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New Record Bid Set for World's Cheapest Solar, Undercutting Coal (bloomberg.com)
367 points by Osiris30 on May 4, 2016 | hide | past | web | favorite | 205 comments

Bloomberg News reports[1] that David Keith, a Harvard professor of applied physics and public policy, used to be a solar power skeptic but has reexamined the economics of current solar power and now expects solar power to be important because the economics have changed.

Professor Keith's recent essay on solar power, "Cheap Solar Power,"[2] shows the facts and calculations to explain why solar power now beats several other sources of primary electricity for many applications. It is very likely that many industries will move to places where solar power is especially abundant and inexpensive.

[1] http://www.bloomberg.com/news/articles/2016-05-04/harvard-sc...

[2] http://www.keith.seas.harvard.edu/blog-1/cheapsolarpower

Thanks for this pointer, it's very interesting!

It's hard to argue with numbers that are already there in front of you. A lot of the cost changes have been driven precisely because there was investment and the industry grew, his prognostications about it never being affordable were an attempt at a self-fulfilling prophecy in that by increasing skepticism about the tech curve, it never gets explored.

I'd be skeptical of his views of the future, though. For example, he mentions gas peaking plants, but grid-scale lithium ion batteries are already cheaper than natural gas peakers for many situations; lithium ion is getting cheaper but natural gas is not. The only advantage of natural gas is lower capex, but in this financial environment that's not a huge advantage. By the time that solar is displacing lots of other energy, lithium ion will be displacing all those natural gas peaker plants. Once he sees those numbers, he'll probably change his mind again.

Lithium ion can't store electricity across seasons, though, which is important anywhere outside equatorial areas. Gas can be left idle during the Summer, and used during the Winter. If the cost of solar power went below the marginal cost for burning gas (i.e. lower than the per unit fuel costs for gas generation), the most cost-effective solution might actually be to use solar during the Summer, and maintain a fleet of gas stations solely for the Winter months.

Still one of the most efficient energy storage systems is to pump water up a hill. There are losses in evaporation and conversion but these losses are low when compared to batteries. A system where we used solar power to pump sea water up into a man made reservoir would be very interesting.

Round trip efficiency of pumped hydro is 70%-80%, maybe up to 87% according to some people:


A standard lithium ion batter is at 87% in the worst case, when it's AC-DC-storage-DC-AC. Going direct from solar panels to storage would save one trip:


In any case, the efficiency of storage is only one aspect; it limits how cheap the storage can potentially be, but electricity lost due to inefficiency is not the primary driver of storage cost with any of the currently used technologies.

The efficiency of pumped heat electrical storage is a little worse than pumped hydro. Short description you use use a compressor to compress and heat gas. Use the hot compressed gas to heat rocks. Later recover the energy using a turbine.

The advantages over pumped hydro are,

The power density is much higher, 100000 joules/kg vs 300-500 joules/kg.

You can locate storage facilities pretty much anywhere that's out of shrapnel range. In case the big tank of gas and rocks blows up.

Doesn't have the environmental impact of dams. And rocks are significantly less precious than huge amounts of water.

What's fascinating is some of the research around combined solar & battery designs which to merge the two functions on a materials level.

I haven't heard of this, do you have any suggested reading material?

I was mostly thinking of this research at Ohio State


But I think there may be other areas that I'm not finding specifically right now... ("solar battery" is a poor search term for this research...)

This sounds fantastic:

- a redox flow battery coupled directly to solar charging

- super high specific energy, ~0.33kWh/kg which is right on par with traditional solid lithium ion batteries

My remaining questions are:

- Compared to PV solar + lithium ion battery, how much insolation is required to store a kWh?

- What is the cost/kWh of the lithium iodide?

- What is the cost/kW of the solar charger, discharger?

- Can the anode and cathode be used to charge the battery from standard electricity, in addition to the (more efficient) solar method?

Thanks for this pointer, this gives me even greater optimism about the future of storage!

You might find this video interesting:


A system that uses solar to desalinate seawater and pump it to a reservoir by day, then used for hydro power at night and again for crop irrigation, would certainly be one of the most exciting green engineering projects out there

Yes. Unfortunately water desalination requires a ton of energy but you can use the sun directly.

