Glossary
RCD
Residual current device: a safety switch that cuts the power if current leaks to earth. Plug-in solar needs modern RCD protection.
A residual current device (RCD) monitors the current going out and coming back on a circuit. If they don’t match, because current is leaking to earth (possibly through a person), it switches off within a fraction of a second. An RCBO combines an RCD with a circuit breaker for a single circuit. Both are usually found in your consumer unit (fuse box).
The DESNZ product specification tells users to check for “modern residual current protection (RCBO)”. Homes with older fuses and no RCBOs should be checked, and upgraded if needed, by an electrician. It adds that circuits with MCBs and an upstream RCD “may also be acceptable, subject to verification through further testing now being undertaken by DESNZ”. It also says you should test the RCBO periodically while the kit is generating (IPS §8.3.2, §8.3.4).
The charity Electrical Safety First goes further. It recommends at least a Type A bidirectional RCD on circuits used for plug-in solar, and says homes with Type AC RCDs should upgrade first (ESF).
If you’re not sure what’s in your consumer unit, ask a registered electrician before you buy.