Hi all I did a paper for the ASES annual conference proceedings, where it suggested from actual 8yr? data for Minnesota, that 3 day even 5 day periods of low sun were common every year, but 7 to 10 days was rare, and longer than 15 days never occurred (in my data set). A Phd thesis by J. Clink UofM has a similar result. Darryl
--- On Wed, 12/2/09, Travis Creswell <tcresw...@ozarkenergyservices.com> wrote: > From: Travis Creswell <tcresw...@ozarkenergyservices.com> > Subject: Re: [RE-wrenches] Other's thoughts on Autonomy? > To: "'RE-wrenches'" <re-wrenches@lists.re-wrenches.org> > Date: Wednesday, December 2, 2009, 1:35 PM > > > > > > > > > > > > > > > > > > > > > Hi > Joel, > > > > > I think we > are all pretty much on the same > page. > > > > > I’m > speaking mainly about a full > time off grid residence, commonly with flooded lead acid > and of course a fossil > back up generator. > > > > > Most of my > full time off gridders don’t > even need to their generator from late April to early > October. They report > that it’s normal that by 10 or 11 am their CC is in > float. Then > winter sets in with frequent 2-3 week periods of > clouds. Like Walt said, > where is the magic cloudy day number for me? Is it > the average of 3 weeks > of sun and 3 weeks of clouds for 1.5 weeks of > autonomy? That’s > grossly oversized in the summer and still inadequate in the > winter. > > > > > From my > view, if you need xxx kWh’s > per month to live that’s how many you need, and days > of autonomy aren’t > that meaningful when you can only generate 1/3rd > of that with your > array. You have to run the generator just as many > hours per month > regardless of how many days of autonomy, right? And I > believe that if you > factor in charge efficiency and self discharge the larger > the bank has a few > more hrs per month of generator usage. > > > > > Thanks for > sharing your thoughts everyone. > > > > > Best, > > > Travis > Creswell > > Ozark > Energy Services > > > > > > > > > > > > > From: > re-wrenches-boun...@lists.re-wrenches.org > [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Joel Davidson > > Sent: > Tuesday, December 01, 2009 > 6:38 PM > > To: > RE-wrenches > > Subject: Re: > [ > RE-wrenches ] Other's thoughts on Autonomy? > wasconcordbatteries, EQUALIZE Them! > > > > > > > > Hello > Travis, > > > > > > > > > > > > I think that 2 > days is not enough battery autonomy in > the Ozarks and many other locations unless you have a > fossil fuel > generator to carry you through long cloudy periods. > Battery > autonomy is site and load specific. I've done systems > with as little as 1 > day and as much as 3 weeks at 80% depth of discharge. > Lately, I've been > generically specing 1.5 days of autonomy at 50% d.o.d. to > get the dialogue > started with the customer. > > > > > > > > > > > > I use > to spec up to 4 parallel strings of T-105s or > L-16s in 2, 4, and 8 batteries in series, but now I keep > the number of strings > down to 3 or less and prefer 1 or 2 strings of > big 2-volt cells to > reduce the number of cells and > connections. > > > > > > > > > > > > Southern > California urban and > suburban > grid-tie PV systems are almost all non-battery although we > still get asked > about emergency power - until they hear how much it adds to > the cost of a > grid-tie PV system. > > > > > > > > > > > > Joel > Davidson > > > > > > > > ----- Original > Message ----- > > > > > > From: Travis > Creswell > > > > > > To: 'RE-wrenches' > > > > > > > Sent: Tuesday, > December > 01, 2009 2:15 PM > > > > > > Subject: Re: > [RE-wrenches] > Other's thoughts on Autonomy? was concordbatteries, > EQUALIZE Them! > > > > > > > > > > IMHO, one > of the worst design > boo-boo’s is going past more then 2 days of > autonomy. Personally, I > no longer size much over one day because it’s my > anecdotal observation that > most batteries die of old age and being ignored long before > cycles get > them. Speaking mostly about quality deep cycle > flooded. > > > > > Lots of > good things result; > > -50%-75% > smaller battery bank means a > $20,000 battery bank just turned into $5,000 bank which > frees up a ton of money > for more modules and now-a-days you can