My last post was about floating nuclear power plants. By coincidence I then ran across a news item about floating solar installations. This is also a potentially useful idea, and is already being implemented and increasing. It is estimated that in 2022 total installed floating solar was at 13 gigawatts capacity (growing from only 3 GW in 2020). The growth rate is estimated to be 34% per year.

“Floatovoltaics”, as they are apparently called, are grid-scale solar installations on floating platforms. They are typically installed on artificial bodies of water, such as reservoirs and irrigations ponds. Such installations can have two main advantages. They can reduce evaporation which helps preserve the reservoirs. They also are a source of clean energy without having to use cropland or other land.

Land use can be a major limiting factor of solar power, depending on how it is installed. Here is an interesting comparison of the various energy sources and their land use. The greatest land use per energy produced is hydroelectric (33 m^2 / MWh). The best is nuclear, at 0.3 (that’s two orders of magnitude better). Rooftop solar is among the best at 1.2, while solar photovoltaic installed on land is among the worst at 19. This is exactly why I am a big advocate of rooftop solar, even though this is more expensive up front than grid-scale installations. Right now in the US rooftop solar produces about 1.5% of electricity, but the total potential capacity is about 45%. More realistically (excluding the least optimal locations), shooting for 20-30% of energy production from rooftop solar is a reasonable goal. If this is paired with home battery backup, this makes solar power even better.

Floating solar installations have the potential of having the best of both worlds – less land use than land-based solar, and better economics and rooftop solar. If the installation is serving double-duty as an evaporation-prevention strategy, this is even better. This also can potentially dovetail nicely with closed loop pumped hydro. This is a promising grid-level energy storage solution, in that it can store massive amounts of energy for long periods of time, enough to shift energy production to demand seasonally. The main source of energy loss with pumped hydro is evaporation, which can be mitigated by anti-evaporation strategies, which could include floating solar. Potentially you could have a large floating solar installation on top of a reservoir used for closed-loop pumped hydro, which stores the energy produced by the solar installation.

But of course no energy source is without its environmental impact. For floating solar one significant concern is the impact on water birds (where there are bodies of water, even artificial ones, there are water birds). This is an issue because water bird populations are already in decline. Unfortunately, right now we have very little data. We need to see how the installations effect water birds, and how those bird would affect the installations. The linked research is mainly laying out the questions we need to ask. I doubt this will become a deal-killer for floating solar. Mainly it’s good to know how to do this with minimal impact on wildlife.

This is true of energy production in general, and perhaps especially renewable energy as we plan to dramatically increase renewable energy installations. There has already been a big conversation around wind turbines and birds. Yes, wind turbines do kill birds. Even off shore wind turbines kill birds. In the US it is estimated that between 150k and 700k birds are killed annually by wind turbine. However, this is a round-off error to the 1-3 billion birds killed by domestic cats annually. It is also estimated that over 1 billion birds die annually by flying into windows. We can save far more bird lives by keeping domestic cats indoors, controlling feral cat population, and using bird-safe windows on big buildings than all the birds killed by renewable energy. But sure, we can also deploy wind turbines in locations designed to minimize the impact on wild life (birds and bats mostly). We should not put them in corridors used for bird migration or feeding, for example.

The same goes for floating solar – there are likely ways to deploy floating solar to minimize the impact on water birds and their ecosystems. The impact will never be zero, and we have to keep things in perspective, but taking reasonable measures to minimize the negative environmental impact of our energy production is a good idea.

We also have to keep in mind that all of the negative environmental impacts of renewable energy (and nuclear power, for that matter – any low carbon energy source), is dwarfed by the environmental impact of burning fossil fuel. Fossil fuel plants kill an estimated 14.5 million birds in the US annually – about a 500-1000 times as many as wind and solar combined. And this is direct causes of death from impact with infrastructure and pollution. This doesn’t even count global warming. Once we factor that in, any environmental impact comparison is very likely to favor just about anything except fossil fuel.

Likely we will have a lot more floating solar installations in our future, and this is also likely a good thing.