Help for newbe?

2 Posts
Aug 18, 2009 01:47 pm
Help for newbe?

Hi Folks,  I just discovered AltE and what a great company and this board is excellent info.  I'm planning a small off-grid system and need some help.  Basically want to use the system as back-up power and to reduce some power costs as well.  I want to start small and have room to expand.  This is what I have in mind. I already have a 2000w inverter and two large batteries in my motorhome which sits unused for most of the year, so I want to take advantage of them for now.  What I want to do is put 4 200w panels on the garage roof and use them to charge the batteries in the motorhome.  I plan on adding 2 more batteries in the bank later.  The distance from the roof to the motorhome is about 25'.  Should I put the MPPT controller/combiner in the garage and just run wire to the batteries, or should I put the controller in the motorhome and run wire to that from the combiner located in the garage? Does it make a difference?  Also what amp controller would be minimum for 1000-1400w of panels?  Eventually I want to expand to this capacity but not want to have to purchase another controller when I do.  Thanks.
 
351 Posts
Aug 19, 2009 02:37 pm
Re: Help for newbe?

I think if you supplied more info, it would be easier to respond to your questions. 
How many watt-hours do you propose taking out of the batteries “to reduce some power costs?  On a foggy day with less solar, will you reduce that figure, or do you need a reserve ?  What Is the figure (watt-hours) for backup power on an occasional basis ?

What make and model is your inverter and how are you going to supply the power to the house ?  Are you attempting to connect it into the house wiring or just running extension cords ?

Just how big are your two large batteries and are they true deep cycle batteries, or are they “RV deep cycle” ? The make and model of them will give us the answer if you don’t know.

What is the general location of this system ?  We need to know the hours of full sun.

With answers, I think we can give you better recommendations.  Right now there is enough gray area that it is hard to say anything.  The batteries in the RV indicate that you are probably thinking 12Vdc, but you might be better off with 24Vdc.   
 
2 Posts
Aug 20, 2009 06:18 pm
Re: Help for newbe?

I don't know what the exact watt-hrs will be as that is hard to predict.  If I lose power in the summer, I just need to run some lights and misc small items.  If winter, perhaps some more.  It also depends how long power is out and time of day.  When I use the inverter in the RV with existing batteries, I can get 4 or more hrs of running TV, lights, water pump and even the heater blower thru the night.  Something similar for the home would be fine.  I have a generator and can use that to charge the batteries if/when needed.  I lost power for 7 days last winter and really didn't like filling the fuel every 2 hrs or so, especially during the night and at $4 a gallon.  Not to mention that when I finally got to shut the gen off after running 7 days, it seized up, prob from being overworked.

The inverter is a TRACE 2000w, I'm not sure what the batteries are, they are deep cycles I got at Sears.  I run them and inverter at 12v in the motorhome.  The motorhome is parked about 20' from the house, I am going to run conduit underground from house to RV.  If power is out in summer, we'll just live in RV till power comes back on and only run a small circulation water pump (28w) on our aquarium in the house.  So, not much load with that and a few lights.

I have a south facing roof and should get sun from approx 10:30 am to 3mp or later.  I'm having 3 trees cut down in the spring and that should give them more exposure in the AM.

Greg at altE has helped with planning and I've got 4 Evergreen 205w panels coming, a 80W MTTP controller, and varius other things to get me started.  In the future I'll be adding 2 more 205w panels and at that time a separate battery bank and invertor for the home.

Thanks,Bob
 
351 Posts
Aug 23, 2009 12:13 pm
Re: Help for newbe?

You don’t know how many watt hours you intend to use and you do not know what size batteries you have.  You feel you are OK because the batteries have served you well in the past.

Step one in the proper design of a solar system is determining how many watt hours you intend to draw from it on a daily basis. (The AltEe university has a calculator that can help)
Step two is sizing the battery bank to support that load, including any reserve that may be factored in.
Step Three is sizing the panel array.
You are apparently doing it by “got my batteries, ordered my panels, will worry about watthours later”. (A lot have people have done that, and end up paying for it later.  They “fry” or “smoke” the batteries.)

Batteries will accept certain loads under occasional use (such as RVing) that are abusive when done 7 days a week, 365 days a year.  RV/Marine batteries are not true deep cycle batteries, and do not stand up well in 7/365 service.

Unless Sears has some battery I am not aware of, your 2 battery bank is about 200 amp hours (plus or minus about 10%).   That is a terrible mismatch with your 800 watts of Panels.

While I wish you the best of luck with your new system, I fear that you will be buying batteries much sooner than you expect to.