Pumped hydro is always brought up, which is bizarre to me because it's highly dependent on your geography, unlike battery storage.

Why is it bizarre? It is a dead-simple, relatively efficient storage mechanism that could potentially coexist with municipal-scale reservoir systems (thus gaining cost efficiencies). Sure, Kansas, US is not the first place one would look to build one. But most of the world is not Kansas.

To flip that around, there exist applications where battery storage isn't reasonable. Is it thus also bizarre to bring batteries?

I can drop cargo containers full of Tesla Powerpacks anywhere in the world. I cannot build hydro pumped storage just anywhere.


You're not answering:

> To flip that around, there exist applications where battery storage isn't reasonable. Is it thus also bizarre to bring batteries?

The post I was replying to called talking about hydro storage "bizarre". I was pointing out that it isn't. The logic here seems analogous to saying that compact cars suck because you can't use them as a dump truck.

My argument is that battery storage will slowly become better than all other energy storage methods as the price comes down. Its also helpful that it can be transported and colocated anywhere necessary.

I'm curious - can you name a scenario in which battery storage isn't reasonable? It seems to me that once we hit the cost/price/weight/density points, they are a solution to pretty much any problem of power storage.

Seasonal imbalances, as stated otherwise in thread. Image you have no sun for a month each year. Good luck building enough batteries to handle that.

The strong part of pumped hydropower is that it scales really really well even if the baseline efficiency isn't stellar.

This is a roughly 12 hour reservoir:


It's a big power station, 1.8 GW, but is only providing service to portion of consumers in Michigan.

Making it 10 times bigger would probably be doable but it wouldn't be trivial.

It's also one of the better places on the planet to build a single reservoir system (otherwise you need 2 enormous reservoirs).

I wonder if the answer to seasonal variation will be to make fuel in the summer.

A larger connected world grid could solve some of the problems 10 years or so ago I read some articles of producing solar power in Africa and then using it in Europe.

Is pumped hydro dependent on geography? I'm no expert and I'm skipping over the research and calculation part, but I'd be somewhat surprised if solar panels on my house could generate enough electricity to pump more water up to a tank on my roof than I could run through for power generation.

It's highly dependent on geography, you need two separate, very large, reservoirs at very different elevations. It takes a lot of water across a big height differential to store electricity.

It kind of reminds me of people that think that we should use the exercise bikes in gyms to power the lighting; yes, brilliant, but actually run the numbers and you realize that humans output very very little energy even at peak exercise. The amount of waste on generators would be phenomenal.

There are some cases where pumped hydro makes sense, but there's limited scalability.

Wikipedia has a nice illustration of the amount of power stored

For example, 1000 kilograms of water (1 cubic meter) at the top of a 100 meter tower has a potential energy of about 0.272 kW·h (capable of raising the temperature of the same amount of water by only 0.23 Celsius = 0.42 Fahrenheit).


Given the much smaller height of a rooftop tank, every 1000 kg of water pumped would support a number of minutes of normal household usage (a decent refrigerator would need several thousand kg per hour).

You can water pump uphill, or, as they're experimenting with here, you can pump air underwater: https://www.torontohydro.com/sites/electricsystem/GridInvest...

I'm sure compressed air in other forms would be a good store. You could also raise and lower weights into a mine, it doesn't matter so long as you can convert between electric energy and kinetic potential of some kind.

Quick calculation:

1000L tank on a roof which is ~4m high.

E = m * g * h = 1000 * 9.8 * 4 = ~40,000J

Which is about 12Wh not taking into account any losses.

You could maybe improve this by having the water fall into a well but still nowhere near what a battery can provide for a fraction of the cost/complexity.

A standard 100Ah battery will provide 1200Wh.

Does it work with seawater? Some countries have a frightful shortage of freshwater, so rather than risking loss due to evaporation, could you pump seawater uphill?

In theory seawater would work but it's important to consider the increased expenses and operating troubles from seawater. Corrosion, bio-fouling, increased need for filters and filter maintenance, etc...

