12 volt battery, natural gas charged. Natural gas range and fridge

Welcome to the forum DJ,

There are "fuel cells" which sound ideal... They are built like batteries with plates in a box. But you introduce hydrogen and oxygen and the "low temperature" burning produces electricitiy. HOWEVER, they generally only work with very clean hydrogen gas (need a reactor to create hydrogen from natural gas, and the plates are made with expensive metals like platinum or palladium (as I recall). If you have a bunch of money sitting around you will never otherwise need ($100k's ???), it can be done.

Another very low power system is a TEG or Thermal Electric Generator system. Basically flame from your natural gas heats thermal couples to generate power. Not too expensive, no moving parts, relatively low efficiency ("free gas"), and reliable (i.e., 125 watts * 24 hours per day = 3,000 WH per day--Just about enough to run a near-normal electric lifestyle with Energy Star Fridge, LED lightning, laptop computer, RV water pump or solar friendly well pump, clothes washer, etc.) :

https://www.tegmart.com/info/guide-to-understanding-and-using-teg-power-and-products/

If your energy usage is low, you can use this to charge a small battery bank and run your loads.

And as Jonr suggests, another option is a natural gas fired genset. This can be done with a spark ignition engine, or you can feed natural gas into a diesel engine (still need diesel to start/run the engine, but natural gas can replace much of the diesel fuel used). The propane/natural gas conversion is probably the easiest/cheapest/most common solution. You probably need to "filter" your natural gas (is this "wet gas" directly from a well?). Natural gas has less "heat energy" vs gasoline in an engine, so you generally have to derate the generator output by 20% or so (as I recall) from name plate rating.

https://duckduckgo.com/?q=natural+gas+conversion+for+generators&atb=v122-1__&ia=web

I assume that you have an RV or Trailer parked on property with a well? So, really a fixed installation and not an RV where you can pipe into a gas meter on trips...

-Bill

Doug,

I have moved your thread to the general Off Grid systems forum. (I missed that you are in a cabin in your first post).

Propane (and natural gas?) refrigerators tend to have issues with needing good ventilation and cleaning (every 6-12 months if you get soot buildup). And can create a carbon monoxide/humidity issue if you do not ventilate outside in a well insulated cabin in a cold climate.

Collecting data (how much energy per day in Watt*Hours or Amp*Hours*Volts, possibly by season), where you are (good solar or poor with lots of trees/shading--Solar electric needs clear sky for most of the day).

Solar heating (hot water, etc.), can be pretty neat--But you almost have to like plumbing (valves, pumps, thermal panels, etc.)--If you get enough sun in the winter. Climates with hard freezes gets a bit more complex (anti-freeze, drain back systems, etc.).

If you are full time off grid, and can swing a solar electric system (call it ~3,300 Watt*Hours per day), you can usually run a full size refridgerator (and get frost free, good cold and freezer sections).

If you are interested in "low power" electric... A 7-10 cuft chest freezer with a refrigerator "range" thermostat can cut you from 1.0 to 1.5 kWH per day for a very good upright energy star fridge/freezer to a ~250 Watt*Hour (0.25 kWH) per day refrigerator only.

You are correct that Batteries (Lead Acid and variations like AGM) have not really changed much in 40 years, other than getting somewhat more expensive.

There are new tech like various Li Ion batteries (LiFePO4 -- Lithium Iron Phosphate) which are getting popular (pretty safe, stable, long life--But do not like sub freezing conditions for charging/discharging). But, there is complexity--Possibly needing a BMS (battery management system) to balance/protect each cell against over/under voltage. A bit cutting edge, and not cheap--But gaining more users over time.

Solar Electric Panels, that is where the off grid energy advancements have come... From 8% efficiency to 15%+ efficiency, and dropping from $10-$40 per Watt to under $1 per Watt (if you shop around). And from 10-100 Watt panels to 200-300 Watt panels (fewer panels, less issues with wiring and mounting--But >~175 panels, you usually need 2 people to move and install).

And MPPT (Maximum Power Point) solar charge controllers... Can (for example) take an array voltage (Vmp--Voltage Maximum Power) of ~20-100 VDC standard test conditions) and efficiently down converter to charging your 12 volt battery bank. The US made/designed MPPT charge controllers are not cheap ($500 to $600 for higher end 80+ amp units), but now have Internet servers (for remote management) and lots of programmable charge settings, and some optional outputs (like using a "dump" load for water pumping when the batteries are full, etc.).

Details matter (amount of power you need, where the system will be installed, shading issues, 120 VAC vs 12/24/48 VDC, what kind of batteries do yo want, etc.).

Even with "free fuel" for your genset--I would highly suggest that a moderate solar array and good quality charge controller and a bunch of lead acid golf cart batteries or larger flooded lead acid batteries (~650 AH @ 24 volts will support 3,300 WH quite nicely). With ~10% rate of charge (don't know where you are at, so cannot work out hours of sun):

• 650 AH @ 29 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,448 Watt array @ 10% rate of charge

Would probably give you enough energy that you could run 9+ months a year on solar+battery bank, and during winter, only run the genset during "bad weather" and/or poor solar harvest conditions.

