--- title: "Solar Calculators UK | Savings, Payback & Battery ROI" description: "Free UK solar calculators. Estimate system size, annual savings, payback years, battery ROI and EV charging cost — all tuned for South East England." lang: en json-ld: | [ { "@context": "https://schema.org", "@type": "Organization", "name": "South East Solar Network", "url": "https://southeastsolarnetwork.co.uk", "areaServed": "South East England", "telephone": "+443335671183", "logo": "https://southeastsolarnetwork.co.uk/favicon.ico", "image": "https://storage.googleapis.com/gpt-engineer-file-uploads/attachments/og-images/1696c2df-452b-4380-b418-fd3f1c9a128a" }, { "@context": "https://schema.org", "@type": "BreadcrumbList", "itemListElement": [ { "@type": "ListItem", "position": 1, "name": "Home", "item": "https://southeastsolarnetwork.co.uk/" }, { "@type": "ListItem", "position": 2, "name": "Calculators", "item": "https://southeastsolarnetwork.co.uk/calculators" } ] }, { "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "How accurate are these solar calculators?", "acceptedAnswer": { "@type": "Answer", "text": "They use conservative South East assumptions — 950 kWh per kWp per year (PVGIS baseline for southern-England south-facing 35° pitch), a 30p/kWh import price and a 15p/kWh SEG export rate. Real-world results vary ±15% based on roof orientation, pitch, shading and your specific import/export tariff. A vetted installer will confirm figures after a roof survey." } }, { "@type": "Question", "name": "What size solar system do I need?", "acceptedAnswer": { "@type": "Answer", "text": "Size to cover 80-110% of yearly consumption. A 3-bed South East home using ~3,600 kWh fits a 4 kWp array on a south-facing roof; a 4-bed with an EV or heat pump typically needs 6-8 kWp. Oversizing beyond 110% pushes more generation into low-value SEG export and rarely pays back the extra hardware." } }, { "@type": "Question", "name": "Do the calculators include a battery?", "acceptedAnswer": { "@type": "Answer", "text": "Yes — the battery ROI calculator estimates the extra self-consumption savings from storing daytime surplus for evening use. On a typical 4-6 kWp South East system, a 10 kWh battery lifts self-consumption from 35% to 75-85% and adds £400-£700 a year in savings on top of the panels alone." } }, { "@type": "Question", "name": "Why is my payback longer than the adverts suggest?", "acceptedAnswer": { "@type": "Answer", "text": "Marketing figures typically assume 100% self-consumption, best-case regional yields (often northern-Europe averages, not conservative UK), and pre-inflation prices. Our defaults use 35% self-consumption without a battery, 950 kWh/kWp/year, and today's real import and export prices. It's less flattering but far closer to what most South East homeowners actually experience." } }, { "@type": "Question", "name": "What import and export prices do you assume?", "acceptedAnswer": { "@type": "Answer", "text": "30p/kWh import (roughly the Ofgem price-cap unit rate at the time these calculators were tuned) and 15p/kWh export (mid-range across popular SEG tariffs like Octopus Outgoing Fixed and E.ON Next Export Exclusive). If you're on a time-of-use tariff like Octopus Flux, your real-world savings will typically be 20-30% higher than these estimates." } }, { "@type": "Question", "name": "Do the numbers factor in system degradation?", "acceptedAnswer": { "@type": "Answer", "text": "The single-year figures do not. Modern Tier-1 panels degrade at roughly 0.4-0.5% per year, so 25-year lifetime generation is around 92% of year-one output. That means a 10-year payback estimate becomes roughly a 10.5-year payback once degradation is modelled — a small effect that we deliberately keep out of the headline number to avoid false precision." } }, { "@type": "Question", "name": "Are the estimates accurate for the whole UK or just the South East?", "acceptedAnswer": { "@type": "Answer", "text": "They're tuned for the South East (roughly a line from Portsmouth to Colchester and everything below). Scotland and the far north of England typically yield 5-15% less per kWp; the East Midlands and East Anglia yield 2-5% less; the Isle of Wight and inland Sussex yield 3-6% more. Adjust the annual generation figure accordingly if you're modelling outside our footprint." } }, { "@type": "Question", "name": "Do I need to enter my exact bill?", "acceptedAnswer": { "@type": "Answer", "text": "No — an approximate annual kWh figure is more useful than a precise bill amount because unit rates change. If you don't know your yearly usage, most bills show it in a summary panel, or you can request the last 12 months of half-hourly data free from your supplier." } } ] } ] --- MCS-accredited · Vetted local installers · Free no-obligation quotes [0333 567 1183](tel:+443335671183) [South East Solar Network ](/) [Services](/services)[Areas](/areas)[Guides](/guides)[Calculators](/calculators)[About](/about)[Contact](/contact) / [0333 567 1183](tel:+443335671183)[Free Quote](/contact) 1. [Home](/)/ 2. Calculators # Solar calculators Independent, conservative estimates for UK homeowners. Model your system size, savings, payback and battery ROI in under a minute. Calculator 1 ## Solar savings & payback Enter your bill and system size — we'll estimate annual savings, export income and payback in years. System size kWp Install cost £ Electricity import price p/kWh SEG export price p/kWh Annual generation 3,800 kWh Yearly bill saving £399 Yearly export income £371 Payback 9.7 yrs Total annual benefit: £770 · Assumes 35% self-consumption without a battery and 950 kWh/kWp South East yield. #### See your personalised recommendations Share a few details and we'll show tailored next steps — or skip to see the generic recommendations. NamePhonePostcode Show my recommendationsSkip and show generic recommendations We'll only pass your details to **1 vetted solar firm** who's the best match — never multiple companies. Calculator 2 ## What size solar system do I need? Size the array to your yearly electricity use and roof space. Yearly electricity use kWh Usable roof area m² Coverage target % Ideal system size 3.8 kWp Roof allows 6.5 kWp Recommended 3.8 kWp Panels (440W) 9 Expected generation: 3,600 kWh/year · Sized to the smaller of roof capacity or your usage target. #### See your personalised recommendations Share a few details and we'll show tailored next steps — or skip to see the generic recommendations. NamePhonePostcode Show my recommendationsSkip and show generic recommendations We'll only pass your details to **1 vetted solar firm** who's the best match — never multiple companies. Calculator 3 ## Battery storage ROI See the extra savings a battery unlocks by storing daytime surplus for evening use. Solar system size kWp Battery size kWh Battery cost £ Import price p/kWh Extra kWh self-used 1,520 kWh Extra yearly saving £228 Battery payback 19.7 yrs Assumes ~300 useful cycles a year and displaces grid import at the difference between import and SEG export price. #### See your personalised recommendations Share a few details and we'll show tailored next steps — or skip to see the generic recommendations. NamePhonePostcode Show my recommendationsSkip and show generic recommendations We'll only pass your details to **1 vetted solar firm** who's the best match — never multiple companies. Calculator 4 ## EV home charging cost Compare charging on solar vs the grid — annual fuel savings on your commute. Annual mileage mi EV efficiency mi/kWh Share from solar % Import price p/kWh Energy needed 2,286 kWh EV yearly cost £549 Petrol equivalent £1,172 Yearly saving £623 Petrol comparison uses 45 mpg @ £1.45/L. Solar-charged miles are costed at the SEG export price you'd have received instead. #### See your personalised recommendations Share a few details and we'll show tailored next steps — or skip to see the generic recommendations. NamePhonePostcode Show my recommendationsSkip and show generic recommendations We'll only pass your details to **1 vetted solar firm** who's the best match — never multiple companies. Get the real number ## Turn these estimates into a firm quote A vetted MCS-accredited installer in your area will confirm generation and price after a free roof survey. MCS-accredited Vetted installers RECC · TrustMark ## Free, no-obligation quote Share a few details and a trusted MCS-accredited installer in your area will be in touch shortly. Full namePhoneEmail (optional)Postcode Notes (optional) Your privacy matters: We will only pass your details to **1 vetted solar firm** who we feel is the best match for your needs — never multiple companies. Get my free quote By submitting this form you agree to our [Terms of Use](/terms) and [Privacy Policy](/privacy). FAQ ## How the calculators work How accurate are these solar calculators? They use conservative South East assumptions — 950 kWh per kWp per year (PVGIS baseline for southern-England south-facing 35° pitch), a 30p/kWh import price and a 15p/kWh SEG export rate. Real-world results vary ±15% based on roof orientation, pitch, shading and your specific import/export tariff. A vetted installer will confirm figures after a roof survey. What size solar system do I need? Size to cover 80-110% of yearly consumption. A 3-bed South East home using ~3,600 kWh fits a 4 kWp array on a south-facing roof; a 4-bed with an EV or heat pump typically needs 6-8 kWp. Oversizing beyond 