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Comment by barney54 | Hacker News Reader

One very important thing missing is that solar is not dispatchable. It does not serve the same purpose as coal and it is an apples to oranges comparison between solar and coal.

Coal provides baseless power--coal plants are designed to run at a relatively steady level for more than 90% of the time. Reliable power is critical for things like server farms which draw power all the time. Solar cannot serve the same purpose without battery or other backup.

At this time of year in places like California, solar doesn't help meet peak demand either. http://content.caiso.com/green/renewrpt/20160503_DailyRenewa... Solar has a role, but comparing it to coal is misleading.

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Correct. But in large enough grid there are many non-fossil ways available using existing, deployable tech to integrate a high-penetration of non-dispatchable renewables.

For example - utility scale storage (pumped hydro); distributed storage (home batteries and Vehicle-to-grid battery Ev cars); demand-side management; power-to-gas (hydrogen); and geographic grid integration.

See more at

http://www.nrel.gov/analysis/re_futures/

https://www.raponline.org/featured-work/teach-the-duck-to-fl...

http://cleantechnica.com/2016/03/02/base-load-power-is-a-myt...

http://cleantechnica.com/2014/08/08/rmi-blows-lid-baseload-p...

But stored solar energy no longer undercuts coal for most of these storage technologies.

Pumped hydro is probably the best bet, but is very geography dependent. Adding transmission is a non-trivial investment.

> Pumped hydro is probably the best bet, but is very geography dependent.

You could build surface level reservoirs as two tank hydroelectric dams, and then use the water as an energy reserve as well as freshwater reserve.

Rail storage is the cheaper, more versatile version of pumped hydro.

https://www.greentechmedia.com/articles/read/First-Grid-Scal...

https://news.ycombinator.com/item?id=11595195

The physics don't make sense for that one. Simple back of the envelope example: How much mass does a train need and/or how far does it need to fall to provide the same kinetic energy as a lake?

We have a pumped hydro solution where I live. It's huge and only supplements a small power plant.

Why doesnt your back of the envelope calculation (did you do it?) match ARES analysis?

Could they perhaps achieve high enough mass in a small volume by using eg. lead?

Could it be that a train is more efficient at converting potential energy than a water turbine?

Could it be that they have a longer drop?

You gotta show your assumptions if you're arguing through back of the envelope calculation.

Did they provide any calculations?

> the same kinetic energy as a lake

Not all locations have a lake (or 2) conveniently located near a large elevation drop.

The article says "They move up and down an 8-degree slope with an elevation change of about 3,000 feet", that's a lot of energy.

No it isn't. A Canadian bulk train 3km long and massing 20 000 tonne at an elevation of 1000m has a potential energy of 20M kg * 9.8 m/s^2 * 1000 m = 196GJ = 54MW-hour. In the winter my house uses about 50kW-hour per day so that will keep about a thousand such houses running for one day. (130m^2, 1950's house, Norway). yes I know my house is not very energy efficient.

A reservoir 10m deep and 45m square at the same elevation has the same potential energy. If you can find a convenient 1000m plateau I think it would probably be cheaper to build a reservoir on top than to build the tracks and trains.

That's just over four miles of track (21,346 ft.) for the run length of the railcars down that slope. (Thanks, trigonometry!)

Now I wonder how fast these railcars move.

http://www.utilitydive.com/news/first-of-its-kind-rail-energ...

"One of the striking things about the ARES project is its size: 50 MW of power capacity and 12.5 MWh of energy. That would be large for a battery storage project, but for ARES, it is on the low side. “Fifty megawatts doesn’t get us to economies of scale,” CEO James Kelly said. “We are more efficient as we get larger.”

Kelly said ARES projects can be sized anywhere from 50 MW to 1 GW. “If we had a 500 MW project, we could double the capacity and it would only increase capital costs by 20%,” he said."

Interesting. Thanks for the link.

Until they build one, it's only potentially cheaper.

This is one of the most insane yet brilliant ideas I have heard of. I love it.

I wonder how hard it is to scale though.

True - but it is also following the same cost reduction curve as Solar.

See this for a comprehensive annual survey by Lazard on storage technologies and costs

http://blog.rmi.org/blog_2016_01_21_how_much_does_storage_re...

Not sure what you mean by "cost reduction curve". Can you expand?

Every doubling of production tends to result in a percentage decrease in cost. I see numbers for batteries and other technologies of 15-25%

>Adding transmission is a non-trivial investment.

Non-trivial in terms of size and politics, but an extremely solid one that will reduce the cost of electricity.

Molten Salts seems to be the way many solar plants are going (concentrated Solar ones versus Photo voltaic).

> "At this time of year in places like California, solar doesn't help meet peak demand".

That's a very specific claim, and I don't think your cited graph even supports it.

