Heat pumps are regarded as efficiency miracles and as the heating technology of the future.
But the calculations, which seem so beautiful, contain two fundamental mistakes in reasoning.
Munich - It's almost too good to be true.
A heat pump converts one kilowatt hour (kWh) of electrical energy into up to four kWh of thermal energy.
400 percent efficiency.
That's as if a mid-size car could travel 200 kilometers on just one liter of petrol.
Climate Minister Robert Habeck (Greens) would like to have the heating miracles in all houses.
"This is the technology of the future," he enthused at the second "Heat Pump Summit" on November 11th.
There should be six million heat pumps by 2030.
And he has now presented a draft law according to which citizens would hardly be able to avoid this heating technology in the house.
As with all supposed patent solutions, it is worth taking a closer look.
Instead of the minister's pipe dream, Germany could wake up from an energy policy nightmare.
The basic principle of the heat pump is similar to that of a refrigerator
The basic principle of the heat pump is the same as in a refrigerator: additional thermal energy is extracted from a cooler medium (the interior of the refrigerator in the case of a refrigerator) and this further heats up an already warmer medium.
In the case of the refrigerator, it is the black grille on the back.
The energy that you put into it drives the necessary compressor.
With the heat pump, the cooling principle is reversed: Thermal energy is taken from the environment and used to heat the water in the heating circuit.
Air source heat pumps have the lowest investment costs.
They are therefore more widespread than ground or groundwater heat pumps.
The following considerations refer to these air heat pumps and only apply to the other heat pumps with restrictions.
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The heat pump heats with the ambient heat
© dpa
Heat pump: More difficult in winter
Let's take a look at the degree of efficiency: a heat pump is more efficient the lower the temperature difference.
In midsummer, when it's 25 degrees in the shade, it's highly attractive to heat the pool water to 30 degrees with a heat pump.
In winter, when temperatures are below zero, it is many times more difficult to reach these 30 degrees and even harder to reach the 55 degrees that you need for an old building heating system.
But even in summer, a solar system could supply the heat – apart from the control electronics and the pumps – without using any electricity.
Even then, if you look closely, the heat pump is at a disadvantage.
It's highly efficient when you don't need it.
The plus melts away when you need a lot of warmth in the cold season.
In extreme cases, the system exits.
Then a heating element kicks in.
The expensive and highly complex energy miracle then mutates into a kind of simple immersion heater.
All this puts the ecological advantage into perspective: Because in the cold season, when solar energy as a power source is practically absent, you need a lot of energy for heating.
In the case of the heat pump, this means electricity, which is then scarce and mainly comes from power plants fed with fossil fuels.
For physical reasons, their efficiency is less than 50 percent.
If the heating element is then used, the nice calculations collapse completely.
Heat pumps: beautifully calculated advertising messages
The more the number of heat pumps approaches Habeck's target of six million, for whose electricity requirements gas and coal-fired power plants are ramped up in winter, the more drastic this effect becomes.
So you can't reach the targeted green electricity share of 65 percent or only by declaring coal-fired electricity - as with electric cars - to be climate-neutral.
Because the huge offshore wind farms that will one day serve the electrical base load are a distant dream of the future.
That was the first mistake in reasoning: One is based on average consumption instead of differentiating the consumption profile over the course of the day and the year.
Because only then would an overall picture emerge that no longer has much to do with the beautifully calculated advertising messages.
The second misconception is closely related: It is the electricity pricing.
There is a fixed tariff per kilowatt hour.
This is an average price, with which the suppliers should get their money's worth.
But this price reflects a grossly simplified picture of the reality of supply and demand.
Supply costs for electricity fluctuate
In reality, the cost of providing electricity varies greatly.
If the wind blows more evenly on sunny days, electricity from solar and wind power is available to grid operators practically free of charge.
When the fossil fuel-powered reserve power plants, which are mainly needed in the cold season, run up on cold winter days, the actual electricity price rises many times over the tariff.
This means: If the heat pumps consume the most electrical energy during the heating period, the realistic supply price for this is significantly higher than the agreed tariff.
In winter, all electricity consumers subsidize the heat pumps, which are supposedly so economical, via their electricity bill.
Tendency: increasing with each individual conversion.
Everyone pays for the expensive electricity that only a few use.
Future variable electricity prices would correct this.
They could be a rude awakening for heat pump operators.
List of rubrics: © Silas Stein/dpa
