Need Help Designing RV System

Re: Need Help Designing RV System

You don't say where you will be traveling and what seasons it will be done in... However, lets start where you live.

Using PV Watts, a 1,000 watts (1 kW) of solar panels (round number, smallest web site will accept). Elko, mounted flat to roof, 0.52 system efficiency, we get (note: this assuming you use an AC inverter for system efficiency):

"Station Identification"
"City:","Elko"
"State:","Nevada"
"Lat (deg N):", 40.83
"Long (deg W):", 115.78
"Elev (m): ", 1547
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 0.0"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 9.7 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 2.12, 31, 3.01
2, 2.86, 39, 3.78
3, 3.97, 61, 5.92
4, 5.11, 75, 7.27
5, 6.51, 96, 9.31
6, 7.22, 100, 9.70
7, 7.16, 99, 9.60
8, 6.59, 92, 8.92
9, 5.40, 75, 7.27
10, 3.80, 54, 5.24
11, 2.28, 31, 3.01
12, 1.90, 26, 2.52
"Year", 4.59, 778, 75.47

Lets toss out the "bad" three months of the year, we get 2.86 hours of sun per day average for February.

Say your 30 AH @ 12 volts is the amount of DC power you need (no inverter losses), then your system efficiency is

• ~0.80 battery eff * 0.77 solar panel + charger eff = 0.62 derating
• 30 AH * 14.5 volts charging * 1/0.62 sys eff * 1/2.86 hours of sun = 245 watts of solar panels.

Say you want to store enough energy for 2 days of "no sun" and 50% maximum discharge (for longer battery life):

• 30 AH * 2 day * 1/0.50 max discharge = 120 AH minimum

To support charging of that battery bank with solar panels, the starting rule of thumb is 5% to 13% rate of charge:

• 120 AH * 14.5 volts charging * 1/0.77 panel+charger derating * 0.05 = 113 Watts minimum
• 120 AH * 14.5 volts charging * 1/0.77 panel+charger derating * 0.13 = 294 watts ~cost effective maximum

So--if you mount the panels flat to the roof, you should install roughly 245-300 watts of solar panels for ~9 months of mostly generator free camping with your defined loads.

Now, if you plan on camping in winter (and/or going farther north), you should consider tilting the panel up. For example, in your area tilting the panel to latitude +15 degrees to ~55 degrees gives you:

"Station Identification"
"City:","Elko"
"State:","Nevada"
"Lat (deg N):", 40.83
"Long (deg W):", 115.78
"Elev (m): ", 1547
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 55.0"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 9.7 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 4.05, 66, 6.40
2, 4.47, 64, 6.21
3, 5.06, 79, 7.66
4, 5.04, 73, 7.08
5, 5.45, 79, 7.66
6, 5.51, 74, 7.18
7, 5.73, 77, 7.47
8, 6.23, 85, 8.24
9, 6.46, 90, 8.73
10, 5.86, 87, 8.44
11, 4.04, 60, 5.82
12, 3.93, 63, 6.11
"Year", 5.16, 897, 87.01

...almost 2x as much useful power in winter (with the added cost and hassles of tilting the array). This will allow you to either consume more power or build out a smaller array.

Here is a nice thread with video from Kevin in Calgary Canada that shows designing and installing solar PV in a small RV trailer.

Questions?

-Bill

Re: Need Help Designing RV System

Josh,

• 5 hours of sun * 85 watts * 0.77 panel+charger eff * 1/14.5 volts charging = 22.7 Amp*Hours

The next question is battery size... Larger batteries should have larger solar arrays to quickly recharge them. Lead acid batteries that spend more than a few hours/day below ~75% state of charge begin to sulfate.

So, how many days of "no sun" do you want to plan for?

Also, you listed a CO2 detector... Did you mean CO (carbon monoxide) instead?

In any case the COx detector is a fair amount of your energy usage... Finding a lower power version and/or only running it during sleeping/heating hours may save you a bunch of power.

-Bill