Second-tank update on the DIY Plug-in Prius

One of the personal projects that keeps me busy is my own plug in car – my 2004 Toyota Prius. I converted the car from a regular Prius to a plug in Prius earlier this year. After a few initial hiccups with a bad battery causing one of the additional battery packs to die prematurely I’ve had a few months worth of plug in hybrid driving. But at the end of the day I have a driveable PHEV Prius, which I have the satisfaction of knowing I converted.
Today I filled up my car after finishing the second full tank of gas since converting the car to a plug in. The last time I filled up was on April 3rd. Today is May 8th. Admittedly, I was away for seven days during this period, but keeping up with this I’ll be only filling up once a month.

Its not a full EV, but I fell better with fuel economy like this...
It's not a full EV, but I fell better with fuel economy like this...

More after the jump
What sort of range? Well, my fuel gauge was showing just one bar’s fuel remaining and as I pulled into the filling station my car’s trip meter reached 209 miles at an indicated 91.8 miles per gallon over the entire tank. The standard Prius gets (on average, using our other Prius as a benchmark) between 55 and 58 miles per gallon, normally traveling between 480 and 510 miles on a charge. Obviously, there’s some fantastic people in the USA who are able to get 90+ mpg out of a stock Prius, but these guys employ some pretty tough tricks to do this. I’ve just driven my PHEV prius as a regular Prius. The only difference has been plugging in every night.
In terms of price, I’m looking at about £38 to fill my car’s tank at present. That’s been the total cost of gas over the past 809 miles. Disregarding electricity costs that works out at approximately 4.8 pence per mile. A regular Prius would work out at approximately 7.8 pence per mile.
Let’s look at the electricity used too.
According to my calculations, Velma, my Plug in Prius, has a little over a 3.5 kWh battery pack. To fully recharge it would cost 28 pence, using a ball-park figure of 8 pence per kWh. In the course of a month I’ve recharged the car on average once a day. Sometimes I’ve charged more – but there were seven days at the start of the tank where the car wasn’t used, so this balances out pretty well.
At 28 pence a day I’m looking at somewhere between £8.50 and £10 for a month’s worth of electricity to run my PHEV.
If this figure is now added to the cost of gas then the total fuel cost for the PHEV becomes £48. This is a price-per-mile of 5.9 pence per mile.
Considering that gas prices are on the rise again in the UK and domestic fuel prices are on the way down again it’s good to see how much of a saving the converted PHEV can give me. But at the moment I’m still paying off the £2,000 costs and materials the conversion drew as I converted the car to a plug in. That’s still going to take a while to break-even on. However, it does show that, for a high-mileage driver with frequent stops it would pay itself off quite quickly.
So, what are you waiting for? Get a plug in already!

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