back to article Sun-seeking Cambridge boffins chase Solar Challenge car crown

Next Sunday sees the starter's flag fall on the 2013 World Solar Challenge, and on the grid in Darwin will be Cambridge University Eco Racing's Resolution - a sleek carbon-fibre monocoque chassis solar-powered vehicle, featuring a "game-changing" solar tracking system. Artist's rendering of Resolution in the Outback. Pic: …

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"optimum gathering angle according to time of day and direction of travel"

Isn't the direction of travel due south for 3,000 km?

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Re: "optimum gathering angle according to time of day and direction of travel"

Nope, lots up curves between Adelaide River & Darwin & plenty between Katherine & Adelaide River. Having done the Katherine-Darwin bit just the other day - it is boring as bat**** and that is driving at the 110 & 130 kph speed limit

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Re: "optimum gathering angle according to time of day and direction of travel"

Isn't the direction of travel due south for 3,000 km?

The sun will rise on the left of the car and set on the right.

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Why GPS to work out where the sun is?

Why not just a half circle hoop of Light Dependant Resistors mounted on that half circle part behind the cockpit.

Each LDR is facing in a slight different direction and which ever one registered the most light is probably the best direction to point the solar cells in, that way the panels are actually pointing at the strongest source of light and not just where the sun should be which could be obscurred locally by trees and landscape.

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Re: Why GPS to work out where the sun is?

Actually, the article doesn't say "GPS". The wording makes me think of compass and clock, but actually their description is compatible with your excellent suggestion. Your suggestion works easily for single axis tilt, and two rings of LDRs at right angles would be accurate enough for double axis tilt.

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Re: Why GPS to work out where the sun is?

I talked to some of the team a few weeks ago, and at that point the tracking was going to be controlled from the support vehicle, with the tracking angle set by dead reckoning, not feedback in the car. When I asked why, they said there's already a couple of feedback loops controlling the motor speed and battery charging in order to maximise performance and adding another control loop for sun tracking potentially made the control theory a nightmare and risked reducing overall performance. Given the nature of the road they decided tweaking the tracking angle every few minutes was good enough.

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Alert

How effective?

It says the polymer absorbs 5% of the usable light but what are the effects on temperature under the canopy? I'd guess it's a bit like a greenhouse, getting rather hot underneath. Generally, efficiency of PV cells reduces with raising temperature. How well are those cells working under this condition?

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Re: How effective?

Again, from talking with the team.

Firstly the PV cells are gallium arsenide, which can AFAIR run hotter than silicon, and secondly the canopy material is opaque to infra red but passes almost exactly the visible and near UV spectrum that the PV needs, so there's less heating than you might expect. Their major worry was the driver overheating, and the car is designed to have an air feed passing over the driver and then over the PV to supply some extra cooling for both.

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Re: How effective?

Thanks, Arthur.

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Solar concentratrors

Anyone have any links to the solar concentrators they are using - all hush hush - but some interesting pictures came out of scrutineering...

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Facepalm

UPDATE: they've crashed the car

According to the Cambridge Evening News web site, the team have rolled the car and buggered the canopy and some of the PV cells. They've got two days to fix it.

Those cells cost about a quarter of a million. Ouch.

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Unhappy

Oh no!

I hope the driver is OK, and I hope they put Humpty* together again in time.

*well, the car is kind of egg-shaped, ish.

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