Smart-Grid - Part 1 of 2

Written by Marc Bevis

Monday, 24 August 2009 00:00

What is this talk about a Smart-Grid? Why do I care?

A two-part series.

Today we will look at the existing US Grid and some of its challenges. Here is a map of the US showing the transmission lines.

http://images.encarta.msn.com/xrefmedia/aencmed/targets/maps/map/000a5302.gif

Electricity is not something that typically is stored. It is a commodity that is made just-in-time for the consumer. Utility operators are constantly anticipating how much electricity their customers will want at any time of the day. The electricity is consumed within a second after it is created. The operators add and subtract power generation capacity to ensure that there is always enough power to turn on your lights and air conditioner. If there is not enough power you will get a brown-out causing the lights to dim and stress electrical appliances. If the shortage is severe you get a black-out resulting in total loss of power. However, the utilities do not want to generate too much excess power because it is wasted and would result in higher electric bills.

The utility companies have a portfolio of power generating assets such as coal, nuclear, natural gas, hydroelectric, wind, and solar plants. Each type of plant has unique attributes such as fuel cost, pollution produced, waste storage, and the speed at which the plant can increase or decrease its power output. Coal and Nuclear plants supply the base-load to the Grid. Their fuel costs are low and they are used as much as possible. Peaking assets such as natural gas plants use more expensive fuel, but their output can be adjusted quickly to the varying demand. As we turn on more lights, air conditioners, computers, factories, etc. over the course of a day, the utility companies activate more electric generators so there is always slightly more supply than demand.

http://www.oe.energy.gov/images/elec101_diagram.jpg

In the Philadelphia region you probably get an electric bill from PECO who delivers the electricity to your house. PECO buys the power from Exelon. Exelon owns the power plants (coal, nuclear, etc) that make the electricity. On top of this is PJM which is a wholesaler of electricity known as an RTO (Regional Transmission Organization). PJM serves 51 million customers in 13 states plus Washington DC. PJM is in the Eastern Interconnection which goes from the East Coast to Oklahoma and up to North Dakota. The rest of the U.S. is served by the Western Interconnection and Texas Interconnection.

The Grid refers to 157,000 miles of miles of high-voltage transmission lines (plus many more miles of lower voltage lines) and equipment transporting electricity from power plants to businesses and residences. The Grid also connects regions of the country together. This allows RTOs to manage the selling of power to each other to balance the supply and the demand.

The point of describing all this is to demonstrate how large and complex our electrical system is. The Eastern Interconnection is arguably the largest machine in the world. It covers 2 million square miles with hundreds of generation plants that are precisely synchronized to deliver 120 volts at 60 Hz (cycles per second) to your house

The blackout on August 14th, 2003 is an example of the challenges of the US electrical infrastructure. A high-voltage power line in Northern Ohio was shutdown when it touched overgrown trees. Through a series of equipment failures and human error the problem cascaded to neighboring systems. Ultimately, 8 northeastern states and southeastern Canada where affected. 50 Million people lost power for up to 2 days. The advantage of an interconnected grid is that the power can be transmitted to where the demand is at any time of the day. The disadvantage is that a problem can propagate through the Grid like the blackout of 2003.

Our society’s per capita use of electricity is increasing because electricity is such a versatile form of energy (think about plug-in hybrid cars being announced like the Chevy Volt that recharge their batteries using an outlet in your garage). So, the capacity of the Grid over time needs to keep increasing. Also, the Grid needs to be extended to new areas of the country. For example, those large wind farms located in rural parts of the country need new power lines to transmit the electricity to the population centers. These changes to the Grid are an expansion and extension to the Grid. There is nothing inherently smart about these needs, but they dovetail in with plans for the Smart-Grid.

Much of our new generation capacity is coming from wind and solar farms. These generators are more intermittent than fossil fuel powered plants. They only make electricity when the wind blows or the sun shines. So, the Grid needs to be able to handle the additional intermittent nature.

http://shakerwoodsfarm.com/solar.htm

A small PV system mounted on a garage.

http://www.wsus1.com/info.html

Exelon Epuron facility in Bucks County, PA

Also, solar is very scalable from a small system on the roof of your house to large utility scale solar farms that use many acres of land. So, not only is solar power intermittent, but it is distributed over many locations. Historically, power generation was centralized at large coal, gas, and nuclear power plants. Newer generation assets such as solar, wind, and micro-hydro are more distributed. This is good but also poses new challenges. It is good because it lessens the congestion on the Grid. The power from your solar system on your roof can go directly to your house. If you generate excess power, you can it sell back to the Grid. The challenge for the Grid is that your home is now a miniature power plant that the Grid needs to deal with.

The Smart-Grid will connect everyone to abundant, affordable, clean, efficient, and reliable electric power anytime, anywhere. http://www.oe.energy.gov/smartgrid.htm

We will look at the Smart-Grid in tomorrows blog.

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