Heat pump with photovoltaics in old buildings: requirements & costs

In principle, heat pumps and photovoltaics can also be combined in old buildings. The prerequisite for this is that the old building is well insulated and has suitable radiators. Otherwise, the energy loss is so great that the use of the heat pump with photovoltaics is not worthwhile and the positive effect on the environment is less. 

Requirements for a heat pump in an old building

In order for a heat pump to be profitable and environmentally friendly even in old buildings, the existing or planned thermal insulation measures are importantThese include energy-saving insulation, large-area heat pump radiators or a general surface heating system, such as underfloor heating.

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Poor insulation increases the heating load of the building enormously, especially in winter when heat is lost through the building envelope. If the heating system is old and consists of small radiators, the flow temperature of the heating system A high flow temperature means that the heat pump requires significantly more electricity to reach this temperature. 

Values of more than 60° Celsius are not unusual. In comparison, energy-renovated houses or new buildings only need a flow temperature of almost 50° Celsius.

The best thing to do is to do a test yourself and set the flow temperature of the heating system to 45-50 degrees on a very cold day. If it gets warm in the building, a heat pump is worth it for you. If it doesn't get warm enough, it may be enough for a heating engineer to replace some radiators.

Requirements for Photovoltaics in Old Buildings

For very old roofs, roof renovation is recommended before installing the PV system. Your roof covering should still be have a lifespan of at least 20 to 25 yearsso that the system does not have to be dismantled again for later renovation.

Solar systems do not require a permit if they are installed on roofs or facades. Only if your house listed building you must apply for a permit from the local building authority.

Which heat pump is best? 

• Water-water heat pumps are particularly efficient. Groundwater often has high temperatures, even in winter. The heat pump draws some of its heat from the groundwater. However, there must be enough suitable groundwater available, for example you have a well on the property that can be used.
• Brine-water heat pumps can be a good alternative if you do not have enough groundwater. The heat pump draws part of the heat from the ground. Specialist companies can equip your property with ground collectors for this, but you will need a larger, undeveloped area in the garden. Otherwise, you can also choose ground probes, but these require a permit for special drilling.
• Air-water heat pumps are the cheapest to buy. The heat pump draws its heat energy from the outside air. However, in winter in particular, this is not particularly warm, which reduces efficiency. In this case, you should definitely use a low heating flow temperature. In addition, the running costs are somewhat higher than with the other two heat pump variants.

Also make sure that the heat pump is sized correctly. 

What types of solar modules are there? 

In principle, a photovoltaic system is best installed on the roof of an old building for retrofitting, as the roof covering remains untouched. You should only consider in-roof photovoltaics if you are completely renovating the roof.

You can freely choose the type of PV modules. There are monocrystalline solar modules, polycrystalline solar modules and thin-film solar modules. Which type of PV module is the right choice for your roof depends on the dimensions and the level of power consumption.

• Monocrystalline modules have the highest efficiency at 22%. This means they produce more electricity on the same roof area. They are particularly worthwhile if you have a high power consumption or a small roof area available.
• Polycrystalline modules are slightly cheaper to produce. However, their efficiency (15 to 20%) is also lower.
• Thin-film solar cells are extremely thin solar modules that are vapor-deposited onto a carrier material, such as glass. They are much cheaper to produce, but their efficiency is only around 10 to 131%. Thin-film modules are usually chosen for purely optical and aesthetic reasons - e.g. for solar facades.

If you are looking for the best solar modules, then take a look at this article. We have extensively tested over 20 PV modules for you and compared them in a ranking.  

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Costs of a heat pump with photovoltaics in an old building

A photovoltaic system with 5 to 6 kWp costs around 8,000 to 9,000 € for a single-family home. Larger 8 to 10 kWp systems cost around €12,000. The costs for heat pumps are between 14,000 and 29,000 €For an old building with a heat requirement of 28,000 kWh, the running costs include heating costs, house electricity and the increasing maintenance costs per year.

To calculate the profitability, you have to compare the running costs with the investment over a period of about 25 years.

What funding is available? 

There are subsidies for renovating energy-efficient houses. These are summarized in the BEG (Federal Funding for Efficient Buildings)You must apply for funding from KfW or BAFA. 

By supplying the house with electricity and heat using photovoltaics and a heat pump, it can be used as "Efficiency House EE" To achieve this, at least 55% of heat supply must be covered by renewable energies.

You must apply for funding before the delivery and contract award. You will receive 35 to 50% of the total eligible costs paid out as a subsidy. In total, investment costs of €120,000 to €150,000 can be covered. Heat pumps in old buildings have a subsidy rate of 45% of the investment costs of a maximum of €60,000, i.e. a maximum of €27,000.

The specialist planning and construction supervision are funded at 50%If you do not have the capital, you can also choose financing. You apply for this with the KfW 262 loanYou will receive a low-interest loan and a repayment grant of €20 to €50,000 up to a maximum of €60,000.

Conclusion

A heat pump with photovoltaics is also possible in old buildings under the right conditions possible and profitable. The purchase costs are the same as those of a new building, only the running costs are slightly higher. Any necessary energy renovations of the house can be easily financed with Funding from KfW and BAFA finances.