rv solar set up suggestions batteries, controllers, and inverters?????

dannycoffin

I am buying an rv soon and studying Solar energy I was considering an 800 watt solar array, connected to 4 110 amp 12 volt batteries.  Should I run them in series or both parallel and series for higher voltage would that be 24 volts at 220 amps and amps or run them 4 for the 440 amps, if I run the 24 volts do I need a diferent inverter, and suggestions on solar controllers, what I would use it for would be tv, computer, lights, short microwave, video games.  a dyson fan-heater there low amp and seem to work good, coffee pot.  some one informed me that I shouldn't drain my batteries daily lower then 20% to 30%  for long term use.  Suggestions on inverters sine vs other,how many watt inverter should I get?  should I get a mttp controller.  when you run a battery bank do they connect directly to the rv power source like the rvs plugs like an 30 amp outside connection to the fuse box, or do you run battery bank separate and use the plugs in the inverter.  some people use 6 volt batteries with higher amps how do they perform cost effective.  Is there anything else I need to know?  Thank You

RV and Solar Newbie

vtmaps

Welcome to the forum,
The first step in designing a system is to know the purpose of the system.  The purpose of the system is to power your loads.  So, what are your loads?  You need to know the peak load (watts) and the daily energy usage (kilowatthours). 

We have all sorts of formulas to calculate battery size, size of array, etc... but these formulas use numbers.  In order to help you, we need to know your energy usage numbers.   Similarly, if you asked us what pickup truck to buy for your trailer, we couldn't answer without knowing the weight of the trailer. 

Some of your loads may be problematic if you only have 800 watts of array... electric heater, coffee pot, microwave.  What about refrigeration?  Air conditioning? water pumping?   Do you have a generator?  Do you have the capacity to carry a thousand pounds of battery?

--vtMaps

mike95490

use propane for the coffee, that is a huge electric drain.  A microwave for 30 seconds is a manageable load.  Heating functions that can convert to propane, have to be done before thinking of solar.   An electric room heater is completely out.
There are several solar design stickies of how to calculate your loads, how to size the batteries for them, and finally calculating the size of the PV array to recharge.

Marc Kurth

Danny, you can waste a whole lot of precious time/energy/money by not following vtmaps simple, but dead accurate first paragraph.

Get a handle on your loads. Figure out what you will run, what the power draw is and how long each one needs to run. Until you do that, you are sort of just peeing into the wind

Once you have a list of your "wants" you can get GREAT input from the experienced folks here, on how to balance what you want and what fits your budget - whatever it is.

Investing the time at this phase is a critical step to success!

Marc

scrubjaysnest

All the above are good points; one not mentioned is how often do you dry camp? a couple of times a year for a week at a time and solar won't pay for itself.

softdown

Unless you have a huge solar array, it is almost always a bad idea to heat water/cook or rooms with solar.

Iceni John

Vtmaps' and others' suggestions are correct  -  know your loads.   However, 800W of panels on an RV roof probably won't generate as much power overall as the same amount of panels on a house roof, because RVs often are not oriented ideally to the sun or are partially shaded.   For this reason alone, I suggest carpeting your roof with as many panels as will fit!   PV is still cheap, so a few more panels aren't much more in the context of what the RV will cost you anyway.   Just don't put panels next to roof-mounted A/Cs or stink pipes or fridge vents or whatever sticks up above the roof  -  even the slightest partial shading such as from RV roof impedimenta will drastically reduce their output.   If you can mount your panels on tiltable mounts they will produce slightly more power in the summer but probably appreciably more power in the winter when the sun is lower.   1000W of panels is about the most that a charge controller can handle for a 12V system (which your RV is).   If you can charge your batteries at a 10 to 13% charge rate they will charge quickly, maybe allowing you to also power opportunity loads in the afternoon after they're fully charged, such as power tools or a washing machine or other non-time-sensitive but power-hungry loads.

Have fun!

