Plug-in solar is now legal in Great Britain SEE THE TOOLS

Free solar and energy calculators, made crystal clear.

Size solar panels, plan a battery, check payback and see what your appliances cost to run. Built for UK and European homes, with every formula shown.

Plug-In Solar Solar Panel Solar Battery Size Watts to Amps Electricity Cost Solar Panel Angle

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UK & EUdefault prices and voltages

Everyformula shown

Calculator hubs

Pick a question. Get a clear number.

Nine hubs built around how people in the UK and Europe actually plan solar, storage and energy use.

New in GB

Plug-in & Balcony Solar

Plug-in solar kits sit on a balcony, wall or garden stand and feed power straight into a normal socket.

7 tools

Solar Panel Sizing & Output

Start here if you are planning a rooftop system.

5 tools

Solar Savings & Payback

Find out what solar is worth to you in money.

7 tools

Battery & Storage

Size, charge and run batteries with confidence.

11 tools

Electrical Calculators

Quick, accurate electrical conversions with European voltages as the default.

8 tools

Energy & Running Costs

See what your appliances really cost to run, then find out how many solar panels it would take to power them.

3 tools

Off-Grid & Van Solar

Plan solar for places the grid does not reach: cabins, campervans, boats and garden offices.

5 tools

Solar System Design

Technical tools for checking a solar design: inverter size, string length, charge controller rating, cable cross section and voltage drop.

2 tools

Solar Angle & Orientation

Find out how much your roof's tilt and direction matter.

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What size home battery do you need?

Evening and night use: 6 kWh a day Days of cover: 1 Battery type Adds an example 10% allowance for conversion losses. Planning estimate only.

Suggested nominal battery size

7.3 kWh

Open the full battery calculator

Every tool

Every calculator

Each one works instantly, explains its formula and cites its sources.

Plug-in & Balcony Solar

Plug-In Solar CalculatorYearly kWh, bill savings and payback for an 800 W plug-in solar kit, with UK rules built in.Balcony Solar CalculatorMonthly and yearly kWh for balcony solar on a railing, stand or wall, with the loss against an ideal roof.

Balcony Solar Battery Calculator

Solar Panel Sizing & Output

Solar Panel CalculatorHow many panels and what kWp you need from your yearly kWh use, with a roof space check.Solar Panel Output CalculatorDaily, monthly and yearly kWh from your kWp, region or peak sun hours, with a monthly chart.Solar System Size Calculator From Your Electricity BillTurn your electricity bill into yearly kWh and the solar kWp and panels needed to match it.kWh per kWp CalculatorTurn a generation meter reading into kWh per kWp and compare it with measured UK benchmarks.Solar Panel Efficiency CalculatorWork out panel efficiency, watts per m2 and roof area per kWp from watts and dimensions.Solar Panel Temperature Loss CalculatorEstimate cell temperature and the watts your panels lose to heat from datasheet values.Solar Panel Roof Area CalculatorSee how many panels fit on a roof face, the best layout and the kWp you can install.

Solar Savings & Payback

Solar Panel Savings CalculatorEstimate yearly bill savings and export earnings from your solar generation and tariff.Solar Payback CalculatorFind the year your solar panels break even, with price rises, degradation and inverter costs.Smart Export Guarantee CalculatorEstimate your yearly Smart Export Guarantee payments from exported solar kWh and your SEG rate.Solar ROI CalculatorWork out 25-year solar ROI, IRR, NPV and payback from cost, self-use and tariffs.Solar Self-Consumption CalculatorEstimate the share of your solar you use and how much of your demand it covers, with or without a battery.

Battery & Storage

Solar Battery Size CalculatorSize a home solar battery from evening use, depth of discharge, efficiency and your daily surplus.Battery Runtime CalculatorHow many hours a battery runs a load, with depth of discharge, inverter losses and Peukert.Battery Charging Time CalculatorHours to charge a battery with losses, a slower final stage and the electricity cost.Battery Bank Size CalculatorAmp-hours, battery count and series parallel layout for an off-grid or backup battery bank.Home Battery Savings CalculatorYearly savings and payback for a home battery from solar storage and off-peak charging.Ah to kWh CalculatorConvert amp-hours to kilowatt-hours and back at any voltage, including series and parallel banks.Solar Panel Charging Time CalculatorHours and days for solar panels to charge a 12 V, 24 V or 48 V battery, MPPT or PWM.

Electrical Calculators

Watts to Amps CalculatorConvert watts to amps for 230 V, 400 V three-phase, 120 V or DC, with power factor.Amps to Watts CalculatorConvert amps to watts for 230 V, 400 V, 120 V or DC, then see daily kWh and running cost.kW to Amps CalculatorConvert kW to amps on 230 V, 400 V three-phase, 120 V, 240 V or DC with power factor.kVA to kW CalculatorConvert kVA to kW with power factor, plus kVAr, phase angle and full-load current.kW to kVA CalculatorConvert kW to kVA with power factor, see kVAr and current, and check generator size.kVA to Amps CalculatorConvert kVA to amps for 230 V single-phase or 400 V three-phase AC, line or phase voltage.Watts to kWh CalculatorTurn watts and hours into kWh per day, month and year, with running cost at your unit rate.mAh to Wh CalculatorConvert mAh to Wh and back, and check a power bank against the 100 Wh and 160 Wh flight limits.Three Phase Power CalculatorFind three-phase kW, kVA, kVAr and line current, with star or delta and 400 V or 230 V input.Power Factor CalculatorFind power factor, phase angle and kVAr, then size the correction capacitor at 50 Hz.Ohm's Law CalculatorEnter any two of voltage, current, resistance or power and get the other two with working.

