Battery generator vs Gas generator

Status
Not open for further replies.
H

Hfalz1

Member
Location
Houston, Tx.
Occupation
Electrician
I'm looking into using battery powered generators vs. gas powered generators. What size battery generator would equal the size of a 45kW gas powered generator? Would putting multiple batteries together be better?
 
Hfalz1 said:
I'm looking into using battery powered generators vs. gas powered generators. What size battery generator would equal the size of a 45kW gas powered generator? Would putting multiple batteries together be better?
Click to expand...

What you're talking about is using an Uninterruptible Power Supply (UPS) vs a generator. There is no such thing as a "battery powered" generator. It all depends on your purpose. If you need just a few minutes of coverage because local power has a lot of hiccups then a UPS might work. If you need hours of coverage, batteries are never going to be economical.

If you are protecting a process that absolutely can't shut down, you'll need a UPS of some sort because the fastest starting generator can't prevent a power outage to the equipment it covers. You may then also need a generator. I know that some semiconductor fabs use a POCO>>UPS>>Process scheme with a backup generator to feed the UPS. The whole fab is on UPS 24/7.
 
Do you need a battery supply (UPS) capable of 45kW-hr output? For how long?

If you need 45kw from a battery bank, it's going to cost a small fortune compared to a gas generator. Every hour would be 45,000w-hrs; on 12V batteries, you'd need 3750A-hrs, or 38 100AH batteries to get 45kw for one hour.
 
JFletcher said:
Do you need a battery supply (UPS) capable of 45kW-hr output? For how long?

If you need 45kw from a battery bank, it's going to cost a small fortune compared to a gas generator. Every hour would be 45,000w-hrs; on 12V batteries, you'd need 3750A-hrs, or 38 100AH batteries to get 45kw for one hour.
Click to expand...

Way more than that. You'll never get 100% of the rated amp-hours out of the battery at a useful voltage at that rate. Amp-hour ratings are typically based on C/10 or even C/20 discharge rate, where C is the nominal amp-hour rating. Maybe you can go down to C/4, which would mean you need 128 batteries.
 
Hfalz1 said:
I'm looking into using battery powered generators vs. gas powered generators. What size battery generator would equal the size of a 45kW gas powered generator? Would putting multiple batteries together be better?
Click to expand...

In general batteries are good for low output and/or short duration, while high output and/or long duration operation (and this is definitely high output), fuel powered generators are the only realistic solution. Sometimes the best solution is both; battery "generators", i.e., inverters, come on line nearly instantaneously while a generator may take a few minutes to start up and stabilize. For true uninterruptability (is that a word?), it might be best to use an inverter to bridge the time between the outage and when the generator can take over.
 
ggunn said:
In general batteries are good for low output and/or short duration, while high output and/or long duration operation (and this is definitely high output), fuel powered generators are the only realistic solution. Sometimes the best solution is both; battery "generators", i.e., inverters, come on line nearly instantaneously while a generator may take a few minutes to start up and stabilize. For true uninterruptability (is that a word?), it might be best to use an inverter to bridge the time between the outage and when the generator can take over.
Click to expand...
I've come across a number of 400kVA UPS installations permanently running large server applications. I can't remember what autonomy they had.

More commonly I dealt with units for emergency lighting in cinemas. These were mostly up to 100kVA with a three hour autonomy. I questioned this three hour requirement - how long do you need to evacuate a cinema in an emergency? "It's in the Cineomatic Code of Practice" was the best answer I got.
 
kwired said:
I was envisioning a battery supplying a DC motor that drives an alternator, seems would be much less efficient then just going with an inverter though.
Click to expand...

I have seen what are called battery powered generators for sale now and then. They are just inverters with a battery - basically a DIY UPS.
 
Knuckle Dragger said:
They should compliment PV sytems very well.
Click to expand...

For some applications. Not for running your house.

Homework Assignment:
Assuming a home with an average power consumption of 30kW-hr/day, size a PV-battery-inverter system to provide complete off-grid power. Further:

Assume: 1,800 kW-hr/kW-hrpeak/yr
Assume: 3.6 kW air conditioning load for 8 hrs on three consecutive days
Assume: 0% insolation 1 day out of every 3
Assume: battery power draw at 25% of max rating for the bank
Assume: solar array life of 20 years, inverter life of 10 years, battery life of 5 years
Assume: No maintenance costs.

