When looking for an energy storage system, one of the key decisions will be choosing the right capacity – 5, 10 or 15 kWh? This choice should not be based solely on the capacity of the photovoltaic installation. Two PV systems with identical specifications may require completely different storage capacities if, in one home, most of the energy is consumed as it is generated, while in another the highest demand occurs only in the evening and at night.
When selecting the capacity of an energy storage system, the most important factors are therefore the amount of surplus energy generated by the photovoltaic installation, electricity consumption outside peak production hours and the purpose the battery is intended to serve. A different capacity may be appropriate if the main goal is to increase self-consumption, another if the aim is to reduce electricity purchased from the grid, and yet another if the storage system is also intended to provide backup power.
The capacity of an energy storage system should be based primarily on actual energy production and consumption data. The key questions are how much surplus energy the photovoltaic installation can generate on a regular basis and how much electricity the home needs after the panels have passed their peak production period.
For example, if on a sunny day the installation exports around 6-8 kWh of surplus energy to the grid, while the household draws a similar amount of electricity from the grid during the evening and night, this range may be a useful starting point when selecting storage capacity. A larger battery will not always be better if the installation cannot regularly charge it or the household is unable to use the stored energy.
Only at the next stage should additional factors be considered, such as a planned increase in electricity consumption, the presence of a heat pump, air conditioning or an EV charger, and whether the storage system is also intended to provide backup power.
5, 10 or 15 kWh energy storage - when is each capacity a good choice?
The capacity of an energy storage system should reflect the actual way energy is used, rather than the assumption that a larger battery is always better. The examples below should be treated as general usage scenarios, as the optimal capacity depends primarily on the energy production and consumption profile.
|
Storage capacity |
When is it worth considering? |
|
around 5 kWh |
For low or moderate evening consumption, smaller PV surpluses and the need to shift a few kWh of energy from daytime production to later hours |
|
around 10 kWh |
For larger and regular surpluses, higher electricity consumption in the evening and at night, and the presence of higher-demand electrical devices |
|
around 15 kWh |
For high energy demand, large regular surpluses, electric heating, a heat pump, EV charging or greater backup power requirements |
When to choose 5 kWh energy storage system
An energy storage system with a capacity of around 5 kWh can be a good solution for households that do not use large amounts of electricity after photovoltaic production has ended. It is particularly suitable where the installation generates moderate surpluses and the main objective is to increase self-consumption and use more self-generated electricity in the evening. This capacity may be sufficient, for example, to power basic household appliances, lighting or electronics during hours when the panels are no longer generating electricity. However, this does not mean that a 5 kWh battery is intended exclusively for small PV installations.
When to choose 10 kWh energy storage system
A capacity of around 10 kWh is an intermediate option that may be suitable for households with higher electricity consumption and regular photovoltaic surpluses. It makes particular sense when a significant proportion of consumption occurs in the evening and at night, or when the home uses higher-demand devices such as a heat pump or air conditioning. If, on a typical sunny day, the installation can supply several to more than ten kWh of surplus energy to the battery and a similar amount is later required by the building, a storage capacity of around 10 kWh may be a good starting point for further calculations.
When to choose 15 kWh energy storage system
An energy storage system with a capacity of around 15 kWh is worth considering primarily in buildings with high electricity consumption and large, regular surpluses from the PV installation. It may be justified in properties equipped with a heat pump, electric heating, air conditioning, an EV charger or where there are greater backup power requirements.
However, a larger capacity does not automatically mean greater savings. If the installation usually generates only a few kWh of surplus energy per day, a 15 kWh battery may remain only partially charged for much of the time and fail to make full use of its potential. It should therefore be selected when actual consumption and production justify this capacity, rather than simply as a larger version of a smaller storage system.
How does Voltmax help select the right energy storage capacity?
The selection of an energy storage system should be based on actual data rather than solely on the capacity of the photovoltaic installation or the nominal capacity of the battery. Voltmax can analyse PV production, the amount of surplus energy generated, the hourly electricity consumption profile and the largest energy consumers in the building.
We can also take into account planned increases in electricity demand, such as the installation of a heat pump, air conditioning or an EV charger, as well as backup power requirements. Another important element is assessing the existing inverter and the technical possibility of integrating the storage system with the current installation. This makes it possible to select a capacity that reflects the actual needs of the building and the way energy is used.
Interested? Contact us – at Voltmax, we will help you choose the right energy storage system for your needs.
