Enter your load as Amp, HP, or kW, pick single or three phase, and get the recommended solar array size, panel count, and battery bank Ah — in one shot.
Fill in your connected load, sun hours, and backup requirement below.
Battery Backup (optional)
Solar panel capacity needed
Enter your values and hit calculate to see a suggested battery Ah rating and configuration.
Sizing a solar power system correctly is one of the most common questions technicians, electricians, and homeowners run into once they decide to move part of their load off the grid. Undersize the array and the system will never fully charge the battery bank on a cloudy day; oversize it and you have spent money on panels that spend most of the afternoon doing nothing. This calculator walks through the same method used by solar installers in the field — start from the connected load, convert it to real power in kilowatts, work out how much energy that load consumes across a day, and then divide by how much usable sunlight your location actually receives.
The first step is figuring out your load in kilowatts, because kW is the unit solar panels, inverters, and batteries are all rated in. If you only know the current draw from a nameplate or a clamp meter, this tool converts it for you. For a single-phase supply, real power is calculated as kW = (V × I × PF) / 1000, where V is the line voltage, I is the current in amps, and PF is the power factor of the load. For a three-phase supply, the same relationship gains a √3 term to account for the phase geometry: kW = (V × I × √3 × PF) / 1000. If your load is already rated in horsepower — common on motors and pumps — the tool first converts shaft power to kW using 0.7457 kW/HP and then divides by the motor's efficiency, since the motor draws more electrical input power than it delivers at the shaft: kW = (HP × 0.7457) / Motor Efficiency. A 10 HP motor at 90% efficiency, for example, actually draws about 8.29 kW from the supply, not 7.46 kW. If you already have the load in kW, the calculator uses that value directly.
Once the load is known in kW, the calculator multiplies it by your daily usage hours to get the daily energy requirement in kWh — this is simply how much electrical energy the load consumes over a full day of operation. That figure is also extended into monthly (×30) and annual (×365) consumption, useful for comparing against your electricity bill or planning payback period.
Next comes the array sizing itself. Peak Sun Hours (PSH) is the number of hours per day the sun delivers energy at an intensity equivalent to 1,000 W/m² — it is not the same as daylight hours, and in most parts of India it typically falls between 4.5 and 6 hours depending on season and location. Because real systems lose some energy to wiring resistance, inverter conversion, dust on the panel surface, and temperature derating, a system efficiency factor (commonly 70–80%) is applied. Putting it together: Solar Array Size (kWp) = Daily Energy (kWh) ÷ (Peak Sun Hours × System Efficiency). An optional 20% design margin can be added on top of this to absorb panel degradation over the years, soiling losses, and future load growth — a standard practice among field installers. Dividing the final array size by your chosen panel wattage then gives the number of physical panels required, rounded up to the next whole panel. Roof area required is estimated from typical panel footprint (roughly 18 sq.ft for a 330Wp panel, scaled proportionally for higher-wattage panels such as the 550Wp modules common in 2026 rooftop installations), and estimated daily generation and annual CO₂ savings (at ~0.82 kg CO₂ avoided per kWh, the approximate Indian grid emission factor) are shown to give a quick sense of environmental impact.
The battery section works independently and is meant for systems that need to keep running after the sun goes down, or through a short outage. The calculator takes your desired backup duration in hours, multiplies it by the load in watts to get the backup energy requirement in Wh, and then converts that into Ah using your chosen battery bank voltage, its usable Depth of Discharge (DoD), and the inverter's round-trip efficiency, since real energy drawn from the battery is always more than the energy actually delivered to the load: Battery Ah = Backup Energy (Wh) ÷ (Battery Voltage × DoD × Inverter Efficiency). DoD matters because deep-cycle lead-acid batteries are typically only discharged to 50% to preserve cycle life, while lithium (LiFePO₄) batteries can safely handle 80–90% DoD, giving you a smaller, lighter bank for the same backup time — selecting the chemistry from the dropdown automatically applies a sensible default DoD, which you can still override. The result is also translated into a practical series-parallel configuration using common 12V unit battery sizes, so you know exactly how many batteries to wire in series (to reach your bank voltage) and in parallel (to reach your Ah capacity) — for example, a 24V 400Ah requirement typically becomes two 12V 200Ah batteries in series.
