More and more people are deciding to add a solar power storage unit to their existing or new photovoltaic system. There are good reasons for this. Here is our advice on what to consider when buying a solar power storage system.

Buying a solar power storage unit - seven reasons:

• increase the self-consumption rate (up to 70 % are possible)
• independence from the time of day and weather
• independence from electricity suppliers
• subsidy programmes
• falling feed-in tariffs - feed-in of solar energy becomes less profitable
• increase in property value
• investment in the future while actively supporting the energy transition

Is retrofitting possible?

For most photovoltaic systems it is straightforward to retrofit a solar power storage system. AC-coupled storage systems are used for this scenario. Their AC battery inverters convert the direct current generated into alternating current prior to feeding it into the battery. The design of DC-coupled storage systems makes them suitable for new PV system installations.

Space requirements and location

For homeowners, the space requirements of a solar power storage unit is usually not a problem. In addition, there are also very compact models available. Most solar power storage units are installed inside the building; therefore described as indoor systems. The ambient temperature of the installation location should be between 15 and 25°C.

Efficiency

If you want to buy a solar power storage system, it is imperative to pay attention to the overall efficiency. It indicates the efficiency of the system's energy conversion. The generated solar energy is reduced by the system's conversion and control processes. The crucial question is: by how much? RCT Power solar power storage systems feature the highest system efficiency, which was confirmed by the annual independent energy storage inspection conducted by the University of Applied Sciences (HTW) Berlin. In both 2020 and 2021, RCT Power storage systems were announced test winners due to their high efficiency.

Solar power storage unit capacity

The required storage unit capacity strongly depends on your consumption behaviour, the size of the household and the output of the PV system. With a smaller storage unit, you can optimise the self-consumption of the photovoltaic system; you use as much as possible of the generated solar power. A larger solar power storage system offers you more flexibility and independence from the electricity supplier. When calculating the required storage battery capacity, the expected energy consumption should therefore also be considered. 

• Purchase tip: Compare the net capacity of the solar power storage units.

Depth of discharge

The depth of discharge indicates how much as a percentage of its nominal capacity a battery has been discharged. Solar power storage units have a depth of discharge rate between 50 and 90 per cent. For longer battery service life, the depth of discharge should not exceed 90 per cent.

Battery technology

If you attach importance to long service life and high efficiency, you should purchase a solar power storage unit based on lithium iron phosphate technology. RCT Power uses this cell technology, namely an extremely safe and environmentally friendly LiFePO4 battery. The cycle stability of this battery is excellent. Even after years of use, the batteries will retain a high capacity.

Charging strategy

Next to a simple and conventional charging strategy where the solar power storage unit is charged when the sun is shining, a more intelligent forecast-based charging strategy has been developed in the meantime. It calculates the optimal charging times for the storage system based on weather data and previous consumption patterns. In simple terms, the battery is charged later during sunny weather so that it reaches its desired state of charge later. At the same time, the amount of excess solar energy that is fed into the public grid at midday is reduced. Losses due to active power reduction are thus avoided.

Many German subsidy programmes for solar power storage units mandate grid-serving charging strategies, such as forecast-based charging, as it is precisely these grid-serving solar power storage units that actively contribute to sustainability.

Conclusion: Buying a solar power storage unit pays off for you and benefits the environment

Electricity storage systems play an important role in the energy transition. They are a key component of a decentralised power supply. State subsidy programmes promote the uptake of these systems. When buying a solar power storage unit, you should consider parameters such as efficiency, battery technology and charging strategy. It will help you to enjoy the benefits of your solar energy storage system for a long time. Our specialist partners will be happy to advise you.