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Old 11-01-2011, 15:28   #1
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Design Ideas, Please

Since there is so much knowledge here about batteries and solar I wanted to ask you for suggestions. I have a friend that is wanting to install a solar aray on the roof of his outbuilding. The building is 3,700 square feet, single story and made of insulated metal walls and roof on a concrete slab. It measures 75 X 50. He keeps a boat, motor coach, tractor and some other stuff in it. He want's to cover the entire roof with panels and use a big bank of batteries to store the power. He want's to be able to supply power to the motor coach in the event he has to rely on it for emergency living quarters for any extended periods...say if the power to his main house goes down in a storm or something worse.

The location is Texas-good sunshine. Money is not much of a problem for this guy.

If this was your project and with plenty of cash, how would you do it?

Thanks
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Old 11-01-2011, 17:07   #2
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The design's easy. It's setting the design parameters that's hard.

First, he has to define "extended period". And once he get's that down, then he needs to figure energy consumption, and whether the battery bank will be designed to go for more than just a single evening without being recharged by the solar panels in the sun the next day.

By far the most economical alternative is to forgo solar power and install a genset in the motor coach, and to equip the building with enough diesel tanks to hold him over until that "something worse" blows over...

Why not equip the motor coach itself with solar panels? He probably already has a house bank of batteries. Install solar panels on the roof, an emergency genset and inverter if he needs 120V power without the genset running. The when the bovine excrement hits the fan, pull the motor coach out of the building and into the sun. That would be a whole lot cheaper than having to provide emergency power via battery backup to the entire building.
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Old 11-01-2011, 17:54   #3
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By far the most economical alternative is to forgo solar power and install a genset in the motor coach, and to equip the building with enough diesel tanks to hold him over until that "something worse" blows over...
Bingo! Sometimes it really needs to be about the money. What could destroy the building would destroy the solar array first. While it is possible to build the whole solar array and sell the excess power back to the electrical utility, you can't make money. If it were even close to possible The power company would be doing it instead of doing demonstration projects so they can get their rate hikes approved to do it the old fashioned way.

My neighbor down the street just redid his whole house with a large array. The payback is about 15 years (it's never been cheaper). The solar hot water heater he added is a huge positive deal. Making hot water has been a good bargain for at least 30 years. The only reason to do it on a boat is to avoid the engine noise of the genset or main engine. A few hours of less noise means a lot on a sail boat. In that light doing all you can is a good idea. For a storage building - I don't see it.
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Old 11-01-2011, 18:09   #4
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I agree, but not diesel. The fuel is too unstable. Use propane for an installation like this, and then it can just sit there for a decade or so... Plenty of propane powered gensets.
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Old 11-01-2011, 18:23   #5
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Use propane for an installation like this, and then it can just sit there for a decade or so... Plenty of propane powered gensets.
If you have the storage it would be the better option. We have a few around the neigborhood. Clearly a lower maintenance problem for the scenario where it's for an emergency backup. A below ground propane tank costs a bit more than a diesel above ground storage tank though installing a below ground diesel tank would in most locations require a concrete vault.

Getting a better perspective on how long it has to run becomes a critical decision.
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Old 11-01-2011, 18:30   #6
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I agree, get a diesel or gasoline generator.
Solar is not cost effective, and batteries are very inefficient.
Solar is suitable for boats before it is low maintenance and quiet, but not efficient or cost effective.
Most boats still have a generator as backup
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Old 12-01-2011, 08:01   #7
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Thank you very much for your feedback. I was incomplete with the info originally furnished...the coach does have a generator.
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Old 13-01-2011, 14:29   #8
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Thank you all for your feedback. He has decided to go with a 36kw propane powered generator and a BIG propane tank.
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Old 13-01-2011, 19:06   #9
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WOW!!! And your really want an answer/advice in a marine cruising forum for an electrical design consisting of solar panels, storage batteries power inverters, distribution panels, hazardous substances and +++??? Really???

Your friend needs advice from an electrical engineer. I do not agree that this is a piece of cake project what so ever. Just my advice.

Foggy

EDIT: I hope he sought out/seeks out professional advice dealing with a 36KW generator, power distribution, along with propane storage!
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Old 14-01-2011, 06:29   #10
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Thanks Foggy. The electrical engineer is where the project started and the 36kw was his recommendation. Still, my friend wanted to consider solar or wind. So...knowing there are people here on the forum with vast knowledge about it, I posted. Sure enough folks responded and I am grateful.
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Old 14-01-2011, 07:29   #11
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I am not sure what things are like down in the US, but here in Canada, solor farms are poping up everywhere. The thing is, why use your own energy and pay for/maintain your own battery bank, when you can pump it back into the grid and sell for .86 and then buy the power you need back at .05?

That is what everyone here does. I have heard that by storing you lose 20% right off the top.
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Old 14-01-2011, 08:41   #12
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Originally Posted by rhr1956 View Post
Thanks Foggy. The electrical engineer is where the project started and the 36kw was his recommendation. Still, my friend wanted to consider solar or wind. So...knowing there are people here on the forum with vast knowledge about it, I posted. Sure enough folks responded and I am grateful.

RH--- Thank you for clarifying. So many times people try doing things not fully understanding the complications.

Foggy
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