Check My Math

[George Stolz]

So, I'm working on a utility interactive solar home.

In the event that the utility goes down, there will be a battery bank so that the inverter can continue to provide power to panels located downstream from it. I am in the process of determining how much / which loads the inverter can supply in that circumstance, and wouldn't mind a second set of eyes.

There will be two 240V 4500W inverters, for a total of 9000W.
There will be two panels on the load side of those inverters.

It seems to me that there is scant little that this setup will power. Am I missing something obvious?

All values with zeroes are items the HO would like to have, but I don't think he can have.

More issues are, the recessed cans are typical resi 75W incandescent cans with little 13W lamps in them, but I have made the homeowner aware that I have to handle them as though they contained 75W lamps. It's going to be a topic of contention when I tell him that although supplying every can in his house is going to be around 7A, I have to pretend as though there are 43A in cans.

 

[Volta]

Do these inverters get paralleled together? Are they made to allow the cyles to sync? I assume the phase A overage of .06 is a non-issue (220.5(B)), especially with the 18-va for the recep. in there.

I agree that the 75 w cans would need to be counted as you say.

Looks ok if the units are designed to work together.

 

[ptonsparky]

Looking at this from experience with a few ice storms, 9000 watts is a lot of power. It is possiple to heat a small house. Run a washer & dryer. Easily a gas furnace and if you are careful most of the lights in a home. I had customers running heat pumps and a well on 8000. The bigger question I believe is how much battery capacity do you have?

Is this expected to give them full and complete use of a 4000sq ft home and 5 kids or just for short durations and some control?

 

[winnie]

Given the way article 220 calculations seem to exaggerate loads, it seems to me a tremendous waste of capacity to use article 220 to determine the loads that an inverter can supply.

It makes sense that the number of 75W capable fixtures on a circuit should be determined by the 75W number, IMHO the customer should be able to connect as many circuits as will not actually overload the inverter.

-Jon

 

[Volta]

This is an Optional Standby System, isn't it? I suppose that if you had a manual transfer you could allow for selection of the loads to be connected . . . 702.5(B)(1)

 

[George Stolz]

It's not an optional standby system. It's always on, making power for the home, or selling excess back to the utility. In the event of a utility failure, it shuts down it's line side, and continues to provide power on the load side.

Given the way article 220 calculations seem to exaggerate loads, it seems to me a tremendous waste of capacity to use article 220 to determine the loads that an inverter can supply.

Which I would concur with morally on a standalone system - but this one feels different to me.

It makes sense that the number of 75W capable fixtures on a circuit should be determined by the 75W number, IMHO the customer should be able to connect as many circuits as will not actually overload the inverter.

-Jon

But let's say in five years the owners get hit by a truck. The house is sold to a new owner that hates the color of the lights, and switches them out for incandescent. My 7A of cans on one circuit need to be on three circuits, now. And the 60A feeder (ignoring the inverter for a moment) is woefully inadequate.

Thoughts?

 

[cadpoint]

Random thoughts

Random thoughts

The first thing I think I?d do is take a creative wire approach, I?d split up some circuits of lights that will go dead to feed some common accessible receptacles.

That the accessible outlet(s) might even be a quad!
I?d rather have an outlet then worry about a light.

In the same respects to insure they have a hard wired phone installed.

Somehow get power to the master bedroom with an outlet, for alarm clock, chargers, etc.

If the GDO is the gas pack, or HVAC that might be my next question
I?m not sure what that it is?
I didn?t see a H2O heater or an igniter for it? Does the oven need an igniter?

Light the kitchen and has a one of the outlet circuits hot.

The time I?ve lost power,(for days) we lived in the great room with the fire place!

You might ask the owner what their plans are in respects to truely what they think they will be doing, when the power drops out, and I'm sure you have.

 

[hurk27]

sounds like a PIA, but label each can to the limit of the CFL bulb?

something like"

"fixture supplied by a limited wattage backup power system this fixture is limited to a 13 watt CFL only"

But we know how home owners love to read instructions right:roll:

 

[George Stolz]

Bear in mind, usually there is a 200A service handling most of the house.

http://forums.mikeholt.com/showthread.php?t=118636

 

[quogueelectric]

So, I'm working on a utility interactive solar home.

In the event that the utility goes down, there will be a battery bank so that the inverter can continue to provide power to panels located downstream from it. I am in the process of determining how much / which loads the inverter can supply in that circumstance, and wouldn't mind a second set of eyes.

There will be two 240V 4500W inverters, for a total of 9000W.
There will be two panels on the load side of those inverters.

It seems to me that there is scant little that this setup will power. Am I missing something obvious?

All values with zeroes are items the HO would like to have, but I don't think he can have.

More issues are, the recessed cans are typical resi 75W incandescent cans with little 13W lamps in them, but I have made the homeowner aware that I have to handle them as though they contained 75W lamps. It's going to be a topic of contention when I tell him that although supplying every can in his house is going to be around 7A, I have to pretend as though there are 43A in cans.

9000 w is a pretty nice sized system that is almost 40 A at 240v you still have to shed loads . Gentran makes some nice panels where you can switch individual breakers from utility to generator feed I dont know if they are listed for solar. You could run most houses with 4.5k comfortably at 9kw. How do you arcfault circuits off the gen/solar?? It is getting warm in here. .............. Need about 50 panels for system like this. 600-1000$ per panel.