Energy & Running Costs

Electricity Cost CalculatorRunning cost of any appliance per hour, day, month and year at the UK cap or your own rate.Electric Heater Running Cost CalculatorCost per hour, day and season for fan, oil-filled, convector and infrared heaters.Dehumidifier Running Cost CalculatorCost per hour, day and year for compressor or desiccant units, with a tumble dryer comparison.Tumble Dryer Running Cost CalculatorCost per load and per year for heat pump, condenser and vented dryers, using your energy label figure.Heat Pump Running Cost CalculatorCompare yearly heat pump and gas boiler running costs from your gas use, SCOP and tariff.Solar EV Charging CalculatorTurn daily km or miles into kWh, kWp and the number of panels needed to charge an EV.How Many Solar Panels to Run an Appliance CalculatorPick an appliance, edit watts and hours, and get the panel watts, panel count and battery size needed.Energy Consumption CalculatorAdd your appliances to see daily, monthly and yearly kWh, cost and the biggest energy users.

Off-Grid & Van Solar

Off Grid Solar CalculatorSize panels, battery, inverter and controller for a stand-alone solar system from daily use.Campervan Solar CalculatorSize van roof solar, leisure battery and controller from 12 V loads, season and driving.Power Station Runtime CalculatorEstimate how many hours a portable power station runs any device on AC or DC output.

Solar System Design

Solar Inverter Size CalculatorMatch inverter kW to your solar array, or size an off-grid inverter for load and surge.Solar Cable Size CalculatorFind the minimum DC cable size in mm2 and AWG for a voltage drop limit on solar circuits.Voltage Drop CalculatorVolts and % drop for mm2 or AWG cables, 230 V, 400 V or DC, checked against BS 7671 limits.Solar String Size CalculatorMinimum and maximum panels per string from cold Voc, hot Vmp, inverter DC limit and MPPT window.MPPT Charge Controller CalculatorCharge controller amps for 12, 24 or 48 V with cold Voc and start-up voltage checks.

Solar Angle & Orientation

Solar Panel Angle CalculatorBest fixed, summer and winter tilt for UK and EU cities, plus the yield your roof pitch gets.Solar Panel Orientation CalculatorShare of best yield for any roof direction and tilt, including east-west splits and kWh.

EV Charging

Home Heating

Guides

Latest guides

Plain-English answers, checked against official sources.

Best Angle for Solar Panels in the UK

The optimum fixed tilt across the UK, how much flat and steep roofs lose, and seasonal adjustment.
Best Direction for Solar Panels in the UK

How much output south, east, west and north-facing roofs give in the UK, and when east-west makes sense.
What Does a Solar Inverter Do? Types and Sizing Explained

How an inverter converts DC to AC, the main types, how they are sized and how long they last.
How Do Solar Panels Work? From Sunlight to Your Sockets

How solar cells turn light into electricity, what the inverter does and where the power goes in your home.
How Much Do Solar Panels Cost in the UK in 2026?

Typical 2026 prices by system size, battery costs, what affects quotes and how 0% VAT helps.
How Many Solar Panels Do I Need for My House?

Panel counts for UK homes by usage and house size, and how much roof space they take.

Why trust the numbers

How we build every calculator

Primary sources

Prices, rules and standards come from Ofgem, gov.uk, the Energy Saving Trust and manufacturer data, checked on the day of writing.

Correct formulas

Every tool shows its working, so you can follow each step from your inputs to the answer.

Tested edge cases

Zero, empty and unrealistic inputs give a clear message instead of a wrong number.

Kept up to date

Defaults are reviewed when price caps, tariffs or standards change. See our editorial policy.

FAQ

Quick answers

Are Solaxyra calculators free?

Yes. Every calculator is free to use, needs no sign-up and runs in your browser, so the numbers you enter are not sent to our server. We do not sell installer leads.

Where do the default prices and figures come from?

UK electricity defaults use the Ofgem price cap for 1 October to 31 December 2026. Solar yields, standards and safety rules come from primary sources such as government pages, Ofgem, the Energy Saving Trust and manufacturer datasheets, cited on each page.

Are the results accurate enough to buy equipment?

They are planning estimates. Use them to compare options and ask better questions, then get a site survey and quote from a certified installer. Electrical work must be done or checked by a qualified electrician.

Can I use plug-in solar in the UK?

Yes. Since 27 August 2026 certified plug-in solar kits with up to 800 W inverter output can be used in Great Britain. Our plug-in solar calculator estimates the yearly output and savings for your kit.