Getting started with solar power

May 9, 2019

Let’s do some math!

One of my top priorities is solar. As I am a bit of a geek, I want to be able to power all of my gadgets. Top priority is my camera, and my drone. Both need 230V… challenge, more on that later. Solar panels have been big in the van community for a long time, and I am not the first one to do this.  They are efficient, relatively cheap, and provide enough power to stay off the grid for days on end. 

First step in building your solar setup is calculating how much you will actually consume during the day (and night). lets say you want a basic setup.. just some lights and a 12v usb charger… Easy! 1m of led strip consumes about 8 Watts. So lets average it out on say 50 Watt (couple of meters LED strip and that usb charger). That means if you leave it on all the time (24 hours) you consume 1200Watts (24*50). Now this doesn’t say much about battery capacity doesn’t it? Most manufacturers label their batteries with Amps. The amount of amps is the maximum capacity that battery stores… because a battery is 12v we have to convert the 1200watts we just calculated. The rule to do this is P=U*I (power = voltage*current. Now we don’t have our current so we have to switch the formula I=P/V in our case that gives us I=1200/12=100A. So now we have the maximum capacity we need , to power this setup for 24 hours without charging the battery we need a battery that is at least 100A. Now this isn’t realistic, leaving the lights on for 24 hour who does that? Lets take an average of 8 hours of usage per day (8*50 =400 Watt). Again calculate that with the formula and you get I=400/12 = 33A if you take the same 100A battery you have enough capacity to last you for 3 days!! 

Now just having a battery that lasts 3 days and then is just sitting there empty is pretty pointless. The whole point of this project is to have it recharge itself during the day when there is sunlight. You actually don’t need direct sun, daylight is enough to power a solar panel. Daylight isn’t going to be as efficient as sun but better than nothing right 😉 Calculating how much solar power you need is basicly the same as calculating power usage. Take lets say a 100W panel and you get 5 hours of sun per day (direct sunlight, so in BEST case). That will give you 500Wats of solar. As we calculated before our daily usage is 400 watt, that meas we have 100wats overcapacity! Perfect! This way you can easily (roughly) calculate how many panels you will need. 

Parts

Every solar setup needs some basic parts, you cannot connect your panel straight to your battery etc… that would actually be pretty dangerous. This solar panel is an example, my solar panel you cannot buy online. This example is 160w and comes with 5m of solar cable! 

Solar panes have these special connectors that click into each-other, this is to ensure that they always have a good connection. You only need these connector on one side. Controller side is just a screw connection. 

I went with the victron 100/20, 100 means maximum panel voltage and 20 means maximum charge current. One panel is on average 35volts (two panels in series is 70v), I overcapacitated because I might upgrade to more panels in the future. 

Placing the panels

Every placement for a solar panel is going  to be different, hell you even could’ve bought one of these flexible solar panels. Because my sprinter is pretty large, i have a lot of space on the roof to put a panel. That the reason I bought a bigger panel. Actually its the same size as the solar panels people put on the roof of their houses.

The panel is not 100% centered, this is due to how the van is build. The width of the panel is just a tad too small to perfectly fit between the lumps of the roof, so the offset is about 2cm which is not that big of an issue. 

Now for the difficult part.. how am  going to attach this big panel to the roof? I first got aluminum brackets and attached them to side of the panel with self drilling screws. 

Now i have some options, I could drill holes in the roof and bolt it down with silicone… that brings a higher risk of leaks. I could screw it down but that leaves with the same risk… Solution? VHB tape. VHB tape is double sided tap that becomes a chemical bonding. Is so strong that this stuff is being used to glue windows onto skyskrapers. 

I went with 3M VHB 5952F this is one of the strongest versions you can get, its not mandatory but the price difference is so small i just bought this stronger one.

It is not nessesary to prepare the two metals, I did it anyway just to be sure that I had a clean surface to start from. I sanded down the metal brackets and the surface of the roof. Cleaned it with isopropylalcohol to make sure that no grease was remeaining. Now use some silicone to keep moisture from going underneath the brackets and weakening the VHB tape.

SET IT UP 

  1. Install the batteries in your van (this is dependent on the type of van, RV, truck you have). 
  1. Install charge controller in a convenient place. In my van I installed it underneath the bed against the side of the wall. 
  1. Using the cables connect the positive terminal of the battery to the positive battery terminal on the charge controller, do the same with the negative terminals. 
  1. Put the panel anywhere you want (on the roof requires drilling a hole in the roof and some VHB tape) 
  1. Its time to connect the solar panel to the solar charge controller, make sure you have the polarity correct of the panels!!! measure this with a voltmeter!! then connect them to their respective terminals 😀 + and – 😉 

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