Recommendations regarding Solar Power

smkettner - 2700 W of solar panels should cost less than $2K. You could conceiviably put 14 x 270 W panels on your roof if you didn't worry about a/c and other protruberance. You could probably get 10 without much trouble. We have 1420 W and could put on another 700 if we really worked at it. The 15,000 BTU takes about 2 kW once one realizes the losses through controller, inverter etc. Solar goes through controller to 9.6 kW-hrs of LFP and then through 4.0 PSW inverter. There are definite power losses at each stage. You can do it if you choose. 10 panels would weigh around 400 pounds.

We run off solar/batteries for a couple of hours to get temperatures down to comfortable but it does drain around 1 kW from the batteries in full solar insolation so we have never run more than 4 hours straight to about 55% DOD (LFP). Once it is comfortable, we use the 12V fans.

We are "Goldilockers", "Not to hot and not to cold, just right!" Go up in elevation or north when hot, reverse when cold. But sometimes that just does not work.

But then again with regards to Goldilocks "...Something very strange about the Three Bears, 'how could the porridge be too hot, too cold, and just right if it was poured at the same time?" from "The Fourth Bear" by Jasper Fforde.
Reed and Elaine

Many thanx, MrWizard

it is sometimes better do to a screen snapshot
and post as a picture



please excuse the colored lines pointing to the correct colums

The only wire in my system on the list is the 10 gauge from the panels to the combiner box. Every thing else is thicker. I've sized for less than two percent voltage drop.

From my notebook to yours

WIRE SIZES !!!

I have used this in the making of test fixtures for about 40 years and acquired it before I had ever heard of or worked for ITT-Gilfillan.

I hope this helps you out.

FILE: Gilfillan_Standard

Current Carrying Capabilities of Wire

Gilfillan Standard

Max Current Circ. Mils Resistance in
AWG in Amperes per Ampere Ohms/1000 ft @ 25 deg C
26 1.4 180 42.9
24 2.0 200 26.8
22 2.5 255 16.7
20 3.7 275 10.6
18 5.0 325 6.57
16 6.5 370 4.85
14 8.5 450 3.05
12 11.5 530 1.92
10 16.5 570 1.24
8 23.0 730 0.726
6 30.0 895 0.444

NOTES: These current ratings are based on 50% of the maximum allowable under
Specification MIL-W-5088A for wires and cables in bundles of 15 or more
carrying no more than 20 percent of the total carrying capacity of the bundle.

Frequently the maximum allowable IR drop (not the current capablility)
will determine the wire gauge.

This is actually a fairly conservative guide. Depending on circumstances you could go up or down on the wire size.

gonzo

PS I see the site has compressed the lines. If I could attach an excel file it would be easier to read.

G

smkettner wrote:

Almot wrote:
One thing that RV-size solar can't do, is A/C.

Some day you are going to read about my ~32' RV with 10x 270w panels (2.7 kW) shading the roof and running the air conditioner :B

That would be cool! I'm glad I won't have to pay for it! ;)

Almot wrote:
One thing that RV-size solar can't do, is A/C.

Some day you are going to read about my ~32' RV with 10x 270w panels (2.7 kW) shading the roof and running the air conditioner :B

Well, then it will be easier for you to embrace the idea of big panels and MPPT controller, as well as alternative ways of heating and cooling the rig, like Fan-tastic vents and cat heaters. Solar can do a lot, almost everything. One thing that RV-size solar can't do, is A/C.

Yes I R an engineer. Now retired. Had many, many different jobs, in the electronics realm. Mostly self-taught; no degree. Worked several companies as a tech and kept getting promoted. Started out USN (ETN3), was department scrounge. Innovation is the ticket.

Gonzo42, what exactly you mean by "topped of"?

To keep the battery from self-discharging while in storage, you only need a tiny panel ~5W per 100 AH battery.

To bring the battery back to full charge after you've been using it all day (or night), you need a solar big enough to harvest this amount of energy. To tell exactly how big, we need to know how much energy you are using in 24 hours.

If you want to go for 2 separate panels for 2 separate batts, I wouldn't worry about starter batt because it is being kept full - more or less - by alternator when truck is running. So a small 5w or 10w panel that you can throw on the hood or on the roof, will do the job.

The panel for a coach battery is a different story. A/C will not run on solar, forget about it. Everything else - will, but as I wrote before, the size depends on what you are going to run and on your location. To give you an idea, in a sunny place 120-160W panel will run everything but 120V devices bigger than LED TV. It won't harvest enough energy to run MW (or just barely), or a toaster, or a big vacuum. People thinking that a compact 700W microwave draws 700W, are in for a big disappointment because manufacturers only specify "cooking power", and never tell you that 700W MW would draw 1,100 or 1,200W.