Advances in PV Technology – 2014 Review 2/4

Achievements of energy technology represent how advanced the industry is. In terms of solar energy, improvements in high efficiency solar technologies, such as PERC and N-Type solar cells, are the highlights of this year. Colored and transparent solar cells which can be integrated with buildings mark the new era of BIPV. Other energy technologies like wind, electric vehicles and energy storage systems have gained progress in 2014 as well. It is obvious that the alternative energy is entering the next generation.

Technologies include solar PV are still progressing. (Photo Credit: jigedine via Flickr)

High Efficiency Solar Cells Enter the Market

1. PERC Technology

Higher level of conversion efficiency is the key to the continuous improvement in the solar industry. Passivated Emitter and Rear Cell (PERC) technology, a solution to increase the efficiencies of P-type mono-si solar cells, has been introduced by some manufacturers, including Sunrise Global Solar Energy, Gintech, Neo Solar Power, JA Solar and SolarWorld this year. Solar cell makers can start using PERC technology simply by adding necessary equipments without purchasing any new machines so the manufacturing costs can be remained relatively low while the efficiency can be increased significantly, making PERC an even potential technology for commercialization.

By adding a dielectric passivation layer (consisted of SiNx or Al₂O₃) on the rear side of a solar cell, the cell can maximize the electrical gradient to reach higher conversion efficiency. Mono-si PERC solar cells could have conversion efficiency 1% higher than regular mono-si cells. The 1% higher in efficiency will substantially increase a PV system’s power output and reduce the power cost per watt. However, light Induced degradation (LID) is a serious problem to P-type cells, whereas N-Type cell technology is another solution to increase solar cell’s efficiency.

2. N-Type Solar Cells

In contrast to P-type mono-si solar cells, N-type cells are able to maintain stable power output because they are almost free from the LID problems. Moreover, a bifacial N-type cell can reach a conversion efficiency of 22%, which is higher than P-type PERC cells’ efficiency target of 21% in the next 2 years. These features make N-type a promising solution to develop high efficiency cells.

However, it requires more equipments and advanced technologies to produce N-type wafers so the costs are much higher than the spot prices of solar cells, demonstrating a relatively harsh situation for N-type cells to take over the mainstream market. Despite the difficulties in commercialization, N-type cells open up a new world to high efficiency cells. SunPower and Panasonic are the leading international manufacturers of N-type cells, while Neo Solar Power and Inventec displayed bifacial N-type cells at this year’s PV Taiwan exhibition to present their advanced technologies as well.

Relate posts:

It is crucial to increase mono-si solar cells' conversion efficiency. (Photo Credit: Oregon Department of Transportation via Flickr)

3. Other achievements in high efficiency cells

The theoretical ceiling of common solar cells is as follow - 25% for mono-si solar cells; 20.4% for multi-si solar cells; 19.8% for CIGS thin-film solar cells; and 19.6% for CdTe thin-film solar cells. The efficiency for commercialized mono-si solar cells is usually 19.4% and 17.4%-17.6% for multi-si solar cells. Multi-si cells with conversion efficiency higher than 17.8% are categorized as high efficiency cells. Improvement of the efficiency is one of the industry’s major aims. In 2014, the most distinctive achievements are:

A new world record conversion efficiency: the multi-junction solar cell co-developed by Soitec, CEA-Leti and Fraunhofer Institute for solar Energy Systems ISE has reached a conversion efficiency of 46%, marking the world’s new record. (related post) Besides, researchers at University of New South Wales successfully increase commercial solar cells’ conversion efficiency from 33% up to 40%, breaking the world’s record. (related post)

JA Solar’s High Efficiency Cell and Module: JA Solar hit a new record by increasing multi-si solar module’s conversion efficiency to 17.2%, substantially higher than mainstream modules’ 15.6%. Meanwhile, JA Solar has successfully developed multi-si cells with efficiency up to 20%. (related post 1, 2)

Improved thin-film cells: this September, German researchers at ZSW institute broke Swedish research team’s CIGS thin-film efficiency record by creating a CIGS cell with 21.7% conversion efficiency. Also, First Solar successfully developed CdTe cells with 21% efficiency and aims to improve it further to 22%; the CdTe cells are planned to mass produce in 2015. (related post) In the mean time, Solar Frontier continues to increase its CIS thin-film cells’ efficiency and its newest record is 20.9%. (related post)

