Solar System for Alaskan off-grid cabin

aktundra · January 2013

Hello,

I have been reading and trying to learn, but electricity isn't my strong point.

I bought two Sharp 224Watt solar panels (I know I should have planned my system first, but I had a general idea). Finding panels at a descent price and getting shipped to Alaska has been tough. I plan on bringing these home on the airplane (we'll see how that goes!).

Sharp Solar Panels
Max power – 224W
Max voltage – 30V
Open circuit – 37V
Short Circuit - 8.6A
39.1X64.6X1.8
44 lbs

Since open circuit voltage is 37V a MPPT charge controller is necessary.

Potential Setup
(2) Sharp 224Watt Solar panels $320
TS-MPPT-60 Morningstar Controller $524 (may be able to go with 45Amp- no room to add more than 1 solar panel. 45amp is only $100 less, so really not worth saving money)
(2) Trojan T-105 in series $300 (Locally)
Morningstar 300Watt Sine Wave Inverter $240 (solar-electric.com)
Trimetric TM2025 Battery Monitor $152 (solar-electric.com)
Mini DC plus breaker box (solar-electric.com)
Heavy gauge copper wire, 500 amp shunt, fuses, junction box (solar-electric.com)

Calculating size of my controller:
224W*2panels = 448Watts *0.77 derating *1/14.5v = 23.7 amps
222W*3panels = 35 amps
60 amp controller should be plenty. I would be able to expand. Looking at the Morningstar Website and calculating with their "String Calculator" they recommend a max of my Sharp 224W panels.
Attachment not found.

My Requirements for Watts:
This will be very simple, cabin residence (full time operation all summer, and most of the winter). I have a 2000W Yamaha generator for charging and higher watt items. I know in Nov/Dec/Jan I will need to run the generator a few hours a day to keep things charged. Things like my power tools, vacuum, sewing machine, will be run off the generator (maybe when charging batteries).

With the winter light, I wasn't able to get enough watt hrs / day with a 2 panel, 2 battery setup. So I thought I wouldn't use the fridge during the dark winter days. In the summer, I will run the fridge daily. In the winter, I will use the natural cold as an outdoor freezer, and not use the fridge (use cellar and frozen water bottles in the fridge to cool the temperatures).

I calculate 736 watt hrs per day required for summer (fridge on). I will have more than 5 lights, (10 total) but only anticipate half on at a time.

Summer with Fridge: Lighting use really varies, and I shouldn't have to use lighting May/June/July except for darker areas of the cabin.
Attachment not found.

Winter: I took the fridge off this one. Another thing is winter lights are on all the time!
Attachment not found.

As far as daylight, in varies throughout the year:
Attachment not found.

In February….
is around 2.81 hours of sun per day. The estimated power output:
448 W * 0.52 system eff * 2.81 hours winter time sun = 655 Watt*Hours of power per day
So if I’m not running the fridge in February, the output of my panels is 655 watts, and the requirements of my system are 622 watts.

Diagram
Obviously I am not an electrician. I know this diagram is missing wire sizes, fuses, and a disconnect. Also I need to figure out how to wire the hookup for the 2000W Yamaha Generator. I am also not sure how to get the power to the DC systems (through a breaker box?).

I am also thinking I should just get one more solar panel, since 448W systems is rather small.

Tools
I know a good crimper is key for making the cables.
Any recommendations for a good crimper?

I read some people like the Hex Crimp but really want some more opinions.
http://solarseller.com/quick_cable_crimper_cutter_stripper.htm

Thanks for the help, after searching the forum I know these questions are asked over and over again. I have tried to figure out some of it on my own, but it seems like I still have alot to learn. If anyone has a book recommendation that would be great. Reading the amazon.com reviews, I haven't found a book that simplifies off-grid and doesn't say to hire an installer.

aktundra · January 2013

Re: Solar System for Alaskan off-grid cabin

Last attachment, I compared sun days throughout the months to see the benefit of one more panel (if it could help me not run the generator so much in the winter)

attachment.php?attachmentid=4407&d=1358790736

attachment.php?attachmentid=4407&d=1358790736

BB. · January 2013

Re: Solar System for Alaskan off-grid cabin

The second post looks a lot better...

One warning, the battery bank on the second system is not right... Are you trying for a 12 volt or 24 volt system? In general, you should not run 12 volt loads off 1/2 of a 24 volt battery bank.

