June 17, 2025, 3:40 am | Read time: 4 minutes
The name is often misunderstood: Zero-energy houses do not promise that you will have no energy costs. They are a way to become more self-sufficient—but not the only one.
A house that only consumes the energy it produces itself–that sounds fantastic, especially in times of high energy costs. However, even a so-called zero-energy house usually cannot achieve complete self-sufficiency. What’s behind this?
What is a Zero-Energy House?
“These are often just marketing promises; in practice, very few houses manage without external energy,” says Arne Kruft from the Federal Association of Building Energy Consultants, Engineers, and Craftsmen in Berlin. So why the term zero-energy house? It refers to a building whose annual balance of purchased and self-generated energy is equal.
This works, for example, with a large photovoltaic system on the building. It generates a lot of solar power in the summer–so much that the household cannot use it all. Therefore, it is fed into the grid for other users.
But in winter, it’s different: The photovoltaic system does not produce enough electricity during the darker months with bad weather to power a heat pump to heat the house and provide hot water. The household must purchase additional energy.
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The Annual Balance Must Be Right
Whether a building can be a zero-energy house is primarily a calculation that should not be misleading. “Feeding excess electricity into the public grid in the summer and buying it back expensively in the winter creates only a seasonal illusion, not low heating costs,” says Georg Dasch, chairman of the Sonnenhaus Institute in Straubing. It is more sensible to fundamentally increase the house’s degree of self-sufficiency.
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This can be achieved by using as much of the self-generated energy as possible. On the other hand, the house should consume as little energy as possible, especially in winter. The following tips are essential:
1. Reduce Energy Demand
“The most important prerequisite for low energy consumption is good insulation of the building,” says Carsten Clobes, head of the Kassel regional office of the Association of Private Builders. “Then a large part of the self-generated heat stays in the house, and not much additional heating is needed.”
This includes insulating the facade, the roof, and, for example, exposed pipes in cold basement rooms. Replacing windows in older buildings can also be worthwhile in some cases.
2. Store Solar Power
“You can’t do without electricity from the grid–especially not in winter when sunlight is insufficient for your own power generation,” says Carsten Clobes. However, a good long-term storage solution for self-produced energy can increase self-consumption.
“For example, it is possible to convert excess electricity from the home’s photovoltaic system into hydrogen through efficient electrolysis and store it,” says energy consultant Arne Kruft. “Fuel cells can later make the energy available again.” However, such a solution is still very expensive.
Currently, storing thermal energy is cheaper. A corresponding system is “a relatively inexpensive and durable way to store excess solar power,” says solar system expert Georg Dasch. It can also be a solution for existing buildings to move away from oil or gas. “A heat pump is often not worthwhile there because too high flow temperatures are required,” says the expert.
Alternatively, a large solar thermal system combined with a biomass heating system, such as pellets, is an option. Using a combination of photovoltaics for electricity production and solar thermal energy for providing heat for heating and water is particularly efficient, says Dasch.
For a house to be as self-sufficient as possible, Arne Kluft suggests planning for five to 15 percent additional costs compared to the expenses for a standard efficiency house. Whether and when the investments pay off depends on how energy prices develop. If they remain high, the costs will amortize more quickly.
with material from dpa