Solar strategy in the east

Hi BFL13,

I was under the impression that 12 volt panels were a nominal 17 volts--not 21.

Almot wrote:

Snowman9000 wrote:
My interpretation is that since voltage drops off in the shade, a 12v panel is doomed. But a 24v one can still get enough volts to charge with.

I think you're wrong, but let other fellow nerds comment in more details ;)...

Nerd here. When a PWM 12v loses voltage from 21 volts (12v panel) it still has plenty to be over 13v so amps don't suffer. MPPT (37v "24v" panel) makes its amps from voltage so it does suffer if voltage goes down.

You can't make something out of nothing and solar is pretty much of an all or nothing deal. You can get an amp or two in the shade instead of your proper x amps, but so what? 1 amp for 8 hours is 8 AH. Whoopee do.

Snowman9000 wrote:

Shadow Catcher wrote:
The advantage of the high voltage panel is that it produces usable current from sun up to sun down and when shaded.

Can you or anyone expound on the part I highlighted in bold? How does a high volt panel make a difference in the shade? Thanks.

I believe the higher voltage series setup will produce more in marginal and shady conditions.

Hard to do a real comparison test because the equipment is a bit different. Such as a 24v panel cannot be operated at 12v. Bypass diodes are configured different etc.

But if someone has 650 to 700 watts in 12v panels in So Cal.....

Snowman9000 wrote:
My interpretation is that since voltage drops off in the shade, a 12v panel is doomed. But a 24v one can still get enough volts to charge with.

I think you're wrong, but let other fellow nerds comment in more details ;)...

My interpretation is that since voltage drops off in the shade, a 12v panel is doomed. But a 24v one can still get enough volts to charge with.

westend wrote:
I guess a guy has to define how much solar he needs/wants and what it does for him. If you're trying to eliminate use of a generator (admirable goal, IME) and have rather standard use requirements, 200W is even on the short end. Add in shade covering and the no-gen goal isn't going to be met.

I would agree with this rather wide blanket statement :)...

Yes, define you needs and "standard equipment". Of all the standard equipment only MW is a burden when on solar, and requires more than 200W panel and substantial battery bank to eliminate the genny. Probably a realistic goal in the shade too, on some conditions - cover all the roof with panels AND wire them in parallel AND carry a lot of batteries OR don't stay there in the shade for too long.

What Don reports on amorphous Unisolar, is interesting - my 490W regular "rigid" panels in series in leafy shade generate next to nothing. If I were the OP, I would go for amorphous because of shade. AND parallel wiring - because there can be situations when one panel is out in the sun, while the other is not, and then in series both panels will work as if both were in the shade.

If they still run into difficulties after meeting all the above conditions, and if not running a genny is important, you can cook and reheat meals without MW. Other than re-heating a cup of milk for a hot chocolate before bed time, I'm having a hard time understanding why people even like MW. I'm using it in a shore life, and I don't like it. MW does a quick, yes, but poor job of re-heating leftovers - meals become dehydrated, meat and poultry dry and rubberized. So what is left - reheating tomatoes and cheese on sandwiches? And running a genny for that? Alright, I'll say no more...

The OP didn't ask about eliminating a genny though. He asked about saving solar money to buy a gas. This could be a break-even situation, depending on their lifestyle. If you don't factor in the genny cost and only consider the gas, for occasional camping it will take years and years to recover the cost of solar.

Snowman9000 wrote:
Camping out in the AZ desert at the moment, I can see that solar is easy out here. Do the math, install it right, and you are golden.

Hm... As I wrote, my rig is in a desert-ish area. Most Rvs there have solar 200W or more, the weather is sunny 80% of time, and no shading because rigs are permanent so they build solar rack next to the rig, while keeping rig in the shade. Half of the camp is running their gennies at least a couple of hours a day. The other half doesn't. Those who don't, all have more than 300W solar and run their MW rarely. With very few exceptions, people in either half never did "their math" and wouldn't know about any math, no kidding.

I would also like to know more about this claim that MPPT does more vs PWM when insolation is less. (It's not the 24v panel, it's the MPPT that goes with it that counts AFAIK) With the sun direct full insolation the story is then that the PWM is almost as good as the MPPT.

Salvo's graph here does show that the MPPT, by being say an amp over the PWM (same as panel direct connection he did)all day, is twice as good as PWM when PWM is getting 1 amp :) and then when PWM is getting 8 amps mid-day, the MPPT is only a little better at 8.5 amps.

I suspect this is what "they" mean by MPPT doing better in less light, but don't know for sure. If so, it is another example of how you can "spin" statistics. Or maybe there is something real to it?

Shadow Catcher wrote:
Our 6X10 teardrop was designed for serious boondocking with LED lights... There is a 185W 66cell high voltage panel which required a Morningstar MPPT controller. We also have a 135W flexible panel which can be staked out in the sun. but have never had to use it. The advantage of the high voltage panel is that it produces usable current from sun up to sun down and when shaded. We spent 8 days on the north shore of Lake Superior and the camp site had maybe one hour with no shade on the panel.
We powered the Waeco 12v refrigerator XM radio TV/DVD and twin computer case fans in place of a fantastic fan. at the end of eight days we were at 64% SOC with out using the 135W panel.
So yes you can go solar, I have yet to use a generator.

Nice info, thanks. Any idea how many amp hours of usage you averaged per day on that 8 day period? It looks like the fridge would be far and away the biggest load.

Can you or anyone expound on the part I highlighted in bold? How does a high volt panel make a difference in the shade? Thanks.

PS: what voltage is it, exactly?

Our 6X10 teardrop was designed for serious boondocking with LED lights... There is a 185W 66cell high voltage panel which required a Morningstar MPPT controller. We also have a 135W flexible panel which can be staked out in the sun. but have never had to use it. The advantage of the high voltage panel is that it produces usable current from sun up to sun down and when shaded. We spent 8 days on the north shore of Lake Superior and the camp site had maybe one hour with no shade on the panel.
We powered the Waeco 12v refrigerator XM radio TV/DVD and twin computer case fans in place of a fantastic fan. at the end of eight days we were at 64% SOC with out using the 135W panel.
So yes you can go solar, I have yet to use a generator.

I was wondering if although the poly got lower amps in low light but you got more poly watts in the same area as amorphous took, if it would be a wash for amps. IE bang for buck of roof real estate the same or not? Which also brings in cost of each type--no idea there. Anyway it could be all calculated if you had the info.

"The easy solution is left to the student"