new solar system

3 Posts

Aug 17, 2008 06:56 pm

OK, where do I start. Bought a small, week long (at most) cabin/RV to use for a few weeks a year.

It came with:
42w Uni-Solar panel (yeah, I know...)
1 - 12v marine battery, 105 Ah
1 - ETS brand 16 amp charge controller w/o LVD
1 Fuse (20amp?) between panel and controller
1 - 2300w generator

runs at most if all were on:
6 - 12v auto bulbs, 2 - 12v fluorescent lights

plus RV stuff incl:

12 - 12v lights, 1 - 12v fan, 1 - 12v Shurflow pump, 1 - propane Refer (only electronic monitor), 1 - RV furnace blower, 1 - 120v sump pump for well off of generator (23'deep)

So, just a few questions:

I just bought 2 - 6 volt GC batteries (210ah ea.) and will run in series for 12v. That means 210AH / 2 = 105 usable AH @ 50% discharge

1) At 50% discharge how long will it take, theoretically, to charge the batteries to full volts (13.7?) with the 42 watt panel (say 4 peak hours/day)?

2) Second, if I didn't destroy the battery when last up there, it has 105ah at full charge (52.5Ah at 50%), then if I connect it in parallel to the 2 new batteries, will I be decreasing the 100% Ah to 105 from 210 for all 3 batteries due to the lower Ah of the marine battery? And thus lose 105 Ah?

3) Third, can (should) I even PUT a 12 volt, marine battery in line with the other 2 - 6v batteries (even though they are in series = 12 volts) to "increase" battery capacity?

4) I want to get an 85-100 watt panel (Kyrocera, etc.)? Can I use the charge controller I have to hook up both panels (or even just the 85-100 watt panel?

5) I would like to get a new C-35 or SunSaver 20 amp CC. Would that be a wise choice?

6) If I get multiple panels and the voltage = say 36 volts, will the CC take that voltage and process it down to 12 volts, so as to not mess up my battery bank?

7) If I run a battery bank at 24 or 48 volts, how do I run 12 volt loads off of that? Do I need to step it down to 12v and if so how do I do that?

Cool

Finally, (sorry), If I get a C-35 or SunSaver 20, if I have the panels go to the CC, then to the battery and then go from the battery to the load, how does the LVD cut the power off when the battery bank gets too low? Or do I have to put an external LVD between the battery and the load?

Whew......Sorry about the long post but I have been reading tons of stuff (on-line and in books) and as it usually goes, the more you learn, the more you realize you don't know. I'm simply trying to not have the lights, etc. go dim after 2 days of no sun ( and that happened!).

Thanks,

Tim

Ken Hall

351 Posts

Aug 18, 2008 02:13 pm

Re: new solar system

1) The straight math answer is about 30 hours, or 7.5 days. I would suggest a 20% DOD (depth of discharge). That will only take about 12 hours to replenish. The smaller DOD should double your battery life.
2) Do NOT mix different capacity batteries in the same bank. You should not even mix new and old batteries of the same type. It can set up circulating currents. Like a chain, your battery bank is no stronger than the weakest link. And sometimes it seems weaker than the weakest link.
3) NO, see #2
4) NO to both panels. You don’t want to mix them in the same array. But yes, you could hook up an 80 or 100 watt panel with that controller.
5) Yes, you will need a larger one before you add a second 100 watt panel.
6) Three 100 watt panels wired in series is 100 watts at 36V. Wired in parallel, they are 300 watts at 12V. So, just parallel them.
7) By the time your system is large enough to require 24 or 48 volts, you should have a 115VAC inverter. You shouldn’t have to worry about 12V.
8 ) You can’t get PV charge control and LVD from one C35. You will need it as a PV charge controller. If you want LVD (and reconnect), you wire a second C35 between the battery and the load, as a load controller.

James Cormican

578 Posts

Aug 18, 2008 04:02 pm

Re: new solar system

#6 - 3 100w modules wired in series = 300w at 36v
3 100w modules wired in parallel = 300w at 12v

yes if you have all the same modules, you can wire them in series and the controller will downconvert the voltage for you. this type of controller is called mppt, and the outback mx 60 is an example of one.

#8 assuming you have selected a charge controller with an lvd, AND your load is the same nominal voltage as the battery bank and the array, AND draws at a rate of less than 10a, you can wire that load to the load terminals on the controller. for example a morningstar sunsaver or prostar.

james
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Tim F

3 Posts

Aug 18, 2008 04:10 pm

Re: new solar system

Ken,

Thank you for the very helpful and informational response. It helped confirm a few things except the charging rate. That is far longer than I had ever anticipated to recharge the battery. Of course, I won't have all the lights and so forth going at once, but I would rather "oversize" my system as quickly as possible so I can at least enjoy a few days of amenities.

Is a DVM better than a hydrometer at determining when a battery is at a particular % of discharge?

Also, I guess there's 1 thing in particular I'm not getting. It is the CC and LVD issue. Is there a CC with a "built-in" LVD that you can use for both functions at once? I just read a paper from 1993 that implied that they were using such a device way back then. And the manufacturers literature implies as much, too (excepting the C-35).

I'll stop with those questions as I feel I've used up my quota of Q&A time.

Thanks for the all the help. I really need it.

Tim

James Cormican

578 Posts

Aug 18, 2008 04:50 pm

Re: new solar system

hydormeter is always better. richard perez from homepower magazine wrote some great articles back in the day on voltage vs state of charge. voltage gets you in the ballpark, but a battery meter (trimetric, link 10) and a hydrometer will get the best data. i am lazy so i go with sealed batteries and a battery meter.

there are lots of controllers that can do pv controlling and load lvd at the same time. morningstar sussaver "L" units, morningstar prostar, some of the speicialty concepts, and the steca solsum 8.8.

I like the morningstar prostar m models especially for new systems because they show battery voltage, pv current, and load current in a rotating scroll. for people just getting used to off grid systems, this is great. all prostars have lvd for the load.

james
altE staff

AltE
"Making Renewable Do-able"
http://www.altEstore.com/

Tel: 877.878.4060 x107 or +1.978.562.5858 x107
Fax: 877.242.6718 or +1.978.562.5854

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