Solar battery storage lets you store electricity when your panels make more than you’re using, then power your house in the evening instead of buying expensive grid electricity – I’ve been fitting these systems for the last 8 years and they’re brilliant for families who use most power after work. A decent 10kWh battery costs about £7,000 fitted and stores enough juice for your evening TV, lights, and kitchen appliances, though you’re looking at 10-12 years before it pays for itself.
What Batteries Actually Do in Your House
How does this battery thing work then?
Dead simple really. During the day, your solar panels pump out electricity. Some goes to whatever’s running – kettle, washing machine, lights. Any leftover either charges your battery or gets flogged back to the grid for buttons.
Come teatime when the panels pack up for the day, instead of buying electricity at 30p+ per unit, your house runs off stored solar power. Battery kicks in automatically, you don’t even notice.
Woman in Bamber Bridge was spending £180 monthly on electricity. After I fitted panels and a 10kWh battery, summer months down to £40-50. Winter’s higher because heating and less solar, but still saving serious money.
Think of it like a water butt for electricity. You collect it when it’s free (solar), use it when you need it (evening).
What size battery do normal people actually need?
Most families I fit end up with 8-12kWh batteries. That covers a proper evening’s worth of electricity without going mental on cost.
10kWh battery runs:
- All your lights on for the evening (maybe 400-500W total)
- Telly and Sky box till bedtime (200W)
- Fridge-freezer through the night (150W average)
- Few cups of tea, bit of cooking
- Phone chargers, wifi, normal house stuff
Bigger houses or electric heating might need 15-20kWh. Small places often fine with 6-8kWh. Had a retired couple with a tiny 5kWh battery – perfect for their needs.
Don’t go daft on size though. No point having a massive battery if your panels can’t fill it. I see people wanting 30kWh systems for a 4kW solar installation – waste of money.
Do they actually save you money though?
Right, honest answer – batteries take longer to pay back than just panels. We’re talking 10-12 years typically, sometimes longer.
Here’s why: storing your own solar electricity saves about 20-25p per unit compared to buying from the grid. But batteries cost £6,000-£12,000 fitted, so takes ages to earn that back.
Where they’re worth it:
- Backup power when grid goes down (proper useful in rural areas)
- You hate the idea of giving away cheap electricity for export payments
- Planning for electric car or heat pump later
- Time-of-use tariffs where evening electricity costs 40p+ per unit
Bloke in Chorley paid £8,500 for his battery setup. Saves about £600 yearly. Maths says 14-year payback, but he wanted energy independence more than quick returns.
Different Battery Types and What’s Actually Any Good
Lithium batteries – what everyone fits now
Everyone fits lithium batteries these days. Reliable, efficient, don’t take up half your garage like old lead-acid ones.
Two main flavors – LiFePO4 (lithium iron phosphate) and NMC (lithium nickel manganese cobalt). LiFePO4 lasts longer and handles our rubbish weather better. NMC packs more power into smaller space but doesn’t last quite as long.
Most house batteries use LiFePO4. Tesla Powerwall, GivEnergy, Solax – all lithium tech. Built-in computers handle charging, temperature, keeping cells balanced. Proper clever stuff.
Typical lithium battery lasts 15-20 years, 6,000-8,000 charge cycles. Warranties usually 10 years, 80% capacity retention. Much better than early systems that conked out after 5-6 years.
What about cheaper battery options?
Lead-acid batteries still exist but rarely worth bothering with for house installations. Cheap upfront but need replacing every 5-7 years, take up loads of room, efficiency’s rubbish.
Only time I’d suggest lead-acid is off-grid shepherd’s hut or allotment shed where space isn’t precious and budget’s tight. For proper houses, lithium every time.
Some newer saltwater batteries around but limited suppliers, higher costs, unproven longevity. Stick with tried and tested lithium for now.
How Batteries Get Fitted and Where They Go
Where do you actually put these things?
Most batteries end up in garages, utility rooms, or purpose-built outdoor cabinets. Need somewhere dry, not too hot, not too cold, accessible for occasional maintenance.
Garage is usual spot – out the way, easy access, protected from weather. Utility room works if you’ve got space. Avoid unheated outbuildings in winter, avoid hot cupboards near boilers.
External cabinets work well if indoor space is tight. Proper weatherproof jobs designed for outside installation. Tesla Powerwall quite compact, mounts on external walls with decent bracket system.
Had one customer with basement installation – perfect temperature year-round, plenty of space, away from family areas. Just needed cable run to consumer unit upstairs.
What electrical work’s needed?
Battery installation needs proper sparky work – new circuits, safety switches, monitoring systems, earthing. Not DIY territory.
Usually need dedicated section in your consumer unit for battery inverter. Surge protection recommended. Emergency isolation switches mandatory for safety.
Straightforward installation takes 4-6 hours typically. Older houses with ancient consumer units might need electrical upgrades first – factor that into costs.
All battery work needs Building Regulations notification. Proper MCS installers handle paperwork as part of service.
AC or DC coupling – what’s the difference?
Two ways to connect batteries – AC coupled or DC coupled. Both work fine, just different approaches.
