Generally you never use all the energy your solar array produces, this gets exported to the grid where you may get paid a few pence for each kWh. Storing this excess energy and using it later when the sun goes down makes much more sense. In addition, if you can get onto a low cost over night energy tariff, you can charge your batteries and run off these during the day. These systems are know as Energy Storage Systems or ESS for short.
After some research I opted for a Victron Energy based system using a LGChem RESU battery. The inverter charger (Multi Plus II 3000) can deliver about 2.7kW. It’s important to remember this is part of a grid connected house, the inverter does not need to provide all the energy to the house. My home runs at about 500W constantly, so the 2.7kW inverter is plenty to run the house 80% of the time and help out when addition power is required limiting the amount of power from the grid. My battery is a 6.5kWh 48v LiFePO4, my advice here would be to get as much storage you can afford, looking back I wish I’d have gone for the 10kWh battery that was available at the time.
The system constantly monitors the main grid connection via a CT clamp with the objective to keep this to a set value, mine is set at 20W.
- If the import goes higher than the set value, the inverter turns on, discharging the battery storage to provide power to loads and get the grid usage back to the set value
- If there import goes negative, ie power is being exported due to excess solar generation, the charger function turns on and charges the battery for use later.
Below is the system as it was originally installed.
- System Controller – Victron Energy Colour GX
- Inverter Charger – Victron Energy Multi Plus II 3000 with CT clamp
- Battery Storage – LGChem RESU 6.5