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Comment by dragontamer | Hacker News Reader

I'm not sure if these numbers being quoted are good for analysis.

The "Nessie Curve" shows that power at 5:00pm is worth more, especially in sunny environments (like Hawaii). Solar energy is taking over those areas, but solar power begins to drop dramatically as the sun sets.

5:00pm to 8:00pm is still quite warm, so you need to turn on the gas turbines to provide electricity. But solar's efficiency has dropped dramatically, so you can't really rely upon solar power in those hours (well... you can... but at dramatically lowered efficiency).

I'm not sure any analysis is worthwhile unless it includes the time-of-day, as well as the number of hours that the batteries can load-shift power. 5:00pm to 8:00pm power is going to cost more in the future than 12:00pm power, simply due to this whole solar energy thing going on.

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I just wanted to make clear that BNEF is talking about batteries threatening fossil peakers that produce expensive electricity, while OP was wondering how inexpensive CCGT generation could be threatened by batteries. CCGT and peakers are distinct and have different costs even when they both burn natural gas.

Hawaii doesn't generate electricity from natural gas but it does consume a lot of petroleum-fueled electricity:

https://www.eia.gov/state/?sid=HI#tabs-4

Here's a story about a Hawaiian island replacing diesel output with solar and batteries from a couple of years ago:

https://arstechnica.com/information-technology/2017/03/kauai...

More recently, the Hawaiian Public Utilities Commission has approved 247 megawatts of new solar capacity backed by nearly a gigawatt-hour of battery storage:

https://pv-magazine-usa.com/2019/03/28/hawaiis-new-reality-o...

"The price for each of these contracts was between eight and ten cents per kilowatt-hour. This is cheaper than both gas peaker plants and HEI’s current cost of fossil fuel generation, much of which is petroleum-based, which the company put at around 15 cents per kilowatt-hour."

Note that these prices are only $80-$100 per MWh, because most of the solar electricity is consumed immediately and doesn't need to be stored in a battery.

I'm positive Hawaii could use geothermal power for base load. All those volcanoes. Iceland and the Azores are already doing so.

> I'm not sure any analysis is worthwhile unless it includes the time-of-day, as well as the number of hours that the batteries can load-shift power. 5:00pm to 8:00pm power is going to cost more in the future than 12:00pm power, simply due to this whole solar energy thing going on.

A big part of the problem talking about these things is that people conflate photo-voltaic with solar thermal (CSP).

What you're talking about when you say 'solar' is just the first one.

Solar thermal plants provide power into the night.

Arguments that it's just solar + storage are perhaps valid, but a) it's still solar, and b) nuclear MSR's aren't called 'nuclear + storage' (ditto anything else using latent heat in fluids, flywheels, etc).

It does seem that Solar Thermal plants are better for the expected future of energy demand. I wasn't thinking of them for some reason.

But yes, people need to be mostly aware about the time-cost of energy. Even if Solar Thermal is less efficient than photo-voltaic cells, the fact of the matter is that 5:00pm to 9:00pm power is the REAL problem that people need to focus on. That's when America uses most of its electricity right now, and is likely the main driver of peaker plants at the moment.

People ignore CSP all the time. I estimate that by 2050, when most of the grid electrical capacity is coming from MS storage with operating delta_K's around 1000+, they'll learn.

I think one thing that needs to be considered is for HVAC you can time shift your demand via thermal lag. So for air-conditioning you can pre-cool the house during the day and just let the temperature rise during the evening.

Would people live with that? They would if doing that saved them $250/month.

There are already ice-based thermal storage systems exactly based around shifting the electricity consumption for cooling to off-peak times:

https://www.ice-energy.com/technology/

So you don't even have to let the temperature rise during the peak-demand period.

A friend in Arizona mentioned having solar panels and setting the thermostat to 65 degrees between 10am and 5pm. And off after that. Later at night they open the windows and close them in the morning.

They're just using the thermal mass of the house to time shift energy.

The feasibility of this is completely determined by the insulation and albedo of the house. Working around the thermal inertia of the house is tricky, blasting the AC hard at night is only effective if your house is moderately well insulated or good at not absorbing heat (reflective roof, wall insulation, reflective blinds etc, and by reflective I don't mean tinfoil, I mean like white or bright colored, basically no black or dark). Building elements are remarkably bad at storing heat/coolth since their sensible heat capacity is quite low. There are ways to enhance this effect though by getting building elements that are doped with phase change materials.

Of course the insulation part of the equation is a double-edged sword. You want insulation, but you always want air circulation at a rate conducive to low CO2 levels. Maybe a compromise using something like Sheetrock with extra paraffin, and the whole thing painted Anti-flash white, with air exchange passed through heat exchangers underground.

It would be pretty expensive to maintain though.

In modern homes air tightness and mechanical ventilation are both required by code in many places to deal with the issues you've raised.

Even a crappy insulated house has some thermal lag. Which is what you are playing with.

I think people get confused because a low carbon grid is going to have a different pricing structure than the current one where 'base load' power is cheap at night. The reverse will be true. Power in the evening is going to be spensive. With the cheapest power at noon.

The solution is to time shift demand. A lot of demand can be time shifted. HVAC can be time shifted using thermal lag and storage. You don't really need batteries for that.

Solar is most effective at 12-13pm due to panel orientation and noon insolation. At 5pm it's sonething like 50-60% of noon insolation during the summer (best case scenario).

>> number of hours that the batteries can load-shift power

Isn't that defined by the price per MAh of the batteries which was mentioned in some of the parallel threads?

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