Off Grid Confoundment

quid_non · November 2007

Hi All!
Great forum here - you all really know yuor stuff and share it openly - thanks!

Current system is ~110W of panels (6 different panels (sizes/makes) all 12-15V wired in parallel. 7Ah shunt type controller, 2 110Ah deepcycle maine batts and a trimetric 2020 monitor. Power is for a remote maountain shack in the mountains of Va (estimate ~4-5hrs sun/day on average). Currently using ~0.6Ah 24/7 for fans dedicated to a composting toilet (that could be reduced by 1/2 if necessary); ~1.7Ah for ~3-5hrs for lights and ~0.5Ah for ~3 hrs for sat radio. Guestimate total Ah used per day is ~20-25. Estimate total from panels is ~20-30 max. Typical residence time is 2-3 days at a time.

Here's the issue....
To get the sun, I need to have the panels place ~170ft from the shack. They are now connected with ~200ft #10UF. I'm aware that I'm losing ALOT of voltage (~15-20%) with this type of setup -so I'm trying to supplement with a small gas generator. Like all of us, I'm trying to keep the cost as low as possible. I'd like to add a small fridge (3-5cft) in the future and realize I'd likely need more power to do so.

So, before I spend more $ unwisely, help me sort through my options:

1. Convert to higher voltage (24 or 48) and add more batts. How do I get the 12V I need for lights and other things??

2. Keep the set up, but fork out the $$$ for larger cable - likely would need at least #1 or double ought for expansion.

3. Others???

I'm looking to buy more panels, a new controller and inverter as I upgrade, but I need to get a better strategy built before I spend the bucks on more stuff.

Thanks for wading through this and taking the time to suggest options!
Best
Wayne

mike95490 · November 2007

Re: Off Grid Confoundment

Getting rid of the wire loss will save a little, but not enough to enable using a fridge.

Putting panels in series, to get higher voltages, requires that you match output CURRENT much more closely, than just "adding some panels"

You could convert 48 or 24V bank voltage, to 12V, for use at the cabin, with DC-DC converters, but thats introducing another stage of losses.

I think the best bet, and the least expensive route, is to add another 50 watts or so of 15V PV panel (problems adding in parallel, is you need to match output VOLTAGE to get the best bang for your buck), stick with the existing wire, unless you find some at a cost effective price. And employ conservation measures. That will give you a little faster recharge time, and as the charge progresses, the current (wire losses) will drop.
I don't know if a shunt controller is the best way, one of the PWM styles I think does a better job. MPPT is for 500W + arrays, not too useful for 200W systems, unless most of your panels are at 19V nameplate ratings.

Do you currently ever get enough sun to equalize the batteries at all ?

If you go the generator route, you could get by with running it for an hour in the AM, to put a fast charge into the batteries, and then let the solar top them off for the rest of the day.

If you get a fridge, you will need a LOT more panels and battery's, even to run it for a few days a week.

crewzer · November 2007

Re: Off Grid Confoundment

Wayne,

I'd suggest you consider building a "60 V" array (STC Vmp = ~85 V) and connecting that to an step-down MPPT controller to charge your 12 V batteries. You'll be able to use smaller/cheaper wire between the array and the controller due to the high voltage / low current, and this'll help pay for the controller.

HTH,
Jim / crewzer

quid_non · November 2007

Re: Off Grid Confoundment

Thanks for the coments Mike and Crewzer!
Mike -
I'm not sure I am getting enough sun time for equalization, yet. Given the time of year and the location the sun time is at a real low...I will keep an eye out for this though.

As for the fridge - I put a "kill-o-wat" meter on a small dorm fridge I'm considering, it uses about 350W/day (120v) - that's not too shabby. Based on that, I'm guessing that I need at least 5-6A (including inverter losses) to run on a daily basis. I'm sure I need to choose the inverter carefully so I get one large enough to take care of the intial surge (est ~12A), but not so large it consumes tons of power in standby? While I know I need more power, I'm still trying to figure out how much so I don't go overboard. Am I missing something (likely...)?

Crewzer -
I'm not familiar with the system you describe - could you send me any links or point me to place to learn more. Is it as simple as wiring panels in series to get ~60V and chosing the "right" MPPT controller? Any suggestions on the latter?

Thanks again for the ideas - much appreciate the time!!
Best
Wayne

mike95490 · November 2007

Re: Off Grid Confoundment

quid_non wrote: »

Thanks for the coments Mike and Crewzer!
Mike -
I'm not sure I am getting enough sun time for equalization, yet. Given the time of year and the location the sun time is at a real low...I will keep an eye out for this though.

