Renewable energy is an important part of meeting rising energy demands and combating climate change, but the negative consequences of such technology are sometimes disregarded. Given the inextricable relationship between climate and ecology, evaluating the effects of energy technologies necessitates taking into account the complete range of global environmental concerns.

We discussed the environmental impacts of three primary sources of renewable energy – hydro, solar, and wind energy – as well as various mitigation techniques. In some circumstances, all three categories might have substantial environmental impacts. Wind power has the fewest and most readily mitigated impacts; solar energy, if built and handled properly, is similarly neutral. Hydropower certainly poses the greatest dangers, especially in certain biological and geographical environments. Given their rapid global expansion, more research is needed to analyze the environmental implications of these “green” energy technologies.

Renewable energy, which is an important part of our global climate change mitigation plan, must be viewed from the perspective of biodiversity and ecosystem preservation. In terms of total ecological implications, our examination of three major types of renewables – hydro, solar, and wind energy – reveals that wind power is most likely the safest form of renewable energy. In terms of possible implications on land and aquatic species, natural ecosystems, and greenhouse gas emissions, hydropower looks to be the most damaging.

More research is needed, however, on the long-term effects of all three types of renewables, as well as the best ways for mitigating them. Recent legislative changes aimed at reducing carbon emissions, such as the historic Paris Agreement, could result in an avalanche of renewable energy projects, necessitating intensive research efforts and practical planning standards to ensure that such developments are truly “green.”

The Rise of Renewables

Growing human populations and rising levels of consumption have elevated energy demands, placing increasing burdens on the environment – particularly on the global climate. In a transition to clean sources of energy, much energy growth will come from renewable energy (see Glossary) sources and, as of 2016, 176 nations have set targets to obtain certain proportions from so-called ‘green’ energy sources. While these efforts are commendable, much of the development of green energy is having large impacts on the environment and biodiversity, particularly in the hyperdiverse tropics where human populations and economies are expanding most rapidly.

Global attention has largely focused on the environmental impacts of conventional energy sources, particularly fossil fuels. However, some recent reviews have compared the impacts of different renewable energy sources. While renewable energy sources generally have low carbon emissions, they are often more land-use intensive than conventional energy sources, thereby creating potential conflicts with the conservation of terrestrial biodiversity and ecological services. In a theoretical comparison of wind turbines, solar photovoltaic (PV) panels, and bioenergy from the perennial grass Miscanthus, bioenergy posed the highest threat to biodiversity – largely because of a high degree of overlap between potential Miscanthus production lands and habitats sustaining high biodiversity.

In another study accounting for electricity price, greenhouse gas emissions, energy conversion efficiency, land and water requirements, and social impacts, wind power was found to be the most sustainable form of renewable energy, followed by hydropower. However, to date, there has been no comprehensive review of the different sources of green energy and their impacts on biodiversity. We provide here a general overview of three of the most important renewable energy sources – hydropower, solar energy, and wind power – and assess their potential impacts on biodiversity and key ecosystem services.

Our review does not cover geothermal energy, with a power capacity an order of magnitude lower than that of the other three types above; nor bioenergy, which is presently based mostly on the production of crops, and differs markedly from the types of infrastructure developments associated with hydro, solar, and wind energy. We describe recent and projected growth in these three energy types, key sites for each energy source, and their consequences for biodiversity and ecological health.

Renewable Energy Developments

In 2016 the installed electricity generation capacity of hydropower was 1096 GW. Actual electricity generation, however, was estimated at only 4.1 PWh, much lower than the potential global annual generation of 52.0 PWh. This could be due to droughts that caused downturns in power production in some regions, including the Americans and Southeast Asia.

Because of significant regional differences in potential hydropower capacity based on river flows and elevation, this global capacity is not distributed evenly around the world; China has the highest potential generation (7.17 TWh/year) and installed hydropower capacity (305 GW), followed by Brazil (3.63 TWh/year, 97 GW). Between 2015 and 2016, global solar PV capacity increased by 33%, from 228 to 303 GW, a remarkable rate of growth. In the last decade, global capacity has expanded 65-fold. China continued to have the most capacity (77.4 GW), accounting for more than a quarter of worldwide capacity.

