Solar & Energy Calculators
Solar PV, battery, inverter, EV charging (NEC 625) and lighting calculators — each with the formula, a worked example and a PDF report.
8 Calculators · Solar, EV & lighting
Solar PV Sizing
EV Charging (NEC 625)
Lighting Design
About Our Solar & Energy Calculators
The energy-systems category covers the calculations behind a modern renewable and electrified building: solar PV sizing, battery storage, inverter selection, EV charging circuits, and lighting design. As rooftop solar, home batteries and electric vehicles move into mainstream construction, these are some of the fastest-growing engineering calculations — and the ones most often done with rules of thumb that don’t hold up.
Solar array size (kW) is daily energy demand divided by the product of peak sun hours and a performance ratio that accounts for real-world losses. Battery banks are sized from daily watt-hours, days of autonomy, system voltage and depth of discharge. PV string limits come from temperature-corrected module voltages against the inverter window. EV charging circuits follow NEC 625, sizing the conductor and breaker at 125% of the continuous charging load. Lighting uses the lumen method to convert a target lux level and room geometry into the number of luminaires. Each calculator states its formula, shows a worked example and exports a PDF.
Frequently Asked Questions
How do I size a solar panel array?
Array size in kW equals daily energy use (kWh) divided by (peak sun hours × performance ratio). For example, 10 kWh/day at 5 peak sun hours and a 0.75 performance ratio needs about 10 / (5 × 0.75) = 2.7 kW of panels.
How do I size a solar battery bank?
Battery capacity (Ah) = (daily watt-hours × days of autonomy) ÷ (system voltage × depth of discharge). A 5 kWh load with 2 days autonomy on a 48 V bank at 80% DoD needs about (5000 × 2) / (48 × 0.8) ≈ 260 Ah.
How is an EV charging circuit sized under NEC 625?
NEC 625 treats EV charging as a continuous load, so the branch circuit is sized at 125% of the charger’s rated current. A 32 A charger needs a 40 A breaker and conductors rated for at least 40 A.
What is the lumen method for lighting?
The lumen method gives total lumens = (target lux × floor area) ÷ (utilisation factor × maintenance factor); the number of luminaires is total lumens divided by the lumen output per fitting.