I desired to have a source of electrical power to recharge the batteries in our Airstream trailer when camping where electrical hookups are not available. While generators are commonly used, they create undesirable noise, have to be lugged from camp-to-camp along with spare gasoline to run them. To avoid such inconveniences, use of a solar panel was settled on. While they do not provide enough power to run an air conditioner, furnace fan, or even more than a few incandescent bulbs, one can recharge batteries during the day enough to enable a more extended stay. One must, of course, be frugal with use of electricity during such periods to enable using power for lights, ventilating fan, and water pump. (LEDnote 1 lamps have been substituted for some of the incandescent bulbs in overhead fixtures, saving substantial power drain on batteries - the overhead incandescent bulbs use a surprising 1.44 amp of current.)
Solar panels are commonly mounted on the roof of recreational vehicles. However, if one is parked in the shade, the power output drops to a trickle. And, professional, roof-top installation is expensive. I was inspired by a setup used by the Sawyers, seen at a camp ground in Florida on the Tamiami Trail, in January, 2010. They had a solar panel mounted on a stand and plugged it into the Airstream using a marine-grade, stainless steel, deck fitting. This provides a corrosion resistant fitting that blends with the Airstream look and is compatible with the 12 V output of a solar panel. It is easy to maintain consistent polarity throughout the wiring system with the polarized plugs used on the fittings. During installation of the solar panel, solar charge controller and associated wiring, care was taken to verify the polarity of connections throughout the system. Reversing polarity can cause damage to components such as the controller and, possibly, electronic components in the trailer. Of course short-circuits are to be avoided.
Solar Panel Support Frame. As shown in the photo above, the solar panel (see parts list) is mounted on a home made stand made of PVC pipe. The stand is hinged to adjust the angle to optimize the angle of the panel with respect to the direction of the sun, which is also aided by the portability of the unit. Optimum output is obtained when panel is inclined at an angle equal to the local latitude of a camp. The stand is a sort-of "A-frame," hinged at the top. The rear support swings up and over the top of the solar panel and is constructed with horizontal cross pieces that are off-set to provide some protection to the front of the panel during storage, when folded "forward." The solar panel (see parts list is robust. They are designed for roof-top mounting on RVs and are not removed when traveling. The front of the panel is made of tempered glass and it is held in a sturdy aluminum frame.
After assembly, the frame was wiped down to remove crude and oils. It was lightly sanded and painted white with Valspar spray paint for plastic (see parts list).
Wiring. The trailer was wired through the side of the trailer near a external door used to access storage under the bed, which is located in the front (towing-end) of the trailer. Wires were run to the power distribution panel (located in the Power Center), and a solar charge controller mounted in the closet above the water heater. Access to both is easy inside of the storage compartment. While the trailer is said to be pre-wired for roof mounting of a solar panel, with wires running to the Power Center, I was unable to find these wires in the neighborhood of the Power Center. To connect the panel to the trailer, an "extension cord" was made from marine sockets and plugs attached to 16 gauge wire used for low-voltage, landscape lighting; this wire is also resistant to UV light. Stranded wire was used throughout and tinned to provide for stronger connections. ("Tinning" of wire is accomplished by stripping-off enough insulation for a connection. The wire is heated with a soldering iron and solder is touched to tip of the soldering iron and the heated wire. Capillary action carries melted solder between the strands and solidifies to make a solid unit of wire plus solder.)
A solar charge controller (see parts list is needed to control voltage and current going to the battery. Installation instructions for the solar panel specified a 30 amp controller. The controller chosen also provides digital readout of battery voltage / condition charging rate (amps delivered), and other monitoring functions. The controller prevents over charging of the batteries and incorporates a blocking diode to prevent back current from the battery when the solar panel is not putting out current, thereby preventing battery discharge at night. (The solar panel also incorporates a blocking diode, providing redundancy.) The controller goes into "float mode" when batteries are fully charged.
Bare frame, pictured above, is hinged at the top using a "slip-slide-tee," pictured above-right (see parts list).
