Free Solar System Calculator: Size Your Solar Array, Battery and Inverter

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.

For reference only. The calculator gives estimates, not a certified design. Confirm your final design with the manufacturer's datasheets and a qualified electrician or solar installer, and follow your local electrical codes.

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.

For reference only. Results are estimates, not a certified design.

Solar panel

Wattage (Pmax) Vmp (V) Imp (A) Voc (V) Isc (A) Voc temp coeff (%/°C)

Inverter and charge controller

Type Off-grid inverter with MPPT controller Hybrid inverter (MPPT, grid + battery) Off-grid inverter with PWM controller Grid-tie string inverter (no battery) Microinverters (no battery)

Inverter rating (W) Inverter efficiency (%) Max PV input voltage (Voc, V) MPPT min voltage (V) Max PV input current (A) Max PV input power (W)

Battery bank

Chemistry LiFePO4 (90% usable)Lead-acid / AGM / gel (50%)Lithium NMC (80%) Battery voltage (V) 122448 Capacity per battery (Ah) Total batteries owned In series In parallel

Appliances and lights

Add a common appliance... Refrigerator (150 W, 35% cycle) Freezer (200 W, 35% cycle) LED lights (10 W) TV (100 W) Laptop (60 W) Ceiling fan (70 W) Water pump (750 W) Washing machine (500 W) Microwave (1200 W) Air conditioner (900 W, 50% cycle) Router and modem (15 W)

Total per day0 kWh

Use this list for daily kWh and peak load

Hours per day is how long the appliance is switched on. Cycle is the share of that time it draws full power, for example a fridge compressor at about 35%. Peak load adds up every row marked "Peak", so untick appliances that never run together.

Energy needs and site

Daily use (kWh/day) Peak load (W) Peak sun hours System losses (%) Days of autonomy Coldest temp (°C)

Panel arrangement

Panels in series (per string) Strings in parallel

Results

Saves your configured design, with every input and result, as a PDF headed with the LearnEaseGuide logo and name.

Disclaimer: This calculator is provided for general reference and education only. Results are estimates based on the values you enter and simplified assumptions (system losses, temperature effects, battery usable capacity, fuse margins). Actual performance varies with site conditions, shading, equipment and installation.

It does not replace a site assessment or the manufacturer's datasheets. Have your final design, wiring, fusing and protection reviewed by a qualified electrician or solar installer, and follow your local electrical codes and regulations. Use of this tool is at your own risk, and no warranty is given.

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.

1. Required array: 4,650 Wh / (4.5 x 0.78) is about 1,325 W of panels.
2. With 400 W panels, that is 4 panels.
3. 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.
4. 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.

How to Size a Solar Battery Bank

A solar battery bank stores the energy your panels make so you can use it at night and on cloudy days. If it is too small, you run out of power. If it is too big, you waste money. This guide shows how to size it step by step, with a formula, examples and a calculator you can export to PDF.

The formula

Battery energy needed (Wh) = Daily Wh x Days of autonomy / (Usable depth of discharge x Inverter efficiency)

Battery bank Ah = Battery energy needed (Wh) / Battery bank voltage

• Daily Wh: your total daily energy use.
• Days of autonomy: how many days without sun the batteries should cover. Many homes use 1 to 3.
• Depth of discharge (DoD): the share of the battery you can safely use. Lithium iron phosphate (LiFePO4) is often about 80% to 90%, while lead-acid is usually limited to about 50%.
• Inverter efficiency: typically 90% to 95%.
• Battery bank voltage: 12 V, 24 V or 48 V, set by your inverter.

Worked example

You use 5 kWh (5,000 Wh) per day and want 1 day of autonomy. Your inverter is 93% efficient, and the bank is 48 V.

• LiFePO4 (90% usable): 5,000 / (0.9 x 0.93) = about 5,970 Wh. At 48 V, that is about 125 Ah.
• Lead-acid (50% usable): 5,000 / (0.5 x 0.93) = about 10,750 Wh. At 48 V, that is about 225 Ah.

The lead-acid bank needs nearly twice the capacity for the same usable energy, which is one reason many people choose lithium despite its higher price per battery.

Try the solar battery bank calculator

Enter your daily or monthly energy use, days of autonomy, battery type and voltage. The calculator gives the battery energy needed, the Ah at your bank voltage, and how many batteries to connect in series and parallel. You can export the result as a PDF.

Solar Battery Bank Calculator

How big should your battery bank be?

Your numbers

Choosing a battery type fills in a typical usable depth of discharge. You can change it. Always match the bank voltage to your inverter.

