Energy storage system deals with sudden draws on the grid

Aug 11, 2010

Time for a quick cuppa? When the final whistle blows, demand for electricity usually soars, causing a headache for energy companies.

Researchers at the University of Leeds and the Chinese Academy of Sciences have now found a way to manage these short-lived draws on the that could halve the fuel needed.

The amount of electricity drawn from the national grid varies enormously at different times of day. It usually peaks in the early evening for a couple of hours after the mass exodus from school and work. Short-lived spikes are also common after major televised sporting events, during commercial breaks and in the morning hours.

But matching the highs and lows in demand with a steady supply is a major challenge. Energy companies typically top up a 'base' supply of energy with electricity from that are just switched on to cope with the peaks. However, the gas-fired generators often used to feed these peaks are notoriously inefficient, expensive to run and sit idle for long periods of time. In short, the system wastes both energy and resources.

University of Leeds Professor of Engineering, Yulong Ding, and colleagues are proposing a more environmentally friendly system that would also be cheaper to run. Crucially, the system would store excess energy made by a plant supplying the 'base' demand and use this to supply the 'peaks' in demand - as and when they happen.

"This integrated system is truly novel," said Professor Ding, who led the research. "Because we are storing the excess energy for later, there is less need to ramp up the output of gas-fired plants whenever a peak in demand is expected, generating electricity that may simply not be used."

The key idea is to use excess electricity to run a unit producing liquid nitrogen and oxygen - or 'cryogen'. At times of peak demand, the nitrogen would be boiled - using heat from the environment and waste heat from the power plant. The hot nitrogen gas would then be used to drive a turbine or engine, generating 'top up' electricity.

Meanwhile, the oxygen would be fed to the combustor to mix with the natural gas before it is burned. Burning natural gas in pure oxygen, rather than air, makes the combustion process more efficient and produces less nitrogen oxide. Instead, this 'oxy-fuel' combustion method produces a concentrated stream of that can be removed easily in solid form as dry ice.

Using such an integrated system, the amount of fuel needed to cater for peak demand could be cut by as much as 50%. Greenhouse gas emissions would be lower too, thanks to the greatly reduced nitrogen oxide emissions and the capture of carbon dioxide gas in solid form for storage.

"This is a much better way of dealing with these peaks in demand for electricity. Greenhouse gas emissions would also be cut considerably because the carbon dioxide generated in the gas-fired turbine would be captured in solid form."

"On paper, the efficiency savings are considerable. We now need to test the system in practice," Professor Ding said.

Full details of the system will be published in the International Journal of Research.

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User comments : 11

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Ravenrant
not rated yet Aug 11, 2010
This is great news, me and the wife decided to add a 4th kid to our future plans after reading about this breakthru. Wonderful, keep up the good work so I can pick out a name for number 5.
marjon
not rated yet Aug 11, 2010
"Flywheels store electricity as kinetic energy, and can dispense that energy back to the grid in quick bursts. They have potential as energy storage devices for renewable energy sources, which are variable and unpredictable. Solar and wind power in particular would be more promising if there was a way to capture and store their energy for later use."
http://www.popsci...r-demand
Here is one way being used now and it does not require a new power plant. Flywheels can be added like batteries.
CHollman82
5 / 5 (1) Aug 11, 2010
You've got to be kidding me...

They weren't already doing this? I ASSUMED that they would be storing unused energy production... like a buffer.

So basically there is no buffer on the electrical grid, no reserves stored to meet unexpected demand?
marjon
not rated yet Aug 11, 2010
You've got to be kidding me...

They weren't already doing this? I ASSUMED that they would be storing unused energy production... like a buffer.

So basically there is no buffer on the electrical grid, no reserves stored to meet unexpected demand?

Are you serious?
Reserves are generators that can be rapidly spun up using natural gas or diesel.
Some have proposed enabling backup generators be used. The challenge is integrating all sources into the grid. Phasing is important as well as economics.
CA demonstrated how not to incentivize such activity a few years ago: fixed retail, market priced wholesale.
CHollman82
not rated yet Aug 11, 2010
You've got to be kidding me...

They weren't already doing this? I ASSUMED that they would be storing unused energy production... like a buffer.

So basically there is no buffer on the electrical grid, no reserves stored to meet unexpected demand?

Are you serious?
Reserves are generators that can be rapidly spun up using natural gas or diesel.
Some have proposed enabling backup generators be used. The challenge is integrating all sources into the grid. Phasing is important as well as economics.
CA demonstrated how not to incentivize such activity a few years ago: fixed retail, market priced wholesale.


I don't think any of this has anything to do with what I was talking about...
RobertKLR
not rated yet Aug 11, 2010
"This integrated system is truly novel," said Professor Ding ... No it is not. Variable frequency AC drives do this all the time. Nothing new here.
fmfbrestel
5 / 5 (1) Aug 12, 2010
I thought i read something about how municipalities could use their water towers to accomplish the same goals. pump water uphill during times of excess and let it spin a generator on the way down during times of peak need.

Already have nearly all the equipment in place. And storing the energy near its point of consumption reduces transition losses. Guess it all comes down to storage/retrieval efficiency though -- which (once again) is an important fact left out of this article.
bswenso2
not rated yet Aug 12, 2010
You've got to be kidding me...

They weren't already doing this? I ASSUMED that they would be storing unused energy production... like a buffer.

So basically there is no buffer on the electrical grid, no reserves stored to meet unexpected demand?

Are you serious?
Reserves are generators that can be rapidly spun up using natural gas or diesel.
Some have proposed enabling backup generators be used. The challenge is integrating all sources into the grid. Phasing is important as well as economics.
CA demonstrated how not to incentivize such activity a few years ago: fixed retail, market priced wholesale.


I don't think any of this has anything to do with what I was talking about...


He covered exactly the point you brought up. Look into peaking plants. They can turn on at a moments notice to fill peak demand. The storage that you're thinking of would be something like a pumped storage reservoir.
CHollman82
not rated yet Aug 12, 2010
He covered exactly the point you brought up. Look into peaking plants. They can turn on at a moments notice to fill peak demand. The storage that you're thinking of would be something like a pumped storage reservoir.


I was talking about storage... to which he replied by stating that "reserves are generators"...

Generators are not storage... Nowhere did he address the wasting of unused generated energy that the article mentions, which is mostly what I was talking about when I asked why they don't STORE it.

He didn't address anything I was talking about.
num3472
not rated yet Aug 12, 2010
Figuring out a way to actually store energy in large quantities is hard, and has inherent inefficiencies.
(you don't get out as much as you put in)

Having chemical batteries/flywheels big enough costs a lot, and the inefficiencies grow as they get larger. Right now the power companies are of the opinion that it's just not worth it.

Lots of different technologies are being tried to find efficient, cheap storage that is accessible at a moment's notice. This is just one of them.
david_42
not rated yet Aug 15, 2010
Sodium-sulfur batteries are much more efficient than this proposal, easily scaled and become more efficient as they get larger. They are relatively small physically and can be positioned near the demand point. Additional energy storage can be added merely by adding larger tanks.