How Do Solar Batteries Work?
A clear, jargon-free guide to home battery storage — what is inside them, how they charge and discharge, and why they are transforming how UK homes use solar energy.
A solar battery is essentially a large rechargeable battery that stores excess electricity from your solar panels for use later — typically in the evening when the sun has gone down but your energy demand is highest.
Without a battery, surplus solar energy is exported to the grid, earning you approximately 10.8p/kWh through the Smart Export Guarantee. With a battery, you use that energy yourself, avoiding buying it back from the grid at 24-30p/kWh. The difference — roughly 15-20p per kWh — is where the financial benefit comes from.
Modern home batteries use lithium-ion technology, the same chemistry found in electric vehicles and smartphones, but engineered for thousands of charge/discharge cycles over 15-20 years.
Key Takeaway
A solar battery shifts your free daytime solar energy to when you actually need it most — evenings and mornings. Self-consumption can increase from 30-40% without a battery to 70-80% with one.
How the Charge Cycle Works
Solar panels generate electricity
During daylight hours, your solar panels produce DC electricity. On a sunny day, a typical 4kW system can generate more power than your home uses at any given moment.
Excess energy charges the battery
Instead of exporting surplus electricity to the grid (earning just ~10.8p/kWh via SEG), a hybrid inverter diverts it into your battery. The inverter converts AC back to DC for storage.
Battery stores energy as DC
Inside the battery, lithium-ion cells store electrical energy chemically. Modern home batteries operate at around 95% round-trip efficiency — meaning 95% of the energy stored can be used.
Evening demand draws from battery
When the sun goes down and your solar panels stop generating, the inverter automatically switches to battery power. Your home draws stored energy first before pulling from the grid.
Grid takes over when battery is depleted
Once the battery is empty, your home seamlessly switches back to grid power. On smart tariffs like Octopus Go, the battery can recharge overnight at cheap rates (7.5p/kWh) for use the next day.
Types of Solar Battery
Not all batteries are the same. Here is what is available for UK homes.
Lithium Iron Phosphate (LFP)
The dominant chemistry for UK home storage. Very safe, long-lasting, and stable. Slightly lower energy density than NMC but better cycle life. This is what we recommend and install.
Brands: Sigenergy, BYD, Tesla Powerwall
Lithium Nickel Manganese Cobalt (NMC)
Higher energy density (smaller for the same capacity). Slightly shorter cycle life than LFP. The Tesla Powerwall uses NMC chemistry.
Brands: Tesla Powerwall, LG RESU
Sodium-Ion
New technology arriving in 2025-2026. No lithium or cobalt needed. Works better in cold temperatures. Not yet widely available in the UK residential market.
Brands: Emerging (CATL, HiNa)
Key Battery Specifications Explained
Usable capacity
5.2-9.5 kWhHow much energy the battery stores. A 5.2kWh battery covers an average evening. Larger homes or EV owners should consider 9.5kWh+.
Power output
2.6-5.0 kWHow quickly the battery can deliver energy. Higher output supports running multiple appliances simultaneously. 3.6kW covers most homes.
Round-trip efficiency
93-97%How much energy you get out vs. what goes in. 95% means storing 10kWh gives you 9.5kWh back. Higher is better.
Depth of discharge
90-100%How much of the battery capacity you can actually use. 100% DoD means you use all of it. LFP batteries typically allow 100% DoD.
Cycle warranty
6,000-10,000Number of charge/discharge cycles before capacity drops below 80%. At one cycle per day, 6,000 cycles = 16 years.
Operating temperature
0-45°CBatteries must be installed in a location that stays within this range. Garages and utility rooms are the most common locations in Wiltshire homes.
What About Power Cuts?
This is one of the most common questions we get asked. The answer depends on your inverter:
Standard hybrid inverter
Most hybrid inverters (including standard Sigenergy models) switch off during a power cut for safety reasons. This is a grid regulation requirement — the inverter must not feed power into a "dead" grid while engineers are working on it.
EPS (Emergency Power Supply)
Some inverters have an EPS function that creates a separate circuit during power cuts. The Sigenergy Gen 3 with EPS can power essential circuits (lights, fridge, router) from the battery. This is an option we offer on all new installations.
Battery Storage FAQs
Battery storage is worth it if you use most of your electricity in the evening (when solar panels are not generating) or if you want protection from power cuts. A battery typically increases self-consumption from 30-50% to 80-90%, making more of your solar investment pay for itself.
Modern lithium-ion batteries typically last 10-15 years, with most manufacturers offering 10-year warranties guaranteeing at least 70% capacity retention after 6,000+ charge cycles. Battery technology is improving rapidly.
Yes. Lumos Energy regularly retrofits battery storage to existing solar panel systems. We assess your current setup, recommend a compatible battery, and install it alongside your existing inverter or with a new hybrid inverter if needed.
Many modern battery systems offer backup power functionality, but not all. If power cut protection is important to you, we ensure your system specification includes this capability. Some systems switch to backup within milliseconds.
Related Services & Guides
Ready to Add Battery Storage?
Book a free survey and we will recommend the right battery size and chemistry for your home, usage pattern, and budget.
Free survey · No obligation · Broughton Gifford, Melksham · Open Mon–Fri 8am–6pm, Sat 9am–2pm