Battery storage of renewable energy

You can increase the financial return from an investment in a lithium ion battery pack by your choice of where to use the energy it stores.

For instance if the retail price of electricity is 20 cents per kilowatt-hour then using stored solar energy to replace the purchase of electricity you use in your home will save you 20 cents for each kilowatt-hour your battery pack delivers.

Tesla’s new “Powerwall” home battery will cost $3,500 for 10kWh units

If you chose to pay for the lithium ion battery pack to be built into an electric vehicle then the financial return may be far greater:

• Suppose a small electric vehicle can be fully charged in 7 hours at the rate of 2.4 kilowatts per hour and travel about 150 kilometres on that charge.
• The total amount of energy stored is 7 hours times 2.4 kilowatts which is 16.8 kilowatt-hours for 150 kilometres, or 11.2 kilowatt-hours for each 100 kilometres.
• Suppose a similar small petrol car would use 10 litres of petrol per 100 kilometres costing about $1 per litre. At this price of petrol the fuel cost is 10 litres times $1 per 100 kilometres which is $10.
• Choosing to put your lithium ion battery pack investment in a small car could save you $10 for each 11.2 kilowatt-hours of energy stored in it. 

This is a saving of $0.89 per kilowatt-hour which is more than 4 times the saving of $0.20 per kilowatt-hour if you use the lithium ion battery pack to replace electricity you use in your home.