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Comment by alex_duf | Hacker News Reader

>because a grid connected system is supposed to shut down when the power fails, the only way out is to stop being grid connected

On that note I believe there are electrical devices that automatically disconnect you from the grid. It allows you to use a battery / solar array to power the house, while not feeding back any power to the grid such that you don't harm anyone trying to fix the grid.

Now whether or not this is allowed is very much dependent on which country you live in.

This video is in the UK and demonstrate such a device:

https://www.youtube.com/watch?v=gP51JjnWvLo

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This is called an 'automatic transfer switch', it basically islands your off-grid installation when the power isn't available. As you already mention whether or not it is allowed is dependent on where you live. As it was the electrical inspectors in Northern Ontario were very much in bed with the power companies and typically would find all kinds of reasons to persuade renewable energy builders to let it go and rely on grid power. Given the state of some of the homebrew systems I've seen they probably had a point.

Automatic transfer switches were technically allowed but at the time I didn't know of a single installation in Northern Ontario that got a stamp of approval and was allowed to be operated un-attended in grid connected mode.

There is some risk, but this is usually exaggerated, the theory goes that a lineman should be able to disconnect a segment and then it should be idle, requiring all renewable installations down-grid to disable themselves. As a rule this is fully automatic anyway because all of the grid connected inverters that I'm aware of stop working as soon as the grid fails because they use the grid to supply them with phase and frequency information required to function.

But that wasn't good enough, the installation needed to be physically disconnected from the grid, requiring a very large relay and somehow it then had to reconnect if the grid came back on for a specified minimum amount of time (I forgot the details). By the time I had worked all this out I figured since I'm going to be in island mode anyway most of the time I may as well take the shortcut, cut the grid entirely (saving a considerable amount of money in the progress) and invest the difference into a nice genset (which I did, a 5.8KW Kubota diesel).

What was the thinking around diesel vs natural gas?

Do you just use heating oil? How do you manage that it has a limited shelf life?

Natural gas is very likely unavailable in remote areas. Usual fuels would be propane or diesel, which can be trucked in.

People seem to think Natural Gas just magically makes its way down the lines. NG requires power as well. If power is out for any period of time you lose natural gas soon after due to compression stations going offline unless you happen to be one of the lucky ones who lives off a branch that is self-powered.

https://geekprepper.com/how-long-will-natural-gas-last-witho...

That article is from 2015. The bulk of natural gas infrastructure is self powered these days because declines in gas prices since then have made that a comparatively better option in more places and the natural attrition and upgrade cycle of equipment.

I don't think "the bulk" is true.

Last year's deadly winter storm in Texas showed that a lot of natural gas infrastructure does indeed rely on electricity.

(New) Compressor stations now must now be electrically powered to get permitted by the federal forces that be. (With very few exceptions.)

Even replacing compressors that were self powered now need to be electric.

It doesn't make any sense, except that it's another regulatory expense resulting in both higher cost and less reliability.

It does make sense - just not by the metrics you're judging it. If what you care about is carbon emissions, electrical power is better. If what you care about is system reliability native fuel power is better.

A lot of times when people say 'Thing thing makes no sense' what they mean is 'This thing doesn't agree with my priorities'

Oh, sorry, I didn't actually mean "natural gas that comes from a magic pipe" -- I meant propane that sits in a big tank in the backyard. I know intellectually that they're different gases, probably with different numbers of carbons in the molecule, but I have the bad habit of using them interchangeably....

In the "rural" areas I spend the most time in (cape cod, not exactly rural but also with sketchy utilities) people mostly have generators running off of big (well, probably medium sized) propane tanks that I imagine may also be used for cooking / heating as well.

I'm more curious about the stability of the fuel over the long term if it isn't cycled often, where I imagine propane / NG has an advantage, but I guess if you're using it as backup to solar and wind, there's an expectation that you'll go through a couple tanks a winter regardless so stability isn't as much of an issue.

Propane and methane are very different, and you should be careful about the differences if you use either. Propane is almost always sold as liquefied propane gas (LPG) at a relatively low pressure, whereas natural gas is almost always sold in its pressurized or compressed gaseous form. The most important difference is that if you have a natural gas leak, it will 'float' in the air, and dissipate; propane will (dangerously) 'sink', and pool around the source, and is liable to explode. Indoor propane installations should always have at least one propane detector.

