PV system with battery – is it worth it?
A photovoltaic system generates most of its power around midday – exactly when many households consume the least. Without storage, this surplus is fed into the grid and later bought back at a higher price. A battery reverses this: it stores the surplus solar power during the day and releases it in the evening, at night and on cloudy days.
As a result, self-consumption typically rises from around 30 percent without storage to 60 to 80 percent with storage. The higher the electricity price and the lower the feed-in tariff, the faster the investment pays off. Whether a battery is worthwhile in your case depends on your annual consumption, system size and usage behaviour – which is exactly what our planner calculates individually for you.
Beyond economics, independence matters to many people: those who generate and store a large share of their own electricity become less dependent on rising prices and, with a suitable backup function, can even keep using power during a grid outage.
What does a battery storage system cost?
The cost of a battery depends mainly on its usable capacity in kilowatt-hours (kWh), as well as on the manufacturer and system technology. As rough guidance, certain size classes have become established on the market, oriented to typical households.
A battery with around 5 kWh of usable capacity suits smaller households with moderate consumption. A system of around 10 kWh is the most common choice for a single-family home with average consumption. Larger batteries from 15 kWh are used when a heat pump or electric car also needs to be supplied.
Important: a low purchase price alone says little. What matters is usable capacity, lifespan in charge cycles, efficiency and whether the system can be expanded later. Instead of working with flat-rate prices, our planner produces a transparent parts list with an indicative price based on your specific system – so you can see what your storage system actually costs.
What storage size do I need?
A common rule of thumb is about 1 kWh of storage capacity per 1,000 kWh of annual electricity consumption, or roughly 1 kWh per kilowatt-peak (kWp) of installed PV power. A household using 5,000 kWh per year with an 8 kWp system would therefore land at roughly 5 to 8 kWh of usable capacity.
But such rules of thumb are only a starting point. A battery that is too small is quickly empty in the evening; one that is too large never fills up and costs unnecessarily. The optimal size depends on how much power you use and when, how large your PV system is, and whether a heat pump or EV will be added. Our planner takes these factors into account and proposes a suitable size – rather than a rough flat figure.
Retrofitting battery storage
An existing photovoltaic system can in many cases be retrofitted with a battery. There are two technical routes: AC-coupled batteries with their own battery inverter can be added almost independently of the existing system and are therefore especially flexible for retrofitting. DC-coupled systems are more efficient but require a compatible hybrid inverter.
Whether retrofitting is worthwhile depends on the age of the system, the remaining feed-in tariff and your consumption. Especially for older systems whose subsidy is ending, the increase in self-consumption from a battery is often the strongest argument. With our planner you can try out different storage sizes and see directly what fits your existing system.
Backup and emergency power: electricity even during an outage
Many system owners are surprised: a conventional photovoltaic system shuts down automatically during a power outage – even when the sun is shining. The reason is the legally required grid and system protection, which prevents a system from feeding into a disconnected grid and endangering people. Without additional technology, you are therefore left without power during a blackout despite owning a PV system.
Storage systems with a backup or emergency power function solve this. They safely disconnect the home grid from the public grid in an emergency and continue to supply it from the battery and PV system. Depending on the solution, this ranges from a simple backup socket to an automatic, uninterruptible whole-home supply (off-grid operation).
Victron energy storage systems are designed for exactly these applications and, depending on configuration, offer a full backup power function. Which variant makes sense for your home depends on your protection needs and the required power – our Victron ESS configurator guides you through the right options.
What components make up a storage system?
A modern photovoltaic storage system consists of several coordinated components. At its heart is the battery, today mostly based on lithium iron phosphate (LiFePO₄), which stands for high safety and a long lifespan. The inverter converts the direct current from the modules and the battery into usable alternating current – in hybrid and ESS systems it also handles charge and discharge management.
There is also an energy management and monitoring system that controls generation, consumption and state of charge, plus the necessary protection and distribution technology. In Victron systems, for example, MultiPlus inverters, SmartSolar charge controllers and a Cerbo GX controller perform these tasks together. To ensure the components match and are correctly sized, systematic planning pays off – which is exactly what our tool is made for.
Plan your storage system online – with the Greenfuture planner
Most providers show you an online shop with products – but no tool to work out what you actually need. This is exactly where our planner comes in: it asks for the relevant key figures, calculates a suitable storage size, assembles the necessary components and gives you a transparent parts list with an indicative price – free and without sign-up.
For Victron-based energy storage systems, our specialised ESS configurator additionally guides you through all the detailed questions: single- or three-phase, number of inverters, storage size and backup variant. This way you end up with a well-thought-out, coordinated configuration instead of a mere shopping cart.