buy a lot more PV > with that > money. More array mean far less reliance on > autonomy. I’ll > take the trade all year long. In the summer we have 3 > to 4 weeks of sun > and one day of clouds and in the winter we get 3 to 4 week > stretches with 1 > sunny day. Autonomy doesn’t really matter in > either case from what > I’ve seen. The larger the bank means more self > discharge losses, > which on large battery banks gets significant as they age. > 5-15 years > later you’ll still have all that array but no matter > what you’re > looking at new battery bank. > > > > > -If you > study the quality deep cycle > manufacturers literature you’ll see that you’ll > see that anything > over 1 day of autonomy is too much to allow the array to > actually charge the > battery bank anywhere near the recommended amps and just > like rust, sulfation > never sleeps. > > > > > -Less cells > to water > > > > > -Less space > required > > > > > -Given that > a surprisingly high percentage > of off gridders totally screw up on their first bank, no > matter how much we all > try we might as keep the stupid tax of replacing a 2.5 yr > old battery bank to a > minimum. > > > > > -All of > this discussion about cross > paralleling, buss bars, TLC with a gazillion connections > and multiple strings > goes away. > > > > > -And the > best part is we don’t have > to carry all of the lead into the basement and even better > back out of the > basement! > > > > > Just my > .02. Feel free to strongly > disagree but let’s be polite about > it. > > > > > Travis > Creswell > > Ozark > Energy Services > > > > > > > > > > > > > > > > > > > From: > re-wrenches-boun...@lists.re-wrenches.org > [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of R Ray Walters > > Sent: > Tuesday, December 01, 2009 > 12:44 PM > > To: > RE-wrenches > > Subject: Re: > [RE-wrenches] concord > batteries, EQUALIZE Them! > > > > > > > > > > > > I > used to think that > one string was optimal; until I had a single cell failure > take out an entire > system for weeks. (try operating a 24 v system at 22v! > ) > > > > > > I > now think that 2 > parallel strings is optimum, 3 is OK, and 4 is > max. > > > > > > At > 4 parallel strings, we start spending more time looking to > make sure all > connectors are the same exact length etc. to insure equal > operation. > > > > > > > > But of course how do you account for > varying internal resistance of the > batteries......?? > > > > > > > > I've done 4 parallel strings at 144 > DC of sealed batteries on an electric > vehicle, but we were very careful with our resistances, I > even switched to > smaller wire, on closer strings, and calculated out the > exact resistance, so > all strings were theoretically equal. This set actually > just died, but achieved > its manufacturer's predicted cycle life. (B&B > battery, 350 cycles to 80% > DOD) > > > > > > So if you're careful, 4 strings can > work well. > > > > > > Worst I've seen was 20 golf carts > paralleled in a 12 v system, (10 > strings) and they didn't pull the main connections from > across the set, just connected > to one end. > > > > > > The results were very predictable, with > the furthest batteries being > chronically under charged, and the closest ones being over > cycled to a > premature death. > > > > > > > > > > > > Ray Walters > > > > > > > > > > > > > > > > On Dec 1, 2009, at 11:28 AM, wind...@wind-sun.com > wrote: > > > > > > > > > > > > > You gotta > wonder about why the customer bought such a > battery layout, or why the installer sold that kind of > configuration (which > ever it was) with so many small batteries. We would > never recommend going > over 2 parallel banks, but sometimes the "customer > knows best...". > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ > > List sponsored by Home Power magazine > > > > List Address: RE-wrenches@lists.re-wrenches.org > > > > Options & settings: > > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > > > List rules & etiquette: > > www.re-wrenches.org/etiquette.htm > > > > Check out participant bios: > > www.members.re-wrenches.org > > > > > > > > > > -----Inline Attachment Follows----- > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
