Renewable energies

The city of Bad Homburg is strongly committed to renewable energies. It has installed many systems itself and supports homeowners with advice.

General information

Even in our latitudes, the active use of solar radiation through solar thermal or photovoltaic systems is now a technically mature and often economically viable way of generating energy. A basic distinction is made between two technologies: solar thermal systems (solar thermal energy) and photovoltaic systems.

Many homeowners and the town of Bad Homburg v. d. Höhe have already had solar systems installed.

The Hesse solar cadastre gives you as a homeowner an overview of whether and how your roof is suitable for a photovoltaic or solar thermal system. You can also carry out various calculations yourself directly and online, including profitability calculations!

You can find the solar register of the Hesse State Energy Agency (LEA) at

Solar cadastre of the State Energy Agency of Hesse(https://www.lea-hessen.de/buergerinnen-und-buerger/sonnenenergie-nutzen/solar-kataster-hessen/)

After selecting your roof area, you will be taken to a sample calculation showing the possible yields of a photovoltaic system / solar thermal system. The results provide an initial estimate, but are no substitute for detailed planning by appropriate specialists.

The city of Bad Homburg v. d. Höhe therefore recommends that you seek independent energy advice from the city. Experience has shown that, despite other representations in the solar cadastre, roof areas are suitable for a photovoltaic system or similar in individual cases.

Energy advice Bad Homburg(https://www.bad-homburg.de/de/stadt/umwelt-und-klima/umwelt-und-klimaschutz/energieberatung)

Solar thermal energy

In this process, part of the sunlight is used to heat a liquid in so-called collectors installed on the roof, which then heats the domestic hot water in the storage tank. This means that less energy from conventional sources is required to heat the water. There are two types of collector that differ in terms of technology, efficiency and cost: Flat-plate collectors and evacuated tube collectors.

For the hot water requirements of an average family of four, an area of 4 to 6 m² is required for flat-plate collectors and a smaller area of around 3 to 4.5 m² for evacuated tube collectors. The costs, including installation, are around 4,500 to 6,000 euros for flat-plate collectors and around 6,000 to 8,000 euros (gross) for tube collectors. The annual coverage rate should reach around 60% of the energy requirement for the hot water supply, which corresponds to around 250 to 400 m³ of natural gas or around 250 - 400 liters of heating oil, and around one ton of CO2 can also be saved annually.

Increasingly, these systems are also being used to support the heating system.

For heating support, the area required, the volume of the hot water tank and, of course, the costs increase, but so do the potential savings. Approximately 10 to 14 m² of flat-plate collectors and around 8 to 12 m² of vacuum tube collectors are required. The storage volume of the heating system should be between 700 and 1000 liters. In addition to the energy savings in hot water consumption, up to 10% of the heating energy can be saved. This corresponds to additional savings of up to 300 m³ of natural gas or 300 liters of heating oil and up to 1 ton of CO2 per year. The costs are around 10,000 to 12,000 euros for flat-plate collectors and around 13,000 to 16,000 euros for vacuum tube collectors. The installation of solar thermal systems with and without heating support is subsidized by the city of Bad Homburg and the federal government.

(see flow chart under Downloads)

Photovoltaics

Photovoltaic systems are another way of using solar energy. Here, solar radiation is converted directly into electricity in appropriately coated collectors. There are various types of modules that differ in terms of efficiency and cost. Photovoltaic modules made from monocrystalline solar cells are expensive, but also the most efficient (efficiency of 14 to 20%) and are therefore particularly suitable for small roof areas. Polycrystalline solar cells have a lower efficiency (12 to 16%) and should be used for somewhat larger roof areas. Efficient operation of these systems requires very good to good alignment of the modules to the sun.

Thin-film modules are very lightweight in comparison and also cheaper, but also only have a low level of efficiency (6 to 10%). Thin-film modules are therefore more worthwhile for very large roof areas on which many modules can be installed cost-effectively. Thin-film modules only lose a small amount of output in low light conditions or at very high temperatures, which is why they can also be installed on less favorably oriented surfaces.

Polycrystalline modules with an output of 3 to 10 kW are most frequently installed in single-family homes. The costs for these are around EUR 2,800 to 3,200 per kWp (kilowatt peak) with a slight downward trend (January 2011). The price for monocrystalline modules is around 10% higher, while the price for the cheaper thin-film modules is around 20% below these costs.

The installation of these systems is subsidized by the federal government through a so-called feed-in tariff. You have the option of feeding all of the electricity into the public grid or using some or all of it yourself. The more solar power you consume directly in your household, the higher the remuneration you can receive. This is because the feed-in tariff has been designed in such a way that you receive additional remuneration for the electricity you use yourself. This increases the profitability of your system and should be taken into account when planning a PV system. Many households that already have a photovoltaic system produce roughly the same amount of electricity that they consume themselves, so that a balanced, if not positive, CO2 balance can be achieved.