Excellent discussion on an experimental off grid home with a series of short articles discussing the system:
http://howtousesolar.com/our-off-gri...-it-all-began/
Excellent discussion on an experimental off grid home with a series of short articles discussing the system:
http://howtousesolar.com/our-off-gri...-it-all-began/
"There seems to be some perverse human characteristic that likes to make easy things difficult." - Warren Buffett
I found a 5 ton ammonia absorption chiller designed for residential applications. I'm looking into it, but here it is: http://www.firechill.com/products/ac500/ Too big and too much electricity for off grid use, but interesting nonetheless.
Last edited by buenijo; 05-16-2013 at 04:15 PM.
"There seems to be some perverse human characteristic that likes to make easy things difficult." - Warren Buffett
My opinions on a suitable battery system for an off grid power system:
I consider overall (long term) costs to be the single most important factor. Getting the best value for the battery is paramount. I write "value", not price. What kills a battery is excessive discharge and temperature extremes. Overcharge is also a killer, but it's not so much a problem as the other two. I say go with a new forklift battery. Size the battery such that a full charge on the battery will provide you with all the electricity you need over a 24 hour period without dropping the state of charge below 60%. You never want to drop below 50% state of charge. The bigger the battery, the longer it will last all else equal. The charging efficiency of a battery is very low while it's at a high state of charge. However, with the price of solar panels down so much I consider it preferable to choose a larger battery that stays at a high state of charge and buy extra panels. The overall efficiency can be improved dramatically by using most of your electricity while the panels are producing as this effectively bypasses the battery charging. One example would be placing a thermal mass in freezers and refrigerators and putting them on timers to operate during the day while the panels are producing. Another example is using any high power electrical appliance only when the panels are producing.
Forklift batteries are hands down the best value I've seen in an off grid battery system. You're looking at about $130-$150 per kilowatt hour of rated storage capacity (80% discharge at 20 hour rate). So, a 1050 pound 24 volt forklift battery will cost you about $2500 delivered in the 48 States (see www.giantbatteryco.com), and will provide 19 KWh electricity at rated capacity. In practice, if you limit discharge to no lower than 60% state of charge and considering inverter losses, then a fully charged battery will provide about 8 KWh of AC electricity, and this is more than most off grid home need each day. Keep a wood gas engine system around for backup charging, and keep a large solar array to minimize wood fuel consumption for this purpose.
As far as the solar array goes, I recommend using two parallel arrays each with a separate controller. These can feed a common battery. I've not found any 48 volt forklift batteries that are not truly massive (way overkill for most off grid set ups). Unfortunately, most solar charge controllers are limited to about 80 amps. At 24 volts this limits the array to no more than 2000 watts. If you're good with what a 2 KW array provides, then fine. If not, then I recommend two parallel arrays, but you'll have to get two controllers. This isn't so bad as it provides redundancy. In my particular case, I'm planning on a 3 KW array to provide a net 6-8 KWh per day in east Texas. I'll get a wood gas engine system at about 2500 watts bulk charging rate for the battery for use only when required to prevent excessive discharge on the battery (bulk charge during early morning, then let the solar array take the battery the rest of the way. Personally, I wouldn't break out the gasifier until the battery voltage shows at or under 50% state of charge. Bulk charging the 19 KWh battery described here at 2500 watts would take about 3.5 hours and consume about 40 pounds of wood).
Well, that's enough ranting for now. Later!
Last edited by buenijo; 05-06-2013 at 09:29 PM.
"There seems to be some perverse human characteristic that likes to make easy things difficult." - Warren Buffett
What is the expected lifespan of those batteries?Originally Posted by buenijo
War; everything in the world wrong, evil and immoral combined into one and multiplied by millions.
It depends on how they're used. In their designed application (i.e. forklift duty) they are often near fully discharged during a work day, and fully charged before the next duty cycle. Often they see at least one full duty cycle each work day. You'll have to verify, but I recall a typical life time of roughly 6-8 years under this heavy industrial usage. However, they are not discarded at this point. Rather, they are often sold second hand (used). The cells at this point might not be able to take a forklift through a full work cycle, but they often work very well in light duty applications (like off grid). In the off grid application, they last 15-20 years by most accounts I've seen. I know of one individual who claimed 10 years on a USED forklift battery, several claimed 15-20 years for a new battery, and one claimed 33+ years for a new battery. Note that this represents information I've mined over the last 5 years or so. NOTE: Personally, I don't recommend that anyone consider a used battery.
http://www.sustainablepreparedness.c...newable-energy
Last edited by buenijo; 05-05-2013 at 10:51 PM.
"There seems to be some perverse human characteristic that likes to make easy things difficult." - Warren Buffett
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