Most PVC pipe and fittings are 3/4".
Closing of the PVC frame: One of the slip-slide-tees, which provide the hinge action, is near the top-most elbow on the left.
Frame closed for storage.
Pipes crossing in front of the panel (1/2" PVC) provide some measure of protection for the panel.
Note that when fully open, these pipes are behind the panel as shown in the first picture of the frame, above.
If I were to do it again, I would make it so the 1/2" pipes do not stick-out so much.
The proper orientation of a solar panel with respect to direction of incident sun light is necessary to get maximum irradiance of the solar cells and maximum current output. Some recommend that the angle between the panel and the ground be the same as the local latitude. Other's (Landau at Macs Lab) make more complicated recommendations to optimize output. Clearly, variation in tilt of the panel is desirable to optimize electrical power output. Mounting the panel on a movable stand facilitates attaining this objective.
Stand and Variable Angles. The hinged construction of the panel support stand enables one to vary the tilt of the panel. To enable variation in tilt as well as to keep the stand from collapsing (spreading apart and falling flat on it's back), restraints were added. Made from braided, stainless steel cables were used, as pictured below, the restraints include loops which allow for variations in tilt.
As shown in the detail views above, a 1/16" cable was used. A small loop is fashioned on one end and it is fastened to the front leg of the stand near the bottom. Further along the cable, several circular loops are formed with ferrules. One of these loops is shown on the left before it is collapsed to a much smaller diameter that just fits over a nut attached to a bolt on the rear leg of the stand. Stainless steel bolts (8-32, 2") and self-locking nuts with a nylon insert were used. On the back leg, one nut secures the bolt to the PVC pipe which has been drilled-through to receive it. A second self-locking nut is screwed onto the end of the protruding bolt; the self-locking nut keeps it fixed in place. The space between the two nuts provides a place for the loop to "seat." The placement of several circular loops along the length of the cable provides for variation in the angle of tilt; as can be seen in the larger picture above, there is "excess" cable, dangling to the right with more loops on it.
Sunforce Solar Charge Controller, 30 amp,. 12 volt. Digital read out of voltage and amperage (see parts list).
Controller mounted in closet which is next to bed in front of trailer.
Controller is reading 4.0 amp output from panel shown above, which was in strong, June, afternoon sunlight. Other status LEDs are faintly visible on the left side of the controller.
The charger controller was mounted on a small piece of plywood cut to hold it in place. This was screwed, from inside, to a panel which runs across the top of the closet, as seen in the pictures above. This location was chosen because it is easier to run wires to the outside of the trailer and to the power distribution panel (located in the Power Center under the bed) - to provide a connection to the battery. When the closet door (removed to ease access during installation) is closed, the controller is hidden from view. Some prefer to mount the controller by cutting a hole in a wall - perhaps the wall of the close facing towards the bed in this case. In this installation, a hidden controller without a hole in the wall was chosen. At this point in the installation, one can see wires dangling down on the inside left of the closet opening.
The pictures which follow show wiring inside of the closet, with drawers removed.
Looking out from inside of closet: wires soldered to lugs attached to rear of controller.
Wires in drawer cavity before securing them.
In the above pictures, wires can be seen passing down after passing through a small gap at left-front of shelf and into the drawer area. Gaps between drawer rails and brackets at rear provide space for feeding wires from controller, behind drawers and over the hot water heater, which is contained inside of the Styrofoam insulator at the bottom rear of the cavity. The white wall at the rear of the cavity is the inside of the curb-side wall of the trailer. (The red pipe carries water from the heater to the sinks, etc.) New wiring pass to the left in this picture, towards the front of the trailer and into the storage space under the bed, accessed from a hatch on the front-curb side of the trailer.
One, two conductor wire is connected to the external, marine-grade fitting near the storage access hatch. This provides incoming power from the solar panel. A second, two conductor wire runs back down from the controller, into the storage area and then under the bed to connect to the power distribution panel in th Power Center. This is the feed to provide power to charge the battery.
