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How efficient is your generator?

I bought two Big Buddy propane heaters for heating, more cost efficient heating the house with the generator. Westinghouse 12kw dual fuel generator (less the 5% thd) with four 100lb propane tanks to run it. Generator will run the AC and well pump. I use 1lb refillable propane tanks for the heaters and have two 5 gallon tanks to use for that purpose…
I got solar but no batteries…. Soon will have powerwalls.
Good non inverter generators use servos to control rpm/hz
 
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wme said:
Local reg gas is 3.78 a gallon. Diesel is 5.53 a gallon. Sorta shoots down the diesels are 20% more efficient and cheaper to run theory.
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You can run the diesel on heating oil, which tends to be cheaper (at least here in Europe). With some care, you can also run off of straight vegetable oil.
 
Checkthisout said:
How about gasoline saved going to lithium?
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Depends what you mean...

LFP batteries tolerate not being charged to full as regularly as lead-acid in my understanding so it likely gives folks more flexibility about just conserving power and waiting for it to get sunny again instead of needing to charge the batteries to keep them healthy.

Another way might be in terms of better battery performance. Round-trip charge/discharge efficiency is probably better. Also higher C charge rates allow generators to be operated closer to their maximum efficiencies.

That said, since I assume we're not talking about lithium primary batteries, it is kind of an apples to oranges comparison. It's also a bit off-topic. Though I'd encourage a parallel thread (there might already be one) that attempts to document those benefits - and the costs.
 
Symbioquine said:
Depends what you mean...

LFP batteries tolerate not being charged to full as regularly as lead-acid in my understanding so it likely gives folks more flexibility about just conserving power and waiting for it to get sunny again instead of needing to charge the batteries to keep them healthy.

Another way might be in terms of better battery performance. Round-trip charge/discharge efficiency is probably better. Also higher C charge rates allow generators to be operated closer to their maximum efficiencies.

That said, since I assume we're not talking about lithium primary batteries, it is kind of an apples to oranges comparison. It's also a bit off-topic. Though I'd encourage a parallel thread (there might already be one) that attempts to document those benefits - and the costs.
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I mean in regards to charging efficiency off the generator.

Less run time and higher loading.
 
wattmatters said:
I think charging batteries is the most common use case people are discussing here. For when solar PV output is inadequate.
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Which is what I was getting at

A direct cost comparison of what it takes to put a Kwh into a lithium VS a flooded battery.

Notably, eliminating the under loading period that occurs. My charger starts out at 120 amps, tapers to 70 and then camps out for a couple hours tapering from 40 down to 10 amps when the Gen shuts off.
 
Checkthisout said:
A direct cost comparison of what it takes to put a Kwh into a lithium VS a flooded battery.
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Well that will be a simple case of the fact a flooded lead acid battery requires more energy to charge (and keep charged) than does a lithium battery. About 15-20% more.

What generation source is supplying the charge isn't really of consequence in that comparison.

You would just size your generator to suit the appropriate charge current for each.
 
I've updated the original post with additional run data. The tank I just started is with the improved charging rate provided by the second inverter I installed. Yielding ~4 kW charging rate instead of closer to ~2 kW. It will be interested to see how the efficiency changes with the increased load...
 
Well, with an average load of (at least) 4.15 kW on this last tank the DuroMAX XP9000iH achieved around 13.9% efficiency.

I also discovered part way through this last tank an issue with how I was capturing load data metrics so the actual average load/efficiency was probably a bit higher. We'll see on the next tank, but it was good to see the efficiency go up so much with the increased load. It gives me some hope that with proper loading, propane won't be such a terrible choice from an efficiency perspective.
 
Symbioquine said:
Code: 
5 (kWh / battery) * 3/4 (battery) = 3.75 kWh capacity to charge
3.75 (kWh) / 2.5 (gal) = 1.5 kWh / gal
$6.42 (USD / gal) / 1.5 (kWh / gal) = $4.28 (USD / kWh)
1.5 (kWh generated) / 33.41 (kWh total energy) = 4.5% efficiency

@Mannfamilywoodworks I suspect something is either really wrong with your generator or maybe you're charging way slower than necessary - basically near-idling the generator while you effectively trickle-charge the battery.

How long is the generator running per charge cycle?
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4 hours usually per cycle lol please help if you suspect an issue
 
Mannfamilywoodworks said:
4 hours usually per cycle lol please help if you suspect an issue
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Well, maybe not an issue per se, but probably quite a bit of opportunity to run the generator less and get more power from the same amount of fuel.

