60 energy calculators that show their work

Solar panel output & payback

Simulates every hour of a full year at your exact location using NASA satellite weather, then turns the energy into savings, payback time and CO₂ avoided.

live data Solar

How many solar panels?

Turns your yearly kWh (or monthly bill) into the number of panels, system size and roof area you need, using NASA satellite sunshine for your exact location, your panel model and roof orientation.

Best solar panel angle

Finds the optimum tilt and orientation by simulating every hour of a real NASA weather year at 30+ panel angles. Includes seasonal angles, roof-pitch losses and an east/west comparison.

live data Solar

Lays out real modules on a pitched, gable or flat roof, with edge and ridge setbacks, obstructions, portrait, landscape or mixed rows and row spacing on flat roofs. You get the panel count, kWp, kWh per year and roof load.

Net metering vs net billing

See what your solar exports are really worth: month-by-month netting, kWh or money credit rollover, year-end true-up, non-nettable network charges and fixed fees, side by side for every scheme.

Solar inverter sizing

Simulates your array hour by hour with NASA weather to show how much energy each inverter size would clip, then recommends the size, the phase and the economic DC/AC ratio.

live data Solar

PV string sizing

Checks a PV string against the inverter’s maximum DC voltage, MPPT window, start-up voltage and current limits at your record cold and hottest conditions, using the NEC 690.7 and IEC methods.

Solar water heater sizing

Sizes a solar hot-water system with the f-chart method used by engineers, fed with NASA satellite climate for your location: monthly solar fraction, savings versus electric, gas or heat pump, and payback.

Wind

Turbine energy, wind shear, power density, Weibull statistics and wind-farm economics.

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Wind turbine energy & payback

Pick a site and a turbine: we download a full year of hourly NASA wind at 50 m, shear it to your hub height, correct for air density and losses, and turn it into kWh, capacity factor, revenue and payback.

live data Wind

Wind farm economics

A utility-scale project model in one page: turbines, capacity factor or wind speed, capex, opex, PPA price and debt → annual MWh, LCOE, project and equity IRR, DSCR, land area and homes powered.

Wind speed at height

Convert a measured wind speed to any height from 0 to 200 m with both the Hellmann power law and the logarithmic wind profile, and see what the extra height does to available power.

Wind power density

Wind power density is the single best number for comparing wind sites. Enter a mean speed, height and Weibull k to get W/m², the NREL wind power class and how much energy hides in strong winds.

All batteries & storage →

Weibull wind distribution

Describe a wind climate with two numbers. Enter k and c, mean speed and k, or mean and standard deviation to get the probability curve, hours per speed bin, energy pattern factor and operating hours of a turbine.

Batteries & storage

Home batteries, backup time, off-grid banks, pumped hydro and storage economics.

live data Batteries & storage

Solar battery size & payback

Simulates your solar panels, your household’s hourly demand and a home battery for all 8,760 hours of a real year at your location, then finds the battery size that actually pays off.

Battery runtime

Runtime of any battery (power station, home battery, UPS or 12 V bank) from capacity, depth of discharge, inverter losses, temperature and age, with Peukert’s law for lead-acid batteries.

Off-grid solar sizing

Sizes a complete stand-alone solar system from your appliances. It designs for the darkest month at your location using NASA satellite climate data, days of autonomy and real battery chemistry limits.

Battery bank sizing

Works out how many kWh and amp-hours your battery bank needs (with margins for depth of discharge, temperature, ageing and efficiency) and how to wire your chosen batteries in series and parallel.

Pumped hydro storage

Turns reservoir volume, head and machine efficiencies into MWh stored, round-trip efficiency, hours of discharge, drawdown, arbitrage revenue and levelized cost of storage.

Hydro & marine

Micro-hydro power, penstock losses, run-of-river and tidal estimates.

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Hydro & marine

Micro hydro power

Turn head and flow into kilowatts, kWh per month and payback. The model includes real penstock friction, part-load turbine efficiency, seasonal flow and a residual (environmental) flow, and recommends a turbine type.

Hydro & marine

Penstock head loss

Friction loss in a hydro penstock or any water pipe with Darcy–Weisbach and the Colebrook equation: net head, power lost, water-hammer surge and the smallest diameter that keeps losses under your target.

Hydro & marine

Tidal energy

Estimate the yearly output of a tidal lagoon/barrage from basin area and tidal range, or of tidal stream turbines from current speed and rotor size, simulated through every spring–neap cycle of a year.

Home energy

Bills, appliances, heat pumps, insulation, lighting and standby waste.

