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Comment by dylan604 | Hacker News Reader

This is where I'm really intrigued of all-house battery packs like the Tesla Powerwall (it's the only name of one I'm familiar to call out). I like the idea that it charges at night during the lower rates, and during the day the house is powered from the battery. Just haven't seen any longevity reports on them in general vs brochure data.

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One thing to consider is that if that's profitable to do at house scale, then it's probably even more profitable to do at grid scale and you'll likely be out-competed by utility companies.

Edit: Unless you're taking advantage of tax incentives to do it at house scale. Its hard to beat the economics of just being handed free money.

An individual can take action now whereas the grid scale action is molasses like. It's even worse when your state is not in the pocket of but the actual pocket of Big Oil

But an individual can't take action without the grid taking action to provide customers with the different pricing rates.

What? The entire premise was that it is cheaper at night. Thanks for jumping into the middle of the convo though and trying to jerk the wheel.

Settle down. A lot of the U.S. doesn't have time-differentiated rates.

And that has precisely squat to do with my intrigue into looking at a system like this. If it didn't make sense, I wouldn't be interested. So what's your point exactly?

> If it didn't make sense, I wouldn't be interested.

It may or may not make sense depending on your location. Many utilities would prefer to make customer-owned solar a very poor financial choice thru rate design (e.g. very high minimum charges, per-kw-installed solar charges, low daytime rates relative to evening rates, wholesale-rate compensation for exported production, etc). Some succeed.

And much of that does is nowhere near the real cost differences. I might see a difference on/off peak price difference of 0.05 on a $0.40/kwh, but wholesale prices fluctuate from negative prices at peak to much higher rates.

If you claim is that "An individual can take action now" by installing a battery to charge at lower rate, then the question of if they can actually purchase power at that lower rate is fundamental.

If household power purchase price doesnt change with time/generation cost, then there is not ability to act faster than the power company.

> One thing to consider is that if that's profitable to do at house scale, then it's probably even more profitable to do at grid scale and you'll likely be out-competed by utility companies.

Depends. It may be more profitable for utility companies, but they keep the profit of the economies of scale. It is almost never passed on to the customer.

If you DIY your own energy system, you're free to keep all the surplus generated by it through the life of the system.

Only if they let you by giving you a big price discount to charge

Their alternative is to find some way to generate a lot more cheap electricity after sunset. If whatever they're doing can't beat the cost of solar panels on your roof + batteries and a small generator to top them up in exceptional circumstances, people will just stop paying them altogether.

> One thing to consider is that if that's profitable to do at house scale, then it's probably even more profitable to do at grid scale and you'll likely be out-competed by utility companies.

Utility companies have to pay for distribution networks, and generally pass that cost on in the price per kWh. Which you avoid the less you use the grid -- and which then become a higher proportion of the prices the utility has to charge the more people do that.

In a lot of urban locations, it is not legal to have a residence that is not connected to the grid. If you have home generation capabilities and storage that means you take the least amount from the grid provider, you can be technically still connected to the grid without using any power. If this continues, I would not put it past the grid provider to come up with a minimum monthly bill so it is impossible to have a $0 payment. Otherwise, who's going to pay for the administrative costs of having you as a customer?

Large minimum monthly fee + required to buy service seems like the kind of thing that would piss off voters.

Ah, I see where you strayed from reality. Your comment seems to be based on a premise that voters are rational.

The rational thing for voters to do is to mostly ignore what the government does unless it directly impacts them in a way they can understand well enough to rally around and get it changed. Which, it turns out, is mostly what they do.

That just has terrible results most of the time, because it means that people generally ignore or otherwise don't understand what the government is doing, which leads to all kinds of inefficiency and corruption.

But "law requires you to buy this expensive thing you don't want" is simple enough for people to understand and get mad about, and affects enough people to make politicians care.

> In a lot of urban locations, it is not legal to have a residence that is not connected to the grid.

Woah, I didn't know this. In any case, surely it's legal to have grid service to the house and simply not use it.

> I would not put it past the grid provider to come up with a minimum monthly bill

My electric company (a community owned co-op) has done this for many years. You pay $15/mo no matter what. Your power usage is billed on top of that.

Good point. Seems like a problem with the utility company's pricing structure if consumers can avoid like 95% of the costs of grid maintenance without having to become fully independent of it. I wonder if eventually they'll have to split electric bills into a fixed "connection fee" and a variable "usage fee".

> if that's profitable to do at house scale, then it's probably even more profitable to do at grid scale

There is a reason home generation wins. It's because retail prices are 3 times what the generator is paid. (That's true where I live).

