TM Building World 1.5.2022 Text by Reijo Ruokanen, Editor-in-Chief
Henrik Grönqvist invests in a heating system that uses solar energy in the summer and stores it for the winter.
Henrik Grönqvist had been thinking for some time about how to replace his old woodchip heating system. He happened to see a TV programme about storing solar heat in the ground and became seriously interested when he found Helio-storage Oy, a Finnish supplier of solar energy harvesting and storage systems. The company handles the supply and installation of the entire system: the heat storage system, i.e. the collection pipes are installed in the ground, in boreholes, and a Heliostorage solar collector roof is installed on the roof of a private house or other building.
The heating of the house and the heating of the tap water
A total of around 250 clove metres of solar collector roofs were installed in Grönqvistie: they convert solar radiation into usable heat. The solar collectors on the roof circulate a water-glycol mixture that is heated by the sun. The mixture is passed through a heat exchanger, releasing heat energy into the water storage tank. The water from the storage tank is used to heat the buildings’ hydronic underfloor heating and domestic hot water.
In spring and summer, hot domestic water and heating of the buildings is provided by the energy generated by the solar collector roof. In autumn and winter, the heat generated by the solar collector roof stored in the clay soil, the collector circuit and the soil’s own heat is used.
Involved in climate change initiatives
“The system has worked well,” says Herik Grönqvist.
“Last August, we completed all the installation work and got the system up and running. Now the heating system is being tuned and optimised to work as efficiently as possible. This winter we will use the heat stored from the previous summer, which was generated by the sun. It feels good to contribute to climate action in this way.”
“The calculated yield of the roof is 120 MWh per year,” says Mats Manderbacka, Managing Director of Heliostorage Ltd.
Return on investment for half the year
“The project started a couple of years ago when I installed hydronic heating in two farm buildings,” says Henrik Grönqvist, a part-time farmer.
Now solar energy heats the buildings for almost half the year.
“If all goes well, I may consider a new project and expand the system to cover our detached house and two relatives’ houses nearby in the future.”
In the clay soil of the Grönqvistie plot, there are a total of 450 metres of nested, ring-mounted pipes at a depth of almost 20 metres. The hottest liquid of all is piped from the solar collector roof to storage in the inner pipes of the ring, and the coldest liquid in the outer pipes.
“When the sun is high in the summer, it heats up the collectors and the warm liquid is fed into the core of the ground storage. When the sun goes down and the air cools, the heat is directed to the outer tubes. Automation takes care of controlling the process.”
The heat pump controls the system
The system takes in the hot fluid needed to heat the domestic hot water and the house. The whole system is controlled by a geothermal heat pump, which Henrik Grönqvist installed in the workshop.
“It rotates all the time, pumping the hot water-glycol mixture from the underground collectors through pipes to a controller cabinet, which sends the hot liquid to the hot water tank next door. During the winter, the heat pump decides when to draw heat from the heat reservoir,” says Grönqvist.
The system can be monitored in real time
In the workshop, a local computer screen on the side of the controller cabinet allows real-time monitoring of the system. It shows, for example, how the heat is distributed in the underground pipes, the collection circuit, or the temperature of the core of the collection circuit. The total amount of energy stored is also displayed in real time. The data can also be read remotely from a computer or smartphone.
“The controller cabinet is the brain of the system,” says Henrik Grönqvist.
“If you have purchased a geothermal heat pump in the past, the cost of the heat collection and storage system is significantly lower. The system can even double the benefits of a ground source heat pump,” says Mats Manderbacka.
For private homes and public buildings
Heliostorage’s solar collector roof is made of an aluminium profile with an absorption coating: it minimises heat dissipation away from the collector. The coating is covered with an air gap of about one centimetre. The top of the roof is made of polycarbonate glass.
“A solar collector roof costs around €200 per square metre. It is waterproof and replaces a traditional roof. Each square metre produces about 400 kilowatt hours of energy per year,” says Manderbacka.
“The roof stores energy in the same way as buying oil for storage. Over the coming decades, the roof will produce about 400 kilowatt-hours per square metre of energy every year.”
“A system for a detached house costs around €20,000 to €30,000. Its calculated payback period has varied between 7 and 10 years in our sites.”
“Solar collector roofs also meet the fire and other performance requirements for roofing in public buildings such as schools and hospitals.” Mats Manderbacka explains.
Interest from abroad too
At the turn of the year, Heliostorage Oy’s system had been installed in detached houses in three different cities, as well as on a farm in Kehde, at Kaustinen College and in two factories.
“We are also currently completing one of the world’s largest heat storages in China,” says Manderbacka.
“We are also working on the world’s first artificial cold store: we are making a permafrost for the Kruunupyy ice rink. Cold is stored in the ground instead of heat, which reduces cooling costs and extends the playing season.”
Heating consumes the most energy
The further north a house is located, the greater the share of heating in the total energy bill. Energy is also used to heat domestic hot water, household electricity and to cool the house.
“Heating accounts for about 50 percent of the energy consumption of a single-family house, 20 percent is used to heat water and 30 percent for household electricity,” says Manderbacka.
“A solar collector roof provides domestic hot water for a detached house for about four months of the year, while the excess heat is stored in the rock, i.e. the rock is also heated. During the winter months, the heat pump receives much warmer water than without the system, thanks to the heat storage system, so the pump only uses water heated by the ground.”
The answer to energy problems?
“For a long time, I was bothered by the fact that in winter you have to heat and in summer you have to cool, and both use energy,” says Mats Manderbacka, Managing Director.
“I started thinking that if you could store heat and cold, the world’s energy problems would be solved.”
In 2008, Manderbacka dug a traditional borehole for his detached house and installed a heat pump.
“At the same time, I designed a new type of solar collector for the garage roof that would harness both solar energy and heat even at low solar angles.”
“I connected the solar collector to the heat pump so that when it’s warmer outside than inside the rock – about 9 months of the year – the heat pump cools the solar collector roof instead of the rock, increasing the efficiency of the heat pump dramatically,” says Manderbacka.
“On average, the water from the rock is only a few degrees warmer than the water from the rock. When the water from the solar collector roof is fed to the heat pump at +15 degrees, the efficiency of the heat pump is much higher.”
“For four months of the year, the solar collector roof heats all the hot water used in our house. At the same time, the surplus heat is stored in the rock, i.e. the rock is also heated, and in the winter months the incoming water to the heat pump is much warmer than without the solar collector roof.”