Outside equatorial areas, lack of sun coincides with demand for heating. Combined cycle (correction: I meant cogeneration) heating plants are that winter months fleet.

Yes, if you could combine gas generation with district heating, that + solar generation really would fit together neatly.

Also, there are projects to do the thermodynamic equivalent of district heating over a single home! i.e. you burn gas to produce electricity, and use the waste heat to heat your house or office. A year or two back British Gas was doing a pilot using a gas boiler with a Stirling Engine to generate electricity (called the Ecogen IIRC). It seems to have been difficult/expensive to maintain, but it's an exciting principle.

If you had battery storage for solar during the Summer, you could use that equally to buffer that kind of gas generation in the Winter.

It seems to me sufficient solar and battery cost reductions effectively solve electricity generation for everywhere close to the equator. Add in that kind of waste heat boiler, generating electricity at a reasonable cost, and you have a solution for almost the whole planet.

composite thin cylindrical flywheels have great energy storage characteristics "greater than 400 Wh/kg can be achieved by certain composite materials" https://en.m.wikipedia.org/wiki/Flywheel_energy_storage -----

You could store the electricity through H2O electrolysis, directly burn for heat or reclaim through a fuel cell for electricity.

Electrolysis is only about 60% efficient. This is why a lot of effort is being put into Concentrating Solar Power which stores heat in molten salt.


If solar becomes 3x cheaper than coal, a 40% loss isn't going to matter.

Better yet, those fuel cells can be "charged" wherever energy is plentiful then shipped as needed.

Sneakergrid anyone?

Is there an alternative to platinum yet?

Fuel cells sound really neat, and I had no idea you could actually by your own until a couple days ago. But the estimate of a small continuous use unit needing to have the catalyst replaced up to annually seems to make them a novelty for now (the existing units that is).

Interested in knowing more if you keep up with it though.

This would of course be incredibly inefficient. Maybe you were joking.

Electrolysis is too inefficient for in-place energy storage, but economies of scale could in fact make this acceptably efficient for long-distance energy transport; available solar resource varies by more than a factor of three even within the contiguous US. LNG tankers are already a worldwide business, and LNG equipment can be used to transport hydrogen, albeit at much lower energy density. (Generating methane or ammonia from the hydrogen to improve its transportability might be worthwhile.)

Transmission losses in the electric power grid are around 6.5%, but that's because the energy is typically only transmitted a few hundred kilometers; about 4000 km is the longest cost-effective distance for AC power transmission. LNG tankers can travel further than that.

Could also use the Hydrogen and CO2 to make methane and utilize existing infrastructure.

The Graduate, 2016: "I just want to say one word to you. Flywheels."

I can't really see widespread use of flywheels. They are good for high power, low total amount of energy situations, namely frequency regulation.

Bearings and motors/generators are very well understood, unlike lithium ion batteries, so I don't see them getting much cheaper as a flywheel industry expands.

Currently, the most expensive lithium ion battery is cheaper than the cheapest flywheel:


Flywheels are really cool. Especially when they explode sending out high velocity shrapnel and/or leaving a molten mass.

Still a flywheel powered car using three flywheels set at opposing angles (so their gyroscopic effects cancel) composed of tightly wrapped layers (so they cannot explode) would be awesome.

It isn't the shrapnel from flywheel failure that's hard to deal with. Frag containment, particularly of composite rotors that have high volume fractions of fiber and low volume fractions of binder, is actually pretty easy.

What's really hard to deal with is the angular momentum. Regardless of how the rotor fragments, angular momentum is conserved. What this means is that the failing rotor will produce amazingly high torques as it encounters stationary surroundings.

For typical rotor failures, you can figure that most of the angular momentum will get dumped into the environment in a few seconds as the fragments dig into whatever they hit and come to rest. So as a napkin exercise, if your flywheel spins up to full charge over a period of an hour, and then dumps all that momentum during ten seconds when it fails, you can kind of approximate the torque drama by multiplying the charging torque times the ratio of the charge duration to the failure duration. (I know the torque varies with the flywheel speed, etc. - this is just a disaster estimation exercise.)

