PV Pointers: Silicon heterojunction solar cell technology moves beyond the lab

There’s been lots of buzz about silicon heterojunction [SHJ] solar cells and rightly so. SHJ is one of the more promising solar panel technologies to come along in some time due to its proven ability to improve conversion efficiency. In addition, panels employing SHJ cells have been able to improve overall temperature coefficient power output — to as low as 0.258 percent — helping to solve a problem that has caused more than a few solar panels to sputter on especially hot days.

How we got here

PanasonicThe history of SHJ goes back to 1980 in a lab at Sanyo Electric (now Panasonic). Sanyo engineered the world’s first amorphous silicon solar cells but given their low conversion efficiency — less than 10 percent — practical applications were limited. In the late 1980s, Sanyo continued to tinker, eventually developing solar cells with laminated amorphous silicon and thin-film polysilicon. Bucking the prevailing wisdom of the day, the amorphous silicon was used only as a conductive passivation material rather than as an electricity-generating layer. The result was greatly improved junction characteristics, and the SHJ solar cell was born. Sanyo researchers presented their findings at the Fifth Photovoltaic Conference in Kyoto, an international gathering of the photovoltaic research community, and excitement quickly spread. Ensuing milestones include the attainment of 20 percent efficiency in 1994 followed by the 1997 rollout of the world’s first commercially-marketed heterojunction solar cell. Since then, SHJ has seen continued improvement with the technology underpinning current records for conversion efficiency and reduced degradation rates.

Why are SHJ cells superior?

Let’s start with base materials. SHJ solar cells are made using a combination of amorphous silicon layers and monocrystalline silicon wafers, a material less prone to degradation under prolonged, intense light exposure. This unique construction lets the solar cell produce electricity at both the front and rear of the cell. Further, the use of multiple materials allows for the insertion of wider bandgaps, which lets the cell respond to multiple light wavelengths. The net result is superior conversion and the ability to maintain near-peak efficiency at higher temperatures.

Given the proven benefits of silicon heterojunction technology, why are some manufacturers sticking with older, more conventional technologies that use amorphous silicon only? While the benefits of SHJ have become widely accepted, high production costs have remained a stumbling block. But with recent advances in the metallization process that leverages SHJ’s ability to be processed at lower temperatures than amorphous silicon cells, SHJ may finally be moving into the mainstream. While SHJ panels still demand higher upfront costs than non-SHJ counterparts, higher conversion efficiencies, guaranteed performance metrics and longer warranties — up to 25 years from some manufacturers — have shortened the payback window enough to win over consumers who see the wisdom in committing to solar energy for the long haul.

Mukesh Sethi is group manager, residential solar team, at Panasonic.

— Solar Builder magazine

See Panasonic’s new 40mm frame HIT solar modules at SPI


At SPI, Panasonic Eco Solutions North America will exhibit be showing off several new products and presenting on the latest advancements in HIT high-efficiency PV modules with innovative silicon heterojunction technology at booth 6701.

The solar panel products that will be on display are the HIT N315K and N320K, Panasonic’s new line of all-black solar panels that have an industry-leading temperature coefficient of -0.258 percent, as well as the N335 and N330 solar panels, the latest in Panasonic’s line of high-efficiency solar modules with a new 40mm frame. These solar modules are manufactured with “N” type cells, which reduce the annual performance degradation from 0.70 percent to 0.26 percent when compared to conventional solar panels.

Earlier this year, Panasonic and Pika Energy Inc. partnered to create the Harbor Flex and Harbor Plus, DC-coupled solar smart batteries with industry-leading performance specifications. Panasonic will also be exhibiting a lithium-ion rechargeable battery, with a wide range of portable electronic applications.

Vote here for the 2017 Solar Builder Project of the Year

— Solar Builder magazine

U.S. Defense Department commits to solar power production across several sites

The Defense Department has been installing solar at military bases at a fairly steady pace the last few years. The most recent projects coming online soon include a large Gulf Coast Solar Center portfolio (across three sites) and a new solar + storage system at a post in Alabama.

Here’s the scoop on those.

Gulf Coast Solar Center

coronal panasonic military solar install

Coronal Energy, powered by Panasonic teamed with Pensacola-headquartered energy provider Gulf Power on the largest combined portfolio of solar facilities on Department of Defense property to date. The 120 MWac Gulf Coast Solar Center spans 942 acres across three Navy and Air Force sites in Northwest Florida.

