Another Newbie trying to build his own system.....

Re: Another Newbie trying to build his own system.....

Hamfast wrote: »

Batteries.. Right now I've the four 12V 125Ah that were going to be run in 2 parrallel strings. I gather this gets me 250Ah@24V=6KW.
I replace them with four 6V 250Ah in series this gets me 250Ah@24V=6KW.

Those battery capacities should be in kilowattHOURS, not kilowatts. And remember, you don't want to use more than half your capacity ever. For regular daily cycling you should use even less.

Hamfast wrote: »

From what I'm getting, my benefit is in equal draw on the batteries and slightly better efficiency due to less connection points.

Not so much equal draw, but equal charging. I don't know if fewer connection points leads to better efficiency. Fewer connection points means fewer places for things to go wrong. Fewer battery cells also means (assuming flooded cells) less maintenance. Far and away the main advantage of a single series string of batteries is the equal charging.

Hamfast wrote: »

Add a second series of four 6V 250Ah batteries. Now I'm running 500Ah@24V=12KW?

that's 12 kwh. If you are going to do that, why not just put all 8 in series and build a 48 volt system? Your energy needs are large enough that a 48 volt system makes sense. If you ever want to grow your system you will be glad you started at 48 volts.
--vtMaps

Re: Another Newbie trying to build his own system.....

Hamfast wrote: »

I've noticed that there seems to be a preference here for water filled batteries (nomenclature escapes me) vs AGM, which is my current preference. Pros/Cons?

Or is it all about pricing?

Nomenclature is 'flooded'.

All things being equal, it is always about pricing. But all things are not equal.

AGMs are better for some applications. For example if they are going to spend most of their lives in float mode with minimal cycling (backup applications). AGMs are better if venting is an issue. They can support larger peak loads.

Flooded are cheaper, more forgiving of mistakes, and last longer when being cycled regularly.

--vtMaps

Re: Another Newbie trying to build his own system.....

If you're far enough along in planning to be pricing things like inverters, I think you should be looking at batteries first and checking all your local distributors for the best price since almost everything else you do will follow from this. I found very large price differences between the five or six battery distributors I visited, and at one place, large ($20/battery) differences depending upon who I spoke with!

It would be very surprising to me if 8 FLA golf-cart batteries (220 ah @ 48 volts) were significantly more money than the 4 360 ah AGMs that you are interested in. The eight golf cart batteries could well be less (they are about the same price in my area). That would get you to the 48 volt bank you want and have more watt-hour capacity, with an arguably more forgiving battery design. But of course you do not want to be shopping for inverters until you're certain you've found the best battery solution for your needs. (Don't buy the batteries until last though, but get price quotes now, if you're ready to go).

Don't rush any stage of this; as you've already seen it's very easy to make potentially expensive mistakes. I planned my current system (my third) for well over a year before I purchased any equipment, and I still didn't get it exactly right.

Re: Another Newbie trying to build his own system.....

Hamfast, I think the basic set up would work but in my (non-expert) opinion you'd have too much battery for the panel. The 370 ah batteries (which are likely L16s?) will want around 37 charging amps, after loads and losses. At a charging voltage of 55 volts, the 1440 watt array will only produce about 26 amps (1440/55 volts charging). That's before loads/losses. This is using a 10% charging rate at the 20 hour amp-hour rating. The usual recommendations suggested here are between 5 and 13%, so you could in principle do it and be on the low-end, but I personally don't think it's a good idea since after you could in loads, losses, etc, you might easily undercharge your batteries.

If you went with 8 T-105 type golf cart batteries instead, you'd only need about 22 charging amps at 55 volts charging = about 1200 watts of panel. A better match, IMO.

I think 2 180 panels in series would likely work, although no one can say without knowing the exact specifications. There may be other configurations which that MPPT controller would allow you as well. Scheider-Xantrex as a string configurator if you click on 'sizing tools' here:

http://www2.schneider-electric.com/sites/corporate/en/products-services/renewable-energies/products-offer/range-presentation.page?c_filepath=/templatedata/Offer_Presentation/3_Range_Datasheet/data/en/shared/renewable_energies/xantrex_xw.xml

Re: Another Newbie trying to build his own system.....

That 3.79 can be knocked down, and with my proposed bank capacity of 17.76 KWHs I'm at about 50% discharge @ 3 days no sun.

But you're on the grid, right? I'm pretty sure the Outback inverter can, with the right controller, be made to switch to grid power long before your batteries are discharged too deeply. I think you need one of the "Mate" controllers to do this; I researched it once but can't remember the details. So why not have a smaller bank and allow your system to go to grid power quickly when the battery voltage falls too low due to lack of sun? Several advantages to this:

- Smaller, cheaper battery bank needed.
- Smaller bank is easier to charge properly with the pv array you have in mind.
- Batteries are protected from deep discharge by the inverter flipping to grid. Consequently, you don't have to worry excessively about overloading the system and can 'tune' your loads to fit the system's capacity over time (and change it as the seasons change too).

I guess the one disadvantage if you went this way is that you have less power available for a long (2+ day) outage; not sure how worried you are about these.

Remember that if you have grid power, the most efficient use of PV is almost always grid-tie, where it's available. If grid tie isn't possible/doesn't make sense (as is did not in my case), I think the next-best thing if you still want a pv array is to try to use the grid to supplement your solar array, effectively using the grid to supplement your system when there's no sun (rather than YOU buying and maintaining a very expensive large battery bank for prolonged cloudy periods).

Re: Another Newbie trying to build his own system.....

Hamfast wrote: »

The 1st method is based on battery Ah.
The 2nd is based on daily KWH consumption divided by "Peak Sun", in this example 1.5 hrs (England). It's probable that "Peak Sun" is different here in SE Wisc.

You can get a pretty good estimate of what your solar resource is here: http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/sum2/state.html