Energy & Solar Tools

Free energy, solar and home-efficiency calculators that run entirely in your browser — solar system sizing, off-grid battery bank, solar payback and ROI, inverter and generator sizing, wind turbine power, R-value/U-value insulation, heat loss, heat-pump COP, EV charging cost, phantom load and net metering. Nothing is uploaded.

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Solar Panel System Size Calculator

Size a solar PV array in kW and number of panels from your daily energy use, peak sun hours, system derate and panel wattage.

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Off-Grid Solar Battery Bank Sizing Calculator

Size an off-grid battery bank in Ah and kWh from daily load, system voltage, days of autonomy and depth of discharge.

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Solar Payback & ROI Calculator

Estimate years to break even and 25-year ROI on a solar system from cost, incentives, annual production and electricity rate.

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Solar Inverter Sizing & DC-AC Ratio Calculator

Recommend an inverter AC size and flag the DC-AC (ILR) clipping ratio from your solar array's DC watts.

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Generator Sizing Calculator (Running + Starting Watts)

Size a portable or standby generator from a checklist of appliances, adding running watts plus the largest starting surge.

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Wind Turbine Power Calculator

Compute a wind turbine's power from rotor diameter, wind speed and efficiency, plus average power and annual energy.

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EV Home Charging Cost Calculator

Work out the cost to charge an EV at home per charge, per mile and per month from battery size, efficiency and electricity rate.

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R-Value / U-Value Insulation Calculator

Add up a wall or roof assembly's insulation layers to get total R-value, U-value and heat loss — imperial or metric.

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Home Heat Loss & Heating Load Calculator

Estimate design heat loss in BTU/hr from U-value, area, ΔT, air infiltration, plus annual heating energy and cost.

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Heat Pump COP / SEER & Running Cost Calculator

Convert HSPF, SEER, EER or measured output to COP and compare heat-pump running cost with resistance and gas heat.

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Phantom / Vampire Load Cost Calculator

Total the always-on standby power of your devices to see the yearly kWh and cost of phantom load — and cut it.

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Net Metering Savings Calculator

Work out annual solar savings, self-consumption, export credits and your net bill from production, usage and rates.

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Solar Water Heater Sizing Calculator

Size a solar hot-water collector and storage tank from daily demand, water temperatures and solar insolation.

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