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Old 05-14-12, 08:00 PM   #1
jameson
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Default Help with Solar/Wind.

Hi all, I'm new to the forum and am looking for a little advice with regard to planning a Solar/Wind setup. I'm well on with a self build on the west coast of Ireland and am looking for any pointers on how to assemble items accumulated over the last couple of years. So far I have a 1 KW 24Volt wind turbine, 6 x 200watt PV panels, a 100amp controller and a 3KW 24-240 volt Pure Sine wave inverter. I also have a 10KVA diesel generator.
I was hoping to use a battery bank rather than a grid tie system and am looking for advise on sizing the batteries bearing in mind I don't want to spend a second mortgage. I would hope to get my power usage down to approx' 10KW per day or less. My location is rural, coastal with plenty of wind and unpolluted clear skies. I realise I won't be able to start off totally off grid with what I have so far but would like to get as close as poss'.
Should I be going down the new battery route of would second hand forklift batteries suffice , and any suggestions of sizes and battery string layouts. Any help would be very much appreciated. Thanks

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Old 05-31-12, 10:14 PM   #2
Mobile Master Tech
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I have found that some battery wholesalers will offer reconditioned or blemished batteries at deep discount. An 8D commercial 12v battery is the largest size commonly used in trucks here (probably in beautiful green Ireland as well!). They usually are 220-250AH and sell for $175 and up. I was able to get a couple reconditioned ones for $50 each and a new "blem" for $80 a couple of years ago for one of my customers from my local Interstate battery dealer. They were willing to take other smaller lead-acid batteries as core exchange.

Commercial truck batteries such as the 8D are built like a deep cycle battery and will withstand rigorous discharges much better than standard batteries, though not as well as dedicated storage batteries with 0.250" and thicker plates!

Unless you need regular backup power, you are probably better off with grid-tie assuming your power company doesn't put you through too many hoops. You will need a lot of wind/solar power available to offset the battery losses, charger losses and of course the inverter losses, as well as having the extra power to equalize the batteries. If you have to use the genny a lot, it will cost.

I read a study that lead acid batteries are 91+% efficient (charge power in compared to electricity back out) below 84% SOC, but that drops to 55% approaching 90% SOC and below 50% at 100% SOC, which you need to do around once/week to equalize and prevent loss of capacity.

Most "high efficiency" chargers and some charge controllers appear to be around 85% efficient, and most inverters are 90-97% efficient. Converting to grid power doesn't cost much efficiency, but storing that juice in a battery and getting it back again sure adds up the losses.

I'm in the same boat, deciding whether to be strictly grid-tie or have offgrid capability. I may just have switching options at the PV panel outputs that will send the juice to the gridtie inverter or be able to charge batteries running an emergency inverter.

Craig
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Old 06-02-12, 01:27 AM   #3
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I have both on my system. Battery hooked to wind and solar to a pure sinewave uninterruptible power supply. This charges up overnight on wind and cheap rate electric and switches from peak rate electric to batteries and solar in the morning. If the solar has fully charged the batteries, then the excess goes out through a grid tie. I would like to be offgrid, but until I can get more pv panels, and a 10kw pure sine inverter just for the electric hob, I am still paying for the mains.
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Old 06-02-12, 01:32 AM   #4
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I should also add that I have mine on 48volt, so my 2 lots of 3x80w panels are wired to give out 9 amps at 51 volt, rising to 66v max, where they taper off to zero current. My charge controller is set to divert at 55 volts to the grid tie. Are you panels configured for 28 volt at maximum current? This would be perfect for charging a 24 volt battery system.
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Old 06-02-12, 10:53 PM   #5
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Check out this site: Solar Beginners Corner

I found it's a good place to get started. They have some major expertise.
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Old 06-03-12, 09:15 AM   #6
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Thanks for the input guys, interesting reading and the Solar Beginners corner looks particularly interesting Xringer, Thanks. I may well be better with grid tie Mobile Master Tech, Think I need to do a bit more research but I'm almost certain the power co will want me to jump through hoops here in Ireland. Thanks again for the info guys and keep it coming, it all helps.
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Old 06-03-12, 10:14 AM   #7
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It seems like you might have to find out how other folks in Ireland have been able to get connected to the grid.
I looked around, but couldn't find much new info.. This looks like old regs..
Solar Panel Planning Permission - Regulations

Problems with some of the regs in some areas of the USA, they didn't keep up
with new technology, so the Enphase type of inverter, which means that 230 AC
comes right off your roof, seems illegal to a lot of city inspectors.

If the price of kW hours stays reasonable, I will likely live out the rest of my life without using a grid tie system.
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Old 10-04-12, 10:19 AM   #8
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Quote:
Originally Posted by Mobile Master Tech View Post
I read a study that lead acid batteries are 91+% efficient (charge power in compared to electricity back out) below 84% SOC, but that drops to 55% approaching 90% SOC and below 50% at 100% SOC, which you need to do around once/week to equalize and prevent loss of capacity.

Most "high efficiency" chargers and some charge controllers appear to be around 85% efficient, and most inverters are 90-97% efficient. Converting to grid power doesn't cost much efficiency, but storing that juice in a battery and getting it back again sure adds up the losses.
Craig
I use an efficiency factor of 60% when using solar through batteries (not including the inverter efficiency factor. You lose a ton of energy in and out of the battery bank.

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