For running a "standard" Energy Star refrigerator, you may need a 1,200 to 1,500 watt inverter minimum. We have one person here (Wayne from NS Canada) who has cracked the code for running fridges of of the MorningStar 300 watt (600 watt) peak AC inverter--But it required a lot of "tuning" on his part to make it work.

Do you need a refrigerator/freezer or just a refrigerator? 0.75kWH per day is a bit on the low side for a standard fridge/freezer in warm weather (yea, Alaska)... But if you need a fridge only, a converted chest freezer may get you down in the 0.25 to 0.50 kWH per per day.

Also, you may want to look at ~140 panels--They are smaller and easier to pack/ship (and more $$$/Watt costs) if that remains an issue.

-Bill

icarus · January 2013

Re: Solar System for Alaskan off-grid cabin

We live off grid with 400 watts of PV, 450 ah of battery, and we consume about 5-800 WH/day. This system is pretty well balanced, with poorest performance in November and December before we get snow. Winter is just fine because of reflection and cold temps. We seldom run a genny to charge and have about three days of automony sine few days we get no charging.

That said, be aware the it's rule of solar installation, (and the second corollary!). That is, people almost always over estimate thier potential solar gain, while at the same time, under estimate thier loading. The second is that loads alway grow with time.

All calcs stem from the loads. Get a GOOD estimate if total loads both peak and WH totals, and work from there, but also build in a fairly good head room factor.

Good luck, welcome to the forum and keep in touch,

Tony

Cariboocoot · January 2013

Re: Solar System for Alaskan off-grid cabin

Since it's a Morningstar 300 inverter it must be a 12 Volt system. Therefor as Bill said the batteries aren't right. The only way to use four 6 Volt batteries on a 12 Volt system is two parallel string of two in series. See attached.

Cariboocoot · January 2013

Re: Solar System for Alaskan off-grid cabin

Also a detail about the shunt for the battery monitor: it goes between the (-) battery terminal and all loads & charge sources. The monitor will have small wires to either side of the shunt as it measures Voltage difference on the two sides to determine which way and how much current is flowing.

You show no positive lead coming from the charge controller to the battery. No fuses or circuit breakers are indicated. I presume these are just oversights.

Eric L · January 2013

Re: Solar System for Alaskan off-grid cabin

I know a good crimper is key for making the cables.
Any recommendations for a good crimper?

This works surprisingly well for $28.00. I use it with a sledge:

http://www.solar-electric.com/hacrtoforlal.html

aktundra · January 2013

Re: Solar System for Alaskan off-grid cabin

Thanks for all the help. I re-did the diagram. I am still needing to figure out a bunch of things, as you can see. One thing is generator hookup.

Screen+shot+2013-01-21+at+3.39.05+PM.png

Screen+shot+2013-01-21+at+3.39.05+PM.png

Money is an issue on this solar system setup, but I am trying to build bigger than I absolutely need...

Cariboocoot wrote: »

Since it's a Morningstar 300 inverter it must be a 12 Volt system. Therefor as Bill said the batteries aren't right. The only way to use four 6 Volt batteries on a 12 Volt system is two parallel string of two in series. See attached.

Thanks for pointing that out. Fixed it in this new diagram.

Also, thanks for explaining the shunt. Now that I understand what it's doing, I think I wired it correctly now.

Many fuses/circuit breakers are missing because I am not sure what I need and where. I downloaded the manuals and found out a couple fuses.

icarus wrote: »

All calcs stem from the loads. Get a GOOD estimate if total loads both peak and WH totals, and work from there, but also build in a fairly good head room factor.

Thanks for talking about your experience with your system! I think you're right about overestimating how much power I'll get while underestimating what I will use. That's why I think my initial 2 panel system is too small. I think I need to go 3 panels, 4 batteries.

BB. wrote: »

For running a "standard" Energy Star refrigerator, you may need a 1,200 to 1,500 watt inverter minimum. We have one person here (Wayne from NS Canada) who has cracked the code for running fridges of of the MorningStar 300 watt (600 watt) peak AC inverter--But it required a lot of "tuning" on his part to make it work.

Also, you may want to look at ~140 panels--They are smaller and easier to pack/ship (and more $$$/Watt costs) if that remains an issue.

