Solar sizing

jmaguire · Mar 8, 2012

I am working on a project to make a mobile solar power station for our RV's. I am going to size the load to run all the 12v. loads in the RV, and charge a dual battery setup during the day to power the loads at night. I need the following information to complete the load analysis.
1. The wattage of the reefer while using lp gas.
2. The wattage of the water heater using lp gas.
3. The wattage of the water pump.
4. Approximate lighting wattages.
5. Any incidental wattages like CO detectors ect.

This will go into my calculations for panels and inverter/controller. Hopefully I will be making a solar panel setup that can be stored in the RV, and then setup when the RV is setup. You should always try and face your panels south, and angle them close to your latitude angle.

brianharrison · Mar 8, 2012

I have not found a comprehensive table for all 12V draws in our trailers. You'll probably have to look at a couple of info sources and estimate some others based on comparative end devices. Remember to multiply draws by time usage to calculate total amps per day; not all draws are working at the same time.

You talk to an inverter - not sure if you are also looking for the 120v draws as well. There are some great links as well for that subject

Here are a couple of links 12v draws:
http://rvservices.koa.com/rvinformation/rvmaintenance/rv-converters-and-amp-draw.asp

http://www.mrsolar.com/pdf/rv/rv_solar_sizing_worksheet.pdf

Inverter links:
http://www.jackdanmayer.com/rv_electrical_and_solar.htm

Hope this helps.

Take care,
Brian

sdrubrecht · Mar 8, 2012

You can remove the fuses and use a multi-meter to measure the amp draw across the fuse prongs. If you really want to save, replacing the most used 12 volt bulbs with LED can save you a panel and a battery. Average incandesent is 1.5 amps, LED draw only .3, plus brighter. Cost about $400 to do my Cyclone but saves over 10 amps when all the lights are on. Costs as much as a solar panel, but cuts way down on draw, especially in winter when lights are on a lot and the sun isn't as strong. Lots of info on LED here and on RV.net. I got mine at superbrightleds.com.
We have a 225 watt system and 2 L16 6volt batteries. Takes care of our needs most of the time, including the inverter to run DVD player and flat screen TV. A little shy in the winter on cloudy days when the heater is on, but the Cyclone has a built in Genny.
Mine are mounted permanently on the roof. Not as efficient but always there and working, nothing to set up.
Good luck with your system.

CrazyCooter · Mar 8, 2012

I can easily give you current draw from any of those components from my Magnum BMK when I get home.

The get you started, the standard 1141 bulb used in most lighting fixtures is 16w or 1.33Ah @ 12V and My Cyclone has a 1.9Ah draw with nothing on other than the memory/clock for the radio and the carbon monoxide detector.

With efficiency losses, that would take 170W worth of panels to recover just those losses in my location winter time.

We have nearly 1200 watts on the roof and 750Ah battery bank for winter camping. Looking into LEDs as every light on in the rig draw almost 80Ah!

jmaguire · Mar 8, 2012

Thanks for the quick replies. I guess the thing to do is add up all the loads, and then size the panel and controller. And then see about reducing the load with the led lights. When you look at what they are you really see how innefficient they are.

CrazyCooter · Mar 8, 2012

OK this is what I observed tonight....

@ 12.7 battery voltage:

Parasitic draw with nothing turned on 1.6A

Water heater .6A when the burner lit, likely another .1-.3A when the switch is on but not lit...I didn't let it warm up so I can't tell ya for sure.
Refer .2 idle and when the burner lit .5A
Light fixture with 2 1141's installed 3.0A
Water pump while not pumping but switch on .2A

If you don't want to spend big money on something to monitor your DC consumption and don't have huge draws like an inverter, you could install one of these and it will do the counting for you.... http://www.powerwerx.com/digital-meters/doc-wattson-meter-dc-inline.html#desc

jmaguire · Mar 11, 2012

Thanks for the info. I can use those numbers to size my system.

porthole · Mar 11, 2012

when you size your system it will most likely be for optimum sun. Many folks overcome that by just adding another panel.

