Solar System Calculator

Calculator

Size a solar system accurately. Calculate inverter, battery, and panel requirements from your appliance list.

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About this tool

What is the Solar System Calculator?

The Solar System Calculator is a comprehensive sizing tool that helps homeowners, solar installers, and business owners accurately calculate the components needed for a solar power system. Instead of guessing or relying on rough estimates, you define exactly which appliances you want to power, how long you use them, and the tool computes the precise inverter size, battery capacity, solar panel array, and expected backup time — all grounded in real engineering formulas.

The calculator is built for both beginners and professionals. Beginners get plain-language explanations alongside every result. Installers get the full calculation breakdown, adjustable efficiency factors, and a downloadable report they can share with clients.

How to Use the Calculator

Add your appliances. Select a category — Lighting, Cooling, Kitchen, Entertainment, Office, Appliances, or Medical — and click any appliance to add it to your list. Every common Nigerian and international appliance is included. You can also add custom appliances with any wattage.
Adjust quantity and usage hours. For each appliance, set how many units you have and how many hours per day they run. The refrigerator runs 24 hours; the TV might run 5. Getting these numbers right is the most important part of accurate sizing.
Configure system settings. Open the settings panel to choose your battery voltage, location, days of autonomy, safety factor, and efficiency values. Sensible defaults are pre-filled for a typical Nigerian installation.
Load a preset if you prefer. Four quick presets are available: Typical Nigerian Home, Small Office, Small Clinic, and Retail Shop. Load one and adjust from there.
View your results. Switch to the Results tab to see your full system sizing — inverter, battery, solar panels, and backup time — alongside warnings if anything looks problematic and a plain-language summary explaining what each number means.
Export the report. Download a text report with all appliances, settings, and results to share with your installer or client.

What the Calculator Computes

Total load (W and kW) — the sum of all your appliances running at the same time. This determines the minimum inverter size your system needs.

Daily energy consumption (Wh and kWh) — how much energy your appliances consume in a full day, factoring in actual hours of use. This is the number that drives battery and solar sizing.

Inverter size (kVA) — the recommended inverter capacity, sized with a safety factor above your peak load. The calculator rounds up to the nearest standard commercial inverter size so you buy something that actually exists in the market.

Battery capacity (kWh and Ah) — the total battery storage needed to run your load for your chosen number of days without solar charging. The result is shown in both kWh (energy) and Ah at your selected voltage, so you can spec either lithium or lead-acid batteries.

Solar panel array (W and kW) — the total panel wattage needed to fully recharge your batteries each day, based on your location's peak sun hours and overall system efficiency. The calculator also gives you panel count estimates for 300W and 400W panels.

Backup time (hours) — how long a fully charged battery will power your load without any solar input.

Core Formulas

Total Load (W)       = Σ (watts × quantity)
Daily Energy (Wh)    = Σ (watts × quantity × hours/day)
Inverter (kVA)       = Total Load × Safety Factor ÷ Inverter Efficiency
Battery (Wh)         = Daily Energy × Days of Autonomy ÷ Battery Efficiency
Battery (Ah)         = Battery Wh ÷ Battery Voltage
Solar Array (W)      = Daily Energy ÷ Peak Sun Hours ÷ System Efficiency
Backup Time (h)      = Battery Wh × Battery Efficiency ÷ Total Load

System Settings Explained

Battery voltage — 12V suits small systems up to about 1kW. 24V works for medium residential systems. 48V is recommended for anything above 3kW, especially systems with air conditioning. Higher voltage means lower current, which reduces cable losses and heat.

Peak sun hours — the number of hours per day when solar irradiance is strong enough to generate rated panel output. This varies by location: Kano and Sokoto average 6.5 hours, Abuja and Kaduna around 5.5 hours, Lagos and Port Harcourt around 4.5 hours. The calculator includes location presets for major cities across Nigeria, Africa, the Middle East, Europe, and North America.

Days of autonomy — how many days the battery bank should sustain your load without any solar charging. One day is standard for grid-hybrid systems. Two to three days suits areas with frequent overcast periods. Five days is typical for critical off-grid installations.

Safety factor — the multiplier applied to your peak load when sizing the inverter. A 1.25× factor (25% headroom) is standard for most installations. 1.5× is more conservative and recommended for systems with large motor loads like water pumps and compressors.

Inverter efficiency — how much AC power the inverter delivers for every watt of DC power it draws. Most quality inverters operate between 90% and 95%. Lower efficiency means more solar and battery capacity is needed to deliver the same output.

Battery efficiency — also called round-trip efficiency, this accounts for energy lost when charging and discharging the battery. Quality lithium batteries achieve 95–98%. Lead-acid batteries typically achieve 80–85%.

