Solar panels for dummies

[Lesherp]

The more I think about this the more complicated I seem to make it. At first I thought the CEA 130 watt folding portable RV Solar System might be the ticket. However it is only 130 watts and has a PWM controller that is attached to the panels that would be maybe 40' from the battery. This is not optimal at a cost of $600.

I than considered making my own portable unit with Kyocera KD 140GX ($285) with Blue Sky SB251i MPPT ($180) with additional cost of wire etc. It seemed like, from what I have read, this setup would maybe be 30% more efficient with an MPPT controller pulse extra 10 watts. The problem I had with this is that the panel is 59" by 26" and 28 lbs. I think handling and storage might be cumbersome. I began to think two 85 Watt panels might be better ($200 each an extra $115)
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If I am going to have two panels I am now considering one roof mounted and one portable. When considering advantages and disadvantages of portable vs roof mounted I was leaning toward portable despite the fact that my batteries discharge when I'm traveling with the refrigerator running on DC. Another advantage would be that electricity used the night before traveling could be restored in transit. For an extra $80 I could put a 140 Watt on the roof so depending on the sun at the camp site and electricity usage I might not even need to set up the portable panel.

I would end up with 225 watts and some versatility that I think might be worth the cost and effort. Panels and controller would run $665 and I am hopping the rest of what I would need would be under $200. It that reasonable thinking?

Does anyone see any problems with doing this?

I have not worked out how to wire it yet and would probably need some consultation.

Here is the controller I am considering. Will work or if there is a better option?

http://www.solar-electric.com/sbchco2512vm.html

I see almost all the panels have CM4 connectors but that you can get some with a junction box. Any thought on what would be better.

Here are the panels I am considering.

http://www.solar-electric.com/so85wa12voso.html
http://www.solar-electric.com/kykd140wa12v1.html

[Brittany Dogs]

And when all is said and done, a Honda 1000 or 2000 just hums away quietly, at about the same price.

I understand your desire to go green and if you have a lot of sunlight every day, the recurring cost is less than an inverter generator and solar is silent. I just happen to live in an area of the country where the generators make more sense than solar panels. So my thinking is skewed.

[B_and_D]

Originally Posted by Brittany Dogs

And when all is said and done, a Honda 1000 or 2000 just hums away quietly, at about the same price.

I understand your desire to go green and if you have a lot of sunlight every day, the recurring cost is less than an inverter generator and solar is silent. I just happen to live in an area of the country where the generators make more sense than solar panels. So my thinking is skewed.

What if you can't buy gas?

[LoveToCamp]

I have not installed this, yet, but I bought a 100 watt panel. for $220. My dad had an 85 watt on his TT, and never ran out of power (single 12v battery). Unless it was raining all day, he recharged almost completely, to completely every day.

Seems like a good price, and sufficient output that I can go for weeks without other charging. I'll find out this summer, as I have a 10-day planned, all dry camping.

I got the 3M tape (don't have it in front of me - will edit when I get the details) online. This is what The Car Show uses to mount their panels. Clean the roof with rubbing alcohol before using, and they say it lasts for years. After installation, seal the edges with white silicone.

[Bill]

Let me toss one more comment into the mix to simplify your choice. You mentioned the possibility of buying an MPPT controller. You should know that although MPPT can get a few more watts out of a solar panel setup, and they are very valuable in large solar applications, they do not pay for themselves in a small solar system.

To illustrate, suppose an MPPT controller can get an extra 10% out of a set of solar panels. If you have a large array (for illustration, say 10,000 watts), then the MPPT controller will get an extra 1000 watts out of those panels. When you balance the extra cost of the MPPT controller against the added value of 1000 watts of capacity, MPPT wins. But if you have a small system - say 100 watts - then MPPT will get you 10 added watts. Again you have to balance the added cost of the MPPT controller against the added value of 10 watts of capacity, and MPPT loses. If you really really need those extra 10 watts, then it is cheaper to buy a 110-watt or 120-watt panel.

Stick with a simple controller such as a PWM.

For more info, check the Arizona Wind and Sun website http://www.solar-electric.com/, which sells both kinds of controllers.

