Abstract:

Wind and solar energy are free, but the cost of integrating them into power grids is not free.  Taking everything into consideration, wind energy is still the least expensive form of electricity we have.  While solar is still about twice grid price, the cost of solar has a downward slope.  And, of course, intermittent power sources are problematic because 1. the wind does not always blow, and 2. the sun does not always shine, but 3. people always need electricity.  This presentation will describe the basics of wind and solar generation while describing two on-going research projects that deal with them. 

The first topic is about wind turbines, synchrophasors, and the independent Texas Synchrophasor Network at U.T. Austin.  “Synchrophasors” is the term used for measuring grid voltages (and sometimes currents) at distance points across grids, approximately 30 times each second.  The purpose to observe relative voltage angle differences from, for example, West Texas and South Texas wind farm regions to central ERCOT (i.e., the triangle formed by DFW-San Antonio-Houston).  Power flow across grids is proportional to the sine of voltage angle differences, thus phase angle differences give a clear indication of grid power oscillations caused by changing load levels and generating unit trips.  When damping is too small and oscillations persist, and it can be concluded that the grid may be too close to instability.  The Texas Synchrophasor Network, which includes monitors at McDonald Observatory, U.T. Pan Am, Austin Energy, and Brazos Electric, record these data.  Recent observations and the key “lessons learned” thus far will be presented here.

The second topic is the impact of high-penetration levels of photovoltaics in power distribution systems, specifically the effect of cloud movement on voltage quality.  As cloud shadows move over, the output of PV arrays drop from full power to about 30% power in a few seconds.  This means that a power distribution feeder will have a varying generation supply that has the potential to create annoying voltage flicker and cause distribution power equipment to try to correct for voltage fluctuations that are too rapid for their designs.  A description of the instrumentation built to observe cloud shadows, which then became the basis for a shadow model for power distribution simulations will be given.  Simulation results for high-PV penetration feeders will be shown.