Whats more energy efficient: Off-grid or Grid-tie ?

[Hedges]

The California market is probably bigger than the entire Australian market and regulations/approvals/restrictions are fairly consistent througout the state so I am not sure that is the issue. I wish it were as simple as you suggest.

One California contractor (who I bought some surplus PV hardware from) stopped doing PV work because every city had different rules. Too much effort for what the business was worth.

If enough cities relinquish authority to SolarAPP+, it would be simplified (Federal on-line design entry to inspection checklist, electronically transferred to AHJ). I understand Australia is even more red-tape free.

That was not the case in my Owner builder permit. It took less than ten days.

Scheduling 10 days out would work for companies. But how many man-hours on your part and government's part?

 

[DIYrich]

This is speculation on my part, but I suspect a strong motivation of this plan is grid Black Start scenarios where they can need as much as 2x the normal KW to be able to restart the grid after a black out. But I'm sure it can also help them for transient load spikes. In the winter on workdays when there's are big storms, I bet they get big spikes in demand at the typical wake up time for people.

Definitely not Black Start of the grid. That requires restarting a plant while disconnected from the grid, energizing transmission lines to get other plants online, and then slowly adding load and production. Your ess won't help because it is at the last step. They have designated plants with diesel generators to do the black Start.

Your ESS program is similar to CT. It is for summer peak (and winter in newengland for electric heat) where it is cheaper to pay for your power (net metering) than the spot price when all the other utilities are looking for power.

 

[wpns]

The power company where I live in North Carolina just started a plan where they will give anyone with a qualifying ESS system a monthly bill credit for the right to use your ESS system a certain number of times a year to support the grid in emergency situations. They have to send you a request ahead of time and you are allowed to say no a certain number of times a year. And to be clear, you get the credit every month whether they actually use it or not. They are basically paying you every month to have the option to use it. And unlike net metering credits that can only offset other power usage, these credits can offset any charge including taxes and fixed charges. And if you accumulate a negative balance, you can request they send you a check.

The amount of the credit is based on the KW's your system can produce to support the grid. As an example, a single Powerwall 3 which can generate 11.4k of power back to the grid gets you a $54 a month credit. The plan will allow up to $600 a month in credits. They don't care how many KWH of energy storage you ESS has. So clearly this is for very short-term support of the grid.

This is speculation on my part, but I suspect a strong motivation of this plan is grid Black Start scenarios where they can need as much as 2x the normal KW to be able to restart the grid after a black out. But I'm sure it can also help them for transient load spikes. In the winter on workdays when there's are big storms, I bet they get big spikes in demand at the typical wake up time for people.

Nice! Of course, there's a question of the timeliness of their request and your response time, if it's "hey, can we have an extra 20KW tomorrow afternoon" that's different from "please give us 20KW right now automatically".

Neither of those will work for grid black start, UL1741 won't let you put power into a dead grid.

 

[Ampster]

They have designated plants with diesel generators to do the black Start.

Years ago I took a tour of an SCE hydro facility and they had a similar issue except they had a small generator with permanent magnets hooked up to a jet and a simple water wheel to be used to excite the coils in the big turbines if they ever had to do a Black Start.

 

[jpwhit]

Definitely not Black Start of the grid. That requires restarting a plant while disconnected from the grid, energizing transmission lines to get other plants online, and then slowly adding load and production. Your ess won't help because it is at the last step. They have designated plants with diesel generators to do the black Start.

There is a step in the Black Start process where ESS will definitely help. When the power has been off more than 30 minutes, then the loads from HVAC, refrigerators, and anything else that cycles on and off periodically in all the homes will come on as soon as the grid is energized. That results in restarting the grid taking much more power than normal. And because the US grid has very limited smart switching equipment installed currently, the power companies can't easily segment the large sections of grid without sending people out to manually throw switches. During storm events, they just don't have the manpower to do that very quickly. So being able to call on ESS systems to contribute power shortly after the grid waveforms are re-established is very beneficial for black start scenarios.

Yes, the grid today has diesel generators for black start, but there aren't enough, and they are very expensive to maintain. So, the power companies would rather not have to deploy more in the future. Especially as they continue to roll out more and more automated switching technology. As automated switching technology allows for black start scenarios to be done with smaller and smaller segments of the grid, having large diesel generators more distributed through the grid is not a cost-effective solution. So being able to call on residential ESS systems distributed through the grid is one of the things the National Renewable Energy Laboratory (NREL) has been modeling and testing.

 

[jpwhit]

Nice! Of course, there's a question of the timeliness of their request and your response time, if it's "hey, can we have an extra 20KW tomorrow afternoon" that's different from "please give us 20KW right now automatically".

Neither of those will work for grid black start, UL1741 won't let you put power into a dead grid.

UL1741 isn't a problem because they don't need ESS to re-establish the waveform, they need it to handle the surge that happens typically 1-5 minutes after the grid waveform is re-established. Most equipment in homes with compressor like HVAC, freezers, and fridges have timers that last from 1-5 minutes after the power comes on before the compressors try to start.

Like other similar programs, I expect the authorization process happens a day or two before storms and other weather events where outages and high demand are expected.

 

[Hedges]

But under UL1741, any inverter operating in parallel with grid (like ESS) will wait and watch grid for 5 minutes before feeding it.
Only if A/C thermostat waits more than 5 minutes would they be of any help.

What is the response time of ESS? Do they try to supply surge and reduce peak drawn from grid, or ramp up only to supply steady-state?

Rather than deploying explody batteries in millions of houses, random delay timers could be installed in those heavy loads. But where's the money in that?

 

[DIYrich]

There is a step in the Black Start process where ESS will definitely help. When the power has been off more than 30 minutes, then the loads from HVAC, refrigerators, and anything else that cycles on and off periodically in all the homes will come on as soon as the grid is energized. That results in restarting the grid taking much more power than normal. And because the US grid has very limited smart switching equipment installed currently, the power companies can't easily segment the large sections of grid without sending people out to manually throw switches. During storm events, they just don't have the manpower to do that very quickly. So being able to call on ESS systems to contribute power shortly after the grid waveforms are re-established is very beneficial for black start scenarios.

But, most ESS systems would be supporting their own load (islanding). Most won't reconnect to the grid for a few minutes until it stabilized (past the startup time for all the HVAC, etc.). You would need special logic to force a reconnect during the unstable time, and subject your house to the instability.

Yes, the grid today has diesel generators for black start, but there aren't enough, and they are very expensive to maintain. So, the power companies would rather not have to deploy more in the future. Especially as they continue to roll out more and more automated switching technology. As automated switching technology allows for black start scenarios to be done with smaller and smaller segments of the grid, having large diesel generators more distributed through the grid is not a cost-effective solution. So being able to call on residential ESS systems distributed through the grid is one of the things the National Renewable Energy Laboratory (NREL) has been modeling and testing.

They don't need that many diesel generators. The Transmission network connects most generation plants, and those can be easily isolated from the distribution system (existing load shedding circuits). They only need to black start one plant, and use the transmission system to bring up other plants. That is why one plant is designated to maintain the expensive diesel generator.

Don't know how difficult it is to phase align two disconnected sub-grids (multiple black start sites). They must do it all the time when parts of the grid disconnect. Or, is there some way the disconnected pieces stay in-phase.

I believe the reason for the diesel generator is the difference between generators and alternators. Alternators require an excitation circuit (which requires power) to generate electricity. A generator does not. So, the diesel generator starts first, and its power is used to excite the main turbines and get them to generate electricity.