The practical effect is that you have to secure the containment really well to make sure it doesn't break loose and roll through your facility on its way out into the street.

The only two ways I've seen of dealing with the angular momentum problem are (1) have two adjacent counter-rotating wheels that jam into each other when there's a failure or (2) have a containment shell that is free to rotate on one-time use mechanical bearings so it can take the failed rotor momentum and dissipate it over a reasonable time with a braking mechanism. Neither solution is cheap.

You could have a two wheel car if have a large flywheel.

This is the best quote imho: "If we can get CO2 from the air at 125 $/t-CO2 then the idea of making fuels at prices of order 1 $/L looks plausible over the next few decades."

It's uplifting to me, both for the high value on a ton of CO2 and the (still) low resulting price of fuel. Solar beats fusion (chance * impact)!

Solar is fusion-at-a-distance, though...

Yeah, with cheap enough electricity you can run the chemistry of burning transportation fuels backwards, and wind up making our current cars carbon-neutral.

Also with a really large number of solar plants, maybe the earth would cool slightly?

> It is very likely that many industries will move to places where solar power is especially abundant and inexpensive.

I suspect over time the cost of producing solar electricity will become negligible against the cost of storage. The key thing will be not so much the lower levels of sun which you get in temperate latitudes, but the variation you get between Summer and Winter levels of insolation, which means you have to maintain backup generation. Variation within a day you can deal with, variation from season to season will be much more difficult. But as you say that is going to drive some interesting changes in geopolitics.

> the variation you get between Summer and Winter levels of insolation

The obvious thing to do is just size the solar array for the winter insolation levels, since the solar part is likely to be so much cheaper than the storage part.

Also, don't forget wind, which is also super cheap at the good sites. It will balance out some of the seasonal shift, and also a good amount of the night time needs.

This all depends on cross-continent interconnects, and energy markets. The entrenched interests are going to resist mightily to anything that might cost them even a cent, and they control the laws to lock out competition.

I view interconnects as important an issue as the interstate system. It will enable so much innovation and drive down costs quite a bit.

Sufficient storage to handle local load + variation should be pretty well predictable in the future. The interesting difference to me is, since storage will probably cost substantially more than generation, what the ratio will mean for cost of energy in various locations. I have no doubt that at some point, the solar generation + storage formula will be broadly cheaper than fossil fuel.

Very large scale storage is fairly cheap as long as it's used every day. The issue is when your pumped storage power plant is only needed 1 month out of the year. However, with solar the daily demand for storage is fairly fixed as excess capacity is all generated at the same time of day.

That's just an overcapacity problem (in this case, overcapacity on generation, not storage). In another post here, I proposed that we build a smart grid that supports pricing arbitrage on generation/storage in order to maximize generation utilization, and then let the market sort out storage requirements with a more distributed, fine-grained storage model - car batteries, for example.

"Bloomberg News reports[1] that David Keith, a Harvard professor of applied physics and public policy, used to be a solar power skeptic but has reexamined the economics of current solar power and now expects solar power to be important because the economics have changed."

I don't follow solar/power/coal news much, so forgive me ...

Is all of this ex-subsidies ? That is, if we remove the subsidies that coal gets and the tax credits / subsidies that solar gets, does the math still pencil out in the way that still makes David Keith no longer a skeptic ?

Yes, solar and wind are both below the cost of coal, natural gas, and nuclear, without subsidies (doesn't take capacity factor into account though). I'm always reposting that data here, so I won't dump a full page of citations here, but if you response with contact info, I'd be happy to send detailed information.

> Is all of this ex-subsidies?

Also ask what price point would be needed to scale back CO2 emissions to something sustainable. Then run the economic analyses.

Dubai has both oil and solar in abundance. They are bound to continue to be one of the richest countries in the world along with the entire UAE. Political considerations allowing.

Abundant sunlight is much less rare than abundant oil...

Dubai has almost no oil, there's a few small gas wells, that's it.

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.

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





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.

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.


"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."

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.

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.

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

Interesting. Thanks for the link.

