Energy storage

Batteries can run off two main energy sources: PV or mains electricity. This may seem odd to think about running a battery from the mains, but many companies are now offering Time of Use (ToU) tariffs. These ToU sell energy cheap at night and then charge a premium during peak demand times. Night tariffs are around 25% of the standard rate, whilst peak tariffs are around 125%. So if you can store energy at night and use it through the day you may be able to radically reduce your energy costs.

Storing your PV energy of course is a good thing, especially if you are out during the day. This could also be combined with a ToU tariff to get you through the darker winter months. The general rule of thumb is that the battery storage should be double the output of the PV array. So a 2.5kWp PV array is best coupled with a 5kWh battery. However, note that if using a ToU tariff if is probably better to oversize the battery to facilitate having enough storage to avoid importing during peak tariffs.

All systems are now ‘smart’ and allow the customer to put on times of use, amount of charge etc and also they switch consumption to prioritise PV and stored energy before importing from the grid. It is better to use one manufacturer / system to ensure that this all works seamlessly.

Note that currently most guarantee periods for batteries are typically 10 years.

Battery installation seems to be around £500/kWh at present (2023) with potential savings from storage around £700 per annum. However, the price per kWh for exporting and importing changes and so if import prices go up batteries become more attractive and vice versa.

You can always use your solar PV panels for creating hot water. You can install a device that detects whether your PV panels are exporting power to the grid, and if so, can divert it to your hot water tank, effectively heating your water at the price you would have received for the exported power (free if you are on FIT, the value of the SEG, typically about 5p/kWh if installed post FiT). See https://myenergi.com/product/eddi/ or the Immersun https://www.immersun.co.uk/all-products/immersun .