Solar photovolaics (PV) have undergone a remarkable evolution, really a transformation, since the beginning of the industry in the 1960s. Initially solar was so expensive -- well over $100 per kilowatt hour -- that only super-high value or remote applications, such as satellite and spacecraft missions, could be justified.

Following the OPEC embargoes of the 1970s, a wave of investment took place in the industry that, while brief, helped to bring a number of largely silicon-based technologies to niche markets. Since then scientific and materials engineering progress in the solar field has been steady, with an evolution away from silicon as the only material, to a truly exciting and promising range of plastic, thin film, nano-based, and organic cells.

While the potential for solar has long been touted as a clean, no-carbon (in the use phase) and very low carbon (including manufacture) technology, just how to implement solar has been an issue. Initial technological breakthroughs and manufacturing techniques had energy analysts planning large-scale "solar fields" to replace fossil fuel power plants.

One such test-bed, the aptly named Photovoltaics for Utility-Scale Applications (PVUSA) built in the 1980s in South Davis, California, took the utility-based plan literally with a then-huge 1 MW field of photovoltaic solar panels. The large-scale, slightly remote PV plan gave way during the late 1990s and the last few years to a far more distributed model of rooftop (both commercial and residential) that has seen sales growth of over 20 percent per year for the last decade and a half, with global production growing by close to 50 percent each of the last two years. Total production in 2006 was over 2000 MW, with installed, unsubsidized costs, now coming close to 20 cents/kWh in the best applications.

This has been remarkable progress, but from such a small base, skeptics note that it will take decades for solar to become a major contributor, and during that time we may be well on the way to irreparably altering the climate system.

What can be done to dramatically accelerate -- or at the very least evaluate the potential for -- a true evolution/revolution in solar energy?

First, it is important to note that several very different models have emerged that have all put large amounts of solar into commercial service. Germany instituted a very generous feed-in tariff that guaranteed early installers a fixed income for the long-term (typically 20 year) solar contracts.

California, the third-largest market for solar on Earth, has over 30,000 home and small-business systems installed, and in 2006 put in place a 10-year, $3.3 billion program termed "Million Solar Roofs" that should add a whopping 4,000-10,000 MW of solar over the coming decade.

Kenya, not a place that comes readily to mind as a PV leader is, in fact, just that. With roughly 30,000 small (truly small, 20-100 watts, not kilowatts, per household) systems sold per year, has the world's highest household solar ownership rate.

These programs are all promising, and so far successful. A tremendously compelling case, and one often cited by less often studied, however, is that of the Sunshine solar energy program in Japan. Over the course of almost two decades, starting in the late 1980s, Japan developed and then implemented a remarkably coordinated, well-designed solar development and dissemination effort.

As can be seen in Figure 1, a steady build-up in solar energy research and development (green and yellow) was then partnered with a more rapidly expanding deployment and dissemination effort that focused on consumer and utility education, trial and test home, business, and industry locations (blue), products and services. This sort of staying power and coordination of both the so-called "technology push" (R&D) and "demand pull" (commercialization) efforts is truly a rare thing of beauty in the world of technology policy.

Figure 1: Japanese national investment in solar energy research (green & yellow, above the 'zero' line) and in solar deployment (blue shadings below the 'zero' line). Source: Sunpower Corporation. At current exchange rates, the total investment (¥91 billion) in 2004 is 744 million dollars.


The Sunshine program is not just pretty on paper, it really worked. During the program annual PV installations grew to over 300 MW of solar/year, and the rate of cost decreases grew to almost 10 percent year.

This is compared to the best rate seen in California to date, at about half of that: a 5 percent rate of cost declines per year. This level of cost improvement is very significant, and took place at the same time that Japanese research laboratories made a succession of scientific and engineering advances.

What is needed next, of course, is replication and scale-up. Programs like the Sunshine effort, or more broadly the efforts of the 'big three' of Japan, Germany, and California, need to be developed, and put in place for the long haul in a far larger range of countries, states, and municipalities.

Second, the lessons of these efforts, in terms of technological leadership, job creation, and climate protection -- need to be well-documented and widely known.

Third, and in many ways the least easy to do, the real benefits of solar need to be monetized. Local solar installations reduce the need for investments in new power plants, and -- critically -- lessen the likely peak power demand on crisis days.

Solar also reduced demand on the transmission and distribution system, and puts emission-free power near people, thus directly benefiting urban air quality and health.

Daniel M. Kammen is the Class of 1935 Distinguished Professor of Energy at the University of California, Berkeley. He co-directs the Berkeley Institute of the Environment and is founding director of the Renewable and Appropriate Energy Laboratory. He has appointments in the Energy and Resources Group and the Goldman School of Public Policy.