LPG stands for liquified petroleum gas, which is sometimes just propane: https://en.wikipedia.org/wiki/Liquefied_petroleum_gas

> Propane and methane are very different, and you should be careful about the differences if you use either.

Also be careful to note that "natural gas" is mostly methane but with a significant mix of heavier hydrocarbons too.

Natural gas was possible but would require more capital up front, a lot more space and a specially prepared site for the tank, annual safety inspections and a place for a 40' truck to deliver it and turn around again (and of course it still required the genset itself). Diesel was by far the easiest solution, especially because we used the generator infrequently and once the windmill was up not at all.

We used wood for heat and limited shelf life for diesel is not an issue at all (it is for ethanol based gasoline).

From experience, you can get through a couple of big propane tanks per year just using it for cooking.

In practice the lineman risk isn't as real as it seems at first. Odds are when the lineman shutdowns a segment, if your system tries to supply power there are enough other people on the segment that you will trip your local overload protection and isolate the grid.

I don't blame lineman for not wanting to trust that though. My understanding is their practice is to always short out the line when working on them as that is the only way to be 100% sure it isn't live. (note that linemen work on live lines all the time, but when they need a dead line they ensure it is dead)

Agreed. But given what I've seen in some off-grid installations I really don't blame them. And I have seen one installation that tried to supply all of Ontario when it didn't go off-line as it should have, that wasn't a really pretty sight. The inverter died quite spectacularly, judging by the scorch marks on the wall above it, all of the magic smoke had definitely gone out of that one.

My uncle was a lineman and lost his leg due to this issue.

Here in the US Midwest I recently observed some crews repairing a fault just upstream of me, and the last thing they did before reconnecting to upstream of that fault was disconnecting a set of yellow cables which were obviously grounding the downstream wires.

Layers of protection. Laws on what can backfeed into the grid, ground the wires, wear safety gear. No different than in computer science using both a firewall AND salting your password. The more layers, the less likely 1 mistake gets you.

Exactly. If you want to get fired in a hurry from any utility or large plant: override someone else's lock-out. If they don't beat you into a coma first.

Those are called grounding clusters, sibling comment explains why.

Just adding from an experience researching solar for a condo development - if you want the fire department to try to save your house, you need to be able to cut the panels off, grid connection or not.

Likewise, putting panels on both sides of the roof makes it difficult, if not impossible, to vent a fire through the roof. The figures are ever changing, but the additional weight of many panels can also be a consideration when fighting a fire.

Really urge anyone considering adding solar panels on their home to speak with their local fire/ems prior to installation/signing a contract to be sure you know their requirements (and in many places this is still evolving).

I am not familiar with house fires or how to fight them.

> putting panels on both sides of the roof makes it difficult, if not impossible, to vent a fire through the roof.

If a fire is bad enough to need to be vented from a hole in the roof, wouldn't the building likely be lost already?

Even if the building is lost, the firefighters still want to put it out to keep it from spreading.

A few weeks ago, the Mount Charleston Lodge in Las Vegas burned to the ground. Firefighters put most of their effort into saving the surrounding national forest.

Not in my experience. There was a fire in the third floor unit of a building I was living in (one floor up and one unit over). It was a three floor building, so that was a roof unit. The firefighters cut vent holes and were able to contain the damage to that unit.

If you're building condos, you aren't in a rural area.

In my rural area, everyone ground mounts because space is cheap. I'm a volunteer firefighter and so far none of the trainings have mentioned solar (venting roofs yes). But then, we joke that we'll arrive just in time to put out your foundation.

Isn’t the new NEC including a provision for a cutoff switch at the meter?

Yes, that was added in NEC 2020. Whole-house disconnect just after the meter, on the exterior of a residence.

Automatic Transfer switches are very common in Server Rooms and datacenters where there is a Generator in use. I'm not sure why they are not more common in Solar. I have a parent with a full house generator that also has a Automatic Transfer Switch, its essentially right above the breaker box. the breaker box either gets power from the generator, OR from the power company, never both. When power comes back on, the ATS senses it, and sends a signal to the generator after 30 seconds or so that it is switching over, and to shut down.

