More Solar for "Us"

[MrWizard]

Ok, I went off.the deep end?
Bought 3 used 37watt uni-solar panels and a blue sky 2000e controller for the hefty price of $400,
They were being listed as 75w panels, they are not

The tested open circuit voltage was 21+, short circuit amps 2.9
I tested each panel multiple times tilted into the sun and laying flat on the ground , got the same readings each way, that was the deciding factor, they appear to put out full power while laying flat, I will try to mount them tomorrow before it gets hot, right now 104°F
I will use the existing wiring until I buy & install the new wire

[toolman1]

pianotuna wrote:
Although they are shade tolerant I would NOT put anything over them and especially not chicken wire that would cause minor shading to the entire panel.

I know that there are many posts/replys, since this was posted, (I have no internet service @ work) 😞

My concern would be the chicken wire scratching the PV surface and ruining the panel(s). Wouldn't a plexiglass sheet or suitable substitute work better?

[KendallP]

OK guys. I get it!

🙂

I was going off my Onan 4.0 manual which states, I believe 0.9 GPH. Perhaps that was at full, rated power.

Nice to know I'm not burning as much as I thought! Learn somethin' new everyday!

Thanks!

[HobbyTalk]

KendallP wrote:

At about a gallon/hr for those 63 hours = about 200 clams in fuel savings!

My Yamaha 2400 will use about it's 1.6 gal tank up in about 6 to 8 hours under normal usage (lights, TV, converter, a pot of coffee and a couple uses of the microwave).

[pnichols]

At about a gallon/hr...

Perhaps a little too generous in favor of solar.

The "common" 4KW Onan approximately burns 0.35-0.40 gal/hr when light-duty powering of common RV items -> not counting a heater, or a microwave, or an air conditioner. The little Honda 1000/2000 class inverter generators of course use way less than this when supplying power for the same items.

(My little 550W Honda is off the charts on gasoline stinginess when battery charging, plus lighting, plus computer/movie use - all simultaneously: About 0.51 gallons every 5.5 to 6.5 hours and it's noise is 54dB while doing this.)

[KendallP]

pianotuna wrote:
Hi,

If the figures are correct it is interesting to note that the voltage is, going back to Oct 28, 14.07; Oct 30 13.91 (cloudy); Oct 31 13.82; Nov 30 was 13.51 and today was 13.37 (I divided the watts per day by the amps per day).

If we assume 700 watts per day Mr. Wizard has accumulated power for 46 days amounting to at least 32200 watt/hours or 2555 amp-hours. Guessing at 40 amps per hour from a generator/converter that's 63 hours of generator time or 1.36 hours per day.

At about a gallon/hr for those 63 hours = about 200 clams in fuel savings!

Pretty much a no brainer investment for a full timer.

Occasional weekenders like some of us WOULD get the noise benefit, but might likely sell the rig before the dollars could be recouped.
.

[pianotuna]

Hi,

If the figures are correct it is interesting to note that the voltage is, going back to Oct 28, 14.07; Oct 30 13.91 (cloudy); Oct 31 13.82; Nov 30 was 13.51 and today was 13.37 (I divided the watts per day by the amps per day).

If we assume 700 watts per day Mr. Wizard has accumulated power for 46 days amounting to at least 32200 watt/hours or 2555 amp-hours. Guessing at 40 amps per hour from a generator/converter that's 63 hours of generator time or 1.36 hours per day.

[MrWizard]

normally I run the generator in the morning when the batteries are at their lowest and the solar output is low, then the solar can top them off and carry.most of the daytime usage

however yesterday was an errand day and I did.not run the genset until super time at dusk , so yesterday was an all day.solar charge day, which provides the type of solar reading many of you are interested in knowing, here are the.numbers

752.5 watt hrs
56.27 amp hrs
141.4 peak watts
10.61 peak amps

not all of this went directly into the batteries
remember we have a residential fridge and the inverter is on to power the fridge

I would estimate that at least 40% of the total went into powering the fridge and the rest went into the batteries

the batteries get the full effect when the fridge is off but get Zero & possibly deficit when the fridge compressor is running, depends on how much solar is being produced at that particular "moment in time", it might be going in at 8amps, the fridge cycles and the inverter draws 10amps for a net loss of -2amps while the fridge runs, it's a give & take process all day long

[pianotuna]

Hi Salvo,

Ah, but they do and will radiate. Just hook up a standard panel with no diode--it will radiate at night just fine, while draining the battery.

