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

[jflorey2]

Well hopefully for the top dollar I am paying, my installer will make sure that the mate3 is doing all this cool stuff.

Don't assume that; many installers have little to no experience with hybrid grid tie no matter how good their sales pitch.

[kingofbanff]

Nope, charge controllers only control charging.
What you have to do, is to program the inverter to start selling after the controller hits ABSORB and then your excess PV goes to the Grid. It can get pretty technical getting all the settings to play well together.

Well hopefully for the top dollar I am paying, my installer will make sure that the mate3 is doing all this cool stuff.

[Mike90250]

I am getting FlexMax 80's so I assume they will do this.
So if the batteries are not fully charged will the FlexMax send "x" power to the batteries and any excess they cant handle will go through to the loads and then the grid?

Nope, charge controllers only control charging.
What you have to do, is to program the inverter to start selling after the controller hits ABSORB and then your excess PV goes to the Grid. It can get pretty technical getting all the settings to play well together.

[MetricAmerica]

It is not only if your system can handle the whole house, it probably can, but how many hours or days, your battery/solar system can preform before getting to 50% of rated battery usage, you don't want to go further down... That is reason why subpanel has smaller load... And if you go further without mains down you going to need a gas generator to supply house and to charge batteries back up...

[kingofbanff]

Too high of a charging current can damage a battery. So a large array needed to harvest winter sun, is too large for summer clear weather. Many charge controllers can be programmed to limit charge current for this reason.

I am getting FlexMax 80's so I assume they will do this.

So if the batteries are not fully charged will the FlexMax send "x" power to the batteries and any excess they cant handle will go through to the loads and then the grid?

[Mike90250]

Too high of a charging current can damage a battery. So a large array needed to harvest winter sun, is too large for summer clear weather. Many charge controllers can be programmed to limit charge current for this reason.

[kingofbanff]

. I too had no idea when I started, but "ripple current" is a crucial factor to keep in mind when sizing a battery. My first set of batteries were about 370 ah @ 48 V, and even at that size did fine for me, but I had to actually limit the PV input at certain times as the system was battery limited.

Hi welcome to these forums and thanks for your thoughts on this thread. Could you explain about limiting the PV input?

Thanks

[sub3marathonman]

OK, maybe a bit late to this topic, but I've usually been over at Arizona Wind & Sun forum, and just found this site.

Now, I can speak from experience, as I have done this, just not at 13kw of PV, but 4.7kw. When I did mine, a 13kw system would have been just about $100K, more than I could put in. It is spectacular to see it is now within reach for people. I'm itching to add another 9kw or so too.

First, a Critical Load Panel is required, not so much because the output of your PV panels is limited, but the output of your battery is limited. And maybe it could do it in full sunlight, but at night running a 10kw heater and a 6kw oven, your TV, refrigerator, and of course heated pool would be a death sentence for the batteries. I too had no idea when I started, but "ripple current" is a crucial factor to keep in mind when sizing a battery. My first set of batteries were about 370 ah @ 48 V, and even at that size did fine for me, but I had to actually limit the PV input at certain times as the system was battery limited.

Now, some talk like these are AA batteries and might run an LED light or two for an hour. I have heavy duty 700 ah @ 48 V batteries, and can run my critical load panel which includes one 3 ton A/C unit, rated 24 SEER, my hybrid GE water heater, two refrigerators, a microwave, and lights for two rooms and a bathroom. It might be pushing things to run everything at once, but I have managed to do this as a test for several weekends. In fact, I wanted to be able to go "off-grid" with this critical load panel, which I informed the local electric company when they were attempting to institute a what I considered unfair demand rate requirement for people with PV. To their credit, the electric company did listen to my concerns and logic, and although they instituted a demand rate, it is only for on-peak times, which is fair.

Also, a generator is just money invested that sits there, needing to be maintained, until needed. I put the money into the PV system, which also allowed me to switch to a TOU rate plan, and now actually a TOU demand rate plan, where I get electricity at about 60% of the regular price. So I am saving on every kwh I do use, such as for my LEAF, and have managed to keep the electric bill to about $70 in the winter here in Florida, and about $120 or so in the summer.

In the end too, it isn't just about economics, although that of course has to be a factor. It was about clean energy, being prepared for a future week or two grid outage, and even more of a total lifestyle commitment.

