Urban energy density

Interesting and impressive analysis.

http://theenergycollective.com/robertwilson190/257481/why-power-density-matters

The cause of MIT’s major power loss

By John A. Hawkinson

STAFF REPORTER

the Tech

December 4, 2012

What actually happened when MIT and much of Cambridge lost power last Thursday night? Why didn’t MIT’s 20 megawatt cogeneration turbine power the campus like a lighthouse in a sea of Cantabrigian darkness? What was the root cause of the failure?

MIT’s Central Utilities Plant, in Building 42, has a gas turbine that can supply up to about 22 megawatts of electrical power to most of MIT’s campus south of Albany St. But the campus regularly draws 25 MW or more, so the cogen turbine cannot supply it all — the balance comes from NSTAR, the local utility.

While the cogen plant provides a measure of redundancy, that’s not its primary purpose. It exists to save energy and improve efficiency by generating heat and electrical power simultaneously.

(The plant is called cogeneration because it produces both electricity and steam. The plant burns fuel, usually natural gas, which mixes with air under compression and spins the gas turbine to produce electricity. The same hot gases are used to boil water and produce steam, which is used to both heat the campus and to run chillers that provide cooling.)

Outage begins

At 4:24 p.m. on Nov. 29, an automated NSTAR relay detected a disturbance and took a 115 kilovolt underground transmission line out of service, affecting 19,000 customers, according to NSTAR’s early diagnosis. NSTAR spokesman Michael Durand said that NSTAR’s analysis was preliminary and that a more detailed investigation was ongoing.

The 115 kV line was one of two parallel lines that would normally back up each other. But maintenance crews were working on the other line, so it was unavailable.

That work is part of NSTAR’s “Cambridge Cooling Line Reliability Project,”. The transmission lines connect NSTAR’s Alewife East and Putnam Stations, and serve all of Cambridge east of Harvard Square, according to NSTAR filings with the city. The work is expected to increase the lines’ load capacity by 20–40 percent. The lines date from 1988 and each consists of three copper cables in an 8 5/8" steel pipe surrounded by dielectric fluid.

Large parts of Cambridge lost power. It affected East Cambridge, Kendall Square, and MIT, as well as many sections along Massachusetts Avenue up to Harvard.

MIT was using 27 MW: 22 MW from cogen, and 5 MW from NSTAR. The cogen turbine couldn’t supply the extra load, so it shut down automatically, as designed. MIT was without power, just like much of Cambridge.

In buildings throughout the campus, generators start automatically. They power emergency lighting, elevators, life-safety equipment, critical research equipment, etc. In some buildings, computer network equipment is on emergency power.

Within the main group, this emergency power comes from a single large generator located at the Central Utilities Plant. But newer buildings are required to have their own generators, so scores of generators started all around campus. The emergency power circuits are connected to automatic transfer switches that switch them to the generator power. Generators are designed to start within a few seconds of an outage.

Central Utilities Plant

At the plant, a number of things have to happen after power fails before the turbine can start generating electricity again. The process takes hours. The first order of business is to start up a steam boiler and restore steam pressure, according to Randall D. Preston, director of utilities for Facilities.

Meanwhile, NSTAR was trying to restore power. Within 20 minutes, NSTAR was able to restore power to 5,500 customers (29 percent of those affected), using remote switching technology and powering them from other parts of the grid, Durand said. For instance, the traffic signal at Main and Vassar was running, but signals on Mass. Ave. were not. Everybody else, including MIT, would have to wait.

After steam is available, MIT’s attention can turn to the cogeneration turbine. MIT can operate the turbine in “island” mode, disconnected from NSTAR’s grid. Preston said that MIT will try to do this unless NSTAR has estimated the outage will be short — but even then they’ll prepare for the possibility of no NSTAR power. MIT does not require NSTAR’s permission to operate in island mode.

A number of services need to function before the gas turbine can operate, Preston said. They include compressed air, cooling water, and exhaust ventilation. Without those, the turbine cannot run. And, of course they need to disconnect from NSTAR to avoid trying to power all of Cambridge.

Plant operators also need to clear any alarms that the turbine control system might report. They need to make sure that neither the turbine nor any other critical component was damaged when the power failed.

The best case is “probably an hour,” Preston said, “but realistically it takes one to two hours.”

Once they’re ready to go, they start by disconnecting almost all the circuits that feed the campus from the plant, so that the turbine can start with a known low load. They then start the turbine.

Then, they slowly add campus circuits to the turbine to control its load and warm up the heat recovery steam generator that captures the heat from the turbine’s exhaust.

