Interested in your comments/impressions on Off Grid system estimate.

Rngr275 · June 2012

McD again... Amish House... 50K to get on the grid... looking to go off grid (Readers digest version:D)

NAWS suggestion... get some professionals involved (great advice) talked to the first installer tonight http://www.four-winds-energy.com/solar.html

I filled out his load evaluation form using data I gathered using my Kill-a-watt and some estimating on how many hours a day and days per week. Depending on how I want to play with the numbers it came in around 3-5Kwh per day. (Wattage*hrs/day*days/week)/7= Summed up gives Kwh per day.

Here is what he likes and was thinking but made it very clear this was simple a place to start and once he sends me all the information I will be able to see and work on how I would like to see the system (with your guys help of course).

1. Likes uses and recommends Outback and Midnight equipment. Sounds good to me.
2. Suggested a 24v system with ~1000Ah battery bank for 3-5 days. 12 6v Trojan Batteries (4 in series, 3 parallel series).
~cost of Batteries, inverter, controllers monitoring equipment installed ~$7.5-8K. This price is dependent on my sweat equity.
Said he usually figures around 1000Kwh per year out of a single 1Kw panel (1000Kwh/year / 365days=~2.7Kwh/day) I am assuming for this area as he lives ~10 miles from my site.
3. Suggest at least 2-3Kw PV. Installed, wired, pole mounted ~$5K per 1Kw (depends on # of panels on pole where/need site evaluation).

He explained that there was a lot of different configurations that we could do: i.e less batteries, more panels, mix and match to my budget and what I feel I might need.
His suggestion was to firm up what I felt comfortable with for a battery bank and then see what we could best do with the $$$ for the PV. His thought being that I can add more PV but is not good to add battery(s) later.

Asked him about the generator and he said a good 5.5 to 6 or 7Kw would be good depending on what other loads would be drawing on the generator when it was running. Which I think he meant taking away amps to run washer, and saws, or anything else other than charging the batteries.

SO what do you think? First contact for me, I have contacted other installers also.
This guy seems pretty decent as a first impression. Didn't push anything really.

Cariboocoot · June 2012

Re: Interested in your comments/impressions on Off Grid system estimate.

Can't speak to the price because I'm not in the area. Otherwise most of his advice and sizing recommendations are right where I'd expect them to be.

I would take issue with the system Voltage and battery bank sizing. Here's why: 1000 Amp hours of battery takes some pretty heavy current, namely 100 Amps. Trojan recommends 10% for their batteries as a minimum, and the L16's (which these would be) prefer more. That means two charge controllers. I also do not like three parallel strings of batteries.

For the amount of power you want per day and in reserve I'd go with a 48 Volt system instead. The same amount of power from half the Amp hours, less charging current needed, fewer parallel battery strings. There are even batteries that could give you one string around 500 Amp hours.

Outback and MidNite are both good equipment. However, all Outback would give better integration between charge controller and inverter. Otherwise you might get a better deal with a Magnum inverter. The MidNite is somewhat more expensive than an Outback, but they are the bee's knees in charge controllers right now.

niel · June 2012

Re: Interested in your comments/impressions on Off Grid system estimate.

i totally concur with coot on this as 3 parallel strings would not be good. i am assuming that the installer was going for 80% soc to be the typical max drawn from the bank allowing for another day and a half reserve before hitting 50% soc which is great, but keeping a higher battery voltage will help to alleviate some headaches. did you specify the number of days of autonomy?

keep this going with updates.

Photowhit · June 2012

Re: Interested in your comments/impressions on Off Grid system estimate.

I don't think he's gouging you, but I'm uncomfortable with a few things as well. 3 strings of batteries to start in a new system would make me uncomfortable with the installer, for the same price you can get a single large traction battery. Coot is on the money for Trojan 'requirements

Your right at the cusp of a 48V system, you can squeeze a 2K array on a Midnite classic controller at 24V, if you go with any larger and need a 2nd controller for a 24V system, I would suggest going ahead with a 48V system (you can go to a 4KW array on a 48V system on a single charge controller at, $6-700 per controller I'd switch to 48V as you could apply that toward the battery bank.

