Solar Help

[MickD]

I have an older Class B motorhome and have been thinking about solar.
I can boondock now for 2 days before I have to recharge my 125ah battery. The only thing that draws power is the 12V fridge which runs about half the time at 3.5A and a light for an hour at most. I have limited space on the roof. My question is: Would a 150W panel like the one here
Click
keep me charged and what controller would be the minimum I should use?

Let me thank you now for all the good info I have gotten from this site.

Mick

[Almot]

From the panel to roof junction box you use the stock cable with MC4 connectors that comes with the panels, #10 or #12. It is UV-stabile, normally. Cables from both panels will connect in parallel on the bus in that box, cut the MC4 connectors off, you won't need them in this scenario. Only if you need to use MC4 extension cable for one of those #12 cables to reach the box, you may keep MC4 connector on that cable. Then you run a single cable of proper ampacity from the box to controller, doesn't matter UV-stabile or not, because it won't be on the roof.

Yes, there is a common recommendation to buy a single MC4 extension cable and cut it in half and connect to the existing pair of MC4 "tails" on the panel, so that it will have bare ends on the roof junction box end (or on the controller end, if controller is really close). The only purpose of this is to avoid cutting the existing MC4 connectors, because cutting would void the panel warranty. I see it this way: if panel works when you pick it up (easy to test with multimeter), then it will work many more years, screw the warranty.

How to test solar panel - note that this one doesn't have cables with MC4 connectors.

[pianotuna]

Hi MickD,

Size doesn't matter much with PWM, so long as there is sufficient ampacity to be safe. In MPPT it does.

The wire chosen should be UV protected.

MickD wrote:
I have another question about wiring the solar panels? I have googled this for two days now and haven't found an answer. I can find a lot about size but nothing about the type of wire that should be used. There are a lot of different types.
Any help would be appreciated.

Mick

[HiTech]

Most but not all of the pre-made cables with the solar connectors on them are the right type, but check to be sure it is outdoor, UV stabilized, or at least understand that you are not getting it if you choose not to.

Jim

[mena661]

Some suggest wire that's UV resistant and weather friendly.

[time2roll]

^^^^^

A single panel with MC4 connectors.... just get an MC4 connector cable. Cut in half so the connectors snap onto the panel and the cut ends hit the controller. Generally it is #10 wire.

If panels are parallel you can buy some MC4 connectors to two panels. That is about max for #10 wire to the controller. Although voltage drop is not a huge deal as the controller clips voltage to the charging level anyway. For more in parallel it is probably best to tie them tegether in a combiner box and use larger wire to the controller.

With series the same cable can be used. No practical limit on RV panels but you will need the proper controller for the high voltage.

[MickD]

I have another question about wiring the solar panels? I have googled this for two days now and haven't found an answer. I can find a lot about size but nothing about the type of wire that should be used. There are a lot of different types.
Any help would be appreciated.

Mick

[Salvo]

Interesting panel mounts.

Sticky Feet

I didn't see the 90A panel advertised at windturbine.ca. Got a link?

[mena661]

wintersun wrote:
very reasonably priced.

Are we talking about the same Kyocera panels? The one's that cost (still) over $300 EACH? For 140W? No friggin way. I can get a 240W panel for $150 and that Eco-worthy MPPT controller for another $100 and use the rest for wiring. Those panels are never worth that much money. It's the OP's money though but you'll NEVER see one of those on my rig. Rip off city IMO.

[wintersun]

I followed the rough rule of thumb of 1 Watt of solar panel output for every 1 AH of battery capacity and it turned out to be more than adequate with our 220 AH of battery capacity and 200 Watts and 11 amps of solar panel output. We never drop below 80% DOD and usually it takes less than 3 hours after sunrise in any kind of weather except rainy days to get back to 100%.

A good panel to consider is the 140 Watt Kyocera which is well made and good size in terms of length and width (narrow enough to both fit in a space and to not be affected by shadows from anything on the roof) for RV's and very reasonably priced.

[BFL13]

Two 90s at 5.7 each, is 11.4a so add 20% -- 2.3a = 13.6a so I thought a 15a fuse would meet that 20% margin, but a 20a is fine

[Salvo]

A fuse between panel and controller will not provide fusing safety. However, many add a fuse, just to be able to disconnect panel from controller. Whenever you disconnect the 12V battery, for example to work on 12V cabling, you will also need to disconnect panel from controller.

A 20A fuse must be installed between battery and controller. It's best to install that fuse by the battery. That locattion not only protects the controller but also the 12V cable.

Sal

[BFL13]

No fuse between panels. No fuse between panels and controller "array" side. 15a fuse (or same amps as controller with the 20% margin over expected panel amps (Isc) on pos wire between controller and battery within 18 in of battery pos post.

If you will be able to get at it, good idea to have an on/off switch on one of the wires on the array side of the controller. This is better than on the battery side because then the controller stays powered up and keeps any settings when you switch off.

Sometimes you want to check battery with no charging happening that screws up your readings, so good to be able to switch off solar. Also when batteries out, so you don't leave the rig loads right on solar with no battery there--can be bad for some controllers. So switch off solar before removing battery.

Controller goes close to batteries for least voltage drop, but not a show stopper if farther away.

If putting controller close to battery then don't waste money on one that has read-outs on it for amps and volts, since you won't be able to see it 🙂

[MickD]

I want to thank everyone for all there input. I think I am going to go with 2 90w panels. I talked to Sun Electronics and they have them in stock an I can pick them up.

Other questions: should I place a fuse between panels? What size?

Should I place a fuse between controller and battery? What size? On the positive wire?

Should I put an on/off switch on the system? Where?

Mick

[Almot]

BFL13 wrote:
The OP has only a small battery bank and low daily AH usage, so IMO he could get by fine with just the one 90w panel.

We don't know his daily AH usage, to begin with.

As to the bank size, I would say - it is TOO small for boondocking, considering 12V fridge. With solar one could live without running a generator on some trips IF the bank is big enough. Solar is highly dependent on weather. With a bigger bank he could ride out a couple of rainy days and then solar kicks in again, and then having 180W is much better than 90W because he has to compensate for 2 lost days of charging.

Small 125 AH bank takes this advantage away - he has to run a generator the next day, if it rains. 90W panel also will result in running a generator after a few days no matter what weather, because it will never collect enough for his daily needs so the bank will go lower and lower.

OP: Whether $1.20 per watt (before controller cost) is high or low, depends on shipping. Note that 24V panel does require MPPT that costs $50-90 more than PWM. I think I saw cheaper panels under 100W, but shipping was expensive. The smaller the panel, the more it costs per watt, generally. Check Solar Blvd, Blue Pacific Solar, Arizona Wind and Sun etc. Most places have a warehouse with free pickup, so it depends where you are.

The single 190w panel weighs 37lb the two 90w weigh 35.28lb

It's not about total weight of 2 panels VS one bigger panel. When total watts are the same, total weight will be close too. It's about one single item that weighs 37 lb, and is so big that you can't see anything around and can't maneuver with it on the roof, and then wind comes and off you go.