Calculate daily energy use, battery bank capacity, solar panels, inverter and MPPT size, charging time, shore power needs, and runtime for RVs, cabins, boats, workshops, backup systems, remote equipment, surveillance, and other off-grid applications.
Pick an editable example or build your own. Presets are starting assumptions, not installation specifications.
Daily energy = quantity × watts × hours × duty cycle. Add any device; the examples never limit what you can enter.
Three inputs produce a useful first estimate. Fine-tune chemistry, losses, charging and existing equipment below.
Chemistry defaults are editable planning assumptions. Always follow the battery manufacturer’s limits.
Voltage and continuous-load assumptions are explicit because electrical rules differ by country and installation.
Likely supports the entered connected loads.
Likely supports loads plus the selected charger.
A useful off-grid design begins with energy, not a panel or battery product. These relationships explain what the calculator is doing and where final engineering starts.
Audit energy use first, choose an autonomy target, size nominal battery energy from usable capacity, then size the solar array for conservative seasonal sun. Finally verify inverter surge, charge sources, controllers, conductors, protection and equipment limits as one system.
Daily Wh ÷ peak sun hours ÷ solar efficiency ≈ solar watts
Watts describe instantaneous power. Watt-hours describe energy. Amp-hours describe charge at a stated voltage, so Ah alone cannot tell you energy without voltage.
W × hours = Wh • V × Ah = Wh • Wh ÷ V = Ah
A bank must cover the load while staying inside the battery maker's state-of-charge limits. Usable percentage, cold weather, age, inverter loss and delivery loss all reduce the nominal label capacity available to equipment.
Usable battery Wh ÷ average load W ≈ runtime hours
Higher voltage reduces current for the same power, which can make larger systems more practical. But every battery, charger, inverter, controller and DC load must be compatible. System architecture and safe conductor design decide the voltage.
Current A = power W ÷ voltage V
A panel does not make rated power all day. Peak sun hours condense variable irradiance into an energy-planning value. Use a conservative seasonal figure and allow for heat, shade, dirt, orientation, wiring and conversion losses.
Panel W × peak sun hours × efficiency ≈ daily Wh
Inverters must handle simultaneous AC demand and startup surge. MPPT controller output current starts with array watts divided by battery voltage, but final PV string design must also verify cold-weather voltage and panel current against controller limits.
MPPT output A ≈ array W ÷ battery V, plus design margin
Charger output amps must be acceptable to the battery and BMS. Compare the charger's AC input with the practical shore capacity after other loads. Recharge slows near charge limits, so energy divided by power is a best-case bulk estimate.
Recharge hours ≈ energy deficit Wh ÷ charger output W
Series connections add voltage while amp-hours stay the same. Parallel strings add amp-hours while voltage stays the same. Use matched, compatible batteries and follow manufacturer rules for balancing, protection and maximum configurations.
Bank V = battery V × series • Bank Ah = battery Ah × parallel
Open an example to see what belongs in the load audit, then select the matching editable preset at the top of the calculator. Values are illustrative and should be replaced with equipment labels or measured power.
LED lighting, phone charging, a small 12V refrigerator, water pump and occasional laptop use.
Choose this preset in the calculator ↑Continuous refrigeration and controls plus lights, fans, pump, electronics and modest inverter loads.
Choose this preset in the calculator ↑Refrigeration, lights, communications, pump and selected household loads with seasonal planning.
Choose this preset in the calculator ↑Lighting and chargers plus intermittent tools whose startup and simultaneous demand drive inverter size.
Choose this preset in the calculator ↑Critical refrigeration, connectivity, lights, medical equipment or other carefully prioritized loads.
Choose this preset in the calculator ↑A continuous communications load where power-management modes can materially change daily energy.
Choose this preset in the calculator ↑Cameras, infrared illumination, recorder, network switch and cellular or satellite connection operating 24/7.
Choose this preset in the calculator ↑Multiple cameras, recording, networking and control equipment with winter and recovery reserve.
Choose this preset in the calculator ↑Remote surveillance is unusually demanding because cameras and communications often run 24/7. Infrared lighting raises nighttime use, PTZ movement varies demand, and cellular or Starlink connectivity adds a continuous load. Winter sun and temperature are frequently the hardest design conditions.
