NERC sounds alarm on solar tripping in ‘sobering’ summer reliability report
utilitydive.com
utilitydive.com
This is entirely the electricity grids own doing. They told everyone who wanted solar that they must use inverters that are super safe and self disconnect if anything unexpected happens. The regulations were written super tight, with frequency limits, harmonic limits, reactive power limits, rate of change of frequency limits, residual current limits, DC injection limits and vector shift detection requirements, presumably because rulemakers were hoping that having a massive thick rulebook would make rooftop solar too expensive. Unfortunately for them, all the complexity is pushed to software, and when that's written once it can be deployed lots almost free.
Fast forward 10 years, and this stuff is widely deployed, meeting all the very strict criteria. Except the grid only stays within those strict limits during the good times. When the grid is stressed, for example low frequency due to insufficient generation, it will go outside the frequency limit, and all rooftop solar generation statewide will disconnect all at once. And now the grid has lost gigawatts of solar production, making a minor incident far far worse. The end result is a cascading failure and within a matter of seconds half the state has a blackout.
Smart rulemakers back in the 2010's would have dropped islanding protection, and vector shift protection (they actively destabilise the network). They would also remove underfrequency protection (again - destabilises the network) and slacken substantially undervoltage protection.
The only protections important to leave in are rate of change of frequency (upwards only), overfrequency, and overvoltage.
What's ironic is there is a more sensible requirement they could have required to make rooftop solar cost more and add substantially to grid stability. They could have required solar systems have a load line equivalent to coal. That pretty much means if the grid frequency decreases, the solar systems must output more power. But solar can't output more power than the sun provides. So in turn, to meet this requirement all solar systems would have to be constantly throwing away say 10% of capacity, so that it could be delivered if and only if the frequency suddenly dropped.
The rulemakers were expecting solar to be a failure and there to never be anything more than a handful of geeks with it installed. The problems only become major when 1+% of statewide generation is solar. 1% is (very approximately) the amount of generation an electricity grid can suddenly lose without failure.
https://www.iso-ne.com/static-assets/documents/committees/co...
https://www.solarpowerworldonline.com/2019/03/smart-inverter...
Grid forming inverters (versus the traditional grid following) are at the finish line of being proven, and paired with distributed storage providing ancillary services (including frequency response), regulators simply need to be dragged to the present to solve for this (distributed energy orchestration, rapid system segment isolation and recovery during transient events [“self healing” for the marketing folks], etc). This is one of those tug of wars between very conservative regulators and a quickly innovating industry (DER power controls).
https://www.energy.gov/eere/solar/articles/powering-grid-for...
https://www.nrel.gov/news/features/2020/renewables-rescue-st...
During sun, a site can island with perfect 60Hz AC power from the ASIC-driven IQ8. No battery –– and certainly no grid –– needed.
The system is not yet configured to support solar only utility disconnected operation due to supply chain issues (additional components, rush to PTO), so I cannot speak to surge start capability of the IQ8+ micros in island mode.
AC is a difficult load. Get the inrush current here: https://www4.enphase.com/en-us/support/faq/how-support-hvac-... and you will be able to figure it out.
Your refrigerator will be fine. Its locked-rotor amperage requirements are small compared to AC.
We also moved the house entirely to heatpumps. They practically sip energy for cooling.
https://www.sma.de/en/partners/knowledgebase/sma-inverters-a...
I’m genuinely unsure what purpose anti-islanding actually serves.
(My inverter is moderately intelligent and formed a one-house microgrid all by itself. That being said, this capability may be at odds with helping the grid survive a major disturbance. When my inverter decides to disconnect from the grid, it cannot support the grid regardless of what its software and the regulators think.)
[0] By which I mean line workers at a company that PG&E contracts with to maintain their distribution network. Apparently PG&E outsources real work. Go figure.
I think it mostly prevents inverters from trying to destroy themselves feeding into a dead short, or creating weird instabilities - the grid segment is either up or down from the inverter's point of view. Any sane inverter will detect it's trying to feed a dead short and shut down. And if you're grid tied and your grid segment is down, it looks like a dead short.
It's a useful enough filter for people who understand power systems and power system work, because, as your linemen pointed out, if safety is a question, the workers simply create a bolted short across all the phases and neutral, and you're not simply not going to make that ring.
And, yes, migratory line workers are a thing. I don't get it, but relatively few people I've talked to out here (Idaho Power territory) actually work for Idaho Power - it's mostly migratory contract workers doing the power pole inspections and such.
Because a typical solar inverter can't handle transient loads. It just spits out whatever power is coming in from the panels. It can't shed if too much is coming in and it can't magically create power to fix a shortfall. The power has gotta go or come from somewhere.
If you have a battery you can soak the transient load and disconnect from the grid and operate as an island but without the grid to act as a buffer for the load the inverter is useless on its own.
