Grid connected UPS - 20KW

[Shah24]

Hello All,

I am not sure if this is the right place for this thread but please move it to different category if not.

I need some information for a back up system which is going to be connected to the grid. I have listed the power usage:

210 Bulbs = 5000 watts > 24 hours a day
12 Fans = 18000 watts > This is peak time but normally only needed to run 2-3 Fans
2 Water Pumps = 3000 watts > Only run 2 hours a day
6 Motors = 4500 watts > Only run 3 hours a day
1 Motor = 1500 watts > Only run 3 hours a day

------

I know it is easier to just get a generator and provide the back up but it is expensive to run the generator due to diesel cost.

I am looking to install a battery bank which could provide a back up power for the above. Please let me know if this could work?

Edit: I should have mentioned back up for 12 hours.

Thanks,
Shah.

[Volusiano]

If you think diesel cost is expensive, wait until you see battery cost for a system that can deliver 20 kw for 12 hours (240 kwh). And whatever cost that battery system is, plan on replacing it every 4-5 years, too.

[Sunking]

How many millions of dollars to you have to spend on batteries every few years? Forget solar, you cannot afford it. Deisel fuel will be 1/20th of solar power. If used infrequently for emergency 1/1000 of solar.

[SunEagle]

How many millions of dollars to you have to spend on batteries every few years? Forget solar, you cannot afford it. Deisel fuel will be 1/20th of solar power. If used infrequently for emergency 1/1000 of solar.

There is a lot of information concerning the cost of an installed "grid tie" system before rebates ($4 - $7/DC watts) but not much in the way of the cost for an "off grid" system.

Based on specific data from some of our "off grid" partners or using current technology it would be nice to see a range of $/DC watt costs for a 24volt or 48volt "off grid" solar pv system.

For those people that believe an "off grid" system is cheaper as compared to a fossil fuel generator for emergency backup power, it might be easier to provide that cost comparison data to make them understand their folly.

[Shah24]

Thank you for replies guys

Well the power outage is about 12 hours a day on a worse day in my area. This outage does not happen continuously. I have a diesel engine generator for the worst case scenario.

The diesel cost about $1.1 per litter and the generator will consume about 4-5 litters per hour. That is about 60 litters and comes to about $66 per day. For a month it will cost around $1980.

I was looking at the APC Symetra LX 16 kVA UPS SYAF16KRMT. Can get this for about $1250 on ebay (used).

The batteries of choice are Exide. These are not deep cycle batteries! and cost around $150 each. Not sure how many I will need? hence the thread

24 or 48 volt system?

[Sunking]

This plan is insane. By my calculations you would need a 600 Kwh battery bank operating at 240 volts DC with a capacity of 2500 AH or around some $120,000. Since they are not Deep Cycle will need replaced every few months.

Got anymore bright ideas there genius?

[Shah24]

haha if I was a genius and had ideas I won't be asking questions!

I was told otherwise about the cost so I thought to check with some knowledgeable people

So how do you come to these numbers. Just want to know the underlying maths

Thanks
Shah.

[Mike90250]

using your #'s, and only 6 hours of fans, I came up with 132,000 watt hours for your 12 hour load. (11Kw cont load)

A 48V battery bank to handle 50% discharge, would need to be at least 5,000 Ah. That is HUGE.

Trojan 4V 1200 ah batteries
4 Volts 1,233 Amp-hours at the 20 hour rate
Dimensions: 22.375"L x 10.25"W x 24.25"H Weight: 370 pounds
$1,200 each, you would need 4 parallel strings (bad idea, 4 parallel) of 12 batteries
That's 48 batteries, 96 filler caps to check, and about 9 tons of batteries to move.

cost would only be $57,000 for batteries only, no cables, no inverter, no charger and no
15Kw backup generator you need to preserve the batteries if the grid does not come back on.

24V, 1500Ah forklift battery pack, you would need 3 parallel strings of 2 batteries
24 Volts 1500 Amp-hours at the 20 hour rate
Dimensions: 38.63"L x 19.19"W x 26.25"H Weight: 2244 pounds
$6,500 ea
you would need 6 of those, and would be a little short of 50% discharge .

So an energy diet would be a good starting place to save $.

[Shah24]

Thank you Mike

Well as far as the energy diet goes the lights have to be switched on all the time plus two fans. The other stuff can be run off grid (when its on) or generator if it comes to worst case scenario.

This leaves me with the following:

210 Bulbs = 5000 watts
2 Fans = 3000 watts

I was only looking at this as I will spend about $20k to $24k a year on diesel!

[Sunking]

UPS systems are designed to carry the load for 15 to 30 minutes until a generator can come on line and supply the load until commercial power is restored.

[Shah24]

Sunking you are absolutely right about that.

I have UPS system for my house as a back up (btw same grid). It is an APC 1000 watts I think with two Exide 200AH batteries. It runs fans, lights and TV! Need to change the batteries every 18-24 months but for $300 it is well worth it.

So was thinking if similar system could be designed at a bigger scale

[Sunking]

So was thinking if similar system could be designed at a bigger scale

It is the scale that bites you in the butt.

I will bet you $1000 USD you project never sees the light of day. If I win you owe me $1. I cannot loose the bet.

[Volusiano]

So was thinking if similar system could be designed at a bigger scale

Looks like you were ready to go bigger scale on the kwh but maybe not ready to go bigger scale on the cost?

[Shah24]

Sunking you would probably win!

Volusiano: I didn't say anything about the cost. I was just trying to compare my annual usage ($20-$24k) of diesel with a grid connected UPS system.

Even if I compare it to what Mike has said about batteries being $57k. The batteries will payback in less then 3 years... (not sure the life of Trojan batteries)

[SunEagle]

Sunking you would probably win!

Volusiano: I didn't say anything about the cost. I was just trying to compare my annual usage ($20-$24k) of diesel with a grid connected UPS system.

Even if I compare it to what Mike has said about batteries being $57k. The batteries will payback in less then 3 years... (not sure the life of Trojan batteries)

What Mike left out in the cost was for every thing else besides the batteries. There will be over 20 kwatts of solar panels, battery charge controllers, wiring, fusing, and inverter to change the battery voltage back to your equipment voltage. You will easily double that $57k to over $115k when you add it all up.

Then after 5 years (if you are lucky) when the batteries fail you get to buy another set which will now probably be more than $57k.