Camper - Permanent off-grid - How to?

System

We are setting up a camper to be used as a permanent hunting camp. We've built gravity feed water tower, installed well, etc.

Now we're trying to figure out how to power it most efficiently. We have a 7550 generator for occasional A/C use when needed, but want to primarily run from battery power.

We have one Everstart Maxx rated for 115 amp hours.

Our MAX load GUESStimate:
Per 24 hour period:

Water Pressure Pump @ 4 amps (intermittent) max x 1 hr = 4 amp hours
4 DC overhead lamps @ 1 amp (3 hrs) = 12 amp hours
LP Fridge (12 hrs) @ 1.5 amps = 18 amp hours
LP Furnace Fan 7 amps x 2 hrs = 14 amp hours

We won't be utilizing any of the 110 outlets, so the converter should not have to run.

Our usage will be just weekends. Friday night, Saturday night. So we need to be able to recharge the battery in one day.

What size solar panel? Do we need more than one battery? What type of charge controller? Can one charge controller work for both solar and generator (if we have a rainy day and need to use the gen to charge?)

I have read and read and read and read and everywhere I go, there are different ideas on the best setup. And no situation is exactly like ours. And I've gone around and around without understanding squat about power stuff, trying to learn, and trying to do it right the first time. But I just don't grasp the technical stuff easily.

We're in sunny central FL, and space is no object re: panels.

Would welcome all feedback.

AntronX

Re: Camper - Permanent off-grid - How to?

Get another battery to double your storage capacity. This way you can take full advantage of the time you are away from your camp to recharge your battery. Your total weekend usage will be 1200 Wh from what you provided. One 190 Watt "Sun" panel with simple PWM controller will work for you.

icarus

Re: Camper - Permanent off-grid - How to?

Your daily usage ~48 ah, or ~ 600 wh/day.

To draw that out, you will need to produce ~125% of that or 750 wh.

Almost never can you can count on more than about 4 hours a day.

Depending on controller loses etc, you might figure ~60% efficiency, so to get your 750 wh/day you will need ~ 300 watts of panels, running ~ 4 hours, 300*.6*4=720 wh.

Remember, that is ideal day conditions, and give you non for cloudy day reserves.

That said, in order to only draw your battery no more than ~25% ( for maximum battery life, you will need a battery of ~200 ah, and that assumes no reserve. Build in a couple of days reserve and the battery would need to be bigger, (or you will discharge it deeper, leading to shorter battery life)

Panel capacity should also be between ~5-13% of Ah capacity, so, once again depending on your controller, 300 watts of panel might put out a bit more than ~15 amps on average. So 15 amps would be 10% of a 150 ah battery, or 5% of a 300 ah battery.

So, just for the record, we live off grid. We use ~ 600 wh/day. To do so, we have ~ 400 watts of panels, a good MPPT controller, feeding into 450 amps of battery. We can fill that draw in ~3 hours of good charging. We can go 3 days before we draw the battery down more than ~20%, and we can get that back in one ideal day.

A couple of things, people over estimate their loads, and under estimate the amount of solar they can get. (loads also grow with time)

A couple of notes on your loads. First, I don't think a LP fridge will draw 1.5 amps except when it is igniting. (Assuming an electronic control board type fridge) Mine draw ~.05 amp just to power the board 99% of the time.

Bottom line, matching the components, PV, controllers, batteries and loads make a system work well. I would spend some time doing some real calcs so you know what our expected loads are likely to be, as well as how much sun you are really likely to get. Remember, in a mobil installation, the chances of having panels perfectly oriented are pretty slim, reducing harvest. by doing your homework now, will help you avoid the worst of the Ready, fire, aim syndrome that many fall prey to, and leads to expensive mistakes.

Good luck,

Tony

PS check the specs on your battery and confirm that it is really a deep cycle battery. If it is not a real deep cycle it's performance may not match expectations.

AntronX

Re: Camper - Permanent off-grid - How to?

Beve wrote: »

Our usage will be just weekends. Friday night, Saturday night. So we need to be able to recharge the battery in one day.

