Hacker News Reader

> The eF150 generator use case always seemed like suburban prepper fantasy bullshit.

Perhaps you didn't hear about the millions of people who were miserable (and several who died) because their power grid is run by morons[1].

Losing power for three days may have been unusual for a long time, but with the combination of radical/unaccountable government, climate change, and aging energy infrastructure, it's easy to imagine that a lot of the warmer parts of the US are at some risk.

1. https://www.texastribune.org/2021/02/19/texas-emergency-comm...

I’m planning for solar cells and looked into the possibility of running my house as a micro grid (ie disconnect it from the main grid) in case of a prolonged power outage. Turns out that unless you redneck engineer it, running your house without a main grid to synchronize to is very costly - among other things you need to supply your own grid grounding and that could easily run into the high €x000.

> you need to supply your own grid grounding

What does this mean? My naive reading would presume a stake in the ground?

Depends on how much electricity is involved. Might require more than a simple stake

What’s more ? Curious what it takes for large setups.

A big ass steel anchor damn deep in the ground!

Proof of stake.

You need to put as much as needed to achieve 4 Ohm to ground or less. This can be up to ~ 10 stakes at a couple of meter interval, it depends a lot on the soil type.

For individual homes, it often takes three stakes, each several meters long (deep), placed in a triangular config, connected above ground.

a stake which doesn't corrode.

For fun, put a nail in dirt. See how long it lasts.

Stake in the ground, as the sister post said, non-corroding, in the simplest case.

But there is more to it: The stake has to have permanent contact to some electrically conductive layer in the ground, so you need to take geology and local climate into account. In central europe, with generally wet climate, you just need to reach the year-long stable, frost-free, local water table at a depth of (usually) between 1m and 10m. If you cannot reach sufficient depth, don't know the required depth, a simple stake isn't going to cut it. Because in case of an electrical fault, the grounding has to withstand and dissipate in the order of a few hundred Ampere. To achieve that you then shallowly bury lines of non-corroding material in a grid, or bury a grounding net something like 1 to 2m deep over an area of 100m^2 to 10000m^2.

If you are on sandy or rocky ground, permafrost, arid climate and no handy body of water is nearby for grounding, you need to have a far larger grounding net or use conductivity-enhancing methods like permanent watering, adding salts or carbon to the soil or replacing it outright with something more conductive. In all, very expensive.

And as for large installations, you just measure the soil conductivity, calculate the necessary grounding current and scale up the aforementioned methods.

Interesting. The receding ground water level in the Netherlands could possibly impact our electrical infrastructure on a local level then, right?

Ground water isn't really receding, it's just pumped to a low level to benefit agriculture at early spring, which then fucks everyone up if the spring and/or summer is dry.

This must be a European design. In the USA, governed by NFPA 70 - The National Electric Code, the ground rod's purpose is to establish the ground voltage reference to reference the electrical systems of a building to it and to dissipate any charge buildup on the circuits.

The ground rod is not there to carry current to interrupt a fault to "protective earth" - the green or green/yellow. The circuit breaker interrupts a short as you bring the protective earth wire back to the main disconnect of a building where it bonds to the neutral wire.

If a fault occurs, an unregulated amount of current flows on the protective earth wire to the breaker panel and a circuit breaker interrupts the circuit.

I'm no expert, but here in Norway we predominantly have IT systems[1], though new installations are mainly TN.

In the IT systems, the protective earth is not bonded to the neutral. Thus in case of a fault, the protective earth should be low impedance to ground so that the circuit breakers trip. At least that's my understanding.

[1]: https://aktif.net/en/types-of-earthing-systems/#IT_System

Thanks for the link. I don't know all the symbology there so it will take some reading up.

Technical nitpick, if it detects earth leakage and trips based on that, it's an RCD, not just a circuit breaker. Otherwise yeah, there's different approaches to earthing - in Australia for domestic stuff we have mandatory RCDs which work as you describe above, but then also in industrial/mining settings we have the big green/yellow cables which will directly sink current (potentially hundreds of amps) to ground, hopefully stopping you from getting bitten.

