Solar power is now the cheapest source of electricity in history according to a 2020 report by the International Energy Agency. But there is one limiting factor to its deployment – space. Most solar farms use land, which could otherwise be used to grow crops to feed our ever-increasing population or to provide carbon sinks and wildlife habitats. Therefore using the water surface is an alternative, and is now a growing industry in Europe.
A recent report in Nature Sustainability, calculated if around 114,000 reservoirs around the world covered 30% of their surface with floating solar, that over 9,000 terawatt hours of electricity could be generated per year. This is around 2.4 times the amount of electricity consumption of the United States in 2021.[1]
How does it work?
Standard solar PV modules are fixed to floating pontoons usually made from high-density polyethylene. These are permanently anchored to the bottom of the water body, typically a lake or reservoir. Electrical equipment such as inverters, are typically located onshore and connected to the array with floating or underwater cables. PV modules are usually mounted at a fixed tilt on the floats or pontoons which are held in place by an anchoring system. The type of anchoring system depends on factors such as the depth of the water body, the float type and the variation in water levels. Most are anchored to the bottom, however smaller installations are often anchored to the banks
Typical applications of floating solar include reservoirs, lakes, industrial and irrigation ponds.
Source: Where Sun Meets Water: Floating Solar Market Report (Washington, DC: World Bank)
What are the benefits?
Aside from avoiding valuable land space, the main benefit of floating solar, is the cooling effect of the water beneath the solar modules, which results in higher efficiency, up to 15%. Solar panels operate at their peak between 15oC and 35oC, however temperatures can rise to around 65oC, hampering efficiency. Other benefits include:
- The solar arrays provide shade on the water surface, reducing water temperature, therefore decreasing evaporation,
- Water quality can improve due to decreased algae growth,
- There is no requirement for land based site preparations such as site leveling and foundations.
- It presents opportunities in countries with high population density and more competition for land.
The graphic below shows the benefits and challenges of installing floating solar.
Source: Where Sun Meets Water: Floating Solar Market Report (Washington, DC: World Bank)
The downsides are the increased installation costs – up to 25% more and the potential to reduce oxygen levels in water which could affect aquatic life. This will depend on the nature and scale of the water body and installation, though and additional research is required on these potential impacts.
Floating Solar Development
The first commercial floating solar installation was at a winery in California in 2008, however larger installations of 1MW and above, were developed in Japan and Korea around 2014. In recent years the deployment has advanced further with plants of tens of megawatts installed in China, which is now the worlds largest market. China has a large number of flooded coal mines, due to the shift from fossil fuel power generation, and this is creating new opportunities for people who previously worked in underground mines, to retrain in solar assembly and installation.
Most installations of floating solar have been on reservoirs and industrial and irrigation ponds, however more recently deployment in hydro-electric reservoirs has been seen. These hybrid systems have the added benefit of using the existing transmission infrastructure and can provide a steady supply of electricity during variable weather conditions.
Off-shore deployment
An emerging use of floating solar is in coastal waters where they can benefit coastal communities, however there are additional challenges in the marine environment, such as:
- Rougher water surface conditions
- Mooring and anchoring are more difficult due to tides and currents
- Salt deposits and marine organisms can affect the function of the components
- Operation and maintenance costs are higher in off-shore installations
UK and Ireland
Although there are no large scale floating solar installations in Ireland as yet, the UK has a number of schemes installed for example, in 2016, Lightsource Renewable Energy completed Europe’s largest floating solar farm of 6.3MW on the Queen Elizabeth II Reservoir, near London.
Research and innovation in relation to floating solar is currently ongoing on the island of Ireland though, for example Solarmarine Energy Ltd, in Co. Mayo has researched and designed an innovative floating hybrid renewable energy system to produce green hydrogen. Their research has indicated that floating solar is ideal for island and coastal communities. The Centre for Advanced Sustainable Energy (CASE) in Queen’s university Belfast is also researching cost effective and more robust floatation platforms allowing solar deployment in more challenging sea conditions along with assessment of potential to integrate solar thermal with PV panels onto one platform.[2]
So, although there are still challenges in floating solar deployment around materials and costs, the market is accelerating and as technologies mature, we may start to see floating solar development closer to home.
[1] Are Floating Solar Panels the Future of Clean Energy Production? | Smart News| Smithsonian Magazine
[2] Floating Solar – Centre for Advanced Sustainable Energy (case-research.net)