As always with sizing calculators, treat the output as an engineering starting point rather than a final purchase order. Local solar irradiance, shading, panel orientation, cable losses, inverter efficiency curves, and battery ageing all shift the real-world number by a meaningful margin. Always get your final design reviewed by a licensed solar installer before purchase and installation, especially for grid-tied or hybrid systems that need to meet local net-metering rules.
An off-grid system relies entirely on solar panels and a battery bank, with no connection to the utility grid — every kWh consumed at night or on a cloudy day has to come from stored battery charge, so array and battery sizing both need to be conservative. A grid-tied system has no battery at all; any solar generation beyond what the building is using at that moment is exported to the grid (often under a net-metering arrangement), and any shortfall is drawn from the grid as normal, which keeps the system simpler and cheaper but offers no backup during a power cut. A hybrid system combines both: it uses solar first, falls back to a battery for backup during outages, and can still draw from or export to the grid the rest of the time. Most urban Indian rooftop installations today are grid-tied or hybrid, while remote or frequently-outaged locations tend to lean off-grid or hybrid with a sizeable battery bank.
Panel wattage (Wp, or watt-peak) is the panel's rated output under standard test conditions. Older installations commonly used 300–330Wp panels, but 2025–2026 rooftop installations increasingly use 540–555Wp monocrystalline PERC or TOPCon panels, which deliver more power per panel and per square foot of roof — reducing the total number of panels, mounting hardware, and wiring needed for the same array size. Higher-wattage panels are usually a better choice unless your roof area is unusually constrained or the installer's inverter/string configuration specifically calls for a lower-wattage panel.
The figures below assume 5 peak sun hours and 75% system efficiency, a common planning baseline across much of India — use the calculator above with your own sun-hour data for a location-specific figure.
| Daily Energy Need | Approx. Array Size | Panels (400Wp) |
|---|---|---|
| 5 kWh/day | 1.3–1.5 kWp | 3–4 |
| 10 kWh/day | 2.7–3.0 kWp | 7–8 |
| 15 kWh/day | 4.0–4.5 kWp | 10–11 |
| 20 kWh/day | 5.3–6.0 kWp | 13–15 |
| 30 kWh/day | 8.0–9.0 kWp | 20–23 |
Figures are indicative planning estimates only. Enter your exact load, usage hours, and local sun-hour data in the calculator above for a precise recommendation.
Content last reviewed: July 2026
Peak Sun Hours measure the equivalent number of hours the sun delivers 1,000 W/m² of solar irradiance. A location may get 11 hours of daylight but only 5 "peak" hours, since morning and evening light is far weaker than midday sun.
Lead-acid is cheaper upfront but needs a larger bank (50% DoD) and shorter cycle life. Lithium (LiFePO₄) costs more per Ah but allows 80–90% DoD, weighs less, and typically lasts 3–4× longer, so total cost of ownership is often lower over the system's lifetime.
A margin of 15–20% is standard practice to account for panel degradation over years, dust and soiling losses, and any future increase in connected load.
The array and energy math applies to all three setups since it's based on your load and sun hours. The battery section is most relevant for off-grid and hybrid systems; grid-tied systems without storage can skip it, but should still check local net-metering rules with their utility before finalizing a design.
As a rough rule of thumb at 5 peak sun hours and 75% system efficiency, a 1 kW load running 5 hours a day needs roughly a 1.3–1.5 kWp array — about 3–4 panels of 400W each. A 3 kW load under the same conditions needs roughly a 4–4.5 kWp array, around 10–11 panels of 400W. Enter your own usage hours and sun-hour data above for a precise figure.
When the load is entered directly in kW, array sizing depends only on the energy consumed (kWh), which is the same regardless of whether that power is drawn through a single-phase or three-phase supply — this is correct, not an error. The phase selection matters when the load is entered in Amps, since converting current to kW requires the appropriate single-phase or three-phase formula, and switching phase in Amp mode will change the calculated load.
