“Our house is our sustainable everyday act”


The Kosonen and Keskisaari family

Who: researchers Anna and Antti, and their daughter Lumi, 5 months
Where: Meltola, about 3.5 km from the centre of Imatra
Home: A detached house built in 2017, geothermal heating and solar power
The Kosonen and Keskisaari family

Our house is our sustainable everyday act

“A house like Meltolan Energia”– this was the title of an article about the family home in the local newspaper Uutisvuoksi. And this family’s house is indeed a veritable power plant. The house is equipped with a solar power system that generates more energy than the house and its residents can use.

Surplus electricity is sold to the network in the summer, and then bought back in the winter at a slightly higher price.

“The electricity network acts as a good ‘storage unit’. It doesn’t make financial sense to buy batteries for energy storage, especially as we don’t have any hour-by-hour consumption or production data,” says Antti.

The family’s home and garage are covered in a total of 82 solar panels. About 40 are located on the south-facing side of the house, 21 on the east side of the garage and 21 on the west side. The system’s total power is 21.1 kWp. The unit kWp (kilowatts peak) is usually used to rate the power output of solar panels under certain standard conditions.

Antti says that the solar panel system’s annual production has been 16.6–18.1 MWh with an hourly peak of 15.3 kW.

Purchased electricity costs less than EUR 200 per year

The house’s geothermal pump runs on solar power whenever it makes sense to do so. The pump is controlled by a smart unit that monitors the spot price of electricity in the network and the production forecast for the solar power system. When the price of electricity is low, the geothermal pump runs on solar power. When the price of electricity is higher, solar power is sold to the network. This provides the best financial benefits.

The home’s smart unit was developed and implemented as a student project, and is therefore one of a kind. Antti says that they can monitor prices and energy production in real time and, for example, run the washing machine when electricity is cheap.

“We just did some laundry with solar power,” says Anna, as the washing machine downstairs announces that its programme has ended.

Geothermal heating provides a heat source for their water-based underfloor heating. The house also has an intake-air cooling system and four fireplaces, one of which is a water jacket fireplace. Intake-air is cooled using liquid from the geothermal well. The incoming air circulates through the heat exchanger and is cooled by the liquid in the underground pipes.

“This system distributes cool air throughout the house and is also good at removing moisture. The system was taken into account when the house was built, as the pipes need to be insulated against condensation. It just uses standard commercial solutions,” says Antti.

For a scientific article that was being published about their house, the couple calculated the carbon footprint of their home’s energy consumption throughout its entire lifecycle. Its emissions from energy consumption are 26.4 tons (CO2e), but -42.3 tons (CO2e) when you take into account the surplus energy sold to the network.

Antti and Anna built their house almost by themselves. The lower floor of the hillside house is made of stone and the upper floor of wood. Antti says that the only thing they paid for was to have the house’s frame erected to roof level. They found a suitable plot – where the house could be positioned in the right direction – in Imatra.

“We considered how to make the house more energy efficient in some other way than using insulation. We wanted to use renewable energy and make it more energy efficient with the aid of machinery rather than insulation.”

Eating their own harvest throughout the year

Sustainable values can also be seen in other areas of the family’s daily life. They’re keen recyclers, grow vegetables in their own garden to eat in the winter, mainly take domestic holidays, and often make use of car sharing to get to their hobbies. On a normal day, they use public transport to get to work in Lappeenranta.

“We recycle plastic, paper, cardboard, glass and metal. We have our own compost for biowaste, which generates mulch. The collection interval for dry waste is currently eight weeks. Before our daughter was born, we could almost have managed with once a year. We generate very little dry waste now that we recycle plastic,” says Antti.

Anna says that, even when they were building the house, they didn’t end up taking many trailers of waste to the dump – everything that could be utilised was utilised. They separated out plastic waste even then. Anna shows us the yard and garden, where they’ve used surplus blocks and stones sifted from the soil. The blocks have been used to make things like flowerbeds and strawberry beds.

“In this vegetable garden, we grow almost everything that it’s possible to grow here: at least onions, potatoes, cabbage, beetroot, parsnips, turnips, swedes and lettuce. I though that, when our daughter starts to eat solid food, we could get the ingredients from our own garden. We also have a cellar where we store home-made juice, and we still have potatoes, gherkins and pickled beetroot from last winter. We haven’t really thought about food in terms of emissions, but we mainly buy Finnish produce from the store.”

A price on emissions

Antti and Anna are happy to share their experiences and knowledge about their zero-energy log house. The first thing that many interested people ask is when their solar energy investment will pay itself back. Antti wonders why people are still only willing to make consumption choices with their eye on the price tag. Emissions should be considered in addition to the price.

“The thing that is generating emissions is money. People should think about how they use their money and how that usage generates carbon dioxide emissions. For example, air travel is one of the worst sources of emissions. This house is our sustainable everyday act. It enables us to set an example of how people could act. It has greater visibility and impact than, for example, recycling.

There can be no price placed on carbon emissions at the moment. Companies should develop services with the smallest possible emission impact – or even negative emissions – and also sustainable products that can be repaired or reused.”