Eclipse v Grid



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Sunday August 20, 2017 Eclipse v Grid On Monday a total eclipse of the sun is going to make its way across the US.  This is going to have a huge impact on the amount of solar power being sent to the electric grid.  The question is can the grid handle this power drop? 


The eclipse will start in Oregon at around 9:06am PDT and will end at around 4:06pm in South  Carolina.  At any given point along the route the eclipse will last around two and a half hours.  During that time the amount of solar generation will drop off by about 70% per hour but will recover at about 90% per hour as the sun comes back Even in areas like Southern California, where there will only be a partial eclipse, solar generation is expected to be highly impacted.


This event is going to be a test of how the grid can handle such fluctuation.  Back in 1964 a component failure caused a cascading effect that Blacked out most of the Eastern United States.  Following this event the North American Electric Reliability Council (NERC) was formed to work out ways to prevent such events from occurring in the future.


Solar is now becoming a significant part of the energy mix feeding the grid, currently accounting for about 5% of grid's capacity nationally.  The question that is about to be answered is, can the electric grid handle a fall off of capacity, about 4%, that will occur during the eclipse.  Utilities will be closely monitoring the situation and have prepared plans that include asking customers to reduce usage if power levels fall to dangerously low levels, and to supplementing power generation with things like increasing the amount of hydro  being generated.


The Utilities have been planning for solar eclipse for a long time so they don't anticipate any issues on Monday.  The future may tell a different story though.  The next solar eclipse to occur over the US will happen in 2024.  By this time the amount of solar in the utility mix is expected to have grown to about 15% of overall capacity making the situation a lot more dangerous. 
What this situation does show is the need to store excess generated capacity so that it can be released to account for higher than expected demand, of loss of capacity such as cases where we get extreme cloudiness or wind power generation is limited because of unusually calm conditions.


Now electricity is a not easy to store in its native form.  The only way to store electricity as electricity is by the use of capacitors but capacitors discharge the stored energy very quickly so are not typically useful for long term storage.


The best known way to store electrical energy is in rechargeable batteries.  Rechargeable batteries are something that we are very familiar with.  Today most Americans have cell phones, tablets, laptops, and cordless tools.  All of these devices use batteries and of course every car on the road also has a battery to provide the electrical energy needed.  In the case of the ICE vehicle the battery is used to start the car and to run accessories like lights, horn, and radio.


These batteries can be enlarged to provide pretty good storage for the electrical grid.  For example a large version of Tesla's Powerwall is currently used to store excess energy from a solar array in Southern California.  Smaller versions can be used to smooth out electrical supply issues with household solar although at the moment, legally, this can only be done on an installation that is off grid.


Batteries don't store electricity directly, they store it in the form of chemical energy.  A battery is made up of three elements, a cathode, an anode, and an electrolyte.  When the battery is discharges a chemical reaction occurs between the electrolyte and the anode creating negatively charged particles that flow to the positively charged cathode.  When electricity is applied to the cell, the reaction is reversed returning the anode and electrolyte back to there original state ready for the next discharge cycle.


There are many other ways to store electrical energy.  It can be stored as kinetic energy in a spinning flywheel,  It can be stored by compressing gas then using the energy as the gas decompresses to generate electricity.  It can be used to pump water up to a higher level where it can then released again to run a turbine to generate hydroelectric power.  It can even be stored as chemical energy by electrolyzing water to produce hydrogen and oxygen then passing those gases through a fuel cell to product water and electrical energy.


The impact the eclipse will have on the grid will very interesting as we will be able to model this to predict what will happen when much more of our electricity is being produced by renewable sources.  In the end I think we will not see any major issues with the grid this time around but it will show the need for grid level storage in the future.


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