Offgrid system - appreciate any advice

System · January 2010

Hi Everyone

Here's what I plan so far:

(9) Canadian Solar CS6P-230P
-230w, 29.8v Vmp, 7.71A Imp, 36.8 Voc
-wired 3 strings of 3
(1) fused combiner
(1) outback flexpower one FP1-2 48v prewired inverter system
-see here http://www.outbackpower.com/products/flexpower/flexpowerone/
(8.) surret s-530's wired 1 series of 8 - 48v 530ah
(1) tracker array
(1) 240v step up/down xfmr for gen - inverter if needed

Current loads:
oven - propane
fridge - propane

12000watt generator runs everything below right now.
(2) 240v well pumps & pressure tank
(1) 240v electric dryer - plan to go to propane
small cabin (lights,TV,pc, fans, misc) ~ 4-6kwh/day

Here's what i think:

small cabin at 8000' + altitude - avg 80F high, lowest ever temp -27F (but usually 0F)
blue sky conditions should get me 125% of panel rating + tracking set up would flatten my sun harvest curve
5.50hrs of sun yr/avg

run the cabin off of 120v subpanel connected to inverter
run well pumps & electric dryer off of 240v subpanel connected to generator
-manual xfr switch to connect 240v panel to generator
-built in auto xfr swtich to connect to inverter to generator
once a week fire up the generator manually on 240v ckt, run well pumps & wash clothes, staging in the loads of course

My main concerns are:

1. Having the generator connected to both 120v inverter and 240v subpanel, and having it work properly through the manual 240v xfr swtich
2. Is 48v my best option? I initially planned 24v but changed my mind. thinking reduced current is better for longer battery life.

Nothing is purchased yet, just all in my head and on paper.
I would appreciate any advice.

pvsd

RWB · January 2010

Re: Offgrid system - appreciate any advice

Sounds like a nice setup, don't know much about the 240v converter from outback but need to figure it out.

I'm interested in hearing what the others advice is on this.

westbranch · January 2010

Re: Offgrid system - appreciate any advice

pvsd, Conservation first , keep the loads against those very expensive PV watts down to a minimum... 4 - 6 Kw / day is still a pretty good load for incidentals
I would look at:
1 getting rid of the clothes dryer unless SWMBO absolutely has to have it. use a power less clothes line, it works summer and winter.
2 consider a holding tank for water, even a large pressure tank will only hold ~ 50 gallons
3 compare running ~ 90 v to 48 v VS 60 v to 48 V, may be more efficient in the down conversion
4 use LEDs for lighting, laptop for computer, new TV - ener star rated
revising the harvest to 100% for planing purposes , more is a freebe then. Have yet to see more than 80% of stated watts from mine @ 3000 ft. on a windy day.

IS this a semi permanent residence? sounds like it.
I concur with the idea of using the genny for the well as long s it is once a week. without a holding tank it may well be a tad more often.
Have you drilled the well yet? How deep do you expect? there are 110 v pumps.
bury your water lines deep ( > 7 feet) to avoid freezing. Having NO water in winter sucks big time...
ps they can stay frozen a long time in spring too...
How far from the array to the building? is this your reason for ~90 V?

lots more questions but these will start the ball rolling.

HTH
Eric.

Cariboocoot · January 2010

Re: Offgrid system - appreciate any advice

Couple of comments from somebody who lives most of the year in the middle of nowhere: me.

1). 4-6 kW/hrs per day is a lot for off-grid. I run up 3 and that's because of the computer set-up.
2). What is your well situation that you have to have 2 240 Volt pumps? These are big power users.
3). Forget the tracker array; chances are it won't add enough to justify the cost. You've got 9 230Watt panels? That's a lot of panel. It should suffice for some serious daily power - like about 10 kW/hrs per day.
4). As much as I like my Outback equipment, it's not the best choice for a 240 VAC set-up. The Xantrex XW 6048 would do you better in this situation.
5). Don't count on "125% of panel rating". Count on "50% of panel rating".

icarus · January 2010

Re: Offgrid system - appreciate any advice

Start by "doing the math"

Calculate ALL your loads, add in some room to grow,then work backwards.

Once you have your total loads, you can count on ~53% of name plate rating of a Pv array being available out of the inverter. Multiply that number by the hours of "good sun" per day, and you begin to get into the ball park as to how much you will be able to generate on a daily basis. (Also run a PV Watts calc)

A couple of things are true off grid in my experience. First, people under estimate their loads, and over estimate how much Pv they can harvest. Next, loads will grow with time no matter how well you have figured. Finally, do everything you can do to conserve firsts, as it will save ~10 times it's cost.

Tony

If you are interested in a freeze free, energy free water system PM me and I can send you some details.

halfcrazy · January 2010

Re: Offgrid system - appreciate any advice

I second the Xantrex XW inverter and then look at Midnite solars Epanel for it that will save you a few bucks as well as make life easier.

