What size of solar system

[Jaust]

I bought my off grid cabin in the foothills of Washington State in July. All of the appliances are gas so we don't use a lot of electricity. It's a weekend cabin with a week or two of vacation times throughout the year. I'm trying to get an idea of what size and type of system I should be looking at to keep the batteries charged so I don't have to fire up the generator and while it's not being used.

I have 12-6volt batteries wired in series and parallel for a 12 volt system with 720 total amp hours and a 2400 watt Xantrex inverter. I only have a chandelier and a couple lamps plus a TV and DVD player. I have estimated the usage well on the high end so I'm figuring we use 6 KWH average on a 3 day weekend up there. I've been reading through the threads and some of it goes over my head but I'm learning more as I read more. I'm just looking for some ideas to hopefully get a solar system setup next spring. Any advice is much appreciated.

[Sunking]

I need some new 6 volt batteries for my golf cart. Where is this cabin located. I should be able to find it easily with panels on top.

[solar pete]

I bought my off grid cabin in the foothills of Washington State in July. All of the appliances are gas so we don't use a lot of electricity. It's a weekend cabin with a week or two of vacation times throughout the year. I'm trying to get an idea of what size and type of system I should be looking at to keep the batteries charged so I don't have to fire up the generator and while it's not being used.

I have 12-6volt batteries wired in series and parallel for a 12 volt system with 720 total amp hours and a 2400 watt Xantrex inverter. I only have a chandelier and a couple lamps plus a TV and DVD player. I have estimated the usage well on the high end so I'm figuring we use 6 KWH average on a 3 day weekend up there. I've been reading through the threads and some of it goes over my head but I'm learning more as I read more. I'm just looking for some ideas to hopefully get a solar system setup next spring. Any advice is much appreciated.

Hi Jaust and welcome to solar panel talk

[Sunking]

I bought my off grid cabin in the foothills of Washington State in July. All of the appliances are gas so we don't use a lot of electricity. It's a weekend cabin with a week or two of vacation times throughout the year. I'm trying to get an idea of what size and type of system I should be looking at to keep the batteries charged so I don't have to fire up the generator and while it's not being used..

There is the conflict. you stated you need 2 Kwh/day while there for up to 3 days. If you get a panel wattage just large enough to maintain the batteries full charge, you are going to have to use the generator. In addition not sure where in the state of WS you are talking about, but if on the west side of the Cascades your solar insolation is really poor in winter months and would almost certainly require and generator if you stayed there in winter regardless of panel wattage.

I can give you a start by at least suggesting a Morningstar Sunsaver MPPT controller made for 12 and 24 volt systems at 15 amps. At 24 volt battery can input up to 400 watts. Do not use battery panels, use grid tied panels as they cost half as much as battery panels and use at least 2 panels wired in series. That pretty much means either 2 150 or 200 watt panels for a total wattage of 300 or 400 watts. It is not enough to properly charge up the batteries, but more than adequate to refresh some of the power while in use up there. At any rate you will still need the genny for maintenance and cloudy days like any off-grid system.

Forget 12 volts, that is for toys and RV's.

[paulcheung]

If it were me, since the applicances are gas, you don't need a lot of electricity, I would just carry a large AGM battery like 12 volts 200 amps and charge it at home, while in the carbin just use the generator for two hours each day to charge it back. use the battery for lights in the night, and maybe a tv for the evening.

[Sunking]

Sunking beat me to it.

No Paul I seen your other answer with the AGM idea. Put it back up, I like that answer better. If not I will and claim it as my own.

[Sunking]

Sunking, From what I've read on this forum your knowledge in this field looks to me to be unsurpassed. Do you not have any suggestions for me?

My comment was in reference is the panels and remoteness makes you a prime target for theft. Any crook seeing the panels would know you have batteries and valuables inside. It is hunting season right now, and even honest hunters may take advantage.

[Sunking]

I just didn't know whether the sarcasm in your first responce was an insult or what.

Not sarcasm, just a warning it could make you a target. I did not answer at first because I was short on time.

Don't be so sensitive, my comment on 12 volts is just an attention getter to make you rethink things. The biggest issue with your approach is making 6 parallel string of batteries. That is asking for big trouble and short battery life. If you needed 720 AH of batteries, you should have bought 720 AH batteries so you only have 1 single string.

