Glass pyramid concentrator for solar cell applications

Image: Stanford University, Nina Vaidya

Stanford University scientists have built an optical concentrator that purportedly harvests more than 90% of the light that hits its surface.

From pv magazine

Researchers at Stanford University have created a glass pyramid optical concentrator that concentrates light on solar cells, regardless of the light incidence angle.

“It’s a completely passive system – it doesn’t need energy to track the source or have any moving parts,” said research coordinator Nina Vaidya. “Without optical focus that moves positions or need for tracking systems, concentrating light becomes much simpler.”

The AGILE (Axially Graded Index LEns) device purportedly harvests more than 90% of the light that hits its surface. It also creates spots at the output that are three times brighter than the incoming light.

“Installed in a layer on top of solar cells, they could make solar arrays more efficient and capture not only direct sunlight, but also diffuse light that has been scattered by the Earth’s atmosphere, weather, and seasons,” the scientists explained, noting that the solar cell could be built with fewer raw materials and at lower costs.

They said a top layer of the concentrator could be used to replace existing encapsulation materials. That would in turn create space for cooling and circuitry to run between the narrowing pyramids of the individual devices. The pyramid was made of different optical glass flats provided by Japan’s Ohara Corp.

“The geometry of the pyramid was a square of side 14.5 mm down to a square of 8.5 mm giving a concentration of three, along a total height of 8 mm with 8 glass layers, with each flat 1 mm thick,” the academics said.

They layered the glass together with polymers that bend light to different degrees. “The layers change the light’s direction in steps instead of a smooth curve,” they said. “The sides of the prototypes are mirrored, so any light going in the wrong direction is bounced back towards the output.”

The prototype can improve optical concentration by a factor of three and achieve a 90% efficiency in capturing light, they claimed in “Immersion graded index optics: theory, design, and prototypes, which was recently published in Microsystems and Nanoengineering.

“Results of the functional prototypes demonstrate that immersion graded index technology can improve the way we concentrate and couple light many fold,” the scientists said. “The AGILE has the potential to greatly improve opto-electronic systems by reducing cost, increasing efficiency, providing a scalable concentration system with built-in anti-reflection and encapsulation without the need for tracking.”

Author: Emiliano Bellini

Single-axis trackers on commercial rooftops increase generation by 37%

Image: Alion Energy

Alion Energy trackers thread the return-on-investment needle with productivity gains from white roofs and bifacial modules, while design aggressively maximizes module count.

From pv magazine USA

Alion Energy’s single-axis tracker racking product was originally designed to be deployed in regions where heavy installation equipment was more challenging to access, but labor might be more available.

One aspect of this design philosophy is that the system is light and can be easily carried and assembled, and doesn’t require metal pilings to be driven deep into the ground. And interestingly, this carries over to commercial rooftops.

Mark Kingsley, Alion Energy CEO, said in a post on LinkedIn that a commercial real estate group had installed a standard rooftop, 10-degree fixed tilt monofacial solar array, as well as a competing Alion Energy system.

The results were as expected – 37.5% greater generation on a per watt basis from the single-axis tracker, on a pristine white thermoplastic roof versus standard modules. Of course, the real breakthrough is that they were able to get single-axis trackers installed on a commercial rooftop at all.

The rooftop in their example has a lot of skylights, and the overall structure is not facing due south. In this configuration, Alion Energy suggests that it can fit 4.55 MW of modules on the Maryland structure with a standard 10-degree installation. This system is projected to generate 1.34 kWh per watt each year.

Alion has designed a system that is 5.4 MW – a full 18% increase in wattage due to systems ability to be installed directly over skylights without needing the standard setback. Additionally, this hardware is projected to generate 1.54 kWh per watt installed per year.

In this case, that works out to 37% more electricity from the same rooftop. And when the trackers are directly attached to the roof – a 2.15 pounds per square foot dead load. Add in one Alion’s customized robotic cleaners, and the company says the levelized cost of electricity from the system falls to 4.67¢/kWh and generates 40% more electricity than a standard rooftop solar install.

And while this rooftop was selected to show off their hardware, it’s still an interesting best case scenario for us to consider.

Author: John Fitzgerald Weaver

US lab reveals top findings for hybrid solar, storage plants

Image: Sharp

US government researchers have collected 10 observations from recent research papers that look at solar- or wind-plus-storage power plants in the United States.

From pv magazine USA

The US Department of Energy’s Lawrence Berkeley National Laboratory (LBNL) has released a top 10 list of observations on co-located wind or solar-plus-storage (hybrid) projects.

LBNL is covering the topic due to rising deployment and interest in such hybrid facilities. Assuming that future project queues can be used to predict the number of actual hybrid power projects that will get built, hybrid systems already make up 42% of the future US potential for 675 GW of solar generation capacity. California’s solar queue, for all intents and purposes, is a solar-plus-storage queue, with its 95% coupling rate.

As of the end of 2021, 5.9 GW of solar was coupled with energy storage, along with 750 MW of wind-plus-solar-plus-storage. LBNL noted the exponential growth of this type of capacity, which is up 133% since the end of 2020.

