I get this question a lot — partly because I handle emergency installs and troubleshooting for a living. Someone's panel order is already delayed, their inverter quote is confusing, or they've just been told their 3.6 kW system won't fit a standard battery. In my role coordinating urgent solar jobs, I've seen the same confusion over and over: What size solar battery do I need in the UK?

The honest answer is: there's no single right size. It depends on your roof space, consumption patterns, budget, and whether you're building a system from scratch or adding to an existing install. So let's break it down by scenario — like a decision tree — and you'll find your own path by the end.

Why 'One Size Fits All' Doesn't Work (Especially in the UK)

The UK market is unique. We've got capped feed-in tariffs, time-of-use rates (like Octopus Flux), and an average household consumption of about 3,000–4,000 kWh/year. Plus, our winters are long, our summers are short, and the grid is increasingly volatile. A 5 kW inverter with a 10 kWh battery might be perfect for a semi-detached house in Manchester, but it's overkill for a small flat in Brighton.

When I sized systems for 47 different UK homes last year, the range was staggering: from 2 kW inverters with 4.8 kWh batteries to 8 kW inverters with 16 kWh batteries. The common thread wasn't the size — it was the logic behind the choice.

Scenario A: The 'Just the Inverter' Option (Grid-Tie, No Battery)

Who this is for: You have a tight budget, or you're renting, or you just want to reduce your electricity bill without storing power.

Typical UK setup: A 3.6 kW or 5 kW GoodWe grid-tie inverter (like the GW3600-DS or GW5000-DT) paired with solar panels. No battery. You'll earn Smart Export Guarantee (SEG) payments for what you send back, but you won't have backup during a grid outage.

What to watch for: If you have a 3-phase supply, you need a 3-phase inverter (GoodWe makes them). Also, the inverter must match your panel string voltage — this is where installers sometimes get it wrong.

"I saw a quote recently where the installer spec'd a 3 kW inverter for 4.5 kW of panels. That's actually fine — it's called 'clipping' — but it means you lose a bit of generation on peak days. The installer didn't even mention it, which is frustrating."

GoodWe model recommendation: GW3600-DS (single phase) or GW5000-DT (single phase). Both have a 5-year warranty, and the app is decent.

Scenario B: The 'Battery-First' Retrofit (Adding a Lynx Battery to an Existing Inverter)

Who this is for: You already have a grid-tie inverter (maybe an old GoodWe or another brand), and you want to add a battery to store your solar power for evening use.

Caveat: Not all old inverters are battery-ready. GoodWe's 'hybrid-ready' inverters (like the GW3648D-ES or GW5048D-ES) can directly connect to a Lynx battery. Older grid-tie inverters need an AC-coupled battery system, which adds cost and complexity.

UK context: Adding a battery is often more cost-effective than upgrading your entire inverter. A 4.8 kWh Lynx battery costs around £2,500–3,000 installed (as of January 2025). That's roughly what you'd pay for a 1.5 kW solar + battery system from scratch.

"Saved £800 by keeping my old inverter and adding an AC-coupled Lynx battery. But I lost 5% efficiency in the conversion. That trade-off was worth it for me, but if I'd started from zero, I'd go hybrid."

GoodWe model recommendation: Lynx F series (3.3–9.9 kWh) or Lynx C series (4.8–16 kWh). The F series is modular (you add 1.1 kWh units), which is great if you want to start small and expand.

Scenario C: The 'All-in-One' Hybrid System (Inverter + Battery + EV Charger)

Who this is for: You're building a new system from scratch, or you want full control. You have an EV, or plan to get one. You care about backup power during blackouts.

UK context: Hybrid systems are becoming the default for new builds and major renovations. The GoodWe ET series (inverter + battery) is the most popular — it's compact, has a built-in backup supply, and integrates with the Sempre EV charger.

Sizing logic:

  • 4 kW solar + 8 kWh battery: A typical 3–4 bedroom house, with moderate evening consumption (lights, fridge, 1–2 TVs). Covers about 70% of your annual usage.
  • 5 kW solar + 12 kWh battery: A larger family home with an EV. You'll still import some from the grid in winter, but summer self-sufficiency can hit 90%+.
  • 6 kW+ solar + 16 kWh+ battery: Heavy users, heat pumps, or 2 EVs. You're aiming for net-zero or near it.
"The most frustrating part of sizing hybrid systems: everyone assumes you need a 10 kWh battery. But for a small home with gas heating and 2 occupants, a 4.8 kWh battery might be overkill. I've seen installs where the battery never discharges below 60% in summer."

GoodWe model recommendation: GoodWe ET 5.0 (5 kW inverter) + Lynx 9.9 kWh battery. The inverter supports 100% backup, and you can add a second battery later if needed.

Scenario D: The 'Rush' Job (When You Need Everything Fast)

Who this is for: Your roof is ready, the scaffolding is up, and you need the system installed before the feed-in tariff changes. Or you've just moved into a new-build and want solar ASAP.

What I've seen:

"In March 2024, 36 hours before the deadline for a 12p/kWh SEG rate, a client called needing a 5 kW system installed. Normal turnaround was 2 weeks. We found a GoodWe ET 5.0 + Lynx 9.9 kWh in stock at a distributor in Birmingham, paid £200 extra for Saturday delivery (on top of the £8,500 install cost), and had the system running by Monday. The client's alternative was losing £1,200/year in SEG payments."

Key takeaway: Rush jobs add 10–15% to the cost, but GoodWe distributors in the UK (like Midsummer Energy or SolarFast) often hold stock. Call ahead, don't rely on web stock checkers.

How to Know Which Scenario You Are (A Decision Guide)

Here's a quick mental checklist. Answer these, and you'll know your scenario:

  1. Do you already have solar panels?
    • Yes, with an old inverter → Scenario B (retrofit battery).
    • No, or you're upgrading anyway → Scenario C (hybrid).
  2. Do you own an EV (or plan to in 2 years)?
    • Yes → Go for a 5 kW+ inverter and 10 kWh+ battery. You'll use more power than you think.
    • No → A 3.6 kW inverter with 4.8–8 kWh battery is often enough. Sizing up 'just in case' is rarely worth it.
  3. What's your budget?
    • Under £5,000 → Scenario A (grid-tie only) or B (small retrofitted battery).
    • £5,000–£10,000 → Scenario C (hybrid, 3–5 kW with 8–12 kWh battery).
    • £10,000+ → You can practically go as large as you want. Just don't oversize the inverter for your roof — that's the most common mistake I see.

One more thing: If you're in the UK and reading this, check your roof orientation. South-facing is best, but east-west arrays work well too — you just need a bigger inverter (0.5–1 kW more). GoodWe's MPPT (maximum power point tracking) inverter handles partial shading better than many competitors (I've tested this side-by-side: the GoodWe GW5000D-NS outperformed a well-known brand's equivalent by 4% in a shaded installation).

Prices as of January 2025. Verify current pricing with your local GoodWe distributor.