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Comment by fooblaster | Hacker News Reader

The thing we should be incentivizing people to use here are batteries, in the exact same configuration. We do not in many places, need more solar power generation, but we need devices that slurp down power at 2pm and dump it out in the three hours after sundown. Utilities should be paying anyone who dumps power to the grid at peak post-sundown demand hours, so that it is a no-brainer to install such a thing.

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At least in the US, no, for one simple reason: grids in the US rarely to never have an excess amount of renewable generation capacity.

In my area natural gas is a consistent 40-60% of generated power, with solar rarely reaching more than about 30-35% at high noon in the summer.

Right now (as in at this very minute, high noon) in CA ~70% of the power being generated is renewable. That's 30% that could be solar, and isn't.

When there's excess renewable generation capacity (or about to be), sure, let's talk about installations for storing it.

In the meantime utilities are deploying battery systems for virtual grid inertia, to avoid having to use "peaker" plants, reliability when transmission lines go down, and for transmission line maintenance.

That might have to do with existing deal structures to maintain a non-renewable base load. Something like, if cloud cover/wind suddenly changes, we want to ensure there is already X% of natural gas running so there is a less sudden surge. There is a lot behind the scenes planning to try and ensure grid robustness.

California is certainly curtailing a lot of energy. EIA report[0] said 3.4 TWh in 2024, which was a 29% increase over 2023. If I am reading this[1] chart correctly, the 2024 California demand was ~275TWh.

CASIO also has pages dedicated to curtailment with much of the data available[2].

[0] https://www.eia.gov/todayinenergy/detail.php?id=65364

[1] PDF https://www.energy.ca.gov/sites/default/files/2024-11/2024_C...

[2] https://www.caiso.com/about/our-business/managing-the-evolvi...

Standby generation -- "spinning reserve" -- doesn't count as generated energy, because it's not. Until you're at that point you still can reduce natural gas consumption with more renewable.

Generators don't ramp up/down immediately. Especially when peak power usage is 4-5pm, people getting off work, but also closer to sunset. That's a lot of power that needs to be generated immediately for stability.

More solar (without batteries) makes that worse.

https://en.wikipedia.org/wiki/Duck_curve

California has huge amounts of excess renewable generation nearly every day, especially in spring and fall. Last April the grid operator curtailed 1.47 million MW/hrs of renewables, or about 2 GW per day. That's excess power the grid did not accept due to no demand. (source: https://www.caiso.com/documents/key-statistics-jul-2026.pdf)

In my mind the ideal solution is in addition to daily BESS time-shifting is seasonal time-shifting: long term storage of April excess for use in July.

I think you had me until you mentioned long term storage. How do you store significant amounts of energy across seasons? I'm just not aware of anything other than pumped hydro power that has anywhere near the cap as capacity to do such a thing.

Green hydrogen. Generate hydrogen from water during excess times and convert back later on.

Is is actively done at scale? I suspect not given the amounts of batteries being installed.

No because there’s lower hanging fruit. We’re still burning dinosaurs on windy days and in summer, seasonal storage is a long way down the list.

Is this curtailment due to overproduction, curtailment due to inadequate _grid_ capacity, or some mixture? In Ireland there's now a _lot_ of curtailment, but it's mostly driven by inadequate grid capacity (wind power in particular expanded quicker than the grid could).

A suggestion I liked was to time-shift water heaters as a thermal battery. Water heaters are a significant sink (~20%) of household energy. They are already installed and well insulated, you just want to over-heat them during cheap noon solar to off-set the heat losses over the day.

this seems like it makes sense. how do you keep the dispensed water from being too hot? is there such a mechanism?

There are mixing valves which combine the too-hot water with cold tap water to produce hot water at a safe temperature.

Mixing valve. Lets me use my water heater like it's 20 gallons larger than it actually is.

