Great companies have a purpose that goes beyond making money. Google wants to organize the world’s information. Walmart seeks to save people money so they can live better. The Walt Disney Co. tries to make people happy. (Or at least it used to; Disney’s current mission statement is a bunch of gobbledygook.)

Purpose matters. It’s a big reason why people go to work every day.

BYD, the Chinese company that makes electric cars, batteries and solar panels, has a grand purpose: It wants to save us all from climate change, which it calls “slow suicide.”

In a new company video (below), BYD says:

Glaciers are melting. Sea levels are rising. Who can guarantee that the next victims won’t be us?

Where is Noah’s ark to save human beings?

Where, indeed?

I’ve been fascinated by BYD — the letters are the initials of the company’s Chinese name, but they have come to stand for Build Your Dreams — since writing a FORTUNE cover story about the company in 2009. Two years ago, I visited BYD in Shenzhen, met with its founder and chief executive, Wang Chuan-Fu, and spoke about the company with Warren Buffett, Charles Munger and especially David Sokol of Berkshire Hathaway, who sits on the BYD board. Through its MidAmerican Energy subsidiary, Berkshire Hathaway bought 10% of BYD for $230 million in 2008. Despite some recent stumbles at BYD, the company’s market capitalization has grown to about $33 billion, so Berkshire’s stake is now worth about $3.3 billion. Not too shabby.

Lately, I’ve been in contact with U.S. investors who are bullish about the firm. One of them, Shai Dardashti, a Buffett admirer who runs a small money management firm, pointed me towards this seven-minute company video. It’s worth watching (although it ends abruptly for reasons that I haven’t been able to determine).

This video is fascinating in light of BYD’s remarkable but brief history. Since 1995, it has evolved from a manufacturer of cell-phone batteries into one of China’s largest automobile companies and it is now making a major push into clean energy, both with the manufacturing of solar panels and  utility-scale batteries to store energy. (For more on BYD’s energy storage plans and MidAmerican Energy, see Warren Buffett’s Big Battery Play at GreenBiz. Recently, the city of Los Angeles’s Department of Water and Power (LADWP) and BYD said they would work together to develop a grid-scale battery project for renewable energy storage.

In an email this week, Stella Li, a senior vice president of BYD, told me that solar power and utility-scale energy storage are key parts of what she calls “BYD’s 0-emission solution” and “total green solution.” The idea is to generate energy from the sun, store it in batteries until it is needed and then use the electricity to power BYD’s electric cars and buses.

As the company’s video says:  “How to transform the unaffordable [solar, battery, electric car] technology into affordable and high quality products: This is BYD’s responsibility and its mission as well.”

BYD has its skeptics. The company postponed the introduction of its e6 electric car. BYD’s auto sales, earnings and share price fell this fall, according to Reuters. In October, BYD was fined $443,000 by China’s Ministry of Land and Resources and seven of its factories were seized by the government because the company illegally built them on land set aside for agriculture; the factories were for future production, the company told Bloomberg.

Given the companies outsized ambitions, more stumbles surely lie ahead.

But there are good reasons to believe in BYD. Among them:

Low-cost brainpower. Chinese manufacturers are the low-cost providers of electronics, toys and textiles because factory workers are paid so little.  BYD’s more significant competitive advantage comes because the company  can hire skilled engineers at a fraction of what they would be paid in the U.S. or Japan, probably less than $1,000 a month. The company employs more than 30,000 engineers. They come from top universities and only those that make it through a challenging, competitive probationary period stick with the company. Its R&D operation, as a result, is vast. BYD can afford to make mistakes.

Battery technology: In BYD’s first business, cell phone batteries, the company dislodged entrenched, global leaders like Sony and Sanyo. Batteries remain central to BYD. Much of the due diligence carried out by Berkshire Hathaway’s Sokol focused on batteries. If BYD can continue to improve on battery costs and efficiency–a big if–the company will improve its competitive edge in three different businesses–rechargeable batteries for consumer electronics, electric cars and energy storage.

The China factor: It’s hard to know what the government’s crackdown on BYD over its factories really means; if the company falls out of favor with the authorities, all bets are off.  But Chinese-owned green businesses like BYD are sitting pretty today. While China’s economy isn’t as centrally managed as it once was, the country still produces five-year plans; as my colleague Brian Dumaine recently reported in FORTUNE, the “government recently decreed that 5 million electric cars will be traveling the nation’s roads by 2020 — up from basically none today.” The government provides all kinds of support (cheap land, tax breaks, low cost loans) to favored companies.

Wang Chuan-Fu

The X-factor at BYD is the chairman and founder, Mr. Wang. He’s obviously an accomplished, driven and brilliant leader. As Charlie Munger, Buffett’s partner at Berkshire, told me back in 2008:

This guy is a combination of Thomas Edison and Jack Welch – something like Edison in solving technical problems, and something like Welch in getting done what he needs to do. I have never seen anything like it.

What’s not clear is how deep and strong the management bench is at BYD. Without speaking Chinese, analysts, investors or reporters can’t get much of a read on the senior managers at the company.

BYD is trying to do so much that Mr. Wang can’t possibly manage it all.

But it’s hard not to root for a company that’s pursuing such big dreams.

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Hat tip  to Shai Dardashti and Scott Rombach for keeping me up to date on BYD. BYD matters because the world desperately needs low cost solar power, battery storage and electric cars.  Given the lack of progress in Washington and, more recently, in Cancun around the climate issue, we’ve got to hope that companies like  BYD deliver the breakthrough clean technologies needed to avert a climate catastrophe. I don’t see any reason why they can’t…

And on that semi-optimistic note, I will close out this blog for 2010. By my unofficial count, I posted 195 times during the year, including guest posts. It’s been fun, but it’s time for week off.

Thanks for reading.

Enjoy the holidays.

See you in 2011.