Model the recorder, PoE losses, network equipment and every camera separately. Use duty cycle only when you can justify it; critical surveillance should not depend on optimistic solar assumptions.
Explore Aegis Towers systems designed around the site, coverage goal, connectivity, battery reserve and available solar exposure.
Divide 1,000Wh by your peak sun hours and system efficiency. With 4 peak sun hours and 75% overall solar efficiency, the starting estimate is about 333W, so a practical design might use 400W or more after considering season, shade, recovery reserve, and the actual panel specifications.
First multiply daily watt-hours by the days of autonomy you want. Then divide by the battery's usable-capacity percentage and expected delivery efficiency. Convert the resulting watt-hours to amp-hours at your system voltage, then choose a valid series/parallel arrangement using compatible batteries.
Multiply battery volts by 100Ah, then apply the permitted usable percentage and system losses. A nominal 12V 100Ah battery stores 1,200Wh. At 80% usable capacity and 90% delivery efficiency, about 864Wh reaches the loads, enough for a 100W average load for roughly 8.6 hours.
Watt-hours equal volts multiplied by amp-hours. A 12V 100Ah battery is nominally 1,200Wh; a 24V 100Ah bank is 2,400Wh; and a 48V 100Ah bank is 4,800Wh. Usable energy is lower and depends on battery limits and losses.
Divide 1,000Wh by voltage. One kWh is about 83.3Ah at 12V, 41.7Ah at 24V, or 20.8Ah at 48V. Those are nominal conversions before usable-capacity and efficiency allowances.
There is no universal RV panel size. Add each appliance's daily watt-hours, then divide by conservative peak sun hours and solar efficiency. Roof area, shade, travel season, alternator or shore charging, battery capacity, and high-draw appliances all change the answer.
Start with a load audit, paying close attention to refrigeration, pumps, heating controls, communications, and occasional appliances. Size for the lowest-sun season in which the cabin must operate and decide whether a generator or shore source will cover prolonged poor weather.
Often yes, provided the solar controller, AC charger, battery, and BMS are designed and configured to work together. Their combined current and voltage must stay within every component's limits, and compatible charge profiles matter.
Divide the energy deficit in watt-hours by the charger's effective DC output watts. A 2,400Wh deficit with a 600W DC charger has a theoretical bulk time of four hours. Tapering, temperature, simultaneous loads, charger limits, and battery behavior make real charging longer.
Use the battery manufacturer's permitted charge-current range, not voltage alone. DC charger power is approximately bank voltage multiplied by charge amps. A 12V 40A charger is roughly 480W DC, while a 48V 20A charger is roughly 960W DC. Confirm the actual charging voltage, BMS limits, wiring, and AC input requirement.
Add the AC loads that may run simultaneously, allow a design margin, and check the largest startup surge. Motors, pumps, compressors, microwaves, and power tools can require much more power briefly than their normal running rating.
12V is common in vehicles and smaller systems, 24V can reduce current in medium systems, and 48V is common for larger inverter and battery installations. The right choice depends on equipment compatibility, current, conductor length, available components, codes, and qualified design—not a single wattage cutoff.
Watts measure power at a moment; watt-hours measure energy over time. A 100W device running for five hours uses 500Wh. Kilowatts and kilowatt-hours are the same units divided by 1,000.
Peak sun hours express a day's solar energy as an equivalent number of hours at 1,000 watts per square meter. They are not the same as daylight hours and vary by location, season, weather, orientation, and shade.
Multiply 400W by peak sun hours and a realistic system-efficiency factor. At 4.5 peak sun hours and 75% efficiency, one 400W panel might contribute about 1,350Wh in the modeled day. Actual production varies substantially.
No. Four hundred watts is a rating under defined test conditions. Output changes through the day and with irradiance, temperature, angle, shade, dirt, wiring, and controller behavior.
Respect the manufacturer's allowed state-of-charge limits and add operational reserve for aging, cold conditions, forecast uncertainty, and critical loads. Editable chemistry defaults in this calculator are general planning assumptions, not manufacturer specifications.
A first output-current estimate is solar watts divided by battery voltage, plus a design margin. Final selection also requires panel Voc, Vmp and Isc, series/parallel string design, cold-weather voltage correction, controller input limits, and manufacturer instructions.