“We were at the point of pushing the start button,” Preston said, when NSTAR restored power.

But because MIT is such a large customer, NSTAR treats it carefully, and wants to bring back large loads slowly.

“NSTAR asked us to wait 15 minutes,” Preston said. And the 15 minutes dragged on to 20 minutes. But Facilities used that time to reconnect the campus circuits that they had disconnected in preparation for starting the cogeneration turbine. Meanwhile, the traffic signal at 77 Mass. Ave. was back on.

What if NSTAR hadn’t come back? Preston said that Facilities would have to leave some portions of the campus without power until they could get unnecessary loads removed from the sections that were powered up first.

“In general, we would power up the campus circuits serving major research buildings and critical facilities first, and then go from there,” Preston said.

NSTAR’s effort

Why did it take NSTAR two hours? Durand said the time taken is actually “expected and normal to get that kind of transmission line back in service given the detailed analysis and numerous restoration steps involved.” NSTAR was “all hands on deck,” including every available management and field crew, he said.

NSTAR had to test the 115 kV line to determine if there was a fault in it. Much of the time is spent eliminating possibilities and making sure that the situation is “what we believe it is,” Durand said.

NSTAR’s preliminary determination was that the relay was operating in error, and there was no damage to the line. “The relay sensed something that didn’t happen,” Durand said.

After concluding that the relay had misoperated, it had to be removed from service.

Durand said Friday that the parallel 115 kV transmission line which had been out of service for maintenance was expected to be back in service on Saturday. No NSTAR workers were injured in either the outage or the response.

http://tech.mit.edu/V132/N58/power.html

Not Your Grandma's Infrastructure: The Urban Energy Revolution | September 2012

A role for microgrids in building more resilient cities?  Wrap up from a pre-Sandy conference in NYC.

Not Your Grandma's Infrastructure: The Urban Energy Revolution | September 2012

Flicking the switch from hot air to usable heat

by Allan Jones

The 21st century has been billed as the century of the city. For the first time in history, more than half the world's population is living in cities. It is also the century of climate change and reliable science says we are already on the brink of irreversible damage to our planet.  Cities are our most profligate consumers of scarce resources and our worst polluters. Cities are the primary cause of climate change and are most at risk from climate change, but they also provide the solution to tackling it.

It makes sense, therefore, to begin finding city-wide solutions to the problems of climate change. Solutions do exist. They have been implemented and shown to work. What is needed is the political will and the co-operation of all levels of government and the private sector to implement solutions on a broader scale.

In the 1980s, I was already convinced that global warming was a reality, so when I joined the Borough of Woking in Surrey, I was determined to do something about it.

As chief engineer of this borough of 100,000 people, I introduced the energy efficiency revolving fund that led to replacing the town's electricity and heating systems with cogeneration, also known as combined heat and power generation.

In centralised power stations, two-thirds of the energy generated is dispersed into the atmosphere as heat, and further losses occur in transmission and distribution across the grid. Fifty per cent of Britain's water resources are used to evaporate this waste heat.

In Woking, we installed a gas-fired system (far less polluting than coal), which generates electricity locally. Heat from the generation process is captured and piped underground to supply heating and hot water. This is cogeneration, and in some countries such as Denmark and the Netherlands, more than 50 per cent of their energy comes from cogeneration.

In a further step - trigeneration - waste heat is converted to chilled water for air-conditioning and refrigeration. Trigeneration has a huge impact in reducing carbon dioxide emissions since it displaces electricity that would otherwise be consumed by conventional air-conditioning, generates more low-carbon electricity and does not use greenhouse gas or ozone-depleting refrigerants.

In Woking, trigeneration - supplemented by fuel cells and renewable energy such as solar panels - enabled the town to produce 80 per cent of its own power by 2004 and to drop its CO2 emissions by 77 per cent in 14 years. The power and heat was also cheaper for customers.

There is now a much greater challenge in London. Centralised energy is responsible for 75 per cent of London's CO2 emissions. The target set by the previous mayor, Ken Livingstone, was to cut emissions by 60 per cent of 1990 levels by 2025. The new Mayor, Boris Johnson, has adopted this target.

I was asked by Livingstone to set up and run the London Climate Change Agency. We are working to shift as much of London's energy use off centralised energy generation and the national grid and on to local, low-carbon sources, including trigeneration. By 2025, we aim to have a quarter of the city's energy coming from local sources and more than 50 per cent by 2050. The balance of emission savings will come through such projects as the London Array, which will be the largest offshore wind farm in the world when it is completed.