Looking out from inside of closet, wires are now largely hidden from view outside of closet.
Wires pass through the small gap between the shelf and door frame and into drawer cavity below.
Wires are secured with wire ties to self-adhesive, nylon "mounting base," pictured below.
Looking up and to the rear inside of the drawer cavity, a wire is secured to the bottom of the closet shelf with self-adhesive restraints.
A second wire is secured to behind the drawer rail on the left.
The Power Center, located under the bed, is pictured here. It contains the inverter, 12 and 110 volt power distribution panels, and fuse panel. To the right of the Power Center, located under the bed, is a drawer.
The area housing the the Power Center, and wiring thereto, was accessed by removing the half-sheet of plywood which supports the mattress at the foot-end of the bed. This exposed the cavity in which the Power Center is located.
Wire was passed under the drawer using a wire-fish to pull it through a metal channel / guide for wires passing under the drawer and into the cavity containing the Power Center.
Before working in the Power Center, the battery was disconnected from the system by switching the "Battery Disconnect Switch" to "STORE." (This switch is located near the entrance door in the 25 ft. Safari FB, on the wall under the sink.) This took the battery out of the circuit being accessed to feed power to the battery. This was verified using a volt meter to check for a hot circuit at the battery connection terminals in the Power Center. Further, the trailer was not connected to any external source of power, neither 120 volt shore power nor to the tow vehicle. Note that the battery could also be taken out of the circuit by disconnecting all positive cables on the batteries.
The new wire providing power from the solar panel, via the charger controller, was fed to the Power Center from the under-bed storage area as noted above. The Power Center had a "knock-out" at the rear which was removed. The new wire was fed though this hole and secured with a standard anchor in this knock-out. The pre-existing connections to the battery are made via large cables connected at the terminals denoted with arrows in the photo above. The red battery cable is marked "BATT POS," and the negative (white cable) is marked "BATT NEG." As can be seen in the photo, the tips of the multi-stranded wire were tinned with solder to provide a sturdy, non-fraying connection. After loosening them, there was enough space behind the large screws, which secure the original cables to the battery, to slide the new wire into the hole behind them. Of course, the screws must be re-tightened to secure both old and new wires. Note the black and red insulation on the two conductor wire coming from the controller. Color coding aided in maintaining proper polarity during wiring. In this instance, the black wire is going to ground and the red wire is hot, paralleling the color convention used in wiring on the trailer batteries.
At this point in the installation, the external connection for the solar panel had been wired-in and the "extension cord," used to connect to the solar panel, was connected to the trailer. The other end was brought inside to check for continuity and proper polarity, end-to-end.
The solar panel is supplied with wire to make connections via the junction box on the back of the panel, as pictured above left. Given that power is always being produced when the solar cells are illuminated, it was decided to install a switch and fuse. A weather resistant, push-switch was installed in a hole drilled into the cover for the junction box. A weather resistant fuse holder was installed in a rubber plug in one of the knock-out holes in the junction box (see parts list}. The fuse and switch are wired in series between the positive terminal of the panel and the hot (red) wire on the two conductor wire exiting the junction box; the black wire is connected directly to the negative terminal of the solar panel. (The panel is supplied with instructions, including pictures, detailing which terminals are positive and negative.) The wire exiting the junction box is terminated with a marine-grade connector plug discussed further in the next section.
Security tether. Visible behind the junction box is a tether to help prevent theft. It was made from plastic coated, braided, steel cable. A loop was formed from a short length of the cable and the ends extended through a hole in the aluminum frame of the panel. They are secured on the underside of the frame using a ferrule. Two security cables were made with loops on each end, formed using ferrules, to allow for placement of the panel at some distance from the trailer. These cable(s) are attached to the security loop on one end and to a secure point on the trailer, e.g., the hitch-tongue.
Shown above, power from the solar panel is fed to the trailer through a cord and marine-grade connectors.
