RV solar system planning....looking for advice

Re: RV solar system planning....looking for advice

Welcome to the forum Ron!

You probably want to look at the mini-split A/C systems... The Sanyo was a great one--But appears to be no longer available since Panasonic purchased the company (not many mini-splits are 120 VAC). Neat thing about them is they had no surge current and when you set them on low, they would run at ~300 watts very nicely (pre-cool, or keep cool starting from morning).

Also, min-split heat pumps can be pretty nice for heating (above freezing, typically).

http://forum.solar-electric.com/showthread.php?5104-Sanyo-mini-split-AC-%28inverter-variable-speed%29

There are some other threads/discussions about other brands of A/C that can work well with solar too.

R/V's are tough because of limited roof space and, many, mount the panels flat... For summer down south, the flat mounting is less solar losses.

Anyway, there is a lot of details to work out (how much power per day, split between daytime and night time). But to start with some "round numbers", say 800 watts for 10 hours per day. That is 8,000 WH per day. Worst case, charge during day and run at night (more battery losses, larger battery bank):

8,000 WH * 1/0.85 inverter losses * 1/48 volt battery bank * 2 days of storage * 1/0.50 max battery discharge = 784 AH @ 48 volt battery bank

Next, we usually recommend charging around 5% to 13% rate of charge for a "happy" battery bank:

• 784 AH * 59 volts charging * 1/0.77 panel+controller losses * 0.05 rate of charge = 3,004 Watt array minimum
• 784 AH * 59 volts charging * 1/0.77 panel+controller losses * 0.10 rate of charge = 6,007 Watt array nominal
• 784 AH * 59 volts charging * 1/0.77 panel+controller losses * 0.13 rate of charge = 7,809 Watt array "cost effective maximum"

And if you are in Florida, using PV Watts for a "flat array" for Daytona Beach:

Month Solar Radiation (kWh/m 2/day)
1 3.07
2 3.91
3 5.06
4 6.03
5 6.40
6 6.28
7 6.25
8 5.72
9 5.07
10 4.02
11 3.42
12 2.96
Year 4.85

So, assuming you need the A/C mostly during lots of sun shine, pick 4.02 hours of sun minimum:

• 8,000 WH per day * 1/0.52 end to end system eff * 1/4.02 hours of sun per day = 3,827 Watt array minimum

Now--This is probably a crazy big array for an RV--Even one where you set up some extra panels when you park for a few weeks at time. You can make different assumptions--Perhaps less power usage (300 watts for 8 hours per day), or only 1 day of battery storage (1/2 size of battery bank), etc...

Not saying the above is correct--But it will give you an idea of what an "off grid" design would be. Nominally, a very efficient off grid home might use 3.3 kWH (3,300 WH) per day for Refrigerator, lights, TV, laptop, washing machine, well pump... You start adding A/C for cooling (or heating), and things get "big" very quickly.

People have done portable A/C--But is usually a very small A/C system and a well insulated "sleeping room" and use the A/C for a few hours to take the edge off the heat)....

Usually, there is a limit on RV's... The maximum number of panels you can fit, the maximum size/weight of battery bank, etc. Sometimes you can do "interesting" things (use solar panels as an awning, get Lithium based batteries, and such). But usually conservation/insulation are going to be your first go-to solutions.

Hopefully some folks can give you some more information. I am not an R/V'er, and I live in a temperate climate. So, I am not the best guy to answer your questions.

-Bill