 

[hurk27]

9000 w is a pretty nice sized system that is almost 40 A at 240v you still have to shed loads . Gentran makes some nice panels where you can switch individual breakers from utility to generator feed I dont know if they are listed for solar. You could run most houses with 4.5k comfortably at 9kw. How do you arcfault circuits off the gen/solar?? It is getting warm in here. .............. Need about 50 panels for system like this. 600-1000$ per panel.

George I have in the past, set up small generators with the above type panels just so a homeowner can choose which loads to switch on or off when on the generator. this was a case where one house had 3 freezers, and the generator could only handle one at a time, so the home owner would let each cycle then another to keep them all from thawing out. yes it was a manual kind of set up but it was their choice because they didn't have the money to buy a larger generator, and in an emergency it was way better then not having the ability to power the freezers at all.

I would give the home owners the ability to have the choice to run the lights. I would say it is their right. if the inverters are protected against over load there is no safety problem.

I do have a problem with the requirement of the system having to be required to be sized for the whole load if there is a way to manually control shedding some of the loads, and the system is protected from overload. to me this is over protecting, and is against our rights.

 

[cschmid]

wow this is actually very small system..you only produce in the sunlight and most of time when you need it is in the months when the sun is low and short in duration the real question is how long will your battery storage system hold?? that is the real question? next is how long will it take to charge the system back up when you are still running off the system during the day? when you have 11 hours of daylight and 13 hours of darkness plus 2 hours of the daylight are not functional light on the system. Only few questions when you consider 9000 watts huge..

 

[George Stolz]

...the real question is how long will your battery storage system hold??

Around 2.5 hours at 9000W. Then the 6500W generator would be turned on to recharge the batteries.

next is how long will it take to charge the system back up when you are still running off the system during the day? when you have 11 hours of daylight and 13 hours of darkness plus 2 hours of the daylight are not functional light on the system. Only few questions when you consider 9000 watts huge..

Not much concern to me. My primary concern is staying to the NEC, and not giving in to the HO's desire to put the whole first floor onto "Critical Power" without giving thought to the load I am putting onto his system.

We worked out a deal today, but I can tell that circuits are going to be moved to the Critical Panel before my taillights are out of view.

Could I / Should I consider the duty cycle of the fridge? I can't see how that could benefit me. If the fridge were on at the same time the power went out, then I would expect the inverter to go down on overcurrent shortly thereafter, if I were counting on it being off half the time.

George I have in the past, set up small generators with the above type panels just so a homeowner can choose which loads to switch on or off when on the generator. this was a case where one house had 3 freezers, and the generator could only handle one at a time, so the home owner would let each cycle then another to keep them all from thawing out.

How did you switch from normal operation to emergency operation? I mean, most of the time all three freezers were supplied from the panel. How did you set it up so that only one of three could get power in an emergency?

Thanks for all the replies.

 

[hurk27]

How did you switch from normal operation to emergency operation? I mean, most of the time all three freezers were supplied from the panel. How did you set it up so that only one of three could get power in an emergency?

Thanks for all the replies.

These little generac transfer panels have individual manual transfer switch breakers for each circuit, they have two wires for each circuit, one runs to the original circuit breaker feeding it from utility power, and one going to the circuit feeding the load, the panel is fed via a common buss with the generator power/ inverter and flipping the breaker switch one way puts it on the utility protected by the branch circuit breaker in the main panel, flipping it the other way puts it on the generator/inverter buss protected by the local breaker, thus allowing the home owner to choose which loads to have on at a time, many come with voltage and current meters and can allow them to know when they have turned to much load on. they come 4, 8, 16 circuits with a veriaty of breaker sizes, including two pole.

simple instruction placed at the panel can direct them of this also.

Another way is if you can find 20 amp current switches, they look like a round donuts with a set of terminals on them, and are NC contacts, the operate from 3 amps up, and when you run the hot of a circuit through one it can turn off another circuit that you don't want to run while this one is running, putting one on both circuits will allow each load to come on one at a time but not both at the same time, this is a way doubling your load capacity for loads that cycle like furnace's fridges, freezers.

the only problem is they will do this on utility or backup so careful selection has to be made of the loads, unless you bypass them with a small contactor, when on the utility, it just shunts them out.

use to get them from a supplyer of industral controls, I think they were made in Japan.
I have not been able to locate them in a long while.

 

[quogueelectric]

These little generac transfer panels have individual manual transfer switch breakers for each circuit, they have two wires for each circuit, one runs to the original circuit breaker feeding it from utility power, and one going to the circuit feeding the load, the panel is fed via a common buss with the generator power/ inverter and flipping the breaker switch one way puts it on the utility protected by the branch circuit breaker in the main panel, flipping it the other way puts it on the generator/inverter buss protected by the local breaker, thus allowing the home owner to choose which loads to have on at a time, many come with voltage and current meters and can allow them to know when they have turned to much load on. they come 4, 8, 16 circuits with a veriaty of breaker sizes, including two pole.

simple instruction placed at the panel can direct them of this also.

Another way is if you can find 20 amp current switches, they look like a round donuts with a set of terminals on them, and are NC contacts, the operate from 3 amps up, and when you run the hot of a circuit through one it can turn off another circuit that you don't want to run while this one is running, putting one on both circuits will allow each load to come on one at a time but not both at the same time, this is a way doubling your load capacity for loads that cycle like furnace's fridges, freezers.

the only problem is they will do this on utility or backup so careful selection has to be made of the loads, unless you bypass them with a small contactor, when on the utility, it just shunts them out.

use to get them from a supplyer of industral controls, I think they were made in Japan.
I have not been able to locate them in a long while.

I have found and bought them on ebay for generator installs. Pretty nice panels and some had ammeters on them so you dont pull down the generator on overload.