110% pushes more generation into low-value SEG export and rarely pays back the extra hardware. Do the calculators include a battery? Yes — the battery ROI calculator estimates the extra self-consumption savings from storing daytime surplus for evening use. On a typical 4-6 kWp South East system, a 10 kWh battery lifts self-consumption from 35% to 75-85% and adds £400-£700 a year in savings on top of the panels alone. Why is my payback longer than the adverts suggest? Marketing figures typically assume 100% self-consumption, best-case regional yields (often northern-Europe averages, not conservative UK), and pre-inflation prices. Our defaults use 35% self-consumption without a battery, 950 kWh/kWp/year, and today's real import and export prices. It's less flattering but far closer to what most South East homeowners actually experience. What import and export prices do you assume? 30p/kWh import (roughly the Ofgem price-cap unit rate at the time these calculators were tuned) and 15p/kWh export (mid-range across popular SEG tariffs like Octopus Outgoing Fixed and E.ON Next Export Exclusive). If you're on a time-of-use tariff like Octopus Flux, your real-world savings will typically be 20-30% higher than these estimates. Do the numbers factor in system degradation? The single-year figures do not. Modern Tier-1 panels degrade at roughly 0.4-0.5% per year, so 25-year lifetime generation is around 92% of year-one output. That means a 10-year payback estimate becomes roughly a 10.5-year payback once degradation is modelled — a small effect that we deliberately keep out of the headline number to avoid false precision. Are the estimates accurate for the whole UK or just the South East? They're tuned for the South East (roughly a line from Portsmouth to Colchester and everything below). Scotland and the far north of England typically yield 5-15% less per kWp; the East Midlands and East Anglia yield 2-5% less; the Isle of Wight and inland Sussex yield 3-6% more. Adjust the annual generation figure accordingly if you're modelling outside our footprint. Do I need to enter my exact bill? No — an approximate annual kWh figure is more useful than a precise bill amount because unit rates change. If you don't know your yearly usage, most bills show it in a summary panel, or you can request the last 12 months of half-hourly data free from your supplier. Explore the topic ## Turn your numbers into a decision Descriptive links across our calculators, guides, services and local installer areas — pick the next step that fits where you are. Get it fitted Solar services in the South East - [Solar Panel Installation MCS-certified solar PV installs across the South East. ](/services/solar-panel-installation) - [Solar Battery Storage Tesla, GivEnergy, Fox ESS and more — fully fitted, fully certified. ](/services/solar-battery-storage) - [Solar Panel Maintenance Annual health checks that protect your investment. ](/services/solar-panel-maintenance) - [Solar Panel Repairs Fast diagnosis and repair, any brand. ](/services/solar-panel-repairs) Learn Guides that pair with the calculators - [Are Solar Panels Worth It in the UK in 2026? An honest, numbers-led look at solar economics, payback periods and RO ](/guides/are-solar-panels-worth-it-uk) - [Solar Panel Costs UK 2026: Real Prices, No Sales Spin What you should actually expect to pay for a residential solar system ](/guides/solar-panel-costs-uk) - [Solar Battery Costs UK 2026: Brands, Capacities, Payback What batteries cost in 2026, which brands lead, and how to size storag ](/guides/solar-battery-costs-uk) - [Solar Payback Period UK: 7-10 Years on Most Homes How to model solar payback honestly — and what drives it up or down. ](/guides/solar-payback-period-uk) Find installers Where we cover - [Solar installers in Kent Maidstone · Canterbury · Ashford ](/solar-installers-kent) - [Solar installers in Surrey Guildford · Woking · Cobham ](/solar-installers-surrey) - [Solar installers in Hampshire Southampton · Portsmouth · Winchester ](/solar-installers-hampshire) - [Solar installers in West Sussex Worthing · Crawley · Horsham ](/solar-installers-west-sussex) Next step Turn a number into a quote - [Request a free, no-obligation solar quote MCS-accredited local installers ](/contact) - [Browse every service we cover Solar, batteries, EV chargers, maintenance ](/services) - [See every town we cover Kent, Surrey, Sussex, Hampshire and more ](/areas) - [Read the flagship solar buying guide Payback, ROI and what to watch for ](/guides/are-solar-panels-worth-it-uk) South East Solar Network MCS-accredited residential solar installers across the South East of England. 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