Calculate installed costs with NO rebates/incentives. Calculate the levelized $/kW-hr over the course of 20 years.

If you can deliver that for under $0.12/kW-hr, my roof is yours.
 
gadfly56 said:
For some applications. Not for running your house.

Homework Assignment:
Assuming a home with an average power consumption of 30kW-hr/day, size a PV-battery-inverter system to provide complete off-grid power. Further:

Assume: 1,800 kW-hr/kW-hrpeak/yr
Assume: 3.6 kW air conditioning load for 8 hrs on three consecutive days
Assume: 0% insolation 1 day out of every 3
Assume: battery power draw at 25% of max rating for the bank
Assume: solar array life of 20 years, inverter life of 10 years, battery life of 5 years
Assume: No maintenance costs.

Calculate installed costs with NO rebates/incentives. Calculate the levelized $/kW-hr over the course of 20 years.

If you can deliver that for under $0.12/kW-hr, my roof is yours.
Click to expand...

don't be hurting the greenies with reality. :)
 
Our local hospitals have a 1 meg generator with a rotary UPS. Lose power the rotary UPS delivers power long enough for the generator to get on line. No batteries to maintain, and much higher capacity.
 
tom baker said:
Our local hospitals have a 1 meg generator with a rotary UPS. Lose power the rotary UPS delivers power long enough for the generator to get on line. No batteries to maintain, and much higher capacity.
Click to expand...
That's a common scheme for many high reliability systems actually. I worked on those at the Bonneville Dam years ago, the rotary UPS were spun up with an 800HP 460V motor (don't ask me why 480V and not MV at that size, I didn't design it) and we did the soft starters for those motors. Anyway they only had to supply power long enough for the DG to come on line, but were over sized by a factor of 4 just to be sure, because there was a backup DG for the backup DG, so you had to go through (potentially) one complete set of 2 attempts to start DG1, then possibly 2 more attempts to start DG2. All of this was just there to power the SCADA system and breaker mechanisms.

To my mind, the difference between a UPS and a "battery powered generator" is in the command structure. A UPS will have on-line monitoring, automatic switch-over, and usually a bypass system for overloads while it is on-line (assuming double conversion type) or take that command from a Transfer Switch (which would be a "single conversion UPS"). The "battery generator" version could have all of that stripped out, you just manually tell it to turn on when you need it.
 
ggunn said:
I am both an engineer (PE) and a green energy advocate. The two are not mutually exclusive.
Click to expand...

I realize that. However, given the parameters of my "Assignment", do you think you could deliver a system to meet the price target? My experience is that non-technical people sometimes fall in love with a technology and often exhibit invincible ignorance when confronted with tough questions. Heck, it's happened to me a time or three.
 
gadfly56 said:
For some applications. Not for running your house.

Homework Assignment:
Assuming a home with an average power consumption of 30kW-hr/day, size a PV-battery-inverter system to provide complete off-grid power. Further:

Assume: 1,800 kW-hr/kW-hrpeak/yr
Assume: 3.6 kW air conditioning load for 8 hrs on three consecutive days
Assume: 0% insolation 1 day out of every 3
Assume: battery power draw at 25% of max rating for the bank
Assume: solar array life of 20 years, inverter life of 10 years, battery life of 5 years
Assume: No maintenance costs.

Calculate installed costs with NO rebates/incentives. Calculate the levelized $/kW-hr over the course of 20 years.

If you can deliver that for under $0.12/kW-hr, my roof is yours.
Click to expand...

Is it enough to run my phone charger, freezer and my blender? If so then it could be worth it. :D
 
Knuckle Dragger said:
Is it enough to run my phone charger, freezer and my blender? If so then it could be worth it. :D
Click to expand...

Look at the last line of my post. If you don't get the costs down to whatever your local rate is, then no, it's not enough, no matter how small the loads.
 
Status
Not open for further replies.
Top