Fisker Karma Solar Roof more gimmick than practical? - Page 1
Forum section: electronics / general

author: edy
author_rank: Super Contributor
timestamp: August 14, 2016, 12:13:58 pm
content: Recent story about solar power roof on rebake of the failed Fisker Karma:http://www.bbc.com/autos/story/20160812-a-car-powered-by-its-roofIs this just a marketing gimmick and is this really the best way to do it? How much difference will it make and is it worth the cost? Any maintenance issues? It looks like a worthy idea but somehow in a Fisker Karma I wonder... Tesla hasn't done it. Why?

author: dannyf
author_rank: Super Contributor
timestamp: August 14, 2016, 12:52:32 pm
content: you can do the math: the energy deposited by the sun onto the surface here is about 1.5kw/m2. That pretty much tells you all you need to know about the story, and then some.

author: SeanB
author_rank: Super Contributor
timestamp: August 14, 2016, 12:55:22 pm
content: Might provide just enough power to run a small really efficient fan so the interior does not get too hot, but otherwise will do very little else.On a race car having a roof that is around 5 square meters, and a total mass without driver under 40kg it will work, but on a half ton or more vehicle it is just added mass.

author: dannyf
author_rank: Super Contributor
timestamp: August 14, 2016, 01:04:19 pm
content: What those anti-carbon people failed to comprehend is that the carbon economy really is an economy that trades energy density for time: the solar energy is a very low-density form of energy - you have to put up a large area of receivers to get a little bit of it, and most often unpredictably and unreliably.What the trees and plants do is to store the energy across millions of years so that they can be released over a short period of time, on demand.If we lived on a planet with reliable / always on sun of 1MW/m2, our energy solutions would have been totally different.

author: digsys
author_rank: Unknown
timestamp: August 14, 2016, 01:40:44 pm
content: It's slowly getting there.Our Aurora Solar car club has been going for over 25 yrs, and there are a few dozens solar race car clubs around the world. We achieve approx 400-500Km fromSolar alone. That's a 6Squ Mtr panel. Yes, these are race cars, only ~200Kg and 1 seat, but since 5 yrs ago, we started a new division of road-legal cars.After 25+ yrs, we needed new adventures. Our next design should do 300Km from solar alone, with 2 people. Some teams have already got 4 seatersrunning. btw the 20 Kg battery pack adds app 500Km. Yes, these are super light cars with minimal "furnishings", but will be ADR capable.On the other side of the fence, a Chinese manufacturer has achieved ~ 30 Km from his solar panels, on a small "production" vehicle.The next World Solar Challenge is Oct 2017 -https://www.facebook.com/WorldSolarChallenge/?fref=tsThere will be several "road legal" solar cars running.Yes it is a slow process, but until we can find someone like Elon Musk on board, from TESLA, it will take quite a long time.He has seriously advanced pure electric cars more than any other entity.One reason governments really aren't interested is - an "ideal" solar electric car cuts deep into petrol / oil / service taxes / revenue.It's getting there.

author: Brumby
author_rank: Unknown
timestamp: August 14, 2016, 01:44:43 pm
content: Quote from: dannyf on August 14, 2016, 01:04:19 pmYes.... and life would have been barbequed before it even got started.

author: dannyf
author_rank: Super Contributor
timestamp: August 14, 2016, 02:34:34 pm
content: Just some simple math:a gas-powered car today can do 30mpg crusing on the highway. At a heat value of 20Kbtu/lb, that converts to about 8.5Kw of power @ 20% of efficiency.At 1.5Kw/m2 and 100% of panel efficiency, you need an area of 6m2.At 1.0Kw/m2 and 10% of panel efficiency, you need an area of 85m2.A typical car has an area of 10m2.the numbers get worse if you consider going up, carrying more weight, accelerating, using a/c and other accessories, or during cloudy days / at night....

author: dannyf
author_rank: Super Contributor
timestamp: August 14, 2016, 02:40:06 pm
content: Quotethat's a myopic view of life, projecting from what we know about life here to a vastly different set of conditions.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 14, 2016, 02:52:05 pm
content: Quote from: dannyf on August 14, 2016, 02:34:34 pmNowadays, even a rather ordinary Camry (non hybrid) gets 35 MPG highway. And the Prius gets 53 MPG highway.And I doubt the intent of the solar was to directly power the car on the road. More sensible would be to charge the battery, since most cars stay parked for much longer than they are driven. But still, if you had a fixed amount of resources to spend on solar, it would almost certainly make more sense to install it on your house.

author: dannyf
author_rank: Super Contributor
timestamp: August 14, 2016, 02:56:35 pm
content: QuoteThat's only a problem now where the cost of collecting from solar vehicles isn't worth the revenue.When solar vehicles become a substantial element of t he transportation industry, the taxman will come. Finding out new ways to collect taxes has never been a problem for any government.The issue with solar powered cars is the fundamentals: there just isn't enough of it for a typical application.

author: SeanB
author_rank: Super Contributor
timestamp: August 14, 2016, 06:29:22 pm
content: Solar car is like solar roadway, you are able to do it with some measure of efficiency, but at a cost. Better is to put the larger cheaper solar panels as a roof to keep the car cool when parked, and use this larger area as a way to charge the vehicle instead. Win all the way, as you do not need to move the panels around, and they do not have the extra stress of having to withstand the rigour and vibration of road use. Plus you have more physical room under the panels to have the requisite power electronics in a non confined space allowing the use of lower cost and physically larger components and allowing lower operating temperatures.