Not just another brick in the wall
Image credit: Solar Build
Scientists want to transform the walls of buildings into vast resources of renewable power generation and storage. Are smart solar bricks, super-capacitor bricks and microbial fuel cells really the future or just ideas built on shaky foundations?
Solar panels are a common sight on rooftops the world over, but what about the vertical façades of offices, apartment blocks and houses, which offer a vast and, as yet, largely untapped resource for power generation, particularly in cities where high rises dominate?
Research teams and tech innovators are aware of the potential and working to develop a range of brick- and block-based products that combine structural strength with electricity generation, electricity storage and even wastewater processing.
For the first time in hundreds of years, walls could gain new intrinsic functionality. In the following panels, we highlight four of the most promising technologies being put through their paces in the lab.
The ability to scale-up power generation across a much larger surface area than a roof alone could support a faster route to delivering energy-positive buildings, which feed surplus energy to local buildings or the grid.
Energy storage infrastructure worldwide currently lags behind renewable energy production, creating an obstacle to the feasibility of a carbon-neutral future. Yet if buildings became large-scale batteries, they could store renewable energy from wind and solar during times of peak production, then feed it back into the grid when it’s needed most. ‘Bricks and mortar’ itself could be used to recharge electric vehicles.
Prototype smart bricks and glass blocks look like their traditional equivalents and therefore offer a potentially more discreet or attractive architectural solution than solar photovoltaics, which are often considered unsightly by the public and local planners.
Ed Reynolds, technical director at Willmott Dixon, told E&T: “A product selling beauty as well as sustainability is what people want to buy and many would pay a premium for. If you have to spend £10-20,000 extra to buy a house that has zero running costs, you’d have to think about it, wouldn’t you?”
However, the benefits of building-integrated power are countered by several challenges. Most solutions remain proof-of-concepts or lab-scale prototypes years away from widespread commercial use. Output and storage capacity are currently below that of conventional solar panels or lithium-ion batteries, limiting their impact. Critics also question reliance on unproven technologies to fight the climate crisis when designers and engineers can act now using existing solutions.
Will Arnold, head of climate action at the Institution of Structural Engineers, says: “Waiting for this future is really dangerous, we are in a crisis today. We need to make the biggest changes possible now, with the technologies currently available to us.”
Rechargeable concrete batteries
Storage capacity (energy density): 7Wh/m2
Stage of development: Proof of concept
Research location: Sweden
The global ubiquity of concrete and its heavy toll on the climate – cement production accounts for 8 per cent of all man-made emissions – make it the ideal candidate for integration with renewables to help mitigate its impact.
A prototype rechargeable cement-based battery, developed by researchers at Chalmers University of Technology, has the capacity to light a regular E14 LED bulb for around one and a half hours, over 10 times the capacity of previous attempts at concrete batteries.
That may be a drop in the ocean compared to the energy potential of commercial batteries, but the huge volume of concrete in the built environment could significantly boost storage. The power could be used either to power buildings themselves or to feed back into the electricity grid.
The prototype exploits an innovative form of rechargeable electrode. It comprises a cement-based mixture containing short carbon fibres, designed to increase conductivity and flexural toughness, and a metal-coated carbon fibre mesh. The mesh integrates an iron anode and a nickel cathode to create a flow of electrons and electric current.
The researchers estimate that a 1,600m2 façade on an eight-floor apartment building could store around 11.2kWh of electricity, enough to power many low-power applications such as lighting, TVs and computer screens. Greater gains are expected in future given the current fledgling state of R&D.
Rechargeable (supercapacitor) bricks
Storage capacity: 1.61Wh/m2
Stage of development: Proof of concept
Research location: USA
The humble brick dates back several thousand years but has seldom served any purpose other than structural. A supercapacitor brick developed by researchers at Washington University in St Louis introduces the idea that walls could become giant batteries able to rapidly recharge electric vehicles or other devices.
The patented technology exploits the porous structure of fired red bricks by filling the tiny cavities with nanofibres of a semiconducting plastic that can store charge.
In laboratory tests, a few pieces of polymer-coated brick lit up a 3W LED for 50 minutes. It may be a while before a product finds its way into homes and offices, however. Energy density is currently only 1 per cent that of lithium-ion batteries, though according to researchers this could be improved in future either by increasing energy density or using more bricks.
Supercapacitor bricks can draw power from anything that can apply a potential difference, but the close proximity of walls to roofs makes solar panels the most practical solution at present, say researchers. Each brick can be recharged 10,000 times.
Power output: Roughly 170-175 W/m2
Stage of development: Product development
Research location: UK
The average rooftop solar panel isn’t generally considered the most attractive addition to the home, but could a glass brick-based alternative provide the right combination of form and function?
University of Exeter spin-off company Solar Build has developed a modular glass brick with an embedded optical device that magnifies light to increase the amount that’s converted into power.
A prototype wall measuring one square metre is able to generate around 170-175W of electricity in sunlight, not far off the average power output of a regular solar panel at around 200-225W per square metre. Performance in a ‘communal space’ drops to around 100-125W.
Solar Bricks combine renewable power, structural performance and thermal insulation, and they also allow daylight into spaces. The optical device can modulate brightness levels inside a building by reflecting and redirecting it to the solar cells, creating a translucent effect on the glass.
Train stations may become the first real-world application of the technology. A recent three-month feasibility study, funded by Innovate UK and supported by Network Rail, HS2 and Arup, highlighted several benefits. Ongoing discussions with the partners are examining the possibility of erecting solar walls in station areas where daylight and electricity are required. Electric bike charging is one potential outlet for the electricity.
Professor Tapas Mallick, co-founder of Solar Build, who also leads the Solar Energy Research Group at the University of Exeter, told E&T: “With our technology, a building could be completely self-sustained, not only getting power from the roof, but from the walls too. It could be configured to feed energy into the building, the grid, or batteries for storage, depending on priorities.”
Power output: 1 milliwatt per 5 millilitres of wastewater or toilet water
Stage of development: Lab-scale prototype
Research location: UK
Home sewage and wastewater is normally flushed straight down the drain, but these by-products contain masses of bacteria that can be tapped for energy.
A selectively programmable bioreactor wall, developed by scientists at the University of the West of England in Bristol, exploits microbial fuel cells to generate electricity and produce clean water.
Each ‘brick’ contains two compartments separated by a membrane; microbes sit on one side and use dirty water such as urine as a food source. A chemical reaction produces electrons that flow into the other clean water compartment, in the process creating electricity.
A prototype version of the system, running on urine at Glastonbury Festival in 2019, generated a continuous three watts of power and a total 300 watt-hours over five days.
Efforts are now focused on harnessing the power of pee to bring electricity to remote households in sub-Saharan Africa. A joint development agreement with South-East Asian manufacturer Siam Cement Group will refine the technology and the design of components to create a viable product.
Professor Ioannis Ieropoulos, director of the Bristol BioEnergy Centre at UWE Bristol, told E&T: “We would like to see the system produced in the country of deployment. It’s not about building it in the UK, then shipping it to sub-Saharan Africa, which is unsustainable.”
If the project is a success, the technology could be scaled up to serve the rest of the global population, he adds. “If it’s engineered appropriately, we can have microbial fuel cells installed everywhere, in every household, communal place, shopping mall, hospital, and hotel.”
If buildings became large-scale batteries, they could store renewable energy from the wind and sun during times of peak production, then feed it back into the grid when it’s needed most, or use it to charge electric cars.
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