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  •  My mini diary on dispatch and capacity factors (5+ / 0-)
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    Lawrence, ybruti, 6412093, BYw, Egalitare

    What mojo working calculated is known in the business as a capacity factor which is

    ratio of the actual output of a power plant over a period of time and its potential output if it had operated at full nameplate capacity the entire time.
    (name plate is the nominal amount the plant can generate at full steam, or rather, full sun).  

    So, since the sun only shines half the time, and only strongly maybe 35% of the time or so, you aren't going to have solar without storage have capacity factors over 50% ever, because night.

    Now, the other thing to consider is that the amount of load (how much power is used) is variable.  Now, usually that means you have
    1) some big stable base load plants taht are the first plants turned on.  These ones stay on and will have capacity factors around 90%.  
    2) Then as people wake up, get active, load goes up and you need more power, the system operators dispatch more power from other plants.  This is, I believe the kind of role played by solar plants.  What this means is that as "add on" plants, their power is not always needed.  It's only needed when the load is greater than the capacity of your base load plants.  This is what I mean by having dispatch priority.  the baseload plants get turned on first.  What this means is that solar plants may sometimes produce power that is not used because the load isn't high enough to take it.  A natural gas plant in this tier also wouldn't have a 90% capacity factor for this readon.

    Finally, there are peakers.  These are plants that only get turned on when load is at its highest.  Since those are rare, they'll only have low capacity factors because they are idle much of the time.

    So, to review, solar plants play a particular role in our grid.  They only generate during the day, and they don't get priority.  Taken together you would not expect a capacity factor of anywhere near 100%.  In fact, 25% capacity for wind is pretty typical, and a good return.  

    What it means is NOT that we can't generate our energy needs with renewable, but rather than we will need a lot of it to do so.

    What this diary boils down to is that there aren't very good renewable baseload generation options right now (but I love concentrated solar thermal storage plants, speaking as a geek).  As Lawrence has pointed out, as we build more renewable capacity, this will mostly fill the middle tier and peaker roles, while baseload is taken up with hydro, coal, gas or nuclear.  by the time we're trying to build baseload renewables, well, we will have some good options (we have them now, but they're pricey).  

    Hay hombres que luchan un dia, y son buenos Hay otros que luchan un año, y son mejores Hay quienes luchan muchos años, y son muy buenos. Pero hay los que luchan toda la vida. Esos son los imprescendibles.

    by Mindful Nature on Tue Jan 08, 2013 at 03:25:02 PM PST

    [ Parent ]

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