Code: 
3.75 kWh / 4 h = 937.5 w average charging rate

For a 6 kW generator, it's not totally idling, however it is far below the charging rate you could have. From your other posts I think I see that you have the 48v EG4 battery which supports up to 100 A charging/discharging. So conservatively;

Code: 
48 v * 100 A = 4800 watts

(Actually, the charging voltage will usually be above 50v so the charging wattage at less than 100 A could easily be in excess of 5 kW, but it's probably best for battery life to keep it in the ~4 kW range.)

TL;DR; If you added some charging equipment to charge at a rate 3 or 4 times faster you would need to run the generator about 2 to 3 hours less to get the battery full and probably only see a nominal increase in fuel consumption - i.e. much higher conversion of fuel into usable power.

Of course nothing's free so you'd need to evaluate how often you actually end up running the generator and whether it is worth it to you by comparing the value of the quiet or the cost of the extra charging equipment against the cost of the fuel & generator maintenance.
 
Not sure if this helps but my 18kw Kohler uses about 3 gal of LP per hour average load.
 
jfpetesn said:
Not sure if this helps but my 18kw Kohler uses about 3 gal of LP per hour average load.
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Not very much by itself. Do you have a sense for what "average load" means in average kW or total kWh for a given amount of run time?
 
Symbioquine said:
Not very much by itself. Do you have a sense for what "average load" means in average kW or total kWh for a given amount of run time?
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No I’m guessing 50-60% of 18 kW. I’ll go look at the manual. I just always used 3 gal/hr for my calculations. Now that we have an AIO inverter it’s not as big an issue since the Gen now only runs to charge the batteries which for us means about 2 hrs a day on a fair solar day. Cloudy or rainy I need about 40 kWh to make it through the day so might mean 3-4 hours of gen time total.
 
So it a 17kW on LP 2.1 gal per hour at 50% load. So I’m looking at probably 3+ gal per hour when charging. Probably closer to 4. When charging I’m looking at 11k for the inverter and another 1.5kW for the house loads. So say 13 total when charging. So let’s say 8 gal LP per day off grid. I have 44 kWh of storage now and a 13.2 kW array. Ultimately I need another 22 kWh of storage and another 2400 watts of panel and I’m pretty well off grid.
 
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jfpetesn said:
So it a 17kW on LP 2.1 gal per hour at 50% load. So I’m looking at probably 3+ gal per hour when charging. Probably closer to 4. When charging I’m looking at 11k for the inverter and another 1.5kW for the house loads. So say 13 total when charging. So let’s say 8 gal LP per day off grid. I have 44 kWh of storage now and a 13.2 kW array. Ultimately I need another 22 kWh of storage and another 2400 watts of panel and I’m pretty well off grid.
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I'm guessing the 2.1 gal/h @ 50% load is from the generator manual. Using those numbers;

Code: 
17 kW * 50% = 8.5 kW
8.5 kW / 2.1 gal/h = 4.05 kWh / gal
4.05 (kWh generated) / 27.988 (kWh total energy) = 14.5% efficiency

If you have a way to measure the run time, actual propane use, and the total produced kWh, it would be interesting to see how those numbers hold up in the real world!
 
Symbioquine said:
I'm guessing the 2.1 gal/h @ 50% load is from the generator manual. Using those numbers;

Code: 
17 kW * 50% = 8.5 kW
8.5 kW / 2.1 gal/h = 4.05 kWh / gal
4.05 (kWh generated) / 27.988 (kWh total energy) = 14.5% efficiency

If you have a way to measure the run time, actual propane use, and the total produced kWh, it would be interesting to see how those numbers hold up in the real world!
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I lost you on the final calc. The 27.998 what is that number? What I see in real life is I usually charge at night with our low TOU rates I see around 23kWh used from the grid at this time with batteries at 100%. Now if I have an average solar day we grid sell after batteries are topped off back to 100% then start grid selling. By the end of the day I usually end up with a total grid sell for the day of 15-20kWh (that’s really 43 kWh but we used 23 to charge at night). In addition we regularly charge or buy our power for 1.5-4 cents per kWh at night and we grid sell during the day at 8-12 cents per kWh so we take advantage of that. What I would expect in a grid outage is almost the same cycle except no grid sell. We would need about 10-15 kWh from our gen to make it through the day. My Sol Ark spec says it’s 96% efficient AC to DC charging.
 
jfpetesn said:
I lost you on the final calc. The 27.998 what is that number?
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It's mentioned earlier in the thread, but that's the amount of chemical energy in a gallon of propane (LPG). If a theoretical propane generator were 100% efficient, you would see that many kWh produced for each gallon burned. The amount of kWh actually produced divided by that number, gives us the on-site efficiency of the generator - it obviously ignores the embodied energy of producing/transporting the fuel though.