Ken
 
Aug 23, 2009 08:22 pm
Re: Help for newbe?

I would tell you to forget about the RV.
Are you planning to turn your existing on grid home to off grid? If so, I say more power to you!. I think its a great idea. Its not going to be easy and its not going to be cheap. Look at your light bill. The national average for grid electricity is about $0.12 per kWh or kilowatthour so if your electric bill is $60.00 a month then your using about 500 kWh's per month or 16.6 kWh's per 24 hours. That 800 watt PV array you want might offset about 3.2 kWh's of that 16.6 it all depends on a lot factors. Namely, the number of hours of equivalent full rated charge you can expect from a PV module. Go here http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/ and enter; Average, Annual, Flat Plate Tilted South at Latitude then find your place on the map. If where you are shows a number 4 then that 800 watt PV array you want, might make 3.2 kWh's.
If you are converting your on grid home to off grid, the smart money is on reducing your dependence on electricity first. To give you an idea, I've lived of grid for about 30 years now. Only within the past 15 have I had the luxury of PV. We use about 72 kWh's per month which if I had to pay $0.12 for it would be about 8 dollars and some change. But I do have an LP bill that averages out to about $25 a month. There is four of us in the household. Sometimes five.

Is it your plan to turn your existing on grid home to off grid? Are you willing to give up air conditioning and outdoor lights that burn all night long? How will you refrigerate and pump water? These are all concerns when making a move to off grid living. Just how much electricity can you live without? Think about it. Oh! Get yourself a subscription to home power magazine. Learn about electricity in particular Ohm's Law and the National Electrical Code. Most importantly, scower the web looking for the best prices. Just when you think you have found a good price, lok again.
 
1 Posts
Aug 25, 2009 08:41 pm
Re: Help for newbe?

Ken, chill.  Yes, I do not know how exactly many watt hrs I intend to use.  If I was going to power my whole house or cabin, then I would calculate this amount.  However, my system will mainly be a back-up to grid system for power emergencies. If you read my earlier post, I specified usage could be different depending on time of day and time of year.  I've been very happy with the power provided by RV batteries and inverter, so anything at that level or better would be sufficient for most power outages.  If I find I need more batteries or more panels I will add them as needed.  Rest assured, I'm not going to "fry" anything. I have a lot of good folks providing good advice. 

You don’t know how many watt hours you intend to use and you do not know what size batteries you have.  You feel you are OK because the batteries have served you well in the past.

Step one in the proper design of a solar system is determining how many watt hours you intend to draw from it on a daily basis. (The AltEe university has a calculator that can help)
Step two is sizing the battery bank to support that load, including any reserve that may be factored in.
Step Three is sizing the panel array.
You are apparently doing it by “got my batteries, ordered my panels, will worry about watthours later”. (A lot have people have done that, and end up paying for it later.  They “fry” or “smoke” the batteries.)

Batteries will accept certain loads under occasional use (such as RVing) that are abusive when done 7 days a week, 365 days a year.  RV/Marine batteries are not true deep cycle batteries, and do not stand up well in 7/365 service.

Unless Sears has some battery I am not aware of, your 2 battery bank is about 200 amp hours (plus or minus about 10%).   That is a terrible mismatch with your 800 watts of Panels.

While I wish you the best of luck with your new system, I fear that you will be buying batteries much sooner than you expect to.

Ken

 
46 Posts
Aug 26, 2009 06:43 pm
Re: Help for newbe?

Not to add carbon emitting greenhouse gas producing gas onto the fire, but I have to agree with Mr. Ken on this one. He may have come across as cross (not to me mind you) but his words ring true.
Having an idea of what you want to power during a power out, and for how long is important. Not essential but important. I did it the other way and its working out just fine. However, i do not intend on releying on it for power outages. Mine is just experimentation, learning, and lots of fun (if not slightly dangerous!).
For you, it sounds like powering the beer fridge and the TV (the essentials)is key. Having an idea of the above will really help. First and foremost for me would be those batteries. Auto batteries (yes, even the deep cycle marine ones) are designed for cold cranking amps, with a dept of discharge in the neighborhood of 3-5%. Solar batteries are the ones that will work better. They are designed to be discharged to, say, 60 or as low as 50%. So when Ken says you may end up smoking them, he's probably right. Car Barteries will still work, but you may want to really oversize things on the batt side.
Either way, like ken said, good luck! Smiley -m
 
26 Posts
Aug 26, 2009 09:08 pm
Re: Help for newbe?

Hello,
Your situation sound s perfect for what I'm selling on this forum.
http://www.altestore.com/forums/Renewable-Energy/For-Sale/Pre-Wired-E-Panel-Inverter-Charger-Ch/index.php/topic,2032.0.html
I bought this system and later regretted not sizing my system properly for our new home. We went a little bigger and now am trying to sell this near brand new system.
It would be well suited for the size array you have ordered and it is very easy to set up.
As the others have mentioned, you should really determine your average watt hours and most definitely upgrade you batteries. I have 16 Trojan T-105's for my system and it has served me well.
Best of luck.
Dave
 
Sep 1, 2009 09:16 pm
Re: Help for newbe?