Result

Checks

Bank size at different days of autonomy

Battery Wh = Daily Wh x Days / (DoD x Inverter efficiency). Ah = Wh / bank voltage. Batteries in series = bank V / battery V, in parallel = bank Ah / battery Ah, both rounded up. Estimates only. Have your final design reviewed by a qualified electrician or installer.

Choosing the system voltage

Higher voltage means lower current, which allows thinner wire and less loss. As a common rule of thumb:

• 12 V: small systems, roughly up to 1,000 to 1,500 W.
• 24 V: mid-size systems, roughly up to 3,000 W.
• 48 V: larger home systems above about 3,000 W.

Always follow your inverter's required battery voltage.

Series and parallel

Connecting batteries in series adds voltage and keeps the Ah the same. Connecting them in parallel adds Ah and keeps the voltage the same. For example:

• 4 x 12 V 100 Ah in series = 48 V, 100 Ah (4.8 kWh).
• 4 x 12 V 100 Ah in parallel = 12 V, 400 Ah (4.8 kWh).

The total energy is the same. Use identical batteries of the same age and type, and follow the manufacturer's limits on how many can be connected.

Lithium vs lead-acid

	LiFePO4	Lead-acid
Usable capacity	About 80% to 90%	About 50%
Cycle life	Often several thousand cycles	Usually a few hundred to about 1,500
Weight	Lighter	Heavier
Upfront cost	Higher	Lower
Maintenance	Very low	Some types need watering

Tips

• Check the maximum charge and discharge current of your battery against your array and inverter.
• Leave some spare capacity, because batteries lose capacity as they age.
• Protect the bank with correctly sized fuses or breakers close to the battery.
• Cold weather reduces battery performance, especially for lead-acid, and lithium should not be charged below freezing unless it has built-in heating.

Try it yourself: Skip the math with our free solar system calculator. Enter your appliances and equipment and get instant results.

Disclaimer: This article is for general information and education only. Numbers are estimates and examples, not a certified design. Have your final solar design reviewed by a qualified electrician or installer and follow your local electrical codes.

How to Calculate Appliance Watt-Hours and Daily kWh

Before you can size a solar system, a generator or a battery, you need to know how much energy your appliances use each day. That number is measured in watt-hours (Wh) or kilowatt-hours (kWh). This guide shows how to work it out for any appliance in a few minutes.

Watts vs watt-hours

Watts (W) measure how fast an appliance uses power at a moment in time. Watt-hours (Wh) measure how much energy it uses over time. A 100 W bulb running for 1 hour uses 100 Wh. Running for 5 hours uses 500 Wh. And 1 kWh equals 1,000 Wh.

The formula

Daily Wh = Watts x Hours per day x Quantity x Cycle

• Watts: the appliance's power draw.
• Hours per day: how long it is switched on.
• Quantity: how many identical units you have.
• Cycle: the share of the time it actually draws full power, written as a decimal. Use 1 for items that run steadily, like lights. A fridge compressor is about 0.3 to 0.4 because it switches on and off.

Where to find the watts

• The label or manual: look for "W" or "watts" on the sticker or in the specs.
• Amps and volts only? Multiply them: Watts = Volts x Amps. A 120 V appliance rated 5 A is about 600 W. For a 230 V appliance rated 2 A, it is about 460 W.
• A plug-in power meter: the most accurate method. It shows real watts and total kWh over days. These meters are inexpensive.

Labels often show the maximum power, so real use is frequently lower.

Example: a small home

Appliance	Watts	Hours/day	Cycle	Wh/day
LED light	10	5	1	50
TV	100	4	1	400
Laptop	60	6	1	360
Refrigerator	150	24	0.35	1,260
Ceiling fan	70	8	1	560
Microwave	1,200	0.3 (18 min)	1	360
Total				2,990 Wh = about 3 kWh

That is about 3 kWh per day, or roughly 90 kWh per month.

Try the daily energy calculator

Add your own appliances below, or pick from common ones. The calculator works out the Wh for each row, your daily total in Wh and kWh, and your monthly kWh. You can export the result as a PDF.

Daily Energy Calculator

Add your appliances and get Wh and kWh per day

+ Add a common appliance...

Wh / day0

kWh / day0

kWh / month0

Cycle = share of time the appliance draws full power (1 for steady loads, about 0.35 for a fridge). Estimates only. Have your final design reviewed by a qualified electrician or installer.

Using your electricity bill

If you only want a rough total, your bill shows kWh used per month. Divide by 30 for a daily figure. For example, 450 kWh per month is 15 kWh per day. A bill is a good way to check that your appliance list adds up.