The Naval Air Station (NAS) at Pensacola’s Navy Outlying Landing Field (NOLF) Saufley hosts the largest of the three solar installations: a 366-acre, 50 MWac solar generating facility. The solar facility at NAS Pensacola’s NOLF Saufley comprises nearly 600,000 solar PV modules that will generate enough energy to power approximately 7,400 homes in Northwest Florida annually. The three-project portfolio, representing one of the largest combined solar projects east of the Mississippi, also includes 40 MWac and 30 MWac facilities at NAS Whiting Field’s NOLF Holley and the Eglin Air Force Base Reservation spanning 336 and 240 acres, respectively. In total the nearly 1.5 million solar panels generate enough energy to power more than 18,000 local homes each year across Escambia, Santa Rosa, and Okaloosa counties.

“Considering the scale of the Gulf Coast Solar Center portfolio, collaboration between our team and the like-minded teams at the U.S. Air Force, U.S. Navy, and Gulf Power has been an essential element of our success in developing these projects,” said Jonathan Jaffrey, chairman and CEO of Coronal Energy™. “The result is a landmark energy project that represents what is possible when our nation’s military and its leading energy companies like Gulf Power commit to renewables. We are honored to take our place alongside these partners for this historic project.”

“Each installation and mission throughout the Southeast is unique and it is imperative for us [the Navy] to have the energy security and resilience needed to support the greater Navy mission. There are eight renewable generation projects that DON is supporting in the southeast and today you are seeing the completion of two solar facilities in Northwest Florida totaling 122.5 megawatt direct current,” said NAS Pensacola Commanding Officer Capt. Christopher Martin. “We are pleased to know these facilities will help provide clean energy to thousands of homes across Northwest Florida.”


Alabama Army post adds solar + storage

sunpower logo

SunPower Corp. has broken ground on a 10-MW solar  system at the Redstone Arsenal U.S. Army post in Alabama and will combine with a newly added 1-MW energy storage system to strengthen energy security and resilience at Redstone Arsenal.

Developed by the U.S. Army Office of Energy Initiatives, Redstone Arsenal’s Directorate of Public Works, and the U.S. Army Corps of Engineers Huntsville Center’s Energy Division, the project was financed by a power purchase agreement (PPA), allowing the Army to buy 100 percent of the power generated without having to pay for the power plant’s construction, maintenance and operation. The Army continues to collaborate with private-sector partners and utilities to build clean, alternative energy projects including onsite power generation, electricity storage, and energy control.

“Solar is cost-competitive with traditional energy sources today, and is helping the U.S. military reduce operational costs,” said Nam Nguyen, SunPower executive vice president. “We commend Redstone Arsenal for managing its significant energy demand with abundant, renewable solar power. The high performance solar and storage technology we are installing for the agency will substantially increase the value of energy produced by the solar plant over the long term.”

Financing beyond FICO: Using asset-backed loans, PACE to get solar deals done

— Solar Builder magazine

How one PV module manufacturer wants to meet the needs of homeowners

Solaria uses a direct contact between cells

Solaria uses a direct contact between cells to reduce power loss as well as achieve an all-black look.

For all of the intrinsic value of solar, selling it on a wide-scale to homeowners might depend more on stuff like emotional appeal and aesthetics. This is driving the influx of black PV panels coming onto the market. LG’s NeON series comes in black. Panasonic just released all-black versions of its popular HIT panels (as we noted last issue). And so on.

A new entrant into this space is Solaria, a technology company that has been developing its technology over the last decade to commercialize a breakthrough product for the industry. As Chinese panels continued to drive down prices in utility-scale projects, that market became less of a focus.

Looking at the market, Solaria CEO Suvi Sharma thinks residential installs are the next big opportunity for high-efficiency, aesthetically pleasing panels that have residential applications in mind from the start.
“If you look at the Chinese model of panels where you basically make two different sizes that you stuff into different channels, that worked when the market was small, but now the market deserves its own product and focus.”

Solaria took its core technology – solar cell cutting, handling assembly and automation and configured a module and design to do two things:

“Produce significantly more power than a standard solar panel using the same bill of materials and, just as importantly, provide a much better looking panel,” he says. “With the industry maturing, those attributes will become more important. We want to break through from the early adopters in the mass market.”

Right now, Solaria’s residential solar capacity is still on the smaller side. Between its line in Fremont, Calif., and its line in South Korea, Solaria is working on adding additional capacity to meet growing demand.

Inside the Design

Conveniently, Solaria’s strategy for designing an efficient panel naturally created a sleek-looking product. The Solaria formula in a nutshell is to cut solar cells (mono PERC) into five strips and then overlap each of them instead of interconnecting them with traditional ribbon wire. The cell architecture of a traditional module leaves dead space between each cell, whereas this overlapping structure creates a uniform, continuous string of strips as well as the aesthetic bonus of covering up the typically visible busbars.

