Thanks for all the great information you provide BHM readers. I’m planning to install a small PV system using the instructions in your article in issue #116. This will be a very small system and used primarily for back-up during a black out. I have a Uni-Solar US-32 panel and Sunsaver 10 amp controller. I’m installing the panel on a carport roof, (I live in Massachusetts), running the wires to connect to one or two 12-volt deep-cycle marine batteries in my attached garage. I’ll be using the 2-pole fused disconnect and correct wire size for the panel and ground wires you recommend.
I have three questions.
1. What can I use as a bracket to mount the panel to the roof? I’ve seen small RV racks for sale and wondered if there is an alternative mounting bracket that can be purchased at a hardware store.
2. The wiring diagram in your article shows the load wires going to two 12 volt lights, hooked-up in parallel. I plan on wiring one light for the garage and continuing the wires about 30 feet to be run to the inside of the house. Those wires will be hooked up to a wall plate with a 12-volt cigarette plug receptacle mounted on the wall. I want to use the plug for a 12-volt TV or any other 12-volt appliance/charger that works using the auto style plug. What do you think of this arrangement and do you have any suggestions or recommendations.
3. Do I need to vent the batteries outside if they are in an un-insulated garage? I plan on putting the batteries in an insulated box for the winter and wondered if I can drill a hole into the top of the box and let the batteries vent into the garage.
Thanks for the help.
I can give you some general answers, but since we would not know everything about a specific installation, we cannot be too specific.
Although most solar dealers offer an “approved” angle “foot” to attach any solar module to a roof, I have taken 1-1/2 X 1-1/2 aluminum angle and installed the leg standing up to the side of the solar module and the flat leg bolted into the roof framing. Keep in mind that if you do not use the pre-drilled mounting holes on the back of the module you will void the warranty, so you might try a combination of two short lengths of angle back to back to make a “Z” shape. This will give you a way to utilize the bolt holes on the back of the module.
As long as your loads are 12 volt DC and wired in parallel, they do not all need to be at the same location. However, I would increase the wire size to the more distant load as there is 10 times the voltage drop at 12 volts DC that there is at 120 volts AC.
Finally, a few RV or golf cart batteries out in a garage will not give off enough gas to cause a problem due to the large space, but don’t locate them next to a gas fired hot water heater. Hydrogen gas is only explosive when highly concentrated like in a small sealed up closet or battery box. If you do place the batteries in an insulated box, you will need a vent at the top. For larger battery systems we use a 1-1/2″ PVC pipe vented outside, with screening to prevent insects from entering. The pipe needs to slope uphill since gas rises, but you will need something to keep out the rain.