What Is a Solar Battery & How Does It Work?

The process is straightforward:

1. Morning to afternoon: Your solar panels generate electricity. Your home uses what it needs directly. 2. When generation exceeds consumption: The surplus electricity flows into the battery, charging it. 3. When the battery is full: Any remaining surplus is exported to the grid and you earn Smart Export Guarantee (SEG) payments. 4. Evening and night: Your home draws electricity from the battery instead of the grid. 5. When the battery is empty: Your home switches seamlessly to grid electricity. 6. Next morning: The cycle repeats.

The entire process is automatic — the hybrid inverter or battery management system handles all switching without any input from you.

Source: Energy Saving Trust battery storage guidance.

Lithium-ion (most common): - Used in 95%+ of UK residential installations - High energy density (stores more in less space) - 10–15 year lifespan, 6,000–10,000 charge cycles - Brands: Tesla Powerwall, GivEnergy, Fox ESS, BYD, Pylontech - Cost: £2,500–£7,500 depending on capacity

Lithium iron phosphate (LFP): - A subtype of lithium-ion — safer, longer lasting - 15–20 year lifespan, 8,000–12,000 cycles - Slightly lower energy density than standard lithium-ion - Brands: GivEnergy, BYD, Pylontech (most use LFP chemistry) - Becoming the UK market standard

Lead-acid (outdated): - Older technology, lower cost but much shorter lifespan (3–5 years) - Heavy, bulky, requires ventilation - Not recommended for new UK residential installations - Only used in some off-grid or budget applications

For a new UK installation in 2026, LFP lithium-ion is the recommended choice.

Source: Manufacturer specifications; MCS product listings.

Battery costs depend on capacity (measured in kWh):

• 3–5 kWh: £2,500–£3,500 — suits low-consumption homes or daytime-heavy usage
• 5–8 kWh: £3,500–£5,000 — covers most evening consumption for average homes
• 9–13 kWh: £5,000–£7,500 — covers overnight consumption for most UK homes
• 13.5 kWh (Tesla Powerwall): £5,500–£7,500 — premium product with backup capability

What size do you need? A typical UK household uses 8–10 kWh per day. Roughly half of this is consumed in the evening and overnight. A 5–10 kWh battery covers most evening usage.

The sweet spot for most UK homes is a 5–10 kWh battery costing £3,500–£6,000 installed.

Source: MCS installer pricing 2026; manufacturer RRPs.

The financial case for batteries is improving but not yet as clear-cut as panels alone.

Without a battery: - Self-consumption: 30–50% - Surplus exported at 4–15p/kWh (SEG) - Annual savings: £700–£900

With a battery: - Self-consumption: 60–85% - Less exported, more used at home value (26.11p/kWh saved vs 4–15p earned) - Annual savings: £900–£1,200 - Additional savings from battery: £200–£400/year

Battery payback: £3,500–£6,000 cost ÷ £200–£400/year additional savings = 9–18 years

Batteries make more financial sense when: - You are on a time-of-use tariff (charge cheaply overnight at 7.5p/kWh, use during peak at 26.11p+) - Electricity prices rise (every 1p/kWh increase improves the battery business case) - You want backup power during grid outages - You value energy independence

Batteries are not yet as financially compelling as panels alone, but the gap is closing as battery prices fall and electricity costs rise.

Source: Ofgem price cap, July-September 2026; SEG tariff data; Energy Saving Trust.

Yes. You can add a battery to an existing solar panel system at any time. The process involves:

1. Survey — an installer assesses your current system (inverter type, capacity, wiring) 2. Option A — AC-coupled battery: A standalone battery with its own inverter. Connects to your existing system without modifying it. Works with any existing inverter type. Cost: £3,000–£7,000 installed. 3. Option B — Replace inverter with hybrid: Replace your existing string inverter with a hybrid inverter that manages both panels and battery. More efficient but requires inverter replacement. Cost: £4,000–£8,000 installed (including new inverter).

If your existing inverter is approaching end of life (10+ years old), Option B makes more sense — you replace the inverter you would have replaced anyway and add battery functionality at the same time.

Source: MCS retrofit guidance.