How to Make Solar Work

Solar energy

UPDATE (2/6/2017): Meng Tao has recently been awarded the 2017 Fulbright Distinguished Chair in Alternative Energy Technology. The Fulbright Distinguished Chair awards are viewed as among the most prestigious appointments in the Fulbright Scholar Program, awarded to eminent scholars with significant publication and teaching records. Tao will be working at Chalmers University of Technology for the 2017/2018 academic year, working with Swedish colleagues on two projects: solar photovoltaic systems to charge electric vehicles and value-added recycling of wafer-silicon solar modules.

(December 2016) Global energy demands are predicted to reach 46 terawatts by 2100. That number is a far reach from the 18 terawatts of energy currently generated around the world. According to one expert in the field, a major shift in the way we produce and consume energy is necessary in order to meet future demands.

Meng Tao, ECS member and Arizona State University professor, discussed how society could move toward meeting those demands at the PRiME 2016 meeting, where he presented his paper, “Terawatt Solar Photovoltaics: Roadblocks and Our Approaches.”

“We just cannot continue to consume fossil fuels the way we have for the last 200 years,” Tao told ECS. “We have to move from a fossil fuel infrastructure to a renewable infrastructure.”

For Tao, the world’s society cannot set on a path of “business as usual” by producing energy via coal, oil, and natural gas. And while solar energy has experienced a growth rate of nearly 45 percent in the last decade, it still only accounts for less than one percent of all electricity generated.

The shift to solar

Historically, solar technology soars when oil prices are at their highest. This is especially true during the oil embargo of the 1970s. During that time, private and public investments began to shift away from fossil fuels and toward solar and other renewable energies. That trend emerged again in the early 2000s when oil prices skyrocketed to a record-setting $140 per barrel.

“In the 1970s, the motivation to invest in solar and other forms of renewable energy was geopolitical,” Tao says. “Now, that motivation tends to focus more on the environment and sustainability.”

Currently, all major scientific agencies in the U.S. agree that climate change is occurring and that humans are contributing to it. Since the 1800s, the global temperature has increased an unprecedented 1.5°F. In fact, 15 of the 16 warmest years ever recorded have occurred in the 21st century. The key instigator for these rapid changes in climate are greenhouse gas emissions produced by burning fossil fuels. While greenhouse gases such as carbon dioxide are necessary for photosynthesis and the overall stability of our atmosphere, the consensus among the scientific community is that sometimes, there could be too much of a good thing.

According to the U.S. Environmental Protection Agency, 30 percent of all greenhouse gasses emitted in the U.S come from the energy sector, followed by 26 percent from the transportation sector and 21 percent from industry. Approximately 67 percent of all electricity comes from burning fossil fuels (coal, natural gas, etc.) and 90 percent of fuel used in the transportation sector is petroleum based (gasoline and diesel).

“We need to take these sustainability issues very, very seriously,” Tao says. “I have two kids and they need a place to live – and their kids need a place to live, too.”

PV everything

For Tao, that means making a drastic change in our energy infrastructure as we know. His vision? Photovoltaic everything. That means every major industry – including transportation – will be electrified via solar.

“My research focuses on pushing solar PV (photovoltaics) into a mainstream energy source by the end of the century,” Tao says.

To do this, Tao hopes to take solar energy production from today’s less than one percent mark to a goal of upwards of 30 percent. Tao is focusing on moving away from small implementation of the technology to scalable and sustainable efforts that could shift our energy dependence away from fossil fuels.

Tao is looking at a few critical issues. First is the availability cost of materials used to develop a solar cell. Currently, all commercial silicon solar cells use silver as their electrode material, which is scarce and expensive. In order to make solar cell production more sustainable, Tao and his team opt for the much cheaper, earth-abundant aluminum as a replacement for the silver electrode.

Another issue Tao is addressing is how to purify the silicon necessary in the development of solar cells. The solar industry was built on silicon, which has long since been the semiconductor material of choice for solar technologies due to our understanding of the material and its promising electrical properties. However, the current process used to purify silicon is very energy intensive. According to Tao, fundamental advancements in purifying silicon electrochemically could take society in a new direction of solar cell manufacturing and mean huge progress in making solar scalable.

On-grid vs. off-grid

But Tao isn’t only focused on harvesting renewable energy, he’s also looking into ways to store it.

“We’re getting to a stage where our grid just cannot handle so much unpredictable, intermittent energy,” Tao says.

For him, the big question here is: Do we need on-grid or off-grid storage? On-grid storage would utilize the current energy infrastructure already in place; adding energy storage options that could help hold the PV generated electricity and push it through the grid. While Tao believes on-grid storage will be a piece of the energy infrastructure of the future, he’s putting his chips on off-grid storage.

According to Tao, off-grid storage would allow for better opportunities in holding large amounts of energy and could more easily deal with the issue of intermittency in renewables. Intermittency in our current grid infrastructure could overload the system, but off-grid storage would be better equipped to handle this unpredictability.

Off-grid storage also opens the door to another renewable energy potential: solar fuels.

“Right now, if you generate energy from PVs, you must use that energy right away,” Tao says. “However, if you convert that energy to fuel, you can store it for long periods of time and even sell it to countries far away or save it for the next winter.”

Of all the energy we consume today, two thirds of it comes in the form of chemical fuels. In order to truly move toward renewables, a viable replacement for these fuels must emerge.

The 28 terawatt leap

But Tao thinks that this issue doesn’t just boil down to emerging technology, it also incorporates social behavior and the mentality of society. A move toward sustainable energy does not mean just supplying technology to the world, it also demands a change in people’s thinking.

“Industrialization got us into the habit that no matter how costly – no matter how environmentally damaging – if we want energy, we’re determined to get it,” Tao says. “In some ways, we’re trading our long-term survival for our short-term convenience.”

However, thanks to Tao and researchers like him, an idea that once seemed so distant is beginning to be tangible.

“It will be a huge challenge to go from 18 to 46 terawatts,” Tao says. “While it may be a huge challenge, it’s also a huge opportunity and I think we’re already beginning to see that shift.”

Read more work by Tao in the ECS Digital Library.