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Comment by tjmc | Hacker News Reader

Not at night it isn't. High costs for storage mean that photovoltaic solar will need to be complemented by other sources for a good while yet.

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Energy usage at night is far smaller than during the day, so much so that we have an excess at night because of all the plants with constant output. You can tell just by looking at how the power companies charge industrial customers. On a residential scale, they bill you per hour. On an industrial scale there are contracts negotiated and a big component of that is what time of day the power is used. Ski resorts run thousands of HP in water pumps and air compressors to make snow, and they do it at night mostly because they all have power contracts with lower prices at night.

Efficiently moving power from one place to another is the big problem - the 'smart grid' is forever over the horizon - but storage only becomes a big problem after we have switched a massive amount of our energy production to solar and we're a long way off from that. Until then we just need to build a better system to move power from constant output plants to areas served by transient power sources.

There are some problems with this assessment. "Night" doesn't begin at midnight, it begins when the Sun goes down, which can be as early as 4pm during winter in a lot of highly populated locales. That period of time is right in the middle of peak electricity usage, not after it. Moreover, off-peak usage is still a substantial fraction of peak usage, not zero. Additionally, in some parts of the country peak power usage is very much during the night, especially in winter when everyone gets home from work and turns on all the lights and appliances and the heat. These facts are a big problem for a power source that produces absolutely zero power after nightfall.

> Ski resorts run thousands of HP in water pumps and air compressors to make snow, and they do it at night mostly because they all have power contracts with lower prices at night.

Umm, no. They do that because of customers and "night is colder".

Agriculture, specifically pumping water, is an example that supports your argument.

> Energy usage at night is far smaller than during the day, so much so that we have an excess at night because of all the plants with constant output.

Until we start charging lots of electric cars then....

Umm, yes. I've seen electrical rates cited on more than one occasion as the sole reason why they are not making snow 24/7 during the pre-season when they don't even have customers on the mountain. But don't take my word for it, it's published on the power company website.

NY: http://www.nyseg.com/YourHome/pricingandrates/daynighrate.ht...

VT: https://www.burlingtonelectric.com/page.php?pid=49&name=...

The difference is almost 30%.

And that's only the tip of the iceberg. When you look at the area around most ski hills, the mountain is sucking more electricity during snowmaking season than everyone else in the area combined. When you are that big, the power company shows up and negotiates everything. Rates, times, usage caps, etc. The mountain can afford to buy its own generators (or diesel powered pumps/compressors) so the power company has a good reason to cut them a deal, but like every negotiation both sides want something and the power company is looking for someone to buy its excess constant capacity.

The relationship is so tight that the power company will call up the mountain and offer a lower daily rate based on usage elsewhere and the mountain will make snow accordingly.

http://www.usatoday.com/weather/news/2006-12-10-vermont-snow...

> I've seen electrical rates cited on more than one occasion as the sole reason why they are not making snow 24/7 during the pre-season when they don't even have customers on the mountain. But don't take my word for it,

Fair enough.

> it's published on the power company website.

Hold it - those cites just say that night rates are lower. They don't say that lower rates are "the sole reason why they are not making snow 24/7", let alone the only reason why ski resorts run their snow machines at night (which was the original claim).

I don't know what fraction of a ski-resort's expenses go to power for snow-making. Do you?

The fraction that goes to power goes to the question whether day-time vs night time actually makes a difference that matters. For example, saving 100% of 1% is only 1%. I doubt that a ski resort would risk pissing off customers to save 1%.

For example, it may well be that day-time made snow is inferior, or that the transion layer from day-time made snow to night time made snow annoys skiiers. (IIRC, most natural snowfall is at night.)

It's funny. If storage costs drop then everything improves. Hydro would become amazingly useful cause you could run the dam all the time and store the energy in batteries. The biggest problem with power generation is the fluctuation of starting and stopping the plants. Solar would not be a sole beneficiary.

You can store energy in a dam. Pump it up during the day, run it through the turbines at night. Probably not too efficient but lack of storage is not a convincing reason for giving up on renewables, IMO.

“Water in lakes has ~300k cubic kilometers ~ 3 * 10^14 kg http://ga.water.usgs.gov/edu/earthwherewater.html Potential energy is ~ 9.81weightheight Storage requirements (USA): 336 billion kWh = 1.2 10^18 J height = 1.2 10^18 / (9.81 * 3*10^14) kg ~ 408m

We would need to pump water in all lakes about 408m high to have 7 day worth of reserves for USA.”

http://physics.ucsd.edu/do-the-math/2011/08/nation-sized-bat...

Actually, that's wrong by three orders of magnitude. One cubic km has 10^9 cubic meters. Each cubic m has 1000 kg of water, so one cubic km has 10^12 kg. If you now have 300k cubic km, that's 3*10^17 kg.

So you actually only need to use 0.1% of all lakes.

Like the sibling comment by hyper bovine mentions, you can store energy behind a dam.

http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity

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