Planning a solar setup can feel like a maze of watts, volts and amps. How many panels do you need? How big should the battery bank be? Will your inverter handle the load? This free solar system calculator answers those questions in one place. Enter your appliances, solar panel specs, battery bank and inverter type, and it works out the array size, panel arrangement and battery capacity, and warns you if your equipment is a poor match. When you are happy with your design, you can save it as a PDF report.
Try the solar calculator
Scroll inside the tool and change any value. Every result updates instantly.
Solar System Designer
Enter your panel, battery and inverter specs. Results update as you type.
Solar panel
Inverter and charge controller
Battery bank
Appliances and lights
Energy needs and site
Panel arrangement
Results
What the calculator does
The tool helps you plan three parts of a solar system:
- The solar array: how many watts of panels you need, how many panels that is, and how to wire them in series and parallel.
- The battery bank: voltage, capacity in amp-hours, usable energy and days of autonomy.
- The inverter and charge controller: whether your equipment's voltage, current and power limits match the array, and whether the inverter can carry your peak load.
It supports five system types: off-grid with an MPPT controller, hybrid, off-grid with a PWM controller, grid-tie string inverters, and microinverters. Once your design is configured, you can also save it as a PDF report that carries the LearnEaseGuide logo and name.
What you need before you start
- Solar panel: wattage (Pmax), Vmp, Imp, Voc, Isc and the Voc temperature coefficient, all on the panel label or datasheet.
- Battery: voltage (12, 24 or 48 V), capacity in Ah, and how many batteries you own.
- Inverter: rating in watts, efficiency, and for MPPT types the maximum PV voltage, minimum MPPT voltage, maximum current and maximum PV power.
- Your loads: every appliance and light, with its wattage and daily running hours.
- Your site: peak sun hours and the coldest temperature your location sees.
Step 1: List your appliances and lights
Start in the Appliances and lights section. Everything else is sized from it. For each item enter the name, quantity, watts, hours per day and cycle percent.
Cycle matters for appliances that switch on and off by themselves. A refrigerator compressor runs about a third of the time, so a 150 W fridge that is plugged in for 24 hours uses roughly 150 x 24 x 35% = 1,260 Wh per day, not 3,600 Wh. For lights and TVs, leave cycle at 100%.
Add common appliances from the dropdown and edit the values, or add a blank row. The tool totals your daily energy in kWh and your peak load in watts. Untick Peak on appliances that never run at the same time.
Step 2: Enter your site details
- Peak sun hours: the equivalent hours per day of full sunlight at your location, often between 3.5 and 6.
- System losses: wiring, heat, dust and inverter losses. The default of 22% is a reasonable start.
- Days of autonomy: how many cloudy days the battery should cover.
- Coldest temperature: panel voltage rises in the cold, and this checks that your strings stay within the inverter's voltage limit.
Step 3: Enter your solar panel specs
Type the values from the panel label, or tap a preset (400 W, 550 W, 200 W 12 V, 100 W 12 V) and adjust. Vmp and Imp describe normal operation. Voc and Isc are used for safety limits.
Step 4: Choose your inverter type
The fields change to match the system you pick:
| Type | What it means |
|---|---|
| Off-grid MPPT | Array voltage can be much higher than the battery voltage. You enter max PV voltage, min MPPT voltage, max current and max power. |
| Hybrid | Like MPPT, with grid connection as backup. |
| Off-grid PWM | Panel voltage must match the battery. You enter the controller's max PV voltage and amp rating. |
| Grid-tie | No battery. The array is sized to offset your daily use. |
| Microinverters | One small inverter per panel, so each panel is its own string. |
Switching type loads typical default values. Replace them with the specs from your own inverter datasheet.
Step 5: Enter your battery bank
Choose the chemistry (LiFePO4, lead-acid or lithium NMC), which sets how much capacity is safely usable. Then enter battery voltage, capacity in Ah, how many batteries you have and how they connect.
Series connections add voltage. Parallel connections add capacity. Four 12 V 100 Ah batteries in series make a 48 V 100 Ah bank, while four in parallel make a 12 V 400 Ah bank.
Step 6: Set your panel arrangement
Enter how many panels go in series per string and how many strings run in parallel. Tap Use recommended arrangement to let the calculator pick a layout that fits your inverter's limits. A small diagram shows the layout.
Step 7: Read your results
- Array size needed: the watts of panels required to cover your daily energy, and the panel count.
- Your array: size and daily production of the arrangement you entered.
- Usable battery: the energy you can safely draw, or total AC output for grid-tie and microinverter systems.
- Color-coded checks: green is fine, orange is a warning, red is a problem to fix, such as string voltage above the inverter limit.
- Detail table: array voltage and current, battery energy, charge current, inverter DC input current and suggested fuse sizes.
Step 8: Save your design as a PDF
When your design looks right, tap Save design as PDF at the top of the Results section. Your browser's print window opens with a clean report that has the LearnEaseGuide logo and name at the top and on every page.
- Computer: in the print window, set the destination to Save as PDF, then save.
- iPhone or iPad: in the print preview, tap the share button and choose Save to Files.
- Android: choose Save as PDF in the printer list.
The report includes your results and warnings, panel arrangement, solar panel and inverter specs, battery bank, site details and your full appliance list, so you can keep it for reference or show it to your installer.
Worked example
Imagine a small cabin that uses about 4.6 kWh per day, with 4.5 peak sun hours and 22% losses.
- Required array: 4,650 Wh / (4.5 x 0.78) is about 1,325 W of panels.
- With 400 W panels, that is 4 panels.
- With a 150 V MPPT inverter, 3 panels in series stay under the voltage limit, so the calculator may suggest a layout with a little extra capacity.
- For 1.5 days of autonomy on LiFePO4 batteries, you need roughly 8 kWh of battery.
Tips for better results
- Measure appliance wattage with a plug-in power meter when you can. Label values are often maximums.
- Account for motors. Pumps and compressors can draw two to three times their running watts at start-up, so size the inverter above your peak load.
- Use the coldest temperature for your area. Cold weather raises panel voltage, a common cause of damaged inverters.
- Leave room to grow. Adding capacity in the design is cheaper than after installation.
Frequently asked questions
Is this calculator free? Yes. Use it as often as you like.
Can I use it for a house connected to the grid? Yes. Choose grid-tie or microinverters to size an array that offsets your daily use.
Can I save or print my design? Yes. Tap Save design as PDF in the Results section and choose Save as PDF in the print window. The report carries the LearnEaseGuide logo and name.
Why do the fields change when I switch inverter type? Each system has different limits. PWM controllers care about amp rating, while MPPT inverters care about voltage windows and power limits.
How accurate is it? It uses standard sizing methods with simplified assumptions, so treat results as a starting point.
Do I still need an installer? Yes. Wiring, fusing, grounding and local code requirements need a qualified professional.
Disclaimer
This calculator and article are for general reference and education only. Results are estimates based on the values you enter and simplified assumptions. Actual performance varies with site conditions, shading, equipment and installation. They do not replace manufacturer datasheets or a site assessment. Have your final design reviewed by a qualified electrician or solar installer and follow your local electrical codes. Use at your own risk, with no warranty given.
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