity is scarce and food provision an ongoing and ever-increasing challenge. While ‘intercropping’ (planting two crops close together, so that one is used to improve the yield of the other) can provide shade, there is vast potential for solar panel arrays to maximise both electricity and food production with the right targeted investment. Solar PV parks could increase the amount and diversity of crops grown in such areas and reduce the reliance on expensive ‘dirty’ fuels that can damage people’s health.
In such a fast-moving area of technology, backed by government funds and big business investment, where there is so much expectation and hope, we can’t afford to lose sight of the bigger environmental picture. There are both negative and positive elements. We don’t understand the extent of the implications of the change in land-use and problems involved, but actively addressing the challenges provides opportunities.
Solar parks could be contributing a great deal more. A more co-ordinated and integrated effort between industry, policy and researchers is now needed, working together on a network of sites internationally to see what’s actually happening and to develop the next generation PV parks that provide multiple benefits from the same land area.
• Amended on 9 July to correct the amount of land needed to hit the PV target from 76,000sq km to 6,900-34,500sq km.
Dr Alona Armstrong is a faculty fellow in energy at Lancaster Environment Centre, Lancaster University