Sydney, like London, produces the greatest proportion of its greenhouse emissions from power generation. Almost 80 per cent of Sydney's emissions come from electricity supplied to homes and businesses, and less than 10 per cent from transport.

The Lord Mayor, Clover Moore, and the city's strategy, outlined in Sustainable Sydney 2030, set an ambitious target for greenhouse emission reductions of 70 per cent from today's emissions by 2030, even as the city continues to grow.

Yet this is in line with the reductions targeted in the Kyoto Protocol, and consistent with the changes that need to be made if our cities are to remain viable and productive. Already, you have developments being planned around the use of trigeneration, for both residential and mixed-use developments.

As we have learnt in Britain, privatisation of the energy supply is not necessarily an obstacle but can also be an opportunity to introduce less damaging forms of power generation and supply. But where there is no single authority able to implement these systems, a collaborative approach is essential.

Where barriers do exist, they are not technological but regulatory and, frequently, they are raised by short-sighted vested interests. They cannot be allowed to jeopardise the future of our cities, and of our children.

Allan Jones is chief executive officer of the London Climate Change Agency. He is giving a free City Talk on "Green transformers: revolutionising energy generation for a sustainable Sydney" at the Theatre Royal tonight at 6.30.

Saying goodbye to the grid

July 23, 2008

A proven air-clearing money-saving scheme is attracting global focus, writes Leesha McKenny.

Allan Jones is a man who has done something that many thought was not possible. The engineer has maybe, just maybe, made the British borough of Woking in Surrey famous for something other than the place where the Spice Girls started their career.

While they were rising through the charts during the 1990s, he was slowly taking their borough off the national electricity grid.

By 2004 he had helped the area cut its carbon dioxide emissions by 77 per cent. His methods were innovative, perhaps, but not new. Some of the technologies he used had been around for more than 100 years. This week he was in Sydney to talk about how he did it.

"We were squeezing the carbon, if you like, out of the buildings from both ends," he says. "We were making them more energy efficient and we were supplying them with low carbon systems.

"Of course, at the time I had no idea it would go the way it did, and just get bigger and bigger."

The idea that caught national and global attention was the borough's successful use of low carbon, or co-generation power systems. First set up in Manhattan in the 1880s, these use gas rather than coal to generate electricity with fewer emissions. Coal-powered energy stations also throw off two-thirds of the generated energy as waste heat. In co-generation, any waste heat from the gas-generated electricity is recycled back into the system. Tri-generation, as the name suggests, takes this one step further by using this heat to cool. In the Sustainable Sydney 2030 plan, both ideas fall under the banner of "green transformers".

Jones says small co-generation substations are built into a city's landscape - in its basements, on its rooftops - to distribute energy locally. In Woking this turned a passive distribution network that fed off a distant national grid into an active network supplying and supporting electricity in its own right.

This was based on an initial investment by council of a fifth of the cost of implementing the project over five years, plus a reinvestment of all savings in the same period back into the process. This was later backed by a public-private partnership.

"By the time I'd left Woking, I'd organised 81 decentralised energy systems, dotted all over the borough and trading with each other," he says. "They collectively became independent and self-sufficient from the grid."

Jones says areas can be organised by energy profiles - homes and business, say, that use peak power at different times - so surplus energy can be traded effectively across the network. In Woking's case, by keeping the power close to where it was used, council was able to bypass middlemen charges generated by inefficiencies in the national grid, and supply energy to households directly at a lower cost, increasing its own income by 400 per cent.

By the time Jones was hired to set up a joint venture project in London as part of the city's plan to cut its emissions by 60 per cent of 1990 levels by 2025, it is little wonder many of the world's largest companies - including two oil companies - were submitting tenders to become involved.

"Rather than taking the approach that this is going to cost lots of money,

I turn that coin on its head and say, 'Actually, you can make a lot of money from this - you just need to do things a different way,' " Jones says.

He says London is now drawing in domestic and international investment in green technologies in the order of £3½ billion ($7.2 billion).

"People want to build manufacturing plants for fuel cells, they want to build manufacturing plants for combined heat and power [or] alternative waste technologies - it's creating jobs."

Jones says he is happy for Sydney to pick his brains about the practical and regulatory detail of Woking and London, and hopes that governments will increasingly see co- or tri-generation power systems as a viable alternative to coal. "A lot of what I'm doing now in London is now being copied across the UK," he says. "And Sydney could be in that same position as far as Australia is concerned."

This story was found at: http://www.smh.com.au/articles/2008/07/22/1216492455066.html