John 

softdown

I believe that poly panels perform better when partial shade is an issue.

BB.

No--I do not believe there is any advantage of mono or poly crystalline panels when there is shading. They both operate with pretty much the same physics (I could be wrong--But I do not see any reason for a "difference" during partial shading).

-Bill

softdown

You are probably right about that. When I was comparing the two technologies, one web site made that claim. Not "scientific proof" by any means. Though "scientific proof" is getting "more affordable" every year. A jab at the current crop of "scientists".

BB.

Some have claimed that Mono panels do better in overcast skies vs poly crystalline--I have no opinion on that (other than it probably does not make enough difference to spend more on Mono panels because of this).

-Bill

toppinish

4 x 110 amp batteries with 800 watt panels seems like a ratio to use if your in sunlight most of the time.

I live up in the Northwest and that panel wattage to batteries amps wouldn't work out very well as often you can go days without sunlight, possibly a week to a couple of weeks, then  several days with sunlight. Depends on you location and altitude, weather in the mountains is usually not the same as weather along to coast, low lying areas,  etc. There are areas that average over 150 inches of annual precipitation, 20 miles or so away only around 20 inches of annual precipitation.

For up here in the Northwest I would want more battery storage as I never know how much sunlight will be available.

However the previous comments are correct. You also need to figure the demand or common daily loads. Do you require AC, TV, Computer, Microwave, etc.?

When off-grid a stock RV won't operate without a certain amount of 12 volts power to run a Fan for RV furnace (which often are 7+ amps, check the amp rating of your RV furnace) and 12 volts to run the RV gas absorption refrigerator. (12 volts is normally required for a RV gas frig to operate) Plus a few other items such as the  water pump,  bathroom and stove fan.

What I did with my RV was to install an additional Catalytic Heater in the RV that requires no elect. to operate. It's best to get a catalytic heater built for an RV such as Olympian or a heater that designed for a permanent installation. One that puts out a constant heat where the btu ratings may not be as high as portable camping heater, etc. These are much more reliable and maintain room temperatures throughout the day and evening.

When the batteries become drained it often requires from a half to a full day to recharge (sometimes a bit longer, depending on the size of your battery bank). If no sun a geny is usually relied upon. Also it's not a good idea to run batteries below 50 percent then recharge again, potentially shortens the life of the batteries.  As a general rule you want to try to keep the batteries maintained and charged somewhere above 50 percent of their capacity. At least this is what I have read about charging battery banks, perhaps others have other ideas about keeping batteries charged.

OldMan

I'm in the same boat as OP Danny Coffin. I'm buying all my solar gear, directly from manufacturers in China. China owns the world solar market can/t beat 'em, buy from 'em. Some vendors will do business with individuals. Others, ehh, not so much. Watch out for shipping costs. Unlike American companies, they will haggle like crazy. One way I  have dealt with them and been successful is offering to buy from them, pay their price without haggling, for a shipping consideration (sometimes even free). I figure the worst they'll do is say no, and honestly it's been a glimpse into a VERY different culture. That alone has been worth the time invested. No money has changed hands, yet, but I can get two (count 'em) 12v 200AH batteries for a grand. I'm so looking forward to the adventure.

jimdiesel

Hi all, I’m new here gathering materials for an install on our RV.  So far 6 Suniva 275w 60 cell panels, my calcs so far lead  me to thinking I need 2 MPPT morning star TriStar 60s . My thoughts are to run 3 panels in series on each charge controller . My system is 12v starting out I’m planning on 6 225ah deep cycle golf cart batteries. 2 batteries in series 3 sets tied in parrellell for 12 v. Also I have  yet to size my inverter charger ,based on my charging needs on shore power.  Anybody have any suggestions or thoughts on my setup. Opinions welcome this is my second setup so far first one was for remote gate opener on1 panel and battery. It worked great but this conserderably more costly, so I don’t want to make any  big mistakes. I want to recover the maximum of output from my panels I’m making dual tilts for the mounts.

