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

[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.

[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.

[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

[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]

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?

[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...

[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.

[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.

[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.