I am curious how SolarEdge’s inverters reduce output, though. It’s not fundamentally hard, but the inverter does not have appear to have a particularly high speed data connection to the MPPTs, and I haven’t found the underlying mechanics documented anywhere. I’m guessing that the inverter pulls the incoming voltage down such that the MPPTs hit their preprogrammed output current limits and curtail production.
(SolarEdge’s system can’t just dump excess power into a battery — their common configurations have the battery behind a DC-DC converter with considerably lower capacity than that of the inverter’s output. The DC-DC can’t fully absorb the solar string’s output if the sun is shining and an island’s load goes away. The battery itself likely could, at least for a little while, but there isn’t any way for the power to get there.)
Scroll up to read about the HNer required to carrying $1M in insurance for having more than 10kW in solar on their roof, which is just...insane. Solar is mired in bullshit to make it seem dangerous, make it look ugly, make it as complex and expensive to install as possible. That's how you end up with regulations requiring what looks like an electrical substation on the side of your home, covered in neon-colored labels. Gotta make sure someone knows the system is "RAPID SHUTDOWN EQUIPPED" from 100 feet away!
Electrical grid operators want you to buy electricity, not make it for them. Their nightmare is becoming "just" a grid.
Their biggest nightmare, however, is you realizing that you no longer need them at all. Lots and lots of people, especially those out in suburban or rural areas, could easily go off-grid these days. Homes are better insulated, heatpumps are quite common, solar costs a fraction of what it used to, lithium ion battery prices are crashing and LiFePo batteries are getting commonplace, etc. So what's a utility to do? Push microinverters that require a grid connection and so on.
Old-fashioned spinning generators also naturally act to stablilize the grid by pulling energy out and dumping energy back in through their inertia as necessary to counteract changes due to varying demand and supply. Solar and wind don't inherently do that: if you want similar behaviour from them, that requires additional software and sensing, and obviously for home solar that would have to be done in a distributed fashion which complicates matters further. (The grid is not in fact at a single frequency and phase everywhere, and can develop all kinds of interesting and undesirable oscillations.)
And then a few decades later, they figured out this was a terrible idea and the newer 1741-SA/CA Rule 21/etc stuff with far greater ridethrough for reasonable disturbances showed up, but I don't think it's the majority of solar installs.
I should probably get a Grid Guard code for my SMA inverters and use the revised ridethrough rules - my utility handwaved at it when I installed stuff, and it's using the CA Rule 21 stuff, but they now have far more explicit guidelines on what they want programmed in the inverters.
I /think/ they mean there's going to be more demand, which could overload parts of the distribution grid, causing its overload protections to trip. Is that right? The solar connection is not clear aside from it contributing more power on the grid when it's sunny.
There are loads of designs for grid isolation, but most are big circuit breakers, and break the connection by rotating the conductor out of contact, powered by gravity or a spring.
So I think you're basically right, and right to be confused. The solar connection of the risk isn't really clear. But as far as I can tell, they're concerned about a positive feedback loop, where a thermal plant dropping offline will cause a solar plant to trip, which might cause other solar plants to trip. Perhaps solar plants' power electronics are more delicate, and more likely to trip, than thermal plants' switchyard gear. Again, it's not totally clear.
That's no longer the sane default and the utilities have been slow walking software and hardware updates to fix it.
...and now that might be a problem.
In many other states run by a certain political party, they have been making it so your net-metered connections are selling back at wholesale rates instead of retail rates, or limiting just how much you _can_ sell back (sell limits).
When I used to work for an energy intelligence company back in 2017 it was worse with legislation across the Midwest and western states that prohibited solar on roofs and required homeowners to pool together for community solar projects (run by the power company) to get their renewable energy.
Now, most 47 states have some sort of net-metering at least for wholesale prices but more and more of them are requiring a minimum service fees and making hardships for people to live without them.
I don't see how this is a problem: the maintenance of the electricity grid must be paid somehow, and this is more or less a flat, predictable cost. If you're coming from a situation where the maintenance was previously factored into the price of energy consumption (not a bad way), you're going to have to redesign your billing.
Are you arguing against a maintenance fee in general or just how much it costs?
:-) In the UK, the term "prosumer" is the official term for an electrical system which produces to and consumes power from the supply. (example https://electrical.theiet.org/wiring-matters/years/2019/74-m... )
(In the past it was widely taken to mean "a customer who wants to buy very high-quality technical products or equipment", https://dictionary.cambridge.org/dictionary/english/prosumer )
Second context: prosumer: Portmanteau of "professional" and "consumer".
A classic large-enough but not too large grid is sized like that to achieve a somewhat constant load so their generator have to supply a certain amount of power without sudden high or low loads spike. A small personal example, I have a small domestic p.v. system for self-consumption, when my dishwasher start heating water my micro-grid load suddenly spike +~2kW my inverter take time to produce more, like few seconds, so without a grid or a battery my micro-grid will simply collapse because the frequency goes too low. Similarly when water heating phase is ended there is a sudden -~2kW load and the micro-grid frequency skyrocket. Again without a grid or a battery my micro-grid will simply collapse due to a too high frequency.
