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ajriding

st clair

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Posted: 08/30/19 02:23pm Link  |  Quote  |  Print  |  Notify Moderator

I did a little experiment.

I have a new poly 100 watt panel. Before installing

I tilted the panel to face directly into the sun. 19.6 volts.

I tilted it the same angle, but away from the sun, so at a very bad angle to still have sun hit it. 18.4 volts, was not that less of a tilt to be 19.6 (1 volt less).

I tilted it to be in the shade, only ambient light. 17.x volts.

I don't feel so bad that the panels lay flat on the roof. The bad angle was about 5% less volts. Shade was 6.x% less volts.

The controller will drop the voltage down to 14 or so, but amps will still be lower, probably 5% too.

5-6% is not bad for being able to just lay the panels flat. I see RVers with rigs where they can angle the panels perfectly and get that 5%, maybe they need it.

Am I missing something?

Lwiddis

Kern County, CA

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Posted: 08/30/19 02:38pm Link  |  Quote  |  Print  |  Notify Moderator

I view tilting panels on the top of an RV as lots of work. Easier to add anothe panel IMO. Good report!


Winnebago 2101DS TT & 2020 Chevy Silverado 1500 LTZ Z71, 300 watts solar-parallel & MPPT, Trojan T-125s. TALL pole for flags. Prefer USFS, COE, BLM, NPS, TVA, USF&WS, state & county camps. Bicyclist! 14 year Army vet - 11B40 then 11A - (MOS 1542 & 1560)


Son of Norway

Denver, Colorado

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Posted: 08/30/19 02:41pm Link  |  Quote  |  Print  |  Notify Moderator

There is a video on youtube, "What effect does tilt angle have on solar panels?" By the altE store. She comes up with numbers that are a lot different. Interesting video worth watching.


Miles and Darcey
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CA Traveler

The Western States

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Posted: 08/30/19 02:42pm Link  |  Quote  |  Print  |  Notify Moderator

Yes, It's the amps that go down with less sun light.


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2oldman

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Posted: 08/30/19 02:45pm Link  |  Quote  |  Print  |  Notify Moderator

CA Traveler wrote:

Yes, It's the amps that go down with less sun light.
X2. Voltage is not your concern, amps are. At your 'very bad angle' it's probably less than 1 amp.

A tilted harvest for me in December in So Cal is about 30- 50% more for a full day. That's significant.

CA Traveler

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Posted: 08/30/19 02:52pm Link  |  Quote  |  Print  |  Notify Moderator

Look at the panels IR curves. As you found out some change in volts but there is a lot of change in amp as the amount of light varies.

naturist

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Posted: 08/30/19 03:02pm Link  |  Quote  |  Print  |  Notify Moderator

Yup, what they said. The power output of your panels relative to sun angle is measurable ONLY when they are charging a battery (or running gear that will absorb all the energy they put out), and then you must measure both the voltage and the amperage, as the power (expressed in watts) is the product of volts times amps. Merely measuring the voltage, especially on an open circuit, is meaningless.

At 19.6 volts, full output from a 100 watt panel would yield 5.1 amps. When you tilted the panel the opposite direction away from the sun, you measured 18.4 volts. I would expect you to get at best 1 amp and probably much less, for no more than 18 watts for AT LEAST an 80% drop off in power output. But that's just a guess.

* This post was edited 08/30/19 03:08pm by naturist *





noteven

Turtle Island

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Posted: 08/30/19 03:14pm Link  |  Quote  |  Print  |  Notify Moderator

And the colder your panels are the more output.

Ed_Gee

Central Oregon coast - Winter in AZ

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Posted: 08/30/19 04:28pm Link  |  Quote  |  Print  |  Notify Moderator

As others have already commented on ... AMPs are your primary concern. If you have a DVM that measures 10 Amps or more, I would suggest you perform a short circuit current measurement on your solar panel instead of measuring volts.. this will give you a more realistic indication of what you are losing when you are not facing the sun....


Ed - on the Central Oregon coast
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pianotuna

Regina, SK, Canada

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Posted: 08/30/19 05:02pm Link  |  Quote  |  Print  |  Notify Moderator

Hi ajriding,

Thanks for taking the time to experiment and share it with us.

Solar panels are a 'constant voltage' device. You may loose 25 to 30% by not tilting. But NO WAY am I climbing the roof in a storm to stow the panels.

I'd consider a remote controlled tilting mechanism--but it is cheaper just to add another panel.

I trust folk's opinions when they have actually done an experiment, rather than guessing.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

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