jfpetesn said:
Now if I have an average solar day we grid sell after batteries are topped off back to 100% then start grid selling. By the end of the day I usually end up with a total grid sell for the day of 15-20kWh (that’s really 43 kWh but we used 23 to charge at night). In addition we regularly charge or buy our power for 1.5-4 cents per kWh at night and we grid sell during the day at 8-12 cents per kWh so we take advantage of that. What I would expect in a grid outage is almost the same cycle except no grid sell.
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That's pretty interesting! I assume days when you sell to the grid are also days when you don't have to run the generator at all right? Otherwise I'd imagine the generator fuel costs would wipe out any profit there pretty quick...

jfpetesn said:
We would need about 10-15 kWh from our gen to make it through the day.
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You'd still need to directly measure the weight or liquid volume of the propane if we wanted to determine what real-world efficiency you're getting from the generator.
 
Symbioquine said:
It's mentioned earlier in the thread, but that's the amount of chemical energy in a gallon of propane (LPG). If a theoretical propane generator were 100% efficient, you would see that many kWh produced for each gallon burned. The amount of kWh actually produced divided by that number, gives us the on-site efficiency of the generator - it obviously ignores the embodied energy of producing/transporting the fuel though.



That's pretty interesting! I assume days when you sell to the grid are also days when you don't have to run the generator at all right? Otherwise I'd imagine the generator fuel costs would wipe out any profit there pretty quick...



You'd still need to directly measure the weight or liquid volume of the propane if we wanted to determine what real-world efficiency you're getting from the generator.
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So I see what you are doing. I guess it would be difficult to be accurate. I can measure the electricity end but the LP would be difficult unless I had the inclination to attach a small cylinder do a test run then weight it. 17% efficiency seems low. But it may be correct. Since our system upgrades this fall I was strictly grid tied and faced with the possibility of having to run the gen 24/7 if grid was down or at least 12 hrs a day. Since the AIO installation we can probably get by with 2-3 hrs a day. We live rural so 400 gal is what we try to keep on hand. So we are now good some 40 days instead of 8-10 days.
 
jfpetesn said:
the LP would be difficult unless I had the inclination to attach a small cylinder do a test run then weight it.
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Yeah, no pressure ? (pun intended)

jfpetesn said:
17% efficiency seems low. But it may be correct.
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Well, I calculated 14.5% above, but either one would be better than any of the real-world propane numbers we've seen so far. (In the right ballpark though so probably possible.)
 
Grid backup is definitely a plus for us. And playing the TOU game increases our efficiency by probably 20%.
 
I drive, among other rigs, a plug in Prius, and on a Prius forum I check into from time to time, I remember one of the major geeks there reporting that, after exhaustive testing, he found that the hybrid Prius was more efficient then any small generator. Easily transportable too!

You can draw up to 1000-1200 watts off of the small 12 VDC battery, which is kept charged by the big high voltage traction battery via voltage converter, all stock Prius stuff, the gas engine coming on from time to time only when the big battery needs to be topped off. While the gas engine is on, it's running at it's optimum RPM/fuel burn/torque curve/charge rate, nothing like idling a conventional gasser to charge a battery, the Toyota engineers really did their homework and it's common for even long time Prius drivers to find new little details on how well the car works. A small 12 VDC/120AC inverter is used on the small battery, mine is 700 watts so I can charge my e bike while on the road, so the power available is limited, but REAL efficient. Some have talked about custom inverters that would work directly off the big battery, with up to 4 KW output, but that seems to be a one off thing.

I'll park mine and just leave the car ON (engine is off), while I go eat or whatever when on a road trip, knowing there is no fear of having "the battery run down," and that the amount of gas used is being burned in the most cost effective way possible. DAYS of output, on very little fuel, so the next time you hear someone diss a Prius and by extension, it's driver (!) keep that in mind. My other rigs are a 1 ton Silverado flat bed, and 60,000 pound 35 ton capacity crane truck, for when I feel the need to look macho, otherwise, at 73 years old, the darn Prius is my favorite car I've ever owned.

45 years ago, when on my first new rural property, and living out of a home made 5 th wheel trailer (it'd be called a tiny home now) I'd drive my dual battery pickup up, raise the hood, and using jumper cables power up the 12 VDC trailer circuits. Parked on a mountain, if I ever ran the batteries down enough to not start, it was a simple matter to start coasting, pop the clutch, and by the time I went into town and back the they were charged again. The yet to be invented Prius would have been a lot more convenient.
 
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