Presumably, you say "this time of year" because you know that the yearly peak in California is driven by air-con usage in the summer afternoons, which correlates very well with solar.

But even right now, in early May, the graph is mostly flat through the afternoon and evening, with only the slight peak at 8 or 9 at night making your statement true in a very narrow sense.

Notably however, the graph only includes grid side solar production, so panels on homes or business roofs are not included in the graph. If you added those to the total demand curve would shift upwards during solar production hours.

The peak demand in California yesterday was at 8:15 pm and solar produced zero electricity at 8:00 pm. http://content.caiso.com/green/renewrpt/20160503_DailyRenewa... But that's that the biggest problem. The problem is that solar is decreasing at demand is increasing. This is the problem they describe with the duck curve. https://www.caiso.com/Documents/FlexibleResourcesHelpRenewab...

Yes, solar can help meet peak load during the summer, but not the rest of the year and it causes stress on the system by requiring a lot of power to spin up to meet demand and solar decreases.

And these are some solutions for the duck curve ramp up problem - how you teach he duck to fly:

https://www.raponline.org/featured-work/teach-the-duck-to-fl...

It would be interesting to calculate what level of storage you would need to store solar electricity from earlier in the day, to meet demand in the evening. For instance, the Powerwall has 6.5 kWh storage, that would support 2kW of continuous demand from 7-10 in the evening, which seems like it could cover a lot of cases.

I don't think you understood my comment.

You don't know when peak demand in California was yesterday, because you're looking at a graph of the utility company's electricity production, not electricity demand. You'd need to add all the self-consumption by "behind-the-meter" solar installations on homes and businesses to find out the real demand peak. From the perspective of CAISO, solar self-generation is indistiguishable from reduced demand.

We know from historical figures that the absolute highest yearly peak in California, the one that you need to build your grid to withstand at great expense even if it only requires that load for a short period of time per year correlates well with solar, and so solar saves lots of money by shaving that peak.

The "duck curve" is also not a demand curve, it's demand, minus self-generated-solar, minus grid-generated-solar. And even then, it only appears in the winter months, when demand in California is on the low end of the yearly cycle something like a third of peak demand in the summer months. (Note the graphs showing the duck curve in your second link are from January and March).

> Yes, solar can help meet peak load during the summer, but not the rest of the year and it causes stress on the system by requiring a lot of power to spin up to meet demand and solar decreases.

Note that Solar isn't "hurting". Because such demand right now is being covered by Natural Gas Peaker Plants anyway.

Natural Gas Peaker plants are expensive, so if we can replace some of their usage with other energy sources, that'd be great. Eventually, we might be able to transition off of them with sufficiently advanced energy storage technologies.

But solar would increase the need for peaker plants if it starts replacing baseload power needs. We are a long ways off from that, but it will limit the usage of solar until solar drops below the marginal cost for natural gas usage.

I'd say lets cross that bridge when we get there. Solar is a very long way from replacing baseload power.

And once baseload power starts getting "replaced", we enter the realm of coal plants and nuclear plants reconditioning themselves so that they can be scaled up and down a bit better.

I know both coal and nuclear power require many minutes to change their energy production, but if a smaller-scale energy storage (~30 minutes) can be created to hold out during the scaling up / down period, the problem could be solved.

As opposed to say, load-shifting pure solar energy (which requires a storage capacity measured in hours, not minutes). High power / low time can be solved with standard Lead Acid batteries or maybe Flywheels (cheaper technology than Lithium Ion, which would be better for hours of storage)

Many homeowners have been told by power companies to shift their power usage to the evening to avoid grid overload... so things like residential AC and pool filters, etc are put onto timers which shift their load to the night. If max power availability is actually earlier due to solar installations, then they should shift their AC to cool during the hot part of the day - leaving the home cooler after they come home...

I don't think that explains everything about the demand curve, but using the current day demand curve to say 'solar doesn't work' isn't looking deeply enough.

I like the Arthur Clarke quote: When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong. - Arthur C. Clarke

This can be attenuated with variable pricing, like in France[1] which has 80% on nuclear—which doesn't ramp up/down very fast. One could call that free-market pricing: more expensive power during high demand, cheaper when supply is high.

Industries and homes find innovative ways to adapt to market pricing. All the appliances there have options to use power at night (when it is cheaper there). For solar, the times may be different but the same idea remains. Commercial power is priced at a premium when the grid is overloaded (typically winter months).

[1] http://residential.edf.com/energy-at-home/offers/electricity...

That's why many solar plants use molten salts to store energy and generate electricity even at night.

"Technicians say that the Noor 2 and 3 plants, due to open in 2017 will store energy for up to eight hours – opening the prospect of 24/7 solar energy in the Sahara, and the surrounding region." http://www.theguardian.com/environment/2015/oct/26/morocco-p...