A thermal breaker won't trip on leakage current or arc faults either. I was trying to describe the classic "dead short" that will trip a thermal circuit breaker or fuse without the circuitry for arc or leakage detection.

Usually you can just tie it to an outside copper plumbing pipe, it's metal and makes good contact with your local ground.

Disclaimer: Not intended in any way as professional electrical advice yada yada. Just what I've read.

(Also all sorts of weirdness can take place around grid earth vs. local earth, eg. during thunderstorms. Earthing is its own entire engineering discipline. :S )

In Europe (EU) every house needs own grounding. You are not allowed to ground on main grid's ground. We have three cables: 1) power 2) zero (=main grid's grounding) 3) own grounding. Only old installations are allowed to connect grounding to zero which is called something like "zeroing".

In the UK, which was until very recently in the EU, most modern (last 20-30 years) houses have what’s called Protective Multiple Earthing where the house earth is just connected to the incoming neutral and there’s no earth spike at the house. Then the power company earth-bonds at the substation and several points between the substation and houses.

Don't most UK houses also have earth bonded to all the water and gas pipes in the house?

There may be no earth spike, but if earth connects to a copper pipe going into the ground, you'd expect them to be at the same potential.

I believe metal pipe bonding is a building control requirement however many new builds use predominantly plastic pipe work. The requirement is to protect the occupant against touching live metal pipe work, not to earth the house.

Gas pipes can't be plastic!

At the first electrical panel in many cases the grid's neutral is connected to the house grounding, this is done in new houses in my country as standard.

Here in the US, I have three wires from the utility: phase 1, phase 2, and neutral. I also have two copper ground rods that are 3-4 meters in length, which are connected to the utility neutral.

You also need a transfer switch to make sure you're disconnected from the grid otherwise you're going to be feeding power back into lines that are supposed to be dead.

I already have a 2000W inverter wired to my Prius' 12v battery. Pop the car in ready mode and I can run things off it for ages, and then unplug them and go refuel the car if needed.

Having the extra storage battery mounted at my house would be cool and all I guess, but you don't need this to back up your house's power supply with a Prius.

(I live in a small, simple house and only run the blower fan for my propane heating system, my refrigerator, my freezer, and a lamp off the inverter. I suppose if you had much more complex power needs, the battery would be a larger advantage, but for emergency power outages, it keeps me from freezing or losing all my food.)

Would you share general info about your Prius setup? I was looking at the below.

https://www.plugoutpower.com/inverters

> unplug them and go refuel the car if needed

Just like standalone generators, this is a tough point. Fuel can become hard to source during a an outage > 5-7 days.

Honestly I kinda already did. Connect 2000W pure sine inverter to terminals on 12v battery in trunk. Plug in extension cord.

It's not terribly sophisticated, but it keeps my pipes from freezing.

Refueling a car is as easy as it gets, though. To refuel anything else, you'd have to put it in a car and take it to the fueling station anyway. This way you just refuel the car the normal way. You can also store whatever gasoline you'd have used in a generator at home too, but the Prius' 10.9 gallon tank holds a lot more than your average portable generator and runs a good, long while.

Running your home off your car's combustion engine sounds like exactly the wrong way around. I want a battery that allows me to save days worth of power from solar panels to use during cloudy days.

Isn't adding more panels a better solution? How else are you going to bridge over the winter?

More panels don't help if you can't store it.

Well, I suppose if you have enough panels to generate power even on short, cloudy winter days, then that doesn't matter anymore; then you just need enough storage for the night. But then what are you going to do with all the surplus power on sunny summer days?

Some sort of cheap long term storage would really help a lot.

Yes, I get it, it's indeed a lot of surplus in the summer.

Long term storage would be the better solution, but batteries don't seems to be able to store a large amount of energy anyway. So in my opinion, it's really a tradeoff.

