Saturday, August 20, 2016

What's New in Solar Power

The sun is the gift that keeps on giving. It showers the earth with more energy in one hour than all energy consumed globally in an entire year.

It's there, it's free and it's non-polluting. The question is how to capture it economically and store it efficiently.

Solar is of particular interest to Florida, "The Sunshine State," where we have not one, but two constitutional amendments on the ballot this year that provide incentives for using photovoltaic power.

Despite the potential and billions of dollars poured into the technology, solar has made scant inroads in the U.S. market. The Energy Information Administration estimates only 0.6% of U.S. electricity comes from solar. (In Florida, the number is only slightly higher.)

Overall, coal provides about one-third of our electricity, natural gas another third, with the remainder coming from renewables -- mostly nuclear and hydroelectric. Renewables are expected to supply 50% of new energy capacity by 2040.

How much of that will be solar remains to be seen, but there are reasons to be optimistic.

  • The Feds agreed to extend the 30% investment credit for solar, a massive subsidy that will keep marginal operations afloat.
  • Congress plans to pump more money into solar research and battery storage technology through 2020.
  • Huge advances in the science are being made, both in universities and in the private sector -- not just in the U.S., but literally around the world.
But will it be enough to propel an industry now largely confined to rooftop units and hampered by pushback from communities opposed to massive solar farms that blight the landscape. (Supplying all of Florida's electricity needs today, experts say, would require solar farms that would cover 25-30% of the state's surface.)

The challenges for solar are essentially three-fold: (1) Reduce cost to allow free-market competition. (2) Increase efficiency of converting sun to electricity, in turn reducing the surface area required for energy generation. (3) Improve efficiency of batteries to store energy when the sun isn't shining.

Advances are being made on all fronts. Here is where things stand today.

The vast majority of solar power, some 90%, comes from workhorse silicon panels, a mature technology whose cost has been driven down by volume-produced cells from China. Conventional panels are thick, heavy, inflexible and dependent on direct exposure to sunlight. Sun-to-electricity conversions are 20-25%.

The next generation of panels will be thin, lightweight, flexible and potentially lower in cost. Efficiencies may also be lower, currently ranging from 10-20%. All will require multiple layers, but will have the capability of being fabricated into thin sheets by conventional milling.

Dye-sensitized solar cells, pursued in Switzerland, South Korea, Wales and the U.S., utilize photo-absorbing dyes that create charge separation in electrolytic solutions. Unlike silicon cells, they can operate in diffuse light, even indoors. Current uses include fabrication in windowpanes to provide electricity in adjoining rooms and continuous powering of small electronic devices, e.g., computers. Rooftop use or mass generation of electricity is many years away, if possible at all.

Organic photovoltaics rely on light-sensitive polymers to drive charge separation in a mini-particle mix. Like dye-sentized cells, the organics are used where flexibility or thin films are important -- windowpanes, backpacks, phone chargers. Start-ups in Denmark and Germany plan to begin production in 2018. As with dye-sensitized cells, the organics would require major breakthroughs to go beyond niche uses.

Perovskite cells are the rock stars, the sexy contenders for the future. With 22% efficiency already booked, they have the potential for eventually replacing silicon. Based on organolead halide minerals, the perovskites are cheap to produce, but are inherently unstable, a shortcoming receiving much attention in start-up companies in England and Poland. Perovskites may initially be paired with silicon cells, a tandem arrangement that would capture a larger portion of the sun's spectrum, jacking efficiency and cutting cost. But don't expect any commercial use before 2019 at the earliest.

Other things are happening as well. In a big attention-grabber, an aircraft powered solely by the sun just completed a one-year around-the-world trip. Swiss-engineered, the plane used over 17,000 solar cells and ran on lithium batteries at night. It's cruising speed topped out at 56 mph.

And in a big advance for battery design, Missouri academics used atomic-layer-deposition techniques to upgrade the charge capacity and operating voltage of lithium batteries. If verified in scale-up, it could cut costs for storing solar energy and powering electric cars. 

What's the bottom line? There's a lot going on. Challenges are being met, and new applications are emerging. Rooftop solar and niche uses will continue to grow. But large-scale electricity generation from the sun is still many years or even decades away. 

1 comment:

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