Details of our previous solar photovoltaic system
Dave and Helen Damouth www.damouth.com
Solar configuration as of late 2001 on our travel trailer
Our photovoltaic (solar) charging system consists of the following hardware:
3 Siemens SP-75 photovoltaic panels: These have a rated load current of 4.4 amperes each, a total of 13.2 amperes. (The rating is realistic - this is just about what I actually get on a sunny mid-summer day in the north, mounted flat)
Heliotrope CC30C Charge Controller:This product has a peak current capacity of 30 amps, which would allow me to add several more solar panels in the future. It has separately regulated outputs for two separate battery banks, and temperature sensors for both battery banks.. One bank has adjustable charging voltage, the other is set at a fixed 14.2 volts (intended for an engine-starting battery). The controller is all solid-state - no relays. It charges at a fixed (manually adjustable) voltage, and hence has the potential for mildly overcharging the battery. If I were doing it again, I'd try to find a multi-stage device that would sense a fully charged battery and taper back to a zero charge current. I've discovered that Trace makes such a product - there may be others too.
Mounting frame: I purchased this mounting system from Backwoods Solar Electric, who have aluminum angle frames cut to length and pre-drilled for the common solar panels. Two additional lengths of aluminum angle stock are provided which can be used to raise one end of the frame, tilting the panels at the proper angle to face the low winter sun. This frame could easily be fabricated from four lengths of ordinary hardware store aluminum angle, 1.5" x 1.5" x 1/8" thick, by approximately 5' long. Four additional pieces of this same angle stock, each about 4" long, are are attached to the roof, providing both attachment points for the four corners of the frame and serving as hinges for front-to-back tilt.
My roof is a rubber membrane over a plywood support deck. Each of these short pieces is attached to the roof with two 5/16" x 3/4" lag screws, with the screw heads and all edges of the aluminum sealed to the rubber roof with polyurethane caulking compound. The roof plywood is relatively thin (perhaps 3/8"?). The mount described above seems adequately strong along the front-to back direction, which is the only direction which currently receives significant stress (when the panel is tilted up in the wind). When I add a sideways tilt capability (see below), I will probably spread and reduce the lateral stress by using a 4" x 4" x 1/4: aluminum plate under each corner of the panel frame, with a lag screw in all four corners of each plate.
Hookup Wire and terminal block:Backwoods Solar also provided a suitable length of weather-resistant hookup wire (measure carefully before you order), and a simple terminal block for interconnecting the battery, the wires from the solar panels, and the controller.
Installation Trivia:
I chose to run the wire from the roof down through the refrigerator vent, which was conveniently located close to the mounting location for my solar panels.
My charge controller is mounted recessed in a living room wall, the back side of which is accessible from the outside refrigerator compartment, via the empty space behind and alongside our sliding pantry adjacent to the refrigerator. This made the wiring task very easy.
My Link 2000 battery monitor and remote controller for the Heart Freedom 10 inverter/battery charger is mounted on this same wall. It is very important to mount these instruments where they are easily visible, so that you get in the habit of looking at them frequently, so as to be always aware of the state of battery charge and the present battery current.
And for completeness, I should note that we have a pair of golf cart batteries, with a total capacity of 217 amphours (giving us a usable capacity of about 110 amphours, since for long life, batteries should never be discharged more than about 50%)
Performance:
Here's a graph of Summer Performance.
And here's the Winter Performance, with the panels tilted up.
Tilting the panels in winter:
I haven't done much careful measurement of winter performance, other than the graph shown above. In one test, the panels produced 6.9 amps flat on the roof. Then, when raised to an angle approximately facing the sun, the current increased to 11.3 amps, a 63% increase. I did a little geometry which suggested I should get 1.89 times as much current by tilting the panels at an optimal angle. Some of the difference is due to the sun being weaker - when it is low in the sky, it must penetrate through much more atmosphere, and I don't have any independent information about just how big an effect this is. The slight coastal haze also has some effect. Stay tuned for the next exiting chapter. Anyway, tilting the panels gives a huge gain in the winter months.
This one brief experiment suggests that by tilting our panels, we should be able to generate about 100 amphours of battery energy per sunny day through the winter months at the latitude of San Simeon (or Sante Fe). We rarely use more than half this much daily energy when boondocking, and so will be able to maintain our normal usage through an occasional cloudy day. Most full-time Rvers will spend the winter somewhat further south, which will improve the above performance. For example, The Slabs, a popular winter boondocking place near the Salton Sea, is about 2 degrees further south than San Simeon, and I'd guess the above numbers will improve by about 5% (I hope to get a chance to find out soon.
With my present mounting system, it takes about 5 minutes to tilt the panels when we arrive at a campsite. I have to climb up on the roof with a wrench, loosen two bolts at one end, remove two bolts at the other end, raise one end of the panel, insert the two support struts, and insert and tighten four bolts. If I did this frequently, I might replace the bolts with toggle pins, so the whole thing could be done without tools.
The present system can only be tilted along the front-to-back axis of the trailer, requiring that the trailer be aligned approximately North-South. I have built additional brackets which will give me the option of tilting the array sideways instead of front-to-back, (making an East-West alignment also efficient) but have not yet installed them.
Source of Photovoltaic Systems:
My solar system components were purchased from Backwoods Solar Electric Systems, http://www.backwoodssolar.com operated by Steve and Elizabeth Willey. They offered to match the lowest advertised prices of other suppliers, and were very helpful in assisting my selection of a system and in answering my questions during installation. They can be reached by Email at info@backwoodssolar.com
Another supplier which has been repeatedly recommended by other RV folks is RV Solar Electric. Two years ago, I found their catalog prices rather high, and they had no Email access. A recent mailing has somewhat more competitive prices, and also offered to match other supplier's advertised prices. They now have a Web Page at http://www.rvsolarelectric.com/, or call (800) 999-8520. They are located at 14415 N. 73d St., Scottsdale AZ