Maybe this will help you see the point. That Morningstar controller I suggested is for 12 and 24 volts. If you make it 12 volt you are limited to a maximum panel wattage of 200 watts. At 24 volts is 400 watts. 12 volts is going to require much larger more expensive wire, and literally doubles your fire risk. It is a matter of efficiency, economics, safety, and power limits. OK?


So don't get offended and run off. Put on your Big Boy pants and ask questions. I will help you. I am ex military officer and that is just my style.

[russ]

Thanks for your responses guys. I had no idea that 12v was wussy. I just didn't know whether the sarcasm in your first responce was an insult or what. I'll maybe look to another forum that doesn't make me feel like an idiot because I m not as knowledgable on the subject as them. That's what I thought these forums were for but I guess I was wrong. I'm out.

Do you want help or do you want to feel good? By people telling you what a wonderful deal you got?

If you want help - this is the place.

If you want to feel good and be told how wonderful you are this certainly is the wrong place.

Russ

[Gyro]

Jaust

Don't let the strong personalities turn you off from this forum. You are getting facts based on expertise and years of experience.They have probably answered similar situations to yours hundreds of times and if they didn't add some sarcasms and "in your face" comments, it would probably be too boring for them to answer. You are getting solid information. It would be worse if they simply did not respond and ignore your question that they have answered many times in the past.

[mschulz]

Not sarcasm, just a warning it could make you a target. I did not answer at first because I was short on time.



So don't get offended and run off. Put on your Big Boy pants and ask questions. I will help you. I am ex military officer and that is just my style.

Gyro -- Theses guys saved me a ton of money and I went in to this thinking solar was the only way. The Generator and AGM battery route is how I went with my weekend cabin. I use a small portable 100watt panel with MPPT charge controller that I set out when i am at the cabin. I run a ARB fridge /cooler when I am there on weekends and charge electronics and run a cell phone booster. I am not runny lights or tv but with my 100 AMP hour battery, I have never dipped low enough to use the generator. The day I leave I fire up the generator and recharge the batter for 3 hours. I leave the battery at the cabin as I have it in a nice out of the way place for it, but because I do not have lights, plugs or panels, no one knows what is in there and they move down the road to the next cabin that has all the fancy bells and whistles.

I know that I am going to probably kill my battery in a few years, but with the $$ I saved, I have 20 years of batteries to buy before I would break even with a complete system. In 20 years, my situation will be totally different.

PS. I know running the generator is ****ty, but with the new quiet ones, you hardly know they are running. A EU1000 or EU2000 would work just fine for you and they run a long time on a gallon of gas. When charging mine runs on eco mode the whole time with a 25AMP charger.

[Gyro]

Gyro -- Theses guys saved me a ton of money....

Exactly!

[mschulz]

How do you monitor the voltage in your batt so you don't run it too low? I check mine with a meter when I first arrive while there's been no load on them but during my time there I don't really know where they're at. I'm thinking I should get some kind of monitor to run from the battery shed into the cabin so I can at a quick glance tell either the voltage or percentage of charge is on the batteries so I'm not charging them unnecessarily. I suppose that's probably a question for another forum. Thanks for your responce.

In regards to battery condition, with the AGM there is no need to take SG measurements so I am really just keeping them from dipping lower than 12.4 volts. I choose the more expensive AGM because of the set it and forget it mind set. I don't want to do SG measurements and water my batteries, but most important, the battery is inside the cabin under a built in, there fore no venting.

I use a volt and ammeter that I installed with a shunt that I look at through out the day to keep track of what is coming in and going out. When I leave the cabin I just flip the battery disconnect so I do not have any phantom losses. When I arrive, I flip my switch, look at my voltage. If my voltage is low, I turn on the generator while I am unpacking and charge it up. I am lucky as I am only 1.5 hours away and get up there no less than 1x per month.

If I were you, I would do anything until you straighten out your battery config. You may decide to step up to 24 or 48 volt battery bank, and this will change the rest of your component needs. So go and get a Kill-a- watt meter ( http://www.amazon.com/Weanas%C2%AE-E...illawatt+meter) and see what you are really using up there each day. Then these guys can start to help you. With out that, we are just guessing at what you need. Also, see if you can decrease your usage with better bulbs in your lights.

