Our Solar Setup
Original Story 10-29-04 updated 2/23/07
Solar Charging System is On Order!
Today I ordered a solar panel system to charge our batteries during extended boondocking. I researched this for several months and finally decided on a kit from RV Solar Electric. We're getting two 120watt Kyocera panels with tilt mounts and a SolarBoost2000e controller. I selected the panels because of their low cost per amp compared to smaller panels, and chose the SolarBoost controller for it's MPPT technology that improves the utilization available voltage produced by the solar panels.
Conserving Battery Power
When we're boondocking we need to be 100% energy self sufficient, and we'd REALLY like to be able to achieve this without running the generator! To achieve that goal our solar panels must replace all the energy we use from the batteries every day. One 120 Watt panel can provide about 40 Amp/Hours of power a day. With two we get 80 AH, and with the SolarBoost2000 we're hoping for another 15%, taking us up to 92 AH daily.
We estimate that our computers and Datastorm will take about 50 to 70 AH each day, and that doesn't leave much for running a fan, or a reading light, or watching TV. My original estimate was for us to use around 120 AH daily, so we'd have a deficit of around 24 AH. That meant we'd have to reduce consumption. Of course, we could just buy a larger system -- but a 120 watt solar panel is about $500. So, where do we start to conserve? I heard about LED light bulbs on an RV forum www.rv.net/forum so I looked for more info on the subject.
Did you realize that a standard little 12 volt, 1141 bulb in your RV uses 18 watts! That's about 1.5 amps! So if you burn just 4 of those 5 hours a day that's 30 amp hours! In contrast, a similar bulb made with LEDs would use only about 200 Milliamps! The same 4 bulbs can burn 5 hours a day and only use 4 AH of juice. WOW. So I ordered a few sample bulbs from Superbright LED's to test them out and see how they perform. I'll report back. (click here for update, disappointing results)
11-7-04 through 11-8-04
On Friday the solar panels arrived and yesterday we worked all day on installing them. It seems every time I do a project I spend 1/3 of the time running around buying supplies, 1/3 of the time scratching my head and trying to figure out how to proceed, and only 1/3 of the time actually doing the project. This one is no exception. On the bright side, I've found a convenient excuse to buy three tools! It's always a good thing to have more tools. :-)
Here's the parts list for this install:
Everything else I had to go out and buy...
Two items were difficult to find. One was the dielectric grease. They didn't have it at Radio Shack (2 stores) or at Home Depot. Finally stopped at Discount Auto Parts and they had it in 1/4 ounce foil packs, and 3 ounce tubes. I bought a tube. Another item that is difficult to find are spade lugs for #6 wire that will fit on a standard screw terminal. Never found what I really wanted, and I may eventually have to "step down" to #10 wire for about 12 inches and connect that to the controller. Some of you are thinking this wire size step-down is bad. Not so. I'm not running #6 wire for it's ability to carry a large current load, I'm using it to avoid voltage loss in the long run from controller to batteries. The max current will be 25 amps, so #10 wire can easily handle this for a short distance. Remember, the cable supplied with the kit for use on the roof is #10.
Well, it took until noon to visit 5 stores and buy all the parts. Back home, eat lunch, then about 1:30 PM finally started assembly of solar panels. I pre-assembled the mounting hardware to the panels on the ground, then took the first panel up to mount it. Immediately noticed a problem. The screws went into the roof way too easy! I thought I had at least 1/4 inch or 3/8 inch plywood under the rubber roof, but I drilled a test hole and it seems it's only 1/8 !!! Way too thin for my liking. What to do? I decided to use the expanding anchors for hollow walls. Went to Home Depot and bought some, and they seem to anchor it down well. Spreading out the load so it's not just a few threads of a screw in 1/8 inch plywood!
Example of anchors used in hollow roof
Next I took a break from the roof and ran all the wire. I estimated 25' of wire needed from controller to battery, and bought 40'. Good thing because it took every bit of 30 feet. Note, this was run to the factory front mounted batteries and was far from ideal. Later I relocated the batteries and shortened this cable significantly. Controller mounted beside the refrigerator in the top shelf of the pantry (now it's the "electronics bay" including the charge controller, Datastorm equipment, and a wireless router). Ran the wire out the bottom of the coach, followed the other wire bundles to the front and anchored with wire ties.
Next day I finished wiring the panels up top, and ran the wire from the panels through the fridge vent to the electronics bay. Had to buy a new vent cover, because the old one was brittle and falling apart. $16 at Camping World. Tied it all up neat with wire ties and clamped the wires down to the roof in several places. Covered the clamps and screws with Dicor so the roof wouldn't leak. Hooked it all up and it works! Yipee, we have solar!
Third Solar Panel Installed
I bought another 120w Kyocera panel, used, for $290. Below is a photo of all 3 panels installed and tilted towards the sun.
4th solar panel installed
I finally decided to max-out our solar charger (a 25 Amp unit) by adding a 4th panel. I only needed 85 W, so now I have three 120's, and one 85, for a total of 445 watts. I also ran new wiring from the roof to the controller. Now I have AWG #10 run from each panel to a central point, and AWG #6 run about 8 feet from there to the controller. From the controller, it's about 8 more feet of AWG #6 to the batteries. I kind-of wish I had #4 in there instead, especially from controller to batteries, so I may do that at a later date.
Wire Size: The reason for larger wire is to reduce voltage loss. Lower voltage requires larger wire; however, the voltage from the panels to the controller is over 17 VDC so the loss is less than from controller to batteries.
Someone might ask 445 Watts = more like 37 amps @ 12 volts??? Well, that would be true, but remember the solar panels are putting out around 17 volts.
I added the 85W panel behind the skylight. See photo below, click it for larger photo:
Click here to continue reading about the rest of our 12 volt system -- inverter, charger, etc.
Click here to read my technical articles on RV 12 volt systems