Tuesday, March 19, 2013

I’ve Got the Power!* – Electricity Production in New Hampshire

My post this week is part informative and part instructional. When we debate and discuss energy issues, a couple of key concepts come up time after time and to be a contributor to an energy discussion, we have to know, or familiarize ourselves with, some technology and terminology. This week I want to explain two fundamental energy concepts. The first is the difference between energy and power, and the second is capacity factor. I will then show how they can be applied to electricity production in New Hampshire.  

Let's start with the difference between energy and power. The terms energy and power are often used interchangeably. This is OK in a general conversation, but in an energy related discussion it can lead to confusion, misunderstanding and bad decisions. It is essential to be specific about which term you are discussing so let's take a crack at distinguishing between the two.
 
The standard scientific definition is that Energy is the ability of a system to do work. It is a quantity which we need to get something to move, heat up, light up, burn, explode, etc. Energy also comes in different forms, for example, electrical energy, chemical energy, nuclear energy, kinetic energy etc. and much of energy technology is about converting one form of energy to another in the most efficient manner. Some of the more common units of measurement for energy are kilowatt hours (kWh), megawatt hours (MWh), BTUs, among others.
 
Power, on the other hand, is the rate at which energy is produced from a fuel source or is converted from one energy source to another. Units of measure for power include kilowatts (kW), megawatts (MW), BTU/hour or horsepower.
 
The confusion between these two often stems from the similarity of the units like kilowatt hours, which is an energy unit, and kilowatts, which is a power unit. However, it is necessary to understand that even though the units seem similar, there is a world of difference between them. This difference stems from the simple mathematical relationship between energy and power;
 
Energy = Power x time.
 
One my students in the Energy and Sustainability program at Franklin Pierce University recently noted that energy and power are analogous to distance and speed. Energy, like distance, is a quantity, whereas power is a rate like speed. Like the relationship between energy and power, the relation between distance and speed is written as;
 
Distance = Speed x time.
 
Let's consider a simple backup generator that I have been eyeing at Lowe's – the Generac 5500 Watt Portable Generator.
 
  (Picture source: Lowes)
 
This unit is rated at 5500 Watts or 5.5 kilowatts (kW), so the power of the unit is 5.5 kilowatts. If I were to run this unit for 1 hour, I would produce,
 
5.5kilowatts (kW) x 1 hour = 5.5 kilowatt hours (kWh)
 
of electrical energy that I could use to run my home. Running it for 24 hours would produce 5.5 kW x 24h = 132 kWh of electrical energy. The power rating of 5.5 kW is a measure of the rate at which the backup generator can take the chemical energy in the gasoline and convert it to electrical energy that I can use to keep my home running during a blackout. The larger the motor on the generator, i.e., the greater the power, the faster is the rate of energy conversion. In automobiles we are looking to convert the chemical energy in gasoline into forward kinetic motion to get us from point A to B. Again, the greater the power of the engine, the faster will be the rate of energy conversion. The pictures below illustrate this point.
 
(Picture source: Maserati)
 
The Maserati with its higher power, and larger, 700HP motor has the ability to more rapidly convert the energy in the gasoline tank into forward kinetic motion than my trusty and somewhat dusty blue Prius with its 80 HP motor. These two automobile engines, under specific circumstances, can produce the same amount of energy, however, the Maserati can do so in substantially less time. The Maserati will do so a lot less efficiently than the Prius but with a whole lot more fun. Even if I can't barrel down the highway at very high speeds, at least I will have my energy efficiency smugness to compensate me for the lack of admiring or envious glances for my ride. We will come back to the topic of energy conversion efficiency in a future blog post.
 
Let's go back to the Generac 5500 generator unit so we can discuss the second fundamental concept for this post – capacity factor. If I could run the generator solidly for 24 hours a day the whole year, I theoretically could produce;
 
5.5kW x 24h/day x 365 day/year = 48,180 kW of electrical energy.
 
However, if I were to use the generator only for 1 week during the year, say during a blackout, I would produce;
 
5.5kW x 24 h/day x 7 days = 924 kWh of electrical energy.
 
Dividing actual produced energy by the maximum that theoretically could have been generated in a 24/365 scenario produces a ratio called the capacity factor. In my case, it produces a figure of 0.019 which converts to a percentage of 1.9% and that would be the capacity factor of my generator for that year. In other words, my generator only ran at 1.9% of its maximum potential output. The capacity factor is a useful measure of how much of the capacity of an energy generating device was utilized over a time period, typically one year.
 