[Sunking]

I have 12-6volt batteries wired in series and parallel for a 12 volt system with 720 total amp hours

Jurst you need to quit getting your feelings hurt. You may not like what you hear, but it is honest and you can learn from your mistakes, and trust me you made some huge mistakes that will cost you dearly. What is quoited above is a huge mistake.

So you have 12 6-volt golf cart batteries configured for 12 volts. That can only mean you have 6 parallel strings which is a huge No-No in of itself. But there is a much bigger problem. There is no way that I know of it is just 720 AH as you stated. 6 volt Golf Cart batteries are 200 to 230 AH range. With 6 parallel strings = 6 x 200 AH = 1200 AH up to 6 x 230 = 1380 AH. Not 720 AH unless those batteries are 120 AH's and I have never heard of a 6 volt 120 AH golf cart battery. What make and model are they? Trojan T-105, US Battery UX 2000, Costo, Sam, or Wally World specials?

Now I know that may not mean much to you but trust me those of us that know what is going on are gasping right now. To charge a 1200 AH battery @ 12 volts requires a 120 amps of current and at 12 volts works out to around 12 volts x 120 amps = 1440 watts of panels. That would take 2 very expensive 60 amp MPPT controllers to do that. If configured for 24 volts still requires 1440 watts but only 1 Very Expensive 60 amp MPPT controller. If configured for 48 volts still 1440 watts but a much less expensive 30 amp MPPT controller.

OK so now you got the batteries and stuck with them. With 12 of them you only have two configuration options of either 12 or 24 volts. To go 48 volts requires a multiple of 8 so you would have to loose 4 of them or gain 4 more.

But what really takes the cake is if you are only using 2 Kwh per day and a part time system with no more than 3 days of use, all you needed was 8 of them wired in series for a 48 volt 220 AH string.

Now this is where the fun begins. If you wire them for 12 volts and use all of them. You need a 12 volt 120 to 150 amp AC charger operating off 240 volts supply on your generator. They do exist but are industrial Telecom rectifiers and they cost big bucks. You can put any amount of wattage of panels up you want to supplement the system. But unless you are talking about 400 watts or more is not going to do much and will require a fairly expensive 40 to 80 amp MPPT controller that does not do much

So get mad if you want, but those are the facts, math does not lie, and the only one you should really be mad at is yourself for not doing some research before jumping in head first into shallow water. I suggest you loose 4 of the batteries, get a 48 volt inverter with built in generator support and built in battery charger. Or use all 12 of the batteries with a 24 volt inverter with gen support and built in charger. That would be the smart money.

Good luck.

[mschulz]

The batteries are less than 2 years old and I certainly am not ready to go out and replace them all. I was watching a video of a guy who had a similar bank as I do and he rewired them in sets of 4 in series for 24 volts and then paralleled the banks together. I don't know if this is something I should consider. And would I be able to eliminate a couple of the batteries I have and still have sufficient power. As for the bulbs the previous owners had already put LED's in all the lamps so they have a minimal draw. I'm still not sure of the disadvantage or problem with the setup I have. If there is a problem what are my advantages of going to 24v. Also what does this mean for all of the things I have plugged in now. The appliances are no problem because they are all gas. But the TV, lamps, my wife's Christmas stuff, cell phone charger...etc. Does that mean I need more equipment. I also have 2 lights in the kitchen that run off a 12v battery that I was planning on wiring into the main system. I'm searching around the internet but not finding the answers I need. Thanks for your input.

Your batteries wired the way they are and being 2 years old, maybe if you are lucky are at there half life, but I doubt. Wiring in 24 volt is better, but still not great.

With your kitchen 12 volt lights, ditch them and run regular lighting and all your charges, christmas lights etc. off your inverter Sunking is recommending. They are expensive but more efficient and will deal with the battery charging you are talking about. Just wait to buy one until you know if you are going to string 24 or 48 volt so you only have to buy it once. With your load anything over 1000 watts is over kill and wasted.

In all reality, we need your battery specs and power usage before anything else can be calculated - especially panel wattage.