I suggest you research Uni-Solar panels documented claims about heat tolerance. I did before I purchased mine.

And metal is an even better conductor of heat than glass. The Unisolar panels that Mr. Wizard and I both have are deposited directly on the metal panel. It does radiate heat. My panels are not flush to the roof as the roof is curved.

But this is all way off topic. So to lighten the the discussion here is something wonderfully funny:

1st and 2nd Laws of Thermodynamics

Salvo wrote:
No, I didn't misunderstand you. I suggest you get a grip on thermodynamics before providing misinformation.

1. The panels do not RADIATE heat. Heat transfer is through CONDUCTION.

2. Glass is a pretty good thermal conductor. It's 100 times better conductor than air. It's conductivity is similar to thermal grease.

3. Since all the heat needs to be conducted to air, air is the weakest link in the equation. The surface area of the panel that makes contact to air is the dominate factor in keeping the panel cool.

Sal

[Salvo]

I'll take you up on that bet any day of the week. If you factor in wind and convection currents that help remove heat from the top of the panel, then the heat flow on the top side is much better than the bottom side. The thermal conductivity of fiberglass (0.04 W/mK) is almost as bad as air (0.024 W/mK). For comparison, glass is 1.0 and aluminum is 250 W/mK. On the bottom side, the heat needs to flow through the thin skin of fiberglass perhaps a half meter in length, and then conduct out to air. We're talking about extremely high thermal resistance.

Sal

pnichols wrote:
I'll bet that the lower surface attached to the roof is a better heat conductor than the Uni-Solar's upper surface that is exposed to only air.

[KendallP]

MrWizard wrote:
...the "thin film" vs "conventional" temp debate

IS OVER

Well given the fact that your a mod for these forums... and therefore have the ability to lock this thread... I'm not going to argue with you. Though I know you rv.net mods don't have much in the way of itchy trigger fingers, which is nice.

You missed a good sale on the Harbor Freight gun unit. They normally sell it "on sale" for 40 bucks, but it was $19.99. Of course I had just bought one for my old man for $25. I have a smaller, cheaper version and it seems to be pretty accurate.

Gun Unit

Mine

The third and cheapest one they sell doesn't sound too accurate.

[MrWizard]

I have both types of panels on my white rubber roof

If one of you will loan me an IR temp gun, I will record all temps and post them here

until such time as this happens, the "thin film" vs "conventional" temp debate

IS OVER

[KendallP]

pnichols wrote:
A dark roof will of course be hot all around the edge of it's area that is covered up by the Uni-Solar panel .... so this heat will travel along into this covered up area and then conduct up into the panel material.

There are several ways to look at this, but yes... the way you describe it is essentially correct, IMHO.

[pnichols]

A dark roof will of course be hot all around the edge of it's area that is covered up by the Uni-Solar panel .... so this heat will travel along into this covered up area and then conduct up into the panel material.

[KendallP]

pnichols wrote:
What makes you think that cooling can't occur on BOTH of the Uni-Solar surfaces?

One being the upper surface that's exposed to the air and the other being the surface that's adhesively attached to the roof - assuming that the adhesive is, or can be, of a heat conductive type? I'll bet that the lower surface attached to the roof is a better heat conductor than the Uni-Solar's upper surface that is exposed to only air.

(The above "bet" on my part is assuming your roof is white! A dark roof will HEAT the backside of the Uni-Solar panel.)

Forgive me, but how can black material "HEAT" something if it's not exposed to light of any kind?

And yes... if you're not concerned about heating up the cabin, then the roof should conduct away some heat. I was always operating under the assumption that you don't want to heat up the interior of the coach so much that you need to run your A/C unit through your inverter or even your generator which, would of course kind of nullify the benefit of having solar.

But for someone who only uses their rig in winter...

[pnichols]

What makes you think that cooling can't occur on BOTH of the Uni-Solar surfaces?

One being the upper surface that's exposed to the air and the other being the surface that's adhesively attached to the roof - assuming that the adhesive is, or can be, of a heat conductive type? I'll bet that the lower surface attached to the roof is a better heat conductor than the Uni-Solar's upper surface that is exposed to only air.

(The above "bet" on my part is assuming your roof is white! A dark roof will HEAT the backside of the Uni-Solar panel.)