To clarify, will you leave solar panel and battery at the camp or take it back with you when you leave?

niel

Re: Camper - Permanent off-grid - How to?

don't forget guys that if the pv is mounted flatly on the camper that he will suffer a huge loss in power production due to a lack of proper aiming. wintertime is when this will manifest itself the worst. if parking in the shade during summer then remotely locating the pvs could be utilized, but that takes away from being able to just leave the pv connected all of the time as you'd have need to pack it up to discourage theft. mounting options to aim the pv while on the camper may solve that with the disadvantage of having to park in the sun and possibly forgetting to lower the pv and secure it before moving down the road.

System2

Re: Camper - Permanent off-grid - How to?

AntronX wrote: »

To clarify, will you leave solar panel and battery at the camp or take it back with you when you leave?

Speaking for OP here,
Panel and battery will remain in place between uses.
I plan to install whatever panel(s) we choose up on the water tower rather than flat on the camper.
I will angle them in such a manner as to maximize gain (another topic) but the mount will be static.
Panels will have 5 days to charge battery for 2 days of use.
Camper. battery, panels, genny all remain in place and doesn't go down the road.

JoeC

Cariboocoot

Re: Camper - Permanent off-grid - How to?

My two cents (Canadian, but now at par):

Your guesstimated loads are about 50 Amp/hrs per day, so as AntronX says you want more battery. I'd go with two 6V 225 Amp/hr is series, as it would save a small headache over paralleling two 12V's.
I agree with Tony about that battery possibly not being a deep cycle, and that you'll need more panel than you might think to charge it.
The concerns over theft are realistic too, which brings us to the question:
Is this the best way to go?
Adding a thousand dollars worth of solar panels to the 1-story roof of a largely unoccupied remote building ...
Maybe you should buy a small, economical generator instead and take it home with you when you go. That way whenever you come back you know you've got power. Not missing panels and a big headache.

I bring my Honda 2000 away with me every Winter, and leave the 1000 behind to appease thieves. If they try to take the roof panels, I'll find them dead on the ground in the Spring (can't negotiate the roof slope on foot).

niel

Re: Camper - Permanent off-grid - How to?

generators aren't good to run all of the time so maybe have the batteries and a charger run from the generator so you nights will be quiet and power available via an inverter.

System2

Re: Camper - Permanent off-grid - How to?

We are leaning toward solar power to keep batteries charged largely because of the amount of time I believe it will take to charge the batteries by running the generator.
My understanding is that the circuitry in the camper provides a very low rate of charge into the battery(ies).
I can listen to a genny for max 1 hour before I lose my mind.
Needless to say, reducing dependence on gasoline to make power is also a benefit.
None of our 12v electric, but for one battery, is in place as of yet so I'm dealing with a blank slate.
Right now I have 110 into the camper until the site is finished, solar, well, water tower etc.
I can easily add another battery, 12v in parallel or two 6v in series, if needed.
My big issue is keeping a charge in whatever batteries we use.

JoeC

MIA till Monday

Cariboocoot

Re: Camper - Permanent off-grid - How to?

Yes I meant use the gen to recharge the batteries. Its often more practical than panels, especially for occasional use. You'd be surprised how quite those little inverter generators are!

Otherwise, you are looking at what Tony said in panels:

Assuming a 225 Amp/hr bank (50 Amp/hrs use times 4 for 25% DOD).
About 12 Amps minimum @ 14.2 Volts = 170 Watts usable which is 213 Watts panel rating (at 80% derating).
Include charge controller loss and line loss and you'd probably want 240 Watts of panel, if you have good insolation. No trouble replacing the Amp/hrs, but from my experience batteries don't like be recharged over a period of days. Otherwise you could use much less panel, but you'd want an even bigger battery bank to compensate for the lack of full recharge in one day.

Of course there again, the trade off of more $ on panels vs. changing out batteries more often ... May not be worth it. Especially if you can give them a good charge from the generator before you leave them.
That would bring up the alternative of the panels being chiefly for maintenance, which means they could be smaller. Providing you don't mind running the gen long enough to fully recharge them before you leave.

Er, I think I'm thinking in circles here so I'm just going to stop!

icarus

Re: Camper - Permanent off-grid - How to?

In addition to all that has been said, I would start here:

http://www.batteryfaq.org/

http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

Read and understand as much as you can about batteries and their care and feeding! Most folks kill at least one set learning how to use them! Remember, there are some very smart folks out there (especially here, present company not included!) who have forgotten more about PV/Batteries/EE/ETC than most of us will ever know. Use their hard won real world experience so you don't have to reinvent the wheel.

