Solar Energy

New model for grid-forming inverter operation

A transformer-coupled, grid-tied inverter. Image: Wikimedia Commons, Towel401

Scientists in the United States have developed a new model to allow utilities to use grid-forming inverters in order to better renewable energy intermittency. They described the inverter main circuit representation, the droop control, and the fault current limiting function.

From pv magazine

Scientists from the US Department of Energy’s Pacific Northwest National Laboratory (PNNL) have developed a model for power utilities to operate grid-forming (GFM) inverter–based resources.

“The model specification was recently approved by the Western Electricity Coordinating Council (WECC), a non-profit corporation that assures reliable electricity in 14 western US states, two Canadian provinces, and northern Baja, Mexico,” the research group stated. “The approval means that the model is available to be integrated into commercially available grid simulation tools used by thousands of utilities in North America and other parts of the world.”

The researchers said their work built on previous work demonstrating that grid-forming inverters can operate microgrids without conventional synchronous power generators. “The outcomes of microgrid research suggested that grid-forming inverters can ensure system stability for integrating renewable energy sources into future power grids,” they emphasized.

In their recent work, published on the WECC website, the PNNL scientists described the inverter main circuit representation, the droop control, and the fault current limiting function. “This model applies to energy storage systems and photovoltaic (PV) systems,” they specified.

“Our preliminary simulation studies based on the model show that grid-forming inverters can impact power system stability in a very positive way,” said Song Wang, president of the WECC Modeling and Validation Subcommittee. “We believe the work done by PNNL will greatly help the utility industry better understand grid-forming inverters and their potential impacts on power systems.”

Looking forward, the US group said it wanted to create an ecosystem for grid-forming inverters and unify different models for grid-forming technologies and their diverse applications.

Author: Emiliano Bellini

Photovoltaics for underwater wireless communication

The solar array was tested in a 7-meter-long water tank that emulated an underwater channel. Source: Jing Xu, Zhejiang University

From pv magazine

Although solar cells lose much of their power yield when submerged, as the devices obviously suffer lower solar radiation, they may not be useless.

Researchers from the Zhejiang University in China used commercially available solar cells to create an underwater optimized lens-free system for high-speed optical detection and have found that the PV devices enable a much larger detection area than commonly used photodiodes. “Solar panels are being increasingly used as detectors in underwater wireless optical communication (UWOC) systems, as the large detection area can significantly simplify the link alignment,” the scientists explained. “However, the greatest problem in such a scheme is the limited bandwidth of the solar panel, which was originally optimized for energy harvesting rather than communication.”

In the proposed system, the solar cells are connected in series and are able to convert sunlight to an electrical signal. They act as detectors that can ease the transmitter-receiver alignment requirement in an underwater wireless communication system. “Until now, achieving high-speed links using off-the-shelf silicon solar cells has required complex modulation schemes and algorithms, which need intense computing resources that use extra power and create a high processing latency,” said researcher Jing Xu. “Using modeling and simulation of connected solar cells, we optimized the peripheral circuit, which significantly improved the performance of our solar cell-based detector.”

A solar array was tested in a 7-meter-long water tank emulating a 35-m underwater channel and was found to achieve a data rate of 150 megabits per second (Mbps) with a frequency domain equalizer. Mirrors were applied to extend the pathlength of the optical signal. “The system showed reliable stability, low power consumption and high performance,” the researchers stated. “As the size of the solar array increases from 1×1 to 3×3, the −20-dB bandwidth increases from 4.4 MHz to 24.2 MHz.”

The system was presented in the paper Series-connected solar array for high-speed underwater wireless optical links, published in Optica. “Because solar cells are mass produced, the proposed scheme is quite cost-effective,” concluded Xu. “Beyond the underwater world, this type of detector could also be used in visible light communication, a type of wireless communication that uses visible light from LEDs and other sources to transmit data across distances.”

The performance of underwater solar cells was investigated in 2020 by scientists from the Birla Institute of Technology and Science and the Indian Institute of Technology Kanpur and Defence Materials. According to their findings, submerged cells benefit from lower temperatures and are in an ideal environment for cleaning. “Although there are challenges and limitations, the results obtained show that there is an enormous potential for solar PV technology in underwater monitoring sensors or devices, and various other commercial and defense applications with modern-day power electronics,” the researchers stated at the time.

Author: Emiliano Bellini


Program ‘switching’ concession payments for solar systems to be expanded

Source: Worksafe Victoria

From pv magazine Australia

South Australia will extend its ‘Switch for Solar’ program in which eligible low-income residents can opt to have a solar system installed in exchange for their next ten years of government concession payments.

The South Australian government has announced it will expand its ‘Switch for Solar’ program, opening up another 5,000 spots for residents on either an eligible Centrelink payment, who meet low income provisions, or hold an eligible concession card.

Program participants will be able to install a 4.4 kW solar system at no upfront cost in return for their annual Energy and Cost of Living concession payments over the course of a decade.

The program was initially piloted in May 2021, opening to 1,000 eligible residents. The state government described this initial pilot phase as “highly successful”, saying the program now has “proven results”.

“Electricity bills of households already in the program have fallen by well over $1000 a year resulting in a net benefit of up to an average of $538 for these low-income households,” Deputy Premier Dan van Holst Pellekaan said.

Concession holders in the state receive up to $215.10 per year from the Cost of Living Concession and up to $231.41 per year towards their energy bill, totalling up to $446.51. Swapping this payment for a decade would mean the government recovers a total of $4,460 for the solar system.

Data from the pilot trial found concession households who “switch” their total concession payment for the solar system receive an average of $538 in savings over and above their existing $446.51 saving from their concessions. This is higher than the initial estimate of $57 to $525 when the scheme was launched, the government said. 

“Around 28% of households so far have opted to co-contribute to get an ever bigger solar system and even bigger bill savings,” Pellekaan added.

“This innovative more than doubles the bill savings we deliver to concession households, through solar instead of cash payments, with strong safeguards for participants.”

South Australian concession holders will now be invited to register their interest in the program with the 5,000 systems to be rolled out from August 2022.

Author: Bella Peacock