Sizing and installing energy storage systems correctly: Here's how
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Stefano Fonseca is an energy and environment engineer with over six years of experience in technical building equipment (TGA). He combines technical expertise with a passion for understandable communication. For more than five years, he has been writing as a freelance editor about renewable energy and sustainable living, in particular about photovoltaics and heat pumps.
An energy storage system increases the efficiency and profitability of a PV system. The right sizing and installation are crucial for this. In this article, you will learn how to correctly calculate storage capacity and avoid typical mistakes.
Why is the right storage size important?
The storage size determines the profitability and efficiency of your PV system. A suitable storage system increases your own consumption and lowers your electricity costs. However, if the storage is incorrectly sized, profitability decreases.
- In the case of a undersizing The storage tank is quickly fully charged and can no longer absorb the excess solar power. As a result, you feed more electricity into the grid and use less electricity in the household. This reduces your own consumption and reduces the profitability of the system.
- In the case of a oversizing The storage system often remains unused because there is not enough solar power available to charge. The higher acquisition costs lead to a longer payback period and reduce the financial benefits. Investing in a large storage system is then not worthwhile.
How big should a memory be?
The storage capacity of an electricity storage system for a single-family home is on average between 5 and 12 kWh. As a rule of thumb, around 1 kWh of usable storage capacity is useful for every 1,000 kWh of annual electricity consumption. In addition, the storage system should match the PV output — with around 0.8 to 1.5 kWh storage capacity per installed kWp. This allows you to make optimum use of the generated solar power and avoid unnecessary costs due to oversizing.
The following is an overview of the storage capacity based on the output of the PV system and the annual electricity consumption:
How is an energy storage system dimensioned?
To size a battery storage system, first calculate the average daily power consumption and set 50 percent of this as usable storage capacity. The appropriate rule of thumb for this is:
Storage capacity (kWh) = annual power consumption (kWh) ÷ 365 × 0.5
This ensures that the storage system can absorb a large part of the electricity generated by yourself every day. An example:
Sample calculation:
- Annual power consumption: 6,000 kWh
- Daily power consumption: 16.5 kWh
- Storage capacity = 6,000 ÷ 365 × 0.5 = approx. 8.2 kWh
You should also include the size of the PV system: per installed kWp of PV power is approximately 0.8 to 1.5 kWh storage capacity useful. This ensures that the memory is sufficiently loaded.
Good sizing achieves the balance between costs, storage utilization and potential savings.
What factors influence memory size?
The right storage size depends not only on power consumption, but also on technical and individual conditions. The most important influencing factors are:
- Annual power consumption: The higher the consumption, the larger the memory should be.
- PV power: The storage capacity must match the amount of electricity generated.
- Self-consumption behavior: Householders with high consumption in the evening or at night benefit from larger storage facilities.
- Heat pump or e-car: Large electrical consumers significantly increase demand.
- Electricity tariff and feed-in tariff: The lower the feed-in tariff, the more worthwhile is a high level of self-consumption.
- Location of the PV system: In sunny regions, the yield is higher and therefore the amount of electricity to be stored is higher.
- Planning for the future: If you want to retrofit a wallbox or heat pump later, you should consider this in terms of the storage tank size.
How does the installation of an energy storage system work?
Installing a power storage system requires a number of technical requirements. First, there must be enough space in the house — ideally in a dry, ventilated room such as the laundry room or cellar. The energy storage system must be compatible with the inverter, the electrical installation must be able to be adapted, and registration with the grid operator is mandatory. Safety aspects such as fire protection and accessibility must also be considered.
The installation of a PV storage system is as follows**: **
- Consulting and planning: A specialist company will test your PV system, power consumption and possible storage solutions. It also decides whether an AC- or DC-coupled system makes sense.
- Offering and sizing: Based on your requirements, the specialist company will prepare an offer with the appropriate storage size and technology. Funding opportunities are also being examined.
- Site selection: The storage tank is installed where it is safe, cool and easily accessible — for example in the basement, technical room or garage.
- Technical preparation: The electrician installs cables, adjusts the meter cabinet and checks the grid connection conditions. A new inverter may also be required.
- Installing the memory: The energy storage device is permanently installed and connected to the PV system, the house network and the grid connection point.
- Registration with the network operator: Start-up must be reported to the responsible network operator. This is usually done by the installer.
- Start-up and briefing: After a successful check, the memory is activated. You will receive instructions on operation, monitoring via app and maintenance.
Professional installation is crucial for safety, durability and full use of the storage system. Therefore, hire a certified specialist company.
Conclusion: correctly sizing energy storage systems pays off
A correctly sized energy storage system ensures that you use more solar power yourself and draw less electricity from the grid. This lowers your running costs and increases the efficiency of the PV system. At the same time, you avoid expensive oversizing. Anyone who takes energy consumption, PV output and future consumers into account sensibly benefits from an optimally coordinated system in the long term.
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