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


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%

> 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.

>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.

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).

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.

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

> 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)

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


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:


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?

*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.

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.

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:


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.

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:


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?

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

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.

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

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”


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.

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

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

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:


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:



> 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.

There's been some discussion of solar generation cost vs storage cost here, with the idea that any generation project is necessarily coupled to storage. But is that really the case? I can see a model where generation and storage are completely decoupled businesses.

Large, somewhat unpredictable fluctuations in the cost of generation (solar and wind) should lead to large fluctuations in price of generated electricity, down to minute-by-minute. Ideally, generators want to sell every kwh they can at peak production, even at a lower cost. With modern computer controls, this makes a delightful opportunity for an arbitrage market.

Storage providers - and this could be giants like lake-scale hydro, or dwarves like the batteries in electric cars - could buy electricity from generators when it's cheap, and sell it when it's expensive (the sun isn't shining, the wind isn't blowing, hot day spikes demand, etc). This can be fully automated. Just plug your car into the wall at night. It might decide to buy electricity, or sell electricity, depending on the price at the time. Aggregators could pool capacity across many small providers. Large storage systems could benefit from economies of scale and long-term contracts.

Create a smart grid that can support this, and let the free market solve the pricing problems for us.

It looks like the markets are already moving in that direction.

The PJM capacity market had a big increase in demand response supply circa 2012, though not much of it was from storage. Still, new players are paying attention to these arbitrage opportunities. CAISO is already seeking out corporate partners to participate in demand reduction.

There is already an large arbitrage opportunity. The difference between peak and baseload pricing is pretty high.

If it was clearly economical, someone like Exelon (who owns nuke plants) would probably be doing it.

Then again, at lest several utilities claims they were going to buy Telsa powerwalls to do it. So maybe the pricing is getting to the point where it's profitable.

Building something genuinely new, like caching electricity, is fraught with technical risks, financial risks, and regulatory hurdles. It's the kind of thing that can put a billion-dollar enterprise out of business. So expect a decade or more of research, small-scale experiments, political negotiation, and more, to bring storage online at any sort of scale. It's really, really hard, and really risky.

Nuclear plants, as you probably know, are almost pure base load solutions. They can't just be scaled up or slowed down arbitrarily. A volatile, arbitrage-based market efficiency would be pretty hard on the existing nuclear base, and could render a lot of plants unprofitable.

Meanwhile, the gas-fired peak load plants are tremendously expensive, because they have so much downtime and are inefficient. One or two decades ago, competing against them with storage was economically impractical. Now, it's becoming feasible. Especially once we start building gigawatts of sitting capacity anyway, in the shape of EV cars.

Right now the model for electric cars is that you charge at home overnight and run it down during the day getting to and from work. But if employers outfit their roofs with solar, you could invert the model. Charge during the day as an employment perk, and run down overnight to power your home.

I don't think I've see anyone argue that they have to be one integrated business; just that both need to exist to make the other useful.

It's not cheap because the costs of building it is cheap, the companies are willing to undercut each other for the benefit of getting the contracts. The question is whether they will ever be profitable at this level.

No - they are able to undercut as they have access to hugely cheap loans, which the others do not, so the bid come in close to the actual hardware and running costs, not that figure plus the loan repayments.


One can suspect that Masdar had access to long-term financing through the wealthy emirate of Abu Dhabi that no commercial banks, the primary source of capital for the other bidders, could match in cost.

From: http://www.apricum-group.com/dubai-shatters-records-cost-sol...

Why would someone bid at a price like this before the project is set up if it was not the least bit feasible?

PR? Hidden subsidies? Lucrative maintenance contracts? Desperation for revenue in a competitive market? Overly aggressive sales staff? Contract loopholes for cost overruns?

High risk, high reward investment by individual actors who don't have to answer to boards and regulators.

I think they mentioned there isn't any support from the government involved.

^ this bot knows what's up.

My guess: looking at the curve, and when they'll actually have to purchase the PV panels (a few years from not), things will be actually cheaper.

They will is they get subsidies to do so.

They mentioned there aren't subsidies involved. It looks like they're trying to beat the curve.

