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Max Zhang

December 9, 2019

The Missing Link: Cornell Prof. finds Hidden Connections Between Energy and the Environment

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With the introduction of congressional bills like the Green New Deal, climate change and the environment have been at the forefront of the nation’s mind. However, for Prof. K. Max Zhang, mechanical and aerospace engineering, it was a class at Cornell s that inspired his current research on High Energy Demand Days — days during the year when energy demand is particularly high.

Zhang’s focus within environmental engineering is the study of particulate matter, or, “the physical and chemical transformations of ambient airborne particulate matter,” Zhang said. “I did my dissertation on nanoparticles and how they transform near highways.”

He was initially introduced to HEDD research when he first taught MAE 5010: Future Energy Systems, where he became familiar with the literature and current research around human energy systems.

The Energy and the Environment Research Laboratory at Cornell, led by Zhang, recently published a paper looking at the most recent data on energy consumption of New Yorkers and how the placement and use of photovoltaics like solar panels can help meet the state’s energy needs.

Photovoltaics on residential home

Zhang estimates that if the threshold of the voltaic cell is set at 10 gigawatts, you would only find 50 to 100 hours per year to be above that threshold. The peak consumption per hour is usually around 13 gigawatts, he said.

Despite the relative scarcity of these spikes in energy demand, the energy production system needs to have the capability to match that demand, even if it’s not all the time.

To put it in perspective, Zhang explained the situation with a car analogy.

“My car is maybe 120 horsepower. The question is: When do you actually use that power? Actually very rarely, maybe once a year, when you really need to accelerate.  But you have to have it, even if you’re not using it, in case you need it,” Zhang said. “In the same way, you need your power plants to be ready to meet the peak demand.”

However, Zhang’s most interesting findings came when he looked at ramping, a measure of the spikes and dips in energy demand, and how energy systems are currently equipped to handle these rapid changes in energy consumption.

“We expected high ramping during summer days, but to our surprise, [high ramping occurs] during sunny winter days,” Zhang said.

According to Zhang, in the winter, energy demand is actually the lowest during midday. But if it’s a sunny winter day, your energy generation from photovoltaics is highest in the midday, exactly the time when you need that energy the least.

When the sun goes down and people return to their homes in the evening, energy demand rises again but energy generation drops sharply in the absence of sunlight — a perfect recipe for high ramping.

Zhang says that this specific issue with sunny winter days is also somewhat exacerbated by the fact that, despite higher ramping during these days, energy demand on the whole is higher during the summer.

Thanks to research like Zhang’s, energy providers are starting to notice and create contingency plans for these kinds of events. One popular idea is efficient energy storage. In the context of sunny winter days, for example, a system would store the excess energy in the midday and distribute it for use when traditional energy production methods can’t meet the demands on their own.

“When we talk about solar resources, or wind resources, that’s all meteorology,” Zhang said.  “Renewable energy is really just a natural way of converting natural resources into an energy form. … That’s why energy and the environment are always coupled together.”

This coupling — a two-way cause-and-effect relationship between energy demand and energy supply — is the primary focus of Zhang’s new research. “When you talk about renewable energy, you’re really talking about the merging of two systems, the energy system and the atmospheric system.” Zhang said.

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But for Zhang, his study is more than just practical: “We are doing this [research] in the context of New York State’s goal of clean electricity by 2040: 6-gigawatt solar by 2025, 9-gigawatt wind by 2025. These are big targets in a short amount of time.”