I do think he's on the money on the battery bank, new to solar people tend to underestimate their loads, so I might favor the "bit too large" battery bank, and a "just in case" genny. Coot is on the money for Trojan 'requirements, and Trojan doesn't recomend equalizing their batteries unless they are measurably out of balance. Other/Most manufacturers recomend equalizing their batteries, this insures things other than equal cells Specific Gravity(SG) it insures a mixing of the electrolite. A maintainance equalizing should ensure that at least once a month your batteries are fully 'topped off' and prevent stratifying (Trojan does have some different charging paramiters which might help this on their batteries, the 10% minimum charge is one)

SolaRevolution · June 2012

Re: Interested in your comments/impressions on Off Grid system estimate.

(At risk of making the battery rating any higher,)

You could get 12 of the 2volt L16s and have a single 24 volt string with 1110ah (C-20).
You would avoid all of the problems with multiple strings and you would probably save +$200 on battery cables and hardware.

A 3kw array could serve you well. That would be an STC rating of 11.4% of the battery C20 rate.
If your PV array is smaller than ideal you should plan on paying close attention to your solar production and battery charging curve. Your batteries will need to get all of the available output from the PV array for the "Bulk" charging cycle. When battery voltage reaches the Bulk/Absorb setting, the current required to maintain the Absorb voltage will begin to taper off. Large loads such as laundry or water pumping can be used once the "float" charging stage begins.

Also,

What are your AC needs? Do you need 120/240vac? (This applies to 60Hz domestic models) If you plan to use a single Outback FX inverter you will only have one leg of power. (120vac) You mentioned a generator rated 5.5-7kw. These are mostly split phase (120/240vac 60Hz) The Outback FX will only charge from one leg of a 120/240vac source. You may want to check out the splitphase Magnum MS PAE inverters.

Alex Aragon

vtmaps · June 2012

Re: Interested in your comments/impressions on Off Grid system estimate.

Rngr275 wrote: »

Suggested a 24v system with ~1000Ah battery bank for 3-5 days. 12 6v Trojan Batteries (4 in series, 3 parallel series).

I agree with the others: avoid three strings of battery. I think you should do 8 of the batteries in a 48 volt system. That gives you 1 string and 2/3 of the energy storage of the proposed system.

I think it is a mistake to go 3-5 days autonomy. That's too much. If you do that, in the summer your overnight consumption will take you down to a SOC of about 95%. Multiple consecutive days of such shallow discharges is not good for the battery (read the battery FAQ). Using just 8 batteries will help reduce the days of autonomy.

SolaRevolution wrote:

You could get 12 of the 2volt L16s and have a single 24 volt string with 1110ah (C-20).

Very good idea, but I don't like the Trojan brand of 2 volt L16. The trojan 2 V battery is really three 2 V cells in parallel. That means three times as many cells to maintain.

--vtMaps

Rngr275 · June 2012

Re: Interested in your comments/impressions on Off Grid system estimate.

I asked about the 24V and the 3 parallel series. He said 3 parallel is his max and ho comfortable with that, but not locked to it, and he chose 24VDC because of the availability of devices that can use 24VDC. He made it clear that this was just just a first pass. I will be using your suggestions in all my conversations and dealing with him. I will also post any other details he provides. He will be out of town for a couple weeks so we will be communicating by email.

niel · June 2012

Re: Interested in your comments/impressions on Off Grid system estimate.

much of this depends on the overall watt hours capacity you are looking to have in conjunction with days of autonomy. i stated wh because going from 24v to a 48v battery system would cut the ah capacity in half. the 1000ah at 24v is roughly 2.5 days of autonomy if i remember what i figured. i stated before "an extra day and a half" which means the initial day plus 1.5 days afterward. i know i think weird sometimes. anyway this is what discharging down to 80% soc translates to.

if you kept the days of autonomy the same for a 48v battery bank this translates to a 500ah capacity. they don't readily have a trojan at that capacity either as it's a case of going up or down from that point. even though a single string is most desirable if 2 strings are combined it could come closer to the overall goal of 500ah. 8 225ah 6v L16s in series x 2 strings for 450ah or 8 325ah 6v L16s in series x 2 strings for 650ah. going up in capacity could mean a shallower discharge % at times as was mentioned.

Cariboocoot · June 2012

Re: Interested in your comments/impressions on Off Grid system estimate.

As much as I like Trojan batteries, I dislike their 2 Volt cells. They are in fact the 6 Volt units internally connected in parallel instead of series to give the high Amp hours. You get three cells to check!

The Crown 2 Volts are better, and can be had from 500 Amp hours to 2550 Amp hours: http://www.solar-electric.com/2voltbatteries.html

Even so, on 48 Volts the need for 500 Amp hours can be had with less expensive options like choices from Surrette or forklift batteries.