Also, UEA don't have taxes and cheap foreign labour to built it.

I work in solar, and here's some quick facts:

1. 1 out of 78 jobs created in the U.S. last year were solar jobs[1].

2. There are more solar employees in California than utility employees[2].

3. Soft costs (non-hardware) were recently 64% of the installed cost of solar[3].

4. Solar is expected to reach a load defection point (i.e. cheaper to leave the grid) in most places in the next 10-15 years[4].

5. Energy over the next 25 years is a potential $200 trillion opportunity[5].

Like OP's article states, this industry's hardware has gotten really cheap, but the software in the industry hasn't kept up in places. So much so, in fact, that an entire startup accelerator program in the bay area, Powerhouse[6], has been created to try and attract tech entrepreneurs into the solar industry to make the next generation of solar software. My startup recently went through the program, and being a part of this industry is one of the most empowering and rewarding things I've ever done. It's one of those extremely rare instances where you can have a solid business model and a positive impact on the world.

And we need all the help it can get. Solar expected to grow 100-200x over the next 25 years[7], but it won't happen if smart people don't join in. Smart grid, machine learning, energy storage, demand response, customer acquisition, logistics, energy efficiency, inventory tracking, IoT, security, and many more software areas are currently in the dark ages in energy. Solar, wind, nuclear, geothermal, storage, and other clean energy sources have to replace 87% of the worlds energy in the next 32 years[8]. PLEASE HELP US!

If you're a tech entrepreneur, and want to do something that matters, please please please consider doing a startup in solar or other clean energy industry. To start, if you're in the bay area, there's a hackathon next weekend around solar software[9]. I encourage you to come and learn more about solar and software in the clean energy sector.

[1]: http://energy.gov/eere/articles/1-78-new-jobs-america-solar-...

[2]: http://www.calseia.org/index.php?option=com_content&view=art...

[3]: http://energy.gov/eere/sunshot/reducing-non-hardware-costs

[4]: http://blog.rmi.org/blog_2015_04_07_report_release_the_econo...

[5]: https://www.citivelocity.com/citigps/ReportSeries.action?rec...

[6]: https://powerhouse.solar/

[7]: http://www.bloomberg.com/news/articles/2015-06-23/the-way-hu...

[8]: http://www.pvsolarreport.com/the-next-internet/

[9]: https://suncode.splashthat.com/

Can you give a quick summary of the non-hardware problems that need solving and can be solved by an outsider to the industry with no connections? Not having any knowledge of solar, it seems like the only thing to do is have something that monitors the panels and their energy output, which as far as I know already exists. IoT solutions (like a smart washer knowing when to run) are still largely hardware driven and not feasible for bootstrapping.

Working on stuff like smart grids, demand response, inventory tracking, security, etc seem like something the big companies who own the infrastructure need to be doing. Some random entrepreneur isn't exactly in a position to make solutions for these giant companies because there's no way to have access to the information needed. And even then, selling software to giant companies is hard as shit, and if you strike out there's not exactly a lot of other customers to sell to.

It just doesn't seem like an environment conducive to entrepreneurship.

Most people will find leaving the grid very inconvenient, whatever the saving. Here in South Africa, rolling blackouts caused chaos. Yet very few people left the grid.

I'm surprised a domestic solar installer hasn't grabbed market share. South Africa should be an ideal market, like Hawaii.

I remember a few days ago when we had a thread about an Indian minister saying the same thing, and everyone was being skeptical and negative. Well look now, seems like he was right.

In the USA heating, HVAC, etc.. account for half of the energy used in residential buildings. https://en.wikipedia.org/wiki/Solar_thermal_energy Direct solar water heating (passive) has been used for quite a while and has a maximum efficiency of solar thermal systems are between .46 & .74. https://en.wikipedia.org/wiki/Solar_water_heating

That compares to a solar panel efficiency of .15; and I guess a lot less when applied to water heating due to conversion. And implementing in dense urban areas, passive is not as viable as active. If we were serious we would first implement passive systems. But we don't. I guess there’s something I don’t understand.

