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The San Diego Alternative Energy Meetup Group Message Board Solar & Electric › Solar Energy and Storage

Solar Energy and Storage

A former member
Post #: 25
"Enough sunlight hits this planet every hour to meet its energy needs for an entire year." Whoa. True?

Some guy at MIT has apparently made good progress toward efficiently electricity storage. That's huge.

A former member
Post #: 255
As I see it this will not get anywhere near the efficiency of solar heated steam turbine solutions that already exist. Those solutions involve the heating something, the "something" varies depending on the manufacturer, which is then used to power traditional type steam turbines. This solution works 24 hours a day and is super efficient.

So this new technique from MIT might make the process of producing hydrogen more efficient. Unfortunately, as I understand it, the basic chemical reactions put the theoretical maximum efficiency of the electricity to hydrogen and back to power at a loss of about 40%. In other words theoretically impossible to achieve the power produced from solar thermal plants already in existence producing power 24x7. These solar thermal plants are what the Bush administration last month was trying to stop. Saying they needed 2 years to study the environmental damage caused by the wide spread deployment of solar power.

However despite not being able to compete with solar thermal hydrogen will be a major energy storage medium of the future. Even at a 40% loss it will be much cheaper than fossil fuel. Perhaps it's cheaper than fossil fuel now. So perhaps this technique from a MIT professor will be the way in which we produce all of our hydrogen for our cars and such in the future. It just won't be what we use to power our electric grid like the article seems to suggest.
Mark C.
San Diego, CA
Post #: 24
Thats because you need to read a more technical briefing on what MIT found:­
And the energy is not in the heat, but in the direct conversion to electricity.
It is pretty amazing.
A former member
Post #: 256
Thats because you need to read a more technical briefing on what MIT found:­
And the energy is not in the heat, but in the direct conversion to electricity.
It is pretty amazing.

Lets assume you can magically convert 100% of the solar energy in to hydrogen and oxygen with no energy loss. You'd still only get back around 50% of that energy when you convert it back with a fuel cell to electricity. Check out this wikipedia entry http://en.wikipedia.o...­
A typical cell running at 0.7 V has an efficiency of about 50%, meaning that 50% of the energy content of the hydrogen is converted into electrical energy; the remaining 50% will be converted into heat. (Depending on the fuel cell system design, some fuel might leave the system unreacted, constituting an additional loss.)

We don't know how efficient MIT's method of photoelectrolysis is. Say it was 100% better than the current best photoelectrolysis mechanisms available and is 15% efficient, see­. It still would not compete favorably with solar thermal to power our electrical grid. (Since solar thermal does better efficiency and tops it off by going directly to the grid instead of getting a 50% loss.)

MIT's method will however, possibly, replace all other methods of producing hydrogen. When we get our hydrogen cars we will probably all switch to something like this for producing our hydrogen. Unless our government decides it is bad for our energy monopolies and outlaws the common citizen the right to produce and store hydrogen. So in some ways this is a break through. However as I originally stated it will not be a replacement for the solar thermal that will power our electrical grid in the future.

I hope this fills in any missing items and clarifies my first post Mark...?
A former member
Post #: 1
Dave has covered several of the questions arising from this topic; just a couple of comments more.

The MIT investigation is basically exploring faster and more efficient catalysts for electrolysis; this may represent a big advance, since current water electrolysis is slow and costly. However, the work reported is still in the early research phase and far from commercialization. We'll see, over time, how important this is for commercial hydrogen production.

As far as any application toward solving the big issue of the contribution of solar energy to base-load electricity is concerned, electrolysis is way off in the future if ever.

Clearly, the questions associated with solar are many; what fraction of load does solar contribute, how does the energy get to market from the (sunny, inexpensive) source location, and, of course, what does it cost in a competitive market? If ( a big if) solar represents a large fraction of anyone's total electrical requirement, then the storage issue needs to be addressed (including that of the fluctuating load on the transmission line). The literature of full of ideas about storage schemes; pumped storage, compressed air, flywheels, etc. etc. Each one of these requires system analysis specific to any proposed solar farm (what kind of solar?), and especially needs projection of lifetime costs.
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