Quick answer
There is no fixed GB minimum battery size for trading under P415. Some providers use 100 kWh as a first filter, but what matters more is how much spare battery power, usable energy and import or export headroom the site has after its own needs are covered. Smaller batteries can still be worth checking.
There is no fixed GB minimum for a behind-the-meter battery to trade via an aggregator under P415. However, some aggregators and Virtual Power Plants set a minimum of 100 kWh per site or client. GridVolt’s approach is to consider all battery sizes where a site has spare battery power and usable capacity.
For your proposal, it’s only worth including trading if an estimate using all the site data, meter details, tariff, connection limits and battery information shows that what the client is likely to receive after fees, losses and revenue share more than covers the controller, service fees and extra battery use.
Why 100 kWh is only a first check
Battery capacity in kWh, and especially usable kWh, tells you how much energy the battery can store. Battery power in kW tells you how quickly it can charge or discharge.
You need these figures to judge whether trading is worth modelling for that site.
For example, take a 100 kWh battery with a 50 kW inverter and a 200 kWh battery with a 50 kW inverter.
Both batteries can deliver 50 kW in a single half-hour settlement period. If either battery discharges at 50 kW for the full half-hour, it uses 25 kWh of stored energy.
The difference between them is how many half-hour trading periods each battery can support.
Before allowing for reserve and losses, the 100 kWh battery could support up to four half-hour periods at full 50 kW discharge. The 200 kWh battery could support up to eight. That means the 200 kWh battery has more stored energy it could use for trading, even though the inverter power is the same.
Even then, two batteries with the same headline kWh capacity can produce very different results because what the client can earn from trading also depends on:
- charge and discharge power
- usable capacity
- minimum state-of-charge settings
- import and export limits
- warranty and cycling restrictions
- site-load requirements
- charge levels when a trading window appears
So treat 100 kWh as a first filter. It suggests the battery may have enough stored energy to leave some stored energy available for trading after peak shaving, backup, solar storage, reserve needs and losses. But it doesn’t mean every battery at or above that size will earn enough to cover the trading costs.
GridVolt can still check a smaller commercial battery of less than 100 kWh. Through GridTrade, GridVolt combines smaller charge, discharge or export changes from several sites. That means one battery can contribute to a larger trade instead of having to be large enough to trade on its own.
Most important is that the site still needs enough spare kW, usable kWh and import or export headroom after it has used the battery for peak shaving, backup, solar storage or other site needs. If the spare kW, usable kWh or headroom are too small, the trading income may not cover the extra costs.
How to check what the battery can actually spare
Before we can give you a trading estimate, collect and send over to us:
- Battery headline capacity and usable capacity in kWh
- Inverter/PCS power in kW
- The minimum battery reserve
- Half-hourly site demand
- When the site normally needs the battery for peak shaving, backup or solar use
- Agreed import and export limits
- Available export headroom
- Half-hourly settlement status
- Controller and communications costs
- Trading fees or revenue share
- Battery losses and extra cycling
- Any bill saving the client may lose if GridVolt uses spare battery capacity for trading
GridVolt uses this information to check how much battery power, usable capacity and import/export headroom are actually available for trading. It also checks what the client is likely to receive after costs.
Do not add trading to the proposal unless the expected payment covers the controller, service charges, trading fees, battery losses, extra cycling and any bill saving the client may lose if GridVolt uses spare battery capacity for trading.
Related questions
Do I need more battery power, or more usable capacity?
What trading revenue is realistic for a commercial battery in Great Britain?