Why "critical load panel only" when grid is down?

[kingofbanff]

I really really appreciate the comments and I'm sorry I have been muddy on my thoughts. I don't want to have everything backed up at all times. When my 13 kW system is bathed in sunshine and the grid is down I would like to have the option to use that power to run any of my normal needs. If my battery bank is full and it's daylight so I'm not running any lights it would be great to run my attic fan or my dishwasher or my laundry or my power saw.
What I seem to be reading here is I will only be allowed by my electrical inspector to have a critical load panel that can be supported just by my batteries regardless if I have 10kw coming out of my modules. So due to not wanting a gazillion batteries I'll just have to let a lot of electricity go to waste on a sunny day if the grid is down.
Is that right?

[gmanInPA]

You're killing yourself to get "everything backed up", but this isn't feasible unless budget and effort are both inexhaustible. With a hybrid inverter, batteries, generator, and pv, you can still get your whole house backed up but in a reasonable fashion. Several of us here are living with such systems.

Think about this... Why have your non-critical loads backed up with batteries? If you did so and decided to run your oven in a power outage - you'll beat your batteries senseless and one or more large inverters will be needed. That's just for the oven. You'll get far better options by finding alternative ways of accomplishing your non-critical functions without power than trying to run them off batteries. Example... Instead of getting 6 tons of batteries that cost $20k so you can run the oven in a power outage - get a wood or propane cook stove for $2k.

[ButchDeal]

In your diagram are the only backed up loads the "essentials panel"? It looks as though once the grid goes down the main panel is dis-connected from the inverter.
One of my requirements is to not have to rewire and thus have everything backed up. Thanks

Get another designer. Besides all the problems mentioned so far it will not work anyway. AC1 will go down if disconnected from the grid. You are finding it hard to do what you are trying to do because it can't be done.

[gmanInPA]

You might seek a second opinion on the wiring up of a critical loads panel if you're bent on going the solar route. An electrician might have better ideas about such then a designer.

[Mike90250]

......

The designer proposes a 200 amp contact switch in between the meter and the main panel. When the grid goes down the switch prevents the back feeding of the grid.....

DANGER DANGER

A home-brew transfer switch is NOT acceptable. You can ONLY use a UL certified transfer switch, That switch is usually internal to the Solar GT inverter.
if not, that DIY switch is not an accepted device, There are " generator Lock-Out" gates that fit over 2 pairs of breakers in a panel, to switch a house from grid to generator power, but these are designed to only allow one or the other, with no chance of both happening.

Your "designer" (or your interpretation of his design) is flawed

[Sunking]

In your diagram are the only backed up loads the "essentials panel"? It looks as though once the grid goes down the main panel is dis-connected from the inverter.
One of my requirements is to not have to rewire and thus have everything backed up. Thanks

City of Denver is not going to sign off on your plan. By code you must rewire your home for an emergency panel. With a Genny, no rewiring, no batteries to replace every few years, no expensive Hybrid inverter, and no limitations on power.

[kingofbanff]

Attached is the more conventional/safer way to do it. [ATTACH=CONFIG]n308361[/ATTACH]

In your diagram are the only backed up loads the "essentials panel"? It looks as though once the grid goes down the main panel is dis-connected from the inverter.
One of my requirements is to not have to rewire and thus have everything backed up. Thanks

[Sunking]

Get a genny and ATS. Everything works in your home while you kick back, relax, and watch your neighbors suffer. Lot less expensive than your way with extremely limited power.

[jflorey2]

Thoughts?

Attached is the more conventional/safer way to do it. inverter.bmp

[jflorey2]

The designer proposes a 200 amp contact switch in between the meter and the main panel.

What is a "contact switch?" Do you mean relay? If so then the relay needs to be a 200 amp 4PDT relay that does two things:

1) One gang switches between utility feed (when energized) and inverter feed (when de-energized.) The armature connects to the busbar in the load center. This prevents backfeeding.
2) Another gang switches between AC out from the panel (when energized) and open circuit (when de-energized.) The armature connects to inverter AC in. This prevents the inverter from trying to charge its batteries from its own AC output.

These can also be two separate relays as long as they are driven by a common source. That source should be a PROTECTED circuit on or near the meter.

Of course the above description is just a long-winded way of saying "automatic transfer switch" of which there are plenty on the market. You can get one for about $500.

[kingofbanff]

Well I'm back again after some huddling with the designer/ installer. It was going to be prohibitively expensive to do the rewiring of panels that the previous iteration required. So the latest idea is much less elegant but appears to address my concerns.

For those who have just joined: I'm installing 13kw and want to be able to use all that power even if the grid is down which means I want to selectively turn on circuits when the sun is shining. I have 19kwh of batteries. I don't want them getting emptied running items like in floor heating or the oven if the grid goes down while I'm out of the house and just turned the oven on.

The designer proposes a 200 amp contact switch in between the meter and the main panel. When the grid goes down the switch prevents the back feeding of the grid. The batteries are feeding the main panel which will drain them quickly. We will set the controller on the Outback Radian to only allow a DoD of 20%. So then when I realize the grid is down it is up to me to manually trip all the breakers that I don't want drawing from the batteries. Then I reset the DoD to 50% to run my current critical loads. When the sun is shining I can run more of the house.

Thoughts?

[Sunking]

I agree with @ButchDeal... If you have a generator backing up the inverter, and you have an auto start generator module, you can just have the generator start up to support the loads that the batteries would otherwise not support very long. Doing so you can avoid the whole switched panel idea and the manual process of switching it over. These hybrid inverters can be setup to be quite smart.

That is the way it is meant to work. Otherwise you spend a fortune on batteries and replacement cost. Small inexpensive batteries to carry a light load for a short time, and genny to do the real work. Much less expensive intially and long term with better reliability. If batteries were the right answer telecom, military, and mission critical applications would use it.

[gmanInPA]

I agree with @ButchDeal... If you have a generator backing up the inverter, and you have an auto start generator module, you can just have the generator start up to support the loads that the batteries would otherwise not support very long. Doing so you can avoid the whole switched panel idea and the manual process of switching it over. These hybrid inverters can be setup to be quite smart.

[inetdog]

thanks again ButchDeal
Can you point to an article on how panels are sized? I have 200 AMP service currently. However, if I add up all the breakers they are way over 200A. Obv I don't run every single load at max Amps simeltaneously. So I figure there is some formula they use...that way I can figure how many circuits I can put on my critical load panel given the two outbacks have a combined max of 50Amps.
thanks

The relevant article is called the National Electrical Code.
It has detailed guidelines for calculating the expected load on a feeder or service, and it does not involve adding up the breakers, not does it even involve adding up the actual current drawn by all connected loads. There are service factors which take into account that not everything will be running at once.

[kingofbanff]

If you have the generator connected with auto start you likely could have quite a bit on the critical load panel without the need for the interlock and switchable loads unless you plan for it to be way over inverter breaker size. l.

thanks again ButchDeal
Can you point to an article on how panels are sized? I have 200 AMP service currently. However, if I add up all the breakers they are way over 200A. Obv I don't run every single load at max Amps simeltaneously. So I figure there is some formula they use...that way I can figure how many circuits I can put on my critical load panel given the two outbacks have a combined max of 50Amps.
thanks