All home energy →

Electricity bill calculator

Build your household electricity bill from the appliances you actually use (or from your kWh), with flat, tiered or day/night tariffs, standing charge, levies and VAT. See which devices drive the cost.

kWh & cost calculator

Turn any power rating and running time into kilowatt-hours and money per hour, day, month and year. Optional day/night tariff, plus a quick check of what the same use would cost at other prices.

AC running cost & size

Sizes an air conditioner for your room (BTU and kW) from floor area, ceiling height, sun exposure, climate and occupants, then calculates the electricity it uses and what it costs per hour, day, month and cooling season from its SEER or EER.

Appliance energy cost

Enter the wattage and daily use of any device to see its kWh, running cost per hour, day, month and year, plus the CO₂ it emits on your grid.

Water heater running cost

Works out how much it costs to heat your water each year with six technologies (electric tank, heat-pump water heater, gas tank, gas tankless, electric instant and solar thermal), including standby losses, purchase price and lifetime.

LED bulb savings

Compare incandescent, halogen or CFL bulbs with LEDs of the same brightness: energy and money saved per year, replacement bulbs avoided, payback time in months, 10-year savings and CO₂. An optional heating-season correction is included.

Standby power / phantom load

Count the devices in your home that never really switch off (TVs, set-top boxes, consoles, routers, smart speakers, chargers) and see their phantom load in watts, kWh, money and CO₂, plus what smart plugs or power strips could save.

Heating & gas

Gas, oil, wood and heat-pump heating costs, boilers, gas unit conversions.

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Heat pump running cost

Models an air-source heat pump month by month for your climate: heat demand, COP at every outdoor temperature and flow temperature, electricity use, running cost versus your current boiler and CO₂ saved.

Heating cost comparison

Ranks nine heating systems (gas, LPG, oil, electric, air- and ground-source heat pumps, pellets, logs and district heating) by cost per kWh of useful heat, annual bill and CO₂, using your own prices.

Heat pump vs gas boiler

Compares an air-source heat pump with a new condensing gas boiler on running cost, installation, maintenance, standing charges and CO₂, and shows the electricity-to-gas price ratio at which they break even.

Gas bill from meter reading

Turns two gas meter readings (m³, ft³, kWh or therms) into kWh using the calorific value and volume correction exactly as suppliers do, then adds unit price, standing charge and VAT. It also estimates your annual gas use from a single bill.

Insulation savings

Enter the area and U-value of walls, roof, windows and floor before and after insulating. Using heating degree days for your climate, it shows the heat loss avoided, kWh and money saved, CO₂ and payback for each measure.

Ground source heat pump

Sizes a ground-source heat pump from your heat demand: kW output, borehole metres or horizontal collector area for your soil or rock (VDI 4640 extraction rates), seasonal COP, running cost and installed cost versus an air-source unit and gas.

Generator fuel consumption

How much diesel, petrol, LPG or natural gas a generator burns at any load, how long a tank lasts and what each kWh really costs once engine wear is counted, compared with grid power and solar plus battery.

Biomass boiler fuel & cost

From your annual heat demand to tonnes and cubic metres of logs, chips or pellets (corrected for moisture content), plus boiler size, buffer tank, store volume and the running cost against gas, oil and a heat pump.

EV & transport

EV charging cost and time, EV vs petrol, range and fleet emissions.

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EV charging cost

What does it cost to charge an electric car? Enter your battery, efficiency and mix of home, public AC and rapid DC charging to get the cost per charge, per 100 km and per month, including charging losses, compared with a petrol car.

EV charging time

Estimates how long an electric car takes to charge between any two states of charge, using the charger’s power, the car’s own AC and DC limits, a realistic DC taper curve above 50–80% and battery temperature.

EV vs petrol car (TCO)

Compares an electric car with a petrol car over the years you keep it: purchase and subsidies, energy, maintenance, insurance, tax and resale value. It adds lifecycle CO₂ (including battery manufacturing and your grid’s carbon intensity) and the break-even mileage for both money and emissions.

Trip CO₂: car, train, plane

Compare the CO₂ of one trip by petrol, diesel, hybrid or electric car (on your grid), bus, coach, train, plane, ferry, motorbike or e-bike, per passenger and in total.

Carbon & climate

Footprints, grid emissions, offsets and avoided CO₂.

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Carbon & climate

Carbon footprint

Home energy on your own country's grid, heating, car, flights, diet and shopping, in tonnes CO₂e per person. Compares the result with your country, the world and the 1.5 °C target, and ranks the actions that cut most for you.

