In the course of our RV plans my wife and I talked about the possibility of boondocking. For those that don't know boondocking is taking an RV camping without the comforts of a park. The only water is what you bring with you and the only electricity is the electricity you can generate.
This can be a costly and limited proposition. However the advantages of being able to take your home while you job hunt can not be understated, and not everywhere we would be applying had nearby parks that were affordable. Still, Running a generator full time to power and charge electronics can be an expensive process, not only in fuel costs but also in maintenance costs. Additionally, generators can be a bit loud, and as such ruin the reason people often go boon docking, to go somewhere unnoticed. After some discussion about cost savings and the ability to have longer stays 'out' Stephanie and I agreed to get a solar system up and working on our 1985 Holiday Rambler. After scouring the internet and designing my own setup I compared it to the other available setups that could be purchased.
Here is our build out:
2 x 80 AH Deep Cycle Batteries - $75 ea
2 x 320 Watt 24 volts Residential Solar Panels - $144 ea
1 x MPPT Solar controller rated to 800 Watts @ 12 volts* - $235 + $50 SH
1 x 2000 watt / 4000 watt peak Harbor Freight Modified Sine Wave Inverter
2 x home-made panel tilt mounts. $60 in hardware
When you add in some loose wires and other items it comes to about an $800 system. Lets talk about the components individually then we will move to how they are actually performing. The first thing is that this battery configuration is extremely small, and that is done on purpose.
Battery banks can get very large and very expensive very quickly. Since my wife and I were only concerned with operating a few laptops during solar hours and not an AC or other large devices it didn't make sense to have a huge battery bank. Also for 150 dollars we can abuse (take levels below 50%) without feeling like we are damaging our investment. Further we didn't have to deal with finding new places to store a larger battery bank. This is a corner we definitely cut, but so far we are not sorry about saving the money and hassle. If we were going to full-time boondock instead of periodically this would be a place we upgraded.
Solar Controller. I am really happy with our controller. I found it on ebay and it had a lot of good reviews. It mounted above the driver's seat and basically does a great job of turning solar energy into the proper voltage to charge our batteries. Because its a MPPT it does so in low-lighting conditions as well as direct sunlight. The relationship between the controller and the panels is key for this low-level charging. Notice that the MPPT charger can service a 48, or 24 or 12 volt battery system. Also notice that the panels are producing voltage for a 24 volt system. What that looks like is actually a voltage of about 40v per panel in good sunlight. The panels are wired together in series so that they produce 80v in direct sunlight. This configuration accomplishes 2 things. First the higher voltage means we can keep the wires relatively small, but it also means that even in horrible light conditions we still are producing much higher than the 12V needed to charge batteries. So the worst voltage I have seen was in the fading evening light with only 32v being produced, but we were still charging batteries at 9PM!!! We lose some on capacity because of this configuration but in the Pacific Northwest the low-level charging is much more important.
Solar Panels are the workhorse of the arrangement, and the costs can pile up. Look at the price per watt before making a decision and look into the cost of shipping. Basically you will pay around $1 per watt for premium 12V RV panels. For the two panels I wanted to order the shipping and handling would have been more than the actual panels, but the price per watt was .65. So i drove down to Los Angeles before I left California. When i go back for my van I will swing through and pick up more panels in preparation for expanding our solar array. (2 more which will be in parallel). I do not want to understate the size of the panels.... they are huge. 6 foot by 3 foot or close to that range for mine, if they were 12v panels they would have been half that size. Some things to know when you are purchasing. The rated watts and voltages are under ideal conditions. It is really important to research the area you will be in. For Washington if we are getting 50% of our rated power then we are doing good. This is why I feel comfortable doubling our total number of panels. There is a lot of cloud cover here and we are pretty far north which lowers the productivity of our panels too. If you are building a rig for Arizona you might want to stay well below your controller's rating, for us I feel comfortable unplugging our second array if things get too bright.
The Inverter is the part of the puzzle that I am least happy with. I bought this inverter when my wife and I would periodically camp out of our full-size van. For powering a laptop, or even a coffee maker this inverter did the job well. But this was before I had really invested time into understanding what makes the electrical world go round (generator / sine wave pun). If you don't know about the difference between a modified sine wave and a true sine wave: here. The 4000 watts peak is just a fabrication and there are a lot of devices that buzz really really loudly or flat out will not run with a modified sine wave. Laptops are okay but the power supply in my gaming PC is not having it. Also any computers that require a constant connection like my media server and wifi-unit do not do well with the switching of power sources. So to ease that burden I brought a 1000 watt APC battery backup that has some power regulating/rectifying circuitry. The battery back up does the job and allows me to run sensitive devices and switch between power sources without losing connectivity. This would be another upgrade if we wanted to boondock full time instead of park hopping. The upgrade for a true sine wave inverter would be about $500 and would almost require a battery bank expansion. This is a corner we cut, and since we already had the power supply backup it made sense to use the equipment we already had lying around instead of spending more money on the stuff that wouldnt get used that often.
In term of performance we are able to work and perform the various tasks we need to on the solar set up, even while its raining. What does work mean? It means that we have 2 laptops, a wifi extender and a home server running while we charge our phones and laptops. Other draws on the power are charging up the motor batteries, and running various fans in the coach to keep the temp cool. Periodically we turn on the lights and mechanical pumps. I suspect that we could run the refrigerator off this solar system but its not needed since we have propane available for that chore. Further expansion would be awesome but it is a monetary sink hole that would only be worth-while if we were boon docking full time or needed AC because we were in the south or southwest of the US.