Solar: battery backup, propane backup

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ltlredwagon's picture
ltlredwagon
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Posts: 87
Solar: battery backup, propane backup

Hi all,

I'm researching solar backup.  Searched the site and got some good data, but not finding exactly what I need (it may be there but I'm not finding it). This is all new for me, so I'm looking at all possibilities.

My system will be a 3.7kw in the mountains (winters not too bad - mostly 20s/30s). Southern California, so generally lots of sun.  Ground mount on perfect south-facing hill.  I expect to be on the grid.  To get the state incentive discount, I am supposed to be connected to the grid for 10 years.  My understanding is that the type of batteries one would want for backup (ON grid, backup seldom used) is different from what one would want if one is OFF grid.  My area is somewhat remote, so if power lines go down it can be as much as 2-3 weeks before power is restored.  So it seems my options are:

1.  Solar with propane generator backup which kicks in automatically if power goes out.  If I want to go off grid – in 10 years, or sooner (and pay the penalty for early disconnection) – THEN I get the proper batteries for being off-grid. 

2.  Solar with battery backup.  Get the proper batteries for a backup system where the batteries are seldom used.   As above, if I decide to go off-grid in the future, get the correct batteries at that time.

3.  Redundancy - having both backup batteries AND propane generator.   I'm partial to redundant systems, but would this be overkill?  I'm assuming (yes?  no?)   a) battery technology could improve significantly in the next 5-10 years;  b) some companies which make good batteries will still be in business in 5 - 10 years.

4.  Skip the state incentive (I can still get the federal benefit, even if off-grid) and go fully off-grid right from the start.

Appreciate any advice.

rhare's picture
rhare
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Joined: Mar 30 2009
Posts: 1323
Re: Solar: battery backup, propane backup
ltlredwagon wrote:

Skip the state incentive (I can still get the federal benefit, even if off-grid) and go fully off-grid right from the start.

I don't believe there is any need to be off grid unless you have too.  Take the incentives and use the grid while it exists.  You can start with that system and then add batteries or generators later with a slightly less efficient battery charging situation and a bit more expense.  Check out AC coupled systems.  SMA has some literature as does homepower magazine.   

With SMA  you basically build a grid tied with Sunny Boys, then if you want you can add battery/generator backup with Sunny Islands.  The cost difference is Sunny Island versus Charge Controllers.  Other vendors have similar solutions.

LG's picture
LG
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Joined: Oct 6 2009
Posts: 59
Re: Solar: battery backup, propane backup

If you have the grid then I would use it. You might use a propane generator and solar panel with batteries as a backup. Batteries-ckeck out the Trojan L-16 6v. Propane generators-the pressure coming from your propane tank is regulated down for your house appliances, if the generator you are considering has a barbecue grill type connection then it requires higher pressure than your house uses. You can bypass the generators internal pressure system, but this is a chore and not recommended for safety proposes.  It is better to buy correct. People at LOWES will not have a clue what you are asking about, buy from a knowledgeable dealer. The pressure is measured in water columns.

Good luck.

LG

silvervarg's picture
silvervarg
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Posts: 57
Re: Solar: battery backup, propane backup

3.7kW of solar panels is a huge and expensive system.
If you have not done anything before (almost regardless of what it is) is would advice you to start in a smaller scale.
If things go bad, e.g. you don't handle the charge of your batteries well, or the charge controller breaks etc, then it is much more expensive lesson if you do it on a big system. 

If I was living in a place where a line down is likely to result in 2-3 weeks of power outage I would defenatly go for a system that is self sufficient.
That means you should have a battery bank of some sort. 

I would personally probably go for a system where the solar panels will be able to charge batteries to cover my needs for the best 4-6 months of the year. For the remaining months and possibly if there is heavy clouds for a few days in a row then you use a backup, typically a generator that will charge your batteries. I would probably go for a disel generator that can run on bio-disel.
Compared to your 3.7kW system this will be cheap, since we are likely to talk about 1/4 the size of solar panels or less. 

E.g. in winter months you might need to run the generator a few hours every other day or so.

I would also keep some extras, like:
a spare regulator, perhaps a simpler and cheaper version than the primary regulator.
at least one extra car battery, fully charged.
minimum of one inverter (AC power from battery power).
At least have two means of cooking. Perhaps 3 (grid electricity, propane and wood)
Have at least two fuels that can heat the major parts of your house.