Carbon & climate

Electricity kWh → CO₂

Converts any amount of electricity into CO₂ using the latest average grid carbon intensity of 210+ countries, and shows how the same kWh would score on cleaner and dirtier grids.

Carbon & climate

Trees to offset CO₂

Calculates the trees and hectares needed to absorb a given amount of CO₂ within your chosen time frame, using realistic growth curves for 11 forest types from boreal spruce to tropical eucalyptus.

Energy finance

LCOE, NPV/IRR, loans, PPAs and project feasibility.

All energy finance →

LCOE calculator

Capex, fixed and variable O&M, fuel and heat rate, capacity factor, lifetime, WACC, construction time, degradation and carbon price → the levelized cost per MWh, broken down by component and compared across 11 technologies.

Project NPV, IRR & DSCR

A compact project-finance model for any power plant: revenues, opex, loan, tax and depreciation year by year, giving project and equity IRR, NPV, payback and debt-service cover ratios.

Solar loan vs cash

Finance your solar panels or pay cash? This compares the loan payment with your electricity bill savings month by month, then the net benefit of a loan, a cash purchase and doing nothing over the system's life.

PPA price & IRR

Solves the power purchase agreement price that delivers your target equity IRR, or the IRR a given PPA price earns, for solar, wind and hybrid projects with debt, tax, indexation and a merchant tail.

All bio, geo & hydrogen →

Capacity factor

Capacity factor = actual energy ÷ (nameplate capacity × hours). Calculate it from production data, turn a capacity factor into MWh, or size the capacity needed, then compare with typical values for nuclear, wind, solar, hydro and gas.

Bio, geo & hydrogen

Biogas, biomass, geothermal, green hydrogen and fuel cells.

Bio, geo & hydrogen

Green hydrogen & LCOH

Size an electrolyzer (alkaline, PEM or SOEC) and see how many tonnes of hydrogen it makes, how much water and electricity it uses, and what each kilogram costs, including stack replacements and degradation, with a capacity-factor sensitivity chart.

Bio, geo & hydrogen

Biogas & CHP output

Enter what goes into the digester each day (slurry, manure, silage, beet or food waste) and get biogas and methane volumes, CHP electrical and thermal output (or biomethane), digester size, loading rate and economics.

Bio, geo & hydrogen

Fuel cell H₂ use & runtime

How much hydrogen does a fuel cell burn, how long will a tank last and what does each kWh cost? Covers PEM, SOFC, PAFC, MCFC and alkaline cells, part-load efficiency, recoverable heat, water output and a diesel-generator comparison.

Converters & physics

Energy, power and fuel unit conversions, electrical basics.

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Energy unit converter

Convert any amount of energy between joules, watt-hours, calories, BTU, therms, tonnes of oil or coal equivalent, barrels of oil equivalent, electronvolts and foot-pounds. Shows all units at once, with real-world equivalents.

Power unit converter

Convert power between watts, kilowatts, megawatts, mechanical, metric and boiler horsepower, BTU per hour, tons of refrigeration, kcal/h and ft·lbf/s. Every unit is shown at once, along with the energy delivered per hour, day and year.

Cable size & voltage drop

Finds the smallest cable that meets both your voltage-drop limit and its current-carrying capacity. Works for DC, single-phase or three-phase, copper or aluminium, in mm² and AWG, with power loss and temperature effects.

kVA ↔ kW ↔ amps

Convert between apparent power (kVA), real power (kW), reactive power (kVAr) and current for single- and three-phase systems. You also get the power triangle and the capacitor bank needed to correct the power factor.

Ohm's law: V, I, R, P

Enter any two of voltage, current, resistance and power to get the other two, plus energy use, running cost and how power changes with voltage across the same load.

Gas unit converter

Converts any amount of natural gas, LNG, propane, butane, biomethane or hydrogen between volume (m³, Nm³, ft³, ccf, Mcf), energy (kWh, MJ, GJ, therm, BTU, MMBtu) and mass or liquid volume, on a gross or net calorific basis.

Three-phase power & amps

Calculates three-phase real, reactive and apparent power from current (or current from power), with line and phase voltages and currents for star (Y) and delta (Δ) connections, motor efficiency and a table of standard voltages.

Fuel energy & CO₂

Energy (lower and higher heating value) and CO₂ for 21 fuels, from diesel, petrol, LPG and natural gas to coal grades, wood, pellets, hydrogen, ethanol, kerosene and uranium. Also works out the true cost per kWh of heat from the price you pay.