Hi Folks,  I just discovered AltE and what a great company and this board is excellent info.  I'm planning a small off-grid system and need some help.  Basically want to use the system as back-up power and to reduce some power costs as well.  I want to start small and have room to expand.  This is what I have in mind. I already have a 2000w inverter and two large batteries in my motorhome which sits unused for most of the year, so I want to take advantage of them for now.  What I want to do is put 4 200w panels on the garage roof and use them to charge the batteries in the motorhome.  I plan on adding 2 more batteries in the bank later.  The distance from the roof to the motorhome is about 25'.  Should I put the MPPT controller/combiner in the garage and just run wire to the batteries, or should I put the controller in the motorhome and run wire to that from the combiner located in the garage? Does it make a difference?  Also what amp controller would be minimum for 1000-1400w of panels?  Eventually I want to expand to this capacity but not want to have to purchase another controller when I do.  Thanks.

Oh! I think I get it now. The mention of an "off grid system" threw me. So, the immediate plan is; the 800 watt PV array will be on the roof of the garage. The 200 amp hour? batteries will be on-board the RV with the 2000 watt inverter and during times of black out, a "drop cord?" will supply 120 vac power to a load in the home from the 2000 watt inverter on board the RV and you want to know where the best place for the charge controller and combiner box would be. 
Then eventually you will add more batteries (to the RV?) and more PV modules to the array on the garage.

(A battery monitor such as the Bogart 2020 is still a good idea to give you an interface with the system.)
Personally, I don't like the idea of having all those cords going to and from the RV and house. Its do-able but what you describe is really mis-matched taboot. Movable and non movable power sources and loads, inside and outside, 200 amp hour battery, 2000 watt inverter, 800 watt PV array, anyway.
If I had to do this, there was no other choice, I would set the combiner box and charge controller and monitor on the outside garage wall as near the to PV array as possible making sure its all Nema 4X and I would use GFP. I'd hard wire in conduit under ground from there to a box above ground near the RV, close to where the batteries are inside, and put a recessed male plug on both the RV and the box, both with in use covers and all of ample amperage ratings. I would make a cord with females on both ends to fit. This is because the batteries are "on" all the time and the PV array should be considered as "on" all the time. I would also want to be able to lock in and lock out everything so curious fingers can't find their way to live terminals. Essentially the same power transfer set up with the vac power minus the controller and all of course.  Whats going to happen with the PV power when the RV is logging milage? What would an electrical inspector have to say about it all? I guess there is no place to mount the PV array on the roof of the RV? Whats going to happen if the vdc cord is not removed and the RV drives off?
« Last Edit: Sep 1, 2009 09:19 pm by Thomas Allen Schmidt »
 
99 Posts
Sep 10, 2009 01:07 pm
Re: Help for newbe?

You need to have a grid-interactive inverter if you plan to use your RV batteries as a back-up to your grid-connected house.  These inverters will cut off the grid so that you don't feed power back out to the lines that the power company may be working on.  Check with your local building inspector for the exact requirements.

You want to have your charge controller as close to the batteries as possible.  Also, over any major distance, you want as high a voltage as possible.  So, if you're going to use 4 panels, and you can set them to output at 24V each, put them in series so that you're driving 96V to your charge controller.  That will minimize line losses and permit smaller gauge wires.  The charge controller can then convert that to 12-15V to charge your batteries (I prefer mine at 24V).  However, I think your battery bank is mis-matched to your intended array size.  You should really just buy a set of dedicated batteries.  Leave the RV out of it.  It wasn't designed for and is not suited for what you propose.

You can get a really nice, long-warranteed, deep-cycle set of Rolls-Surrette (546 Ah) batteries for about $2500.  Add in an Outback grid-interactive inverter for about $2000, your 800w of solar for about $5000, and another $1000 or so for various accessories and wire, and you're looking at about $10.5k for a great back-up system and a great start to an off-grid system.  You could easily scale that up (with sufficient scaling down of loads) to power your home full-time.
 

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