The next question to ask is, how much solar power do I need to generate? What is needed to keep up with my daily power consumption and recharge my batteries to 100% under marginal to good weather conditions every day? Some weeks it is going to be overcast and rainy. This may lead us to shore power (plugging into the grid) but so long as we can get by most days regenerating our power usage daily we should be good for an off-the-grid lifestyle. Once we know the optimal size of our solar system we can start looking for the right solar panels.
Quick Links for this Truck Camper Solar System Series
- Solar System Introduction
- Solar Panels & Charge Controller
- Solar System Pieces
My Solar Calculation
Looking back at our calculated power load (Part 1 of Our Solar System), I figured at 490W/hr maximum that my average would be well below half that. For this reason, I used 200W as my target to get started. 200W/12V = 16.6Amps/hour which is well within the range of my batteries. Still, if this was true with 12 hour nights I would have been pushing past my personal desired 50% level on the batteries. Meaning I would struggle to recoup that amount daily. I thought that it was close enough. If push came to shove we would ration at night. The 330Ah batteries are the largest ones that I am able to fit into our camper so we had to make do.
What this means is that every day while potentially continuing to use 16.6Amps per hour during the day that I would need to also store back 16.6A/hr as well for my max night use. My solar panels needed to be capable of generating 33.2amps/hr or about 400W/hr. Since solar panels aren’t ever going to pull down there max rating, I decided that 400W would be a good starting point for my system but that I would make sure the system was expandable to 600W.
Polycrystalline vs. Monocrystalline Solar Panels
While not all solar panels are the same, they are rated the same way. The rating for solar panels is by how many watts they are capable of generating each hour. There are basically two types of solar panels: polycrystalline panels and monocrystalline panels. Both come in numerous sizes and either rigid or flexible (attached to a hard plastic backing). The monocrystalline panels are supposedly more efficient, but again all are rated by watts/hour. So, if a monocrystalline panel is rated at 100W and the polycrystalline panel is rated at 100W they are capable of generating the same amount of energy per hour. This being said, I fell for the marketing and choose the monocrystalline panels.
Our Solar Panels
I decided because of space and weight that I would go with two 100W HQST monocrystalline lightweight flexible solar panels. I would mount these on the roof of the camper. Initially, I also ordered two 100W rigid portable panels. Portable panels are nice because you can face them towards the moving sun and maximize power generation throughout the day. The earth is really moving and the sun is static, but you know what I mean. However, it also means that while the truck is going down the road, they are stored and no power is being generated. They can also be easily stolen if you aren’t around.
After the two types of solar panels arrived on site, I quickly decided the rigid ones weren’t worth the hassle or weight for our rig. I have a limited amount of space and a certain GVWR (Gross Vehicle Weight Rating) on the truck that I am trying not to exceed. I resold the rigid ones and eventually purchased another three flexible solar panels to give me a 500W solar system. All of them permanently fixed to the roof.
The charge controller is one of the easiest decisions I had to make for our solar system. It can be difficult depending on the desired size of the system. For our small system, there was a clear winner. Tons of bloggers who have built this size system swear by the Bogart SC2030 Charge Controller with the Bogart Trimetric 2030-RV Meter.
I will add to those other bloggers and rave about this product. Bogart has made two amazing devices that pair really well. The controller and meter talk to one another through a standard 4-conductor phone cable (aren’t these extinct?!) :). This allows the user to see power generation and consumption in real-time directly on the meter. The solar controller through the input on the meter does a great job of using the specs for your specific battery and customizing the different phases of the battery. This allows the charge controller to charge the batteries to the battery manufacturer’s specifications. Making sure to reach a max charge in a way that maximizes the longevity of those expensive batteries. These aren’t cheap devices, but some of their competition is way pricier. There are also cheaper charge controllers out there but why get chintzy on something that maintains your super expensive batteries.
Like I said in the video on the first page of the post, the only issue that I have had with this system was the phone cable not being manufactured correctly. The 4-conductor cable is how the meter talks to the charge controller. The charge controller was working, but I had no way to see what it was doing. It was an easy fix and I am sure that this isn’t a common issue. I just had bad luck of the draw.