So yes, in absolute terms power generated by home solar costs more than a utility generating it. But it's not 3 times more, so if you install home solar and use the power, it's always a big win. It will be the same with batteries.

The traditional forms of generating power, coal, gas, hydro and nuclear only win because home generation costs using those technologies (eg, putting a coal mine and generator in your back year) costs far more than 3 times. You can't put wind, or pumped storage in your back yard either.

But solar and batteries are different animals. They are different in other ways too. It always makes sense to over provision solar. The question is not whether to do it, but by how much. So home generators will always be looking to sell power, and since it's free selling it at 1/3 of what they would pay for the same power looks like money for jam to them. It makes you wonder how many utility generators will be left standing if solar takes over the world.

> it's always a big win

AFTER you finish paying off the financing of the source of home generation. so maybe it'll be a big win for the people in your location after you're gone???

This brings up an interesting consideration. Is it possible that in the age of solar, power grids are simply uneconomical in areas of insufficient density? That people in more rural areas would be better off not having a grid and just installing rooftop solar and batteries instead? My gut tells me that the added reliably of a grid is probably worth paying 3x the price, but its hard to be sure.

Does this reduce your energy usage though? You're still using the same amount of power during the day. So it saves you money, and takes some load off the grid during peak usage. What does that do to reduce emissions from power generation? Without solar, you're still charging off the same infrastructure.

As if someone trying to save money is such a ridiculous thing to do? WTF?

I subscribe to a power company that produces power via wind. So my money is supporting green energy generation. So yeah, it would still be doing plenty. Not really sure why you gotta be so negative about something

Do you even actually save money, accounting for the financing and installation of the solar panels?

A while back there was a thread on the SolarCity subreddit linked from HN where the OP discussed his savings thanks to nice weather, but still figured he had a 20 year payback period on his setup.

That is crazy.

I never even suggested solar. I just want a battery pack that charges when grid prices are cheap, and powers off battery when grid prices are high. Complicating it with solar is beyond the scope of the original intent.

That seems like it would be hard to ever make a financial return.

Say a battery costs $10k and a home uses $100/ month electricity. If you assume electricity is free at night to fully charge the battery and meet energy demand, that’s 100 months (8 years) to break even. Real world costs are going to make it quite a bit worse than that.

As they say, "location location location". In a Texas summer, it is easily 3x that per month for 4 months out of the year for a house. So, that's 12 months in one quarter based on your math. The vast majority of that is just running the A/C. So again, this makes much more sense when you look at the nuances vs just some lame internet posting of using averages. If it makes no sense for you, that's too bad, but to come out with broad brush comments alluding to it not making sense ever is just naive.

I guess you could further insult me or provide your own napkin math.

Sure, let's say the summer months bump the Texas electric bill to $167/month (8$100 + 4$300). The previous model was assuming free electricity. My quick search is revealing that using differential pricing in Texas, the difference from the normal rate (~$.16) and the low rate (~$.08) saves ~$.08/kwh. Assuming you could perfectly offset all usage onto the cheap rate, that would yield a monthly savings of $83.5. Which yields a $10000/$83.5 = 120 month or 10 year payback period.

Then again, we forgot to right size the battery system. This site[0] claims an AC is going to use 16kwh/8 hours. A Tesla Powerwall is 13.5kwh. If you want the battery to fully cover your AC needs alone, you will need at least one additional battery system.

Naturally, we are missing out on maintenance, opportunity costs, grid connection fees, potential rebates, etc, but I think we have indeed landed on a more nuanced model.

[0] https://learnmetrics.com/how-much-electricity-kwh-do-air-con...

On a modern grid, off-peak, cheaper energy coincides with low carbon.

Tesla warranties the Powerwall for 10 years, 15 years if part of one of their virtual power plants (orchestrated by Autobidder [1]). Look into the 30% federal tax credit for it, as well as state, local, and utility incentives.

If you don't yet have solar and your site is favorable, I strongly recommend considering it if you can have it installed at a reasonable cost.

[1] https://www.tesla.com/support/energy/tesla-software/autobidd...

Solar doesn't work for my property. There are too many trees doing exactly what they were intended to do by shading the roof top. Otherwise, it would be great as the roof alignment is pretty ideal.

Can you submit a residential battery to Autobidder?

If Tesla has a virtual power plant program in your geography.

https://www.tesla.com/support/energy/tesla-virtual-power-pla...

https://news.ycombinator.com/item?id=32500926

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