Off Grid Building

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
I'll take a look at that, thanks :)

Looking through Kohler and CAT literature that also offer sets with a prime rating.

Would you happen to know the most kw per dollar for gas and diesel units size wise?
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
I'll take a look at that, thanks :)

Looking through Kohler and CAT literature that also offer sets with a prime rating.

Would you happen to know the most kw per dollar for gas and diesel units size wise?
I'm going to hazard a guess that for prime service, diesel is what you want. The reliability of diesel over gas is significant, or so I've been told. Not my specialty.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
I'm going to hazard a guess that for prime service, diesel is what you want. The reliability of diesel over gas is significant, or so I've been told. Not my specialty.

My plan is gas normal, diesel back-up.

Waste heat reclaim on the gas units.
 

kwired

Electron manager
Location
NE Nebraska
Lots of things to consider here that are maybe even more important than the one-line.

You don't want the typical standby generators, they should be continuous duty. Maintaining the generators while they are running is another consideration (can filters be changed without shutting the generator off?)

What about transfers? They probably aren't going to be very happy if there is a short blackout on every transfer.

I'd also consider paralleling generators.
My thought right away. Transfer switch more practical for isolation from utility.

No utility - parallel all sources so that you can take one off line for servicing without any interruption. You still can arrange distribution according to how critical a load is or use smaller standby sources for some the most critical things.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
My thought right away. Transfer switch more practical for isolation from utility.

No utility - parallel all sources so that you can take one off line for servicing without any interruption. You still can arrange distribution according to how critical a load is or use smaller standby sources for some the most critical things.

Right, but that means single point failure modes. Also should something go wrong, most sparks aren't familiar with advanced paralleling controls.
 

kwired

Electron manager
Location
NE Nebraska
Right, but that means single point failure modes. Also should something go wrong, most sparks aren't familiar with advanced paralleling controls.
Or they could hire people qualified to operate it. Sounds like the will need staff they normally wouldn't need if it were utility supplied anyway, plus you said it is government operation so there is probably overqualified individuals in some positions anyway.

If it is military operated, they have qualified people to draw from.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
Or they could hire people qualified to operate it. Sounds like the will need staff they normally wouldn't need if it were utility supplied anyway, plus you said it is government operation so there is probably overqualified individuals in some positions anyway.

If it is military operated, they have qualified people to draw from.

You really want to go parts hunting in an emergency? Or go credentials hunting during an emergency when an average electrician or tech could figure it out instead?
 

kwired

Electron manager
Location
NE Nebraska
You really want to go parts hunting in an emergency? Or go credentials hunting during an emergency when an average electrician or tech could figure it out instead?
Government don't care about that though :)

And critical parts are good idea to have spares already on hand especially when even makeshift replacements would be rather impractical to depend on.

The needs of the operation sort of dictate what is or is not acceptable, can you withstand even a short outage while startup and transfer to another source occurs? If not cost to own and operate likely goes up in one way or another.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
Government don't care about that though :)

And critical parts are good idea to have spares already on hand especially when even makeshift replacements would be rather impractical to depend on.

The needs of the operation sort of dictate what is or is not acceptable, can you withstand even a short outage while startup and transfer to another source occurs? If not cost to own and operate likely goes up in one way or another.

You really want to pay double for all the computers and PLCs that go into parelleling gear, only to lay around? With an ATS manual bypass levers can take care of any electronic failures.


Loads requiring constant power will have a UPS.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
Government don't care about that though :)

And critical parts are good idea to have spares already on hand especially when even makeshift replacements would be rather impractical to depend on.

The needs of the operation sort of dictate what is or is not acceptable, can you withstand even a short outage while startup and transfer to another source occurs? If not cost to own and operate likely goes up in one way or another.
Don't get me wrong- there are places using paralleling gear right now:

1614958918340.png

But sometimes simplicity is key. As well as not putting all your eggs in one basket.
 

kwired

Electron manager
Location
NE Nebraska
You really want to pay double for all the computers and PLCs that go into parelleling gear, only to lay around? With an ATS manual bypass levers can take care of any electronic failures.


Loads requiring constant power will have a UPS.
Now you mention UPS.

But still, you don't need double of everything on hand- unless you expecting everything to go down all at same time. Even with all your ATS you proposing you maybe only have one or two spares on hand and not "one for one", presuming they are mostly all the same model/size.

Having diesel and gas generators also means having more spare parts on hand than if they were all the same thing... though it does potentially help should one fuel source become scarce. Still all design considerations and importance of the mission can factor in to those designs
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
Now you mention UPS.

But still, you don't need double of everything on hand- unless you expecting everything to go down all at same time. Even with all your ATS you proposing you maybe only have one or two spares on hand and not "one for one", presuming they are mostly all the same model/size.

Having diesel and gas generators also means having more spare parts on hand than if they were all the same thing... though it does potentially help should one fuel source become scarce. Still all design considerations and importance of the mission can factor in to those designs
Right, however there are many things that can fail in paralleling gear, and of those many a good chunk can render the whole system inoperative.

With islanded sets, you have several independent sources of power.

The building has a life safety and critical branch yes, but the offices, operations center, labs ect have circuits from both the EM and general light and power branch.

Further, with standard gear and you can use rack out jacks and roll generators in offsite. No need to worry about paralleling them.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
So- I am close to have something like this:


Debating whether I should rotate the feeders around that the total load served by any gas unit has leads to more than one diesel unit but I can't see any technical need for that.

Still not 100% set on number of units or ther size- ie keep all the gas units the same size or have different sizes.

Or if I should combine any of the diesel units since they are physically smaller (and more inrush tolerant).
 

JoeStillman

Senior Member
Location
West Chester, PA
The problem for me is it looks like you could easily have a situation where you have lots of generator capacity, but you can't use it where you need it. That's the problem with eschewing parallelism.
 
Have you considered paralleling with bus-ties? Keep the six generator busses but either tie them end-to-end or add single paralleling buss above them. That still allowed the units to operate islanded but also allows capacity sharing. Would dictate refeeding the B side of most ATSs.

Whatever you do, it's going to be a lot of controls and the with that much generation and switching, there ought to be a qualified operator on-site or readily available.
 

topgone

Senior Member
I've read that typical 1,800 rpm engines come in prime and continuous ratings. Any input on this?
Best for you to look at the engine drive specs. The generator itself can deliver the claimed rated power but the engine driving the generator cannot! Most genset salesmen would claim what is never there in their units!
Another problem would be oversizing the generator too much! Make sure your load is above 35% of the generator capacity normally!
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
Best for you to look at the engine drive specs. The generator itself can deliver the claimed rated power but the engine driving the generator cannot! Most genset salesmen would claim what is never there in their units!
Another problem would be oversizing the generator too much! Make sure your load is above 35% of the generator capacity normally!

Agree! :)
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
Have you considered paralleling with bus-ties? Keep the six generator busses but either tie them end-to-end or add single paralleling buss above them. That still allowed the units to operate islanded but also allows capacity sharing. Would dictate refeeding the B side of most ATSs.

Whatever you do, it's going to be a lot of controls and the with that much generation and switching, there ought to be a qualified operator on-site or readily available.

I have, in my thought paralleling would be way more complex than a few ATSs. Further most of the electricans here can service an ATS system, but not one with paralleled sets.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
The problem for me is it looks like you could easily have a situation where you have lots of generator capacity, but you can't use it where you need it. That's the problem with eschewing parallelism.


Agree, but as I see it parelleling reduces reliability via common mode and common point failure.
 
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