The connector attached to the trailer is a 2-pin, West Marine electrical connector, (model 181867, see parts list}, which includes a plug for connecting to the socket mounted on the trailer and a grommet which provides a seal between the base of the connector and the body of the trailer. To mount this connector, a hole was bored through the inner and outer aluminum plate that forms the wall of the trailer. The wire to be connected was covered with several layers of electrical tape and shrink wrap. Small, self-tapping, stainless steel screws (4-40, 1/2") were used to attach the connector to the trailer. As can be seen in the pictures, this makes for a neat looking point of attachment that blends well with the "look" of the Airstream and is also weather proof when the protective cap is attached for travel.
Connection between the panel and trailer is made with a cord made of UV resistant, 12 V landscape wiring (available at Lowes). Pictured above-left is the plug-and-socket connector used, a Cole Hersee Round Body Connector, 2-pole (see parts list}. The rubber boot provides for weather resistance. While it is not easy to see in the photos, one pin is larger than the other and they are made from different colored metals. This helps maintain proper polarity in the circuits between the solar panel and the trailer. The plug and socket for the body-mounted connector also have differently sized poles to enable maintaining proper polarity.
About fifty feet of cord was used to make of two unequal length "extension cords." The shorter one is terminated on one end by the plug that came with the West Marine connector, and on the other end with Cole Hersee connector. This cord connects directly between the solar panel (which has a Cole Hersee connector socket) and the trailer. If a longer cord is needed, so that the panel can be moved to a sunny area, the second length of cord, terminated on both ends with with Cole Hersee connectors, can be added as an extension between the solar panel and the shorter length of cord.
As noted before, power is produced by the solar panel when it is illuminated. Thus, the plug which connects to the trailer will be hot if connected to the panel, making possible a dead-short. Concern for this possibility provided added justification for installation of a switch on the solar panel.
Adjacent to the Cole Hersee connectors pictured above is an alternate connector that may be used on the side of the trailer - a Perko Watertight Deck Connection, Model 1189 (see parts list}. This connector has the advantage of being more flush with the side of the trailer but is likely to be less weather proof than the Cole Hersee connector used in this installation.
|West Marine two-pin connector, model 181867 (link to item)||1||$18.00||$18.00|
|Perko push button switch, model 0701DP (link)||1||$6.94||$6.94|
|Cole Hersee round body, 2-pole connector, Mfg Part # M-121-BP||2||$18.00||$36.00|
|Landscape cable, 50' Lowes Item 157086||1||$9.98||$9.98|
|Miscellaneous lugs, solder, nylon mounting base, wire-ties, etc. (supplies on-hand)||—||—||—|
|Slip-slide Tee (link)||2||$1.51||$3.02|
|S&H for slip-slide tee||1||$8.98||$8.98|
|Elbow, 90 deg||8||$0.67||$5.36|
|Bushing, 3/4" to 1/2"||4||$0.35||$1.40|
|Pipe, 3/4", 5 ft||5||$1.36||$6.80|
|Pipe, 1/2", 5 ft||2||$2.12||$4.24|
|Valspar white plastic spray paint||1||$4.97||$4.97|
|Plastic pipe cutter||1||$11.04||$11.04|
|Ferrules, 1/16", 2 pack||5||$1.24||$6.20|
|Wire cable, 1/16", 7'||1||$1.75||$1.75|
|Ferrules, 1/8", 2 pack||3||$1.48||$4.44|
|Wire cable, vinyl coated, ~40' (price estimated - reciept not retained)||1||$15.00||$15.00|
|Bolt, SS pan head, 8-32, 5 pack||2||$1.41||$2.82|
|Lock nut, 8-32, 5 pack||2||$1.97||$3.94|
Solar Panel, Sunforce Item No. 39810, polycrystalline by Sharp (NE-80EJEA). Max output: 80 watt / 4.67 amp, 12 volt (nominal). The manufacturer recommends fusing with a 10 amp fuse. June 2010 price on Amazon.com's "Warehouse Deals," for an "used / open box" unit: $338. The author paid $365 for an "open box" unit at WareHouse Deals. Other sources for new panels: $475 at Northern Tool, $400 at Amazon.com.
