Solar panels generate most of their energy during the middle of the day. If you are at work, that electricity goes to waste — or gets exported to the grid for 7–15p/kWh. Then you come home in the evening and buy it back at 28p/kWh.

A battery changes that equation. It stores your daytime solar to use in the evening, overnight, and on cloudy days. The question everyone asks: is it worth the extra cost?

The short answer is yes, for most households. Here is the longer answer with real numbers.

What Does a Home Battery Cost

A home battery system costs between £3,500 and £6,000 fully installed, depending on the capacity and brand.

  • 5–6 kWh battery: £3,500–£4,200. Suitable for smaller homes (1–2 bed) or lower energy usage.
  • 10–12 kWh battery: £4,800–£6,000. Suitable for 3–4 bed homes with typical family energy usage.

These prices include installation, all electrical work, and commissioning. They are at the 0% VAT rate, which applies to residential battery storage until March 2027.

At Depth of Light, we install Fox ESS and SigEnergy battery systems. Both come with 10-year manufacturer warranties and are designed to work seamlessly with solar panel systems.

How Much Does a Battery Save Per Year

A well-sized battery typically saves £500–£600 per year on top of the savings from solar panels alone.

Here is how that breaks down. Without a battery, a typical household uses about 50% of its solar generation directly and exports the other 50%. With a battery, self-consumption rises to 80–90%.

The maths:

  • A 10-panel system generates roughly 4,000 kWh per year in Milton Keynes
  • Without a battery, you export ~2,000 kWh at 7–15p/kWh = £140–£300 export income
  • With a battery, you use that energy yourself instead of buying from the grid at 28p/kWh = £560 value
  • Net benefit of the battery: £260–£420 extra per year, plus additional savings from tariff optimisation

Smart tariff optimisation adds further value. With a battery and a time-of-use tariff (like Octopus Flux or Intelligent Go), you can charge the battery from the grid at off-peak rates (7p/kWh) and use that stored energy during peak hours (28p+/kWh). That alone can add £150–£200 per year in savings.

What Is the Payback Period

Based on £500–£600 annual savings:

  • 5–6 kWh battery (£3,500): payback in 6–7 years
  • 10–12 kWh battery (£5,000): payback in 8–10 years

Battery lifespan is 10–15 years. Both Fox ESS and SigEnergy warrant their batteries for 10 years, and real-world performance suggests most will comfortably exceed that. After the payback period, every year of savings is pure return.

If electricity prices rise (which they have consistently done over the past decade), the payback shortens. Every 1p/kWh increase in the grid rate makes your stored solar worth more.

When a Battery Makes Sense

A battery adds the most value if:

  • You are out during the day. If nobody is home to use solar as it is generated, most of your generation gets exported. A battery captures it for the evening instead.
  • You want evening and overnight coverage. Solar panels stop generating at dusk. A battery keeps your home running on stored solar until bedtime or beyond.
  • You want backup power. Some battery systems (including certain Fox ESS models) offer emergency power supply (EPS). If the grid goes down, the battery keeps essential circuits running.
  • You are on a time-of-use tariff. The ability to charge cheap and discharge expensive adds a significant extra income stream from your battery.

When a Battery Might Not Be Worth It

Honesty matters. A battery is not always the right call:

  • You are home all day and already use most of your solar. If you are retired, work from home, or have high daytime usage, your self-consumption is already high. The battery has less surplus to store.
  • Your budget is tight. If you are choosing between a larger solar array or a smaller array plus battery, the larger array usually wins on lifetime value. More panels = more generation for decades.
  • You have very low energy usage. If your annual consumption is under 2,500 kWh, a small solar system may cover most of your needs without storage.

We always discuss this honestly during the survey. If a battery does not make sense for your situation, we will say so.

What Size Battery Do You Need

The right battery size depends on your evening and overnight electricity usage. Most UK homes use 8–12 kWh between 4pm and 8am.

  • 1–2 bed home / low usage: 5–6 kWh battery
  • 3 bed semi / average usage: 8–10 kWh battery
  • 4+ bed detached / high usage or EV: 10–12 kWh battery (or more)

Oversizing slightly is fine — the battery will simply charge fully more often, giving you more grid independence. Undersizing means you still buy some grid electricity in the evening, but you still save significantly more than having no battery at all.

Fox ESS and SigEnergy: What We Install

Fox ESS is one of the fastest-growing battery brands in the UK. Their hybrid inverters are excellent — combining the solar inverter and battery management into one unit, which simplifies installation and reduces cost. The Fox ESS range covers 5 kWh to 12 kWh capacities. Ten-year warranty as standard.

SigEnergy is a premium option. Build quality is outstanding, with longer warranty options available. SigEnergy systems are particularly well-suited to larger installations and offer advanced monitoring through their app. If budget allows, SigEnergy is the premium choice.

Both brands are well-proven in the UK market and both integrate cleanly with solar panel installations. We have installed both extensively across Milton Keynes and Buckinghamshire.

Can You Add a Battery to Existing Solar Panels

Yes. This is called a retrofit, and it is becoming increasingly popular as battery prices come down.

If you already have solar panels, adding a battery does not require changing your panels or roof-mounted equipment. The battery connects to your existing system via a hybrid inverter or AC-coupled battery unit.

Retrofit batteries qualify for 0% VAT just like new installations. There is no requirement to install the battery at the same time as solar panels.

A typical battery retrofit takes one day to install, with minimal disruption to your home.

Solar and Battery Together: The Best Value

Installing solar panels and a battery at the same time is the most cost-effective approach. You save on installation costs (one visit, shared electrical work) and the system is designed as an integrated unit from day one.

Our solar and battery packages start from around £7,500 for a 10-panel system with a 5 kWh battery. A larger 12-panel system with 10 kWh battery is typically £9,000–£10,500.

Combined savings of £1,000–£1,400 per year are realistic for a 3–4 bed home with a well-sized system. That puts the full payback at 6–8 years, with 15–20+ years of returns beyond that.

What to Do Next

If you are considering a battery — either with new solar panels or as a retrofit — the best next step is to get a quote based on your actual energy usage and property.

Use our free online quote tool to get an instant estimate. We will then follow up with a free home survey to confirm the best system size and battery capacity for your needs.

Based in Milton Keynes. MCS certified. Fixed prices with no hidden costs.