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Toyota to sell solar panel equipped Prius July 7, 2008

Posted by fukumimi in Energy, Japan.

The Nikkei is reporting that Toyota is planning to sell a version of its hybrid Prius with solar panels integrated into the roof of the car, starting 2009.

The PV panels will be procured from Kyocera, from whom Toyota have procured panels in the past for various other PV projects (such as setting up PV panels at the factories, and also with their residential housebuilder subsidiary).

The aim is to use the PV panel to supply some of the power required to drive the car’s air conditioning system. PV+AC is obviously a good fit, with AC demand tracking solar irradiance pretty well in general.

But make no mistake, the solar panels derive nowhere near enough power to actually power the drivetrain, nor can it really be used to trickle charge the batteries in any meaningful way (because of the limited battery capacity).

Some basic maths.

Available roof area: approx 1400 x 1200 (mm) = 1.68sq. m

Kyocera PV panel output approx 135Wp/sq. m

Max output per panel (assuming full roof area utilization)= 230Wp

Loss due to non-optimal placement (horizontal vs 30deg incl.) = 11.6%

Loss due to thermal heating of panel = max 20% (June-August) for residential roof installed panel – for car roof application, losses will be greater due to greater restrictions in thermal management

Other losses (due to dirty panels, electrical losses) = 5%

Peak power output per car = approx 150W

Which means one could generate up to 0.75kWh or so a day, given sunny conditions. Another problem is the battery capacity of the Prius Ni-MH battery itself, which is just 1.3kWh (201.6V,6.5Ah), combined with the battery management software in the Prius which appears not to allow deep discharging, which means that even if you put the car in a sunny place without driving it, the amount of electrical charge the car can generate and store peaks out as soon as the battery hits maximum charge.

The net result is that over the course of a year, one would do well to save just one or two tanks worth of petrol.

Probably good business for Toyota, for whom it might cost $500 to add and be able to charge at least a couple of grand to pander to vain green types.

The added weight up at the top of the car won’t do anything for vehicle dynamics, dragging up the centre of gravity, but I’m guessing enthusiastic drivers aren’t buying the Prius for its handling.

Related, when I was in the UK a couple of weeks ago, I caught Top Gear (the popular BBC car show) on TV, and they had a couple of hilarious segments.

The premise was that BBC management were berating Top Gear for not doing more eco-friendly stuff. (On a show for petrolheads who like their non-PC cars???)

So the Top Gear team did a segment to find look for the most fuel efficient….. supercar…… doing laps of a race track. They took some fast cars (Ferrari 430, Lamborghini Murcielago (probably), Mercedes SLR McLaren, and an Audi R8), and made them do fast laps around their race  track, with just a gallon of petrol in the tank for each of them. Turns out, the Ferrari ran out of petrol first, and the last man standing was the Audi R8. Irrelevant, irreverent, and bloody hilarious.

The other eco-friendly segment had the Prius up against a BMW M3, and had the Prius lap the circuit as quickly as it could, whilst the M3 tagged along behind. The M3 came out with about 10% better than the Prius on fuel efficiency in that particular test. Of course, it doesn’t reflect ordinary driving conditions, and pitting a 1.5litre Prius against the 400bhp 4litre may not be fair, with the BMW able to shadow the Prius at its limits without breaking into a sweat, but I think the point was made.

Given that the majority of my own driving is on the motorway to and from the golf course, I think my next car will be the one that returns the best fuel consumption at highway cruising speeds. I wonder when BMW will release their 330d/530d diesels in Japan? Mercedes has a E-class diesel which appears increasingly popular with well-to-do golfers here in Japan. Actually, I wouldn’t mind saving a bit of money and go with a domestic diesel model if they actually made one (and no, the diesel Nissan X-trail SUV-thingy doesn’t count).

OK, I should probably give up golf whilst living here in Japan if I were really trying to be maximally eco-friendly, but we all need our indulgences, don’t we? It is less wasteful of energy than a motorboat.


1. Japan - July 17, 2008

Excellent write up, very interesting read!

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There’s talk in nanotechnology circles about recreating a building process in which carbon molecules are preprogrammed to self replicate, echoing a blueprint first evolved in natural processes some 400 million years ago. As complex a technology as is …

3. Chuck Kottke - May 22, 2011

Very nice writeup, I agree! I think it would help if more of the solar electricity gained could go into the batteries, every drop of energy adds up to make a pail full of electrons, even a trickle charge at a time. I’ve often wondered, with all the baking hot asphalt parking lots, if solar canopies were installed on them, with a grid inter-tie or the direct charging of electric vehicles, this would seem to make sense on many levels – less cooling requirements since cars would be parked in the shade, direct use of the solar energy with less transmission and conversion losses, and greater comfort to people walking out to find their cars. Even so, .75 KWh is pretty good, considering the battery capacity is only 1.3 KWh; multiplied by all the autos, that could save quite a few tankers of oil!

4. Supply and fit Photovoltaic Panels - August 2, 2011

your post is quite interesting and informative. totally agree with your thoughts and point of views.

5. Supply and fit Photovoltaic Panels - August 2, 2011

your post is quite interesting and informative. totally agree with your thoughts and point of views. keep on doing the work like this

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