Solar without a battery vs solar with a battery:what changes

What actually changes when you add a battery?

Without a battery, solar power has two places to go. Your home uses what it needs at that moment, and the rest is exported to the grid. The share you use yourself is called self-consumption. Every unit you self-consume saves you the full import price. Every unit you export earns the Smart Export Guarantee (SEG) rate your supplier offers, which Ofgem requires to be above zero but otherwise leaves to the supplier.

A battery adds a third option. Surplus daytime power charges the battery, and the battery runs your home in the evening instead of the grid. You export less and import less. The money a battery makes from solar is the gap between your import price and your export rate, multiplied by the extra units it shifts.

How much of your solar do you use, with and without a battery?

MCS-certified installers must estimate self-consumption using the MCS guidance note MGD 003. The figures below come from its lookup tables for a household using 3,500 to 3,999 kWh a year with a system generating 3,900 to 4,199 kWh, which matches a 4 kWp south-facing roof in London on PVGIS modelling (4,089 kWh).

Two things stand out. First, without a battery most households use well under a third of a 4 kWp system's output, lower than the "about half" often quoted. The 50% figure is an old assumption from the Feed-in Tariff era, which MGD 003 itself notes. Smaller systems relative to your usage do reach higher shares. Second, the first 5 to 6 kWh of storage roughly doubles self-consumption, while doubling the battery again adds far less.

What is a battery worth in pounds each year?

Here is the arithmetic for the "in half the day" household above, with our assumptions stated so you can swap in your own numbers:

• Generation: 4,089 kWh a year (PVGIS, 4 kWp, London, south, 35°).
• Self-consumption: 23% without a battery, 57% with 5 to 6 kWh usable (MCS MGD 003).
• Import price: 26.32p per kWh, the Ofgem price cap from 1 October 2026 for direct debit, GB average.
• Export rate: shown at 5p, 10p and 15p per kWh, because SEG rates are set by each supplier and vary.
• The battery shifts an extra 1,391 kWh a year from export to self-consumption (34% of 4,089 kWh).

Notice the pattern: the better your export rate, the less a battery adds, because exporting is already paying you well. These are upper figures. The Energy Saving Trust points out that storing energy and releasing it later always loses some along the way.

So does a battery pay for itself on solar alone?

Usually not. The Energy Saving Trust puts a 5 kWh battery system at around £4,600 and its typical lifespan at 10 to 12 years. At £157 to £295 a year, simple payback is roughly 16 to 29 years, longer than the battery is expected to last.

The panels themselves are a different story. The Energy Saving Trust estimates solar panels with export payments pay back in about 9 years in London and 10 to 12 years further north. If budget is tight, fit the panels first. A battery can be added later, and retrofitted batteries also qualify for 0% VAT until 31 March 2027.

How do time-of-use tariffs change the maths?

A time-of-use tariff charges different prices at different times of day, with a lower-priced overnight or off-peak window. A battery on one of these tariffs can charge from the grid when electricity costs less and run the house through the expensive evening peak, all year round. That matters most in winter, when a London 4 kWp system averages only 4.7 kWh a day in December and the battery would otherwise sit half empty.

The Energy Saving Trust's 2026 research found batteries are better paired with heat pumps than with solar panels, provided you are on a suitable tariff, because the battery can supply the heat pump with low-cost off-peak electricity. Homes combining a heat pump, solar and a battery on the right tariffs cut bills by around £800 a year in general, and the best combinations by around £1,000 or more.

When is a battery worth it, and when is it not?

A battery is more likely to make sense if:

• you have or are planning a heat pump or an EV and will use a time-of-use tariff
• your export rate is low, so shifting solar into the evening is worth more
• you are installing solar now, so scaffolding and electrical work are shared
• you value less exposure to future changes in export rates or peak prices, which the Energy Saving Trust lists as a genuine benefit

It is probably not worth it yet if:

• you use little electricity in the evening and have no heat pump or EV
• you have a good export rate and no plans to change your heating
• you expect to move within a few years
• the money would do more in insulation, which cuts the heat you need before any technology is added

What should you check before buying a battery?

1. Usable capacity, not headline capacity. MCS tables use usable kWh, and systems stop discharging before empty to protect battery life.
2. The self-consumption estimate on the quote, calculated with MCS MGD 003 for your occupancy pattern and your actual annual usage from bills.
3. The export rate and import tariff the savings assume. Ask for the figures with and without a time-of-use tariff.
4. Warranty length and what capacity the battery is guaranteed to keep, compared with the 10 to 12 year lifespan the Energy Saving Trust expects.
5. Where it will go. The Energy Saving Trust describes a typical unit as about 100 x 60 x 25 cm, usually fitted in a garage, utility room or on an outside wall.
6. Whether it can back up any circuits in a power cut. Not every system can, so ask rather than assume.

Ask any installer, including us, to quote solar with and without storage side by side. As a guide, Smart Energie's typical range for eight panels with a 5 kWh battery on a three-bedroom house is £8,500 to £13,000, confirmed at survey. Try the payback tool with your own numbers, or read what solar PV is if you are starting from scratch.

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