Grid tied home solar is usually about economics (and sometimes happy feelings), not reliability.

If you want automatic transfer, you need to add storage, and a more complex inverter that can operate in bridge tied and island mode, and that cuts into the economics. You might also need to get more panels to handle projected loads during projected outages, but most net metering tarrifs I've seen won't compensate you if you over generate.

I can assure you that reliability factors in heavily in Grid tied home solar.

That must depend on the area.

People in the Netherlands or the UK have reliable power anyway, but there are still some home solar installations.

That varies greatly. In my area, the grid is extremely reliable. I rarely see systems that are setup to handle outages as the cost isn't really worth it on its own.

This. Normal solar relies on the grid as it's "storage". The economics of solar become very different if you have to provide local storage.

This is also why there is an ongoing fight over net metering and in some places solar connections aren't even allowed. So long as solar is a small fraction of the total power it has basically zero effect on the grid. Now, however, there are a lot of solar setups. Look what happens to the grid:

The total delivered power drops, but the peak power (when the cloud passes in front of the sun and all those panels quit working) stays the same. They need to spend just as much on generators as before but they aren't selling as much power. Historically, the cost of being able to produce the power has simply been folded into the cost of the power but with the two going out of sync this model no longer applies. Solar gets a substantial hidden subsidy from this, without this subsidy solar is almost never economic.

Second, look at what happens when *lots* of homes go solar. Lets say the local substation is delivering 1000A of power to it's area. Lots of panels go up, the combined power is 1500A. Now the substation transformer is being asked to push 500A back up to the distribution wires--and it's probably not built to survive that. Either those substations must be upgraded or the power company simply prohibits the situation from arising the in the first place by not allowing too much solar on any given segment.

1) we here in Germany, for non-standard connections (including using the grid as backup for local generation), have split price between max-power-reached-in-any-15min-rolling-average, and per-kWh. The former is low-medium single-digits per kW and year, depending on whether you hook up to the 6kV (to neutral; low-voltage would be 240V) medium voltage or they have to keep a 6kV->240V 3-phase transformer ready for you.

At 20-30ct/kWh, this sums up to (assuming low-voltage) 0.3% duty cycle getting you to spend as much on energy as you spend on power/capability.

As for the substation: it doesn't care beyond possibly having to switch some taps that are used to correct for load-current-dependant voltage drop in that 6kV network, but I doubt they get anywhere near their delivered voltage limits in normal operation, anyways.

I believe that inverters with integrated transfer switches are more common these days, due to the popularity of battery systems like Powerwall. I was reading the manual for one, and it had both a grid connection (to your main panel), and a "protected power" connection for a subpanel that will remain powered regardless of grid power.

They must still have some kind of internal transfer switch (as opposed to double conversion), but I would think as a single listed device with anti-islanding, they would be a lot easier sell to an inspector. Then again that AHJ sounds a bit dodgy ("specified minimum amount of time") so maybe they're still resisting.

Reminds me of the days when you needed written permission from the telco in order to connect a fax machine or modem to the phone line. I remember standing in line at the local phone company office and explaining to a nice chain-smoking office lady (you could still smoke in windowless offices in those days) what a "modem" was and why I wanted to plug one into their sacred network.

Err wasn’t that correct in hindsight with robocalls and whatnot becoming prevalent?

It is quite reasonable--the idea is that your local system must not backfeed power even in case of failure. You don't rely on how it should operate, it must be *impossible* for a failure to backfeed.

Thus, physical switches. The power company doesn't care what throws the switch, just that it exist.

The problem here is that different power suppliers in different locations have different standards here. My 6.6kW array here in rural New Mexico is connected to the grid via an inverter that will, putatively, shutdown if the grid side drops.

How does the inverter make it impossible for a failure to happen? How different is this from an automatic transfer switch (which would not be allowed)?

What they usually do is design the inverter to only use line power as the reference to generate the output. No sine wave from the line, the circuit is completely unable to produce an output and thus shuts down even in case of failure.

> Now whether or not this is allowed is very much dependent on which country you live in.

So basically, to clarify, you're either 100% on the grid, or 100% off. There's no using both depending on conditions, is that it?