Competition between Panasonic and Sharp: Panasonic released its HIT® solar cells, possessing a high conversion efficiency of 25.6%, for residential use in April. In the same month, Sharp unveiled solar cells with 25.1% efficiency. (related post)

BIPV Applications with Various Kinds of Solar Cells

A building with facade covered by solar cells in Paris. (Photo Credit:La Citta Vita via Flickr)

Building-integrated photovoltaic (BIPV) is a popular application for solar power. To overcome silicon solar cells’ color and light-shading limitations, many researchers have endeavored for developing solar cells using various materials and technologies. For example, thin-film solar cells are one of the candidates for solar windows because they have better transmittancy than silicon cells. Heliatek, a German organic thin-film solar cell manufacturer, has unveiled a solar cell with 40% transmittancy. The new product is suitable to be installed on buildings and car roofs for solar generation and glare reduction

Coating is another option to create new types of solar cells. A research team at Michigan State University has developed a “transparent luminescent solar concentrator” that absorbs only ultraviolate and near infrared wavelengths to generate power – allowing the solar cell to be almost transparent. The efficiency, which is as low as around 1%, is the major defect and the team hopes to increase it up to around 5%.

The transparent solar cell developed by researchers from Michigan State University. (Photo Credit:Michigan State University )

In addition, New Energy Technologies, an American developer of organic photovoltaic (OPV), has made certain achievements for their see-through SolarWindow™ coatings. The Research Center for New Generation Photovoltaics of Taiwan’s National Central University is doing a similar OPV project, too. Even though OPV cells’ conversion efficiencies are lower than crystalline silicon cells, they can generate power under shady light conditions, a feature that makes them suitable to buildings.

Colored cells are also ideal choices for BIPV applications. By working with Sony, theResearch Center for Advanced Science and Technology of the University of Tokyo used dye-sensitized solar cell technology to create colored solar glass that will change their color according to the battery charging status. Likewise, six university students from Taiwan have established a creative studio and unveil solar cells that are “painted” with graphics. With these innovative technologies and designs, it is expectable for BIPV to go into the next generation soon.

Summary of 2014’s Innovative Green Technologies

There emerges a lot of interesting and potential technologies in 2014. Let’s see a pick of them!

Apple Inc. has applied a patent to the United States Patent and Trademark Office for a technology of inserting solar panels under touchscreens of mobile devices. (related post)
SunPartner and 3M co-developed a transparent solar panel called “Wysips” that can be embedded into smartphones to generate solar power and connected to Li-Fi signals. (related post)
By pasting solar panels, Tommy Hilfiger unveiled an innovative solar-powered jacket. (related post)
WeWi Telecommunications, a Canadian company, has developed “SOL” the sun-powered laptop. By connecting to three solar panels, SOL can be fully charged within only 2.5 hours under sufficient sunlight.
UK-based Arup and Pro-Teq respectively developed “solar dust” that absorbs ultraviolet during the day to generate power and glows during the night for lighting. (relate link)
IBM and AirlightEnergy cooperated to develop the High Concentrated Photovoltaic Thermal (HCPVT) system to generate solar power and take advantage of the heat simultaneously. (related link)
A professor from UCLA developed a new manufacturing process to create perovskite cell. The new type cells use cheaper materials and have lower pollutions; moreover, they can reach a 20%-level efficiency. (related link)
By adding a specially patterned layer of silica glass with pyramid structure on the surface of ordinary solar cells, it is able to slow down the cells’ aging process because the structure can help the cell to cool itself, reducing the temperature increased when generating power.
U.S.’s physicists believe that nano technology could be a considerable way to increase solar cells’ efficiency.
The solar roadway is one of the most-focused projects on campaign site IndieGoGo. Besides, it appears the world’s first solar bike path in Netherland. (related post)
The “BAT” (Buoyant Air Turbine) created by MIT and Altaeros Energies is now undergone necessary tests. The innovative wind turbine can float 30~90 meters above the ground to be swept by stronger winds.

The "BAT" floating wind turbine. (Photo Credit: Altaeros Energies)

Panasonic unveiled the world’s smallest lithium-ion battery, with a 2-cm length and a 3.5-mm diameter. The tiny lithium-ion battery is especially designed for wearable devices and is already started massive production. (related post)
Bath, a U.K.-based bus company, transforms people’s poo and kitchen waste into biofuel to power the special “poo bus.” (related link)
Japan’s Toyota launched its FCV “Mirai” this year. Currently, many Japanese companies are striving to develop fuel cells for residential and vehicle uses. (related post)

2014 Reviews: