AC vs DC generators

[ChrisOlson]

For several years we've used a gas engine driven DC battery charger for standby power.  With gas at $4.05/gallon now I was not happy with the efficiency of the unit.  My fuel cost/kWh was coming in at about 77 cents.

I looked at a Alten Duke 80 DC unit with a Hatz diesel.  But the price of the Alten was more than I wanted to pay, and even with off-road diesel at $3.69 the cost/kWh still figured out to about 62 cents.

After a lot of research we bought a Generac 6 kW EcoGen.  We've had it installed for just about two weeks now and very happy with it.  The fuel cost/kWh comes in at about 44 cents.  It has a slower running 2600 rpm Generac OVHI engine that is VERY quiet.  It comes with a factory two-wire start system that hooked up to our Xantrex inverter and works very nice.

The best part is that the Generac was half the price of the Alten Duke 80, has a three year/2000 hr warranty, and it is totally Made in USA with no imported parts, right here in Wisconsin.  This is the unit we bought, and we also got the 240 volt conversion kit for it:
http://www.generac.com/Residential/EcoGen_Series/Product/6kW/
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Chris

[None54]

  Cris,
   3 years ago I installed a 16KVA Genertec at my parents home for emergency stand by power, runs on propane. Its twice as large as they need, but it will run everything with ease. You'r right, very quiet, very dependable, and delivers the goods in any weather.
.....none54                 

[wpowokal]

Seems to tick the boxes, but for me a diesel unit will always out last a gas/propane unit, yes it costs more but the long term cost is lower, and usually fuel costs are lower, yes I did say usually.

Realy depends on expected usage of said back up unit as to how cost effective one is over the other.

As to DC over AC for me it depends on what DC unit you are using, usually DC implies either a generator with brushes (high maintenance) or an AC unit rectified to DC for battery charging, I know which works for me.

Realy it is like everybody has an opnion on battery banks, it comes down to what works for each individual install, I do not believe there is a universay solution.

Oh and did I say two more sleeps and I am out of here and living in the jungle.

Allan   

[ChrisOlson]

One of the factors with a diesel generator is being able to get it started in the winter time here where it gets -35 F for days at a time in January and February.  The Alten DC generator I looked at was this one:
http://www.alten-dc.com/products/item/114-24-volt-80-amp-diesel-powered-battery-charger.html

The absolute minimum starting temp is 14 degrees for that unit and 14 degrees is a really warm day here in the winter.  Otherwise it needs a 80 watt 24 volt DC block heater and preheat glow plug and it still won't start at 20 below with those on there without additional preheat.

I have lived off-grid here for 8 years this coming June and there was way too many times in the past 8 years that I have had to get out of bed at 3:00AM to start a bone dead cold generator because the low voltage alarm sounded on the inverter.  I decided I want something that will start automatically, and at the same time is fuel efficient.  This Generac seemed to fit.

As to a diesel being more efficient, that may be.  But the price/BTU for LP gas is cheaper here than either diesel fuel or gasoline.  I bought 400 gallons of LP last fall for $1.48.  IIRC, LP gas is about 92,000 BTU/gal and diesel fuel is around 130,000.  The price of off-road diesel last fall was $3.14.  So the price per unit of energy in the LP is about 66% that of diesel fuel at last fall's prices (when I usually buy my fuel) and the thermal efficiency gains of the diesel do not make up for that in operating cost.

My previous DC unit was a homebuilt with a Tecumseh engine driving a 145 amp Leece-Neville 24 volt alternator (I used to have a Delco 10SI on it and burned that out) and it worked fine for many years.  But we wanted something to make life a little more comfortable for us, and this EcoGen being designed for people in our situation, seemed to be the right thing to do.  We've only put about 9 hours on it but very happy with it.
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Chris

[tanner0441]

Hi

I would prefere a good petrol engine on propane than a poor diesel. It is cleaner, quieter, and the exhaust gasses are mainly CO2 and water vapour, if propane is not available you can run on propylene and several other things if you can get it before they polymerise it. If you have a heated vapouriser you can use butane, butaline, etc.
Calorific value 19,500 Btu per pound.

I spent several years installing propane systems on cars and the engine life for mini cabs was trebled.  We also did bulk installations with liquid withdrawl for atmosphere control ed heat treatment plant.  Add to the fact you could go to 15,000 to 20,000 miles between oil changes, the governing factor is the use of the additives not carbon contamination of the oil.

It is also carbon deficient in its combustion and will clean carbon out of an old engine.

Brian

[Basil]

Take that gas gen and make it run on wood gas.
It's simple to do. Wood is cheaper than gas.

[ChrisOlson]

For now, since we have a fairly economical and plentiful supply of LP gas, I will continue to run it on that.  The unit is under warranty for three years/2000 hours and I don't know how burning alternative fuels affects the warranty.

Some of the things you guys mention as fuel sources are very intriguing though and I may eventually look into that.
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Chris

[12AX7]

Chris..   would you mind saying how much the generator set you back?

Years ago I purchased a Generac  xl4000 (standard gas) ,  primarily to run our sump pumps (back up power to the grid).

It's never taken more than three pulls to start it, even after sitting unused for a year.  I've a manual transfer switch with my furnace, well pump and three sump pumps.   It's been able to handle the loads (and start ups) and my only complaint is ...  it's LOUD.  DANG LOUD.

Been thinking of buying a new back up generator, although I've not really used this one for more than six to ten hours.  I don't have propane and I do have natural gas.    I've read some things online (yeah I know..  can't believe everything ya read) and seen comments that if the power grid goes down long enough that some of the gas feeds may also go down.   Not being on the grid,  I suspect that you don't have natural gas hook up,  but IF you did... would you have gone with a natural gas generator?

Is your genny quiet enough that you'd consider setting it up in your basement?
A while back I had a chance to pick up a lightly used Kohler   However I'm less than 10 miles from the Kohler company and know a couple of guys that work there and have all commented on how their quality is not what it was.

ax7

[ChrisOlson]

Chris..   would you mind saying how much the generator set you back?

It was $3,739 and the 240 volt kit for it was another $140.  And then there was sales tax.  So by the time everything is said and done you might as well say $4,100, give or take a few.

Not being on the grid,  I suspect that you don't have natural gas hook up,  but IF you did... would you have gone with a natural gas generator?

I don't really know for sure because I have no experience with natural gas.  But I don't think I would because I sort of like to have my system self-contained so I know what I got to work with.  To my way of thinking, depending on a natural gas line is sort of like depending on the grid - you're "hooked up" and at the mercy of whoever has control over the switch or the valve.

Is your genny quiet enough that you'd consider setting it up in your basement?

Standing right alongside it when it's running, it's about as loud as somebody talking in normal voice tones.  So if you can sort of imagine that amount of noise in your basement, yes you could put it there.  It is the quietest running generator I have ever heard run - really no louder than a central AC unit is another comparison I can think of.  No real engine noise - mostly fan noise with a slight sort of "purring" sound.  It's a V-twin engine in it.

A while back I had a chance to pick up a lightly used Kohler   However I'm less than 10 miles from the Kohler company and know a couple of guys that work there and have all commented on how their quality is not what it was.

I can't speak for the Kohler units but I did look at a Kohler diesel that I thought I might drive my DC generator with to make it more efficient.  When I found out the engine was built in China and is very noisy I decided to not buy one.  I did try a Yanmar diesel generator and it was too loud.  It had an annoying hammering noise from diesel ignition while it was running - louder than my gas Tecumseh on the DC generator.  I decided I couldn't listen to that because it could be heard thru the house walls.

We put the generator on the east side of the house where the DC unit was, about 10 feet from the turbine tower.  So the generator is only about 5 feet from the house.  We didn't get a good power day yesterday and the batteries were hanging around 24.9-25.0 volts last night when we went to bed.  I have the inverter set to start the generator if the batteries fall below 25 volts for more than two hours.  Our bedroom window is about 20 feet from the generator and when we got up this morning I discovered the gen had started during the night and clocked 1.3 hours.  We never heard it start and run, and my wife hears everything.

I guess that's why we bought it - it's automatic and it's very quiet.
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Chris