Is a virtual power plant (VPP) worth it for your battery?

A virtual power plant links many home batteries so a provider can draw on them when the grid needs power. In return you get credits, a sign-up bonus, or a special plan. The catch is that energy the VPP takes during an event is energy your home can't use that evening, so you may buy more from the grid at your peak price.

The simple sum

Net value = the credits you receive − the cost of the home use you lose.

The cost of lost use is roughly: the energy taken in events that you'd otherwise have used at home × (your evening price − your feed-in credit). A VPP that pays well but runs many deep events can leave you worse off than one with smaller credits and few events.

Questions to ask before you join

• How many events a year, and how much energy is usually taken in each?
• How low can they discharge your battery, and can you set a minimum reserve?
• Do you have to switch retailer or move to a particular plan, and how do that plan's prices compare?
• Is there a lock-in period or exit fee, and do you have to repay a sign-up credit if you leave early?
• Will they control when your battery charges as well as when it discharges?
• Does joining affect your battery's warranty?

Spread one-off credits over the lock-in

A large sign-up credit looks attractive, but divide it by the years you're locked in to compare it fairly with offers that pay every year.