Why would you expect physics to dominate economics?

For investors, a big power station like this is a purely economic decision (will it be profitable or not).

For a homeowner, a few dollars a month for hot water is not a significant motivator to make a change (replacing a thing that works to save money after several years is not exciting).

It would probably be a good idea to figure out how to incentivize rental property owners to increase building efficiency. Or maybe just pay for it directly in exchange for a few years of not capturing the benefit in the rent.

It's nuclear power from a remote reactor, and it isn't too cheap to meter but is heading that way.

Wait, these are still projected costs, right ? How can they guarantee they'll be able to recoup their costs and honour their prices?

From the discussion of this yesterday, I understand that most other companies could also meet these costs, if they had the same access to very cheap loans. These bids are supported by near minimal cost loans, that are being offered to help kickstart the industry in these areas, and to acquire skills and knowledge. Plus in the hope that the continued improvement in solar panels, rather than relying on the tech they can get their hands on today.

Vast majority of solar power costs are upfront capital costs. So if you know how much the panels/installation costs, what are your financing costs for ~30 year amortizing loan and how much the sun is expected to shine in the installation place, calculating the cost of electricity price per kWh is not too advanced Excel trickery.

The potential desalinisation this could lead to is also pretty exciting

Why not just put water pools in plastic domes, collect the dew at night?

Creating electricity with a lot of effort and using it for heating water doesn't make sense.

State of the art desalination, reverse osmosis, doesn't heat the water it pushes it through semi-permeable membranes.


Ah, I now realize what stupid assumptions my question had!

Cost. Large scale desalination is really cheap as in gallons per cent.

Desal is not the panacea many believe it to be. There are serious environmental consequences associated with all the brine discharge.

Can't you just dump it back in the ocean where it came from?

The sea critters are already happy to swim around in it, and you're not going to meaningfully change the concentration of the ocean. You could mix it with sea water near the exit point to avoid temporarily raising the concentration there.

Nope, not if it's not carefully dispersed. Brine is denser than saltwater. It tends to sink to the bottom, where there is little wave action or tidal flow, and remain there. It's believed that many marine organisms are negatively affected by the increased salinity, although the overall impacts are not well understood.

Is that because it's actually hard to avoid the consequences, or because a lot of plants are lazy about diluting brine to save pennies? Let's think big, willing to bump the cost by 50% to make brine disposal safe. How hard is it then?

I haven't read more than the summary, but this California study seems to say that mitigation can be effective:


Or, you know, you sell it as salt

(though you might need more sun and space for that)

It's not just salt, it's also the rest of the contaminants that came out of the seawater. The processing costs are greater than all the other ways to get salt.

Regular table salt do come from saltwater, you know that, right? https://en.wikipedia.org/wiki/Salt#Production

"All the other ways" is salt mines

Since you don't want to just Google the answer for why they're not already doing this, I'll do it for you.


Second question down.


"Whereas they concentrate seawater 1.5 times, recovery of salt would require seawater to be concentrated ten times. Under such conditions the first crystals would appear in the brine"

You'll just start with something more concentrated instead of seawater

Yes, you might have a reason to not want to do that, it might be easier/cheaper to just throw it back into the sea

Based on Dubai's recent history, I'd speculate there is some slave or slave-like labor involved to make it viable.

Slave labor doesn't help much for high-tech projects. Slaves are mostly useful for manual labor that doesn't require literacy or complex skills.

Remember, before we invented tractors, if you wanted to move a thousand tons of rock a mile, it had to be done largely by hand. That is a use case for slave labor. Before we invented harvesters, cotton had to be picked by hand. That is a use case for slave labor. Domestic servants are a use case. But the invention of powered machinery made most slave jobs obsolete.

This is great news in terms of econometrics, but I think the major looming questions still exist.

1/ Can solar impact CO2 emissions beyond single digit percentages?

2/ On what order of magnitude would battery storage capabilities have to improve to match performance characteristics of natural gas peaker plants or dare we say Oil/Natural gas?

