Electricity Forecast For Today? Partly Solar, With Intermittent Base Load Adjustment Or Demand Management
by John Laumer, Philadelphia on 06.17.07
Wind is often characterized as an unreliable power source because 'when the wind dies, so goes the power.' This is easily countered by explaining that wind does not blow uniformly across a geographic region in which multiple wind farms are connected to the same grid, and by the corollary thought - the height at which wind velocity has historically been recorded does not always represent the heights at which wind turbines do their work. However, scientific investigation, not logical debate, is needed if renewable power is to become a common source of electricity. Good thing, then, that the parallel issue for regionally dispersed solar photo voltaic power systems is examined with some rigor in The Character of Power Output from Utility-Scale Photovoltaic Systems, a study conducted by Aimee E. Curtright and Jay Apt, published as Carnegie Mellon Electricity Industry Center Working Paper CEIC-07-05 Available for download, with advance password authorization, here. Following is a brief excerpt from the Discussion section of the paper.
"The intermittency of large-scale PV power for four sites in the American southwest desert is significant, even during daylight hours. These data also imply that site diversity over a ~280 km range does not dampen PV intermittency sufficiently to eliminate the need for substantial firm power or dispatchable demand response. The high correlation between geographically dispersed arrays may indicate that high, widespread clouds are responsible for a portion of the intermittency. Observed rapid and deep fluctuations at time scales of 10 seconds to several minutes may indicate that a component of the intermittency is due to low, scattered clouds with significant opacity. We observe a number of examples of output power rising above nameplate capacity before and after deep drops in power. This may be due to focusing of sunlight around the edges of low clouds."
Sidebar:- How do investor's hedge large scale photovoltaic array bets in the face of climate change? In other words, how does the prospect of a changing climate affect future "sunlight focusing" or alter the regional average intermittancy variables (frequency and wave length variations)?
Other recent TreeHugger posts referring to work by persons associated with Carnegie Mellon includes:(*several others are available in the archives).
One Graph Is Worth A Thousand Back Room Deals:
Solar Decathlon: Pittsburgh's Synergy House
If your library has access to scientific journals, you might want to look up "Renewable and Sustainable Energy Reviews", "Renewable Energy" or "International Journal of Sustainable Energy". These three journals, and others, have enormously complex models by which the potential renewable resources are appraised and mapped on paper long before they are exploited in the field.
There are articles on how to map the wind potentials of sites using geology, meteorlogy and mathematics, and preditcitng the economic payoff of geo- and bio- power sources. I'm sure the serious investors are all over this stuff, or should be!
(Access can be is quite expensive. so it's probably limited to academic libraries, however abstracts are free. Single articles are purchasable online, or likely gettable through your public library's interlibrary loan deparment.)
John, this would be a better link to access the working paper.
+++ THANKS. I pasted that link in place of old one. JL
The radio communications and radio meteorology community in Europe have data about cloud correlation which might also be useful for renewables planning. See for example some of the papers on this page: http://www.cost280.rl.ac.uk/documents/WS2%20Proceedings/ws2.htm.
There is a really really easy way to overcome this problem - add a small amount of storage. For these short durations ultracaps would be fine. For longer storage vanadium flow batteries would be ideal.
This does not apply so much to solar thermal as there would be plenty of thermal inertia in the system to not even notice these fluctuations.
I cannot see why this would be a showstopper.