You can have a backup generator (with a transfer switch)--which many do in more rural areas at least in the US.

I'm not sure about Ontario, but in many places you can be grid tied which means that you use both. While it is possible to change depending on conditions, the equipment to do that isn't very common. Solar systems are just starting to come out with single outlets that can run while the sun shines without the grid, but that is rare, most assume 100% on grid, or 100% off grid.

The vehicle I'm currently sat in at the moment has a 32A electrical cable running in the back, currently pulling 2881W into a magic box provided by victron inverter/charger, that is used to charge a battery (which is currently fully charged). That battery is currently being drained at a rate of 2881W to run the equipment (via the inverter back to 230V)

If I pull the 32A cable, everything carries on working (I believe it's a sub-20ms switchover). If the power goes for some other reason it carries on working. The truck can run on a 230V/13A source just as well (although when the aircon is on - not needed currently - we'll be pulling more than 13A so the battery will slowly drain). I can even plug into two different inputs.

Now this is a mobile vehicle, and I'm no electrician, but my understanding is this is perfectly fine -- the victron presumably switches from the grid if the input is lost and doesn't feed anything back into the grid.

Presumably the same setup could be used to power a home instead of several racks of equipment in the back of a truck.

That Victron box has an automatic transfer switch in it, and is certified for permanent grid connection.

That depends on your generation capacity and what the rules of your grid are.

If you're capable of producing enough power to run your home most of the time, then being grid connected and buying peak load from the grid itself rather than browning out your own devices might be a worth while tradeoff.

Most of us with grid tied solar installations (like me) transparently buy and sell electricity to and from the grid depending on day conditions. I buy from the grid overnight, and sell excess capacity during the day. Depending on how much electricity you use a battery system will smooth those out, but you need a lot of batteries to eliminate the need completely (OP mentioned 48KWh, which is about 3.5 Power Walls).

In my area the grid is really reliable and fees are low, so buying batteries is not economically viable. I'm currently paying $5.24 per month for a grid tie, which is below my threshold for caring.

It's also more viable to be grid tied if your winter needs are more than X times your summer needs. My 6.6kW array generates roughly 3x what we need during summer. But our home is heated in winter (at 6000' in New Mexico) using electrically powered air-source heat pumps (aka "minisplits") and that takes about 3x what we generate during the winter.

Adding either on-site storage capacity or sufficient additional panels to cover our winter needs really makes no sense. The storage capacity would have to be immense, because no matter how you slice it and dice it, we do not generate enough power to heat our home for several months (and that's with adobe and some passive design). The additional panels would take up a large amount of ground space, and result in us generating 9x our needs in summer.

I prefer to put my faith in the emergence of grid-scale storage solutions than try to solve this on a just-my-home level.

If the grid wasn’t reliable, a hypothetical I know, it would probably be cheaper to switch over to a ground source heat pump rather than increase your panels by 3x. That would lower your winter electricity demand, albeit at the cost of significant capital expenditure.

Does a ground source HP use that much less electricity than an air source HP?

Yes, by far. It’s much easier to extract heat from ~55F ground water than from ~20F exterior air. Ditto for dumping excess heat into ~55F ground water than 90F exterior air. On average the water coming out of a geothermal loop will be more advantageous to work with than exterior air, which is why it’s a thing.

In some areas, there is both, but it requires having a correctly installed automatic disconnect, that cuts you off from the grid if the grid loses power.

Many/Most home solar installations do not correctly install one, which can be dangerous to linemen.

I'm getting a manual transfer switch installed - I live in the city (although it's rural-ish where I live) but we get occasional power outages and it's often enough (and long enough) to be worth the annoyance of getting a generator and switch installed, but not enough for me to shell out big $$$ for a natural gas generator and automatic transfer switch to ensure 100% uptime for my house.

This works well as long as there is a reasonably high chance of someone being in the building when the power fails. For many rural setups (for instance: weekend cottages) that isn't the case so more and more inverters come with an automatic transfer switch built in or for a small surcharge as an option.

Or if you travel. If I ever get a generator installed (with automatic transfer switch), it would be primarily for the case of a power outage during the winter when I'm not around.

Not even which country, which sub-entity within your country. Here in America it's going to vary on a state by state basis.

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