 

rhare's picture
rhare
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Joined: Mar 30 2009
Posts: 1323
Re: Solar: battery backup, propane backup
silvervarg wrote:

3.7kW of solar panels is a huge and expensive system.

Really?  That's only 16 panels.  With an expensive rack on a pole mount with lots of concrete, your looking at maybe 25K pre-tax for a grid tie system.  It comes down to under 18K after federal tax incentives and maybe even lower with state/utility incentives. You can probably whack 5-6K off that with a roof mounted system.  The batteries are what crank up the price.

GiraffeOK's picture
GiraffeOK
Status: Bronze Member (Online)
Joined: Apr 14 2009
Posts: 36
Seeking advice re solar batteries

Does anyone have experience with / knowledge of batteries from Power Battery? My solar installer wants to use these and already has some on my site, but now tells me the company is bankrupt and out of business. I am reluctant to accept batteries made by a company that is out of business and can’t service the warranty, and I also wonder why they went out of business if they had a good product. Advice, anyone?

Damnthematrix's picture
Damnthematrix
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Posts: 3998
Solar battery backup

We have two systems here, one grid tied only, the other is hybrid grid/battery tied. http://damnthematrix.wordpress.com/2010/10/04/powering-up-for-the-collapse/

We haven't had the power down for more than 24 hours in the past six years, so our batteries get very little use.  All the same, I recommend you stay well away from gel cells.  They have caused me nothing but grief, they cost more and last less long than flooded cells.  I've only had the current sealed flooded cells for a few months, but so far I think they are marvelous.  Of course being in Australia I have little idea of what is available in the US, but I would have thought Yuasa had a presence there.

I also recommend thin film panels.  Our first array was thin film, and I will never live down buying monos for our new array....  though temperature derating may be no problem for you as it sounds like you live somewhere really cold (compared to us).

I always recommend anyone going solar take extreme measures to improve the energy efficiency of their lifestyle FIRST.  This is way cheaper (and hence more sustainable) than trying to feed an energy blackhole with huge arrays and battery banks.  I agree with rhare re hooking up to the grid first and adding batteries later.....  this way you will get a better feel for how much energy you use, how much you generate, and that sort of data is very handy to evaluate and size the backup mattery bank.  Whatever you do, make sure EVERYTHING is sized to suit your consumption and your local climate.

Good luck

Mike

GiraffeOK's picture
GiraffeOK
Status: Bronze Member (Online)
Joined: Apr 14 2009
Posts: 36
Solar batteries

The batteries I have are gel cells, touted as being long-lasting and requiring no maintenance. Do you know other people who have had bad results with gel cells?

Dutch John's picture
Dutch John
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Posts: 50
Gel cels

Do not use a cheap charge controller in combination with gel cels. Gel cels hate a too long or high absorbtion charge. Ask your battery supplier at what absorbtion voltage your controller needs to be set. Overcharging will dry them out.

I like my deep cycle flooded forklift batteries. But I would kick them out today, if I could lay hands on the old fashioned nickel-iron batteries. Perhaps not the most efficient, but they last a life time and can be abused. There is a Chinese manufacturer, but besides that new ni-fe's are very expensive, the quality seems not to be very constant.

Regards, DJ

Damnthematrix's picture
Damnthematrix
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Posts: 3998
gel cells
GiraffeOK wrote:

The batteries I have are gel cells, touted as being long-lasting and requiring no maintenance. Do you know other people who have had bad results with gel cells?

Sure do.......  To be fair, I only ever bought cheap ones.  But three of my friends have 200Ah 48V banks that cost over $6000, and they ALL have problem cells that will not hold charge, even after meticulous maintenance.  They are all under warranty still, but none of them are holding their breath that the warranties will be upheld because there are so many carefully worded exclusions in them, and how do you prove anything, really?  One of these friends is an electrical engineer who used to install stuff for our national telecom compamny and knows this stuff backwards.

Another friend, who originally installed our first system and has an identical setup to ours gave up on gel cells and now has Li Ion cells (because he can, long story..)

GiraffeOK's picture
GiraffeOK
Status: Bronze Member (Online)
Joined: Apr 14 2009
Posts: 36
gel cells

Thanks for the info. I really hadn't researched types of batteries. Are other types of batteries also maintenance-free? Are the choices gel, LI, and flooded? Is there a website that compares battery types?

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