Apple’s renewable energy enthusiasm is spreading to China – that was big news last week. But the story’s more interesting player might be SunPower, with its efforts to expand deployment of concentrator photovoltaics (CPV).

The two 20-megawatt plants that Apple and SunPower have partnered on in China will use CPV, long thought to be a promising solar technology but one that has been slow to gain a market foothold. Now CPV is getting its best shot ever at growing to meaningful levels, thanks to SunPower and with a little assistance from Apple.

What is CPV? It might be easier to start with what it’s not: concentrating solar power (CSP), the more common of the “concentrating” solars. CSP uses the sun as a heat source, with mirrors concentrating the solar energy to boil water in an otherwise standard thermal generation process. We’ve seen it in tower configurations as at Ivanpah, and in parabolic configurations as at the recently completed (and water-guzzling) Abengoa Mojave Solar. CPV, by contrast, is like PV on steroids. Concentrating optics – lenses or mirrors – are used to focus intense sunlight on high-efficiency photovoltaic cells, maximizing power generation while minimizing the use of those very expensive PV cells.

CPV and CSP both thrive in areas of high direct normal irradiance, where the atmospheric conditions – low humidity, with cloudless skies free of pollution, smoke and dust – allow a lot of sunlight to reach the earth undiffused.

CPV is commonly broken down into high concentration (HCPV) and low concentration (LCPV) forms. As a recent report [PDF] from the Fraunhofer Institute in Germany and the U.S. National Renewable Energy Lab outlined:

More than 90% of the capacity publicly documented to be installed through end November 2014, is in the form of high concentration PV (HCPV) with two-axis tracking. Concentrating the sunlight by a factor of between 300x to 1000x onto a small cell area enables the use of highly efficient but comparatively expensive multi-junction solar cells based on III-V semiconductors (e.g. triple-junction solar cells made of GaInP/GaInAs/Ge). Low concentration designs – those with concentration ratios below 100x – are also being deployed. These systems primarily use crystalline silicon (c-Si) solar cells and single-axis tracking, although dual axis tracking can also be used.

HCPV is the splashier of the two forms, commonly used with multijunction cells that boast eye-popping efficiency – up to 46 percent per NREL’s certifying. But while HCPV has done better than LCPV, together they don’t add up to much in the now-giant solar market, accounting for one-quarter of 1 percent of total deployments in 2014, according to Greentech Media.

SunPower’s play is with the low-concentration variety. As the company explained in its China/Apple announcement last week:

The technology combines single-axis tracking technology with rows of parabolic mirrors, reflecting light onto high efficiency SunPower Maxeon cells, which are the world’s most efficient commercially available mass-produced solar cells.

The first commercial deployment of the SunPower system, called C7, came two years ago at the Arizona State University Polytechnic campus. By using concentrators, SunPower said it  needed just 172 kilowatts of solar cells to hit a capacity of 1 megawatt of power there.

A 7.3-MW C7 system was recently completed in Arizona for Tucson Electric Power, and a 19.9-MW installation in partnership with SunPower pal Apple is reportedly near completion in Nevada. Last fall, SunPower told solar watcher Ed Gunther that it was “installing its second-generation SunPower C7 Tracker, which has improvements in efficiency over the Gen 1 design,” at the Nevada site.

SunPower has long said C7 can be the cost-effective choice in the right super-sunny spots, with a 20-percent lower levelized cost of energy than competing technologies. There are also potential pluses in using less land area, and in providing better late afternoon output.

But these are long-advertised advantages that haven’t proven persuasive in the U.S, where confidence in cheap and predictable standard PV runs high. The sense of CPV as a still-uncertain quantity was captured in the statement by Ted Burhans, a senior program manager in Tucson Electric Power’s renewable energy department, after the TEP plant opened recently: “A lot of people will be interested in how this system performs and whether it can be successfully deployed on other landscapes.”

Not that that’s a real problem for SunPower in the U.S.; it’s been doing big business here with systems that use its standard high-efficiency-cells without the concentrators.

Meanwhile, the company has found a market for LCPV in China, and this past November it told analysts that robust LCPV growth is expected.

In 2012, SunPower formed a joint venture to manufacture its cell receivers in Inner Mongolia. The company says the planned 300-MW plant now has three 50-MW production lines going. But with a goal of 3 gigawatts of deployments in China, much of it LCPV, SunPower knows it will have to get beyond Inner Mongolia – and the Apple plants are being built in the southwestern Sichuan province.

In a further sign of SunPower’s confidence in LCPV in China, the company late last year said it would break ground on a 1 GW LCPV manufacturing plant in the Philippines.

That Fraunhofer/NREL report kind of treated LCPV as an afterthought, focusing mainly on the high-concentration sector, but you have to wonder about that, given the way the roster of HCPV players has been dwindling. Even the company at the top of the cell-efficiency heap, Soitec, is struggling mightily, although there are indications that reports of its CPV demise might be premature. Meanwhile, SunPower presses on in China with its low-concentration system, and it will be interesting if large-scale success there, should it unfold, might put CPV back on the radar in the U.S.