Batteries of different sizes for solar parks

By choosing a modular energy storage system, it is possible to start with a smaller configuration and later expand it easily according to needs. For example, the Pixii Powershaper system allows the system capacity to be scaled by adding additional battery modules in increments of 12.9kWh, and the battery power can be scaled by adding 3.3kW inverter modules. See more Pixii products.

Battery power (kW) – shows how much maximum power the battery can be charged or discharged with.

Battery capacity (kWh) – shows how much energy can be stored in the battery.

Historical data on electricity consumption can be found in Elektrilevi’s self-service. It is possible to save hourly data for the previous 12 months. Based on this, a graph can be created that shows the average electricity consumption per hour for the entire year.

Optimum battery power = average consumption per hour per year.

Optimum battery capacity = 2 to 4 times the average hourly consumption.

• Battery charging takes place at night during the cheapest hours.
• The battery is discharged during the daytime and evening hours when the price is the highest.

The greater the capacity, the greater the energy saving potential.

A battery used in the frequency reserve market should have a relatively high capacity compared to the battery capacity. A 1C rating (power = capacitance) is ideal, but a 0.5C rating (power = ½ capacitance) is also suitable.

Such a configuration allows the battery to be quickly charged or discharged in the most efficient manner according to the offers made on the frequency market and their activation by the system operator. The battery participating in the frequency market is kept at a 50% capacity level, because in this way the battery can be quickly used both in the direction of consumption and production according to the needs of the frequency market.

The solar park located in the Estonian climate produces 90% of the total annual energy during 7 months: March – September.

The average daily electricity production of a 50kW solar plant over 7 months is 168 kWh.

The purpose of the battery is to perform price arbitrage during the peak period of solar energy production. Instead of being produced immediately in the grid, the produced electricity is first stored in the battery and fed into the grid in the evening when it is more expensive.

The battery capacity would be approximately the size of the average daily electricity production, i.e. also 168 kWh.

The battery capacity should be 50 kW, so that it is possible to return the charged energy to the network within three hours. With less capacity, it takes longer to feed back into the grid, meaning peak hours with the most expensive prices cannot be used to the maximum.

In summary:

• Battery capacity: up to 3x the power of the solar park
• Battery power = solar park power