> It is increasingly common practice around the world to regulate the storage water temperature to above 60 °C (140 °F), and to circulate or distribute water at a temperature less than 50 °C (122 °F). Water above these temperatures can cause scald injuries. Many countries, states, or municipalities now require that the temperature of all bath water in newly built and extensively refurbished domestic properties be controlled to a maximum of 48 °C (118 °F). Installing thermostatic mixing valves can ensure that water is delivered at the required temperature, thereby reducing the risk of scalding accidents; it also reduces hot water consumption from a supply that is maintained at a higher temperature.

https://en.wikipedia.org/wiki/Thermostatic_mixing_valve

I see these a lot in commercial domestic hot water systems, a lot of them use steam or boiler loop water to heat the domestic hot water.

When we bought our house we had a heat pump water heater installed. The nominal tank water temperature is 80°C, and it mixes it to the desired temperature on output. It can also circulate water in a heat exchanger to keep your bath water from going luke-warm while you're in the bath.

We don't have solar but we do have a solar energy plan from our power company, so power during solar hours is charged at 0.5x rate in trade for the solar during the duck curve hours being 2x. So we have the hot water heater set to only heat during the solar hours and A/C set to shut off during duck curve hours.

This has resulted in our electricity costs for our house being lower than the combined electricity+gas costs for the apartment we lived in before (which was much smaller).

This is basically how solar hot water heaters work today (I have one). They are superheated during the day (75C/170F) with a mixing valve to produce warm, but not scalding, water to the tap. The tanks are also oversized with a backup electric heater for the top half of the tank.

It works pretty well for my climate. I wonder how it compares to PV panels driving an electric heater though. Neither is going to work very well during the winter but the hydronic based system probably needs to get above some base level of solar input to meaningfully heat the water. Whereas PV will always produce some electricity in the winter which can always be converted to heat.

I'm getting a battery soon so I can get paid £1/kWh to dump power at specific times with axle energy https://vpp.axle.energy/landing

Be careful with these kind of long term sell back agreements.

In the USA lots of early adopters of solar did so under net metering agreements where excess electricity is sold back at full price. After a number of years it was costing the utility companies too much money. So they updated the terms such that residents with solar buy electricity at retail prices (~$0.25) but sell it back at wholesale (~$0.04).

Yes, I think the key thing here to to not guarantee that pricing like they did in California over decades. Yes, the benefit will eventually be reduced. But that is considered success is it not?

>But that is considered success is it not?

Not if you took out a $50k loan for an early gen solar system and it now only saves $30 a month.

well, California currently is guaranteeing that benefit to nem 1 people for twenty years. I would much rather penalize those people than make everyone else pay a subsidy to them, as we are currently doing. They should bare the risk of their investment and get paid market rate.

My issue today is .. I cannot be paid market rate for giving back to the grid, even in hours when California needs the power.

Don't expect that to last. £1 per kWh = £1000 per MWh. Even when things went crazy as sanctions kicked in and Russia were attempting Blitzkrieg in Ukraine the wholesale prices never hit £1000 per MWh.

They say £1/kWh is a Beta price, that makes sense as a way to burn investor money to get people interested. Their real price is TBD. Would you take 25p per kWh with a £5 per month guarantee ? That could be at least in the ballpark of working.

Well it's just a bonus on top, I'm not counting on it. Storing solar and backup is the primary reason for the battery. On June 24 at 19:00, agile octopus prices were about £0.85/kWh, there isn't a single simple price for electricity.

It's true that there isn't a "single simple price" but the only way you're getting more for your power than a wholesaler can sell it for is that they're paying far more than it's worth. Stability services aren't free, but we're not talking about a 10% premium here, closer to 10x

> batteries

Not exclusively. A few power companies (like SRP) innovated here with TOU plans that have variable costs throughout the day. You can save huge amounts of monthly spend by moving energy intensive work to off-peak hours and by “priming” things ahead of peak hours, like over-cooling your house ahead of the peak window.

The most costly part of an infrastructure build out is supporting peak-of-peak - that capacity exists year round to service the demand generated by peak mid-day usage during a heatwave in July.

If you can “lop off” that peak - it dramatically reduces the infra build out cost.

Peak-of-peak tends to correspond with sunny days: mid-day in summer. I could see battery-less solar being a useful tool there.

related tangent: install costs of batteries and solar in California are insane. I recently had battery and solar installed, and labor and permitting were 60% the cost of the system. Systems without either of those markedly bring down the cost.

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