With these basic terms, energy, power and capacity factor under our belts, let's turn back to New Hampshire energy issues and particularly electricity generation. I have examined the 2011 electricity generation figures for New Hampshire that were published by the Energy Information Agency (EIA) and have combined, in one table, the number of generating units, their combined power, the energy produced from these units and the overall calculated capacity factors.
 
  
In 2011, there were 149 energy generating units in New Hampshire ranging from the large nuclear power at Seabrook, four coal fired plants, the wind farm in Lempster and 93 small hydroelectric operations, among others. The combined nameplate capacity of the generating units was 4,490 Megawatts or 4.5 Gigawatts, and they generated just over 20 million megawatts of electrical energy in 2011.
 
On examining the capacity factors, it is interesting to note how far they are from 100%. The only way a generating device can run at a capacity factor of 100% is by running 24 hours 365 days a year which is simply not practical or realistic. Equipment breaks down and has to be repaired or has to be shut down for maintenance. Moreover, power plants generating electricity make operating choices, based on prevailing wholesale electricity prices, fuel prices as well as demand to throttle back their units from their name plate capability. This reduces the amount of electricity produced which, in turn, reduces the capacity factor.
 
The units with the highest capacity factors are nuclear and wood fired operations which operated with capacity factors of 76% and 70%, respectively. These operations supply a great deal of the base load power to the electrical grid and therefore tend to run all the time except for maintenance shutdowns and reduced output during periods of low demand such as late evening and early morning hours.
 
Coal and natural gas ran at about 50% of their capacity and wind energy, which is very much dependent on wind speed and availability, has a capacity factor of 0.31 which is typical for wind projects. Oil and diesel based generators only have a capacity factor of 0.017 or 1.7%, which indicates these units are seldom used, due to the cost of producing electricity from oil. They function as back-up generators and are only used in an emergency. In many respects they are just like the small Generac 5500 unit, my present object of desire.
 
Even though the 149 New Hampshire based generating units are run by different operators with different technical and economic considerations, it is useful to consider their aggregated capacity. As noted above, the combined nameplate capacity of the generating units is 4,490 Megawatts or 4.5 Gigawatts. This combined capacity in a single unit would be one mammoth sized generator - we could call it the "New Hampshire Megarac 4500" – which is almost a million times larger than that unit I have my eyes on at Lowe's. 
 
 
 
(Generator Picture source: Lowes)

Based on 2011 data, this NH Megarac 4500 was operated at a capacity factor 0.51 which means the combined NH generating facilities only generated 51% of the energy that was theoretically possible. So, if we lose some of generating units in state, we have some excess capacity. However, we need to keep in mind that practical considerations such as cost and availability of fuel and maintenance requirements need to be taken into account when we shutdown generating units and expect others to operate at higher capacity factors. We also need to keep in mind that New Hampshire electricity generation is not an island unto itself. We feed into and draw electricity from the ISO-New England bulk power generation and transmission system which coordinates electricity supply and demand throughout New England. The six New England states have a combined capacity of about 35,000 MW of electrical capacity from 860 generating units.
 
Hopefully this has been an informative and instructional post and you now know the difference between energy and power and you have an appreciation for capacity factors. As you can see, we have a lot a capacity for generation in New Hampshire but it is crucial to appreciate that not all this capacity can be tapped at any one time. Running these generators depends on complex number of issues which include demand, cost of and availability of fuel, maintenance shutdowns and financial considerations and it all functions remarkably well most of the time due to the coordination of supply and demand that happens in the ISO-New England grid system.
 
In the meantime, if you see me in the parking lot at Lowe's trying to load a Generac 5500 into my dusty blue Prius, stop and give me a hand. Until next time, remember to turn off those lights when you leave the room.

Mike Mooiman
Franklin Pierce University   
mooimanm@franklinpierce.edu
3/18/13

 
(*The title of this week's blog comes from 1990's tune by Snap!, a German rap/pop group. Their song "The Power", features an incessant "I've Got the Power!" refrain. You do know the song, but as soon as I thought of it, the refrain became a relentless mind worm burrowing its way into my brain and I have not been able to get rid of it. Annoyingly, I now mentally hear it every time I flip a light switch. Here is the Youtube clip but be forewarned about that mind worm.)

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6 comments:

  1. Very interesting discussion and contrast between power and energy. In addition, I was grateful for the analysis of a portable generator.

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    Marty

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  3. That was beneficial and in layman terms - nicely done. Thanks for the details on the generator as I am in the market for one as well.

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