If you don't use a full size energy star rated refrigerator, and go with propane/natural gas... You could probably get down to ~1,000 WH per day quite nicely (LED Lighting, RV Water pump, Laptop computer, LED TV, cell phone charging. And with the smaller loads, I would not even bother with a genset except for bad weather. Avoid the noise and oil changes vs running the genset as your only source of electricity.

-Bill

You really need good sun from around 9am to 3pm at least.

Take a look at this website for how much sun you will get. Fixed array, facing south, tilted for best harvest year round:

http://www.solarelectricityhandbook.com/solar-irradiance.html

The new editor software does not let us post tables (hope to fix soon). But if you are there from March through October, you get 3.29 (March) to 2.73 (October) hours of sun (long term average per day).

Say you start with a gas fridge... 1,000 WH per day is a good start for a cabin (LED lighting, reasonable size LED TV, RV water pump, cell phone).

You should get a Kill-a-Watt type meter to measure your AC loads to be sure (i.e., 30 Watt TV * 5 hours a day = 150 WH, cell phone ~10 WH per day, LEDs 18 watts * 5 hours = 90 WH per day etc.) and add it all up.

Say 1,000 WH per day is good, and during bad weather, you can cut back on power usage and/or start up a genset every 2 days if needed.

• 1,000 WH per day * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days storage * 1/0.50 max discharge = 392 AH @ 12 volts

Or 4x 200 AH @ 6 volt golf cart batteries--2x in series (for 12 volts) and 2x parallel strings (for 400 AH).

Charging with solar, suggest 5% to 13% is a good range. 10%+ recommended for full time off grid:

• 400 AH * 14.5 volts charging * 1/0.77 solar panel eff * 0.05 rate of charge = 377 Watt array minimum
• 400 AH * 14.5 volts charging * 1/0.77 solar panel eff * 0.10 rate of charge = 753 Watt array nominal
• 400 AH * 14.5 volts charging * 1/0.77 solar panel eff * 0.13 rate of charge = 979 Watt array "cost effective" maximum

And then based on hours of sun per day... Say October at 2.73 hours of sun (break even month--probably need some generator time):

• 1,000 WH per day * 1/0.52 off grid AC system eff * 1/2.73 hours of sun per day = 704 Watt array October "break even"

You should never plan on using 100% of predicted power from a solar system... So the amount of array "oversizing" depends on your needs (closer to 1,000 or 500 WH per day, running genset near winter OK, or larger array to cut genset runtime--your choice).

Solar panels are pretty cheap these days, and over sizing the array can keep your batteries "happier" longer (undercharging/over discharging is not good for them).

If you ignore March and October (questionable weather months), the rest of the season you are >4 hours of sun per day, which when paired with a 753 Watt (10% rate of charge) array, will give you:

• 753 Watt array * 0.52 AC system eff * 4.0 hours of sun = 1,566 Watt*Hour per day average

Not a bad harvest for New York.

I would suggest adding a ~300 Watt TSW AC inverter with 12 VDC input--Such as the MorningStar unit--Has remote on/off switch and standby mode (low power search mode, when >8 Watts is detected, the inverter turns on 100% to power loads). Or similar:

https://www.solar-electric.com/kiacpomome.html (kill-a-watt meter)

https://www.solar-electric.com/morningstar-si-300-115v-ul-inverter.html (MorningStar 300 Watt inverter)

https://www.solar-electric.com/sa300wa12vos.html (Samlex 300 Watt TSW inverter)

Add a >=40 amp MPPT charge controller (or slighting larger PWM controller--depends on what solar array you design), and you have your basic system (+ panel racking, wiring, grounding, circuit breakers, outlets, and a few tools like a voltmeter and hydrometer).

This is what I think would meet your needs. Run for a few years then decide if you need more power or not.

Just be aware, it is not easy to expand a solar power system by a lot without needing new hardware (12 vs 24 volt battery bank for larger inverter, larger charge controller, new batteries usually, larger array, etc.).

-Bill

In general, is not AC vs DC that is the problem with longer wire runs, it is low voltage/high current that is difficult to send long distances.

For example, 10 amps * 12 volts = 120 Watts, and so does 1 amps * 120 Volts.

With 12 volts, you can have about 0.5 volts of voltage drop in your wiring. With 120 VAC, you can have 3% or 3.6 volts of drop at 1/10th the current (V=I*R). So need much less copper (lighter wiring) to send the same amount of power for a long distance.