The fundamental reason that solar-plus-storage works is that the price of batteries has come down to a point where it now makes financial sense. Battery pricing has declined by roughly 25%, from $40/MWh to $95/MWh of PV in 2017, to $30/MWh to $75/MWh of PV in 2021.

Second, and more importantly, LBNL modeled the revenues versus the costs of adding batteries to solar. They found that the value gained by adding energy storage to solar and wind exceeds the costs.

Taking into account the battery inverter versus solar plant inverter size, LBNL found that adding four hours of energy storage to a power purchase agreement (PPA) increased the price of that agreement pretty linearly. Considering the most popular ratio of solar vs. battery inverter capacities – 1 MW solar to 0.5 MW batteries providing four hours of storage – the addition of energy storage increases PPAs by $0.01/kWh.

LBNL also sees that there are financial penalties associated with the current techniques of coupling solar with energy storage. For instance, if the solar power is fully using the site’s interconnection at any point, the batteries cannot. Also, if the batteries must fully charge from the onsite solar to meet incentive requirements, that can be a penalty for hybrid systems, resulting in a slightly less financially efficient system.

In terms of financial incentives, the Federal Investment Tax Credit seems to be motivating hybridization. Without this incentive, it is believed that there would be more standalone energy storage.

Since California dominates the volumes of hybrid solar plants in the queues, it also heavily influences the averages. Leaving California’s four-hour heavy market (which is at least partially driven by an evening peak period that lasts four to five hours), the researchers found that California’s batteries tend to have shorter durations in most other markets.

The chart above models the value of energy being delivered by hybrid systems as more battery duration – from two to eight hours – is added to a facility in various power grid regions around the nation.

There is still a lot of learning going on with these technologies. For instance, a 100 MW solar farm plus a 50 MW battery does not equal a 150 MW power plant in terms of capability. Having an intermittent, highly predictable solar generation resource, coupled with an instantly dispatchable multi-talented re-generation battery resource means that sometimes interconnection must be shared – and it’s usually the battery that takes a backseat to the solar facility during generation periods.

This is the hybrid penalization referenced earlier. Asset owners and markets are still learning how to maximize the utilization of these resources.

The document notes that the ancillary service markets provide valuable revenue streams to this young battery market, but that this service market quickly sells out. These large scale markets of independent system operators – where wholesale electricity rates and ancillary services exist – are not where most batteries are earning their revenue these days.

LBNL said that by the end of 2020, most operating hybrids earned revenue via incentive programs or capacity and transmission demand charge markets, instead of wholesale market price signals.

For instance, a battery used for peak shaving behind the meter at a business, or to maximize onsite solar utilization, does little for the broader wholesale market – although they do offer some general peak demand reduction. A battery at a home only running during power outages offers far less than a peak shaving solution; however, some VPPs are beginning to step into this space to monetize these underutilized resources.

We’re also observing a separation of attachment rates, as residential solar-plus-storage is growing faster than small business, commercial, and industrial. LBNL has also observed that residential energy storage solutions are getting larger.

This split – where residential storage is surpassing commercial and industrial storage – is mirrored by residential solar as well, as it outpaces business, commercial, and industrial solar in terms of capacity deployed annually.

Author: John Fitzgerald Weaver

Wireless EV charging coming soon to US market

Source: WiTricity

From pv magazine

Electric vehicle owners may soon be able to simply park and charge, no wires needed, with a new product under development from WiTricity.

The company has announced a limited beta release of its Halo wireless charging station this year, with wider availability in 2023. WiTricity has already been providing EV automakers with factory-installed EV wireless charging tech, and it now plans to make a consumer-level aftermarket product.

The Halo system can deliver 11kW of wireless charging. It consists of three key components, including a power receiver installed on the vehicle, a wall box that connects to wired power, and a charging pad installed on (or in) the ground.

The system uses core magnetic resonance charging to power EVs. WiTricity’s charging system, peripheral systems, and controlling software have been awarded more than 1,200 patents. The technology is has been instrumental in developing global wireless charging standards, including SAE International, International Organization for Standardization (ISO), the International Electrotechnical Commission (IEC), and the Standardization Administration of the People’s Republic of China (GB).

A pilot Tesla Model 3 has been running fully on wireless charging in Watertown, Massachusetts, since October. The vehicle can be fully charged in less than six hours, which is just as fast as plugging in at home. 

“Our successful upgrade of the Tesla Model 3 is resonating with consumers as an easier, more convenient way to charge their EVs,” said WiTricity CEO Alex Gruzen. “With the WiTricity Halo solution you just park and walk away, knowing you will return to a fully charged car. Day to day, it’s as if your car had infinite range, which will help accelerate EV adoption and propel us to a greener future.”

The company said it is currently evaluating which models to offer wireless upgrades for, based on customer demand, technical feasibility, and automaker support. Companies interested in the beta program can follow on the WiTricity website.

Author: Ryan Kennedy