Bill

[Lesherp]

Thanks for the information Bill. I had seen some discussion in other threads on this but must have misinterpreted conventional wisdom on this. I thought most were going with MPPT. Interestedly I called Arizona Wind and Sun yesterday and the fellow I talked to recommended I go with a $400 MPPT Morningstar controller over the Blue Sky MPPT controller I was considering if I wanted to be satisfied with the system. He told me he could not recommend going any other way even after I told him that that additional cost would price me out of buying. When I was done talking with him I was unconvinced and confused. I told him I was considering two panels with different watts. So this may have been a reason for his recommendation as he said one of the things this controller would do is equalize the power coming from the panels. Wouldn't they all do that? I now wonder if using two panels of different watts would create a problem if I decided to use a WPM controller. It looks like I need more information. I am not sure I want to call them back as I am not confident I am getting good advice. Any thoughts?

If I am reading correctly the panels I am considering I will be under 15 amps. I just looked at the WPM Morningstar controllers (just one brand the carry but from what I can tell a very respected company) I see two that look like they might work. They are both about the same price with different features and I am not sure how to determine the best one. Any suggestions?
http://www.solar-electric.com/modubachco251.html
http://www.solar-electric.com/pros15solcha.html

[scrubjaysnest]

We have the sunsaver 10 on our two 80 watt panels. It worked great last year out west where could easily reach the 10 amp capacity. Here on the east coast the best we have seen is 9 amps. Even under heavy cloud cover the two panels will produce about 1 to 2 amps which handles our slight needs. I over sized for us on the east coast because of the sun/shade mix we typically see. Ours was a kit from ebay, two panels, 30 feet of 12awg wire and the controller. I replaced the wire with 10 awg marine grade between the panels and the controller. From the controller to the batteries I used 8 awg marine grade. While on the trip last year I connected 1 panel without the controller to a friends camper. I used 15 feet on the 12 awg that came with the system. We monitored his batteries and after 4 hours in full sun in Telluride Co; he had a better charge then with his Honda 2000 genset.

I am surprised with the comments from wind and sun. They have always been great to work with. You should not have issues with mixed panel capacities as long as they are both 12V panels ( vs a 24V and 12V mix). Bill is correct on the controller. The MPPT is more efficient but on a small system adding a larger panel vs more efficient controller is more economical. One suggestion. Get a controller with a capacity a little higher than what you need now. This allows for the addition of another panel in the future. The cost of a slightly larger controller is less than the cost of a second controller if you expand later.

[Bill]

OK, I'm confused as well. Your conversation with Wind-Sun makes no sense to me. By the way, are you sure he didn't mistake your two-different-panel statement to mean two-different-batteries? One of the controllers you linked to was a two-battery controller, for which you have no use.

To try to reduce the complexity of the situation, I spent an hour on the Wind-Sun site looking at controllers. This should be a pretty good cross-section.

MPPT controllers:
Blue Sky 2512I - 25 amp - $182
Morningstar SunSaver15 - 15 amp $223.60
BlueSky SolarBoost SB2000E - 25 amp $253.50 - includes digital meter

PWM controllers:
Xantrex C12 - 12 amp - $77.22 - LED "meter"
Sun Saver SS20L - 20 amp - $78.00
Xantrex C35 - 35 amp - $83.54 - LED "meter"
Morningstar ProStar15 - 15 amp - $85.80

Except as noted, none of these includes a meter, though a meter is often an extra-cost option. I wouldn't bother with a meter unless you are a geek like me.
ALL of these controllers have four stages of charging - bulk, absorption, float, and equalize. As Wind-Sun says in one of its articles, some manufacturers refer to this situation as "four stage charging", while some call it "3 stage charging plus equalize." They are exactly the same.

Having read through all of the specifications and manuals for all of these controllers, the only significant difference I can find is that the MPPT controllers will extract "up to 30% (daily average 10-15%) more power from your panels".

All of this assumes that your panels are nominally 12-volt, not 24-volt, and that you are charging a single battery (or battery bank if you have 6-volt batteries). Using different size panels, or different manufacturer panels, makes no difference.

For an RV application such as we are talking about, I cannot imagine why anyone would recommend (or buy) a $225 MPPT controller over an $80 PWM controller.

Final question to the group - does anyone here keep up with the Wind-Sun solar forum? I used to, but I gave it up several years ago.

Bill

Originally Posted by Bill

...
For an RV application such as we are talking about, I cannot imagine why anyone would recommend (or buy) a $225 MPPT controller over an $80 PWM controller.
...

Bill, you are letting your financial good sense over-ride your inner geek.

What I would like is an MPPT controller complete with computer inter-connect and software to monitor every aspect of the system. Anything else is a mere appliance.