Imagine you no longer need stoves or electric heaters to boil water. Imagine you can simply boil water by ambient sunlight. Seems impossible?
Well, a group of scientists at the Massachusetts Institute of Technology (MIT) don’t think so. They have created a novel device made up of a sponge covered in bubble-wrap that can make steam by simply using sunlight. The low-tech and low-cost nature of this tool means it can have various applications like sterilization of medical tools, treatment of waste water and desalination of seawater. The paper was published in Nature Energy journal.
The device, dubbed as “solar vapor generator” is quite cheap as it is sponge-like and does not need lenses or mirrors to intensify the sunlight to boil water at 100° C. The solar vapor generator uses a solar-absorbing structure that the team created two years earlier. The structure was made using foam and graphite giving it a sponge-like appearance. This device intensified the natural sunlight 10 times to heat the water to its boiling temperature. The newest version of the device performs the same function but uses ambient sunlight instead.
“It was relatively low optical concentration,” says Gang Chen about the original invention. “But I kept asking myself, ‘Can we basically boil water on a rooftop, in normal conditions, without optically concentrating the sunlight? That was the basic premise.”
In the earlier version of the device, it was discovered that although black graphite is a good absorber it is also an emitter, releasing unwanted heat into the environment eventually. So, instead of graphite, they used copper sheet coated with an absorber that is spectrally-selective in the current version. This material absorbs the visible light area from electromagnetic spectrum and does not release infrared radiation in return. This means sunlight is absorbed and no unwanted heat is emitted.
Next step was to cover the device in bubble-wrap in an attempt to insulate it from heat losses. Every time the water boils, steam escapes either from one hole or several smaller ones encasing the foam device. One of the team members Ni, says:
“We have a small wick through the thermal foam, which is connected to the opening in the copper sheet. This draws water to the opening. Because water is evaporating in this opening. This cooling sucks heat from the surrounding copper, which is generating heat from the sun.”
As the steam enters the external environment, the “air bubbles” in the bubble wrap significantly reduce heat loss through convection and increase the temperature of the system. The team discovered another important feature of the device i.e. it can boil water even during cloudy or cooler days. The team also intends to modify the device so that only the top of the device would need the bubble wrapping and not the entire body.
This device is ideal for producing solar steam for a short time. It is inexpensive due to lack of optical concentrators like lenses. Although the device would need replacement every year or two, the availability and cost-effectiveness compensates for its short lifespan.
“It’s kind of a different approach where before, people were doing high-tech and long-term (solar absorbers),” says Ni. “We’re doing low-tech and short-term.”
Now you can simply boil water using this novel device and going outside. Let us know what you think of this brilliant engineering!