British companies plan a new kinetic hybrid flywheel system

Innovation!

Sounds great, clever Brits.

Good idea, but probably won't be able to beat the market as the lithium-based hybrids roll out. This mechanical technique might still be more efficient, but if the lithiums are paired with plug-in technology then who can argue with getting the first 10-20 miles of your morning commute for pennies?

A tiny motor on the flywheel could spin the RPMs up while you sleep.
So when you roll out the driveway, you also go the 1st 10 miles on stored plug-in power, without the environmental disaster from the toxic battery production and disposal.
(my company designs battery-powered products for over a decade, so we know something about this area).

Time will tell, we probably won't see anything efficient and cheap to run available to us for another 10 years, I hope the auto industry proves me wrong!

the fly-wheel has the advantage in efficiency, and would be able to absorb energy much more quickly than batteries, but you would need some sort of cvt between the drivetrain and the flywheel. Think about it... As drivetrain rpms decrease, flywheel rpms must increase. And the cvt needs to be able to handle a lot of torque. Which hasn't really been cvt transmissions strong point.

It can be done easier without mechanical connections.
If the flywheel was an electric motor/generator (along the lines of GM's truck hybrids) and you put a separate motor/generator on the flywheel, then (using electronic, variable-speed drive technology) you could attempt to accelerate the flywheel so fast that it would cause the drive-wheels to skid and nearly lock.
With a motor/generator at every wheel and smarts equivalent to an ABS system, you could put maximum braking at each wheel, independantly (including ESP functions) at recover all the power.
Meaning, you could drive the car like you stole it, and still use less fuel than a battery-electric hybrid ... which sounds very appealing to me!

Clarification: I meant: "If the ENGINE'S flywheel was an electric motor/generator (along the lines of GM's truck hybrids) and you put a separate motor/generator on the ENERGY-STORING flywheel," ....

yes, but the article suggests a fully mechanical design. Your design also loses energy in the conversion to electricity and back to mechanical energy. If the generator and motor are both 85% efficient, then together you have an efficiency of about 72%. But that only gets the energy to the fly-wheel. Getting the energy back out, again at about 72% efficiency results in a total efficiency of about 52%. If they can come-up with a mechanical system that is about 10-15% efficient each way, you would have a total efficiency of 72-81%

Sorry, typo: By 10-15% efficient, I meant losing only 10-15%. That would be 85-90% efficiency.

This will be mated to an 8 speed ZF automatic.

This idea came out in the 1970's. It was technologically viable 30+ years ago.
However, its been killed by concerns about safety.
Anyone who knows the story about Don Garlits designing the first rear-engined dragster after losing his foot to a clutch blowing up at < 10,000 RPM would think twice about buying a vehicle with a heavier flywheel spinning at 10x that speed.
If you got in an accident and it was damaged, the shrapnel could kill everything within 1000 feet!
You may as well load your trunk with TNT.

So the technological challenge has been to build a SAFE flywheel ... and I presume their invention is a technology to address that issue.
If they can do it, then its a much greener solution than anything with batteries.