An Example Of Green Future Hype

Here's a feel-good story about our "green" future:

Solar Impulse 2, which flew over the Statue of Liberty on its historic solar-powered global journey Saturday, continues to prove the vast potential of renewable energy, according to pilot Bertrand Piccard.

The plane landed at New York’s JFK airport at 4 a.m. ET on Saturday, completing the 14th leg of its trip.

“In the 21st century, liberty is to be free from fossil energy and pollution,” said Solar Impulse chairman and pilot Piccard, during a press conference at JFK. “We can have clean technology that creates jobs, sustains growth – it’s a new market for the world.”

The record-breaking plane has travelled 18,540 miles without a single drop of fuel since setting off on the first leg of the trip from Abu Dhabi to Oman in March 2015.

A larger version of a single-seat prototype that first flew six years ago, Solar Impulse 2 is made of carbon fiber and has 17,248 solar cells built into the wing that supply the plane with renewable energy, via four motors. The solar cells recharge four lithium polymer batteries, which provide power for night flying.

To accommodate the solar cells the plane has a 236-foot wingspan, similar to that of a Boeing 747. The aircraft weighs just 2.3 tons, similar to a family car.

However, Solar Impulse 2’s comparatively low speed (it typically flies at 30 to 40 mph) could prevent the adoption of solar-powered technology for commercial passenger aircraft.

You can read the rest @
http://fxn.ws/1U6SlyF

Almost sounds too good to be true, right? And the "only" drawback is the slow speed (30 to 40 mph).

But here is another story which reveals the other side of this coin:

... if a Boeing 747 were equipped with perfectly efficient solar cells on its entire upper wing surface, it would receive at most approximately 600 kilowatts, or about 800 horsepower from the solar cells. This compares with approximately 100,000 horsepower required for the 747 to maintain cruising speed and altitude. Thus, solar power can provide only 0.8% of the needed power to a conventional 747, even if the solar cells are 100% efficient and the sun is directly above the airplane. With typical very good cells, solar power can provide only 0.3% of the needed power to a 747.

The conclusion is that a very special airplane is needed--one that can fly on very low power while gathering lots of solar energy.

Consequently, it's unlikely you and I will be getting around via solar-powered planes ...

You can read the rest @
http://m.seattlepi.com/local/science/article/Boeing-patents-strange-looking-plane-that-could-7973913.php

Aha! So the real impediment is the power-to-weight ratio.

Why didn't they just say that in the first place?

"Too cheap to meter". R-i-g-h-t.