The technology bringing solar power to the masses

Solar power will become one of the world’s most important clean energy sources in coming decades. But unlike traditional power, which comes from relatively few centralized sources, photovoltaic panels (PVs) are often scattered across rooftops of residential and commercial buildings, and small-scale solar farms.

This provides power in a pattern known as distributed solar (DS) — an arrangement that presents technical challenges compared to conventional power supply, leading to a fluctuating supply and potential safety issues.

Xiangning He, a professor of power electronics engineering at Zhejiang University in Hangzhou, leads a team that aims to solve these problems. Over the past 15 years, the researchers have developed a slew of technologies designed to make DS electricity safely and efficiently available at the flick of a switch. Their work has led to several spinoff companies.

Smart orchestration

“DS technology is still a long way from maturity,” says He. “But by taking the lead at this comparatively early stage,” he says, they aim to make breakthroughs that will quickly move the field forward. For their contributions, in 2017 his team received one of China’s highest honours for research, the State Natural Science Award.

Take communication across the different components of a DS system, which is essential for fault detection, responsive energy production, optimizing energy output and maximizing the life of components.

Currently DS components talk to each other using a mix of wired and wireless protocols, including power line communication (PLC) technologies that send data signals down the lines that also carry power. Meanwhile, PV converters within the DS system step up the output of PV panels into higher, more useful voltages.

In 2020, He and his team challenged those conventions when they developed talkative power converter (TPC)¹ technology, linking power conversion and communications. TPC encodes information within the pulse patterns that converters use to change DC voltages, including the information in the power signal right from the start.

To explain this difference, He draws an analogy contrasting apples that have labels of origin stuck on after harvesting, with apples that are engineered to grow with labels already on them. By eliminating the need for a separate communication channel, he explains, TPC will improve efficiency, reliability and safety, and reduce the cost of DS systems. Most importantly, it will enable the regulation of the charging and discharging of batteries within the systems that store power.

Fruitful field

Hundreds of academic papers on TPC have been published. In August 2024, the Institute of Electrical and Electronics Engineers (IEEE) dedicated a special issue of the IEEE Journal of Emerging and Selected Topics in Power Electronics to the subject, with contributions from researchers in the US, Europe and China.

Wuhua Li completed his PhD under He, and is now the Zhejiang University College of Electrical Engineering’s vice dean. In describing the college’s mission, he underlines how its interests align with those of humanity, including the need for affordable, renewable energy.

“The way to ensure that DS fulfills its potential is simply to make it safer, cheaper, more compact, more convenient, more reliable, and more durable,” he says.

Li was part of He’s team that made dramatic improvements to inverters. These are the key modules in DS systems that convert the low voltage DC output of PV panels to the high voltage AC current found in grids. He’s team was one of the first in the world to work on high step-up conversion technology, says Li.

Firstly, in 2011 they designed a novel electronic DC to DC converter that was compact, safe and capable of a high voltage step up². By eliminating the need to string PV panels together in series to achieve high voltages, this cutting-edge technology enhanced safety. It also increased efficiency because when connected in parallel, instead of series, the output of a solar array is not limited by its lowest performing panel.

The following year the team built on this achievement with something many engineers considered impossible. In a paper that has been highly cited³, they outlined a topology — the way in which different PV units, energy storage systems and the grid are connected — for achieving both high voltage boost and DC to AC conversion electronically. The topology also eliminated ‘leakage’, which is the term engineers use for unintended current flow.

“Traditionally, converting DC to AC would require large, bulky analogue transformers, and there would be an extra step to increase the voltage,” explains He. By electronically combining both DC to AC conversion and voltage boosting in a single phase, the team’s inverter design reduced power loss, while increasing safety³.

Reliable power

These breakthroughs are the foundation of spinoff company Hoymiles, also based in Hangzhou, which was founded by Bo Yang, an alumnus of Zhejiang University and He’s former PhD student.

With much of its sales in the US and Europe, Hoymiles is today the world’s second-largest manufacturer of microinverters — the all-important boxes that lie at the heart of DS systems.

“The high conversion efficiency of our product allowed us to provide a 10-year warranty, although we expect them to last for 25 years,” says Yang.

Since TPC’s invention four years ago, Hoymiles has started using the new technology to optimize the output of PV arrays. Making DS electricity more akin to grid electricity will also require fine-tuned co-ordination between PV generation and on-site batteries. That is why BMSer, another company started by a Zhejiang alumnus that specializes in energy storage, is also incorporating TPC in its products.

He makes it clear where he wants the technology to go. “We hope that in future, when the industry is mature and its standards have been established, TPC will be one of them,” he says.