“All of the active areas of a cell are exposed. Busbars on a typical module shade about 3 to 4 percent of the module and cell, so we eliminate that through the overlap mechanism,” he says. “By creating a direct contact between one cell and another, we get better electrical performance because we don’t have the traditional losses associated with ribbon wires.”

Why high-efficiency modules are the best value for installers, homeowners

Part of the value from increasing system efficiency within the module architecture itself — and wiring in a combination of parallel and series — is also reducing the need for efficiency-boosting or shade-mitigating MLPEs. You may still want to incorporate optimizers in certain applications, but the need is reduced.

Add all of that up, Sharma says a Solaria panel (60-cell, 330 Wp) should be expected to produce 15 to 20 percent higher power than conventional panels using the same cells and materials to pair with that all-black appearance. The price point for Solaria is higher than a conventional Chinese panel, but priced below a high-efficiency SunPower back-contact panel.

Looking Ahead

Beyond improved aesthetics, simplicity is another big factor in the residential market. For that reason, Sharma wants to put Solaria on the path toward smart AC modules.

“How does solar become truly mainstream? The installation of the system needs to be simplified more and more. Plus, it’s a complex sell. The broader we can make the installer base, where more electricians get into it, the bigger it’s going to grow. We want to simplify the installation and that’s where we see the opportunity for integrated AC modules.”

Be on the lookout for more news on that front from Solaria as it tests out concepts with various microinverter manufacturers until it feels comfortable enough to offer an integrated product and stand behind the warranty.

Why Mono PERC?

Key to Solaria’s solution is the mono PERC cell. CEO Suvi Sharma explains his reasoning behind that choice.

“You typically get about 1 percent absolute improved power today from a standard mono cell, but the roadmap to improve that power is better with mono PERC,” Suvi says. “There are more dials to play with in terms of efficiency. Not only does mono PERC have higher power than a traditional mono cell, but the difference is going to grow over time. Could become 2 percent absolute over the next 18 months.”

“One issue with PERC is its light-induced degradation [LID]. The PERC manufacturers have worked on that a lot over the last 18 months. The LID is similar to mono cells now. Sometimes in multi PERC there tends to be more LID.”

“Mono PERC is growing in market share because it’s an add-on. If you already have an investment in a mono cell line, you can leverage it for mono PERC as opposed to new cell contents like heterojunction and bifacial, which require a fundamentally new investment in equipment. We believe that within three years probably, all mono cell capacity is going to be converted to mono PERC.”

— Solar Builder magazine

Panasonic names its first group of Premium Solar Installers

Panasonic solar solutions

Several authorized installers of Panasonic’s HIT solar modules were just promoted to the exclusive “Premium Installer” status. Panasonic unveiled this program last year to provide valuable assets to partners who meet Panasonic’s high standard of excellence.

“The growth of Panasonic HIT modules across North America has allowed us to partner with several exemplary solar panel installers who share the same dedication to quality customer service and superior product performance as we do,” said Mukesh Sethi, Group Manager of the Solar Division of Panasonic Corporation North America. “We are thrilled to offer additional benefits to these valued partners and we look forward to working with them for years to come as we expand our presence in the North American residential solar market.”

Those partners are… (drum roll, please)…

• Sullivan Solar Power – San Diego, CA
• LA Solar Group, Inc. – Van Nuys, CA
• Westhaven Solar – Santa Cruz, CA
• Sierra Pacific Home & Comfort – Rancho Cordova, CA
• Diablo Solar – Martinez, CA
• RevoluSun – Burlington, MA
• SUNation – Ronkonkoma, NY
• SunRay Solar – Concord, NH
• NJ Solar Power – Bayville, NJ

What’s a premium installer?

Panasonic’s Solar Installer program is comprised of “Authorized” and “Premium” installers. Premium installers are those companies that have completed a minimum requirement of HIT module installations and have met an annual wattage target. These installers also promote Panasonic as their primary brand of solar modules, and they receive a range of benefits from Panasonic to enhance their offerings to customers.

Premium installers will be part of continuous efforts with Panasonic to promote the HIT brand among the installers’ area of operation. They will receive leads generated through Panasonic’s website, where the installer will be listed as premium. Premium installers are also the beneficiary of cooperative marketing funds provided by Panasonic, at twice the level of funds provided for Authorized Installers, to help grow their business and attract even more customers.

Panasonic will aim to expand the reach of the Solar Installer program and bring industry leading companies into these mutually beneficial partnerships.

— Solar Builder magazine