Solar energy plays a critical role in the transition to a low-carbon future, and development is advancing rapidly in Finland as well. Taaleri Energia is wind and solar developer and fund manager and one the largest wind power producers in Finland. Taaleri SolarWind III Fund’s investment in a 129 MWp solar farm in Finland is one of its kind and sets a benchmark for responsible renewable energy development. Luontoa evaluated the project’s climate and environmental impacts and established a framework for monitoring and reporting, ensuring alignment with Taaleri’s broader sustainability strategies and reporting standards. Additionally, Luontoa provided technical guidance for construction planning to minimize negative impacts and maximize positive outcomes.
Constructed on a drained peatland
The solar power plant is being built on Tervajoensuo, a peatland that was drained over 50 years ago. Originally, the area was mostly treeless, but drainage has profoundly changed its ecological state. While trees have slowly grown in the area, the site’s poor productivity makes it of little economic value for forestry.
Environmental impacts related to land use change
Solar farms inevitably alter local ecosystems, but both site selection and construction methods influence the scale and nature of these impacts. Tervajoensuo has been under human influence for a long time, and there are no endangered habitats or species in the area. As the area has low economic and environmental value, it is well-suited for solar energy development.
The solar farm will be constructed while minimizing further drainage of the area. Floating road structures are used to reduce soil disturbance, maintain the natural flow of water, and use only a fraction of the amount of land mass that would normally be brought to the site. After construction, the natural hydrology of the peatland will be restored, promoting gradual vegetation recovery under the solar panels. Trees from the area will be utilized as road foundations, sequestering the carbon stored in the trees in the re-wetted peatland.
From a water conservation perspective, building on Tervajoensuo is considered safe. Tervajoensuo receives water mainly from rainfall and has limited external water inflows and outflows. The site is bordered by the Tervajoki river and surrounding ridges. While tree removal and construction will cause some nutrient runoff, the area is naturally low in nutrients, and our calculations showed that runoff will be minimal with the suggested preventive measures during the construction phase. After construction, nutrient runoff from the area will decrease from its current level, meaning that the plant will have positive impacts to water conservation over time. Unlike most solar farms, the site will remain unfenced, allowing terrestrial mammals to move freely across the area.
Climate impacts of land use change
According to our calculations, the Hallanvahti solar power plant will generate annual emissions of approx. 500 tons CO₂-eq. This includes the impacts of expanding the transmission grid. The emissions primarily result from tree removal. At the same time, groundwater restoration will slightly improve the soil’s carbon balance, and more importantly, preserve the carbon stored in peat. Our calculations indicate that the peat layer holds 80 times more carbon than the area’s trees. The risk of methane emissions from water table restoration is considered low due to the site’s characteristics. The emissions generated by the project represent only 1.7% of the project’s expected overall annual emissions reduction, which is achieved by replacing fossil energy sources.
Social considerations and community involvement
Renewable energy projects’ environmental impacts are closely linked to social acceptance. Local stakeholders have been actively involved in the Hallanvahti project from the start, providing critical insights into the area’s natural environment.
One of the most significant initiatives tied to the Hallanvahti project is the rerouting of the Tervajoki river to its original course. When Tervajoensuo was drained decades ago, the river was rerouted, increasing the nutrient and sediment flows into Lake Sysmäjärvi. By restoring the river to its original course, the waters now run through a wetland, improving the water quality in Lake Sysmäjärvi. The project was spearheaded by local resident and environmental advocate, Mr. Sakke Häyrinen. Häyrinen has personally witnessed the changes in Lake Sysmäjärvi’s water quality over the past decades. He recalls water visibility of three meters, while typical visibility today is only 30 centimeters. The rerouting works of the Tervajoki river were completed in 2024, and the impacts will be monitored.
Monitoring and future research
Our calculations indicate that Tervajoensuo is well-suited for solar energy development, considering both climate and environmental impacts. So far, there has been limited research on the emissions and ecological impacts of solar farms on drained peatlands. The Hallanvahti project will provide valuable insights for future development, with key factors such as groundwater levels and vegetation changes being actively monitored. The goal of the Hallanvahti project is to achieve net-positive climate and environmental outcomes, following the mitigation hierarchy. This means that negative impacts are primarily avoided through careful site selection, and secondarily, negative impacts are reduced and positive impacts are increased as part of construction and maintenance works. The possible need for ecological compensation and the feasibility of generating biodiversity credits is also being assessed as part of impact monitoring. Furthermore, the impact assessment will be expanded beyond the project site to include the materials and components used in solar panels and infrastructure, providing a more comprehensive understanding of the project’s overall impacts on nature and climate.
The developed methods for transparent and science-based impact assessment will help Taaleri Energia continuously improve its sustainability strategies and provide investors with measurable impact reports. The demonstrated holistic approach to sustainability – encompassing climate mitigation, biodiversity conservation, and community-driven initiatives – ensures that the investment delivers long-term positive outcomes at various levels.
Text has been published in Taaleri Energy’s Sustainability Report 2024.
Text and photo: Lauri Tamminen, who acted as the leading expert in the project.