There are kits already on the market that include knock down PVC frames to mount the panels and set on the ground. You could do it yourself just as easily.

CrazyCooter · Mar 11, 2012

porthole said:
when you size your system it will most likely be for optimum sun. Many folks overcome that by just adding another panel.

There are kits already on the market that include knock down PVC frames to mount the panels and set on the ground. You could do it yourself just as easily.

This is why mine is so large. I didn't want a portable system of have to go up on the roof to tilt them. Sometimes we get gusts over 60 mph out of nowhere in the desert and neither of those setup would "Fly" with us...no pun intended there.....

The best efficiency to date is 88%

wdk450 · Mar 11, 2012

CrazyCooter:
Another reason you might want to overrate the needed solar panels is that recent data says that they deteriorate in power output with age, and especially deteriorate in high heat (which you get on good sunny solar days). This from an investment newsletter writing about solar power.

CrazyCooter · Mar 11, 2012

Yepper...just like almost everything in life, it is best the day you get it and only gets worse from then on out!

I remember reading some of the technical data that was supplied with these panels that was bragging about the longevity of the output with age as compared to another leading brand.....

I could use more PV up there for the winter months, but it really isn't practical. I already drained my pocket enough so we'll have to live with a little bit of generator run time now and then. Besides, I have yet to see a larger RV system. Nothing to prove now.....

brianharrison · Mar 12, 2012

CrazyCooter said:
I already drained my pocket enough so we'll have to live with a little bit of generator run time now and then. Besides, I have yet to see a larger RV system. Nothing to prove now.....

I had to laugh at this one - the DW always tell me "the difference between men and boys is the size of their toys".....

Take care,
Brian

wdk450 · Mar 12, 2012

The company cited in the investment report was making a stockholders report saying that although they warrantied the panel's outputs for 25 years at above 80% of original output, they now expect a high percentage of sales to make warranty claims on this issue. Let's see if they are still in business for another 25 (or 5) years.

Urban350 · Mar 12, 2012

I have 2 75 watt panels on my trailer that were purchased in 2002 and I have not really noticed any performance drop in them (this is the 4th trailer they have been on).

CrazyCooter · Mar 12, 2012

wdk450 said:
The company cited in the investment report was making a stockholders report saying that although they warrantied the panel's outputs for 25 years at above 80% of original output, they now expect a high percentage of sales to make warranty claims on this issue. Let's see if they are still in business for another 25 (or 5) years.

My thoughts exactly!

With wiring the pairs in series like I did, it only takes 1 bad seed to reduce output by 1/3.

CrazyCooter · Mar 12, 2012

Urban350 said:
I have 2 75 watt panels on my trailer that were purchased in 2002 and I have not really noticed any performance drop in them (this is the 4th trailer they have been on).

With an array of your size, you would have to be in a controlled environment to notice the 7% loss of output over 10 years. That's like 9 Wh loss over 10 years.

My controller stores 128 days of data. Over this first year, I'll be making notes as to what max output voltage/kw outputs are. With an array of this size and the tracker keeping record, I'd notice 78 Wh lost pretty easy.

readytohitheroad · Mar 12, 2012

panels lose 1% of their generating power per year

Solar sizing

jmaguire

Well-known member

brianharrison

Well-known member

sdrubrecht

Active Member

CrazyCooter

Well-known member

jmaguire

Well-known member

CrazyCooter

Well-known member

jmaguire

Well-known member

porthole

Retired

CrazyCooter

Well-known member

wdk450

Well-known member

CrazyCooter

Well-known member

brianharrison

Well-known member

wdk450

Well-known member

Urban350

Well-known member

CrazyCooter

Well-known member

CrazyCooter

Well-known member

readytohitheroad

Well-known member

Similar threads