[Djcoak]

Naive, I don't think so but if you'd have said it was none of my business, I'd have no argument with that.

I was only giving him a little guff because I've lived about 30 miles from his location most of the past 50 years and can't remember ever having the power out for more than a few hours once every 5 or 10 years or so. We have different pocos but live in almost identical climatic conditions except the wind here in Boulder county is probably a lot worse. Maybe kingofbanff's poco situation is bad though (I'd be surprised), or maybe he's just got cash burning a hole in his pocket. Doing what he's doing just seems extreme to me. I know of no one else around here who's worried about it. I was only suggesting that he reconsider how important it really is before charging down the path...

Extreme, I agree, sorry I came off like a jerk. My back up system and solar needs ar so much less. Heat, water and fridge. Other than that I can work around things.

[DaveDE2]

seems fairly naive. Although his goals seem lofty, to just wait it out is what most the population will do, till it doesn't come back for a day, a week, 2 weeks...... Been in two situations with no power, once for two weeks during an ice storm and a week after sandy. Better prepared than not

Naive, I don't think so but if you'd have said it was none of my business, I'd have no argument with that.

I was only giving him a little guff because I've lived about 30 miles from his location most of the past 50 years and can't remember ever having the power out for more than a few hours once every 5 or 10 years or so. We have different pocos but live in almost identical climatic conditions except the wind here in Boulder county is probably a lot worse. Maybe kingofbanff's poco situation is bad though (I'd be surprised), or maybe he's just got cash burning a hole in his pocket. Doing what he's doing just seems extreme to me. I know of no one else around here who's worried about it. I was only suggesting that he reconsider how important it really is before charging down the path...

[Djcoak]

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?

i don't understand why you feel these are needed items. Do you not understand the situation you will be in during a long term power outage? You'll live without AC, do the dishes by hand and get a grill for cooking. Honestly the other items are nice but you're ignoring the advice being given to you. The laundry I get but the others I don't. Attic fan, Really???? Stop being a selfish yuppy and understand that your not going to get all the extras in the system you want and are not needed in an EMERGENCY
Geez.

[Djcoak]

Guest How often does your grid power go out? Is it worth worrying about? Geez, the last time that happened here I think I fell off my dinosaur. If and when it does, good time to go for a run or take the dog for a walk till it comes back up.

seems fairly naive. Although his goals seem lofty, to just wait it out is what most the population will do, till it doesn't come back for a day, a week, 2 weeks...... Been in two situations with no power, once for two weeks during an ice storm and a week after sandy. Better prepared than not

[inetdog]

Some hybrid inverters support the loads all the time, and then direct the surplus toward the "grid". If the inverter is in a branch circuit from your main panel, then the "grid" includes the main panel and the surplus power is available to the demands on the main panel. After those demand are met (if) the power is fed to the utility. The only time the inverter cannot direct surplus power back to the main panel in this scenario is when there is a loss of grid power. This is a purposeful feature of hybrid inverters to prevent harming line workers.

You can self-consume all your pv power - except during a grid outage at which point you can only consume power for your critical loads.

And the way that they make it safe is with an internal transfer switch that disconnects the inverter output, and the critical load panel that remains connected to it, from the AC in (AC1 in) terminals when the grid goes away.
This is an automatic function, unlike the manual switching the OP is proposing to use.

[gmanInPA]

Some hybrid inverters support the loads all the time, and then direct the surplus toward the "grid". If the inverter is in a branch circuit from your main panel, then the "grid" includes the main panel and the surplus power is available to the demands on the main panel. After those demand are met (if) the power is fed to the utility. The only time the inverter cannot direct surplus power back to the main panel in this scenario is when there is a loss of grid power. This is a purposeful feature of hybrid inverters to prevent harming line workers.

You can self-consume all your pv power - except during a grid outage at which point you can only consume power for your critical loads.

[jflorey2]

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.

Why the heck not? You can get an electrician to put in a second panel (and relocate all your critical loads) for $500-$1000, less than you will spend on all that other stuff you are listing. You are already saying things like "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" - that means there are loads you don't want drawing power. Those stay on the main panel. Your critical loads stay on the essentials panel. And then the system is foolproof - and more importantly, will actually be legal and safe.

And the bonus is that once you do this you don't even need a transfer switch. It's built in to the inverter.