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 > How much power does solar panels actually generate?

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Acei

Toronto

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Posted: 06/13/13 08:55pm Link  |  Quote  |  Print  |  Notify Moderator

Lets say the solar panel is rated at 500w, how much power should I expect it to generate on a sunny day vs cloudy day vs rainy day?

As a separate question, is it possible to run a residential fridge 24/7 on a solar panel + batteries? If so, what kind of setup would I need? This will be done on a full-timing 5th wheel unit pulled by a dually, so weight should't be a problem.

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Posted: 06/13/13 09:10pm Link  |  Quote  |  Print  |  Notify Moderator

A 100 watt light bulb will use 100 watts of electricity.
If you have a 500w solar panel that is what you should get on a sunny day.

I can run our fridge on battery for several days and we have a very small solar panel just to maintain charge.


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westend

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Posted: 06/13/13 09:26pm Link  |  Quote  |  Print  |  Notify Moderator

Don't know of any module that produces 500 watts but that doesn't mean there isn't one. Theoretically, solar panels will produce full output when in a laboratory with the correct luminescence supplied. That is how they are rated. Angle towards the sun, time of day, and amount of available sunlight all factor into the output. Practically, my 235 watt module still is producing some power, albeit very little, at dusk and dawn. It will also make some power on cloudy and rainy days, but not near the rating watts. This is a polycrystalline cell module. Monocrystalline, especially thin film, will produce, relatively, more power in lower light conditions.

Yes, you can run an electric fridge with solar and sufficient batteries for storage. I'm using a small 120v dorm fridge that draws 80 watts when operating. I have 320 AH of batteries and a single 235 watt module. I have yet to test all of it out full time but I'm pretty confident it will work out well.


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pianotuna

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Posted: 06/13/13 10:02pm Link  |  Quote  |  Print  |  Notify Moderator

Hi,

I would venture a guess of about 50 watts of output from a 500 watt array at solar noon in moderate rain. That would depend on the choice of panel and the type of cell. I get about 36 watts from 256 watts of Uni-solar panels in moderate rain.

In perfect solar conditions a 500 watt panel may only output about 450 watts.

50 watts doesn't sound like much--but it is enough to cover parasitic loads and do a smidgen of charging too.

With a properly sized battery bank and enough watts of panels a residential fridge can be run.

* This post was edited 06/13/13 10:26pm by pianotuna *


Regards, Don
Full Time in a Kustom Koach Class C 28'5", 256 watts Unisolar, 875 amp hours in two battery banks 12 volt batteries, 2500 MSW watt inverter.

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Posted: 06/13/13 10:08pm Link  |  Quote  |  Print  |  Notify Moderator

No problem running a residential fridge with a few hundred watts of solar and at least four batteries. If you are in consistent shaded condition (read rainy days) you will have to step up the size of the battery bank and/or dollar array.


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Posted: 06/13/13 10:09pm Link  |  Quote  |  Print  |  Notify Moderator

A 500 watt solar panel sure would be nice
If you find one lemme know where to get one.

In other news:
Expect about 100 watts per panel at around 5 amps full exposure.
60-70% light cloud cover.
Negligible output during rain.

This has been my experience with middle of the road panels.





Golden_HVAC

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Posted: 06/13/13 10:17pm Link  |  Quote  |  Print  |  Notify Moderator

I have a total of 415 rated watts on my RV. I get about 21 amps peak, or about 100 - 120 amp hours per day. Not nearly as much as the rated output, but that is what it is.

My RV uses about 35 amp hours per day to run the refrigerator, CO detector and propane detector. I have changed over several lights to LED, and have a 300 watt inverter to run the TV and satellite system when dry camping. I can camp for about 5 days before needing to recharge a little bit, or can avoid recharging at all by not watching so much TV.

To run a refrigerator, you will first need to figure out how many watts the refrigerator will use. Say it is a 2 door with a 300 watt compressor without ice maker (probably don't want to use the RV water to make ice anyway). It can run about 5 hours per day, for a total use of about 1,500 watts.

If it has a ice maker, then the 300 watt heater in the ice maker will need to be taken into account, along with a lot more run time on the compressor, so figure about 3,000 watts per day, and minimum 1,800 watt pure sign wave inverter.

Even the smaller refrigerator would require about 1,000 watt pure sine wave inverter to run the compressor. Start up wattage is about 3 times the running watts, and might drop the voltage to low if the inverter is not large enough.

A low cost modified sine wave inverter is not going to work. They do not produce a sign wave clean enough to run a high torque motor.

I would recommend Outback, or another higher quality inverter. After all you want it to last for many years, and provide reliable power.

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Acei

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Posted: 06/13/13 10:26pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks for the responses.

When I mentioned 500w, it's not a single panel - say two 260w panels. I never looked at the roof view of a 5th wheel before though. How much panels can a typical 33ft 5th wheel handle on the roof?

I just read up a bit more on the solar panels. So it appears that there are 3 different types of panels - mono-crystal, poly-crystal, and amorphous. Unfortunately, none of them are best in all conditions so it will be either mono-crystal (for sunny days) or amorphous for cloudy/shady days. Is it possible to mix the two types of panels on the same roof?

I'm still not sure if I should go residential for the fridge, but we do expect to be off grid for perhaps 2 weeks at a time. So the solar panel might not be able to handle that if we end up with couple of rainy days in a row. If we are forced to get a Norcold 3-way fridge, how long does a can of 30lb propane last, assuming no furnace use?

I'm thinking of installing either 4 or 6 golf cart batteries.

Acei

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Posted: 06/13/13 10:30pm Link  |  Quote  |  Print  |  Notify Moderator

Golden_HVAC wrote:

I have a total of 415 rated watts on my RV. I get about 21 amps peak, or about 100 - 120 amp hours per day. Not nearly as much as the rated output, but that is what it is.

My RV uses about 35 amp hours per day to run the refrigerator, CO detector and propane detector. I have changed over several lights to LED, and have a 300 watt inverter to run the TV and satellite system when dry camping. I can camp for about 5 days before needing to recharge a little bit, or can avoid recharging at all by not watching so much TV.

To run a refrigerator, you will first need to figure out how many watts the refrigerator will use. Say it is a 2 door with a 300 watt compressor without ice maker (probably don't want to use the RV water to make ice anyway). It can run about 5 hours per day, for a total use of about 1,500 watts.

If it has a ice maker, then the 300 watt heater in the ice maker will need to be taken into account, along with a lot more run time on the compressor, so figure about 3,000 watts per day, and minimum 1,800 watt pure sign wave inverter.

Even the smaller refrigerator would require about 1,000 watt pure sine wave inverter to run the compressor. Start up wattage is about 3 times the running watts, and might drop the voltage to low if the inverter is not large enough.

A low cost modified sine wave inverter is not going to work. They do not produce a sign wave clean enough to run a high torque motor.

I would recommend Outback, or another higher quality inverter. After all you want it to last for many years, and provide reliable power.

SolarOnSale.com

SunElec.com

Fred.


Very useful, thanks.

I don't mind getting a good quality components up front - this rig will be used for 8+ years so I'm trying to get everything as close to ideal as I can get. I'm trying to install the maximum (within a sensible limit of course) amount of solar system on this rig. I may still carry a generator for emergency use though.

pianotuna

Regina, SK, Canada

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Posted: 06/13/13 10:32pm Link  |  Quote  |  Print  |  Notify Moderator

Here is a simple flow chart.

Budget-->Energy Audit-->Battery bank size-->number of watts-->PWM or MPPT.

Here is a link to the rather special spreadsheet that N8GS has created to help size solar battery charging systems!

Solar spreadsheet by N8GS

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