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points by LeFantome 14 hours ago | 0 comments

Where I live, hydro is the dominant power producer.

My electricity costs 40% less from 11 pm to 7 am and 30% more from 4 pm to 9 pm.

A hydro dam can also be thought of as a battery. When you are not using it, the dam fills up (charges).

My utility buys inexpensive excess power from the NA grid when electricity is cheap and drains the dams when third-party electricity is expensive. Adding other renewables to the mix plays a similar role. The pricing incentives shrink peak demand as you suggest.

One of the reasons residential solar is a tough sell for me is that electricity is relatively inexpensive and likely to stay that way.

[–] _heimdall 14 hours ago

There are interesting large scale projects that use hydro directly as power storage for renewables.

When the sun is out or wind is blowing, use excess energy to pump water up hill. When you're low on energy supply, open up the dam to run the water back down hill and through a hydro plant.

I've toyed with the idea of doing the same thing at a small scale on our farm but would need to build a second decent sized pond up hill of our main one.

[–] PaulDavisThe1st 12 hours ago

I've read that globally almost all the places that can do pumped hydro "storage" already exist. I don't know if that's true, but if it is, then while this is a really cool technology, we won't be getting much further with it.

[–] vivaldi_bt 11 hours ago

AFAIK, it is not really true. But you need several things to do a pumped storage: a big source of water (and it better to not be a salt one), a place where a reservoir can be made and an elevation difference between them. So I'd assume that the most of the places that can be easily used to make a pumped storage already have one.

[–] PaulDavisThe1st 8 hours ago

Isn't that more or less precisely what I said?

[–] very-old-sw 11 hours ago

It's possible in the Catskills in New York State (USA) but a proposed project there was killed by the greens. Who also killed fracking in NYS and a power line from Quebec to Mass and closed a nuclear plant and ....

[–] _heimdall 4 hours ago

Local concerns in my area killed a project as well, though I can say I agreed with their concerns. The power company wanted to cut the top off of a mountain to build the reservoir and were likely going to force a small community to relocate entirely. Not the best solution IMO.

[–] Smoosh 8 hours ago

Interesting that “the greens” have so much power in a country which is very strongly two-party in its politics. Or did you mean “environmentalists”?

[–] mixdup 10 hours ago

you would be way way better off just buying some actual batteries

[–] _heimdall 4 hours ago

That's where I ended up, we have a combination of repurposed batteries from wrecked cars and, soon at least, new batteries with CATL cells. I would prefer the hydro project bit digging a pond is a surprisingly expensive project today.

[–] toomuchtodo 14 hours ago

Have you priced residential batteries and time of use to charge at night? That's Base Power's value prop, they partner with ComEd, install batteries at your home and become your power provider charging a lower rate than ComEd. Batteries charge at night when nuclear generators are still humming and demand is low, and then serve daytime load.

Solar may not pencil out, but energy arb over system lifetime might, especially if you have any battery subsidies available. Just keep in mind flexibility to add solar in the future so its as trivial as installing racking and panels and running power to the storage and load center (optimize for optionality).

https://www.chicagotribune.com/2026/07/28/base-power-battery...

[–] very-old-sw 11 hours ago

I get service from San Diego Gas & Electric, have solar and powerwalls, and am part of Community Power's VPP. I am prohibited from charging my powerwall from the grid.

[–] toomuchtodo 11 hours ago

Is this a utility requirement? My understanding is this was due to previous IRS guidance about battery tax subsidies that potentially no longer applies, although I wouldn't be surprised if this is a utility requirement to be on a time of use plan to prevent you from maxing savings by having solar and charging from utility mains at night.

https://diysolarforum.com/threads/new-irs-requirements-for-b...

> The private [IRS] letter ruling was from 2016, prior to the explicit credit for batteries.

From 2023:

> “Batteries and the federal tax credit at a glance: Residential batteries installed in 2023 can qualify for the 30% federal tax credit, even if they aren’t attached to solar panels. The value of the tax credit will vary depending on the equipment installed and labor costs. The battery must be installed at the taxpayer’s residence and be owned by the taxpayer to receive the tax credit.”

(the setting is controlled by Tesla and I have heard some folks, anecdotally, having it removed with a support ticket, ymmv)