Battery Storage Installers in Cornwall

Cornwall is the south-west tip of mainland Britain and receives more sun than anywhere else in the country. The Met Office records show Cornwall's average annual solar irradiance is 1,298 kWh/m²/year, compared with a UK mean of 1,089 kWh/m²/year — about 19% higher. That extra sunshine is the reason a 4kWp Cornish solar array typically produces 3,800–4,200 kWh per year, versus 3,200–3,500 kWh from the same array in Manchester or Newcastle.

The catch is the duck curve: your solar generates most of its output between 10am and 3pm, but your demand peaks at 7am and 6–10pm. Without a battery, you export huge volumes of generation at the Smart Export Guarantee rate (typically 5–25p/kWh depending on tariff) and then re-import in the morning and evening at the Q1 2026 Ofgem cap of 24.67p/kWh. A battery flips that economic equation: store at midday, discharge at peak.

The second Cornwall factor is the unusually high penetration of off-gas-grid properties. 47% of Cornish homes are not connected to mains gas (against a UK average of ~15%), so households rely on oil, LPG or direct electric heating — which is exactly where battery + heat pump + time-of-use tariff combinations deliver the largest savings. If you'd like to step back and read the broader solar context, see our Solar Panels Cornwall guide first.

A modern lithium iron phosphate (LFP) home battery stores DC electricity generated by your solar panels (or imported overnight at a cheap-rate tariff) and discharges it back to your home through a hybrid inverter when you need it. Three components matter:

• Usable capacity (kWh) — how much energy the battery stores. A typical 4-bed Cornish family home uses 8–14 kWh per day, so a 10–13.5 kWh battery covers most evenings.
• Continuous power output (kW) — how much demand the battery can support at once. Important if you run an induction hob, EV charger and immersion at the same time. The Tesla Powerwall 3 delivers 11.5 kW continuous; the FoxStar EP5 delivers 5 kW per module stacked to 25 kW.
• Round-trip efficiency — how much energy you lose to heat in charging and discharging. Modern LFP systems hit 90–96% round-trip; older lead-acid systems were 75–80%.

All systems we install are AC-coupled or DC-coupled with a single hybrid inverter — there's no "solar inverter plus battery inverter" double-conversion loss. For a deeper component-level explainer see our battery storage guide and the glossary for terms like SoC, DoD and LFP.

The single biggest mistake we see in the Cornish market is oversized batteries sold as "future proofing" by national companies. A battery that's twice the size you need still costs twice as much, doesn't cycle as often, and never pays back. The right size is the one that empties most evenings and refills most days.

Here's the rule of thumb we use during free Cornwall surveys, validated against 200+ CCS installations from St Ives to Saltash:

• 1–2 bed cottage, no EV, gas heating — 5 kWh battery (FoxStar EP5 single module). Covers evening base load.
• 3 bed semi, 1 EV charged at home weekly, mixed heating — 10–13.5 kWh battery (Tesla Powerwall 3 or FoxESS ECS 10.5). Sweet spot for Cornish payback.
• 4–5 bed detached, heat pump, EV daily — 14–27 kWh battery (FoxESS modular or Sigenergy stack). Pairs with 6–8kW solar for near year-round self-sufficiency.
• Off-grid or grid-tied with frequent outages — Tesla Powerwall 3 with Backup Gateway 2 (whole-home backup, 11.5 kW continuous).

We always model your last 12 months of consumption from your DCC-connected smart meter (we can pull this with your authority) before quoting capacity. No guessing.

We're authorised installers for every battery we mention here — there's no commercial reason for us to push one over another. Here's the honest summary based on Cornwall installations we've completed this year:

Tesla Powerwall 3 — 13.5 kWh usable, 11.5 kW continuous, integrated 11.04 kW solar inverter with three MPPTs. Best for new-build installations where the Powerwall replaces a separate solar inverter, and for households wanting whole-home backup. App is the best in the industry. From £9,500 fitted in a single-battery install with up to 4 PV strings.

FoxStar EP5 / FoxESS ECS — modular 5.18 kWh blocks stacked to 25 kWh+. AC-coupled, so retrofits onto any existing solar system with any inverter brand. Lowest entry price (£4,500 fitted for a single-module retrofit). Excellent UK warranty support out of Coventry. Our most installed brand in Cornwall.

Sigenergy SigenStor — all-in-one hybrid inverter with stackable battery (8, 16, 24, 32 kWh), three-phase ready, EV-charger integrated. The premium pick for large detached homes or smallholdings. From £11,800 fitted for 16 kWh + 12 kW inverter.

SolarEdge Home Battery — paired with SolarEdge HD-Wave inverters and optimisers. Best for shaded or complex roofs (common on Cornish granite or thatched cottages) where optimiser-level MPPT genuinely improves yield.

