Hacker News Reader

Comment by skybrian | Hacker News Reader

A problem with processes based on using excess power is that they use equipment inefficiently. If cheap power is only available for a quarter of the time then it would take 4x as long to pay for the investment in the equipment. Whatever scheme you set up to use excess power needs to be pretty cheap to make it worth running only a small part of the time, or it needs to be doing something especially valuable.

Compare to the strategy of locating somewhere that electricity is always cheap and running all the time.

View on HN

Solar produces only during the day, but wind is at any hour. And these days, the idea of massive over-provisioning is being discussed to overcome the intermittent problem since solar/wind keeps getting cheaper and cheaper. The idea is simple, how to overcome the cloudy winter day issue? Simply overbuild a lot of solar/wind so it can still provide enough on a winter day. Then during summer, shutoff the excess power generation.

But what a waste of potential to do that! All that overbuilt power generation, simply turned off during summer. Batteries don't help here, it would store it, but then the question of what to do with it is still here.

If society goes the route of massive overbuilding solar/wind, then there's an opportunity to do something with effectively free power during summer. But it's ONLY during summer, so it needs to be something valuable that can also act as a energy storage.

Carbon fuel is perfect for this. Millions of ICE cars exist and are still being produced. Long distance airplanes will be carbon fuel based for a long time. And so many other uses. I think another option is water. Water can also be seen as a valuable resource that acts as energy storage. Use the excess summer power to fill up a near empty dam with desalinated water? Sounds like a perfect fit for regions like southern California or Arizona.

Oh, but look at the equipment that's shut down, doing nothing, all winter! What a waste. Sure, the electricity is a bit more expensive, but it's still fairly cheap so why not turn it on and get some use out of it?

All processes have some waste. In the end, you need estimates done with real numbers to see if it's worth doing. We aren't going to settle it with casual chit-chat.

>Use the excess summer power to fill up a near empty dam with desalinated water?

Pumped storage hydroelectricity is the biggest form of power storage at the moment, and has efficiencies around 70-80%. The losses for desalinization (pumping through media) are ruinous compared to just pumping uphill, and storing desalinized water means you can't use it without spending potential power. There might be good reasons not to mix desalinization and energy storage.

As I understand it, the main challenge with pumped storage is that you can't do it everywhere. You need fairly specific geography for it, and it's a big civil engineering project. Here's a good video on by Practical Engineering:

https://youtu.be/66YRCjkxIcg

Good video, thanks. It briefly mentions the idea of pumped seawater storage. Is that really any different from using freshwater, other than location?

I imagine the main difference would be salt content, but I can't speak to how that would affect things.

seawater is saline, you have to be careful what you do with it because you dont want to literally salt the earth where you are (soil remediation friggin sucks).

seawater is also not valuable. You don't care about the water quality in the reservoir, you just let it fall back into the sea. If it evaporates you're losing energy but you aren't losing potable water that you sell, and it doesn't require a connection to a water distribution main.

> You need fairly specific geography for it, and it's a big civil engineering project.

You need elevation difference and fairly stable soil. Everything else is technologically solveable. It's a big civil engineering project but its a profitable one and not particularly challenging.

I think the idea here was simply to use the excess energy to stock up on potable water, which people could drink later, rather than to also use it for pumped storage.

> I think the idea here was simply to use the excess energy to stock up on potable water, which people could drink later, rather than to also use it for pumped storage.

If it was a reasonable and profitable use of energy we would already be doing it, but we're not because its ruinously expensive. You also run into storage issues (how much of your excess power is being evaporated from the surface of your storage reservoir? The longer you hold your potable water the more you throw away). You also need to consider what you're going to do with the highly saline byproduct of any such process.

There's nothing wrong with purifying water but its very energy intensive and already something we do. Adding more expensive potable water from excess energy generation doesn't make much sense.

One issue with carbon fuel is air pollution, we have seen during the pandemic that getting people out of cars is a big part of solving that.

Re water, in addition to filling dams with desalinated drinking water we could also refill aquifers that are being emptied by overconsumption of water (often leading to intrusion of saline water into the water table and associated problems).

If BEVs capture even a fraction of the market then you've effectively a massive distributed battery which could help soak up the excess renewable electricity. Quick estimate - if 1% of the US passenger vehicles were BEV each with 50KWh batteries on average is 100GWh of storage.

It would require dynamic pricing to the consumer to work as off-peak prices would need to be low or very low to encourage all BEV owners to take on the excess power at particular times of the day.

By the way, unfortunately dynamic pricing seems to be a very unpopular idea as far as I can see.

Yes, you can't do your price calculations based on 24/7 utilisation. But that's true for almost every other bit of technology as well. What's the average utilisation of a theatre? Of a plough?

Reply on news.ycombinator.com