Musk’s favorite phrase when trying to disparage something is to say, “It sucks.”
Should this crude term be applied to the Powerwall?
The Tesla Powerwall battery is to be used in conjunction with PV rooftop solar installations, and not for commercial or utility applications.
The 10 kWh Powerwall costs $3,500. Reportedly, it costs over $7,000 installed.
Can the Powerwall provide the following fundamental benefits?
- Backup power for grid failures
- Monetary savings by not using electricity from the grid
- Demand response for shaving peak load
To be useful and worth the cost of installation, the Powerwall must be able to do at least one of these functions well.
Let’s examine each function to see whether the Powerwall provides the anticipated benefits.
Essential household loads include:
- Heating system blowers
- Hot water heater (if electric)
- Microwave oven
These are needed for any household to function at a basic level: The ability to cook meals, to keep food safely in a refrigerator/freezer, to maintain home temperatures that are safe, and to provide hot water and lighting.
These loads will vary by time of year and by whether the activity is provided by electricity.
During the summer the Powerwall can provide backup power for 2 to 3 hours. The air-conditioning load is large, so in the winter the Powerwall might be able to provide backup power for 5 – 6 hours.
Adding television usage would slightly decrease the length of time the Powerwall can provide backup.
While many utility interruptions are fairly short, less than an hour or two, the major outages are caused by ice storms, wind storms and hurricanes.
These outages last for several days, so a Powerwall unit cannot supply backup power for these outages.
If backup is to be provided for lengthy outages, the Generac, or equivalent, costing $4,000 and using natural gas, is a much better investment. It also provides backup for the short nuisance outages.
Objectively, the Powerwall is unsuitable for providing backup power.
Can the Powerwall avoid using electricity from the grid at night, after the sun goes down? If so, this might make a $3,500 investment in a Powerwall unit worthwhile.
Fully recharged, the Powerwall might be able to save $1.10 per day by providing power after dark, with a utility rate of 11 cents per kWh. This amounts to approximately $400 per year in savings, so it would take approximately 9 years to recover the Powerwall $3,500 investment. Or 18 years if the total cost of installation is included.
With a 30% rebate for batteries used in PV rooftop systems, the payback would be closer to 6 years, or 12 years if the $7,000 installed cost is used.
But why degrade the Powerwall battery to save on electricity usage when the owner of a PV rooftop system with net metering can sell the excess electricity from his PV rooftop system to the utility for the retail rate of 11 cents per kWh?
Or, if the utility only pays 5 cents per kWh, the real money saved by using the Powerwall battery to save on using electricity from the grid is actually 6 cents per kWh, not 11 cents. This increases the payback period to 14 years without including installation costs.
There is also some question as to how often the Powerwall battery can be fully discharged and recharged.
A payback period of 9 to 14 years, or 6 years with the 30% rebate, (not including installation costs) is terrible for a product that may only last 10 years.
Clearly, the Powerwall battery is not suited for storing electricity to avoid buying electricity from the grid.
Theoretically, utilities could group a large number of Powerwall batteries from homeowner PV rooftop installations, and install the necessary controls to use electricity from the batteries during peak periods.
This is obviously impractical since the homeowner would stop using solar power and start using power from the grid, offsetting any reduction of load that might be achieved by the utility drawing power from the Powerwall battery. The Powerwall battery can’t simultaneously serve two masters.
This differs from commercial and industrial customers in states where time of day pricing is used. In these situations the price for electricity can be very high during peak periods and commercial and industrial customers can avoid those high prices by using electricity from batteries they own.
Powerwall batteries cannot routinely provide demand response.
The Powerwall battery is inadequate for providing backup power, doesn’t save much money and can’t contribute significantly to demand response.
What term does Musk use to describe an inadequate product?
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