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View Diary: Solar Energy Cheaper than Coal? (351 comments)

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  •  Hydrogen electrolysis is 50% efficient (2+ / 0-)
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    SarahLee, offgrid

    But, cheap and abundant solar could make the efficiency loss moot.  Although, losing 50% causes some cost savings problems due to the required surface area increase.  But, there could be a number of other methods for storage.

    If distributed solar became the wave of the future utilities could switch to primarily providing storage.  Hydrogen is one method, batteries, super capacitors, gravitational potential energy... If you have a reservoir below your primary generating reservoir the water can be pumped up to the upper reservoir during the day and released to generate power at night.  Wind, geothermal, and nuclear could also provide night time or bad weather backup as well.  

    I think large scale fixed storage is a simpler problem than the small scale storage for transportation.  When size and weight are essentially non-problems and the primary consideration is cost and efficiency there are probably many alternative I cannot even think of.

    And, even just eliminating fossil fuels during the day should provide a huge impact and extend supplies and reduce carbon emission a lot.  

    •  Other stats? (0+ / 0-)

      What is the efficiency of pumping water uphill and using it for regeneration?

      And what is the transmission loss when moving electricity around the country?

      Where is the best discussion of current options?

      •  Not sure... (1+ / 0-)
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        I know batteries and super capacitors hit over 90%..  But, other than that it would take more research than my laziness is willing to do right now. :)

        •  Turns out to be pretty good (0+ / 0-)

          I found an article on Pumped-storage hydroelectricity in Wikipedia and it turns out that where available, it's pretty good.  It's 70-85% efficient, making it "currently the most cost-effective means of storing large amounts of electrical energy on an operating basis."  The article goes on to note the challenges of locating suitable sites and and making the capital investment.

          A table at the end of the article lists around a hundred such sites, including 28 in the U.S. (which also has the world's second largest). So it's more common than I realized.  And such facilities can respond with within 15-60 seconds of demand.

          A sister article on Grid energy storage makes the point that "There is over 90 GW of pumped storage in operation around the world, which is about 3% of instantaneous global generation capacity. However, due to their limited total energy capacity, pumped storage systems are not so useful for covering for electrical supply outages [. . .] If the UK was entirely dependent on wind power, a wind outage lasting just two days would require 140 storage stations with the same generating capacity as Dinorwig to maintain normal power supplies."

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