diy solar

diy solar

How efficient is your generator?

Symbioquine said:
Well maybe... I think it is a key aspect to all this is that the generator isn't the only thing in the system.

Hard to prove (and highly situational), but I suspect the embodied energy of a given off-grid system would be way worse if it had tons of tiny "engines" that burned fuel directly to apply the chemical energy at the point-of-use as heat or mechanical energy.

Another interesting aspect that is a bit more on-topic is what's the total fuel efficiency (or fixed cost efficiency) of folks' off-grid systems. i.e. if you have an off-grid system that produces/consumes 4 MWh/yr but uses 200 kWh of generator-derived power at 10% chemical conversion efficiency and $1.50/kWh to get through the year, how well are you doing overall?

Code: 
0.2 (MWh / yr) / 10% (conversion efficiency) / 4 (MWh) = 50% effective chemical conversion efficiency
200 (kWh / yr) * $1.50 (USD / kWh) = $300 (USD / yr)
$300 (USD / yr) / 4000 (kWh / yr) = $0.075 (USD / kWh)

Obviously, the above doesn't include up-front equipment or ongoing maintenance costs.
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Heat recovery for heating in the winter which happens to coincide with reduced insolence I think could make it a win.

That is one thing that I haven't seen on this site. Someone with a gen in their system who has come up with a nifty and SAFE way to recover engine cooling and exhaust heat.
 
Checkthisout said:
Heat recovery for heating in the winter which happens to coincide with reduced insolence I think could make it a win.

That is one thing that I haven't seen on this site. Someone with a gen in their system who has come up with a nifty and SAFE way to recover engine cooling and exhaust heat.
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If the engine is water cooled you could use a heat exchanger. Very common for marine applications.

My thought to recover exhaust heat was to repurpose a gas water heater tank. Delete the burner and pipe the exhaust into the bottom. Feed the water outlet into your primary water heater tank. Should make an effective water dampened muffler.
 
Delmar said:
If the engine is water cooled you could use a heat exchanger. Very common for marine applications.

My thought to recover exhaust heat was to repurpose a gas water heater tank. Delete the burner and pipe the exhaust into the bottom. Feed the water outlet into your primary water heater tank. Should make an effective water dampened muffler.
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Yeah but I was thinking along the lines of the smaller air-cooled inverter gens. Off the top of my head, the smallest water cooled engine Honda are the old ES6500's?? but those aren't inverter.

Would be a fun little project. You would definitely want to recover the exhaust heat which would also be easy.

Just have to do it and make it work in a practical way.
 
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.
 
I use a 6kw generator with a 5 gallon gasoline fuel tank.
My battery is a 5KWH eg4 LiFep04
If I run my battery down to %25 I can charge it to %100 on 2.5 gallons of fuel.
I can usually do this twice before it’s empty.
It’s about $20 for the 5 gallons.
So it’s about $10 per charge.
Not the best for my pocket.
The panels help a lot.
 
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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It's usually recommended to run ethanol-free gasoline in small engines like generators if you care about their longevity and reducing maintenance. I doubt you'll be finding ethanol-free gasoline for $3.78 if regular gas is selling for that. Realistically you're probably looking at a similar price for ethanol-free gasoline and diesel.

That said, even with the numbers you've provided (and the relative efficiencies others in this thread have reported), diesel is cheaper (in terms of raw fuel cost) per kWh than gas.

The math to back up that statement;

Code: 
Diesel generators are being reported as producing ~10 kWh / gal of diesel
Gas generators are being reported as producing ~6.5 kWh / gal of gasoline

So if you needed 10 kWh of power you'd need to buy;

10 kWh / 10 (kWh / gal of diesel) = 1 gallon of diesel @ $5.53 = $5.53
10 kWh / 6.5 (kWh / gal of diesel) = 1.54 gallons of gas @ $3.78 = $5.82
 
I use a champion 8500 whole home standby generator, inverter type, i run it strictly to charge my batteries thru the sol ark in an off grid situation. I usually pull 6000 watts from it while charging. Propane powered. I can tell you that this is an expensive endeavour and am looking for alternatives.

In canada I am paying $0.90 / pound of propane. It consumes 1.1 Gal per hour at half load. If we do the math. 1 gallon is 3.78541 liters. Given my above 50% load I am best guessing that i'm using 1.3 gal per hour. The full load specs show that it uses 1.6 gal per hour at full load.

I just need to figure out why the power is getting "dirty" and the inverter unlocks from the generator when i try to push it past this limit. It shows the hz dropping to about 58 past this point. I feel like I need to adjust the governor on the unit, but my HZ meter bounces all over the place when I try to do this so I have to have someone watching on the sol ark while adjusting (and is the solark hz super accurate? I don't know. )

So in canadian dollars to you americans this is actually a cheap way to go. But for me, solar is the cheapest, pray for more sun :D
 
Mannfamilywoodworks said:
I use a 6kw generator with a 5 gallon gasoline fuel tank.
My battery is a 5KWH eg4 LiFep04
If I run my battery down to %25 I can charge it to %100 on 2.5 gallons of fuel.
I can usually do this twice before it’s empty.
It’s about $20 for the 5 gallons.
So it’s about $10 per charge.
Not the best for my pocket.
The panels help a lot.
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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?
 
crazydane said:
Rated load details are:

Power Rating5kW, 0.8 pf @ 4000ft/120°F; 110% Max Power; De-rate: 3.5%/1000 ft from 4000 to 8000 ft

I'm testing into a 5kW dummy load (1.0 pf) at 760 ft and temps around 70F. So it makes sense that I'm doing a little bit better than 0.57 gph.

I also have a MEP-803A, which is basically a 802A with 2 more cylinders and a larger generator head. It is spec is 0.97 gph @ rated load, which is:

Power Rating10kW, 0.8 pf @ 4000 ft/120°F; 110% Max Power; De-rate: 3.5%/1000 ft from 4000 to 8000 ft

I bet I can squeeze 10.5 - 11 kWh / gal out of it.

Btw, I buy off-road diesel which is about $0.25 cheaper than on-road. As of this morning, the off-road was $5.44 at my local service station.

You can never have too many generators, lol:

View attachment 120323
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Off road here is $4.85.

I like those generators but hard to find here over 5kw.
 
myles said:
I just need to figure out why the power is getting "dirty" and the inverter unlocks from the generator when i try to push it past this limit. It shows the hz dropping to about 58 past this point.
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Generators will drop engine speed as loads increase. Falling below 58Hz under full load isn't uncommon as a lot of generators advertise fairly optimistic load capacity specifications. But they can also need some service, things like the carburettor might need a clean if the jets are not pristine it may be slightly restricting fuel flow. Or the governor is not quite operating as well as it should. The governor control springs do lose their capacity for control over time.

My generator is an inverter generator, so the power wave form is high quality.

In terms of power output quality, Inverter generator >> generator with an AVR > no AVR > brushless generator.

No all charge controllers will accept poor waveforms.
 
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.
 
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