PV curtailment despite battery storage: causes, examples and correct sizing

Many industrial and commercial businesses invest in PV systems and battery storage in order to use as much solar power as possible themselves and to avoid curtailment. A storage system creates additional flexibility and can usefully absorb surplus PV output. When this succeeds, and in which situations curtailment is unavoidable despite storage, is explained below.

When is PV curtailed?

1. Curtailment at negative electricity prices

In direct marketing, remuneration is based on the exchange electricity price. If this temporarily falls below zero, feeding in means: the system operator pays money to deliver power.

In such quarter-hours it makes economic sense to throttle the PV system.

Commercial example:

A manufacturing business feeds its PV system in via direct marketing. On a sunny Sunday at midday, exchange prices are negative. Although the system could produce technically, part of the PV output is deliberately curtailed to avoid losses.

2. Curtailment due to grid feed-in limits

Regardless of the electricity price, many grid connections are technically limited.

Example:

• PV system: 500 kWp

• Grid connection permits a max. of 200 kW feed-in

On sunny days the PV system can briefly generate more power than may be fed into the grid. Without an additional consumer or storage, the surplus portion must be curtailed.

How does a battery storage system help against curtailment?

A battery storage system acts as a buffer between generation and use. It absorbs PV surpluses and shifts them in time – for example into the evening hours or into phases with positive electricity prices.

Example:

The business additionally installs a storage system with

• 300 kWh capacity

• 150 kW charging power

At midday, a large part of the PV surplus flows into the battery instead of into the grid. This significantly reduces both grid feed-in peaks and curtailment losses.

➡️ Important: The storage reduces curtailment – it does not guarantee that it disappears entirely.

Why is PV still curtailed despite battery storage?

PV curtailment becomes unavoidable when three factors occur at the same time:

• High PV production

• The grid feed-in limit is reached

• The battery is full or limited in its charging power

Concrete example:

• PV production: 480 kW

• On-site self-consumption: 80 kW

• Remaining surplus: 400 kW

Usable power:

• The battery charges at a maximum of 150 kW

• The grid accepts a maximum of 200 kW

➡️ Total usable: 350 kW

➡️ 50 kW remain and must be curtailed

Conclusion: weigh storage size deliberately

A battery storage system can significantly reduce PV curtailment in the industrial and commercial sector, but cannot fully avoid it in every case. Particularly with high PV peaks and limited grid connections, fully avoiding curtailment would often require a significantly larger storage system.

Whether this additional storage size is economically worthwhile is not a given. Often, high investment costs are set against only a comparatively small reduction in the curtailment volume. PV curtailment should therefore be realistically taken into account as early as the planning and sizing stage.

Good system sizing does not aim to avoid every kilowatt-hour of curtailment, but to find the economically sensible optimum of PV output, storage size and grid connection.