Sizing Your Solar
We all dream of solar panels at night when we think of our first conversion. It's exciting to learn and work with solar, and we can feel it when we talk with clients. We sometimes hear people say they "need 3000 Watts of solar panels" for their "basic electrical needs." Others say they "don't need solar power at all" because the van already has a battery.
Before rigging your van like the Millennium Falcon, let's figure out the basics together.
DAILY POWER DRAW
Without this information, there's nothing we can talk about, really. The first thing you need to do is figure out how much power you need in a day. To do that, you need to:
Make a list of all the electronic components in your van,
Find how much current each component uses, in Amps.
Write down how many hours a day you use each component,
Multiply each component's current by the number of daily hours use to have a number in Amp-Hours.
For example:
I have a Maxxair fan. (component)
The Maxxair fan draws a current of 2.8 Amps when it's on level 10. (current)
I use it for around 10 hours every day. (time)
This component draws 2.8 Amps x 10 hours every day = 28AH.
Repeat for every component and add all your numbers.
You will have your daily AH consumption. Write it down. Let's say we have 100 AH daily for your build.
INVERTER SIZE
People seem to compete for the largest inverter size possible. Let's remember those machines draw current as well, even if they provide you with alternative current (AC). To figure out the ideal inverter size, add the maximum power (in Watts) that you need for components that you use simultaneously.
For example, many people power laptops while using another cooking component:
MacBook #1 = 87W.
MacBook #2 = 85W.
Magic Bullet Blender = 250W.
TOTAL = 422W.
For basic stuff like the ones listed above, a 1000W inverter charger would be enough. If you plan on using an induction cooktop (1800W) while cooking with a microwave (1200W), you would need a minimum of 3000W or more if you don't want to blow up your van every time you cook.
BATTERY BANK
Your battery bank can be recharged by other power sources than solar, including your van's inverter (while you drive) and shore power (when you are plugged in). The remaining question here is: how many days without solar are you comfortable living with? This will give you an idea of how big your battery bank needs to be if you don't drive or plug in for several days.
Let's say you want enough batteries for 3 days without sun, driving or shore power (ideal scenario).
Based on your calculations for step 01 (Daily power draw), let's say you ended up with a daily consumption of 100AH. A simple way to calculate your battery bank capacity would be to multiply the daily consumption by the number of days of autonomy you need.
Example:
3 days of autonomy
100 AH of consumption per day
3 days x 100 AH = 300 AH battery bank.
*This ideal 300 AH needs to be multiplied by 2 if you have AGM batteries because their depth of discharge is only 50%. So 600 AH with AGM batteries.
*This ideal 300 AH needs to be multiplied by 1.25 if you have Lithium batteries because their depth of discharge is a good 80%. So 375 AH with Lithium batteries.
In this case, we would recommend going with solid 400 AH of Lithium batteries. A setup like this would do the trick in any scenario, considering you also have two other recharging methods (alternator and shore power).
SOLAR PANELS
Remember, available solar energy varies enormously depending on where you live, where you park, the weather, the shadows around your van, etc. In general, you need 4 Watts of solar panel to gather 1AH every day.
Based on your (fictional) 100 AH/day, you would need around 400 Watts of solar panels to use your van's electrical components on a sunny day:
100 AH daily x 4 Watts = 400 Watts of solar panels.
WRAP UP
See, nothing too complicated, even if it sometimes feels like an advanced physics class where you probably took a nap in college:
1- Find your daily power draw,
2- Choose an inverter that suits you well,
3- Set up a battery bank size that will sustain you when the sun disappears,
4- Choose your solar panels accordingly.
Considering you are charging while driving with your alternator AND charging with shore power once in a while, your solar panels are essential but far from being the only lifeline you have. When it comes to off-grid electricity, a little planning is good enough to start.
And if you want to rig your van like the Millenium Falcon because of the big toys you have, we'll gladly help you do that.
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