Instead a small sudden load change, like a light that turn on or off, have essentially no impact since such so small amount of power vary the frequency of the micro-grid so little that the solar inverter have no issue to keep anything in place.
At a classic grid scale ±2kW are just background noise on the frequency, like for my microgrid the led light turned on and off.
However at a classic grid scale with massive p.v. things start to be far less constant, sudden spike for so many microgrids means sudden spikes projected to the main grid causing much more frequency perturbations. Also Sun power tend to peak really fast witch means that a grid with an actual production of let's say 1GW at 10 a.m. this morning around my latitude suffer a sudden drop in demand, witch means a high frequency peak because that when most p.v. systems in sunny days quickly goes from few hundreds W to few thousands W in a very little time. So the grid need to reduce power quickly, let's say a quick perturbation pass varying much the p.v. production, again a load peak for them, a big drop in frequency they need to boost production in very few seconds to keep up the frequency. The alternative is rolling blackouts to cut most perturbation and keep the overall grid up, something that do not touch much those how have a p.v. system with battery storage since actual inverters are fast enough to keep homes powered on most load cases BUT touch all other citizens...
grid-connected EVs can help quickly absorbing loads and quickly releasing energy BUT for far such applications are just on paper and I doubt we can allow private EVs to talk with the public grid since any vehicle is a mass of proprietary crapware crap built by countless of private parties, many outside national Govs. control, in unknown health shapes, response time, ... such grid is theoretically possible, but practically probably as unstable as without such system, with many smaller rolling blackouts and much higher risks of large scale ones...
Long story short:
- with climate change we know we have to adapt and adapt means change, changes we can't much design up front due to too many variables, witch means we can't build large/complex systems because they solve a PRESENT issue, taking years to be built, and we do not know if such issue will be solved in the same way once we finished such large systems.
- the ideas some from Green New Deal push is: we need to cut such complexity. Witch means making autonomous homes who can be powered locally without a grid, smaller cities with their own local small networks etc instead of nation-wide systems. The very same happen for transportation networks where we start preferring small/medium water and air born systems because we can re-organize them fast instead of rails and roads that take decades to be build and changed.
- the issue here is that PERHAPS we can do so, but very unlikely for anyone, probably only of less than a third of the whole humanity and of course those who are excluded for a reason or another would not be happy of that, and not "being happy" means unrest, revolutions, violence, instability etc that beside the carnage and suffering also impede to build pretty anything for anyone.
Energy grids operators are just some of the party who start understanding the amplitude of such issue and start blowing all whistle they have alerting: "we can't do that, we do not know alternatives to put on the table".
Probably the sole viable alternative we have is PUBLIC only nuclear waiting for tech progress, but so far build such massive nuclear move takes decades.
[1] https://www.economist.com/science-and-technology/green-power...
In most locales it’s now more cost effective to heat your water with photovoltaic panels & an electric water heater.
Rough math is
NG -> Electricty is 50% efficient thermally.
A heat pump can have a COP of 4.2.
100 * .5 * 4.2 = 210% efficient, thermally
A hot water heater powered directly by gas is ~100% efficient thermally.
I use the heat pump mode only when there is little solar for few days where there is not enough overall energy production, otherwise being able to produce 120-130% of the overall consumption (of course ONLY when the Sun shine, so NOT independent as some sell just playing with absolute numbers) why care about efficiency? I can't use the extra energy anyway...
Maybe with a very complicated system with an extra large storage tank, and perhaps integrated with the home heat (so a single heat pump). I feel like the tech isn't quite ready yet, and I don't like being a pioneer.
It seems like a no brainier if you heat with electricity, but not quite ready yet for those who heat with natural gas. Right now it seems better suited for southern climates.
- with p.v. I'm formally less efficient BUT in winter/cold but still sunny days my p.v. peak at a certain time for a certain time and my water heater start full power when there is enough energy, a solar thermal system take time to reach a sufficient temperature to make water (glicole) flow;
- almost no external maintenance, just panels and wires, no leaks or freeze risks, no pipes etc;
- no extra energy to make heat transfer fluid flow, witch means no pump, actually my heater is just an isolated "bowl" with a heat pump + classic electrical resistance and a big spiral pipe inside, so I have even no pressurized tank issues (water expansion) nor legionella problems etc;
- for my needs 300l of waters heat also in the winter enough 100% on p.v. except if more than two days without Sun, overall cost is very limited, potentially I can use the optional thermal solar integration with a classic wood burning stove to heat water in emergency conditions.
Why bother for thermal solar? With a big pool I understand but except for such case in witch solar anyway can't suffice for more or less large part of the year...