Author Topic: Powering AC with solar  (Read 4481 times)

0 Members and 1 Guest are viewing this topic.

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Powering AC with solar
« on: June 24, 2013, 12:19:53 AM »
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:


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

Offline oztules

  • Forum Advisors
  • Hero Member
  • ****
  • Posts: 1054
  • Karma: +89/-5
  • Village idiot
Re: Powering AC with solar
« Reply #1 on: June 24, 2013, 03:21:47 PM »
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
Flinders Island...... Australia

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: Powering AC with solar
« Reply #2 on: June 24, 2013, 07:15:20 PM »
So could not have driven that sort of load without about 40kw of solar.... diesel looks better in this case.

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.
--
Chris

Offline rossw

  • Senior Moderator
  • Hero Member
  • *******
  • Posts: 790
  • Karma: +27/-0
  • Grumpy-old-Unix-Admin
Re: Powering AC with solar
« Reply #3 on: June 24, 2013, 08:51:30 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.

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!

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: Powering AC with solar
« Reply #4 on: June 24, 2013, 09:08:06 PM »
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

Offline gww

  • Newbie
  • *
  • Posts: 21
  • Karma: +0/-0
Re: Powering AC with solar
« Reply #5 on: June 25, 2013, 04:23:37 AM »
Chris
When running on just solar, does your inverter have any start or run issues on the ac?
What is your start surge and run watts?
Thanks
gww

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: Powering AC with solar
« Reply #6 on: June 25, 2013, 07:33:09 AM »
The compressor's running amps is 9.6 @ 240V.  Plus the fan in it draws like 1.2 amps @ 120V.  And then you have to have the air handler in the house and that draws about 1.5 amp @ 240V.  Without looking at the nameplate I believe the normal starting amps for the compressor is 28.7 @ 240V and locked rotor amps is around 50 @ 240V.

No, the inverter has no issues at all with it.  The little diesel generator can't start the AC though.  But using Gen Support the generator only has to deliver 2.4 kVA and the inverter does the heavy lifting like starting AC compressors.  What I mean by that is that we can have a larger load on the system than what the generator can actually produce, like below, and it don't bother the generator or overload it because our inverter assists a small generator for overload and surge:

Like, this is total load on the system:


But this is the part that the generator is supplying to the loads on the AC2 input:


That's why we can use a tiny little generator for prime power to carry the base loads, and still run anything we want with it without fear of overloading the little generator.
--
Chris

Offline gww

  • Newbie
  • *
  • Posts: 21
  • Karma: +0/-0
Re: Powering AC with solar
« Reply #7 on: June 25, 2013, 02:58:29 PM »
When you talk locked rotor amps, you are saying starting the ac wile it is under pressure? 

So the 12000 watt start up, How long does this last, tenth of a second, ten seconds or three minutes? 

I know you have a zantrax inverter and know this thread is more about how good it works with a generator. 

I have the grid but am just trying to see what inverters can handle.  I have the 2 outbacks for 7200 watts but believe that the surge on them is only about 10000watts so it looks like it would not start your air conditioner. If I even understand the ratings.   

Your pictures had more loads then just the air conditioner?  I would love to be able to use the grid as you use your generator but in a way that it is impossible to have sell back.

I do understand how with the inverters help you can run heavyer loads then the generator will handle on its own.  I am not quite understanding how your batteries get charged If you have heavy long term loads like the ac.

Thank you for your responce.
gww

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: Powering AC with solar
« Reply #8 on: June 25, 2013, 03:24:10 PM »
The startup load for the compressor is maybe 1 second or so.  The locked rotor amps is when the compressor is shut off and then try to restart it right away before the high side bleeds off.  It tries to start for about 2 - 3 seconds maybe then the overload on the compressor kicks out and it re-tries again after the overload resets.  The inverter can put out 60 amps on both legs for 15 seconds, so it don't kick out when it does that.  And it only does that if somebody turns the thermostat up in the house then turns it down again right away.

The diesel is taking the load off so the batteries can get caught up.
--
Chris

Offline gww

  • Newbie
  • *
  • Posts: 21
  • Karma: +0/-0
Re: Powering AC with solar
« Reply #9 on: June 25, 2013, 03:39:08 PM »
I get it the generator is running as much as it can.  The solar is charging the batteries and picking up what the generator can't with the extra doing what it normally does, charge the batteries.  Got it?

The generator only gets involved in the above fassion if the load is more then the inverter can handle on its own.  Then the generator trys to take over and the inverter supports it.

This is based on amps needed and/or battery voltage.

So this would never work with the grid cause when the grid got called for it would handle it all with out help.

If I have screwed the above up let me know, other wise thanks very much.
gww

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: Powering AC with solar
« Reply #10 on: June 25, 2013, 04:22:32 PM »
The inverter can handle it fine.  The problem is the batteries and solar panels.  If the solar is putting out good power (like it is today) then the diesel isn't running but the AC is.  And our batteries are in Float right now.  Which is good.  But rather than suck the batteries dry overnight to keep the house nice I'll start the diesel again at sundown and leave it run all night.

For somebody with grid power running an AC is no big deal - you just pay the bill and it runs.  On off-grid power it's a bit more of a challenge.  But the tiny diesel works and doesn't burn much fuel.

So basically I'm using it to take the load off the batteries at night right now (and on bad days when we get no solar or wind power).  That way the solar and wind can charge the batteries and carry loads just like normal.  And the diesel provides prime power to put the batteries on "hold" instead of cycling the snot out of them and then having to recharge batteries with the big generator.

Recharging batteries with a generator (either AC or DC) isn't that efficient because batteries waste like 15% of everything you dump into into 'em during absorb.  If you live off-grid you're going to use gen power anyway unless you want to go without when the batteries go dead.  So why not use the gen power with a properly sized little generator to directly power loads on prime power instead of charging batteries on standy power?
--
Chris

Offline gww

  • Newbie
  • *
  • Posts: 21
  • Karma: +0/-0
Re: Powering AC with solar
« Reply #11 on: June 25, 2013, 05:25:07 PM »
Yea,  I don't dissagree with what you are pointing out.  I also am probly mixing threads abit from some of your previous threads where it was mentioned that support of high amp pulls started your generator.

I don't mean to do this.  My situation is different then yours as of now I still have the grid.  I believe I have more solar then I need to support my planned battery bank.  I know we get more sun in the summer then in the winter.  I intend on using your hot water opertunity load. But I keep thinking that on really good days I might like 3 or 4 hours of air conditioner more then hot water.  I think on really good winter days I might like some kind of heat better then hot water.

I like the hot water best cause it seems to be kind of seemless in operation.

Since I have more solar then battery and could add about 2000 watts more which would max out my charge controllers.  5640 now + 2000 = 7640 watts.  I would have direct load capability but would have to watch having to much to the batteries.  416 ah battery bank.  I am not going to grid tie and don't want to get rid of it yet cause I like air conditioning.

Mostly I am trying to figure what can and can't be done.  I also want to get installed and see how things work with the grid and if I am successful, I may emulate you and go off grid.

All I wanted to do was build a couple of wind turbines and look where I am now.

I also thought you said your wife wasn't going to let you dig up the yard again but it looks like new wire from your new generator shed.

Heck you probly didn't want to know half of the above.

You post so much that you probly don't remember how dence I am but you have taken time enough to help me understand on several things I am actually going to incorperate in my system.  I probly won't use a generater starting out but do thank you for the info just in case.
gww

Ps some day I am going to post a thread where I can try and figure what you use and what setting, when you shut down your turbines through your classic.

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: Powering AC with solar
« Reply #12 on: June 25, 2013, 09:52:34 PM »
I also thought you said your wife wasn't going to let you dig up the yard again but it looks like new wire from your new generator shed.

Yeah, well.  She went to our daughter's place and when she got home I had the wire trenched in already.  At that point it don't matter if she likes it not.
--
Chris

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: Powering AC with solar
« Reply #13 on: June 25, 2013, 10:19:18 PM »
Yea,  I don't dissagree with what you are pointing out.  I also am probly mixing threads abit from some of your previous threads where it was mentioned that support of high amp pulls started your generator.

Nothing has changed with the Honda being used on auto-start for peak load.  I just added another generator for prime power (totally different application).  And added some new panels in the utility room for it







Up to now I've been using both gensets on the AC2 input.  This afternoon I got the new disconnect installed for the prime power set hooked up to AC1
--
Chris

Offline gww

  • Newbie
  • *
  • Posts: 21
  • Karma: +0/-0
Re: Powering AC with solar
« Reply #14 on: June 26, 2013, 04:17:23 AM »
Chris
Thanks, and I always like pictures.
gww