Sunforce Solar Charge Controller, 30 amp, model 60032. 12 volt. Digital read out of voltage and amperage. "Open box" price paid by author from WareHouse Deals: $76. Elsewhere: $90 at Northern Tool, $88 at Amazon.com.
The Perko push button switch is their model 0701DP, 10 amp at 12/24/32 V. Listed by Boater's World as "Perko Push Button Switch," Stock No. MP80809914, $6.94. The switch has a rubber boot that addes water resistance.
The Perko connector, described above as a possible alternate for the West Marine connector, is a Perko Watertight Deck Connection, Model 1189. It comes with plug and boot (to attach to external electrical cord) and was available at Boaters World, Stock No. # MP80824616, $14.94.
West Marine connector was purchased at a local West Marine store. They also maintain a web site.
Slip-slide-tee: purchased on-line from FlexPVC (link to part). This unique part could not be found locally; its use enable making a hinge. FlexPVC has some unique PVC fittings that can be useful for PVC projects. For example: make a handle with a "dog-leg" or "wye." Another alternative for a hinge is a "snap tee."
Prices are as paid by the author, not including local sales tax (6% in author's home state). Price comparisons made in June 2010. Links to items may disappear from vendor web sites as time passes but are given to aid those seeking parts because they are hard to find on web sites. A visit to a well-stocked marine supply store is useful to learn what is available in weather-proof connectors, etc.
Note 1 LED replacements for overhead lighting bulbs: Airstream fitted overhead lighting fixtures with Sylvania bulbs, labled "1141 12V21CP." Sylvania's specs for this incandescent bulb indicate that they consume 1.44 amp at 12.8 V (equivalent to 25 watts). I have substituted LED lamps for incandescent bulbs in several overhead fixtures. The replacements chosen are from SuperBrightLEDs.com, model 1156-PCB-WWHP9 (warm white). This replacement is rated at 0.19 amp and produces a "warm white" (3100° K) light, which was found by the author to be more pleasing than the illumination from some other LED replacement lamps. The lamp has 9 high-output LED elements attached to a backing plate which, in turn, is wired to a BA-15 base (plug, single contact) for plugging into the sockets used in overhead fixtures. The LED lamp is attached to the reflector inside of the fixture with double-sided, adhesive foam tape. By using one LED lamp per fixture, adequate lighting is available for most purposes and less cost is involved than if all incandescents were replaced with LEDs. The SuperBright LED lamps are $21.95 each plus S&H.
Several other SuperBright LEDs were tried before settling on the model chosen. The "G4 side-pin" lamps, with an adapter plug to fit the BA-15 sockets, did not work well because of the fixed angle between the adapter plug and the socket in the trailer; this resulted in the lamp being "aimed" at an odd angle. "Tower type" bulbs with 18 and 45 LED elements were also tried. The 18 element bulb was not as effective in illumination as the lamp that was chosen. The 45 element, tower type bulb produced too much light and was needlessly expensive.
Notes about replacement LEDs and power consumption updated August 10, 2010
Use of this information is at your own risk. The author hopes that the in information provided herein may be useful to others planning installation of a solar panel. However, the information is provided without warranty of any kind. The user assumes the entire risk related to its use of this information (as well as that provided via links to other web sites). The information is provided "as is," and author disclaims any and all warranties, without limitation). In no event will the author be liable to you or to any third party for any direct, indirect, incidental, consequential, special or exemplary damages or lost profit resulting from any use or misuse of this data. The author expressly warns that the installation of a solar panel and associated wiring involves the potential of sever shock from high currents. Other hazards to person and equipment are associated with the installation of solar panels and the tools discussed herein; they may include damage to components being installed as well as to travel trailer systems. Thank you for your understanding and enjoy your travel trailer.