Want to slash your energy bill? Try these record-breaking solar cells

16 Nov 2022 James McKenzie

Could a new solar cell with a record-breaking efficiency of 30.1% transform the commercial potential of solar panels, asks James Mckenzie

Bright future Combining silicon and perovskite, “tandem” solar cells such as this one developed by researchers in the Netherlands could transform the solar sector. (Courtesy: Niels van Loon)

Solar panels have been around for decades – in fact, they are now a common sight on houses even in the largely cloudy and dark nations of northern Europe. Cheaper and easier to install than ever before, the question is why aren’t solar panels fitted to every single house? Mostly, it’s down to cost. Consumers simply want a quick return on investment.

Having worked in the light-emitting diode (LED) sector for many years, I remember how hard it was to convince people to buy something – LED lighting – that cost more than an old-fashioned filament lamp. Why spend the money when you’d not get any payback for 10 years or longer? The new-fangled light bulbs were fine for green-minded eco-warriors but not for ordinary punters.

Fortunately, the efficiency, cost and quality of LEDs improved and consumers began to realize the LED lighting would survive long enough to recoup the initial outlay. Once payback times dropped below five years, things really started to motor. In fact, today’s LED lighting can provide more than 100 lumens per watt (twice that for high-end products) meaning they’re the only practical choice – with payback in months.

Selective bans of inefficient light sources helped, of course, but LEDs succeeded because of technical progress coupled with economies of scale. So is the same thing about to happen with solar panels? In the UK, the government kick-started things in 2010 with feed-in-tariffs (FiTs). Anyone who put electricity generated by solar panels into the grid was awarded payments of 41.3 p/kWh (pence per kilowatt hour) – at a time when electricity was about 10 p/kWh. The tariffs led to many people fitting solar photovoltaic (PV) panels, with installations rising from 140,000 in 2011 to 1.2 million by the end of last year.

Efficiency gains

Back in 2010, commercial solar PV panels were silicon based with efficiencies of typically 15%. If you bought them from a reputable manufacturer, some panels could last for tens of years, which was long enough to achieve a payback on investment. But as a 2020 report from the International Renewable Energy Agency found, the cost of solar PV globally dropped by 82% between 2010 and 2019, with panel efficiencies now close to 22%.

In fact all renewables have been dropping in price, including on-shore and off-shore wind as well as concentrated solar power, with solar falling by 13% during 2019 alone to just over 5 p/kWh. Despite the upheaval to the UK’s solar sector following the ending of FiTs in 2017-2018, the UK is likely to install more than 1 GW of solar PV by the end of 2022 according to the physicist Finlay Colville, head of market research at Solar Media.

In addition, indications suggest that the UK could have a total of 40 GW of solar PV installed by 2030 on the roofs of homes and offices and in ground-mounted solar arrays. Earlier this year as part of its Energy Security plan, the UK government will also look to increase the UK’s current 14 GW of solar capacity, which it estimates could grow up to five-fold by 2035.

Cost is key. The world record for solar-cell efficiency is currently 47.1%, which was achieved in 2019 by staff at the US National Renewable Energy Laboratory, who built six junction concentrator solar cells of various materials under the illumination of 143 Suns. No solar cell can ever be as cost effective as good old silicon, but a new “tandem” solar panel, unveiled at the recent World Conference on Photovoltaic Energy Conversion in Milan, could be a game-changer, having an efficiency of 30.1% under just one Sun’s illumination.

The new cell could be a game-changer, having an efficiency of 30.1% under just one Sun’s illumination

Developed by a team from various universities and institutes in the Netherlands, the cell combines a conventional silicon cell with one made from perovskite, allowing it to exploit a bigger fraction of the solar spectrum. That’s because the silicon part works well with visible and infrared light, while the perovskite is better with ultraviolet and visible light. The perovskite also allows more than 93% of near infrared light to reach the silicon cell.

Many teams around the world are working on tandem cells, including the UK firm Oxford PV. By coating an ordinary silicon cell with a thin perovskite film, it has achieved an efficiency of 29.52% in 2020, with the company saying its synthetic perovskite material is affordable and sustainable. With a factory already built, Oxford PV intends to be the first company to sell these next-generation solar cells. Initial products, designed for residential roofs, will generate 20% more power from the same number of cells.

Sunny future

Solar power has lots of potential, with 87% of the world’s nations able to power themselves using less than 5% of their land. As Elon Musk has pointed out, the US could do the job with just a few hundred kilometres of solar panels in a small corner of Utah. But the UK is not one of those lucky countries: 12.5% of the whole nation would have to be blanketed with solar panels to power itself. That’s a lot given that only 6% of the country is built on.

Solar PV will therefore be part of the mix but not the entire solution. We need to boost the efficiency of solar cells while keeping a lid on production costs, inverters and installation costs to really encourage take-up. The average four-person house in the UK currently needs about 16 solar panels operating at efficiencies of about 20% to power itself. Given the low levels of sunlight in the UK, the rule-of-thumb until recently was that it would take 11–14 years for solar panels to pay for themselves.

But according to some estimates, the pay-back on solar panels is now as little as four years and further improvements could shorten that time even more. With rocketing energy prices and the cost-of-living crisis, it seems that the time for solar PV has finally come.

James McKenzie is the writer of the Transactions column for Physics World about physics in industry. He is writing here in a personal capacity

from physicsweorld.com      7/12/2022