When Nick Pfitzner recently claimed his power bill had dropped 92 per cent in a year after installing a Tesla Powerwall, many were sceptical.
So sceptical, we decided to get our hands on his bills and do our own analysis.
Mr Pfitzner, a programmer from Sydney’s northwest, his wife and two children were the first to have a Tesla Powerwall version 1 system installed in Australia, and therefore the first capable of a full year’s analysis of use during all seasons.
He gave us five Energy Australia bills covering 426 days up to February 17, 2016, the changeover date, and another five from Diamond Energy from that date covering 350 days. Because of the unevenness of these time periods, amounts were converted to per day values for a comparison.
On the surface there’s no comparison. His five Energy Australia bills totalled $2578.26. His five Diamond Energy bills after Powerwall was installed totalled $178.71; that’s way less than a single Energy Australia bill.
The figures include three discounts of $35 for referring customers to Diamond and 9 per cent Energy Australia early payment discounts. Diamond Energy charged a regular service fee, and offered a 6 per cent discount and a renewable energy reward worth under $10 each bill. Overall, he claims a 92 per cent bill drop. If you exclude the three referrals worth $105, the drop is 89 per cent — still impressive.
The other main factor is energy savings. With Powerwall installed, the Pfitzners returned more power to the grid than they used in every billing period. They consumed 1349.83 kilowatt hours worth $277.91 and sold back 3807.40kWh worth $304.59.
Pre-battery, the family used on average 23kWh per day; with the battery installed, usage dropped to almost 4kWh of grid power daily. Mr Pfitzner said the battery generated 13-14kWh and, when you add the 4kW from the grid, you had about 17kWh daily. He attributes the 6kWh saving from pre-battery days as “becoming more efficient through knowing what I use”.
He was exporting on average almost 11kWh back to the grid daily and being paid for it. That’s equivalent to half his daily pre-battery usage being returned. The trick was to maximise the amount of power that he uses directly from the solar panels. Basically, when he’s not using solar power directly, he stores it, and when storage is full, he sells energy back to the grid.
“You try and use as much direct solar energy as you can during the day,” Mr Pfitzner explained.
“You might set your dishwasher to run after you leave for work, at midmorning, because you know it’s going to be sunny and it’s going to cost you nothing to run. The washing machine might be the same. It just depends on what individual needs are.
“The pool pump, things like that, you try and time it so that it’s not running first thing in the morning or in the evening when there is no sun. I try and do the ironing on the weekend when the sun is out, little things like that.”
Some appliances have to run no matter what, such as the airconditioner.
“We’re in western Sydney, Kellyville Ridge. It hit 49 degrees here one day. So you’re going to use it. It’s the same principle for the dryer. If it’s been raining all week in Sydney, you have to use a dryer, that’s just the way it is.
“So some days I need the grid, and some days it needs me. But you can see from the figures, quite often I’ve got the upper hand on the grid.”
His efforts to minimise power consumption is aided by a smart controller with software developed by Canberra-based start-up Reposit Power. It learns your energy usage patterns, checks the weather and develops a strategy for using off-peak grid power to minimise cost.
“If it was the off-peak time of day and it suddenly got cloudy, the system would start using grid power and leave as much in the battery as it could. When peak time hit, I’d be using my battery and not drawing from the grid.”
The Reposit system cost him $800. “It’s almost gaming the system, but also making power use more efficient,” Mr Pfitzner said. He was using a Reposit feature called GridCredits where he gets $1 per kWh for uploading power at peak usage times. Otherwise, he gets about 8c per kWh.
So overall is this cost efficient? The Powerwall system he bought cost $15,990, which was $4024.80 less than it would otherwise be due to a federal government subsidy. It included the battery, inverter and 5kW of solar panels. He added more panels to reach 6.5kW capacity.
Mr Pfitzner calculates that he will break even after 9½ years of use. He has factored in the interest he would save had he used the $15,990 for mortgage payments and not to buy the battery system.
The solar panels have a 20 to 25-year warranty and the inverter hardware a five-year warranty. Tesla’s warranty acknowledges the capacity of lithium-ion batteries deteriorate over time and currently guarantees 10 years use at 70 per cent capacity.
Mr Pfitzner says he mostly has enough battery power to make it through the night.
“For me the battery is the top layer on the sponge cake with the icing on,” he said. “On about 75 per cent of days, I have battery power through the night. I’ll get through to midnight and maybe through to the morning.”
There was more icing last week with the local release of Powerwall 2, which Mr Pfitzner said would change the dynamics again. Instead of passing through 3.3kW from solar panels for direct use, 5kW is available for use straightaway. Powerwall 2 then offers 13.2kWh of storage where its predecessor offered just 6.4.
That means more available power by day, even better odds for making it through the night on battery power, and the potential to supply even more power to the grid at peak load times.
So would he replace Powerwall after 10 years’ use? “The way it’s going, that’s a decision after four years because the pricing is just going through the floor.”
In the end, Mr Pfitzner’s costings show him slightly ahead with the government subsidy included, and behind without. But there’s no argument in terms of the energy saving.
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