Hi All, This is a very interesting thread for me. I like low cost renewable energy, and I don’t jump to buy MPPT charge controllers when I believe that the setup I am planning works close to Vmpp inherently. I find that the panels used for grid tie with Vmpp around 31V actually work beautifully here in Scotland on a sunny day. Maybe in exceptional conditions there might be issues with equalising a battery but does this justify spending that much more on the system or settling for lower energy yield by buying controllers with money that can be spent on more modules?
So for best value (where wire runs are short) I would recommend using 2 standard mass-produced panels/modules on a 48V system here in Scotland, and go with diversion charge control. That’s another big issue over which I differ with the majority. I like to maximise usage of renewable energy whereas most seem to ignore the surplus once the battery is charged. Hardly any MPPT controllers have built-in facilities for diversion of surplus. So in most cases I think the extra energy is rejected, while the homeowner burns propane to heat water. A well-designed system will have plenty of surplus, or the battery will not last long. OK so there could be issues with equalising batteries on solar-only systems, but most systems I design are hybrids. And even the solar-only ones don’t seem to struggle in hot weather here. And on the rare occasions when it is very hot in Scotland you are not going to feel any shortage of solar energy. Days are long. Charge current is low. As I said it’s a very interesting thread on which I often feel like a lone heretic. cheers Hugh > On 13 Sep 2018, at 02:55, Sindelar Solar <[email protected] > <mailto:[email protected]>> wrote: > > Bill and all, > > To elaborate a bit on Ray's accurate suggestion with a bit of history... in > the early days the general consensus developed that for general use, 36 cells > (given that one cell produces just shy of 1/2 volt, regardless of cell size) > was the standard cell count for battery charging. This was based on the > understanding that a typical Vmp of 17.1-17.6 for a 36 cell module was > necessary to equalize a 12V FLA battery to ~15.5 VDC in hot ambient daytime > temperatures after all system losses due to various resistance in wire, > connections, controllers, etc., were accounted for. You'll occasionally see > early modules with 35, 33, 32 and even 30 cells, tried as "self-regulating" > modules - didn't work, as it couldn't account for voltage variations due to > temperature. Anyway, 36 cells is the default standard to charge a 12V > battery. Extrapolating from this, there's a direct correlation between cell > count and voltage in most applications: as 36 cells > 12Vnom, 72 cells > 24V > and 60 cells > 20Vnom. Go outside of these rules of thumb only with clear > understanding of these limitations. > > Three 60 cell modules is a nominal 80V; ideal for a 48 Vnom battery bank, > while still below the 150V limit of many standard controllers in record cold > temperatures. Three 72 cell modules, or 72 Vnom, is on the ragged edge of > voltage compliance in cold winter climates. > > Allan > > On 9/12/2018 10:30 AM, Ray wrote: >> A 2nd option: A pair of 72 cell modules should be enough. >> >> Ray Walters >> Remote Solar >> 303 505-8760 >> On 9/12/18 9:21 AM, Mac Lewis wrote: >>> Hi Bill, >>> >>> I agree with Allen. We get similar peak temps here and two 60 cell modules >>> doesn't charge a 48V battery bank adequately. This effect would become >>> worse over time with voltage degradation. I try to be at least 15% above >>> highest expected battery voltage with Vmp of the strings. With 150V input >>> limit on the Outback controllers, that leaves you with only one option, >>> strings of 3, with our low temps. >>> >>> On Tue, Sep 11, 2018, 4:24 PM Sindelar Solar <[email protected] >>> <mailto:[email protected]>> wrote: >>> Bill, I wouldn't, especially with FLAs. I have seen this situation here, >>> where the summer highs are similar, with a few homeowner/hack installations >>> and no, 60-cell modules will not finish the charge in hot weather. Strings >>> of three work just about perfect with modern charge controllers, especially >>> in winter, as they range high enough but well below 150VDC limits. >>> >>> Allan >>> >>> On 9/11/2018 4:04 PM, Bill Battagin wrote: >>>> I've been on hold with OB for about 40 minutes now and I need to know if 2 >>>> SW PVs with a Voc of 39.9 and a Vmpp of 31.3 will do an effective job of >>>> charging a 48 volt LA battery especially with temps of 95 degrees. >>>> Anybody have experience with this or similar, Appreciate the feedback. >>>> It just seems I'm a little low in Vmpp if I want to equalize when its hot. >>>> Will it be even more questionable in 10 years as PVs age? >>>> >>>> OB did just pickup only to tell me I need Java for the string sizing tool >>>> and he can't help me with this configuration. >>>> >>>> Bill >>>> >>>> -- >>> Allan Sindelar >>> [email protected] <mailto:[email protected]> >>> NABCEP Certified PV Installation Professional >>> New Mexico EE98J Journeyman Electrician >>> Founder (Retired), Positive Energy, Inc. >>> 505 780-2738 cell >>> >>> >>> _______________________________________________ >>> List sponsored by Redwood Alliance >>> >>> List Address: [email protected] >>> <mailto:[email protected]> >>> >>> Change listserver email address & settings: >>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >>> <http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org> >>> >>> List-Archive: >>> http://www.mail-archive.com/[email protected]/maillist.html >>> <http://www.mail-archive.com/[email protected]/maillist.html> >>> >>> List rules & etiquette: >>> www.re-wrenches.org/etiquette.htm <http://www.re-wrenches.org/etiquette.htm> >>> >>> Check out or update participant bios: >>> www.members.re-wrenches.org <http://www.members.re-wrenches.org/> >>> >>> >>> >>> _______________________________________________ >>> List sponsored by Redwood Alliance >>> >>> List Address: [email protected] >>> <mailto:[email protected]> >>> >>> Change listserver email address & settings: >>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >>> <http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org> >>> >>> List-Archive: >>> http://www.mail-archive.com/[email protected]/maillist.html >>> <http://www.mail-archive.com/[email protected]/maillist.html> >>> >>> List rules & etiquette: >>> www.re-wrenches.org/etiquette.htm <http://www.re-wrenches.org/etiquette.htm> >>> >>> Check out or update participant bios: >>> www.members.re-wrenches.org <http://www.members.re-wrenches.org/> >>> >> >> >> >> _______________________________________________ >> List sponsored by Redwood Alliance >> >> List Address: [email protected] >> <mailto:[email protected]> >> >> Change listserver email address & settings: >> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >> <http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org> >> >> List-Archive: >> http://www.mail-archive.com/[email protected]/maillist.html >> <http://www.mail-archive.com/[email protected]/maillist.html> >> >> List rules & etiquette: >> www.re-wrenches.org/etiquette.htm <http://www.re-wrenches.org/etiquette.htm> >> >> Check out or update participant bios: >> www.members.re-wrenches.org <http://www.members.re-wrenches.org/> >> > -- > Allan Sindelar > [email protected] <mailto:[email protected]> > NABCEP Certified PV Installation Professional > New Mexico EE98J Journeyman Electrician > Founder (Retired), Positive Energy, Inc. > 505 780-2738 cell > > > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: [email protected] > <mailto:[email protected]> > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > <http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org> > > List-Archive: > http://www.mail-archive.com/[email protected]/maillist.html > <http://www.mail-archive.com/[email protected]/maillist.html> > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm <http://www.re-wrenches.org/etiquette.htm> > > Check out or update participant bios: > www.members.re-wrenches.org <http://www.members.re-wrenches.org/> >
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