Author Topic: Solar Thermal + Molten Salt Storage  (Read 11293 times)

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Offline Kleinstein

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Re: Solar Thermal + Molten Salt Storage
« Reply #25 on: March 11, 2016, 01:23:08 pm »
Currently PV is cheaper than electricity from concentrated solar if you just count the energy. But the concentrated solar-thermal plants often do offer some degree of storage too. PV gives most of there power over something like 3 hours around noon and little over the rest of the day. In central Europe there is already so much PV installed that for these times when PV is really working the price (utility level) for electricity is down (sometimes all the way to 0)  and the grids are nearly saturated with PV. This is a little different in hot countries, where air conditioning is a major demand and peak rates are still paid on hot sunny days.

Also development of concentrated solar is a little behind PV. So there is more room for lowering prices compared to PV.

PV will need some storage like hydrogen or batteries, but this will add to costs and reduces efficiency. Using energy when it is available helps a little, but it does not work for everything may not be practical for all the small things. So if the climate allows it concentrated solar can be more useful than PV.  Concentrated systems can deliver there power to a later time and thus get a better price. They also have the option to use alternative fuel (e.g. gas) to deliver a backup for days without sun.

Offline djacobow

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Re: Solar Thermal + Molten Salt Storage
« Reply #26 on: March 11, 2016, 05:12:48 pm »
I showed that PV is so much more cheaper that concentration is not the future (opinion).

You will get no argument from me on that point. I think CSP has mostly run its course. It /could/ have been different, the industry itself was unable to deliver on promises and the PV industry, in part aided by massive investment, really delivered more than was promised. (Look at $/kWh cost projections from the 2000-2005 era. NREL had a bunch of papers. CSP looked good at the time.) In the end, CSP is far behind on raw cost. CSP also has some limitations that gave it an uphill battle, like it could really only be cost effective at huge scale, meaning huge, difficult to fund projects, and of course, it requires DNI (direct normal irradiance) which means it has to be only in the sunniest places. So it will probably be a niche technology, though I'd be surprised to see it completely disappear.

Also, let's not forget that wind eats PV's lunch cost-wise -- at least in windy places!

I think what will happen: we use excess power to generate hydrogen.

This I'm a bit more dubious about. Yes, PV energy is cheap in sunny places, but to convert that energy to hydrogen (say, 60-70% efficiency electrolysis) then convert it back to electricity (say 40% in a combined-cycle plant or 40-60% in a fuel cell) is a pretty big hit -- you just increased the $/kWh cost of your energy by 4x. Now, you could say, well PV will be cheap enough, but I think PV is not going to get all _that_ much cheaper.

I gather you're in the industry. If you have access to a detailed (or non detailed) model of a new PV project, do the experiment of zeroing out the panel cost entirely. I think that will set an interesting near-term lower bound on PV energy prices. Land, insurance, racking, wire, labor, etc, are not going to get much cheaper.

Cars will run on it. No exhaust gas, and they clean the air (because they have a large capacity air filter, since they require large amount of clean air for the process to work).

H2 also has some issues a a motor fuel, doesnt it? Namely that to store a reasonable amount of it in a vehicle you need to compress it to insanely high pressures. Is that feasible cost wise and safety wise? Also, replacing gas as a motor fuel requires complete replacement of the fueling infastructure. (EVs do not have this problem to the same degree, because you can at least charge you daily driver at home.) These are surmountable barriers, but barriers.

Hydrogen generation is not really efficient now, but can ultimately solve the energy issue.

I agree, hydrogen as a storage medium with renewables as the energy source can solve our energy issues. But I am unconvinced that it will be the solution. I see a landscape too complex to want to make that prediction. I think we can agree that hydrogen is off to a slow start relative to battery EVs, though. This is important, because to a degree investment is destiny. It could be that H2 is the better technical solution, but if the $billions are pouring instead into batteries, it might not happen.

We are already at the point, where the solar inverters have to be switched off in the summer, because the voltage level of the grid is too much. Efficiency is secondary concern.

You say that as if it were a good thing, but it's actually awful. What it says is that on electrical grids that already have a lot of PV on them relative to total demand, that the value of incremental PV is zero. That doesn't make adding more PV cheap, it makes it exceedingly expensive. You have to find something to do with that energy, or you do not want to pay for it. If you can time shift it, you have solved the problem, but all the time shifting available today (battery, hydrogen, thermal storage) is expensive and/or inefficient. What it means is that PV energy during non-solar hours is actually expensive.

Each situation is different, but in most cases, PV is a great up to a point, then its marginal value starts to tank. Most places around the world are not near this point. In some places, they are at it, maybe past it. You do not have to take my word for it.

2012 LBNL high PV penetration study:

Or check out the entire research output of Paul Denholm at NREL: . These papers mostly are about the value of energy storage, but they show are calibrated in terms of penetration level of wind and solar. The value of storage is low at first (don't need it) and then it goes up, showing the same effect I'm talking about. You can also see it in the price duration curves. In low penetration scenarios there are fewer hours where the system price of energy drops to or below zero, in high penetration scenarios there are a lot more. These represent overgen periods; when PV output is potentially less than worthless.

I'm still just learning the PV and renewable industry (new job), but I hope I will be able to shine some more light (pun intended) on the topic.

Enjoy yourself, it's a fun and fascinating industry. Let me humbly suggest that you also look outside the  industry to get a rounder picture of what PV can and cannot accomplish: utilities, regional transmission operators and independent system operators, public utilities commissions, other renewable technology developers, national labs, etc. Yes, they all absolutely have agendas -- this is a space where bullshit abounds, so set your engineering FUD detector  to high, but there is truth and good people mixed in.

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