Renewable Energy Calculators
7 free renewable energy calculators — standards-based, with formulas, worked examples, and no sign-up.
Renewable sizing is mostly a fight against optimistic arithmetic, so each of these tools carries its loss model in the open. Solar PV sizing works backward from your utility bill: annual kWh to array kW using the PVWatts convention of 14% system losses plus your local sun-hours, then to panel count and roof area. The tilt tool encodes the latitude rule and its seasonal ±15° adjustments, and reports what percentage of optimal a compromise roof pitch actually captures — usually more than people fear. The separate solar PV yield tool (in Electrical & MEP) does the forward problem per IEC 61853; solar water heating applies the Hottel-Whillier equation with collector efficiency curves.
Wind and hydro get the same honest treatment: swept-area power with the Betz limit (59.3%) shown explicitly so nameplate claims can be sanity-checked, and net-head hydraulic power with turbine efficiency to annual energy. Battery storage sizing converts a load in kWh through depth-of-discharge and system voltage to amp-hours, series/parallel string counts, and a C-rate check. EV charging rounds out the category from the demand side — charge time and cost per session, a gas-cost comparison, and the NEC 125% continuous-load breaker sizing that a home charger circuit legally requires.
All Renewable Energy Tools
Wind Turbine Power Calculator
Swept area, available wind power, electrical output, Betz-limit fraction, and annual energy production with a power curve.
Hydroelectric Power Calculator
Net head, hydraulic and electrical power, and annual energy from flow rate, gross head, penstock losses, and efficiency.
Battery Storage Sizing Calculator
Battery bank sizing for off-grid and backup systems: usable and nominal capacity, series/parallel count, and C-rate.
Solar Water Heating Calculator
Flat-plate solar thermal collector sizing and output via the Hottel-Whillier equation: useful energy gain Qu, instantaneous efficiency, daily hot-water energy, required collector area and solar fraction.
Solar PV System Sizing Calculator (How Many Panels)
How many solar panels you need from your electric bill via the NREL PVWatts methodology: monthly or annual kWh converted to a daily average, target DC array size = daily kWh × offset / (peak sun hours × (1 − losses)) with the source-verified PVWatts v5 default of 14% total system losses, whole-panel buy count at your panel wattage (default 400 W), installed array kW DC, a representative 21.5 ft²-per-panel roof-area estimate (400 W-class module — actual dimensions vary by product), annual production of the installed array, and the achieved usage offset with net-metering framing for oversizing up to 200%.
Solar Panel Tilt Angle Calculator (Best Angle by Latitude)
The best solar panel tilt and direction from your latitude via the standard solar-engineering rules of thumb: annual tilt = latitude, winter = latitude + 15°, summer = latitude − 15° (clamped to 0–90°), facing the equator (south 180° in the northern hemisphere, north 0° in the southern — negative latitudes handled end-to-end), a seasonal table of all three goals with a side-view tilt sketch, and an optional roof check that grades your actual roof tilt and azimuth against the annual optimum as a first-order "≈ X% of optimal" estimate displayed only in honest 5% bands, with NREL PVWatts pointed to for real simulation.
EV Charging Calculator (Time, Cost & Breaker Size)
Home AC (Level 1/Level 2) EV charging in three modes: charge time between two states of charge from battery kWh and charger kW (presets L1 1.4 kW, L2 3.3–19.2 kW) at a representative 90% onboard-charger efficiency displayed as hours and minutes, session cost from the wall including charger losses with an optional per-mile cost and a gas-car $/mi comparison, and NEC branch-circuit sizing — 125% of the continuous EVSE current per NEC 625.41 matched to the first NEC 240.6(A) standard breaker size (15–100 A), with the inverse 80% rule for the largest EVSE an existing breaker supports.
Frequently Asked Questions
My roof faces southeast at 30°. How much solar production am I giving up?
Usually less than 10% versus a perfect south-facing latitude tilt — the production surface is quite flat near the optimum. Run the tilt angle tool with your real pitch and azimuth: it reports the percentage of optimal directly. Panels are cheap enough that adding one panel typically beats re-engineering a roof; shade, not orientation, is the loss that actually kills arrays.
Why can't I use my battery's full rated capacity?
Depth of discharge. Lead-acid banks are typically cycled to only 50% to reach their rated cycle life; lithium chemistries tolerate 80–90%. The battery sizing tool divides your required energy by the DoD you select, which is why a 10 kWh load can need a 20 kWh lead-acid bank. The C-rate check then verifies the bank can deliver your peak power without exceeding its discharge rating.
A turbine ad claims it captures nearly all the wind's energy. Possible?
No. The Betz limit caps any wind turbine at 59.3% of the kinetic energy in the swept area — physics, not engineering. Real machines reach 35–45% at their best operating point. The wind power tool computes ideal power, the Betz ceiling, and the realistic output side by side, precisely so that marketing numbers can be checked against the swept area they must obey.