Playing with a voltage drop calculator, say you want to send 120 Watts 50 feet. Using a simple voltage drop calculator (50 feet, 10 amp & 12 volts vs 1 amp and 120 volts):

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=1.296&voltage=12&phase=dc&noofconductor=1&distance=50&distanceunit=feet&amperes=10&x=64&y=29

6 AWG carrying 10 amps @ 12 VDC:

Voltage drop: 0.40

Voltage drop percentage: 3.29%

Voltage at the end: 11.6

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=84.22&voltage=120&phase=ac&noofconductor=1&distance=50&distanceunit=feet&amperes=1&x=64&y=18

24 AWG carrying 1 amp @ 120 VAC:

Voltage drop: 2.57

Voltage drop percentage: 2.14%

Voltage at the end: 117.43

That is, roughly 6x heavier copper wire for same 120 Watts at 12 vdc vs 120 vdc (roughly, every 3 AWG change in gauge is 2x or 1/2x the cross sectional area of the wire).

Of course, you would not use 24 AWG wire to carry 120 VAC (14 AWG is generally the smallest diameter you would use for house wiring).

Loss in efficiency of using an inverter of 85% (typical inverter), can be made up by making your solar array and battery bank 1/0.85=1.18x larger ... or ~18% larger. Generally, the costs of sending DC anything more than 10-20 feet from your battery bank (heavier wiring, larger fuses/breakers, non-standard DC "power plugs" other than "cigarette lighter" style), it just becomes an expensive method to distribute low voltage DC power.

There are secondary issues--Such as 12 volts and above, DC sustains Arcs better than AC voltage/current. So you need switches and fuses/breakers rated for DC. And many "12 volt" DC loads don't "like" the 10.5 to 15-16 VDC that a deep cycle battery bank "bus voltage" runs at. It has been known to "kill" 12 VDC adapters for laptop computers and such (which seem to be designed for roughly 12.0 to 14.4 (typical automotive battery voltage range).

For example, you design one/short heavy power connection for the AC inverter (designed to run 10.5 to 15-16 VDC). A 300 Watt @ 12 volt branch circuit would be:

• 300 Watts * 1/0.85 inverter eff * 1.25 NEC derating * 1/10.5 battery cutoff voltage = 42 amps ~ 50 Amp 12 volt DC branch circuit wiring+breaker that is only a few feet long

A good quality AC inverter should last 5-10+ years.

But, yes, extra costs, extra things to go wrong. Longer term, generally worth the hassles and expense.

Regarding sending power 100 feet from "sunny area" on your property to the cabin. In general, you have two ways of doing this. One is to put the solar+battery shed in the sunny area and send 120 VAC back to the cabin. This sort of becomes a pain, in that you have to trek 100 feet when you need to do maintenance and monitor your battery bank.

Or, you install the solar array 100 feet away, and set it up with higher Vmp-array of say 90 VDC and use a (not cheap) MPPT solar charge controller. The controller can take high voltage/low current and efficiently (~95%) from 90 VDC at 6 amps to ~14.5 volts at 37 amps.

3x solar panels at 250 watt per panel at Vmp~30 volts would be nice with a higher end 40-60 amp MPPT charge controller:

https://www.solar-electric.com/mnclassic.html

https://www.solar-electric.com/motr45ampmps.html

The first link is a "high end" MPPT charge controller (96 amp output @ 12 volts) with Ethernet/Internet server/connection support.

The second is 45 amps max output, no internet connection, and no fans--Fans can be noisy and if the controller is mounted inside the cabin, can be irritating (during the day when the sun is up).

Just two choices linked. There is a lot out there, including some pretty inexpensive stuff from China/Overseas (variable quality).

To send 750 Watts 100' at 90 VDC (~100 Vmp maximum for cold climates with a 150 VDC max input controller) would require wiring of:

• 750 Watts * 1/90 volts (3x panels in series with Vmp~30 volts each) = 8.33 amps Vmp-array

Using 8.33 amps and 1% to 3% voltage drop (typical wire loss design for solar) and voltage drop calculator (8.33 amps and 100 feet):

8 AWG, 100 feet, 8.33 amps:

Voltage drop: 1.05

Voltage drop percentage: 1.16%

Voltage at the end: 88.95

And the minimum suggested AWG:

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=5.211&voltage=90&phase=dc&noofconductor=1&distance=100&distanceunit=feet&amperes=8.33&x=56&y=21

12 AWG, 100 feet, 8.33 drop

Voltage drop: 2.65

Voltage drop percentage: 2.94%

Voltage at the end: 87.35

2x X AWG cabling (your wallet) from array plus a 6 AWG (minimum) grounding conductor from Array frame/ground rod to Cabin ground rod (for electrical safety and lightning protection).

I suggest that you do not put the batteries inside the cabin (charging gasses and sulphur fumes). Outside insulated shed/ground contact to keep batteries from roughly 40-80F, ideally). Suggest that genset+fuel in separate structure away from cabin/battery bank to reduce chance of genst fire (or battery+wiring fire) from taking "everything" out) in one incident.

I will stop typing here. Still lots of details to workout/understand for your needs. But you can start a paper and pencil designing and see where it takes you for your needs.

-Bill