May 22, 2023, 3:12 pm | Read time: 10 minutes
No electricity is cheaper than that from renewable energies. And that includes solar power. What you need to consider with a solar system and why a storage unit makes sense are explained by two experts in a conversation with myHOMEBOOK.
In times when heating with oil and gas is increasingly becoming a thing of the past, renewable energies are coming to the forefront for homeowners. A classic among them is the solar system on the roof, which can supply your household with electricity. What you don’t use yourself can be fed into the grid. By the end of 2022, a total of 2.65 million photovoltaic systems (PV systems for short) were installed in Germany. But there are some questions to answer beforehand. Is a PV system on my roof worth it? Do I need a power storage unit? What are the regulations? myHOMEBOOK asked the experts Carsten König from the German Solar Industry Association and Adrienne Gehre from the solar online provider Zolar.
The First Step in Installing a Solar System
myHOMEBOOK: What permits are necessary for private solar systems? Are there differences between roof and small balcony systems?
König: “A building permit is generally not required for solar power systems on private homes. However, private roof solar systems must be registered, which is mandatory in Germany. The first step in installing a solar system—whether on the roof or the balcony—should be registration with the grid operator or the market master data register of the Federal Network Agency. If you feed excess electricity into the public power grid, you must also inform the tax office, as you become a power producer, thus an entrepreneur. Additionally, you should inform your insurance company about the installation of the solar system to include it in the insurance coverage.”
What other requirements does a solar system have? Are there any regulations regarding the load-bearing capacity of the roof?
König: “Of course, the roof’s structural integrity should be ensured. Good insulation is also recommended, as a roof system is generally expected to last around 30 years, ideally without needing roof access during that time. The orientation of the PV modules on house roofs is largely predetermined by the location of the house and the roof shape. A PV system achieves the highest yield when sunlight hits the solar cells at a right angle for as many hours as possible. In Germany, many PV systems are ideally oriented to the south. Minor or even larger deviations are relatively unproblematic.”
Also interesting: 3 persistent misconceptions about rooftop solar systems
The Role of Orientation and Tilt Angle
But what if the south side is not possible?
König: “Then the east-west orientation of the PV modules is a good alternative. The system produces less electricity but achieves two daily performance peaks, meaning the electricity is produced relatively evenly throughout the day. This is advantageous if you want to use a large portion of the electricity yourself. Additionally, with an east-west orientation, the entire roof area can be used for installing the solar modules.”
Does the roof tilt angle play a role in the installation of PV modules?
König: “Yes. Since the PV system is usually mounted immovably on the roof, a tilt angle is chosen that favors the highest possible yield over the entire year. In Germany, this tilt angle for PV modules is between 30 and 35 degrees. The angle tends to be slightly lower in southern Germany because the sun is higher there. In northern Germany, it is slightly higher because the sun is lower there. It is also important to avoid shading the system with trees, antennas, other buildings, or power lines.”
Space-Saving Alternative: Solar Systems for the Balcony
Are there any special features for small balcony systems?
König: “There are no special ‘balcony modules’ yet. Standard solar modules are usually used, and in some cases, modules manufactured to special specifications. These modules are configured into plug-in solar sets with standard module inverters and other accessories. Here, too, it is advisable to securely attach the modules in a shadow-free area of the balcony (ideally the railing).”
What size is optimal for balcony systems?
König: “That cannot be said in general terms, as it depends on the orientation and yield of the system and what the generated electricity is used for: lighting, heating, hot water, operating household appliances, charging the car, and much more. Generally, it is assumed that 2 to 3 modules are needed for 1 kilowatt of solar power.”
More on this: When a solar system on the balcony is worthwhile
Can unused electricity always be sold to the local energy supplier?
König: “About 30 percent of your own solar power can be used by yourself. The rest can be fed into the public power grid and is eligible for compensation under the recently improved conditions of the Renewable Energy Sources Act (EEG).” (Editor’s note: The current feed-in tariff is 8.20 cents per kilowatt-hour).
How to Easily Install
A private individual with DIY skills can install a balcony system themselves. What about a roof system?
König: “It is always advisable to have a roof system installed by a professional, if only for insurance reasons.”
What safety regulations must be observed during installations?
König: When installing PV modules, it is essential to comply with the relevant building standards, such as those for timber construction, steel construction, light metal construction, and structural standards for wind and snow loads on structures.
How much electricity do a roof and a balcony system supply?