3/ Don't the fluctuations in peak demand make solar less attractive because they require rapid natural gas peaking plants when there's increases in usage? (Outside of summer is a great example)

4/ What would be the desired performance characteristics of batteries that would make Solar a no-brainer for the environmental impact and actual viability? Cost, capability, and reusability.

Comprehensive annual report on the state of various deployable grid storage technologies - and answer to your questions here:


Everyone is talking about storage, but why not route power to need? Put 4000 square miles of solar in the Mexican desert and sell the power to to the northern US and Canada all winter. Run power over Siberia and Alaska to get across time zones.

Ideally, yes we would do that! But see other comments about the cost and efficiency of power transmission for the physical challenges involved.


I recently came across an interesting new approach to store renewable ebnergy by moving large masses on rail cars up a slope. Here is some more information on the approach http://www.aresnorthamerica.com/

Are these articles on how solar is poised to make it big Real Soon Now (tm) an instance of pg's submarine? [1]

[1] http://www.paulgraham.com/submarine.html

This is the far more common someone-wrote-a-press-release-that-makes-for-a-headline.


> the Dubai Electricity & Water Authority, the utility for the Persian Gulf emirate

Curious that Bloomberg opted for the Persian, over Arabian, Gulf when referring to the United Arab Emirates.

> The body of water is historically and internationally known as the "Persian Gulf". Some Arab governments refer to it as the "Arabian Gulf" or "The Gulf", but neither term is recognized internationally.


Isn't "Persian Gulf" the globally recognized name of that body of water (at least in the anglophone world)?

And yet trying to work out the finances in my condo building, its not adding up... We can get solar and do the right thing, but it will still cost us.

Is your condo located in an extremely sunny desert?

No the northeast. (massachusetts). Brick building. Flat roof that gets good sun.

That additional 20°s of latitude makes a big impact on the amount of sun you'll see, regardless of how suitable the site is.

For us its that the common part of the building doesn't use a lot of power. Individual units do use more than we can generate. So we have to plug the solar into individual units, which can be problematic and kind of a pain.

Is it this cheap because it is subsidized by oil revenue tho'?

Big giant government projects never have cost over runs.

Actually they do, but they also result in dramatic changes (Railroads, Highways, Apollo, TCP/IP, etc).

Sometimes, yes - more often they result in cronyism and officials and bureaucrats amassing power to trade for $$.

Since you brought up trains, look at the giant mess that is the California 'bullet' train. Not a single section of track has been completed, and it's already doubled in budget, reduced dramatically in speed (current projections put the trip time at ~4hrs due to a number of issues including track sharing), with ticket prices 70% higher than promised, and the legal requirements for private investment have been ignored because no private company is willing to touch it with a ten foot pole.

Dramatic changes indeed...

However for every Apollo, there's a dozen Solyndras.

Hmmm, looks like the US Government made the money back from that one. As a whole, American Recovery and Reinvestment Act of 2009 is MAKING money from the loans.

Even Solyndras is just one tiny failure in a massive pool of wealth-creation with regards to the entire program. US Government makes money from the loans. US citizens created jobs for each other. Solar energy development got accelerated.

The only answer to Solyndras is... damn, that was a single battle lost (0.5 Billion loan default), but the US definitely "won the war" on the $800 Billion program.

Just pointing out it was an estimate and the end cost might be very much higher.

"Prime Minister Justin Trudeau of Canada grabbed international headlines recently with a simple explanation of a cutting-edge technology called quantum computing."

While dodging a question about his understanding of economics. Forgive me, I'm just a bitter Canadian upset that we're now running a huge deficit and passing the buck on to our children.

I can tell you as an American, that after a while you get used to the feeling of a huge national deficit and multi-trillion dollar debt. It becomes something like a warm blanket of guilt that helps you sleep at night.

Issuing debt is just an accounting trick to maintain credibility of the currency (i.e. That we aren't just printing dollars willy-nilly to fund the government)

The huge chunk of debt is owed from one part of the government to the other.

No one ever cut their way to growth. The key is almost always to grow the GDP faster than you grow the debt on average. The nominal debt number will never go down - ever - but it should stay fixed or shrink relative to GDP if possible.

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