Common mistakes

• Forgetting standby power: chargers, routers, TVs and set-top boxes draw small amounts all day. Add them up.
• Treating a fridge as always on at full power. Use a cycle value or measure it.
• Ignoring start-up surge: motors like pumps and compressors can draw 2 to 3 times their running watts for a moment. That does not change daily Wh much, but it matters for sizing an inverter.
• Using summer numbers only. Heating, cooling and lighting change by season.

Next step

Once you have your daily kWh, you can work out how many solar panels you need and how big your battery bank should be. Read our guides: How Many Solar Panels Do I Need? and How to Size a Solar Battery Bank.

Try it yourself: Skip the math with our free solar system calculator. Enter your appliances and equipment and get instant results.

Disclaimer: This article is for general information and education only. Numbers are estimates and examples, not professional advice or a certified design. Have your final design reviewed by a qualified electrician or installer and follow your local codes and utility rules.

Series vs Parallel Solar Panels

When you connect more than one solar panel, you choose between wiring them in series, in parallel, or a mix of both. The choice changes the voltage and current of your array and decides whether your inverter or charge controller can handle it. Here is how it works.

The Basic Rule

• Series: connect the positive of one panel to the negative of the next. Voltages add, and current stays the same.
• Parallel: connect all positives together and all negatives together. Currents add, and voltage stays the same.

The total power in watts is the same either way. You are only choosing how to split it between volts and amps.

Example with four panels

Take four identical panels, each 400 W, with Vmp 37 V, Imp 10.81 A, Voc 45.2 V and Isc 11.4 A.

Layout	Vmp	Imp	Voc	Isc
4 in series (4S)	148 V	10.81 A	180.8 V	11.4 A
2 series x 2 parallel (2S2P)	74 V	21.62 A	90.4 V	22.8 A
4 in parallel (4P)	37 V	43.24 A	45.2 V	45.6 A

All three give 1,600 W, but they suit very different equipment.

Series: pros and cons

• Pros: lower current, so thinner and cheaper wire and less loss over long cable runs. Needed for MPPT inverters that want a higher voltage.
• Cons: the voltage can exceed your equipment's limit, and one shaded or faulty panel can drag down the whole string.

Parallel: pros and cons

• Pros: a shaded panel affects only itself, and the voltage stays low, which suits 12 V and PWM systems.
• Cons: high current needs thick wire, and a combiner box or fuses are needed, especially when you have three or more parallel strings.

Check the cold-weather voltage

Panel voltage rises as temperature drops. To check your limit, correct Voc for your coldest day:

Cold Voc = Voc x (1 + temperature coefficient x (coldest temp - 25))

With a coefficient of -0.27% per degree C and a coldest temperature of -5 C, the factor is 1 + (-0.0027 x -30) = 1.081. One panel's Voc becomes 45.2 x 1.081 = about 48.9 V. Four in series reach about 195 V. If your MPPT controller allows 150 V maximum, then 4 in series is too many, but 3 in series (about 147 V) fits.

Choosing a layout

1. Find your equipment's maximum input voltage, minimum MPPT voltage and maximum current.
2. Pick the number of panels per string so the cold Voc stays under the maximum and the hot Vmp stays above the minimum.
3. Add parallel strings until you reach the power you need, while keeping total current within the limit.
4. Use matching panels in each string. Mixing different panels in series limits output to the weakest one.

Try the series vs parallel calculator

Enter your panel datasheet values and your equipment limits below. The calculator checks cold-weather voltage, shows every layout for your panel count, and lets you export the result as a PDF.

Series vs Parallel Array Calculator

Check voltage, current and cold-weather limits

Panel specs (from the datasheet)

Conditions and equipment limits

Your layout

Array result

Safety checks

All layouts for the same number of panels

Leave a limit blank to skip that check. Hot Vmp uses the Voc coefficient as an approximation. Estimates only. Have your final design reviewed by a qualified electrician or installer and follow local codes.

Tips

• Avoid shade where you can. If part of the array will be shaded, consider separate strings or microinverters.
• Use PV-rated cable and connectors, and fuse or protect parallel strings as required by code.
• Never mix panels with very different voltages in the same string.

Our MPPT vs PWM guide explains how your controller type affects this choice.

Try it yourself: Skip the math with our free solar system calculator. Enter your appliances and equipment and get instant results.

Disclaimer: This article is for general information and education only. Numbers are estimates and examples, not professional advice or a certified design. Have your final design reviewed by a qualified electrician or installer and follow your local codes and utility rules.