Even though CSP (Concentrating Solar Power) capacity has climbed to 4.8 GW, it still contributes to only 1.6 percent of total solar PV capacity. Wind power capacity climbed by 54 GW in 2016, increasing global capacity to 487 GW. The wind was the biggest source of new energy capacity in Europe and the United States in 2015, with China coming in second. China has the largest capacity (168.7 GW), accounting for more than a third of all capacity worldwide. Globally, offshore wind farms now produce 12 GW, up 3.4 GW from 2014.

Global renewable energy investment reached an all-time high of US$312.2 billion in 2015 [excluding significant hydropower projects of more than 50 MW]. Emerging countries (including the BRICS nations of Brazil, Russia, India, China, and South Africa) have now outspent industrialized countries in terms of renewable energy investment for the first time, with China alone accounting for 32% of total global expenditure. For the first time in 2015, renewables accounted for the majority (53.6 percent) of newly created energy capacity globally. (Except for huge hydropower).

Between 2015 and 2030, China, the world’s top energy consumer, is anticipated to increase its energy consumption by 60%. Between 2020 and 2050, China’s hydropower generation is expected to increase from 11.4 to 15.5 TWh (while falling from 13.1 to 11.1 percent of total energy generation), while wind generation is expected to increase from 3.2 to 10.4 TWh (from 3.7 percent to 7.5 percent), and solar generation from 0.3 to 4.8 TWh (from 0.4 percent to 3.4 percent ). Hydropower will continue to contribute the highest percentage of renewable energy generation, both globally and inside China, according to these forecasts, followed by wind and solar.

Prescriptions for Growing Renewable Energy in a Sustainable Manner

It’s crucial to note that research on the three renewable energy sources is still inconsistent, with a particular gap in knowledge of solar energy and its effects on biodiversity. However, based on the findings, hydropower is the most likely source of major biodiversity and environmental consequences, followed by wind power and solar energy. All three cause environmental disruptions, some of which have gone relatively unnoticed but which may be alleviated in many cases.

It’s tough to offset the consequences of hydropower facilities on biodiversity since they’re so big and take up so much territory. The fact that hydropower necessitates the construction of vast water reservoirs on formerly dry terrain is an unavoidable issue. Large-scale effects on flooded habitat, as well as secondary effects on land-use change from related highways and electricity lines, constitute a major danger to terrestrial biodiversity. The effects on freshwater species and ecosystems are also significant, though they are still poorly understood, and there is a growing recognition that hydropower is frequently a significant source of greenhouse gas emissions.

Fortunately, the Conservation Strategy Fund just released the Hydro Calculator, a free tool that allows local communities, scientists, and policymakers to assess the predicted carbon emissions produced by planned hydropower dams, which could influence future dam construction decisions. The location of these energy facilities is a critical aspect in determining their biodiversity impacts. The geographic terrain often constrains hydropower dam development plans, although there is a growing recognition that many decisions must be taken at the river-basin size. Several of the Mississippi River’s major tributaries support more than 80% of the large-river specialist fishes found in the river’s mainstem.

However, we know that the effects of solar energy can be considerably decreased if future development is centered on regions that are already degraded and lack threatened species, based on current evidence. Solar power plants should not be built in ecologically vulnerable areas. Even without accounting for advances in solar energy efficiency, there is currently 1.1 billion ha of degraded lands worldwide, and to double current solar PV capacity, only 0.1 percent of the available degraded lands would be required – even without accounting for advances in solar energy efficiency. More research into the specific effects of solar energy breakthroughs is critically needed, especially considering this energy source’s rapid rise.

Wind farm design can be significantly improved to help mitigate biodiversity issues. In general, the fatality rate grows with the height of the turbine. Building wind turbines at the lowest possible height can dramatically reduce the death of birds and bats, while there may be tradeoffs between having fewer large turbines against many smaller turbines. Turbine placement is crucial, and high-volume transit areas for flying species, such as ridgelines, should be avoided if at all feasible. Wind farms should not be developed near bird or bat habitats, and migratory paths for flying creatures should be avoided at all costs.

Furthermore, wind turbine technology should be developed to reduce turbine noise and heat. Wind energy is arguably the safest kind of green energy in terms of biodiversity, as it requires a smaller footprint than either solar or hydropower, and its impacts are more easily rectified. There is, however, room to improve tactics to reduce the negative effects of new wind projects on biodiversity and ecosystems.