How much solar power do I need

In this short post, I will help you find out, how much solar power suits your purpose best. It's mainly focused with a campervan in mind, but will also apply to small stationary setups like a small off-grid cabin.

TL:DR

If you are the lazy type of a person and you just want a solar system on your van without thinking too much, here comes my TL:DR solar advice: For small to midsized campers like a VW van, a Ford Transit, or even the small Sprinter from Mercedes, just go with a 200 Watt system. This will suit most people with this kind of vans and an average energy need. You can power a fridge, some chargers for smartphones and laptops, and some lights in the van easily with this setup. To achieve this you need Solar panels with a 200 Watt Peak, in most cases 2 panels with 100Wp each, a charge controller with 10A, and some 6mm² cables if you connect them in series. Boom, that's it. 🔥

If you like to know why this is the case, read on and find out how to calculate your system yourself.

Where to start

To find out how much solar power is needed is not that hard. Basically, you only need to know how much energy you will consume in a certain amount of time and where in the world, and when during the year your setup will be used most of the time. Location and usage during the year are important because the sun is not delivering the same amount of energy during a cold cloudy day in fall in Norway compared to a sunny day in summer in the south of Spain. But more on that later.

Add up your needs

The formula is pretty simple. Add up the power consumption of all electrical devices during one day and your good to go. Wait what? But how? you may ask now. Easy: On basically every device, or on the charger if it is external, is written down how much power (measured in Watt) it needs. Just follow the next 5 simple steps and you're done:

1. Find all electronic devices you will use.
2. Check how much power this device uses (sticker on the device or on the charger)
3. Think about how many hours you will use this device during a typical day
4. Multiply the Watt with the hours you will use the device => you will have the Watt-hours (Wh) which measures the power consumption
5. Sum up all the Wh values you got to get the final global power consumption of your setup for a day

If you can not find any hints on the device about power try the manual or consult Mr. Google.

Find out the needed solar power

To calculate this very accurately we need to consider a lot of things and it gets super complicated quickly. Because of that, we'll calculate with some default and practical values. For most people, this will give a first impression of how big your solar setup should be.

Now that we understand how much energy we will consume with our off-grid setup, you need to know where and when during the year you will use your setup most. If you use it only in the summertime you can make it a little smaller. If you use it all year round and live in northern Europe for example, you need to make it bigger. To find out how much energy you can get in your area, head over to globalsolaratlas.info and search for your location. It does not need to be super accurate, as you will travel around with your camper anyway.

When I do this for Basel, a city in Switzerland pretty much in the middle of Western Europe, I get a value of 3.184kWh/m² of potential energy per day over the year. The rule of thumb is, that 2/3 of this energy will hit the ground in the 6 months of the summer half year.

The capacity of solar panels is typically measured in Watt Peak. The measurement means, that the panel can deliver 100W when:

• The sun delivers 1.000 W/m²
• Modultemperatur is 25 °C

We get the same energy when we assume that only 3.184h of sunshine is available with the Watt Peak measurement of 1.000 W/m² from our panel. Now it's super easy to calculate the daily potential during the year.

This means we can just divide our energy needs in Wh we summed up earlier by the kWh/m² value. This will result in a very rough number of Wp you need on your roof.

needs: 560Wh
location: Basel - 3.184kWh/m²
calculation: 560 / 3.184 ~ 175

In the scenario above I would tend to go with a 200Wp setup at least (you can never have too much solar power, never). This should be solid to compensate for your daily power needs.

In the winter months, you will maybe not get enough energy with this 200Wp, in summer though the batteries will be fully charged all the time.

It's a starting point to find out if you need a 100Wp panel on your roof or 5 of them. These calculations are not an exact science, but more of a rule of thumb but with real localized data.

Now it is time to buy some panels? I made really good results with panels that use cells from Sun Power. It's a company from the US and we use panels with Sun Power cells for years now, never disappointed. Following a list of products, we use in our van, which I can recommend. All links lead to Amazon DE from the Offgridtec store, an excellent source for solar products.

Panels

Charge controllers

I love products from Victron Energy. A lot of devices have built-in Bluetooth so that you can connect them with your Smartphone. On the Victron app, you can monitor your system and keep track of your loads.

Batteries

Again, I can recommend Victron Energy products, also for batteries. Here you find a Lithium battery, but also the cheaper AGM and Gel batteries are top notch.

Complete system

If you like the "carefree package", you could go for a complete system from Offgridtec. They include everything you need, also for mounting them on your vehicle. Everything is included except for the battery; you don't need to hassle calculating cable diameters and stuff. I link a 200WP system which is ideally suited for a VW bus with average energy needs.

If you have any further question or if you want to connect, send us a DM on Instagram @oh.north or send us an email to hello@northway.blog