Home battery storage
London

Battery sizes and what they cost

Includes battery, hybrid or AC coupled inverter, electrical installation, DNO notification, commissioning and 0 percent VAT. Backup power in an outage is a separate specification and adds cost, so say if you want it.

The two ways a battery makes money

1. Storing your own solar

Without a battery, a London house typically uses only 40 to 50 percent of what its panels generate, because the panels produce most at midday when nobody is home. The rest is exported for a few pence and bought back later at four or five times the price. A battery flips that: self-consumption rises to roughly 70 to 85 percent.

2. Time shifting on a cheap tariff, with no panels at all

This is the case nobody explains properly. On a time-of-use tariff with a cheap overnight rate, you charge the battery at night and run the house on it through the expensive daytime and evening rates. There is no generation involved. The saving is purely the difference between the two prices, multiplied by the kilowatt hours you shift.

For a house with an air conditioning system running through July afternoons, or a heat pump running through a February, that difference adds up quickly, because those are exactly the loads that fall in the expensive hours.

Sizing it from your real usage

Most battery quotes are sized from the number of bedrooms, which tells you almost nothing. The right method is to look at your half-hourly consumption data, which your supplier can provide if you have a smart meter, and size the battery to cover the expensive window rather than the whole day.

• Typical London household, no heat pump or EV: 5 to 8 kWh used between 4pm and 8am. A 5 to 10kWh battery covers it.
• With a heat pump: winter overnight use can double. 10 to 15kWh.
• With an EV: the car is usually better charged directly on the cheap rate than through the battery, because putting energy through the battery twice loses some of it both ways.
• With air conditioning: the load falls in the afternoon peak, which is the most expensive part of most tariffs and the best case for storage.

What we fit and why

We use lithium iron phosphate batteries rather than older lithium chemistries, because they are more thermally stable, tolerate daily cycling better and hold capacity longer, which matters a lot when the battery is cycling every night on a time-of-use tariff rather than only when the sun shines.

Everything we install is notified to the distribution network operator and commissioned properly, with the certificates issued to you. A battery installed without DNO notification is a problem you inherit when you sell the house.