Solar panel advice needed

[firetrucker]

John, I thought you were going to use #8 from the panels, which seemed overkill. Does your combiner have breakers that let you switch panels in and out of the circuit?

Do you have a high current ac clamp meter? I got a couple from HF that I carry in the rig. I'm still going to get the Hall effect dc current sensors, and since they'll measure ac as well, I'll hook them to an oscilloscope or an A/D converter attached to the computer so I can monitor the waveforms, too.

Looks like most of the nasty weather is going north of us here. With any luck, I'll have the tower finished and the new antennas attached, and everything back up in the air this weekend. Winds slowed me down yesterday. Next radio job will be to get antennas for the truck and trailer.

Bob

[WorkerB]

Bob, You made me go out to the Monty and measure with a tape. It's worse than I thought.
The distance from the top of the fridge vent to the bottom of the belly is 9 feet. From that point to the batteries it is in a conduit and it is exactly 18 feet plus a couple of feet for routing. That is a total of 29 feet. I'm running 28.6 Amps out of the combined panels to the controller. What does your chart say? Mine says NO. I may have to re-engineer and come down the Black Tank Vent. Then it would be about 6 feet from the roof vent to the ceiling of the basement and 4 feet across the basement ceiling and 2 feet into the battery compartment for a total of 12 feet. I have a 500 ft roll of #8 and 4 50 foot rolls of #6. I think #6 won't be overkill. YOU?

[firetrucker]

#6 is right on the edge of losses for that run, fine for ampacity. If it weren't for the losses, #12 would be just fine. Can you mount the combiner somewhere on the belly? #12 would get you 30 feet at 5 amps with 2% loss from the panels.

Bob

[WorkerB]

That means I would have to run 12 conductors from the roof to wherever. Sure would be nice to have test access indoors. Hmmmm Robbie may have had a point about moving the combiner off the roof. I have 3 options for combiner boxes. More study required. I'll let you know what I come up with. I guess we are on topic. Doing all this on the ground would have been even more interesting. There, On topic....... sort of.
John

[firetrucker]

Well, John, it IS your topic!

Working with that calculator and some different scenarios, if you paired the panels on the roof, you could still use #12 with a 15 foot run, with 2% loss, at 10 amps. Then you'd only need to run six #12 wires to the combiner down below.

Bob

[WorkerB]

You've got a point. In answer to your previous question my combiner boxes are nothing more than weatherproof plastic boxes with the ability to add two posts. One for the positive and one post for all the negative. No fuses or breakers although one box has an 8 position buss that all the positives could attach to making it possible to get an amp meter is series to test if necessary. I want to use the KISS method wherever possible. I think I'm just going to go to ebay and buy a DC amp meter and be done with it.
Since I have #10 wire and it's just sitting there that is what I will be using instead of #12. Same with #6 wire.

[firetrucker]

I'd be tempted to use some of those Anderson PowerPole connectors from PEI, at least up at the panels...low resistance, high current, and convenient if something needs to be disassembled. The 50 amp connectors will handle #6 on up, and the 30 amp will take #12, and you can make a 'Y' pretty easily to pair up the panels. They also make it easy to put a dc meter in series.

[WorkerB]

I don't think those connectors are designed for outside use. They would also create 4 more connections per panel increasing potential trouble. I plan on having a pair of panels up front on the right and left sides and two panels toward the rear one on the left and one on the right side of the trailer. Your idea of combining each pair of panels and reducing the conductors by half make sense. The spec sheet for one panel says 4.62 Amps. Considering they are used it's safe to say they will never make that much in their remaining lifetime. 4.62 times two panels = 9.64 amps. My book says I can run 10 amps at 12 Volts on #8 wire for 18 feet. That is where the combiner box will have to live. From there I will take #6 down to the battery plant. You mentioned that your book says x amount of feet round trip. I didn't understand that. My book say "Maximum one way Distance for less than 2% voltage drop" The wind is really getting with it here. Light rain. How is it in Nevada?
http://i20.photobucket.com/albums/b2.../WireChart.jpg

[simonsrf]

You know, just about anyone could jump in here and offer their wisdom...nah, think you guys are way over everyone else's head.

Carry on. :-) I'm still reading, anyway.

[firetrucker]

Winds are mild, upper teens, and the temp is going down with the sun, but we're still in the 50s. A few winds clouds, but I think everything is north of us.

Round trip means the plus and minus lead length, which I read then forgot about. Forget everything I said about AWG and current. My calculator agrees with your book, now that I'm doing it right.

I could be wrong (sometimes a pretty high probability), but I thought I saw weatherproof boots for those connectors, though the voltage isn't high enough to have a problem.

[WorkerB]

Jump in Robbie. Any wisdom or technical help is always welcome.

[firetrucker]

Robbie, have you ever measured the output of your panels under different conditions, like time of day, orientation, and latitude?

Is this something we should set up for Q? I'm going to invest in several Hall effect sensors to measure dc amps without interrupting the circuit, so we can take measurements pretty easily for each panel and for the entire system.

Do you have a maximum power point tracker for your system?

[simonsrf]

Not sure what you mean by a "maximum output tracker", but I do have a monitor that tells me how much is hitting the batteries and how much is being used...is that what you mean?

You're welcome to explore my system all you want. It has been working without complaints from us for 3 years.

[firetrucker]

Well, sometimes things are best left to their own devices, right?

A maximum peak power tracker (MPPT) is a microprocessor-controlled converter that goes in between the panels and the load and adjusts the load so that it looks like the optimum load to the panels. This will make the panels operate at their most efficient operating point. It increases the operating efficiency of the panels, as opposed to the solar conversion efficiency, which you get by tilting, rotating, cleaning, and cooling the panels. (Sounds like a lecture, doesn't it?)

Bob

[simonsrf]

quote:Originally posted by firetrucker

Well, sometimes things are best left to their own devices, right?

A maximum peak power tracker (MPPT) is a microprocessor-controlled converter that goes in between the panels and the load and adjusts the load so that it looks like the optimum load to the panels. This will make the panels operate at their most efficient operating point. It increases the operating efficiency of the panels, as opposed to the solar conversion efficiency, which you get by tilting, rotating, cleaning, and cooling the panels. (Sounds like a lecture, doesn't it?)

Bob

Nope, not a lecture; but an opportunity to learn..."esplane" it all to me at Q.... :-)

There will be several rigs to play with there.

[WorkerB]

Bob,
I have several hall effect sensors left over from Satellite tracking systems. I suspect what you have is different, at least in configuration. You have a link describing the hall effect sensors you have?
John

[firetrucker]

Those sensors are just on/off I believe, John. Here are some links to sensors (