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People have been harnessing the sun’s rays for millennia. New technologies combined with old ideas are helping expand the reach of Earth’s original heat source.
Stand outside on any clear day and you can feel the power of the sun, even in Antarctica. Which is where Adam Plesniak found himself in December 2015, trying to figure out how to use solar to heat guest pods at a tourist camp in Queen Maud Land on the Antarctic coast.
“Antarctica is a very strange place,” Plesniak recalls. “When you’re on the coast of Antarctica, it’s a very dynamic landscape, where ocean meets ice shelf meets land. …So imagine you’re the size of an atom standing on top of an ice cube. That’s effectively what it feels like. And of course the sunlight there — because you’re so high and you’re at the bottom of the planet — the sunlight is very intense, it’s probably twice the intensity of anywhere else, because of the thinness of the atmosphere.”
The tourist camp was using space heaters powered by a generator that ran on jet fuel. “Jet fuel is expensive to begin with, but to get it delivered to Antarctica is really expensive,” Plesniak says. The owner of the company brought him there to “research the use of other heating techniques to keep his guests comfortable.”
Plesniak has been working in solar power for more than two decades, but his trip to Antarctica led him to start a business, Arctica Solar, making simple panels that, instead of creating electricity, collect the sun’s heat and pump it into a house. Using the sun’s heat directly is called solar thermal.
And while photovoltaic panels that generate electricity are one of the cleverest and fastest-growing ways to harness solar power, solar thermal has a long history — and maybe a bright future. “Until about 45 years ago, 40 years ago, solar thermal was the only solar, right?” Plesniak says. “When Jimmy Carter put solar panels on the White House, he put solar thermal panels on.”
Some solar thermal technologies are simpler and older, some newer and more complex. But all rely directly on the heat of the sun.
Solar Thermal at Home
Long before people started harnessing the sun to generate electricity on their roofs, solar thermal panels created hot water for millions of Americans in places like Florida and Southern California. About half of the homes in Miami, for example, had solar hot-water systems in the years after World War II.
Those systems fell out of favor as cheap fossil fuels and electricity became widely available. In other parts of the world, however, solar thermal is still standard: In Israel, about 90% of homes heat their water with solar, and solar water systems are substantially cheaper there thanks to scale and familiarity. Barbados, Cyprus, China, Greece, Turkey, and even chilly Austria have solar water heating in much higher numbers than the U.S. These solar hot water systems can also be used for radiant heating.
Then there are solar air heating panels, which simply collect the sun’s heat and transfer it into the home through a small fan, generating free heat whenever the sun is shining. Plesniak says the best uses for solar air heating are outbuildings or structures in cold, sunny climates where extra heat is desired.
These panels need to be on the south side of the house, but Plesniak says installation is fairly simple. “Because there’s no electrical connection for the product to the building, it’s like installing a dryer duct,” he says.
Lightspring Solar in Bismarck, North Dakota, installs solar thermal air panels from 8th Fire Solar, which makes panels on the White Earth Native American reservation in Minnesota. James Kambeitz, one of Lightspring’s founders, sees solar air heating as a piece in the heating puzzle in cold climates, where heating typically uses more energy than anything else.
Until about 45 years ago, 40 years ago, solar thermal was the only solar, right? When Jimmy Carter put solar panels on the White House, he put solar thermal panels on.
– Adam Plesniak, founder of Arctica Solar
Although it’s easy enough to install panels on existing buildings, he says, growth in solar air heating “really depends on a perspective shift in building new construction in northern climates. People should automatically think of building [solar thermal] right into the south-facing walls, and orienting a building around how it could capture the solar thermal of the building on the front end.”
Another solar thermal technology, hybrid photovoltaic and thermal (PVT) panels, create both electricity and hot water. With the water absorbing excess heat from the PV panel, the efficiency of the panel itself actually increases.
Finally, there’s “passive solar,” which simply means designing a house or building’s windows, walls, and floors to collect, store, and distribute heat from the sun when it’s cold and reflect and reject solar heat when it’s hot. There are dozens of strategies to use passive solar, and they can reduce a building’s energy use by more than 75%, depending on how carefully the structure is designed. The basic principles of passive solar design were developed in ancient Greece, Rome, and China; before the advent of modern heating and cooling, many buildings were designed to use the sun to their advantage.
Still, even after 100-plus years of solar thermal systems and 50 years of interest in environmental technologies, solar hot water and other systems remain a small part of the energy picture: Less than 1% of U.S. homes use solar hot water, even though 7% have PV panels.
Plesniak says that the modular, one-size-fits-all nature of PV has helped it scale, but “solar thermal, while very useful when it’s done correctly, and a very quick payback when it’s done correctly, it’s just technically more complex and does not lend itself to scaling as well.”
