Energy Storage
Why is Energy Storage Important:?

• Stored energy is what we use now Fossil Fuels

• 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 (KHW/kg)

 Gasoline  ------------------------ 14
 Lead Acid Batteries -------------- 0.04
 Hydrostorage --------------------- 0.3 (per cubic meter)

 Flywheel, Steel ------------------ 0.05
 Flywheel, Carbon Fiber ----------- 0.2
 Flywheel, Fused Silica ----------- 0.9
 Hydrogen ------------------------- 38
 Compress Air --------------------- 2 (per cubic meter)

The classic argument against hydrogen:

This just means that Hydrogen should be produced where there is no grid but there is resource (wind, solar, waves, etc) - DUH!

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.

The most widely known and used energy storage system is the chemical battery:

New class of Lithium-Sulfur batteries looks promising

Hyundai Sonata Hybrid: First to Use Lithium Polymer

Prius Hybrid: Very Slow Evolution of Battery Technology

Chevy Volt: 16 KWH battery pack of which 10.4 KWH is "useable" (this is designed to maximize the battery lifetime). Lithium-Ion Battery Back weighs 435 lbs (197 kg) energy storage is therefore 80 WHs per kg (about twice that in NiMH batteries).

And then there is this a Veritable Pressure Cooker

Note the above real life problem did delay the Toyota Prius PHEV which uses Lithium Ion Battery Pack

Figure of Merit:

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

• At energy density of 100 watt hrs per kg it would require 10 kg of batteries to store 1 KHW of energy. Therefore it would take 4000 KG of batteries to store 400 KWH of energy. 4000 KG 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!

  

  World's biggest battery energy storage system came on line in 2003 approximately 14,000 individual batteries can store 40 MW of power and discharge that in 7 minutes.

  • Mode 1: 40 MW x 7 Minutes = 280 MW minutes of energy
  • 60 minutes per hour: 280/60 = 4.66 MWH of energy = 4666 KWH (approximately 2 months worth) of energy use for a typical house.

  • Mode 2: 27MW x 15 minutes = 405 MW minutes = 6.75 MWH = 6750 (approximately 3 months worth)
  
  
  
  
  The difference between modes is due to a fundamental property of most batteries - maximual discharge rate vs average discharge rate.

  Note: at the maximal discharge rate, the batteries get pretty hot!

  Its purpose is to store temporary power to ease a short term blackout. The total cost of this project was about 30 million so that's 0.75$ per per watt.

  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 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!

  

  Further Readings:

  More on Batteries Good overview of different types; advantages and dis-advantages and the like. Read this resource in detail.

  United States Advanced Battery Consortium

  Military applications are a major driver for advanced batteries

  China and the PLI batteries