Solar Panel Decisions UK 2026: Five Things That Count

Your installer is coming round on Saturday to quote for solar panels. They'll measure the roof, take some photos, talk about south-facing aspects and MCS certification (the industry quality standard for installers), and leave you with a number. What they probably won't do is walk you through the five solar panel decisions that determine how well the system actually performs for your household over the next 25 years.

That's not a criticism. It's just not their job to tell you what to ask for. That part's yours.

How many solar panels does a UK home actually need in 2026?

The rule of thumb is 1 kWp per 1,000 kWh of annual electricity use. A typical 3-bed house using around 3,400 kWh a year needs a 3.5–4kWp system — roughly 10 panels. A 5-bed house at 4,200 kWh needs closer to 5kWp, or 14 panels. Each 350W panel generates around 265 kWh per year in average UK conditions, according to The Eco Experts. For a full breakdown by house type and consumption, the UK solar planning guide has the detail.

The decision this post is concerned with is slightly different: what size should you actually choose, given not just what you use today but what you might use in three years?

If an EV is on the horizon, add 2–3 extra panels to the system now. Coming back to retrofit them later means another scaffolding hire, a second installation visit, and significantly more cost than it would have been to include them from the start — for what is, in the end, a modest increase in capacity. If a heat pump is in the plan, the same logic applies: a system sized for current electricity use typically needs an extra 1.5–2kWp once the heat pump arrives and your demand rises accordingly. Adding panels after the fact is possible. It is rarely described as a pleasant experience.

For a full cost breakdown by system size — including what's in the quote and what usually isn't — see the 2026 UK solar panel cost guide. For reference here: a 3.5kWp system typically costs £5,000–£7,000 installed; 4kWp is £5,500–£8,000; 5kWp runs £7,500–£10,000 and up. England average is £1,565 per kW installed, based on MCS database figures.

Should I add a battery now, or is it fine to wait until later?

Add it now. This is the decision with the biggest long-term financial impact, and the case for doing it alongside the panels is stronger than most solar content lets on.

Here's the starting point: without a battery, your solar panels typically cover 35–50% of your household's electricity needs — the rest is generated during the day and exported to the grid. Self-consumption rate is the term for this: simply what percentage of your own solar electricity you actually use, rather than selling back. Add a 5–6kWh battery, and that figure rises to 70–85%, according to data from Cucumber Eco and Sunsave. The battery stores electricity generated at midday and holds it for the evening, when you're actually home and running things.

That gap matters because every unit you use yourself saves you 24.67p (the Ofgem Q2 2026 rate), while every unit you export earns around 13p on average under the Smart Export Guarantee. The battery captures that 12p difference, every day.

Over 25 years, Sunsave's analysis of 600+ installed systems puts the lifetime saving at £21,842 without a battery and £38,360 with a 5.8kWh battery — even after accounting for one replacement halfway through. That's a £16,500 difference. For how those numbers translate into payback periods across different system sizes, the UK solar payback guide breaks it down in full.

Now, why add it now rather than later?

Retrofitting a battery to an existing solar system is a bit like adding underfloor heating after you've already laid the tiles. Technically possible. More expensive than doing it right the first time. A battery installed alongside the panels can be wired directly into the system through a hybrid inverter — a single unit that manages both panels and battery in one box — so electricity flows from panels to battery without being converted back and forth. Retrofit batteries can't do this; they require an extra conversion cycle and a dedicated battery inverter you're paying for on top of the rest of the installation. It's not ruinous, but it's not the efficient path.

There's also a VAT point: solar and battery installed together qualify for 0% VAT as a combined system until 31 March 2027. On a £4,500 battery, that's roughly £225 saved.

On battery size: for a typical 3,400 kWh household, a 5–6kWh battery is the right fit. For higher consumption or an EV to charge, go for 9–10kWh. And if you want one quick sense-check when your installer names a battery: ask whether it uses lithium iron phosphate (LFP) chemistry. That's what reputable brands are using in 2026 — it runs cooler than older lithium chemistries and degrades more slowly over the battery's lifespan.

Does it matter which way my roof faces — and what if it doesn't face south?

South-facing is the ideal, but east-west panels often deliver comparable financial savings for homes that are occupied morning and evening — and that's most UK households.

South-facing is optimal for total annual electricity output. East or west alone produces around 20–25% less per year, according to Solar By Postcode. That's the standard answer. Here's where it gets more interesting.

A roof with panels on both the east and west slopes generates 10–20% less total electricity than a pure south installation — but it produces a completely different shape of generation across the day. South-facing panels hit peak output between 10am and 2pm, which is typically when nobody is home. East-west panels spread generation across morning (east, covering breakfast and showers) and late afternoon and evening (west, covering cooking, TV, and charging). Solar generating at full tilt while you're sitting in a meeting is considerably less useful than solar trickling through while you're actually running the dishwasher and charging your phone.

The financial result is that an east-west installation often reduces midday export — which earns around 13p per unit — and increases evening self-consumption, which saves 24.67p per unit. Lower total generation, higher proportion used on-site, similar or better financial outcome. Solar By Postcode puts it plainly: east-west "reduces export and raises self-use" in a way that can match or beat south-facing savings for a typical occupied-in-the-morning-and-evening household.