König: “This cannot be said in general terms. It always depends on the system, the orientation, and the size. The average electricity consumption of a single-family house is also not really generalizable, as it varies greatly depending on the number of people living in the house, the number and age of devices, and the number and frequency of use.” (Editor’s note: According to the Consumer Center, a standard module measuring 1 by 1.7 meters provides between 350 and just over 400 watts of electricity.)
Questions and Answers About Power Storage
The optimal solar system also includes a storage unit. How does the electricity get into this battery?
König: “The electricity from the storage unit enters the private power grid via a so-called inverter. Using PV modules mounted on the roof or balcony, sunlight is converted into electrical energy. As soon as sunlight hits the silicon of a solar cell, energy is released in the form of direct current through the so-called photovoltaic process. To be used in the household, it is converted into alternating current using an intermediate inverter.”
What types of batteries are there?
Adrienne Gehre: “Lead-acid or lead-gel batteries have long been obsolete in the home sector. Instead, high-performance lithium-ion power storage units dominate the market today. A special form of lithium-ion batteries is lithium iron phosphate storage. Both technologies are used by major manufacturers today and enable high performance over a long period.
Meanwhile, the demand for environmentally friendly storage solutions is growing. So-called salt storage units, which are both environmentally friendly and efficient, are considered a promising alternative. However, their technology is not yet as advanced as lithium-ion batteries.”
How Long Electricity Can Be Stored
Can PV electricity be stored “forever”?
Gehre: “A power storage unit offers homeowners more flexibility for daily electricity consumption. It is mainly used to store excess solar power during the day so that it can be used in the evening when the sun is no longer shining. A storage unit should therefore be able to hold the average amount of electricity needed between evening and morning. A battery storage unit is not intended for long-term storage, let alone seasonal storage. That would not make economic sense either.”
Is it disadvantageous if someone buys a battery that is too large?
Gehre: “As a rule of thumb: For every 1,000 kilowatt-hours of annual electricity consumption, the power storage unit should have about one kilowatt-hour of storage capacity. However, we already recommend including future large electricity consumers such as electric cars or heat pumps in the planning. Because our electricity consumption will increase significantly in the near future due to the increasing electrification of our mobility and heating. If a four-person household in a single-family home currently consumes an average of 4,500 kWh of electricity per year, an electric car adds around 2,500 kWh per year. A heat pump requires about another 5,000 kWh annually. This means the same family with a heat pump and electric car has an annual electricity consumption of around 12,000 kWh.”
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How Long Power Storage Units for Solar Systems Last
What is the lifespan of a solar storage unit?
Gehre: “A power storage unit has a lifespan of about 10 to 15 years. Solar modules, on the other hand, last 20 to 30 years. This means a storage unit must be replaced once during the lifetime of a photovoltaic system.”
How expensive are PV storage units?
Gehre: “Prices for small storage units with 5 to 7 kWh storage capacity are around 6,000 to 8,000 euros. Storage units with slightly larger capacities of 8 to 10 kWh cost around 7,000 to 10,000 euros. Large storage units with around 15 kWh storage capacity cost up to 15,000 euros.”
In what sizes are PV storage units available?
Gehre: “Battery storage units come in various sizes. They start at about 5 kWh and go up to 20 kWh. The right sizing for the individual needs of each household is important.”
Can such storage units be used for other purposes, such as emergency power generators?
Gehre: “It is possible to connect selected storage units with an emergency power socket. In the event of a power outage, the refrigerator or cell phone charger, for example, can be plugged in and continue to be powered. If you want to continue supplying the entire house with electricity in the event of a power outage, you need a storage unit with a backup power function. These are usually very expensive and often make little economic sense for homeowners.”
Systems Should Be Installed by Professionals
Can you install them yourself?
Gehre: “The installation of a battery storage unit is reserved for certified electricians only. The house connection and the application for the grid connection must also be carried out by an electrician. Self-installation can also negatively affect insurance coverage and the performance of the system—it is therefore not allowed and absolutely not recommended.”
Where should the storage unit be installed?
Gehre: “There are no regulations on where a storage unit must be located. It should be dry and easily accessible. Like any other electrical device, the storage unit should also be regularly maintained.”
Where can a PV storage unit be disposed of?
Gehre: “Photovoltaic storage units are subject to the applicable battery law. Both manufacturers and sellers of storage units are required to take back used devices from consumers free of charge and dispose of or recycle them properly. Municipal recycling centers do not accept photovoltaic storage units.”