As for the fridge - I put a "kill-o-wat" meter on a small dorm fridge I'm considering, it uses about 350W/day (120v) -

1) If you are not equalizing at all, you are likely not fully recharging, and are destroying your battery bank.

2) 350W/day is not a useable number. Watt Hours is a useable number. is it 350W for 5 hours a day, or for 14 hours ? You will need to consider a true sine inverter, as the mod sine wave will often burn up the fridge motor, and yes, they (sine inverter) are expensive.

System2 · November 2007

Re: Off Grid Confoundment

Maybe it's 350 watt-days? about 15-watt hours?

Or about 128 kwh/year. Bruce

icarus · November 2007

Re: Off Grid Confoundment

Couple of comments,

I agree with Jim, get a mppt controller and send the power to the mppt cc at higher voltage, hence lower losses.

Second. Consider a good Propane fridge. Ours burns so little as to be barely noticeable. (somewhere I have the btu calcs but not off the top of my head). They are available fairly cheap to buy used from RV places. I use many Dometic's at remote bush sites and have had great luck with them, one that has been running 24/7 for 15 years!

Third. I spent years trying to get composting toilets to work well in our remote site(s) What I found was that if you didn't introduce heat I could never get them to work properly. I build propane burners for heat because I didn't have the electric power available. After many years of trying I was able to make one work fairly well, but it was a huge maintenance item. what I finally decided was that old fashioned out houses made much better sense! Easy/cheap to build, easy to maintain. Cold at -40 though!

Icarus

crewzer · November 2007

Re: Off Grid Confoundment

Crewzer –

I'm not familiar with the system you describe - could you send me any links or point me to place to learn more. Is it as simple as wiring panels in series to get ~60V and chosing the "right" MPPT controller? Any suggestions on the latter?

Wayne,

It’s basically just that simple. For example, a system could consist of five Kyocera KC-130 W PV modules wired in series (“60 V” nominal, ~88 Vmp) connected to an OutBack MX60 controller, which in turn would be connected to a 12 V, 24 V, or 48 V battery bank.

The 650 W STC array might deliver 75 v x 7 A to the controller at ~noon on a good day. The controller would convert this input and deliver, say, 14 V x ~35 A to a 12 V battery bank. The low current from the array to the controller would allow you to use relatively smaller/cheaper wire between the two.

Here’s a link to the MX60’s user manual: http://www.outbackpower.com/pdfs_manuals/MX60_REV_B.pdf

Don’t forget fuses or circuit breakers between the PV array and the controller, between the controller and the batteries, and between the batteries and downstream loads (i.e., inverter, DC loads, etc.).

HTH,
Jim / crewzer

quid_non · November 2007

Re: Off Grid Confoundment

Thanks for the input - really got me thinking now!!!

Icarus - thanks got sharing your experience with composting toilets and fridges. I've been seriously considering going the propane fridge route as an alternative - good to hear some encouraging words for that source. I continue to look for cost effective propanne fridges, but keep coming up with prices in the $800 - 1000 range, a bit steep for me. Any issues around buying a used one??

As an aside do you have any experience with any of those propane "instant hot" hot water heaters? As you mentioned, I'm considering using propane as much as possibel (cooking, hot water, etc...) Heat to the shack will be by wood stove.

Crewzer - Thanks for the follow up on the MPPT controller - I did read up on these in the other forums and it appears that any issues with the fans are now solved? They are steep, but I agree with your logic - they will allow smaller wire and expansion possibilities.

Mike - as for the fridge - "kil-a-wat" meter was 4.38kW consumed in 105 hrs - that's how I came up with the ~350W/day. My ignorance in the numbers...

Thanks all!

crewzer · November 2007

Re: Off Grid Confoundment

Wayne,

I believe the MX60’s fan problem has been resolved. The current production units are shipping with a higher quality fan. Another MPPT controller option is the new Xantrex XW controller. It’s passively cooled, but it’s new and not yet proven in the market.

If your fridge consumed 4.38 kWh in 105 hours, then that’s 4.38 kWh / (105 hours / 24 hours/day) = 1.00 kWh/day – not bad!

HTH,
Jim / crewzer

icarus · November 2007

Re: Off Grid Confoundment

"I continue to look for cost effective propanne fridges, but keep coming up with prices in the $800 - 1000 range, a bit steep for me. Any issues around buying a used one??

As an aside do you have any experience with any of those propane "instant hot" hot water heaters? As you mentioned, I'm considering using propane as much as possibel (cooking, hot water, etc...) Heat to the shack will be by wood stove."

