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Campervan Solar System Calculator

Watt Calculator (Amps x Volts = Watts)

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List Your Devices

Enter number of Watts each device uses and your estimated max hours of use per day. Click the to add a new row. Click the to delete a row. Select whether your device is DC powered or will be using an AC inverter.


Estimated Watt Hours

This is the maximum power you will expect to use on any given day. If using heaters and fans, it is helpful to do a calculation for a winter month and a summer month (including sun hours below) and use the larger of the two.

Daily Power Usage


12V Battery Size

Battery Type

Select whether or not you will be using a Lead-Acid (AGM) or a Lithium battery chemistry. AGM batteries wear out quickly if you use more than 50% of their charge, so they require a larger battery bank to compensate.



Solar Panel Size

Recommended Min Solar Watts

This is the fewest recommended solar power based on the daily power usage and battery size. Check out the FAQ for info on charging while driving and upgrading panels. PWM charge controllers are much cheaper but less efficient than MPPT technology, so they take more minimum solar watts to charge the batteries.

Charge Controller Type:
Estimated Sun Hours:
Solar Watts (PWM)


Charge Controller Size

MinimumCharge Controller Size

This is based on your solar panel wattage. It is the smallest size charge controller that you will want to use. Going smaller will be giving up power from your panels. Remember to check the requirements of your specific charge controller to make sure it will work with your panels before buying it.

Min Charge Controller


Inverter Size

Recommended Max Inverter Size

This is based on your battery size and is a recommendation of max discharge rate from your devices. If it is significantly lower than your needs, consider getting a larger battery bank to compensate. See the FAQ for further reading on running a larger inverter.

Max Inverter


Your Solar System


12V Battery


Min Solar


Charge Controller


Max Inverter

Recommended Brands


Lithium: Battle Born

Solar Panels

Option: Mighty Max
Option: Renogy

Charge Controller

Standard PWM: Anself
Budget MPPT: Renogy
Premium MPPT: Victron


Pure Sine Option: Wagan
Pure Sine Option: Novopal

Battery Extras

Battery Isolator: Blue Sea Systems
B2B Charger: CTEK


Battery Monitor: Bayite
Fuse Box: Blue Sea Systems

Frequently Asked Questions

How Do I Use This Solar Calculator?

  1. Make a list of your devices
  2. Enter the watts for each device
  3. Enter your estimated hours of use
  4. Select whether it is an AC or DC powered (AC uses an inverter)
  5. Choose which battery type you want to use
  6. Choose your charge controller type
  7. Enter your estimated sun hours (direct sunlight you expect on the panels)

How do I find the Watts of my device?

In most cases you can find the Watts listed online, in the owner’s manual, or on the product itself. In some cases, a product will list Amps and Volts instead.

Remember: Amps*Volts=Watts

If you still don’t know how to find these numbers, read our article on calculating your power usage for each electronic device for some tips and real-world examples.

What if I know my total Wh and just want to get calculations for components?

You can enter it as one component line. Type in your total Wh for “Watts” and 1 for “Hour” and the rest of the calculator will function as normal.

Why is my solar system so big?

You are probably still planning to use power like you would in a house. Living in a van requires cutting down on unnecessary electronics as much as possible. The size of your system is directly related to cost. Here are some tips to cut back on electronic use.
Some general rules to follow are:

  • Aim to use as many 12v DC powered electrics as possible
  • Cook efficiently – fuels like propane and butane will make your system smaller than cooking with electricity. Try to cut back on induction burners, coffee makers, crockpots and other high-energy devices
  • Make sure you have the correct hours listed for your refrigerator and electronics. Your fridge will not be running 24 hours per day. In cold weather, a the compressor in a fridge may only be on 2-4 hours per day. In hot climates it may be running as many as 8-16 hours. Similar to laptops and induction burners; they are not usually running at their max rated watts.
  • Look back at your components. See what is drawing the most power and look at ways to reduce or eliminate it.

How much does AC vs DC power change the numbers?

We based our calculations on a 10% efficiency loss that occurs when using an AC inverter.

What is the difference between AGM, FLA and Lithium Batteries?

There are many differences between these batteries. But the main difference (as it relates to this calculator) is the depth of discharge – DOD.

A lithium battery can be safely discharged up to 90% without shortening its lifespan. AGM and FLA batteries should only be discharged up to 50%.

Because of these discharge rates, you will need a larger AGM or FLA battery for your system than you would with Lithium. You can read more about batteries here.