Going Big on Solar Thermal
While passive solar has been around for millennia, and smaller-scale solar thermal for homes has been around for over a century, there are new technologies that generate power on a large scale. These are used in concentrating solar power, or CSP, plants, which use mirrors (“heliostats” in solar jargon) to focus the sun’s rays on a single point, generating intense heat that is then used to create steam to power a turbine in the same way a coal or nuclear plant would.
CSP plants have gone up all over the world — largely in warm, sunny climates like Spain and Australia — but there are only two in the U.S.: The 110MW Crescent Dunes project in Nevada and the giant 377MW Ivanpah plant in California. Both use thousands of heliostats to focus sunlight on towers almost 500 feet tall, where the intense heat is collected in molten salt and piped down to make steam that powers turbines.
As might be expected when new technology is involved, both CSP facilities in the U.S. have had problems, and neither has produced the energy promised. Crescent Dunes suffered a series of technical issues that interrupted generation several times, and the company that built it went bankrupt; it’s now generating power mostly at night through stored heat, one big advantage of CSP.
Ivanpah has had more public problems, including concerns about its massive size (3,500 acres), visibility (along busy Interstate 15), and desert habitat destruction. Also, birds that unwittingly fly into the intense beams of heat between the reflectors and the towers can get incinerated on the wing; estimates of bird fatalities suggest at least 6,000 birds annually die this way, though plant operators have made efforts to reduce these figures.
The worst impediment to CSP is cost. It’s currently among the most expensive electricity in the grid. And although improved technology and know-how may reduce the cost of future CSP plants, the dramatic reduction in costs of solar PV made the $2.2-billion Ivanpah effectively obsolete the day it opened. Ivanpah was even scheduled to close to save ratepayers money, but California regulators, concerned about having enough cleaner electricity to meet rising demand, are forcing it to stay open at least temporarily.
It really depends on a perspective shift in building new construction in northern climates. People should automatically think of building [solar thermal] right into the south-facing walls.
– James Kambeitz, co-founder of Lightspring Solar
Plesniak notes that the lessons learned from these less-than-successful CSP efforts may prove valuable in the future. He points to CSP’s contributions to innovations in heat storage and solar tracking.
“Often, as an engineer working in these technology spaces, you look for derivatives,” he says. “So if you see a lot of money going into a technology development where the core economic thesis is wrong, or becomes wrong, you often are looking for ways to redeploy or pivot that technology into something else.”
Sunny Days Ahead
The up-and-down history of solar thermal, for both small-scale heating and large-scale electricity generation, defies both the steady nature of the sun and its potential to help us meet our green energy needs.
Plesniak, with his long experience in solar, has seen solar’s evolutionary dead ends up close. “I worked for a startup in 2010 that was looking at concentrator photovoltaic,” he says. “Instead of the PV panels you see on folks’ roofs, we would put a lens in front of some photovoltaic material and concentrate the light before we collected it.”
This increased the efficiency of the panels tremendously, but as standard PV panels became cheap, concentrator photovoltaic was no longer cost-effective. “That industry came out of nowhere and scaled very quickly, and just as quick as it showed up, it was gone. In the span of five years, it went from billions and billions invested to complete and utter wipeout.”
These winners and losers provide an interesting case study in how new technologies develop and get deployed. There are simple, century-old, money-saving, home-based solar heating and hot-water systems that have become common (and cheap) in some parts of the world but not in the U.S., based on incentives from both the government and the market. And there are other technologies — like CSP electricity plants or concentrator photovoltaic — that seemed like promising investments a decade ago, but now represent the Neanderthals of solar power.
The uncertainties in the market are not stopping Arctica and Lightspring from trying to harness the heat of the sun for economical and clean power. They’re not alone: GlassPoint, a solar thermal company focused on industrial applications, just raised $20 million in funding to go forward with several large projects. As long as the sun shines, there will be innovators working to harness it.
Five Takeaways
- Though the vast majority of solar power is photovoltaics that generate electricity, solar thermal captures the heat of sunlight directly.
- A variety of proven solar thermal technologies for homes exist for hot water, radiant heating, air heating, and passive solar design. Many of these technologies are deployed on a large scale in other parts of the world.
- Large-scale solar thermal electric plants concentrate the sun’s heat to create steam and generate electricity like a conventional power plant. The technology has proven tricky and comparatively expensive.
- Scaling a new technology can be tricky and often relies on government policies to become established.
- Even when specific technologies fail to scale, the lessons learned can have value in future iterations.
What You Can Do
If you’re building a new home or taking on a home improvement project, look for ways to incorporate solar thermal technology, whether with solar hot water or radiant heating, solar air heating, or simple passive solar concepts. You can also join organizations that fight for solar energy, like Vote Solar, support pro-solar politicians and policies, and get involved in Sun Day to raise awareness that solar energy is cheap and plentiful. And talk to your neighbors about solar. One of the most powerful predictors of a home having solar is if the neighbors do.
