PV self-consumptionA BESS battery storage application for business
How it works
PV produces most exactly when the exchange price is lowest — at midday. In the evening, when the price jumps, the panels give nothing. The battery shifts that surplus a few hours forward, turning a dumped export into a peak-price purchase avoided.
Surplus measured
How many kWh a day actually flow to the grid and in which hours — this sets the capacity needed.
Charging at midday
The battery absorbs the surplus instead of exporting it. The grid is not loaded and the PV is not curtailed.
Discharge in the evening
The same energy covers the evening load — at a price several times higher than at midday.
Why PV without a battery loses money at midday
All PV plants produce the most in the same hours. That is why supply on the exchange is highest exactly at midday and the price is lowest; on some days it falls to zero or turns negative. The surplus is then sold for next to nothing, or the plant is curtailed.
In the evening the picture is reversed: the sun has set, consumption is high and the price is the highest of the day. A site without a battery buys at exactly that time.
How to size a battery for PV
The first step is to measure the surplus: how many kWh a day the plant produces above what the site is consuming at that moment, and in which hours. The second is the evening load — how much energy the site draws from the grid after sunset.
The battery is sized to the smaller of the two: there is no point in storing more than the site will use, or in a battery larger than the surplus that can fill it. Power is chosen according to the strongest midday surplus and the limit of the grid connection.
For a new or an existing plant
The battery connects on the AC side, so it also works with a plant that is already built, without replacing the inverters. For plants that sell all their energy, the same battery shifts the sale from midday to the evening.
For rooftop plants at business sites we use cabinets of 233, 261 and 418 kWh, and for ground-mounted plants of around 1 MW and above, containers of 2,170 and 5,015 kWh.
Questions and answers
What battery is needed for a 500 kWp PV plant?
It depends on the surplus and on the evening consumption, not just on the capacity of the plant. Send us your hourly generation and consumption and we will size the battery for your site.
Can the battery be added to a plant that is already operating?
Yes. It connects on the AC side and does not require the plant’s inverters to be replaced.
Does the battery also work in winter, when there is little sun?
Yes. When the PV surplus is not enough, the battery can charge from the grid in the cheap hours and operate as arbitrage.
Want the same for your site?
Send your load profile and tariff — we return a configuration, a diagram and an indicative price.