To answer some of your questions.
Used fridges are a crap shoot. The biggest issue with propane fridges is have they been run out of level? An ammonia absorption fridge works by putting in heat and having the gas thermo-siphon through the system. If the fridge has been run out of level it will develop a hot spot and can destroy the cooling unit. Consistent overheating can also cause the ammonia to harden and reduce the cooling effeciency some what. A good source of used Dometic RV fridges is RV wrecking yards. I also have a source for used/rebuilt fridges. I am a fan of Dometic as I have used them for years. I have also used Danby, Sibire, Explorer, and several others. Size for size the Dometic wins hands down. Try this link. http://www.rvmobile.com/ If it sends you to a service business in Everett WA. it is the right place. For some reason it sends me to a place with the same web address but is an RV dealer. RV Mobil in Everett is hands down the countries best expert on absorption fridges. They host a forum similar to this one for these fridges.

If you are in Canada there is a rebuilder in Moncton NB who sells used Dometics at reasonable prices with a good warrentee. (A good thing to have with one!)

If you treat a a propane fridge well it will run for years (decades) with out trouble. I have one that has been going 24/7 for 18 years. I also have a '50 vintage one that is still going strong.

As for Propane demand hot water. I have used demand hot water for decades. Depending on your needs, water pressure etc. there are several considerations. Paloma makes a "legacy" series of standing pilot light water heaters. I currently use a PH6 which fills our needs just fine. The nice thing about the Palomas is that service parts are cheap and available. (I have never needed one after 15 years on one however. I have used Bosch Aquastars as well, but I have had problems getting replacement parts for older models. I also don't think that they have kept as much pace with technolgy however. If you are into a fancier, modulated heater, I have installed Takaki, as well as Rinnai. I have had great luck with the Takagi's as well as the Rinnai's These models require 120vac to opperate, as opposed to the Bosch's and the Paloma's.

There are many Propane gas ranges out there. Just make sure that you get one that has standing pilots rather than hot surface type ignition. Standing pilots require no electrcity.

I hope this helps a bit.

Icarus

A quick look on the Dometic site reveals that a typical 125 litre fridge will burn 380 grams of propane per hour, or .8377lbs NOTE: Propane weighs ~ 5lbs/gal. A standard 100# cyl holds ~20 gallons. Therefore, if you figure that it burns 380 gph, and burns 1/4 time (It shouldn't burn that often if it is filled). it would burn ~1520 grams per day or 3.35 lbs or .67 gals. In that case it would burn through a 100# tank in ~30 days. In our situation we rn the full firdge, gas range and demand water heater and we burn 100# about every 5-6 weeks, so this shows the calcs to be somewhat conservative. If you live in a hot or humid climate you should adjust these numbers upward.

stooper2 · December 2007

Re: Off Grid Confoundment

Hello All.

I was reading this post and reply that Crewzer had made - it read as follows:

It’s basically just that simple. For example, a system could consist of five Kyocera KC-130 W PV modules wired in series (“60 V” nominal, ~88 Vmp) connected to an OutBack MX60 controller, which in turn would be connected to a 12 V, 24 V, or 48 V battery bank.

The 650 W STC array might deliver 75 v x 7 A to the controller at ~noon on a good day. The controller would convert this input and deliver, say, 14 V x ~35 A to a 12 V battery bank. The low current from the array to the controller would allow you to use relatively smaller/cheaper wire between the two.

The question I have is, What are the advantages or disadvantages of either putting 5 - 130 Kyorcera panels in series or parallel?

Sorry if it's an easy answer - just learning the ropes here.

Thanks very much.

icarus · December 2007

Re: Off Grid Confoundment

The higher voltage allows you to sent the power down a smaller wire, therefore making the system cheaper to wire with no loss of effeciency.

Search for the link to wire size vs amps, and if you don't know, learn about the relationship between volts, amps and watts.

In your case you would be sending ~7amps at 60vdc to the controller, instead of 35 amps at 12vdc. 7 amps requires small wire, 35 amps huge wire. (Don't have a chart in front of me now.

Icarus

Chuck46 · December 2007

Re: Off Grid Confoundment

Quid non,
I have been using a LPG instant hot water heater for 3 years now and have no complaints. The propane usage went down so much my supply company thought I was buying from a different source. Just make sure you size it for your needs and get it installed correctly.
Chuck

niel · December 2007

Re: Off Grid Confoundment

stooper2,
the higher voltage does allow lower losses if you keep the larger wires or as said you can have smaller wires and get the same losses, but with a smaller price tag for the wire.
now there are 2 more things overlooked here. firstly, the mx60 is an mppt controller so it will recoup typically about 10% more current. secondly is the fact that the larger the voltage difference between input and output voltages the larger is the loss of efficiency in the controller. it is advisable to go say 24v or maybe even 36v rather than 48v or higher if downconverting to 12v.

Off Grid Confoundment

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