Lithium-ion storage systems have become the market standard. The technology is well-known and proven from smartphones and electric cars. These storage systems offer high efficiency, high energy density, and a comparatively long service life, even with intensive use. According to the Consumer Advice Center, in addition to lithium-oxide batteries, lithium iron phosphate (LFP) batteries are currently gaining a stronger foothold in the market.

In addition to the storage unit itself, other devices are required for operation. These include a battery management system, the electronics for monitoring the system, and a dedicated inverter. Hybrid inverters are now also available that can be used for both the photovoltaic system and the storage unit. The inverter is necessary to convert the direct current from the storage unit and the system into alternating current for household appliances.

There are also devices that can serve as emergency power generators in the event of a short-term power outage. However, complete independence from the power grid cannot be achieved. In the winter months from November to January, photovoltaic systems in our latitudes do not generate enough electricity for an average household. Even battery storage cannot change this.

In recent years, the purchase costs for storage systems have fallen. Prices for battery storage systems are often quoted in euros per kilowatt-hour of storage capacity. According to the Consumer Advice Center, prices in Germany—including installation—currently range from about 400 to 800 euros per kilowatt-hour of storage capacity for systems with a capacity of five kilowatt-hours or more.

In addition, annual operating and maintenance costs of one to two percent of the purchase price must be taken into account. The storage system itself consumes electricity and can also slightly increase the cost of photovoltaic insurance. As part of the PV system check, it is also recommended to have the battery inspected every four to five years.

The Berlin University of Applied Sciences (HTW Berlin) compares battery storage systems from well-known manufacturers annually. The website also features an independence calculator that helps determine the appropriate storage size. You can find the HTW Berlin homepage in the list of links below. In Germany, there is no uniform subsidy program for energy storage systems. Furthermore, funding opportunities are quickly exhausted due to high demand. You should check in advance whether any subsidies are available to you. The Rhineland-Palatinate Consumer Advice Center offers free energy consulting, including at the Mainz Umweltladen.

At 10 to 15 cents per kilowatt-hour, solar power is significantly cheaper than electricity from the grid. The more solar power generated by the photovoltaic system that is consumed directly during the day, the greater the cost savings. As a rule, a household’s electricity consumption is highest in the morning and evening hours. Unfortunately, this is also when solar output is lowest, and electricity must be purchased from the grid. The percentage ratio of self-consumed electricity to electricity fed into the grid is referred to as the self-consumption rate. Without a battery storage system, this rate is approximately 30 percent. With a battery storage system, self-consumption rates of 60 to 80 percent are possible.

Currently, when electricity is fed into the public grid, photovoltaic system owners receive a payment from the government known as the feed-in tariff. For each kilowatt-hour, a fixed amount is paid for 20 years; for example, for a system up to 10 kWh with partial feed-in (where part of the electricity is used by the owner), this amounts to 7.78 cents per kilowatt-hour. There is currently a political debate about eliminating this feed-in tariff for new PV systems (up to 25 kWp of installed capacity) for cost reasons. This would mean it would take longer for the system to pay for itself.

The extent to which purchasing an energy storage system is actually worthwhile depends on many factors. These include, on the one hand, the prices for purchased and sold electricity and the self-consumption rate. In addition, factors such as the cost of the storage unit, the inverter, and installation play a role, as does the storage system’s lifespan (10 to 15 years) in the cost-benefit analysis. Therefore, individual consultation and an on-site assessment of the circumstances are advisable before making a purchase.

The decision to purchase a home battery depends on many factors. The calculations involve numerous variables that affect cost-effectiveness. Household electricity consumption, the size of the solar system, and the current electricity price can all have a positive or negative impact on the bottom line. However, financial considerations often play only a secondary role for buyers. Greater independence from the utility company, increased self-consumption of solar power, and a personal contribution to the energy transition are often the main reasons behind the decision to purchase.