solar budget of 2700.00 Canadian

[pianotuna]

Hi all,

I'm going to beef up my solar system. The budget is $2700.00 including installation costs.

I'm considering these because I will be able to pick them up from Calgary and save the (considerable) shipping costs:

poly 245 watt

or

mono 240 watt

Which would you choose for low light performance?

The ones on the roof will be non tilt. I am considering a "wing" on the rear of the RV. That would need to tilt--and cleaning may be an issue. (Cover with six mil poly while traveling? Any other brain storms?)

Assuming four to six panels, what MPPT controller would you choose?

I love my unisolar system. I may be removing it to allow for even more than six panels. I'd really rather keep it in place and simply add a second controller as an independent system.

[nomad_289]

Thanks Sal.

The very bottom of this page documents a series vs parallel test; conducted by an Electrical engineer and his Physics DW. The results astonished me also, which is the only reason I passed it on. Good discussion of the pros and cons of series/parallel, tilt, low light, etc.

http://roadslesstraveled.us/rv-solar

I don't have solar yet so will leave it to the forum to ascertain the best installation for the $2700 panels PT is .not. buying.

One panel partly shaded:

10.0 amps parallel.

1.6 amp series.

They went parallel for their 3rd system. Sailboat solar

[Salvo]

Here you go. Salvo's summary of Gale's shading test:

Thanks for running this test. This scenario is more prevalent than you think. Trees can easily shade one panel and leave the other in the sun. In summer, I'm usually partially in shade to keep the RV cooler. It's always a trade off between maximizing solar charging and minimizing solar load to the rest of the RV.

Reading your graph, I get:

Series or parallel in full sun is about 28A, or 14A per panel.
Series with one panel shaded: 4A
Parallel with one panel shaded: 15A

This is the classic reason why parallel is better. A series array will limit current to that of the least producing panel. The bypass diodes do not help.

The series vs parallel debate is not as clear cut as some think.


In series, you only get 4A out with one panel shaded. Parallel gives you 15A. That's quite significant.

Parallel vs. series test

Sal

[time2roll]

Salvo wrote:
If you "hard" shade a portion of a panel the diodes will conduct. The diodes will not conduct from "soft" shade. A tree some 20 meters away will create soft shade. Your TV antenna will create hard shade.

OK so what do you lose when the diodes conduct? It would seem that would be the maximum loss. Yes you would lose all power added from the covered panel but I would like to quantify how much is lost or held back from the others in series to push the power through the diodes.

[KJINTF]

Remember Gale did a test last year - check the thread details
His results proved for his panels in a series conection worked better for shade tolerance. Some panels, not all do indeed work better in a series mode when it comes to shade tolerance as compared to a parallel connection.

For me a series connection supplying a higher voltage thus less current and lower line losses along with a proper MPPT controller is the only way to go.

Some folks prefer older less expensive technology and the PWM style controllers

To each their own.....

[Salvo]

Funny, usually coming from you is "no test needed".

This test was done perhaps a year or two ago. Don't recall name, but he's a cb guy.

If you "hard" shade a portion of a panel the diodes will conduct. The diodes will not conduct from "soft" shade. A tree some 20 meters away will create soft shade. Your TV antenna will create hard shade.

smkettner wrote:

Need a test on this.

[time2roll]

So the bypass diodes do not actually allow current to flow through?
Not sure why the diodes are even there.

Need a test on this. Going to be a couple weeks to visit this issue myself.

[Salvo]

If one panel is shaded it will still output current. But the shaded panel current is significantly less than the others. The diodes in the shaded panel will not conduct (the panel is producing power). Due to the series string, the shaded panel will significantly reduce total power production.

The parallel configuration will be much better.

You can test this by placing all panels directly into the sun but one. One panel is offset 45 degrees to the sun to simulate shade.

Sal

smkettner wrote:

Salvo wrote:
If however an entire panel in a series string is shaded, the string will output a fraction of its power. Advantage goes to parallel.

If one panel in three is shaded what is the voltage drop of the diodes? I thought it was 2 to 6 volts. But I don't know.

[pianotuna]

Hi,

A VAXT would be nice but I doubt it would come in under $2700.00. Traditional designs are noisy. Deploying in sub freezing temperatures would not even be close to my idea of fun.

[time2roll]

Salvo wrote:
If however an entire panel in a series string is shaded, the string will output a fraction of its power. Advantage goes to parallel.

smkettner wrote:

Except these large panels have bypass diodes that divide the panel in three sections. In parallel a small amount of shade will pretty much take out that panel completely. Series does not shut down the entire array for a few cells getting shade.

If one panel in three is shaded what is the voltage drop of the diodes? I thought it was 2 to 6 volts. But I don't know.

In my case each panel makes 30 volts so one shaded I get 60 volts less the voltage drop of the diodes in the third panel.

I may have to make some measurements one of these days.

Slight shading of all panels may also have your 12v panels all drop out with less than 12v while the series panels making only half voltage would still provide some charge.

Lots of different situations. Shade is always an issue whether series or parallel.

[Salvo]

If however an entire panel in a series string is shaded, the string will output a fraction of its power. Advantage goes to parallel.

smkettner wrote:

Except these large panels have bypass diodes that divide the panel in three sections. In parallel a small amount of shade will pretty much take out that panel completely. Series does not shut down the entire array for a few cells getting shade.

[noteven]

Edited-OP said "solar". Sorry about getting off track.

[pianotuna]

Hi Jim,

And with diodes between all cells series or series parallel may be a better wiring choice.

[HiTech]

And some like Unisolar have a bypass on every solar cell. Major effect on partial shading performance.

Jim

[nomad_289]

smkettner wrote:
large panels have bypass diodes

Good to know, I'll check those other threads. Something to consider when buying new panels, seems not all panels have those.

[time2roll]

nomad 289 wrote:
Pretty convincing case to wire panels in parallel...

"if the panels are all wired in series, when one panel shuts down due to a palm-sized bit of shade, then the entire array of panels shuts down. A tree branch or part of a boat’s standing rigging or mast/boom can cause the entire array to shut down if it is wired in series."

roadslesstravelled-solar

Except these large panels have bypass diodes that divide the panel in three sections. In parallel a small amount of shade will pretty much take out that panel completely. Series does not shut down the entire array for a few cells getting shade.

We have had lengthy threads and testing on this already. Shade is always a big drag but not a disaster.