Published 2021-05-26

This post is also available in Swedish

Solar panels may change geothermal market

The goal of the SmartSol project, which is under way in Mistra Innovation 23, is to develop an integrated heating, cooling and electrical system solution for European buildings, with improved land use. The technology has proved workable in simulations, and pilot studies are now being prepared.

Mistra Innovation 23 (MI23) is aimed at enabling small and medium-sized enterprises (SMEs) to develop innovative ideas for commercial and environmentally sound products, processes and services in collaboration with academia. Work in is based on the previous Solhybrid project, which was funded through Mistra’s earlier Mistra Innovation initiative.

Solhybrid addressed the problem of solar cells’ decreasing efficiency with rising temperatures, and developed a solar-hybrid panel with cooled solar cells to boost electrical efficiency and use cooling water as a heat source. Solhybrid’s successor as a Mistra project, SmartSol, is now focusing on development of hybrid solutions with cooled solar cells for geothermal heating systems. Its goals are higher energy efficiency, lower investment costs and improved use of land for drilled energy wells.

The MI23 project is being carried out in collaboration with the commercial enterprise Solhybrid, KTH Royal Institute of Technology, MegaWatt Solutions Nordic and Bengt Dahlgren Stockholm Geo. The project manager Magnus Johansson, Solhybrid’s CEO, explains that the geothermal boreholes are cooled down, thereby losing power. In his view, the solution is to place the boreholes relatively far apart. This means that the potential for geothermal heating is reduced for densely built-up areas with large properties. The technology they are now developing further is based on the fact that the heat created by cooling the solar cells is conveyed down into the boreholes used for geothermal heating, which prevents them from becoming too cold and losing efficiency.

‘Cold water is brought up from the borehole and cools the solar panel to boost electricity production. That heat then goes back down into the borehole, thereby recharging the hole — and efficiency increases. Instead of 0°C water, water at 10°C goes down; and instead of depleting the core (the rock itself being the heat source), we constantly get energy back. This means that the number of boreholes, but also the distances between them, can be reduced, and we’re opening up for a completely new market that can compete with district heating,’ Johansson says.

Testing on KTH’s roof

The technology has been tested in simulations at KTH Royal Institute of Technology in Stockholm. These show that the borehole distance can be reduced by 20–30 per cent. It now remains to be seen whether the simulations match reality. Two tests are planned: first, a small-scale one on KTH’s roof and, second, a larger test on a block of 50‒60 apartments is being discussed. The system will be monitored in real time to see the output, energy and how the borehole reacts.

Johansson points out that it is important to see what happens at differing temperatures, and whether the output varies from one part of Sweden to another. Obtaining heat from the hybrid panels does not require warm days and strong sunshine: the ambient air needs to be only 4°C higher than the temperature in the boreholes for the technology to have an output. This means that heating is also provided at night and for much of the year. But even if the technology proves successful, major challenges await, according to Johansson.

‘If the results are good, the biggest challenge in the long run is for the industry to embrace the technology. That would take jobs from the people who drill the holes, and the solution must be compliant with the legislation. Suppliers of geothermal heat pumps have also optimised their pumps according to the prevailing temperature, so their products probably need further development.’

Nevertheless, Johansson sees great potential for the technology, and points out that only a third of all large properties can use geothermal heat owing to the boreholes being so far apart. The hybrid geothermal-heating solution is relevant mainly for the Nordic countries and Canada. But hybrid solar-panel technology can be used in other areas as well. Johansson mentions heating of energy-intensive facilities, such as swimming pools, and the capacity to reduce heat losses for hot water by running colder water in the pipes, and raising the temperature by using panels on individual buildings.

‘As a small company, it’s wonderful to work with KTH and share in the latest technology and cutting-edge solutions. We don’t have those resources. At the same time, they get to be out with us in the real world. Big projects are often undertaken, and then the results are presented later. In these project, we’re going in tandem throughout the journey.’