Intelligent Warnings

The calculator automatically detects common sizing problems and displays them as errors, warnings, or tips:

Running air conditioning loads on a 12V system triggers an error — high-current 12V systems require dangerously thick cables and are inefficient above 1kW. Systems with total loads above 2kW at 12V or above 5kW at 24V receive an upgrade recommendation. High-draw appliances that should not run simultaneously are flagged. Short estimated backup times prompt suggestions to increase battery capacity. Location-specific low sun hours warnings appear when recharge may be insufficient. If lighting accounts for an unusually high share of your energy use, the calculator suggests switching to lower-wattage LEDs as a more cost-effective alternative to increasing system size.

Appliance Presets

Lighting — LED bulbs (9W, 15W), fluorescent tubes, security lights.

Cooling — ceiling fans, standing fans, 1HP, 1.5HP, and 2HP air conditioners.

Kitchen — refrigerators (200L, 300L), deep freezers, microwaves, electric kettles, blenders, rice cookers, toasters.

Entertainment — LED TVs (32", 43", 55"), DSTV decoders, sound systems, game consoles.

Office — laptops, desktop PCs, monitors, printers, WiFi routers, phone chargers.

Appliances — water pumps (0.5HP, 1HP), washing machines, irons, hair dryers, vacuum cleaners.

Medical — CPAP machines, oxygen concentrators, medical fridges, nebulizers.

Privacy

All calculations run entirely in your browser. No appliance lists, system configurations, or results are sent to any server or stored anywhere.

How to Use

1
Add your appliances
Select a category such as Lighting, Cooling, or Kitchen and click any appliance to add it to your list. Adjust the quantity and daily hours of use for each item. You can also add custom appliances with any wattage.
2
Load a preset (optional)
Use a Quick Preset to instantly load a typical appliance list for a Nigerian home, small office, clinic, or retail shop. You can then add or remove items from the preset.
3
Configure system settings
Open the System Settings panel to choose your battery voltage, location, days of autonomy, safety factor, and efficiency values. Select your city from the location dropdown to automatically set the correct peak sun hours.
4
View your results
Switch to the Results tab to see your recommended inverter size, battery capacity, solar panel array, and estimated backup time. Read the plain-language summary for a clear explanation of what each number means.
5
Export your report
Click the Export button to download a text report with all appliances, system settings, and results. Share it with your solar installer or use it as a reference when purchasing components.

Frequently Asked Questions

How do I know what wattage my appliances use?↓

Most appliances have a label on the back or bottom showing their power rating in watts (W) or kilowatts (kW). If not, check the product manual or search for the model online. The calculator includes accurate wattage values for over 40 common appliances so you can add them with one click.

What battery voltage should I choose?↓

Use 12V for small systems under 1kW — a single fan, some lights, and a TV. Use 24V for medium residential systems between 1kW and 3kW. Use 48V for anything above 3kW, especially if you have air conditioning. Higher voltage systems are more efficient and use thinner, cheaper cables.

What are peak sun hours and how do I find mine?↓

Peak sun hours are the number of hours per day when solar irradiance is strong enough to generate rated panel output. It is not the same as daylight hours. The calculator provides presets for major cities: Lagos and Port Harcourt average 4.5 hours, Abuja and Kaduna 5.5 hours, and Kano and Sokoto 6.5 hours. Select your location from the dropdown and the value is set automatically.

What does days of autonomy mean?↓

Days of autonomy is how many days your battery bank can power your load without any solar charging — for example during heavy cloud cover or rainy season. One day is standard for grid-hybrid systems. Two to three days is common for areas with frequent overcast weather. Five days suits critical off-grid installations like clinics.

Why does the calculator add a safety factor to the inverter size?↓

Inverters should never run continuously at 100% of their rated capacity — it causes overheating and shortens lifespan. A 1.25× safety factor means your inverter is sized to run your full load at only 80% of its capacity, leaving headroom for startup surges from motors and compressors. Use 1.5× if you have large pump or AC loads.

How many solar panels will I need?↓

The calculator computes the total panel wattage required and then estimates the number of panels for both 300W and 400W panel sizes. For example, if you need 2,400W of solar, that is 8 × 300W panels or 6 × 400W panels. Your installer will choose the exact panel size based on availability and roof space.

Can I use this for a commercial or industrial system?↓

Yes. The calculator handles systems of any size. For very large loads above 20 kWh per day, it suggests considering a hybrid grid-tied system rather than a fully off-grid setup, which is sound engineering advice for commercial installations.

Is the calculation accurate enough for purchasing decisions?↓

The calculator uses standard solar engineering formulas and real-world efficiency values. The results are a reliable starting point for component selection. However, a professional solar installer should perform a final site survey and system design before purchase, especially for systems above 5kW.

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