Can I also charge batteries using my vehicle?

Yes! Absolutely, and it is recommended to supplement any solar system unless you plan on driving infrequently. The best option is a battery to battery charger, many of which double as a charge controller. A cheaper option is to go with a battery isolator.

What is the difference between a PWM and MPPT charge controller?

The difference lies in efficiency. A PWM controller uses less complicated and less efficient technology. With that said, for smaller 12V systems, it is often advisable to get a PWM controller and more solar panels get more bang for your buck. We recommend reading our post on charge controllers for more information.

Can I get a bigger charge controller and add more solar panels later?

Yes, this component can benefit from upsizing if you’re not sure if you’ll need more solar or not. With that said, it’s usually a lot of work to add more panels on the road so we like doing them all at once. Check out our article on charge controllers for more in-depth info.

What number should I use for Sun Hours?

The amount of power you get from the sun is determined by how much direct sunlight your panels get. If you are in the sun more often, then you need fewer panels to charge your batteries.

Basing your calculations at 4 sun hours is a good conservative estimate for most van dwellers’ varying lifestyles. If you have tilt-mounted panels or are mostly living in a sunny place like Arizona, then you might need less solar watts because you’ll be getting 5-8 hours of direct sunlight. You are welcome to play around with this number, and even combine it with your winter/summer total watts to see what a comfortable system size is for you.

Do I need an inverter?

No! If you don’t have any AC electronics you do not need an inverter, saving some money and efficiency.

How much lower than the max inverter size should I go?

As a general rule, smaller inverters are more efficient. If the biggest item you will be running is a 150W laptop, then getting a 1000W inverter is a waste of money and efficiency. Go with the smallest inverter that you will need with a bit of wiggle room. In this example, a 200W or 300W inverter would be fine for a 150W laptop.

Why is my inverter sized so small? I see other people recommend 1000W+ inverters all the time with a small battery bank.

Battery life is affected by how quickly you are using power. This is relative to how much total capacity the battery has, so larger batteries can discharge more quickly (hence a larger inverter). If you occasionally are using more power – such as a hair drier for a few minutes once a week – then you won’t be doing too much damage to your batteries. But if you’re twice daily using a 1200W induction burner, you’ll want a large battery bank to handle the heavy loads or else will be replacing your expensive batteries quickly. Read our article on inverters for more information. As a side note, the discharge capabilities of lithium batteries are significantly better than those of AGM or FLA.

Why didn’t you list ALL of the components I need? Wires, Fuses ect.

Your wire size is going to vary greatly depending on how far you are running them. Read our wiring guide for more details on how to size your specific system. It is difficult to predict how much wiring each different van build will have and the lengths needed, and we don’t want to have you ordering things that you don’t need.

Ok I got everything, now how do I put it all together?

Awesome! Pick the solar panel wiring guide closest to your numbers and get started! If you want more information on electricity, head over to our electrical home page.

This calculator is awesome! How can I support it?

Thanks! We fund our effort and research through affiliate links and advertising, so just by being here and using the site you’re thanking us. We want to share access to this amazing lifestyle with as many people as possible so this is our contribution.

That said, if you want to give us an extra boost, order your products through our Amazon Links!

Visit for more information

This interactive campervan solar panel calculator is a must save for anyone who wants to build a campervan conversion for #vanlife Just put in your electronic devices and it will tell you what size solar system you need, battery size, inverter size, charge controller type and more! Add everything from bathroom and kitchen appliances to adventure equipment. It even gives tips tricks and hacks to layout your solar kit!
This Post Has 5 Comments
  1. Thank you for such a well laid out info site, W/ LINKS! I’m using 2- 100 Ah AGM battery’s that I’ve wired together in paralell w/ 2, 8 gauge cables. I’m WAY over powered as I only use 3 low wattage fans and recharge my tablet and phone. I recharge with a NOCO GENIUS that i hook up and plug in at work, which is an amenity they allow, a grace of God really. I’m looking to eventually hook up a refigerator/ freezer, around 25 quarts? Hence the large batts. I reside in my van all year when not at my sister’s down the street. I’m able to save alot of money on rent this way, and thanks to being knowledgeable about electricity/electronics, I’m very comfortable.

  2. Great article Very good explanation of solar basics. I would like to know how I add alternator charging as I drive as well as shore power charging at RV parks. Also any tips on mounting ridged palels to roof. Is some type of rubber flex system a good idea?

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