This Week in Engineering explores the latest in engineering from academia, government and industry.
Episode Summary:
Electrostatics have long been a high-efficiency technology for removing pollutants from the air, from residential air cleaners to the electrostatic precipitators in coal-fired power plants. A new use for this technology has been developed by an MIT spinoff that promises to capture water vapour emitted by industrial and commercial cooling towers. Captured water is pure enough to be practical for human consumption or as boiler feed water for generating plants.
Battery storage of electrical power is an essential part of intermittent clean energy systems like photovoltaics and wind turbines. But batteries can have a secondary and equally important purpose: grid forming. Frequency control of large AC grids can be difficult with multiple generating sources and varying loads across a system. With advanced computer control of inverters, battery storage systems can act as a frequency regulator in large grid systems, forming an electrical equivalent of the large rotating inertial mass of a mechanical generator. Technology makes battery storage for grid purposes both more useful and cost-effective.
Access all episodes of This Week in Engineering on engineering.com TV along with all of our other series.
Transcript of this week’s show:
To see any graphs, charts, graphics, images, and/or videos to which the transcript may be referring, watch the above video.
Segment 1: Production and distribution of clean drinking water is an essential engineering challenge everywhere, but even in developed nations, it can be complex and expensive. Surprisingly, in the US about 40% of all water drawn from lakes, rivers and wells isn’t used for the traditional needs of drinking, irrigation or sanitation but is used to cool thermal power plants. Two thirds of thermal plants use evaporative cooling, which produces the characteristic white plumes seen over fossil fuel and nuclear power plants. That white plume is water vapour, a potentially significant source of clean water if it could be collected and concentrated.
A small company launched as the winner of a 2018 MIT entrepreneurship competition, may have the answer. The firm is called Infinite Cooling, and it uses research developed at MIT by the Varanasi Research Group to improve on a basic fog collection technology used in coastal areas worldwide. Current systems use cloth or metal meshes suspended in moving fog to collect 1 to 3% of available water. The research group improves efficiency by using similar principles to that seen in electrostatic air cleaners. A charged grid imparts electrical charge to water droplets passing through which are then attracted to another grid of opposite polarity. Microscopic droplets agglomerate, then fall by gravity for collection. The system was tested at MIT’s thermal generation plant and also at the university’s nuclear research reactor and has shown to produce water 100 times cleaner than the original cooling feedwater.
This very pure water has an immediate commercial value to the powerplant, as boiler water in the primary loop. Another advantage is the elimination of the characteristic clouds of white water vapour seen over commercial and industrial cooling towers, which can impair visibility for low-flying aircraft and occasionally road traffic as well. Testing in the MIT plants showed no effect on powerplant operation, and the systems are expected to achieve regulatory approval relatively easily. For nations suffering freshwater shortages, seaside power plants that use seawater for cooling may harness this technology for drinking water production. The team plans to install test systems at a Midwest chemical plant and a 900 MW commercial powerplant by the end of the year. We’ll report back as testing continues.
Segment 2: Grid scale battery storage is a major growth industry worldwide as power utilities attempt to integrate renewable energy sources such as wind and solar into national power grids. Supplying reliable power isn’t as easy as it looks. Solar photovoltaics produce DC current, which must be fed through inverters to produce alternating current. Wind turbines can produce AC, but like conventional generators, they are dependent on the rotational speed of the alternator to produce the desired frequencies. For grid requirements, batteries are the best solution currently available for power generation systems that are intermittent in nature.
An example is a recently announced project by Australia’s AGL Energy Limited, who have ordered a 250 MW system to be installed on Torrens Island in South Australia. The system will be supplied by Wartsilla and will be the second largest of its kind in the country. The battery system will store energy produced by both renewables and conventional thermal generators and when initially deployed will operate in a conventional grid following mode. Less well understood however is the potential of advanced battery storage to do more than store and release electrons. AGL plans to operate the system eventually in a grid forming mode, making the battery a virtual synchronous generator.
VSG technology has been explored for years in conventional power generation. The concept is simple: in a grid system powered by a single generator, the frequency of AC output is relatively easy to control. It’s highly dependent on the rotational speed of the generator, and at commercial power scales, uses rotational inertia to providing good damping of the system, if load is consistent. Add variable load and more power sources to a grid however and frequency control becomes more complex. With the appropriate controller, batteries can be used with inverters to act as a virtual form of that inertial mass, stabilizing frequency throughout a system.
For large scale photovoltaic projects, battery storage is a necessity, so the combination of storage and grid forming not only reduces the effective cost of green energy but improves overall system efficiency where power supplies can vary from solar, wind, hydroelectric and thermal. AGL expects the Wartsilla project to be operational in early 2023.