Thanks in advance for any advice,
Jim

Estragon

You mentioned "system is 12v starting out" - does this suggest you may consider going to a higher voltage system in future?

jimdiesel

Sorry I mis spoke 12vdc always, I  left out a comma. Starting out with 6  batteries.

Estragon

I'd suggest sizing the inverter based on AC loads, not shore power charging capacity. Depending on loads, you may want to consider a standalone charger or chargers.

Basing the inverter on charger capability may lead to choosing a much larger inverter than required (eg 2500w), which means higher self-consumption just to have the big inverter supplying small loads. A big inverter can use 30-50w on top of the small load, which could be (eg) 40w x 24hrs = 960wh/day. The bank will be 675ah@12v= about 8kwh. You don't want to run in down more than about halfway, and a 2500w inverter can get there pretty fast.

Using 3 strings of batteries in parallel isn't ideal. You'll want heavy, short interconnect wire, quality connections, and a fuse on each string. A clamp-on current meter would be helpful to ensure balanced charging.

jimdiesel

Ok that’s good advice, the lager than normal charging capacity was more for when we are on shore power. But your point is taken. I have T&B crimping tools for up to 250MCM so good connections are no problem. I have 400 amp welding cable for interconnects on bank.

jimdiesel

Ok sounds like good idea ,and sound advice thanks for your thoughts. Your suggesting larger Ah batteries and fewer as more optimal solution?
Jim

Estragon

Yes.  Ideally whatever AH capacity required in a single series string.  This can be done using large lower voltage batteries as needed (eg 6x700ah 2v cells), or by increasing system voltage (which is why I asked about possibly wanting to increase it later). 

Two strings (eg. 4x350ah 6v L16 type batteries) can work if monitored carefully.  I use this setup for my 700ah 12v bank, and it has worked well.  As the number of strings increases, so does the difficulty in keeping strings balanced.  Three may work okay with your good connections, and regular monitoring and maintenance.  If one string is reading low during regular specific gravity checks, it should be charged separately to get it to the level of the other strings.  6v GC type batteries are nice in that they're widely available and generally pretty cheap for their capacity, so it may make sense to use them anyway.  It's just a bit of a trade-off in terms of a bit more careful  monitoring and possibly periodic remediation with the three strings.  With more than two strings, you should also fuse each string as well as breakers on the controllers and inverter, because a short in one can put the current available from the remaining strings across the short in the bad one.

SupraLance

JimDiesel, Just a thought, but it seems to me you could save some money and hassle by using two less expensive 40a mppt controllers into four 6v batteries wired in series at 24v, a 24v inverter, and then a 24v to 12v converter for any 12v loads.  Your controllers get cheaper, batteries less complicated and failure-prone, and less wiring losses and the more efficient inverter should offset conversion losses for 12v loads.   Don't rule out 24v just because you have some 12v loads...

OldMan

softdown said:

I believe that poly panels perform better when partial shade is an issue.

That is so, according to my reading. It's why my system will be a movable, ground-sitting setup. Three 250 watt panels. Tools to point the panels effectively. Store them in the coach when we're moving, set them out as soon as the rig is leveled in the next spot. Make juice.

I agree with those who say run your AC appliances in the peak generating hours of the day. I also agree, using propane for coffee. That Coleman stove-top drip coffeemaker is pretty cool, just be sure you have a spare carafe in a soft, safe place, or an alternative you can use until your new carafe arrives. But I'd also say, you can run your AC more if you're using lithium-iron batteries (LiFePo4) because you can draw them down 80 percent, as opposed to lead-acid's 50 percent usable power.

westbranch

 RE: LiFePO4 batteries...  unless you want to obsess about the batteries being "100% FULL"   that is the zone between 80% and 99.9999%,    use 60% available power as the safe bottom is 20%, the safe top is 80%