Heinineva Solar Park supports the government’s guidelines in utilising areas previously used for peat production as areas of renewable energy production. The large, open area of Heinineva in Lapua is ideal for collecting solar energy because it is unshaded, but the size of the solar park, the marshy ground and the acidic, sulphate-rich soil set high requirements. Menna Luhtala had submitted a drainage plan, as specified by the ELY Centre, 60 days in advance. “But the centre requested a more detailed plan, which was ultimately provided by Maveplan,” she explained. In addition to the drainage plan, Maveplan prepared road network and detailed plans for the site. Maveplan was already familiar with EPV through previous peatstack measurements and road design work linked to peat production. “Maveplan was selected on the basis of our previous cooperation, which had been very good,” Luhtala explained. “We knew they would provide a smooth, independent service. We didn’t see any need to change design agencies.” The solar park has been commissioned step by step. “The park consists of 11 blocks, which will go into operation as they’re completed,” Lärka said. “All construction needs to be completed by August 2025, and the park has to be operating at full capacity by 1 January 2026.”

A demanding area for green commercial use

The ground in Heinineva presents a challenge for the construction of roads and solar panel rack foundations. ”There was no bearing ground, and the open field ditches ran in the wrong direction for the racks,” Lärka explained. “The drainage at least was the right solution from that point of view.” Maveplan’s plan combined new controlled drains with existing water treatment structures originating from peat production. “There is now a controlled drainage system in the area, where the water flows through control wells to sediment basins, from where it is pumped to the vegetation field freed up from peat production,” Luhtala said. “As such, all the water exits through one point, and we can monitor its quality. Taking this approach, we’ve taken the best existing aspects and applied them to our new solution.” Benefits of controlled drainage:

• The levelling of the field facilitates the construction phase and the laying of foundations
• Soil acidity control
• Climate emissions control: acid sulphate soil oxidation and emissions can be prevented using drainage control wells, and raising the water level also prevents carbon dioxide emissions from peat decomposition
• Controlled temporary lowering of the water level, e.g. for maintenance
• Vegetation management using water level regulation: deep-rooted plants will not take root below the water level
• All water from the site is discharged through a single point, with the water’s quality being monitored and water being pumped into the vegetation field
• Regional water management: 18 control wells in 11 blocks of the solar park for regional water management

The total area of Heinineva Solar Park is 140 ha, of which the area covered by panels is around 120 ha. Its design and implementation had to be done right first time, since any subsequent remedial work on the soil would be almost impossible to carry out. Controlled draining is also a risk management measure. “Open ditches get clogged up,” Luhtala stated. “Moreover, soil rich in acid sulphate is risky, so even from this point of view the best solution to control it was to use controlled drainage and control wells. By raising the water level, acidic soils can be kept in an acid-free state. And the 18 control wells allow the water levels to be regionally controlled.” Luhtala and Lärka are satisfied with Maveplan. “There was no need for our people to accompany them to the site or supervise their activities,” Luhtala said. “Their work in very self-managed. Our cooperation was seamless and spared our resources. We kept the lines of communication open with the idea that there’s nothing too small to ask the other side about. And on top of all that, they take care of everything even after their actual work is done.” For his part, Lärka thanked Maveplan’s Seinäjoki office for the promptness of their responses whenever contacted.

Maveplan team leader Juha Laakso sums up the starting points and solutions at the Heinineva site

Juha Laakso has decades of experience of peat mines and arable land in South Ostrobothnia, where the conditions in Heinineva were known to him as much as 20 years ago. His own job description includes preparing drainage and soil extraction plans and dealing with environmental permit issues. Starting points:

• The area of South Ostrobothnia contains acidic subsoil from the ancient Litorina Sea.
• The Heinineva project was one of the first solar parks built on an acid sulphate peat bog in Finland, meaning it was something new for authorities as well.
• EPV and Maveplan devised the modus operandi for the implementation of peatland solar parks.
• The drainage and water and acidity management solution was driven by factors such as ground relief and peat layer thickness. Heinineva has a predominantly thick peat layer.
• Heinineva had field ditches every 20 metres, which previously acted as a solution for the improvement of the soil’s bearing capacity and water management in the energy peat bog.
• The field ditches were transverse to the panel rows, so the terrain had to be levelled and the ditches filled.

Solution:

• Controlled drainage was chosen because it can control the amount and acidity of drainage water in the area and reduce greenhouse gas emissions from soil decomposition.
• It was possible to design the drainage in unobstructed soil because the solar panels were not anchored to the ground with piles, but with pressure plates tested by EPV.
• The locations of the controlled drains were mainly marked on the terrain using automated machine control based on the national ETRS TM-35 coordinate system.
• To control the water, the controlled drains were put into use with as little water as possible.

To be continued…

The use of peatland for solar parks requires good planning, as the soil beneath the peat determines implementation on a case-by-case basis. “In Heinineva, only one foundation method was used, but the drainage style and foundation vary from case to case,” Lärka explained. “On some sites we might use two or three foundation methods. For the future, we have learned that drainage plans need to be made in advance to allow for the regulatory phase of the permit process. As such, drainage must continue to be done all at once. It can’t be done retrospectively, as this would delay the completion of the project.” Luhtala adds that this is linked to possible future subsidies, which could be lost if the project does not keep to schedule. EPV Energia Oy and its subsidiary EPV Aurinkovoima Oy are pioneers in emission-free energy production. Solar energy complements their product portfolio. A dedicated solar energy measurement station is being used to study and improve the predictability of solar power. Decentralised energy production is also better in supporting energy security. Heinineva is the first solar power project of EPV Aurinkovoima Oy, which also created an operating model for the construction of a solar park. The establishment of the park in a marshy area, and the size of the project, set high standards. The lessons learned can be applied to similar, less demanding projects. The company’s next solar power project is already in the pipeline. ”Each project is different, but the core concept has now been established,” said Lärka. “There’s always room for improvement when creating the first one, but all in all, the process has gone smoothly at Heinineva, and the boundaries between partners were clear. Responsibilities were taken over by one partner from the other, such as Maveplan’s designs being taken to their partner’s more detailed level, for instance where the electrical engineering was concerned. And in addition to learning, there’s also been development. Finnish-made energy collectors are being tested at Heinineva.” Luhtala adds that they are employing local companies and continuing to work with partners like Maveplan, who they wholeheartedly recommend. The Heinineva Solar Park project was granted NextGenerationEU funding of 12 million euros from the EU Recovery and Restoration Fund (RRF) on 8 December 2022. The total value of the project as noted in the application was 64.5 million euros.