All prices below are fully installed, including hybrid inverter (where required), wall mount or floor stand, G99 DNO notification, MCS commissioning, building control sign-off and 10-year manufacturer warranty registration. All figures include 0% VAT (running to 31 March 2027).

If you're adding a battery to an existing solar system the cost is typically £500–£1,200 lower than the figures shown because there's no scaffolding or roof work involved. See our solar panel costs page for combined solar+battery package pricing.

The reason batteries pay back is tariff arbitrage — buying cheap and consuming or exporting at peak. As of May 2026, the best three options for Cornwall homeowners are:

• Octopus Cosy (4-rate) — 12p/kWh in cheap windows (4–7am, 1–4pm, 10pm–12am), 38p peak (4–7pm), 22p shoulder. Battery fully charges overnight at 12p and discharges through the 38p peak. Typical Cornwall battery owner saves £900–£1,400/yr versus standard variable.
• Tesla Energy Plan (Powerwall owners only) — flat 15p import, 15p export. Simple, predictable, no peak penalty. Best for households with predictable usage.
• Octopus Intelligent Flux — pays you up to 32p/kWh export from your battery during winter peak windows. Best for households with >10 kWh battery and >6 kWp solar.

The current Ofgem Q1 2026 price cap is 24.67p/kWh electricity and 5.74p/kWh gas — so any time-of-use tariff with a 12p off-peak rate beats the cap on imported energy alone. The Smart Export Guarantee best rates run up to 25p/kWh (Good Energy, Octopus). Our installs include SEG registration and tariff onboarding support — see our SEG arbitrage calculator to model your own scenario.

About 60% of the battery jobs we complete in Cornwall are retrofits — adding storage to a solar PV system that's been on the roof for 5–12 years. The good news is that almost any existing system can take a battery, whether the original inverter was a Solis, SolarEdge, SMA, Fronius, Growatt or anything else. We add an AC-coupled battery (typically FoxStar EP5 or Tesla Powerwall 3) downstream of your existing inverter, with its own grid-tie inverter built in. No need to replace the solar inverter you already have.

The retrofit process is:

1. Free home survey (we measure your consumer unit, check spare ways, photograph your existing solar inverter and meter setup).
2. DNO G99 application (we handle — typically 11 working days for Western Power Distribution).
3. Quote and 0% VAT invoice.
4. 1-day installation (battery wall-mounted or floor-stood, CT clamp on tails, commissioning, app setup).
5. MCS certificate, building control notification and SEG handover.

If your existing solar system was MCS-installed (most pre-2019 systems were) we transfer your installation onto our books to keep your FiT export payments running smoothly.

Every CCS battery storage install in Cornwall follows the same proven sequence:

1. Free survey (typically same week) — our engineer (not a salesperson) visits your home to inspect the proposed battery location, your consumer unit, your incoming supply, and your existing solar (if any). 30–45 minutes on-site. We bring the kit so you can see exactly what's being installed.
2. Tailored quote within 48 hours — we send a fixed-price quote with a clear bill of materials, a cable run diagram, a payback model based on your actual smart meter data, and a copy of our public liability and professional indemnity certificates.
3. DNO G99 notification — Western Power Distribution requires 11 working days' notice for any battery installation. We file electronically, you don't need to do anything.
4. Installation day — one or two engineers, typically 6–9 hours on site for an AC-coupled retrofit, longer for new-build solar+battery. No scaffolding for retrofit. Power is off for around 30 minutes during consumer unit work.
5. Commissioning, app setup and handover — we configure the battery operating mode for your tariff (Cosy, Flux, Tesla Energy Plan), pair the app to your phone, and register the MCS certificate. SEG export tariff registration follows within 7 days.

For wider services and to see other parts of our Cornwall coverage, browse the services overview and areas we cover.

There is no direct grant for battery storage in Cornwall (the old Energy Saving Trust Solar Battery Grant closed in 2017), but the financial environment is still strong:

• 0% VAT until 31 March 2027 — all home battery installations, whether retrofit or new-build, are zero-rated. Saves you ~20%.
• Smart Export Guarantee — battery owners can export surplus at up to 25p/kWh (Good Energy) or use Octopus Flux to time-shift exports for higher peak rates.
• ECO4 + battery — if you qualify for ECO4 on income or benefit grounds, batteries can be added to ECO4-funded solar at much reduced cost.
• Warm Homes: Local Grant — administered by Cornwall Council; covers solar + battery for EPC D–G homes with household income under £36k.
• CCS Finance — 0% APR over 24 months or low APR over 60–120 months via Phoenix Financial Consultants. Spreads a Powerwall 3 install at £158/month over 60 months.

See our full grants page and the finance options for full eligibility and current offers.