Since you have a clean slate,, start with a truly clean slate, and give up any preconceived notions as to what you think you should do. Start with the battery knowledge, then figure out your loads, using realistic real world numbers, add in some fudge factors, then you can begin to design a real system.

Two additional things to remember. While loads will always grow with time, PV systems are sort of doubly expensive to grow. It is cheaper to start out with any given system then it is to grow a system to that size. Panels can usually be added (up to the limits of controllers, I'm on my 3rd controller!) and up to the limits of batteries. Controllers don't grow very well, you end up buying a bigger one, and the old one goes for scrap or spare. Battery banks don't grow well if the existing batteries are more than a few months old. Inverters are best sized for their most efficient load range,,~75% maybe?

So spend the time now, and you will save time and money going forward. I would also look carefully at your lighting. My guess is your use of 12vdc lighting is likely to be with incandescent bulbs, and ergo not very efficient use of power. You might consider a good inverter, wiring a 120 vac circuits and use of some 120 vac CFL bulbs. They are cheap to buy, and fairly cheap to operate. (LEDs are beginning to be a very real alternative, and are widely available in 120vac versions fairly reasonably.

Good luck,

Welcome to the site,

Tony

AntronX

Re: Camper - Permanent off-grid - How to?

Eh, guys, you make it sound more complicated that it is.

The OP got 7 days to capture enough energy to allow for 1200 Wh to be drawn. After losses 1540 Wh will have to be generated by the panel during 7 days. With 4 hours of sun per day, 66 Watt panel with MPPT controller will be needed. With PWM controller, 85 Watt panel will be roughly equivalent. It's ok to parallel bunch of 12V batteries. It's ok to discharge them little below 50% once a week. They will last few years. It's not like the OP is going to space or something. I suggested 195 Watt panel. It is about twice as large as calculated, but that is good. Smaller panels are about same price, so why not pay extra $50 for double the size to allow for more room for mistake and bad weather? There will be weeks of a lot of rain in the summer. Also, loads eventually will grow.

icarus

Re: Camper - Permanent off-grid - How to?

AntronX wrote: »

Eh, guys, you make it sound more complicated that it is.

The OP got 7 days to capture enough energy to allow for 1200 Wh to be drawn. After losses 1540 Wh will have to be generated by the panel during 7 days. With 4 hours of sun per day, 66 Watt panel with MPPT controller will be needed. With PWM controller, 85 Watt panel will be roughly equivalent. It's ok to parallel bunch of 12V batteries. It's ok to discharge them little below 50% once a week. They will last few years. It's not like the OP is going to space or something. I suggested 195 Watt panel. It is about twice as large as calculated, but that is good. Smaller panels are about same price, so why not pay extra $50 for double the size to allow for more room for mistake and bad weather? There will be weeks of a lot of rain in the summer. Also, loads eventually will grow.

Antrox,

I don't disagree with you in general principal. However, he suggests that he has a "blank slate" it seems a pretty good idea to look at the issues clearly and understand the ramifications. I personally lived with a car battery and a 53 watt panel for several years. So you are absolutely right in the concept of KISS your suggestion is fine. (I do think that we all too often make the simple complex in the pursuit of perfection). That said, I second my suggestion about learning about batteries, and designing for known (or expected) loads. Bottom line, if it works for you, and you can live with the limitations (short battery lifespan, limited draw down capability, slow recharging etc) then great.

Tony

System2

Re: Camper - Permanent off-grid - How to?

Thanks to each of you for your thoughtful responses! After reading through each one, it seems we have a wide variety of options/suggestions.

The expense rules out 400watt panels with an MPPT controller. It's just weekend use and we aren't flush, unfortunately. We're trying to do this as inexpensively as possible (of course).

I guess, after sifting through everything, we're probably going to go with a smaller panel, perhaps 85-110 watt, and definitely another 12v battery (yes, it does say marine deep cycle on it), and it's only a month old. I think we'll plan on replacing those with the coupled 6v batteries when the others wear out.

Obviously, due to the limitations, we won't be trying to restore the batteries to capacity in a day, as was my original wish, we'll use the generator for fast refresh and leave the batteries on the solar charge controller for the week when we're gone.

Thanks to everybody for your suggestions and sharing your knowledge!!

Much appreciated,
Bev (and JoeC)