System2 · February 2010

Re: Offgrid system - appreciate any advice

The XW series inverter with a midnite solar Epanel looks like a good set up.

question - would running everything through this 120/240v inverter with a backup generator shorten my battery life because i am depleting and charging constantly with higher loads? Or will the system just go into bypass mode when the generator comes on to take care of the larger loads?

pvsd

halfcrazy · February 2010

Re: Offgrid system - appreciate any advice

any time the generator runs the relay closes running the house of the generator. You can also set the generator to start based on the load so if a large load comes on the generator will start. And another feature of the XW is generator support say you have a 5kw generator and it is running and you turn on a 8kw load the inverter will kick in the other 3kw to run the load this gives you the ability to run some larger loads.

BB. · February 2010

Re: Offgrid system - appreciate any advice

I am not quite sure how to answer your battery life question vs the XW system...

Yes, it will go into "bypass" mode if the genset is running and, since it has an internal battery charger, can start recharging the battery bank. And it has a fairly sophisticated energy manage where (if I recall correctly) you can do things like program the generator's maximum supported load and the XW will share that max setting between the external loads and battery charging.

Reading through the details of the operator's manual should help--or ask specific questions here that others (with more experience than I) can answer directly.

In general, things that reduce battery life:

Undercharging/Deficit Charging (many people simply do not have enough solar panels to support their loads--tend to run loads until inverter shuts down--very hard on batteries)
Not keeping flooded cell electrolyte above plates with distilled or filtered rain water
Over charging/equalization (boiling batteries dry, causing positive plate corrosion, for AGM's--venting and early life failure for catalyst).
Storing/operating flooded cell batteries below ~75% state of charge for days/weeks/etc. at a time (sulfate hardening)
Cycling batteries below 50% state of charge very often
Cycling batteries below 20% state of charge ever (often one or more cells become "reversed" charged--kills cells

If you avoid the above--you will generally get good battery life.

Note, deep cycling (down to 50% or even greater) vs only discharging 10-20% -- If you work out the math, it almost works out to, for example buying 8 batteries that last 7 years or two sets of 4 batteries that last 3 years each. More or less, in the end the total price is almost the same... 2x the bank size/cost and it will last a bit more than 2x as long.

If you have not yet--read the two following Battery FAQ's--they will give you a lot of information about how to best manage your battery bank.

Deep Cycle Battery FAQ
www.batteryfaq.org

If you can keep your battery bank between 75-90% state of charge and avoid very heavy loads vs bank size (recommendation is 600 AH minimum 48 Volt Battery Bank to run a 6kW/12kW surge XW inverter).

Depending on how you size your bank/inverter and your actual 240 VAC pump loads, you may be able to run them from your battery/solar system just fine.

If you can review your pumping for a) efficiency and b) things to reduce pump cycling (large storage tank for well, small pump for home pressurization, etc.).

In the end, it is almost always cheaper to spend your money on conservation first--Only spend the money on generation once pretty much all conservation measures have been exhausted.

-Bill

Dave Angelini · February 2010

Re: Offgrid system - appreciate any advice

Who will install your system? If there is a local offgrid installer and even if you do the installation consider paying for a consult. There are dozens of questions that they will know about that you may not. The Wind and Sun store will do consults also. The internet forums are great but they are often a slice of the big picture. Sounds like a fabulous location!

System2 · February 2010

Re: Offgrid system - appreciate any advice

An electrical contractor friend of mine will do the install. Together we are figuring this system out as we go.

My house panel is currently 240v, with all the 120v ckts only running off of one hot leg in the panel. Since I dont have two separate panels (one for 120v and one for 240v) I am re-thinking my setup.

I am re-evaluating my loads to dbl check everything and I am definitely doing away with the electric dryer and switching to propane. All the other major appliances are currently propane. The well pumps are the only heavy load items that will remain. Also they are the only 240v items.

I am still leaning towards the outback 120v prewired system because its a complete system less a combiner box/fuses,batteries, and all the wire. However, since my panel is 240v I will need a step up xfmr.

The only potential problems with this inverter I see are its 29.2amp continuous output (33.33amps - 30 minute overcurrent) and the need to use a step up xfmr to get 240 for the well pumps.

The well pumps only come on as needed, so i am thinking that if the loads from the pumps @ 240v are no more than half of my available continuous output from my inverter, even if I had on some lights, TV, etc...i should be able to use this inverter, step it up to 240v, and back up the system with a generator?

What do you guys think?

pvsd

halfcrazy · February 2010

Re: Offgrid system - appreciate any advice

don't sell your self short if you get an Epanel for the XW from Midnite solar they will be all wired for the inverter and if you request they will wire it for the Charge Controller as well. They are very simple to wire from there.

885kcdtq · February 2010

Re: Offgrid system - appreciate any advice

Have an XW 4024 and E-panel. Cuts down on wall space usage. Wiring is easy.
The xw will do everything you need it to. You will need the control panel and gen remote though. Preset everything and she does the rest.

NO regrets going with either XW or E-panel. (Should have went bigger though)

885kcdtq · February 2010

Re: Offgrid system - appreciate any advice

Just re reading here. Don't forget ohms law. 1 Amp @ 240 volt=2 Amp @ 120 Volt
Remember ohm's law using step-up step-down transformers.

Offgrid system - appreciate any advice

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