Panels and batteries explained

This stage covers what actually matters when you're reading specs and quotes — not the marketing terms. The aim is to give you enough vocabulary to read a quote critically and ask the right follow-up questions, not to make you an engineer.

Panel technology — what matters at the buying level

Cell types

• Mono PERC — the previous-generation mainstream. Efficiency typically 20-21%. Still fine, still cheap, but being superseded.
• TOPCon / N-type — the current mainstream. Efficiency typically 21.5-22.8%. Better low-light performance. Better degradation curves (typically 0.4%/year vs 0.5%/year). Marginal £ premium per panel — usually worth it.
• Heterojunction (HJT) — premium tier. Highest efficiency (~23%). Best low-light and high-temperature performance. Notably more expensive — usually only worth it on roof-area-constrained installs where you need to squeeze max kWp from limited space.

Watt peak (Wp)

A panel's peak power output in ideal conditions. Modern 60-cell (residential) panels are 380-440Wp. Higher Wp = same roof area gives you more kWp. But Wp ratings are tested at “STC” (standard test conditions) which are unrealistic — real-world output is 75-85% of rated under UK conditions averaged over a year.

Efficiency vs Wp — which to care about?

If your roof has plenty of space: care about £/Wp installed. Higher-efficiency panels are pricier; pay for them only if needed. If your roof is tight: care about efficiency and Wp/m² so you can squeeze max kWp.

Degradation rate

Panels lose efficiency over time. Typical annual degradation: 0.4-0.55% in year 2 onwards (year 1 has a one-off ~2% drop). Modern N-type panels have lower degradation than older Mono PERC. After 25 years a 0.4%/yr panel is at ~90% output; a 0.55%/yr panel is at ~86%.

What “Tier 1” actually means (and doesn't)

“Tier 1” is a manufacturer-financing classification — it means a bank considered the company creditworthy enough to lend against. It tells you the manufacturer is solvent and large; it tells you nothing about panel quality, efficiency, or reliability. Don't accept “Tier 1 panels” as a spec on a quote — ask for the actual brand and model.

When you read a panel spec sheet, look for:

If a panel ticks most of these, it's a credible residential panel. If multiple fall short, ask why before agreeing to install.

Can I actually choose my own panels?

Short answer: yes, but it's not free, and the process has friction. Here's how the choice actually works in UK residential.

Installers have go-to brands. Most UK installers buy in bulk from 2-3 panel manufacturers they have wholesaler accounts with — typically Jinko, JA Solar, Q Cells, Trina, or Longi. These are good panels (they're what most homes in the UK now have on the roof), but they're the installer's default, not a hand-picked recommendation for you.

You can request alternatives, but expect a markup.If you want SolarEdge, REC, or SunPower panels, ask the installer to quote them. They'll source through a different wholesaler at lower discount, and the panel itself costs more. Expect 20-40% higher install price for premium brands.

Inverter choice is tighter than panel choice.Many installers are trained on, certified by, and stock spares for one specific inverter brand (SolarEdge, GivEnergy, Sungrow, Solis). Asking for a different inverter brand often means changing installer entirely. The inverter is the most-likely-to-fail component and aftercare matters — accept your installer's default inverter unless you have a strong reason.

Battery choice is similar to inverter choice. Some installers are Tesla-certified (and only install Powerwall); others are GivEnergy specialists; others stock multiple. You can swap but you may be swapping installer too.

Practical strategy:

1. Ask each installer up front: “What brand and model panel are you proposing, and why that one?” Bad answer: “Tier 1 panels.” Good answer: “Jinko Tiger Neo 425Wp because they're our standard, we've installed 200 this year, and we've had zero warranty claims on the model.”
2. If you have a preference, say it on day one. Don't ambush them on the second visit with “actually I want SunPower.” Most installers will quote your preferred brand if you ask early.
3. Ask for both prices. “Quote me with your default panel; quote me again with [brand X]. I want to see both prices.” If they refuse to quote the alternative, that's the answer.
4. Watch for “we only install X.” Sometimes legitimate — they're a certified Tesla / SolarEdge installer with manufacturer-backed extended warranty. Sometimes laziness. Ask why.
5. Don't fight on inverters as hard as on panels. Pick the installer for inverter support and panel availability together.

Battery chemistry — LFP vs NMC

• LFP (Lithium Iron Phosphate) — current mainstream for home batteries. Safer (very low fire risk), longer cycle life (5,000-10,000 cycles vs 2,000-3,000), can be discharged 100% without damage. Slightly heavier and bulkier per kWh stored. Tesla Powerwall 3, GivEnergy, Sonnen all LFP.
• NMC (Nickel Manganese Cobalt) — older home battery chemistry. Higher energy density (smaller for same kWh), but shorter cycle life, higher fire risk, and only safe to discharge to ~80%. Becoming uncommon in residential.

For most UK home installs, LFP is the right answer. If a quote includes NMC, ask why — and consider it a signal of older inventory.

AC-coupled vs DC-coupled batteries

Solar panels produce DC; your house uses AC; the inverter converts DC→AC. Where the battery sits in this chain matters.

• AC-coupled — battery connects to your existing AC wiring with its own internal inverter. Best for retrofit — you can add a battery to an existing solar setup without replacing the inverter. Slightly less efficient (DC → AC → DC → AC round trip).
• DC-coupled — battery sits on the DC side of a hybrid inverter. Best for new installs — fewer conversions, slightly more efficient. But you have to commit to a battery upfront (or pay to replace the inverter later).

If you're installing solar today and might add a battery later: ask for a hybrid inverter (DC-coupled-ready). It costs ~£200-400 more upfront but saves you ~£800-1500 in inverter replacement when you add a battery in year 3-5.

Inverters — the most overlooked component

The inverter is the most likely component to fail. Five things to check on a quote:

• Manufacturer: SolarEdge, GivEnergy, Solis, Sungrow are common. Avoid no-name brands.
• Warranty: 10-12 years is the modern baseline. 5 years is a signal of compromise.
• Hybrid vs string: hybrid = battery-ready. Worth it.
• Optimisers vs microinverters vs string: if your roof has shading or multiple aspects, ask for optimisers or microinverters so a shaded panel doesn't drag the whole string down.
• Monitoring: all modern inverters come with an app. Check that the app is reasonable — SolarEdge has the best, others are mixed.

The shortlist test — three rules to read a quote

1. The quote names the actual brand and model for panel, inverter, and battery — not “Tier 1” or “premium quality”.
2. Panel warranty is ≥25 years performance and ≥12 years product. Inverter warranty is ≥10 years. Battery warranty is ≥10 years with a stated degradation guarantee.
3. Annual yield estimate is given with the methodology disclosed (e.g. “MCS standard assessment procedure” or “PVGIS”). If the quote says “your home will generate 4,500 kWh per year” without saying how that was calculated, ask.

If any of these three are missing, ask. If the installer can't answer, walk.

Stage 6 lets you compare specific panel and battery models — apply the rules above as you browse. Continue to Stage 6 →