If your roof faces south and has no shading problems: go south. But if you have a gable roof with an east-west ridge — which covers most terraced houses and many semis in the UK — east-west isn't a compromise. It's often the sensible call.

One more thing on orientation: shading matters more than orientation. A clear west-facing roof will frequently outperform a south-facing one where a tree or chimney casts shadows across three panels from 2pm. Walk your property at different times of day before you talk to any installer. More on assessing your roof's suitability in the complete UK solar planning guide.

Do I need a special energy tariff to make solar worth it?

You don't need one for solar to be worthwhile. But pairing a battery with the right tariff noticeably improves the numbers.

Without a time-of-use tariff, a battery raises your solar self-consumption rate — the share of your own solar electricity you actually use rather than exporting — from around 35–50% to 70–85%, according to Cucumber Eco and Sunsave. Every unit you use yourself saves 24.67p (the Ofgem Q2 2026 rate) vs the 13p average you'd earn from export. That gap alone makes the battery worthwhile.

Cucumber Eco puts battery payback without a time-of-use tariff at 11–14 years. Add the right tariff and that shortens to 8–10 years — plus a further £150–£300 a year on top of self-consumption savings.

The mechanism is simple enough: charge the battery overnight at around 7p/kWh, then draw on that stored electricity during peak hours when the grid charges 24.67p. On a 10kWh overnight charge, that's roughly £1.77 saved through load-shifting alone — before the panels have generated a single unit.

One note on framing: the battery payback period (11–14 years, or 8–10 with a tariff) and the 25-year lifetime saving mentioned earlier aren't in conflict — they're different measures. Payback is when you've broken even on the battery's purchase cost; lifetime savings is how far ahead you are by year 25. A good tariff speeds up the payback period more than it changes the eventual lifetime total. For the full breakdown of payback by system size, see the UK solar payback guide.

One important 2026 update: Octopus Flux and Intelligent Octopus Flux — which offered solar owners export rates of up to 32p/kWh at peak hours — were paused for new signups in March 2026 (Octopus Energy, 2026). A lot of solar content still recommends Flux as the obvious battery pairing. That advice predates the pause. For new solar owners in 2026, Octopus Agile is the available alternative: a tariff where the import price changes every 30 minutes based on what electricity actually costs the grid at that moment. On a windy night when supply outstrips demand, Agile customers have imported at under 2p/kWh — meaning a 10kWh battery charge can cost under 20p.

For export income, the best available SEG rates in April 2026 include Good Energy at 25p for the first 12 months, OVO at 20p, and EDF at 18p. The average across all suppliers sits around 13p/kWh. A full breakdown of available VAT relief and grant programmes is in our solar grants and schemes guide.

Someone's offering me a solar lease — should I take it?

No.

Solar leasing still exists in the UK, but the economics shifted dramatically when the Feed-in Tariff closed to new applicants in 2019. Here's the structure: an installer owns the panels, installs them on your roof at no upfront cost, and keeps all the benefits — including your Smart Export Guarantee income.

For a 4kWp system, SEG income typically runs £120–£200 per year. Over 25 years, that's £3,000–£5,000 going to the leasing company rather than you. And that's before accounting for the self-consumption gains you'd get from owning and controlling your own system.

On the property side: when you sell, the buyer inherits the lease. They need to agree to it, their solicitor needs to review it, and some buyers walk away entirely when they see a 20-year contract attached to the roof. Some mortgage lenders aren't enthusiastic either.

Solar Advice UK is blunt on this: "For most homeowners, leasing panels makes less sense now than it did a decade ago." A 3.5kWp system costs around £6,100 to buy outright and pays for itself in 7–10 years — after which every penny of savings is yours. If upfront cost is the issue, personal finance or a credit union loan is a better path than signing something that outlasts most car loans and several marriages.

What's the right order to make these decisions — and how long does all this take?

These five decisions work in sequence: sizing, battery, orientation, tariff, and the lease question. The battery decision depends on system size. Getting the tariff right depends on knowing you have a battery to pair with it. And none of it is worth mapping out until you've confirmed what your roof can actually do.

In order:
1. Confirm the roof works — orientation, shading, area, condition
2. Size for future loads (EV, heat pump), not just current consumption
3. Add the battery at the same time — one scaffold, one installation, 0% VAT on the combined system
4. Set up a time-of-use tariff and the best available SEG rate before commissioning
5. Buy outright or finance — don't lease

If you want to see what all five decisions add up to for your specific roof and consumption before sitting down with an installer, PV-Freund's free solar calculator runs the numbers on system size, battery payback, and 25-year savings in one go — no sign-up required.

On timing: the 0% VAT deal on combined solar and battery ends 31 March 2027. For larger systems (over 3.68kW), your network operator needs to formally approve the grid connection first — that approval alone takes 4–11 weeks. Most installer queues currently run 3–6 months from initial contact to installation day. If you want to be generating before that VAT deadline, the window to start the process is now, not January.

After installation, the paperwork — DNO registration, MCS certificate, SEG application, insurer notification — is a separate process covered step by step in the solar panel registration guide.