sort of an add on to the CA thread

[petersonra]

just curious. If I understand things correctly, the vast majority of installed residential solar PV can't be used if the grid is down. so people are going to have all these PV modules in full sun when the grid craps out, but can't make power from them.

Is there some relatively simple way to get around this limitation of residential PV systems?

I am thinking if there is, someone is going to make a ton of money installing such modifications in CA.

 

[zbang]

Isn't this what the powerwall+ is supposed to do?

I can't see a "simple way" that doesn't include a real transfer switch and a frequency/voltage reference to trick the inverters into operating.

 

[winnie]

The SMA Sunny Boy inverters include a 'secure power outlet'. These get around the stability problem )how do you maintain output when solar input drops) by making the output much smaller than the PV capacity, and then ignoring the remaining stability issues.

Oh, and this doesn't work if you have panel level rapid shutdown.

Personally I expect more DC coupled loads in the future. Why take solar DC, convert to AC and then rectify to DC and back to AC in the heat pump inverter, for example.

Jon

 

[GeorgeB]

just curious. If I understand things correctly, the vast majority of installed residential solar PV can't be used if the grid is down. so people are going to have all these PV modules in full sun when the grid craps out, but can't make power from them.

Is there some relatively simple way to get around this limitation of residential PV systems?

I am thinking if there is, someone is going to make a ton of money installing such modifications in CA.

As @zbang said, Tesla powerwall is that, but unique to Tesla. Enphase offers Encharge but is is unique to their newer IQ inverters, not older units. The solar firm and electrician used their M215s on my home now 6 years ago.

 

[wwhitney]

As @zbang said, Tesla powerwall is that, but unique to Tesla. Enphase offers Encharge but is is unique to their newer IQ inverters, not older units. The solar firm and electrician used their M215s on my home now 6 years ago.

I believe M215s can now get a firmware upgrade to work with Encharge:

Enphase Storage for M-series microinverters | Enphase Storage

Enphase Solar systems with M215 and M250 microinverters are now fully compatible with Enphase Storage through a quick upgrade process.

enphase.com

Cheers, Wayne

 

[GeorgeB]

I believe M215s can now get a firmware upgrade to work with Encharge:

Enphase Storage for M-series microinverters | Enphase Storage

Enphase Solar systems with M215 and M250 microinverters are now fully compatible with Enphase Storage through a quick upgrade process.

enphase.com

Cheers, Wayne

Thanks for that. In MY case, I won't do it for a combination of financial and environmental reasons; 2 outages over 2 hours in 8 years here. The value isn't there. I survived the long outages, luckily in moderate weather, with a portable gasoline generator and extension cord to our refrigerator and freezer. We have a gas stove which can be lit with a match, so cooking was ok. The oven relies on electronic controls so isn't available.

I've not put my scope on the generator output; I keep hearing horror stories of equipment failures from the atrocious PQ from them so haven't looked into a transfer switch installation or one of those plug-in-to-the-dryer-outlet abominations.

 

[ggunn]

just curious. If I understand things correctly, the vast majority of installed residential solar PV can't be used if the grid is down. so people are going to have all these PV modules in full sun when the grid craps out, but can't make power from them.

Is there some relatively simple way to get around this limitation of residential PV systems?

I am thinking if there is, someone is going to make a ton of money installing such modifications in CA.

You understand correctly; the purpose of grid tied PV is to reduce or eliminate the net consumption of energy from the grid, not to replace it in case of an outage. A PV system that will power a house during an outage is certainly possible, but it will be a lot more expensive, so such a system will very likely never pay for itself in purely economic terms.

 

[wwhitney]

A PV system that will power a house during an outage is certainly possible, but it will be a lot more expensive, so such a system will very likely never pay for itself in purely economic terms.

Under the current market we have with its various failures. Which range from on the one hand unpriced pollution to on the other hand the lack of a capacity market in Texas.

Cheers, Wayne

 

[petersonra]

It will be "interesting" to watch how this plays out over the next few years.

 

[pv_n00b]

just curious. If I understand things correctly, the vast majority of installed residential solar PV can't be used if the grid is down. so people are going to have all these PV modules in full sun when the grid craps out, but can't make power from them.

Is there some relatively simple way to get around this limitation of residential PV systems?

I am thinking if there is, someone is going to make a ton of money installing such modifications in CA.

Due to the components used in the typical grid-tied system converting it to a backup system is usually not possible without replacing at least some major component, like the inverter. But for most people with the typical grid uptime in the USA, having a backup system just does not make much sense. I've lost power in my area in CA for maybe an hour in the last year and a half, how much would I have to pay to have backup power during that hour? Probably a lot more than I would be willing to pay. Now someone living in an area with significant and long power outages, like the southeast US, might be a better candidate for a backup system. If the power goes out for a few days or a week, then the extra cost will be offset significantly by keeping the refrigerator and freezer running and HVAC working.
Going forward it does seem like proposed rate structures will heavily favor non-export PV systems. Tariffs in Hawaii already make storage a requirement for new residential PV systems since selling energy to the utility does not pay off. But even then most of the PV+storage systems do not have a backup mode, they only perform time-shifting, storing energy during the day and releasing it in the evening. They still require a grid connection to operate. Installing the additional components to have a backup system adds costs that most people are not interested in paying if they have a high grid uptime in their area.

 

[wwhitney]

But even then most of the PV+storage systems do not have a backup mode, they only perform time-shifting, storing energy during the day and releasing it in the evening.

