Design idea: RV battery system

Re: Design idea: RV battery system

Is that 200 watts or 200 Watt*Hours per day? Using PV Watts for San Diego, CA (note, I have entered 1.85 kW for panel size and moved decimal point one place to the left--PV Watts only accepts a minimum of 1 kW of solar panels):

"Station Identification"
"City:","San_Diego"
"State:","California"
"Lat (deg N):", 32.73
"Long (deg W):", 117.17
"Elev (m): ", 9
"PV System Specifications"
"DC Rating:"," 0.19 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.1 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 32.7"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","12.5 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 4.83, 13.3, 1.662 (i.e., $1.66 of power per month)
2, 5.35, 13.3, 1.662
3, 5.91, 16.3, 2.038
4, 6.52, 17.2, 2.150
5, 6.05, 16.5, 2.062
6, 5.98, 15.5, 1.938
7, 6.26, 16.6, 2.075
8, 6.62, 17.4, 2.175
9, 6.02, 15.5, 1.938
10, 5.88, 15.9, 1.988
11, 5.16, 13.7, 1.712
12, 4.67, 12.7, 1.588
"Year", 5.77, 184.0, $23.00

Say you you generate ~15.5 kWH per month per 184 watts of panels during the "sunny months"

• 15.5 kWH * 1/30 days * 1,000 w/kW = 517 Watt*Hours

So, you will generate around 500 WH per day of "useful" AC power per day... If most everything is DC power, back out the 0.85 efficient AC inverter derating:

• 517 Watt*Hours / 0.85 = 608 WH of DC power per day

I would also look at the physical size/weight of a 185 Watt solar panel... You might be better off with a pair of 135 watt panels instead.

At 185 watts--getting close to needed two people to setup/pack that large of solar panel.

Also, remember to stake/secure the solar panel--A gust of wind (or theft) could ruin your day (shattered solar panel from a simple fall is useless).

-Bill

Re: Design idea: RV battery system

Tom Cleary wrote: »

Hello Bill:

Thank you for taking the time to respond to my request for feedback. Correct me if I am wrong but it sounds like the calculations show that my proposed rig may be 'underpaneled?' Is that a useful summing up?

Generically, everyone is under paneled and overloaded when using solar power--It goes with the territory.

I am not sure I understand your power need though... If you are talking about a 200 Watt steady 120 VAC load:

• 517 Watt*Hours / 200 Watts = 2.6 hours of run time minimum for 8 months of the year...

Assuming the panel(s) are setup correctly (tilted around latitude, pointing south, etc.).

This is where conservation comes in--Perhaps a 20 watt fan instead of a swamp cooler. Net book running at 20 watts, two 9 watt CFL bulbs, and a 2-5 watt LED spot/reading light = ~43 watts:

• 517 WH / 43 W = 12 hours per day run-time...

I would suggest going back and measuring your loads (Amps*Hours or Watt*Hours) with a Kill-a-Watt meter for your 120 VAC loads and/or a DC Amp*Hour/Watt*Hour meter like one of these...

It really depends on your needs and your environment. Are some of your loads optional or must be powered (i.e., is computer for play or work).

And how much you expect your loads to grow (more electronics, charging a camera, Internet hardware, etc.). It is not out of the question to expect your loads to double over the next months/years as you find more things to do with your power.

The other feedback about larger panels being more difficult to maneuver and place is something that I have been wondering about... Dimensions of both panels suggest to me that these are objects that are clunky, and difficult to handle. On the other hand, the difference in terms of size isn't that great, the Kyocera 185 is about a foot wider, and about the same length as the Kyocera 135. The difference in weight isn't that great at roughly 8 pounds, but when you have clunky objects to carry, maybe 8 pounds makes a big difference. I haven't personally handled these panels and this is my first pv project, so I don't have a clear idea.

Certainly, your physical size and condition will enter into what you feel comfortable with. As will your storage area for the panel(s) on trips. Also, how often you are going to break camp (5x two week trips a year, or 40x 2 day weekend trips, etc.).

These guys are single thickness tempered window glass (typically) in aluminum frames. It is, more or less, like moving around an aluminum window of similar size--but 3-5x more expensive if you break it (tempered glass tending to shatter the whole panel instead of snapping a small corner off).

You can probably manage a 185 watt panel without too much problem (virtually the same size as a 175 watt panel which one guy can handle pretty safely).

Then you are left with the packing issue--one or two 185 watt panels, or two 135 watt panels (or whatever mix you decide on).

Also, if you look at getting more panels--Say 2x 185 watt panels and you put them in series for 48+ volt Vmp, then you may have to look at the MorningStar TS 45amp MPPT controller--It has a higher input voltage rating than the Rogue.

In the end--You probably will need to do two or three paper designs (different panels, controllers, packing space, energy output, costs) and see what the pluses and minuses are for you--Vs the energy output you need.

I am sorry Tom... It probably looks like a I am waving my hands way too much here--But I cannot make any exact statements based on your needs. Much of this will be just personal choices and your requirements.

-Bill

Re: Design idea: RV battery system

A husky on the tongue of the trailer and a bowl of dog chow?

-Bill