Franswa is on it... once you start down this path the itch to keep improving it is irresistible.
On the one hand, some people look to simply put on a panel and forget about it - to add some assistance or a bit more time out of the battery, but not relying on it for anything substantial.
On the other hand, some people find the
solar experiment to be an interesting hobby that fits hand and hand with the camping. Like running a 12v
fridge off of batteries, etc. (just teasing you here, I saw your other thread). In this situation, building with flexibility for future alteration makes a good amount of sense.
Some random stuff I've learned:
Panels are all different shapes and sizes. Even an aluminum framed panel of 100 watts may vary in dimensions a bit from manufacturer to manufacturer. So if holes are drilled for a specific panel, they may need to be filled and re-drilled if the panel is replaced or moved. Not a big deal, just have the head ready for the possibility. I've wondered about a frame that is wider than needed, with crossbars that could accommodate variations in size.
Panels are all different watts, volts and amps. Even 100 watt panels, when from different manufacturers, will have different volts and amps. Look at the specs in the descriptions. The reason this is of interest is that the combination of panels will be subject to the weakest link among them. I think its that they will all run at the lowest voltage panel among them. This results in some lost power because the stronger panels don't run as hard in the group as they could have if matched to equals. The ultimate solution for mismatching seems to be a separate charge controller for each panel or each matched set or, simply live with the limitations of mismatching them and be ok with that. The best practice is to have the panels matched not only in watts, but also manufacturer and model so the volts and amps are matched as well.
Batteries are like that too, but that's a different discussion.
Shadows matter. You see Jim's awesome placement of his panels in his pictures. His panels do not run right up against the roof-top appliances, and they are spaced so that it is not likely for an air-conditioning shadow to cross the corner of one of his panels. This is important. Even a tiny shadow on part of a panel drops its output tremendously. Don't know why, just what I've read.
Tilting at different angles at different times of year can have a substantial impact on productivity. Face to face with the sun is best. Rooftop does not lend itself to tilting unless you wanted to get up there to monkey with your frames when you park, and park your rig at the appropriate relationship to the sun.
My last rig was big and I roof-topped it and loved it. I didn't tilt, had a few more panels instead, and didn't have to do anything but get there. You have to get sunny sites though so your rig is in the sun. This time I've got a tiny egg so I'm going with panels I set out when I get there. This will add an ability to find the sun with them too.
Mono is more productive than poly, especially for cloudy days. It's priced accordingly however. I'm in Ohio so I'm going mono this time.
Size matters... when it comes to 12v wires thicker is better. You can Google oodles of wire size charts so the information is plentiful. Its not just fire safety, the larger wires have less resistance, so they loose much less energy to heat, so more ends up in your battery. The sizes are numbered backwards... bigger wires have smaller numbers because they have smaller resistance. Think at least 10 gauge thick for a rooftop system. You can add thicker wires too for the longer runs (like 8 or whatever). Its like water flowing in a pipe. The pipe opens up for a bit along the way and looses less heat at least during that portion. Always fuse it for the smallest wire in the run. Lots of charts on that too. 30 amp for 10 gauge, 20 amp for 12 gauge, etc. (Check that though I'm just some fool typing on the internet).
Length matters... when it comes to 12v wires shorter is better. 12v hates distance. Route and re-route the system in the mind over and over to come up with the shortest possible wire runs. Less distance is less loss to heat is more electrons making it home to the battery.
Size your
solar charge controller for amps. Use the short circuit amp specification x 1.25 = minimum size controller. Soooo... four 100 watt panels each with a short circuit amp of 5.7 would be like this... 5.7 x 4 x 1.25 = 28.5 amps. So basically a 30 amp controller is called for because they come in round numbers. (Check that though I'm just some fool typing on the internet).
Size your solar charge controller for voltage. A panel
sold as a 100 watt 12v panel may vary in open circuit voltage (Voc) from 16 to 24 volts, or whatever, depending on manufacturer. Just check the open circuit voltage on the panel specs and the maximum voltage spec of the charge controller. 12v is "nominal" voltage that gets you into the ball park of what works together but look at the details to select your pieces.
MPPT and PWM solar charge controllers work differently. I've always had PWM which needs voltage that is in the ball park (my 30 amp PWM controller has an input maximum of 25 volts so 12v panels with Voc up to 24 are in its ballpark). I've read that MPPT is far superior and allows you to use much higher voltages on the input side but I don't know enough about it other than I would be researching MPPT if I was buying a charge controller right now.
Edit-
Weight matters for
fiberglass eggs. A 100 watt aluminum framed panel is about 23 pounds. A 100 watt flexible panel is about 8 pounds. I think the consensus is that the aluminum panels are more physically robust, however, in terms of the glass or whatever, and in using feet to stand them off the roof a bit so heat is dissipated better. I'm thinking flexible this time around (like Jim's) for
weight savings.
Have fun!!!
The Mountain Egg AKA 2006 13' Scamp
2009 Escape 19
"The Breeze"
Linear Mode