Solar thermal is not really comparable to solar PV. This article, if I'm not mistaken, is talking about PV, which is an entirely separate technology, with unrelated learning curves / cost reductions.

> Solar cannot serve the same purpose without battery or other backup.

Think of the battery as a really big capacitor operating on a larger time-scale. It's perfectly reasonable to smooth out power this way, and as battery technology improves, you will certainly see more reliable power from solar for things like server farms.

More reliable, but more costly, too; this solar price comparison is skewed if you don't also include the cost of said batteries / battery capacity. Of course, comparing with coal is also missing the environmental impact.

Also note that there are cheaper energy storage methods than batteries. Compressed air, pumped water, flywheel and the recently discussed Ares gravity-rail systems have various price points for storage (kWh) and delivery (kW). Here is the ARES discussion:

https://news.ycombinator.com/item?id=11595195

I agree storage (if required) and environmental impact should both be considered when comparing different energy options.

A lot of people use the battery argument when it comes to solar, but isn't Musk's home battery pack designed specifically for this purpose?

No. They discontinued the larger battery and it isn't designed to operate at grid scale. http://gizmodo.com/tesla-is-discontinuing-its-10-kilowatt-po...

FWIW, your article says that the remaining Powerwall is designed exactly for this purpose.

> The larger Powerwall was positioned as a longer-term back up power supply, which GTM noted was looking like a hard sell, with other market alternatives that were priced far below the $3500 price tag.

> The remaining 6.4 kwh device has less capacity, and is designed more to shift the load of available power, such as from a solar panel, to times when the production of such energy is lower.

Yes and no. Tesla has decided that it won’t be making the 10kWh stationary storage batteries it unveiled in April 2015, instead focusing exclusively on the 7kWh version.

There's nothing stopping anyone from getting more than one battery to make up for the capacity that was offered by the larger model.

They announced three products initially. Two Powerwall products (7kWh daily cycler and 10kWh emergency backup) and a grid scale product called Powerpack. The product that was canceled was the 10kWh emergency backup. They are still selling the grid scale Powerpack.

They discontinued the battery with the lower number of charges because the people actually prefer the more expensive one (per KWh) with higher number of charges.

Also the Powerwall is for home use. For utilities they offer Powerpacks, and they are already on sale:

https://www.teslamotors.com/powerpack/design

*Tesla's, Musk is only the CEO of the company that designed that device, and attributing Musk with its invention or production isn't flattering for the (faceless?) engineers behind the brand.

Yes, we should cite the brilliant engineer who came up with the idea of storing electricity in a battery instead of the CEO that enabled low enough production cost of said batteries to make it feasible... There are many things Musk shouldn't be credited with, but this is not one of those things.

As are CAES, Redox Flow Batteries, Pumped hydro, and other utility-scale energy storage.

Energy storage is improving rapidly. Lithium-Ion batteries are but one technology that I don't personally expect will become the norm at grid-scale.

I thought that was a UPS, designed to cover outages for a short time. Not all night.

It's misleading to say solar doesn't help meet peak demand in California. For at least the past 20 years in California, the annual peak electricity usage has ALWAYS occurred between 2pm and 5pm:

https://www.caiso.com/Documents/CaliforniaISOPeakLoadHistory...

It's true that the daily peak is in the evening and that won't be helped by solar. But grid generation capacity is built to handle the annual peak, not the daily peak, so the annual peak is what matters. And because the annual peak tends to be hot afternoons, solar actually will replace other generation in the long run.

I used to analyze this stuff professionally when I worked at a California utility.

There's something I never understood though. Technically there's always a side of the Earth that is under the Sun, so why can't countries make some sort of equal-sharing energy agreement to avoid needing batteries, if not at all at least hugely decreas the need for them? So that when it's night on one side of the Earth, everything just runs off the surplus on the other side?

Is it just too hard to move electricity so far away?

So you are saying run a power line across the ocean, so the US can power Europe and Vice Versa?

Maintaining fiber optic cables can be hard across the ocean. How about a power line that has a diameter of 50 feet? I can't even imagine the engineering of that.

Info on losses here: https://en.wikipedia.org/wiki/Electric_power_transmission#Lo...

No idea on the math for what % of power we would lose across the ocean.

Seems local batteries would win out..

The article says that a 100-mile 765kV transmission line loses 1.5% to 0.5%. Let's be optimistic and assume we can get closer to the latter and deliver 99.5% of original power over 100 miles. NYC-LON is 3,466 miles on the shortest possible path. Let's call it 3,500 miles. Over that distance, we'd deliver 99.5% ^ (3,500 / 100) = 83% of our original power.

