Open Educational Resources & Applied Engineering
Engineering Energy Guides & Reference
Rigorous, formula-backed technical explainers for homeowners, engineering students, and trade professionals. Every guide pairs real-world electrical standards with live, interactive calculation engines.
NEC 705.12 120% Rule: Solar & Battery Panel Busbar Sizing Guide
Master the NEC 705.12 120% busbar rule for solar and battery storage backfeed. Includes 100Aā400A busbar derating matrix lookup tables, 125% continuous duty calculations, supply-side taps, and EMS power control.
How to Calculate EV Driving Range & Efficiency (Formula, Speed Drag & Winter Losses)
Master the mathematical physics of electric vehicle range. Calculate real-world highway range from usable battery kWh, aerodynamic speed drag (vĀ²), rolling resistance, winter cold derating, and battery degradation.
Central AC & Heat Pump Electricity Cost Guide (SEER2, Tons & Power Draw)
Calculate central AC and heat pump operating costs. Master SEER2, tonnage power draw, compressor cycling duty cycles, and heat pump vs. natural gas break-even economics.
Emergency Generator Sizing & Motor Inrush Load Guide (LRA & NEC 702)
Learn how to size whole-home and portable emergency generators accurately. Master inductive motor starting surge (LRA), sequential load stacking, and fuel derating under NEC 702.
Voltage Drop & Wire Size Calculation Guide (NEC 3% Rules & Table 8)
Master the mathematical formulas for DC and AC voltage drop. Size copper and aluminum AWG conductors using NEC Chapter 9 Table 8, Ohm's law, and the 3% branch circuit efficiency threshold.
Battery Backup Runtime Formula & Calculation Guide (Ah, Wh & Inverter Losses)
Master the battery runtime formula for LiFePO4, AGM, and Lead-Acid. Calculate Amp-hours to Watt-hours, inverter conversion losses, idle tare draw, and Peukert high-rate discharge capacity derating.
How Many kWh Does an Average House Use Per Day?
Complete empirical breakdown of residential electricity consumption based on EIA utility benchmarks. Includes home size square-footage tables, heavy appliance duty cycles, and daily kWh formula calculation.
MPPT vs PWM Solar Charge Controller Sizing Guide & Formula
Engineering guide to sizing solar charge controllers. Calculates continuous charging amperage, winter sub-zero Voc voltage expansion limits, and MPPT conversion efficiency gains.
Level 2 EV Charging Speed, Amperage & Breaker Sizing Guide
Definitive electrical engineering guide to Level 2 EV charging speeds, breaker sizing, wire gauges, and the NEC 80% continuous load rule for 16A through 48A home chargers.
Solar Payback Period & Net Metering ROI Financial Guide
Master solar payback and ROI financial formulas. Calculate net capital basis after the 30% Federal ITC, project utility inflation, model NEM 3.0 avoided cost rates, and calculate 25-year cash flows.
Space Heater vs Central Heating Electricity Cost Guide (1500W & Duty Cycles)
Thermal and electrical engineering guide: calculate space heater electricity cost, 1,500W power draw, thermostat duty cycles, zone heating economics vs. heat pumps, and NEC 80% circuit limits.
Solar Panel Tilt Angle by Latitude & Season Guide
Master the mathematics of solar panel tilt angles, seasonal summer vs. winter adjustments, azimuth orientation, and cosine irradiance capture by latitude.
Residential Battery Storage Lifespan, Cycle-Life Degradation & Thermal Loss Guide
Calculate home battery lifespan, cycle-life degradation mechanics, calendar aging kinetics, and ambient temperature derating. Compare LiFePO4 vs NMC capacity retention under IEEE 485.
Solar Inverter Clipping & DC-to-AC Ratio Sizing Guide (ILR, Saturation & Economics)
Master solar inverter clipping, DC-to-AC Inverter Loading Ratio (ILR), Sandia inverter saturation curves, clipping loss economics, and NEC 705.12 120% busbar interconnection rules.
EV V2L & V2H Home Backup Power Guide (Wiring, Inverters & Blackout Sizing)
Master powering a home with EV bidirectional energy. Calculate essential blackout runtimes, compare V2L vs V2H vs V2G, wire manual transfer switches, and resolve neutral-ground bonding under NEC 250 & 702.
Continue from a Guide to a Planning Tool
Turn the concepts from these guides into a practical estimate with the connected PowerLab calculator system.
š 2026 Engineering Guide Editorial Roadmap
1 New Engineering Guide Every 2 DaysOur engineering research group publishes peer-referenced, formula-complete sizing guides paired with deterministic computation engines:
Academic Integrity & Open Courseware Standards
Open Research & Preprints ā
Explore our citable technical reports (Harvard Dataverse, Academia.edu) covering EVSE continuous load, heat pump COP decay, and generator motor inrush.
Engineering Glossary ā
Detailed physical definitions, mathematical formulas, and code references for electrical, thermodynamic, and solar terms.
Regional Climate & Solar DB ā
50-state meteorological irradiance, peak sun hours, and ASHRAE extreme dry bulb design temperatures.