Tesla Powerwall: Number Crunching Pricing And Payback Times

Back in May, 2015, we crunched the payback figures for the Powerwall, based on an assumed Australian cost and example electricity prices. Now there are local installed costs available, we have broken out the calculator and gone over the figures. The question is, can the Powerwall give a decent payback time?

This post originally appeared on Lifehacker Australia.

Check out our previous numbers, or catch up with the announcement of Powerwall in Australia. Of course, there are other companies offering competing technologies, for various prices.

But for now, this is what the Powerwall will cost. Hot tip, the juicy bits are in bold.

Assumptions

The prices used for this calculation are from the Natural Solar quote system. Due to various factors, such as install issues, prices will vary on a case by case basis.

The calculations are quite simplified and don’t account for a lot of financial factors, which can vary from person to person. But it’s a starting point.

Electricity prices are based on my own AGL bill and the calculations simplified. Swap your own power usage and costs in and re-run the numbers for a more personalised figure.

Prices used are $0.2377 per kWh, and $0.7596 a day surcharge for peak. Off Peak numbers are $0.0674 a kWh and $0.0517 a day supply charge. Solar feed in tariff is $0.051 per kWh.

We have used an average daily production of 3.9 kWh per 1kW of solar, for a Sydney location, based on figures from Solar Choice.

Powerwall + Solar

Natural Solar quote $16,390 for a 4kW solar system and 7kW Powerwall, installed. A 6kW system bumps the price up $18290. The prices includes any Government rebates.

If ordered before the end of January, 2016, there is a $1000 discount on the prices, which we have not included.

The prices are for single phase installations – three phase saves a little of the price. For our numbers, we used the single phase prices.

As of January 15, the prices are as below (with $1000 discount) for a Powerwall + solar and inverter, installed.

The 4kWp Three Phase $13,990

The 4kWp Single Phase $15,390

The 6kWp Three Phase $15,990

The 6kWp Single Phase $17,290.

The 4kW system will produce 15.6 kWh a day, about which 7.5 kWh is used to charge powerwall. The remainder is fed back to the grid, earning $0.4131 per day.

The Powerwall can offset around 6.5 kWh of power usage, saving $1.54505 a day.

The total saved and earned is $1.95815 a day, or $714.73 a year.

Payback is 22.9 years.

The 6kW system saves the same power each day, but earns $0.8109 a day from the feed in tariff.

The 6kW system saves $2.35595 a day, or $859.92 a year.

Payback is 21.3 years.

4kW Payback: ~ 23 years.

6kW Payback: ~ 21 Years

Powerwall and Existing Solar

For owners with solar already installed, there is also an option to just have the Powerwall installed. Costs vary a bit depending on if a compatible inverter is owned, but given as $9500.

We assume that the current solar system has fully paid for itself (not just been paid for), otherwise it’s remaining cost needs to be factored in.

The Powerwall can offset around 6.5 kWh of power usage, saving $1.54505 a day.

Any potential feed in tariff is not included in the price, as it’s production is not included in the Powerwall cost. It could be giving additional savings however.

By charging the Powerwall (7.5 kWh), instead of getting the feed in tariff, $0.3825 is lost. Total saved is $1.16255 a day, or $424.33 a year.

Payback time is 22.4 years.

Powerwall + Offpeak charging

With no solar, offpeak power could be used to charge the Powerwall.

Assuming the full supply costs, charging the Powerwall costs $0.5572 a day. It can offset $1.54505 a day, giving a total saving of $0.98785 a day, or $360.57 a year.

We assume the same install cost as existing solar – $9500.

Payback is 26.35 years.

Going Off Grid

By ditching the connection completely, we can avoid the $0.7596 a day supply charge, but can’t sell back any excess power.

Each Powerwall needs around a 2kW of solar to be fully charged on an average day. Adding more powerwalls into the system gives greater capacity, but does not increase or decrease payback time.

No specific cost is given, but we have assumed $25,000 – the cost of a two Powerwalls, plus a 4kW to 5kW array, based on a combination of the above numbers.

Likely a real off grid system would need more Powerwalls, but the payback time is the same.

The system can save $3.0901 of electricity costs a day, plus the $0.7596 supply charge, for a saving of $3.8497 a day, or $1405.14 a year.

Payback time is 17.8 years.

Summing Up

For now, most people won’t get a very economically viable result from a Powerwall. Considering the warranty is for 10 years, a payback time higher than this is not ideal.

To get a 10 year payback, electricity prices would need to be $0.40 a kWh – not an overly high figure. Some providers do variable pricing, but the Australian average is closer to 30 cents a kWh, which gives a 14 year or so payback time.

For many people (such as myself), better payback can be had from simply keeping the money in an offset account. In the future, financing plans may improve the proposition.

There are a lot of factors that could affect the payback times, most importantly the cost of electricity. It’s hard to predict what electricity prices will be in the future, but with an increase in solar and battery storage, it is possible they could drop, further increasing the pay back time.

Still, the future of solar and battery storage is a bright one!