SunPower announced today that it produced a full-scale solar cell in one of its factories in the Philippines that can convert 24.2 percent of the sunlight that strikes it into electricity, which constitutes a record in the industry.

That's both good and scary news for the solar efficiency leader.

First, the good news. The new cell demonstrates that SunPower continues to be able to increase the efficiency of its products. The company now sells modules containing solar cells exhibiting a 22 percent efficiency. (Module efficiency is lower than cell efficiency, but higher efficiency cells lead directly to higher efficiency modules.) Later this year, the company will begin to commercially produce solar cells with 23.4 percent efficiencies. SunPower produces monocrystalline silicon solar cells, which are generally higher in efficiency than multicrystalline silicon cells. The new record cell was produced using the same basic technology SunPower uses in its production line today.

Other firms in the industry have had trouble keeping up with SunPower. Suntech Power Holdings out of China announced the high efficiency line of Pluto cells and modules a few years ago to close the efficiency gap with SunPower. Earlier this month, however, Suntech admitted it was having trouble producing the Pluto cells in volume. As a result, the company will keep Pluto production at the 4-megawatts-a-month level for now. Before, it had hoped to increase production to 450 megawatts a year by the end of 2010.

Now, the bad news. With this achievement, SunPower is staring down the ominous laws of physics. Crystalline silicon solar panels can, in theory, convert 29 percent of the light that strikes them into electricity, but the real number is closer to 25 percent, SunPower CEO Tom Werner told me last year. Thus, the 24.2 percent figure is awfully close to the realistic max. So is the 23.4 percent number, to be honest.

Further gains will be more difficult to achieve, and this situation is already forcing the company to examine things like concentrators and different materials for making solar cells, which to date have had virtually no success in the market.

It will be an interesting race to watch. But one thing is certain: it will be entertaining. Over the last several years, SunPower has proved to be one of the most adept solar outfits when it comes to tweaking its business model to try to capture new opportunities.