RV solar system planning....looking for advice

I just bought an RV and want to add as much solar as possible.

It's a 32' Class A. It's got two house 12v batteries and one chassis battery now.

My goal is to be able to run a single roof a/c if needed. I don't know the size but guessing no larger that 13,500 BTU. I've heard these use about 1000-1500 watts.

I am looking to have a combination roof top and portable panels. The rooftop would be on mounts that can tilt.

So I would be grateful to receive recommendations for:

- total panel watts
- charge controller size and reputable brands
- number of batteries or total amp-hour capacity
- inverter size and reputable brands
- good websites to buy from

I live in South Florida and most trips will be in Florida.

Thanks! Ive been enjoying reading through the threads here! Ron

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    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
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: RV solar system planning....looking for advice
    BB. wrote: »
    R/V's are tough because of limited roof space

    Welcome to the forum,

    Normally when we design a system, we design it to meet a need (the need = the load). It's like buying a truck... you figure out what you need to haul or tow, and then you buy the correct truck (half ton, one ton duelly, etc). That's what BB. did in his response... he started with a load (800 watts for 10 hours) and designed a system.

    In your situation, you will need to decide two physical limits... how many pounds of battery can you carry and how many sq ft of solar panels can you manage. Then we can "reverse" design the system and see what load it can support. My instinct (and I'm not an RVer) says you can't do what you want to do :cry:

    Are you familiar with those little honda eu1000 generators? They can provide quite a bit of power for air conditioning, and with an inverter that has generator support they can run a conventional "hard start" air conditioner. Also dometic makes a device that allows their air conditioner units to work with small generators.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • ChrisChris Solar Expert Posts: 135 ✭✭
    Re: RV solar system planning....looking for advice

    I also have an "off grid" RV.....and after doing alot of reading on the topic have given up on ever using my roof top AC unit......it just isn't freezable. As suggested, if your dead set on using it, then a genset is the best way to go.
  • SolInvictusSolInvictus Solar Expert Posts: 138
    Re: RV solar system planning....looking for advice

    A 32 feet long, maybe 8 feet wide RV should have quite a bit of roof area. If 8 meters x 2.4 meters are usable and he uses 17% efficient Sanyo PV's, he might be able to squeeze a 3,200 W PV array on the roof. If the panels are mounted with an air gap underneath, then they will shade the RV reducing the solar heat gain and the heat the air conditioner must remove. Some insulated aluminum window inserts on the sunny side would help to reduce the heat load too.
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