- Thanks for pointing out the 24v wiring on my batteries.
- I plan on running Sundanzer R165 fridge only. Right now I have a propane fridge/freezer. While it works, it uses alot of propane in the summer. The Sundanzer is too expensive for my budget for a couple years, so maybe I should look at mini fridges.
- I email Sun-electric.com and found out the shipping rates to Alaska weren't calculating right, so shipping is less than I thought. Although I already bought the other panels...

westbranch · January 2013

Re: Solar System for Alaskan off-grid cabin

Do you get much lightning? If so look at MidNite Surge Protection Devices (SPD's) http://www.solar-electric.com/nsearch.html?catalog=wind-sun&x=0&y=0&query=SPD

Cariboocoot · January 2013

Re: Solar System for Alaskan off-grid cabin

Uh, your battery wiring still isn't right. You've got the inverter and monitor connected to only one 6 Volt. Their positive wires need to go to the same terminal as the one from the charge controller. Also, for best results the positive should be connected to one string and the negative to the other. This helps keep the current flow even between all batteries.

Your generator being 120 VAC is going to need a battery charge to connect it to the batteries. You need something like this: http://www.solar-electric.com/dls-45.html

If you want the generator to take over the AC loads at the same time you will also need a transfer switch to move the loads sub-panel between inverter power and generator power.

BB. · January 2013

Re: Solar System for Alaskan off-grid cabin

It looks like you are getting there (fix the battery connections and add an AC battery charger to the genest, and an AC transfer switch of some sort between the Inverter and Genset AC outputs so you don't have to move cords around).

And, depending on your loads, may need to revisit the MorningStar inverter--It is a wonderful inverter and probably the best bang for the buck out there--But it does not usually power a refrigerator type load (not enough surge current).

There are larger/more complex inverters that also have integrated AC transfer switch and internal AC battery charger---But they are not cheap. And if you are in the middle of no-where, you probably would prefer a couple less expensive spares if something breaks vs on do-all inverter where you cannot afford/justify a spare on the self.

Back to "sizing the system"--I am a big believer in balanced system design. And normally, that would be driven by the loads. But in this case, we can start with the battery bank and work out from there.

First, there is the battery bank. At this point 4x 6 volt @ 220 AH golf cart type batteries. You can connect them in two 12 volt strings at 440 AH or one 24 volt string @ 220 AH. Note that either configuration is identical from an energy storage point of view... 12 volts * 440 AH = 24 volts * 220 AH = 5,280 WH.

Looking at the size of the solar array, we usually start with ~5% to 13% rate of charge--And around 10% being a healthy rate of charge:

440 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 414 Watt array minimum
440 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 829 Watt array nominal
440 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 1,077 Watt array maximum

So, your 672 watt (3 panel array) is not bad--But you could easily justify another panel or two with that battery bank.

Then there is the "practical" loads that such a battery configuration could support (note that 12@440 and 24@220 give the same answers--just a 24 volt wired system can be cheaper in wiring and a bit easier to maintain--also else being equal--which it rarely is):

12 volts * 440 AH * 0.85 inverter efficiency * 1/8 rate of discharge = 561 AC Watts max continuous
12 volts * 440 AH * 0.85 inverter efficiency * 1/2.5 rate of discharge = 1,795 AC Watts max surge current

Most good quality inverters will surge about 2x their rated output. So, your "optimum" AC Inverter would be around 600 watts to ~900-1,500 watts (allowing for surge power).

And with your AC Genset--Assuming 1,800 watt max continuous output--The maximum AC battery charger would be around:

1,800 watts * 0.80 charger eff * 0.67 PF * 1/14.5 volts = 66.5 max rated "typical" AC battery Charger
1,800 watts * 0.90 charger eff * 0.95 PF * 1/14.5 volts = 106 max rated "best of class" AC battery Charger (efficient, power factor corrected)

A 440 AH @ 12 volt battery bank should be charged around 5% to 13% to 25% (not good idea to exceed):

440 AH * 0.05 rate of charge = 22 amp minimum
440 AH * 0.10 rate of charge = 44 amp nominal
440 AH * 0.13 rate of charge = 57 amp healthy maximum
440 AH * 0.25 rate of charge = 110 amp with remote battery temperature sensor/monitoring suggested

Running your genset at ~50% of rated load or better is usually more fuel efficient. Battery charging is an interesting load in that you can sustain "High" AC loads on a genset for hours at a time--And most "inexpensive" gensets are not really designed for operating at max continuous for hours on end (i.e., get good quality genset for this type of operation). Yamaha's have good repuations, and so do some of the Honda's.

-Bill

niel · January 2013

Re: Solar System for Alaskan off-grid cabin

i might add that a junction box most likely will not be needed for 1 series connected pv string unless you are going to parallel other arrays in series together. (didn't read whole thread if i got this wrong) anyway, if paralleling other strings of pvs you will need to combine the negatives as well.

Solar System for Alaskan off-grid cabin

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