Energy Storage

Why is Energy Storage Important:?


  • It's what is required to make low duty cycle alternative energy sources viable especially solar. Need to store the excess energy when the collector system is being irradiated

  • Energy storage is also important for power leveling for the power companies Generating stations operate more efficiently if they run at constant output level want to shove unused energy to a storage system and recover it later at times of peak demand.

  • Energy storage must consider both the amount of energy that can be stored (energy density of the material) and the efficiency at which it can be recovered. Some materials have high energy storage capacity but low rate of recovery.


    Energy Density of Some Materials (KWH/kg) 

       Hydrogen ------------------------- 38
 Gasoline  ------------------------ 14
 Lead Acid Batteries -------------- 0.04
 Lithium Ion Batteries ------------ 0.15
 Flywheel, Steel ------------------ 0.05
 Flywheel, Carbon Fiber ----------- 0.2
 Flywheel, Fused Silica ----------- 0.9


Energy density storage drives the choices that can be made and is essentially a tradeoff between stored power density and stored energy density.

Power = energy x time of usage so systems with large power densities but small energy densities means that they discharge their power relatively quickly. Systems with large stored energy densities generally mean systems that discharge power at relatively slow rates.

Only gasoline and hydrogen have both high power and high energy storage capacity. Batteries have good power storage but they tend to discharge pretty fast which compromises their energy storage.






Industry goal is to reach at least 400 watt hours per kg on a production scale - Envia Systems But as of Dec 2013 Envia Systems is no more and this is a major setback. But They may be back now . In addition, the The Battery 500 Project is now real



The global race to build a better battery - the search for the right material: New form factor - Lithium Polymer (LiPO) - has emerged and these can have energy densities as high as 250 watt hours per kg.





Figure of Merit for "practical EVs":

A driving range of 300 miles requires about 400 KWH of storage energy (e.g. 10 gallons of gas).

At energy density of 150 watt hrs per kg it would require 2666 kg of batteries to store 400 KHW of energy - this is more than the weight of the vehicle. This is the basic problem with current battery technology and current vehicle design.

Now let's suppose one has a lightweight vehicle that could get 60 mpg (like the Insight does). At 60 mpg one would use about 5 gallons to go 300 miles and that's equivalent to about 200 KWHs of storage. With a battery material that could get 500 watt hours per kg, then you would need a mere 400 kg to cover this range. Those technologies would make pure electric vehicles feasible. We are not there yet (or even close).

Who killed the electric vehicle Poor energy density storage of batteries! Physics, not conspiracies.

Read This: Material in it will be on the Quiz:

More on Batteries Good overview of different types; advantages and dis-advantages and the like. Read this resource in detail especially the section related to Annode and Cathode materials. This is one area of Research the the Knight Campus needs to invest in!



Flow Batteries:

Excitement over flow batteries derives from their attributes, which combine aspects of conventional batteries and fuel cells. They are relatively simple, efficient, scalable, durable, and can optimize either power or energy output, as desired. Flow batteries can respond in fractions of a second and can cycle rapidly and deeply at high or low power output with minimal battery degradation.

Flow batteries are scalable from a few watts and kilowatt-hours to tens or hundreds of megawatts and megawatt-hours.



The Turlock Project

1 MW Iron-Chromium (ICB) Flow Battery



The concept of using large flow batteries at Wind Farms, which you would think would be a no-brainer, has finally started to catch on. Duh!



Alas the expansion of this project from a 2.5 MW wind farm to a 600 MW wind farm, however, has now been scrapped but some wind+storage facilities do exist