Author: Brian February 27, 2017

I recently posted about my experiences of getting quotes for Solar Power (Obtaining Quotes) and one of the questions I have been asked is “Are you getting a Tesla Battery?”

Here are my reasons why not

Tesla Battery

The total installed cost of a Powerwall 2 battery is being quoted at $10,150.

With 13.5 kilowatt-hours of storage that means a cost of approximately $750 per kw hour that’s quite an effective price.

Background

My solar system is limited by suitable roof space to just over 3.00kw

The estimated power generation is around 4000kw hours  a year with a monthly average in summer of 16kw hours a day.

In winter it is much lower at an average of 6 kw hours per day.

Evaluation

Prior to the solar installation we were using about 7- 8 kw hours/day without using air conditioning. and another 4-5 kw hours with air conditioning.

It would probably be more if we were home all the time but we both have part time jobs.

In Summer we have a lot of excess solar power, but we are only using  2 – 4 kw hours of grid power when the panels aren’t generating so the battery will only save us around 2 -3 kw hours per night.

In winter we won’t have much excess power during the day so I would estimate that we will only be able to put 1 – 2 kw Hours per day into the battery which will get used up every night..

Overall it looks like we would probably average 2kw hours, or less, of power from the battery a day.

With our supplier, Powershop, the benefit of using power from a battery is approximately $0.25 /kw hour (The difference between the ‘Feed in rate’ and the ‘Anytime rate’)

Our saving = Days in the year x Average kw hours saved x Benefit from battery use

= 365 x 2 x $0.25

= $183 per annum (a rate of return of less than 2% on the $10,000 investment)

This is a much worse rate than overall solar installation . . . see Reviewing Solar 

Conclusion

With battery life guaranteed for 10 years you won’t be seeing any real savings, not even if the battery lasts a further 5 years.

If Tesla, or someone else, were to offer a battery system with a quarter of the capacity(say 3kw hours) for a quarter of the price ($2500) I might get excited.

If you have got a lot more panels and a high evening, and night time use, then a Tesla Battery may work for you.