Large scale grid energy storage based on aluminum technology

Abstract

Grid energy storage is very challenging due to its large scale, required quick response, versatility, round trip efficiency, and new system infrastructure. However, the benefit is also huge because it would enable utilisation of intermittent renewable energy, leverage load, and allow energy management in hours/diurnal to seconds/minutes. A new invention is described to store up to 4-6% the entire grid energy by aluminum production, while returning its baseload back to the grid by idling aluminum smelter cells. The round trip efficiency will be close to 100%; switching between storage and load release can be instantaneous.

What is claimed: 
     
         1 . A method to store excess electric energy from the grid in intermittent production of aluminum metal by electrolysis, while returning its baseload back to the grid by idling or lowering the production rate of the aluminum smelter during high electricity demand; 
     
     
         2 . The aluminum smelter cell, according to  claim 1 , is modified or redesigned in order to maintain molten temperature of aluminum metal and electrolyte for at least 6 hours without electricity input; 
     
     
         3 . The aluminum smelter cell, according to  claim 1 , is modified or redesigned in order to maintain molten temperature of aluminum metal and electrolyte for at least 24 hours without electricity input; 
     
     
         4 . The aluminum smelter cell, according to  claim 1 , is modified or redesigned in order to maintain molten temperature of aluminum metal and electrolyte for at least a week without electricity input; 
     
     
         5 . The modification of the aluminum smelter cell, according to  claims 2 - 4 , includes addition of thermal insulation with vacuum jacketed double wall structure, vacuum insulation panel with porous solid insulation material between evacuated double walls, or refractive insulation material; 
     
     
         6 . The vacuum jacketed insulation or vacuum insulation panel in  claim 5  is maintained with periodic evacuation; 
     
     
         7 . The vacuum jacketed insulation or vacuum insulation panel in  claim 5  is maintained by getter material that reacts and removes trace amount of gas molecules in order to maintain vacuum level; 
     
     
         8 . The aluminum production rate in  claim 1  increases to effectively store electricity energy when intermittent power or cheap power is available from the grid, while the aluminum production decreases to effectively release its baseload to the grid during high demand period; 
     
     
         9 . The interval between high and low throughput intermittent production of the aluminum smelter in  claim 8  is between milliseconds to weeks; 
     
     
         10 . The interval between production and idling of the aluminum smelter in  claim 1  is between milliseconds to weeks; 
     
     
         11 . A computerized smelter cell in  claim 1  is programmed to switch between production and idling automatically depending on electricity input either as price or availability; 
     
     
         12 . The flexibility of aluminum smelter plant production in  claims 1 - 11  is used to balance the grid load; 
     
     
         13 . The flexibility of aluminum smelter plant production in  claims 1 - 11  is used to arrange aluminum production at low electricity cost and avoid aluminum production at high electricity cost; 
     
     
         14 . During idling period in  claims 2 - 4 , the smelter cell needs to have at least a portion of its content in molten status; 
     
     
         15 . For prolonged idling period in  claim 14 , a small electric current is supplied to the smelter cell between anode and cathode for joule heating to maintain the temperature without significant production of aluminum; 
     
     
         16 . For prolonged idling period in  claim 14 , the external heater is used to maintain skin temperature of the aluminum smelter, effectively stopping heat transfer in order to maintain molten temperature inside the aluminum smelter; 
     
     
         17 . The said aluminum smelter cell in  claims 1 - 16  is connected to the electricity grid; 
     
     
         18 . The said aluminum smelter cell in  claims 1 - 16  has its own power generation facility and is benefited in the same way as  claims 1 ,  8 ,  12  and  13 ; 
     
     
         19 . The said insulated smelter cell in  claims 5 - 7  is used to reduce heat and energy losses instead of improving grid electricity quantity and quality, therefore, reducing cost and improving competitiveness in aluminum production.