Grid Energy Storage



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Sunday September 2, 2018 Grid Energy Storage I was reading some articles about global warming and came across an article in The Verge about the issues that are being faced at San Onofre nuclear power plant here in Southern California.  I often see articles about how nuclear power is the only way to provide enough energy to provide for the world's needs without burning fossil fuels, usually written by someone in the nuclear power generation business.


San Onofre power station was decommissioned on June 7, 2013 after issues were found with one of the reactors that would require extremely expensive repairs or risk a radioactive leak.  The decommissioning process requires that spent fuel rods be moved to a safe location.  With  no safe location currently available in the US the fuel rods are being stored in place.  Initially they are being stored in giant pools of water madeofconcrete so that they can cool.  Now the process has started to move the fuel rods to large steel and concrete containers known as dry storage.  This process has currently been halted temporally due to safety concerns while procedures are being reviewed and more training is being given to the work force.

The fuel rods will then sit there by the ocean until a permanent place is created.  During this time they will require security to be onsite at all times to monitor and protect the containers.  The fuel rods themselves will remain highly radioactive for hundreds of thousand of years presenting a danger to everyone and everything that could come in contract with them in the future.

Nuclear proponents would have us build more nuclear plants without any mitigation for the real danger that nuclear power presents to the population.  They say that it is necessary since renewable energy is too dependent on the elements.  What happens to solar when the sun doesn't shine, or to wind power when the air is still.  An alternative solution is to build grid level storage so that energy created by renewables can be stored until it is needed.


The electric grid requires that the energy being added to the grid equals the energy being taken from the grid at all times.  When the energy being pulled from the grid is greater than the energy being put into the grid the voltage drops.  If the voltage sags enough then sections of the grid have to be taken off line to reduce load and the result is a brown-out.  If more energy is added to the grid than is being pulled out this results in heat being generated in the grid infrastructure.  You might notice power lines that sag an night due to expansion as the lines heat up.  To remedy this power generation has to be taken off line.


Adding a generation source that might produce energy at times when you don't need it and not producing any energy at peak demand is not optimum for the grid.  For example solar energy is often not being produced during peak demand in the early evening.  Fortunately this is typically the time when peak output happens for wind energy, but since both  are intermittent there needs to be away to deal with a potential shortfall.  There is a solution; grid energy storage.


There are many ways to store energy generated by wind or solar and many of them actually help  balance the grid by taking energy  from the grid when an excess is being produced and adding back to the grid when demand exceeds supply.  Such energy storage has been in existence for a while now in the form of Pump Storage.  Pump Storage using excess energy to pump water from a lower level lake to a higher level lake.  When demand exceeds supply the water is allowed to flow back down to the lower level lake using turbines to generate electricity.  When energy generated is greater than the requirement the excess energy drives the turbines as pumps to send water back to the upper lake.


Another solution that has been in the news lately is battery storage.  Tesla has recently installed large capacity battery banks in Australia and Puerto Rico and these have proved to be very effective in smoothing out the grid and making renewables more viable as a solution to our energy needs.  Several other companies, including Nissan, are looking at grid level storage as a way to use batteries that no longer have the capacity for use in an EV but still have plenty of life left in them.   A variant of this is the use of batteries to allow for off grid use for rooftop solar.


Thermal solar sites are also being developed that use the heat reflected from mirrors to heat up salts to the point where these salts become hot enough to generate steam, which is then used to generate electricity.  For hours after the sun goes down the salts remain hot enough for continued electricity generation.


Other ways of storing energy are by storing it using flywheels, or by compressing air into a storage chamber, similar to the way that natural gas is stored underground.  The compressed air is then heated and expands through  a turbine to generate electricity when needed.  Excess energy can also be used in electrolysis to generate hydrogen, which is stored under pressure until can be fed into a fuel cell to generate electricity.


There are plenty of solutions to smoothing out the variability of renewable energy so there is no need to build expensive and dangerous nuclear power plants or go back to generating energy using fossil fuels.  It should also remember that we can also use hydro and geothermal energy as baseline energy as both these sources are not subject to the factors that make most other forms of renewable energy intermittent.

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