The circumference of the earth at the equator is 24,901 miles. Halfway around the world, we'd deliver 29% of original power.

at that scale, thousands of miles, and enough power to drive a continent, maybe superconducting cables are worth it.

Local kinetic storage like pumped hydro have an efficiency advantage over batteries (at least with current tech)

Yes, it's very difficult to move electricity far distances. I believe it has to do with the natural resistance of copper. While its quite low, it's not zero and it adds up over hundreds of miles of copper. IANAE so anyone feel free to correct me on that

It doesn't seem feasible without low cost superconducting power lines.

For context, the average transmission loss between generator and consumption in the US is ~11%. This is generally over relatively short distances when compared to actual transmission.

In the short term, transmission lines are congested during peak hours so we often can't pipe enough power to high demand markets.

Look up High Voltage DC. Answer - It is hard - but not insurmountable. Technology and financing is readily available. It's lack of will, vision and integrating policies across national boundaries that's the problem.

“Let’s Build a Global Power Grid - IEEE Spectrum”

http://spectrum.ieee.org/energy/the-smarter-grid/lets-build-...

I think you are forgetting that the earth is big. Running power lines big enough to power half of the planet thousands of miles across the ocean will be very difficult.

Transmission losses over large distances are high. And long distance transmission infrastructure is expensive. High Voltage DC (HVDC) is very expensive.

The holy grail in transmission is high temperature super conductors. We're not there yet.

If you think HVDC is expensive, I'm not sure why you think HTSC's would be better.

When you call coal baseload (I assume this is what you intended with baseless), you are contrasting it with dispatchable generation. Coal isn't nearly as responsive as hydro or natural gas or whatnot.

The difference between solar and coal is that the output of coal is more reliable.

No. According to the US Energy Information Administration, coal is dispatchable. https://www.eia.gov/forecasts/aeo/electricity_generation.cfm

It is correct that coal does not ramp up or down quickly, but that is not a characteristic of dispatchablilty.

There are varying levels of dispatch-ability. You can ensure coal is on. And you can also turn it off. You just can't do it near instantaneously.

It's exists between something like nuclear (which has to just be on for months at a time) and natural gas peaker plants (which turn off and one during the day to meet demand.

You could, for example, run coal plants during the winter (when there is little sun) and not during the summer. Or you could run coal on cloudy days. Or just turn it off on weekends.

You see a shortcoming of solar, I see a shortcoming of energy storage technology.

(I understand your actual point, and agree with it)

Coal is usually designed to run all the time rather than be dispatchable on a minute-by-minute basis. To make it dispatchable you need to run it as "spinning reserve" and increase generation. But it cannot be turned on in a few minutes like a modern gas plant. And for it to be economical coal needs to be turned on all the time.

Solar reduces the base load required and makes the maintenance and capital costs of coal stations higher.

Until you do concentrated solar thermal using molten salts to store heat to drive a generator. See this announcement of one of the world's largest solar plants:

http://electrek.co/2016/05/03/worlds-largest-coal-supplier-b...

To give you some illumination on how to deal with intermittent solar checkout out the best paper I've read on this subject: Jacobson, Delucchi on Wind, Water and Solar https://web.stanford.edu/group/efmh/jacobson/Articles/I/JDEn...

well the US's next Manhattan style project should be a nationwide distribution and storage system. We certainly have the tech and resources to move the majority of the country onto renewable sources within a decade.

the only question is, can politicians be convinced to do something good for the country which may not keep them in office?

You would think CSP would at least get a mention on these subjects and how well it integrates with present structure of how we allocate of energy and can complement for those who require use of molten salts for dispatchability… its not like we burn coal in our cars to power steam turbine anyways…

We have never had to deal with the problem of storage for solar power. That's still in its infancy, but as it becomes more mainstream that will change.

It's a different game altogether - batteries etc instead of train cars full of coal. But it will happen.

This is absolutely true. But the solar can still be used to nip in the use of fuels. If you have a fast acting source that can follow the solar signal, you'll still make a dent in the consumption of the fuel that creates the energy.

Not when you realize the desalination is a big thing around the world.

Also need wind to provide base load of course. It's always windy somewhere.

Transporting electricity is not trivial.

Actually, it kind of is, the technology (high voltage DC) is well understood and being deployed at high rates in China. It's also affordable. Assuming no new breakthroughs in wind or solar technology, and ignoring storage, we can use HVDC with lots of wind and solar to eliminate 75% of our electricity emissions, and even slightly lower the cost of electricity. And that's even without shifting any use right now:

http://arstechnica.com/science/2016/01/making-a-single-us-el...

http://rameznaam.com/2016/01/31/how-far-can-renewables-go-pr...

> Solar cannot serve the same purpose without battery

Elon Musk, CEO of Tesla is some 2 to 5 years away from fixing that battery issue and getting extremely rich in the process.

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