June 17, 2025, 4:45 am | Read time: 5 minutes
Electricity and heating have become expensive. Those looking to save in the long run can become more independent, such as by using solar energy—for solar power or heating.
The sun shines for free–and we can capture some of its energy and convert it into heat or electricity. This works with solar thermal systems and photovoltaic systems.
Solar Thermal or Photovoltaic–Which Is the Better Option?
Is solar thermal or photovoltaic the better choice? “That depends on several factors, not least the condition of the building,” says Carsten Körnig, CEO of the German Solar Industry Association. He gives an example: An old house with poor energy efficiency needs about ten times more heating than a modern building. However, the hot water demand is nearly the same for both.
There’s also the consideration of how you want to use the generated energy. “Solar thermal naturally provides more power (per square meter) for heating and hot water, but PV systems also power the refrigerator and the electric car,” explains Körnig. Therefore, you often have to see which technology is better suited for which household. An overview:
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How Does a Solar Thermal System Work?
“It supports the heating system and also produces hot water within this cycle. It is the more sophisticated technology,” says Andreas Skrypietz, an expert at the German Federal Environmental Foundation.
In the collectors of a solar thermal system, a mixture of water and antifreeze flows, which is heated by solar radiation. The heat from the water is transferred via a heat exchanger to a combination storage tank. This serves as an interim storage for the heat. The cooled liquid is pumped back to the collector. From the combination storage, the heat is transferred to the heating system or the hot water system.
More on this: Can solar thermal reduce heating costs?
What Are the Benefits of a Solar Thermal System?
The solar thermal system “definitely helps reduce the need for additional fuel–whether gas, oil, wood, or electricity,” says Körnig. Energy consultant Johannes Spruth from the Consumer Center NRW considers the system “particularly useful when there is a higher demand for hot water.” This is generally the case in households with four or more people. The energy gain of a solar thermal system on the same roof area is higher than that of a photovoltaic system.
Can a Solar Thermal System Heat Alone?
Solar systems achieve almost 80 percent of their annual yield between March and October. So not in the deep fall and winter when heating is needed. Therefore, the system always requires an auxiliary heater.
This is usually still an oil or gas heater, but a heat pump or pellet stove is also an option. Alexander Steinfeldt from the nonprofit advisory company co2online recommends a pellet heater as a supplement. “It is suitable for single and two-family homes. In summer, you can partially turn off the pellet heater. The solar thermal system is then sufficient to meet the hot water demand.”
If the sun doesn’t shine on a few summer days, there’s no need to worry, says Carsten Körnig. “With a sufficiently large heat storage, solar heat can be stored for several days.” And: “Storing heat is significantly cheaper than storing electricity.”
How Does a Photovoltaic System Work?
Its solar modules capture sunlight. Through an inverter, the generated solar direct current is converted into household electricity at 230 volts.
What Are the Benefits of a Photovoltaic System?
With self-generated solar power from photovoltaic systems, all kinds of electrical devices, as well as electric cars and e-bikes, can be powered. “More and more applications run on electricity, so our electricity demand is increasing,” says DBU expert Andreas Skrypietz. Therefore, photovoltaics is also a heating and hot water solution in systems that require electricity. The solar power system can be coupled with an electric heating element in the combination or hot water storage tank, or it can operate the heat pump.
Therefore, Alexander Steinfeldt from co2online says: “In many cases, we recommend photovoltaics, even if it is slightly less efficient. It has the edge when you have higher electricity consumption.” Another plus: Energy that you cannot use yourself can be fed into the public grid–you get paid for it. This is an advantage of photovoltaic technology over a solar thermal system for Alexander Steinfeldt: “I can’t feed hot water into the grid.”
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Can a Solar Power System Heat Year-Round?
A photovoltaic system can also only cover a certain portion of the electricity supply over the year, as it produces little energy from fall to late winter. And summer-generated electricity cannot yet be stored for long with the common storage systems, according to the Consumer Center NRW.
However, you can still increase your self-consumption with short-term storage. According to the Consumer Center, with a typical PV system, about 30 percent of the generated electricity can be self-consumed, and with battery storage, it’s about 70 percent.
This can be financially worthwhile. Because: For new photovoltaic systems up to 10 kilowatt-peak, the compensation for a kilowatt-hour of electricity fed into the grid is 8.2 cents and up to 13 cents for the full feed-in of the yield (since July 2022). For comparison: The valid electricity price cap as the upper limit for electricity that must be purchased is 40 cents per kilowatt-hour.
with material from dpa