Off Grid Living / Camping > Off Grid Living / Alternative Housing
Powering AC with solar
ChrisOlson:
Basically, my theory last spring about throwing more solar power at our new Trane central AC unit to power it on hot days in the summer, don't work. Well, it kind of does. But it only works when the sun shines. It can be dense overcast for days at a time, with thunderstorms, and so hot and muggy that you can cut the air with a knife. And a 2-ton central AC unit consumes an incredible amount of power - no way in hell can you run it off battery power. It can suck our bank totally dry in only 8 hours.
This is what they make diesel generators for.
So I built a brand new powerhouse and put the generators in it, and buried service and control wiring to the outfit:
That Robin diesel on the left is a little 3 kVA split-phase unit and it only burns .22 gallons per hour on prime power duty. As of this writing it has been running since this movie was made:
//www.youtube.com/watch?v=Rn82oAcQqD0
The fuel tank on it holds 3.5 gallons of fuel so I have to refuel it every 12 hours. But it sure is nice and cool and comfy, with low humidity, in the house. Diesel prime power works every time. Solar - not so much - kind of like hit and miss.
--
Chris
oztules:
Nice setup.
Fossilized fuel still has it's pace when the real continuous loads come on board.
The sun don't always shine, and the wind don't always blow... and for the last month I have had neither... weird... thick 8/8 clouds, and still nights ( fogs), and very gentle breeze days.....
So could not have driven that sort of load without about 40kw of solar.... diesel looks better in this case.
...................oztules
ChrisOlson:
--- Quote from: oztules on June 24, 2013, 03:21:47 pm ---So could not have driven that sort of load without about 40kw of solar.... diesel looks better in this case.
--- End quote ---
Definitely better in this case. You would not believe how much power a 2-ton AC unit consumes. Adding the AC basically doubled our daily power consumption. The tiny Robin diesel can produce ~57 kWh in a day loading it to 80% of its rated load. And that's where it appears to run the most efficient. It's not loaded so heavily that its leaning into the smoke screw on the injection pump, but it's running hard enough so its good and hot and it produces about 8.78 kWh/gallon of fuel.
Today the sun came out nice, but it's just hot and muggy and we ran the AC all day just on solar. No wind to speak of and the turbines are just idling on the tower - I think I got .2 kWh from each one. But with the sun going down I'll start the little Robin and let it run all night again.
The tiny diesel does produce enough power to run the AC plus other normal loads like the 'fridge and freezer and fans that we got going in the house to circulate more air, plus charge batteries at about 3 amps. So once we go back on diesel power for the night, the little diesel generator will basically just maintain the batteries where they're at at sundown.
We like the AC a LOT. We've never had it before and it's really nice. This was the only practical solution I could come up with to run it. Finding a little tiny diesel genset that puts out split-phase power is not that easy though. I was ready to buy a brand new Yanmar YDG3700. But then I found the little Robin on craigslist for only $775.
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Chris
rossw:
--- Quote from: ChrisOlson on June 24, 2013, 07:15:20 pm ---The tiny diesel does produce enough power to run the AC plus other normal loads like the 'fridge and freezer and fans that we got going in the house to circulate more air, plus charge batteries at about 3 amps. So once we go back on diesel power for the night, the little diesel generator will basically just maintain the batteries where they're at at sundown.
--- End quote ---
Did you think about, investigate or compare the efficiencies of running your aircon compressor from a diesel directly (as for example on freezer trucks, shipping containers etc)? Or were there too many downsides? (noise, vibration, distance, ready availability of existing units etc).
Just seems to me that an engine driving an alternator driving an inverter driving a motor driving a compressor couldn't compete (efficiency wise) to an engine driving a compressor!
ChrisOlson:
Ross, we did look at putting in a Polar Power co-gen unit. We got a Cummins 4BT 45 kVA co-gen unit that heats and powers our big equipment shop. It has a turbocharged Cummins 4BT engine with a 45 kVA three-phase Winco gen head and a Sanyo heat pump on it, as well as the cooling system for the engine being plumbed into the heat exchanger in the shop. It works good in the equipment shop - we figured not so good for the house.
For the house we needed the option to run the AC on renewable power. That's hard to do with a co-gen unit. Basically, today, when the sun came out for bit we were able to run the AC and all our loads (but didn't get any battery charging done) from the solar from about 7:00 this morning until just a couple hours ago when I restarted the little diesel. The batteries have basically maintained around 75-80% SOC today, and they will all night too with the little diesel running. We'll see what tomorrow brings and maybe we can run the AC all day on solar again - it's supposed to be in the mid-90's for temperature tomorrow again.
So basically that's why we decided against the Polar Power unit and decided to buy a conventional AC. We can run the electric AC off our solar and wind power when possible (I originally thought I could power it totally from wind and solar). But the AC load bumped our battery bank discharge rate from a normal 50 hr discharge to less than 10 hours. The batteries don't have as much amp-hour capacity when discharged over 10 hour that they have when discharged over 50 hours. I think they call that the Pukert Effect or something.
So I threw the tiniest little split-phase diesel generator at the problem that I could find. I think when we factor in that we can run our AC half the day on solar and the other half on diesel, that the way we got it set up probably burns less diesel fuel (or propane, etc..) than it would using just a co-gen that would have to run 24 hours a day.
I'm still learning as I go here with this.
--
Chris
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