The Outback's 120 VAC power can be run through an autotransformer for 240 Volts (half the Amperage) or it can be stacked with a second unit if the higher Voltage (or more current) is needed. Usually a Magnum or Xantrex is a better choice if you need 240 VAC out of the box.

Windsun · June 2012

Re: Interested in your comments/impressions on Off Grid system estimate.

Cariboocoot wrote: »

As much as I like Trojan batteries, I dislike their 2 Volt cells. They are in fact the 6 Volt units internally connected in parallel instead of series to give the high Amp hours. You get three cells to check!

Wow, that is something never noticed about the 2V L16RE. I don't think we have ever sold any, as the Crown and Trojan industrial seem to be the best of the bunch on 2 Volt cells, but we do list them on our site. I don't get into the sales side much anymore, but they do not sound like something we would want to sell.

Cariboocoot · June 2012

Re: Interested in your comments/impressions on Off Grid system estimate.

Sorry; should have specified which 2 Volt cells I was talking about. Trojan makes tons of different batteries. But yes the L16RE-2V are the same case as the 6 Volts right down to the three caps: http://www.solar-electric.com/trl111ah2dec.html

Kind of silly, really.

I like the Crowns better.

BB. · June 2012

Re: Interested in your comments/impressions on Off Grid system estimate.

Just to give credit where credit is due--almost two years ago Dave Sparks told us the "secret" about the Trojan 2volt "3cell" batteries. As I understand, you still have to check the electrolyte in each "cell" (they are parallel connected electrically, not using a common electrolyte chamber):

Dave Sparks wrote: »

Bill wins the cupie doll! Why would one buy a battery with three cells to check when there are batteries with only one cell for roughly the same capacity? Why would one design a battery this way? Are there just three of the 6V L16 cells in parallel rather than series?

This has nothing to do with Mangas's selection on the 6V L16's. I would love to hear what Trojan says but I have lost so much faith in seeing what they did here with the 2V L16. Maybe there is some better explanation than my worst fear. Is this the converse of "less is more" design?

As for my non answer previously, this has to be fun for me also. If you want instant answers I have an option for those folks! Clienthood!

-Bill

SolaRevolution · June 2012

Re: Interested in your comments/impressions on Off Grid system estimate.

vtmaps wrote: »

...but I don't like the Trojan brand of 2 volt L16. The trojan 2 V battery is really three 2 V cells in parallel. That means three times as many cells to maintain.

I agree that the three seperate internal cells are not ideal but I would still venture to say it is a better choice than three seperate strings of 6 volt batteries. The greatest advantage is fewer interconnect cable connections and a solid "bus bar" paralleling each set of cells.

Many larger sealed racks of batteries are similar in that they are constructed of parallel cells within each battery "module". I just finished taking some at-rest-voltage readings on three, three year old banks of +/-2100ah VRLAs. The 2v "modules" were three 700ah cells in the same external case. So for labling sake they are Cell 1A/1B/1C, Cell 2A/2B/2C... If you look at the picture you can see that the vertical series connections just use a single bar from A-A, B-B, C-C. When the strings reach the top or bottom of a row there is a parlleling bar which bolts across all cells (A/B/C) of each module. The layout makes it so there are 2 modules with paralleling bars on both the + and - terminals. When I did my at-rest voltage readings, I had removed the paralleling bars so I could get accurate reads on each cell. The cells (A/B/C) which are regularly connected with the paralleling bars have readings which are very close whereas the the voltages of cells (A/B/C) in the middle of the vertical strings (no parelleling bars) are often quite different.

I would be interested to see how the trojan 2v L16s would do as compared to three strings of 6 volt L16s. Unfortunately it is very unlikely to come accress two systems which would be otherwise similar to provide an "apples to apples" comparison.

Alex Aragon

Attachment not found.

Mangas · June 2012

Re: Interested in your comments/impressions on Off Grid system estimate.

When I replaced our 64 Trojan L16s' 6 volt with their new L16 REBs' 6 volt, I considered the 2 volt version but decided against them.

I wouldn't design a system past about a day and half of autonomy. Batteries are hideously expensive compared to panels and a good oversized genny picks up the slack cheaper and more reliably. The best you can afford and preferrably 1800 rpm water cooled. Maybe go bigger say, 10 Kw.

Two charge controllers with plenty of headroom capacity for panel/battery expansion. 48 volt system building for future capacity.

Despite judicious premeditated conservation, you'll use everything (and more) you build your system around.

Interested in your comments/impressions on Off Grid system estimate.

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