I'm curious about this statement. If there are batteries, the extra functionality to work off grid are (a) a microgrid interconnect device (grid disconnect relay) and (b) the battery inverter needs to be dual mode, capable of island operation. My product knowledge is not so broad, but the two main options I'm aware of are Tesla Powerwall 2 and Enphase Enstorage, and they both offer those options. Perhaps there are a lot of previous generation products out there I'm unaware of?

Cheers, Wayne

 

[petersonra]

You understand correctly; the purpose of grid tied PV is to reduce or eliminate the net consumption of energy from the grid, not to replace it in case of an outage. A PV system that will power a house during an outage is certainly possible, but it will be a lot more expensive, so such a system will very likely never pay for itself in purely economic terms.

It would be nice to be able to use that generating capacity locally during the many times the grid will be going down in CA, even without storage capability.

 

[zbang]

the many times the grid will be going down in CA

That comes across as unfounded paranoia. For "the grid" to "go down" would mean many (hundreds?) of transmission lines all being out of service at once; not likely. Yes, some areas do have outages, but lots of areas have very reliable supplies.

 

[petersonra]

That comes across as unfounded paranoia. For "the grid" to "go down" would mean many (hundreds?) of transmission lines all being out of service at once; not likely. Yes, some areas do have outages, but lots of areas have very reliable supplies.

It is a very good bet that the grid will be shutting off power to a lot of people in CA the next decade or so. It does not matter if it is just one home. For that home it is a grid down situation whether the grid is off deliberately or because it crashed, nor does it matter how many others are down.

Given the state has shown no ability to effectively manage a relative handful of producers, I see no reason to believe they can effectively manage millions of electricity producers.

 

[zbang]

It sounds like you're comparing apples to artichokes- What is this "the grid" that you're talking about?? If you mean the PoCo's, just say so. Or the CAISO. PG&E is doing it's "public service power shutoffs" in an attempt to prevent starting more fires, butthose generally only affect more rural areas. Or are you talking about the famed "rolling blackouts" which are directed by the CAISO due to projected demand greater than supply?

If you mean that you expect more people to experience outages in the future, that's a whole lot more descriptive that say that "the grid turns them off"- "the grid" does nothing of the kind, more likely a tree falls over the service lateral (or similar).

 

[pv_n00b]

I'm curious about this statement. If there are batteries, the extra functionality to work off grid are (a) a microgrid interconnect device (grid disconnect relay) and (b) the battery inverter needs to be dual mode, capable of island operation. My product knowledge is not so broad, but the two main options I'm aware of are Tesla Powerwall 2 and Enphase Enstorage, and they both offer those options. Perhaps there are a lot of previous generation products out there I'm unaware of?

In order to have the PV + BESS system work in an island mode, there needs the be a way to isolate the home wiring from the grid, load shed since most systems are not designed for whole-house backup, and the PV inverter output needs to be controllable so it can be reduced if the PV production exceeds load. All these costs are over and above what a grid-connected system costs. The system you describe would allow the battery to supply the whole house with power but would not allow the PV system to recharge the battery or provide power. Without load shedding and the PV system to supply power, the average home-sized battery would probably discharge in a couple of hours and that would be it until the grid came back up.

 

[petersonra]

It sounds like you're comparing apples to artichokes- What is this "the grid" that you're talking about?? If you mean the PoCo's, just say so. Or the CAISO. PG&E is doing it's "public service power shutoffs" in an attempt to prevent starting more fires, butthose generally only affect more rural areas. Or are you talking about the famed "rolling blackouts" which are directed by the CAISO due to projected demand greater than supply?

If you mean that you expect more people to experience outages in the future, that's a whole lot more descriptive that say that "the grid turns them off"- "the grid" does nothing of the kind, more likely a tree falls over the service lateral (or similar).

I would be willing to bet in the not too distant future that gird off situations will be more common and have little to do with trees falling on wires.

 

[wwhitney]

In order to have the PV + BESS system work in an island mode, there needs the be a way to isolate the home wiring from the grid, load shed since most systems are not designed for whole-house backup, and the PV inverter output needs to be controllable so it can be reduced if the PV production exceeds load.

Good points on the load shedding and the PV throttling. The latter is generally done by frequency shifting, and I think that's supported by current products (not sure if it's a current listing requirement). As to load shedding, that's certainly required for non-technical homeowners and when there are large motors that normally start automatically (e.g. single speed or dual speed HVAC equipment).

I'd say this is definitely a rapidly evolving sector at the moment. The load shedding is still a bit troublesome to implement, I think.

Cheers, Wayne

 

[analog8484]

Thanks for that. In MY case, I won't do it for a combination of financial and environmental reasons; 2 outages over 2 hours in 8 years here. The value isn't there. I survived the long outages, luckily in moderate weather, with a portable gasoline generator and extension cord to our refrigerator and freezer. We have a gas stove which can be lit with a match, so cooking was ok. The oven relies on electronic controls so isn't available.

I've not put my scope on the generator output; I keep hearing horror stories of equipment failures from the atrocious PQ from them so haven't looked into a transfer switch installation or one of those plug-in-to-the-dryer-outlet abominations.

You may want to consider an inverter generator for clean power. Recent prices have dropped significantly.

 

[gadfly56]

You may want to consider an inverter generator for clean power. Recent prices have dropped significantly.

I recently made the mistake of looking at the specs for my CyperPower 1500VA UPS. THD of 40%!!!