AC coupled means separate battery inverter connected independently to your house. Can add to existing solar setups easily. Electricity gets converted twice so slightly less efficient.
DC coupled uses one inverter handling both panels and battery. More efficient, tidier installation, but means replacing solar inverter if retrofitting to existing system.
New installations, I usually go DC coupled with hybrid inverter. Adding battery to existing solar, AC coupling often makes more financial sense.
Real-World Performance and Usage
How much can you actually store and use?
10kWh battery gives you about 8-9kWh usable power – can’t run batteries completely flat without damaging them. Modern systems handle this automatically.
Family using 15 units daily might use 5-6 units during day while solar’s generating, leaves 9-10 units for evening. 10kWh battery covers most evening usage spring through autumn.
Winter’s tougher – panels generate less, heating uses more. Battery might cover lights, telly, kitchen stuff but probably not electric heating all evening.
Customer with 20kWh system covers virtually all evening usage year-round. Another with 6kWh battery just covers essentials. Depends on your usage and budget.
What happens when power cuts happen?
Most battery systems provide backup power during outages – brilliant if you work from home or need medical equipment running.
System automatically disconnects from grid during power cuts, switches essential circuits to battery power. Usually covers lights, key sockets, heating controls for several hours.
Not everything gets backup power – depends how system’s wired. Usually prioritize lighting, fridges, heating, important sockets. Electric showers, cookers often excluded because they hammer power.
Rural customer near Garstang loses power regularly in storms. Battery backup keeps WiFi, computers, heating running during outages. Saved his bacon multiple times working from home.
How long do these batteries actually last?
Quality lithium batteries typically good for 15-20 years. Gradual degradation rather than sudden failure.
After 15 years, battery might hold 70-75% original capacity but still perfectly usable. Like old phone batteries – don’t last as long but still work.
Temperature affects lifespan significantly. Extreme heat or cold knocks years off battery life. Proper installation in stable environment crucial.
Modern systems much smarter about battery management.
Money Side – Costs and Payback
What do battery systems actually cost?
Battery costs depend on size, brand, installation complexity. Prices dropped loads over past five years but still significant investment.
Any government help with costs?
No VAT on batteries installed with new solar panels – saves 20%. Retrofitting batteries to existing solar currently pays VAT though.
No specific battery grants but some councils offer green loans covering whole renewable energy packages including storage.
Smart Export Guarantee still applies to excess electricity after battery’s full. Usually 3p-15p per unit depending on supplier.
Smart Tariffs and Clever Features
How do smart electricity tariffs work?
Time-of-use tariffs charge different rates throughout day. Cheap overnight (7p-12p per unit), expensive peak times (35p-50p per unit).
Battery can charge from cheap overnight grid electricity, discharge during expensive peaks. Saves money even without solar panels.
Octopus Go does 7.5p overnight, 30p+ day rates. Battery arbitrage saves £300-£500 yearly just from smart charging. Add solar generation and savings increase significantly.
Customer in Preston on Octopus Go charges battery overnight at 7.5p, uses stored power during 30p+ day rates. Combined with solar, electricity bill dropped from £150 monthly to £40-60.
What clever features do modern batteries have?
Current battery systems connect to internet, weather forecasts, smart home tech. Proper space-age stuff compared to early systems.
Weather prediction algorithms decide overnight charging based on tomorrow’s forecast. Sunny day predicted? Might not charge overnight, save space for solar. Cloudy forecast? Charge full from cheap grid electricity.
Load shifting moves appliances to optimal times. Dishwasher, washing machine, immersion heater programmed to run during solar generation or cheap overnight periods.
Apps let you monitor everything remotely. Battery status, solar generation, electricity usage, system optimization. Some learn your patterns automatically.
Choosing Batteries That Actually Work
Which brands are worth buying?
After fitting loads of different systems, some clear winners and losers:
Tesla Powerwall – expensive but brilliant.
GivEnergy – good value, decent app, growing installer network.
Solax – reliable Chinese brand, competitive pricing, solid performance.
Pylontech – modular design, works with various inverters, scalable capacity.
Avoid unknown brands or grey imports without UK support. 15-20 year products need proper warranty backing and local service.
How do you work out proper battery size?
Start with evening electricity usage after solar stops generating. Everything running teatime onwards – heating if electric, cooking, entertainment, lighting.
Check your electricity app or smart meter for evening usage patterns. Add 20-30% buffer for seasonal variations and occasional high usage.
Don’t exceed your solar surplus capacity. No point having 20kWh battery if panels only make 5kWh surplus daily in summer.
Consider future plans – electric car, heat pump, family changes. Sometimes worth slight oversizing for future needs.
Adding batteries to existing solar
Retrofitting batteries to existing solar perfectly doable but needs planning.
AC-coupled approach works with any existing solar setup. Separate battery inverter connects independently. Bit less efficient but very flexible.
DC-coupled retrofit needs compatible hybrid inverter. Might mean replacing existing solar inverter. More efficient but higher upfront cost.
Check existing electrical setup first. Older consumer units might need upgrading to handle additional kit safely.
Thinking about battery storage? Get someone round to look at your setup properly before making any decisions. Every house is different.