Question

2. Tesla Motors is offering for sale a residential battery unit (“Powerwall”) that can store 13.5 kWh of energy, can cycle daily, and has an expected lifetime of 5000 charge cycles. The device is listed as costing about $7500. (including extra parts but not installation labor).

a. If you were to fully charge and discharge the device every day for its full lifetime of cycles, what would be your effective cost of the device per kWh of energy delivered? Assume an interest rate of 5%/yr.

b. Suppose I could install solar panels on my roof that will produce electricity at a net cost to me of $0.05/kWh. But I also need to install a Powerwall that allows me to use this electricity at night. At the current cost of a Powerwall, this would be more expensive than just buying my nighttime electricity from the utility at a cost of $0.15/kWh. What price would the Powerwall need to have in order to make it cheaper for me to make my own nighttime electricity via solar?

c. If we wanted to store half of the daily electricity used in residences in the entire US, how many such Powerwall units would the country need per person?

Answer 1