Maybe mine some bitcoins during summer? ;)

I looked into this. Even assuming PG&E's buy back rate is 50% of current numbers, the ASICs have an expected profitability horizon of over one year of uptime. I'm not convinced they'll be profitable much longer after that, since hash/kWh keeps improving.

Also, I bought the panels to reduce carbon emissions, and would rather sell the power back.

At least for our install, we spent about half the money on batteries and half on solar. It fairly reliably gets through the night unless we run the AC (but those are sunny days) or charge the car (car batteries are about the same size as the house batteries).

On a cloudy day, the panels provide 90% of our normal power usage. Anyway, to scale it up, we'd want to increase panels and also batteries. Increasing only one would leave us with no power at dawn or with a large battery that would never reach 100% in winter. One night of batteries with panels that reliably provide enough electricity to get the batteries to 100% is a good tradeoff for sunny climates. As it gets cloudier, batteries might have more incremental benefit, but multi-day storage probably doesn't make sense.

Also, you can tie a gas/propane generator to the battery to handle the "a few times a year" cases. That's probably less carbon intensive than 5x-ing the system for 1% of the days.

(Since the 1% days for us are in winter, we have a wood stove.)

> But then what are you going to do with all the surplus power on sunny summer days?

> Some sort of cheap long term storage would really help a lot.

Run a still to make ethanol from waste biomass. Store it (don't drink it!!) and use it to fuel a generator in the winter.

I'm only half joking.

Generating some sort of fuel is probably the best idea indeed. Hydrogen is often suggested because it's easiest to create out of water, but it's also hard to store. Ethanol is definitely easier to store, but requiring a lot of biomass is definitely a bit of an obstacle.

Genuine question - how many engines can run on straight ethanol? Are there any negative consequences for running straight ethanol in an engine expecting gasoline?

You can damage the engine if it isn't designed for ethanol:

https://www.car-engineer.com/adapting-an-engine-to-ethanol-f...

> But then what are you going to do with all the surplus power on sunny summer days?

You don't have to do anything with it. Panels are dirt cheap these days, and if you want reliable off grid storage then you have to size them to keep up with baseload power under your target range of conditions anyway. Figure out how many days a year you're happy to run a generator or turn your fridge off, find stats on your local daily kWh/m^2 solar energy, size panels to cover baseload with that incoming energy.

I have 2kW of second hand panels hooked up to a 200AH 24V battery pack (again second-hand) to power a server rack, it uses about 4.5kWh of solar power per day without running the batteries down too far. The panels can generate 8kWh/day in summer, the rest is headroom for cloudy winter days. The last time the server saw mains power was... December, I think?

> Some sort of cheap long term storage would really help a lot.

I mean yeah, but so would Mr. Fusion.

I'm referring to emergency situations, not off-grid living. You probably don't want to use your eF150's lithium battery as backup power bank either.

> The eF150 generator use case always seemed like suburban prepper fantasy bullshit. The actual use case is for running power tools on site.

I think the Hybrid F150 / generator case is pretty decent; not so sure about the EV only generator one, but running tools could be useful. Rolling a truck over to my well when the power goes out will be a lot nicer than rolling out a portable generator by hand. Could be maybe useful for cell towers that rely on generators driven to the site during outages as well; although that depends on if they usually drop off a generator on a trailer and let it sit without local supervision or if they stay with the generator. My well servicing company has a box truck with a generator in the back, that they use to confirm that the problem isn't related to utility electric service; not sure if a built up f-150 would be sufficient for their storage/transport needs though.

Let me introduce you to the Eastern Seaboard and Gulf Coast of the United States of America, where people often run generators intermittently for weeks after a hurricane in order to keep their refrigerators and freezers cold until power can be fully restored.

> days or weeks

The eF150 gives you a couple days. The Prius is a better solution if you really need backup power.

They're not running it non-stop though. They run it about 4 times a day for an hour each time, and ONLY for those appliances.

In that case, the prius prime battery alone is probably sufficient for several days. And it's 30K less than the eF150. And you can actually buy one off the lot today. :)