Dr Hossein Ardekani, Principal Project Researcher at nanotechnology specialist NextGen Nano’s NanOLED division, explores the potential of transparent solar cells in the home, and the opportunities at the community scale.
We might rely on coffee for our daily kick but imagine an energy source 13.5 billion years in the making, vastly overlooked and underused. The sun, revered in ancient religions since the dawn of humankind, holds a power waiting to be fully harnessed — a fusion of ancestral reverence and innovative technology.
Photovoltaic (PV) cells are non-mechanical devices that directly convert sunlight into electricity. By utilising semiconductors, they generate electrical energy through a process where photons from sunlight dislodge electrons from the semiconductor material.
Conventional photovoltaic cells commonly employ silicon semiconductors, doped with boron and phosphorus to alter their electrical characteristics. Despite their efficiency, capable of generating 1 kW of energy per square metre, a notable limitation arises from the inorganic composition of silicon semiconductors — they lack recyclability, posing a significant drawback.
As society advances, as does solar technology. Organic photovoltaic (OPV) cells use indium tin oxide as a transparent electrode material. Despite its recyclability advantage upon reaching obsolescence, the greater cost of indium poses a significant challenge.
There have now been breakthroughs in technology which involves an OPV design employing fluorine-tin-oxide glass instead of indium tin oxide as the substrate. This innovation significantly reduces costs and brings additional benefits, including enhanced flexibility and improved recyclability.
Presently, OPVs have evolved to a state where they exhibit transparency, enabling the passage of unused photons while generating electricity from photons interacting with the semiconducting material. These transparent OPVs (TOPVs) present a new era in green energy production.
The solar home of tomorrow
Per the Building Regulations 2010, approved document F, a room’s window area should typically constitute a tenth of the dwelling’s floor area. For an average dwelling of 94 m2, according to the English Housing Survey 2018-2019, this equates to approximately 9.4 m2 of glazing.
If every window in this average home was replaced with TOPVs, and considering an average of 4.1 hours of daily sunlight, the cells could potentially generate 7.7 kWh per day, or 231 kWh a month. If this energy was procured by a standard energy provider, this energy output would incur a cost of £59 per month, if we assume an average price of 28.62p per kWh.
Unfortunately, buy-back on solar-generated power is significantly lower compared to the cost of purchasing an equivalent amount of energy from the grid. However, the solution lies in solar batteries, which efficiently store surplus energy generated by solar panels during inactive periods.
Envision a future home equipped with affordable transparent OPVs on its windows generating energy that is seamlessly stored in solar batteries. This system allows for complete self-sufficiency, enabling a household to function off-grid.
Although these new OPVs come at a lower cost compared to traditional PVs (£100 per square metre compared to £350), they exhibit lower efficiency in generating electricity when compared to conventional solar cells. Nonetheless, this situation need not be an either-or scenario. Houses could be equipped with both traditional PVs and TOPVs, working in tandem to collectively generate significantly more electricity than either system could produce independently.
A community approach
This perspective does not account for a community of such households. Diverse electricity usage among homes, based on varying appliance usage and occupancy patterns, results in certain residences generating surplus electricity, or using more than they produce. For instance, a household mostly vacant during the day may produce more energy than it consumes, enabling surplus energy storage.
Adopting a community-orientated approach, this excess energy could be efficiently shared among neighbouring houses, ensuring equitable benefits regardless of individual housing contexts.
Furthermore, by embracing this community-oriented approach, we unlock a plethora of possibilities for intercommunity power generation. This extends to diverse infrastructures; bus stops fitted with TOPVs storing electricity for household usage; shopfronts, high-rise flats, and office spaces also contributing to this communal effort with minimal intervention.
As we explore the potential of TOPVs, we tap into the untapped power of our universe’s primary energy source — light.
