Power to transform energy
makes hottest days easier

The August heat is causing near record temperature, driving a lot of us to turn on the fans and air conditioners, leading to the highest peak electricity usage ever.

The peak last week reached 1,291 megawatts for the island of Oahu. That is a lot of power, nearly one and one-third billion watts -- that is 1,291,000,000 watts -- the equivalent of 21 million 60-watt light bulbs.

To understand the magnitude of this and compare it to our own paltry powers it is illustrative to examine the concepts of work and energy, and distinguish them from power.

Although the unit of "watt" is commonly associated with electricity, it is actually a standard physical unit derived from mechanics, which is that branch of physics that deals with forces and motion.

The unit is named in honor of James Watt, whose steam engine was the first to capture the energy stored in steam to power machinery. It is also the electrical unit that is the result of multiplying voltage by current.

The translation of the units of work, energy, and power across the seemingly unrelated area of mechanics and electricity is testament to the utility and unity of the physical sciences in describing and understanding the physical universe.

Work, energy, and power are related through the concept of conservation of energy, which is the central, if not the most important, concept in all of science.

Conservation of energy is not what you might think. When we speak of conserving energy, we mean to use as little as possible by turning off lights and other electrical devices that are not being used.

In physical science, conservation of energy means that energy is not created from nothing. It cannot be created or destroyed, but can be converted from one form to another. The ultimate outcome of this fundamental theorem of physics is that the total amount of energy in the universe is constant.

Energy gained in one place is gained at the expense of energy somewhere else. For every gain in energy there is a corresponding loss of energy elsewhere.

Work is done whenever a force is applied over a distance, and under some conditions it can be stored, for example in the motion of a car. Energy is what we call this stored work.

Work must be done to get the car moving. While it is moving, we say it "has energy." If it happens to run into a wall, the work is recovered in crumpling the metal. If the brakes are applied, the energy is dissipated as heat, which is another form of energy.

Work and energy are measured in joules, named after James Joule, who formalized the concept of conservation of energy. A joule is the work done when a force of one newton is applied over a distance of one meter.

The "Newton" is named in honor of Sir Isaac Newton, whose laws of motion and gravitation set the foundation for all of physics, and whose methods of analysis were later applied to the study of heat, electricity and magnetism. The principle of conservation of energy was incorporated to form a unified system of principles and standard units that forms the core of all of modern science.

The basis for the concepts of work and energy comes from Newton's laws of motion, one of which defines force in terms of the acceleration.

One newton is the force required to accelerate a mass of one kilogram such that its speed increases by one meter per second every second. It is a little less than one quarter of a pound or about the weight of a medium-sized apple.

One joule of work would be done when that apple was lifted one meter (3 1/3 feet).

The distinction between work and power is a simple one. Work and energy do not involve rate; it makes no difference whether the apple is lifted one meter in one second, or in one hour. The same amount of work is done either way.

Power is the rate at which work is done, or equivalently the rate at which energy is transformed: Lifting the apple in one second requires more power than lifting it in one hour.

One watt is work done at the rate of one joule per second; lifting the apple one meter in one second consumes one watt of power. That may not seem like much, but a typical person would be struggling to produce enough to light a 40-watt light bulb for any length of time.

Taken as an average, the 895,000 people on Oahu could generate that 1,291 megawatts of power if we each contributed 1,442 watts, or roughly 36 times our capacity.

Twelve hundred ninety-one megawatts is peak demand, not continuous production and varies with season and time of day, but the typical power used is about two-thirds of that peak demand, about 860 megawatt-hours, or just under 1 kilowatt per person, continuously.

That amounts to about 23 kWh (kilowatt-hour) per day per person, which is 25 times the power we could generate with our muscles if we worked at full capacity 24 hours a day, seven days a week, every day of the year.

We are energy hogs, consuming far more per capita than anywhere else in the world, while a good portion of the world's population uses muscle power (both human and animal) for energy sources.

Most of the energy we use comes from oil, all of it imported into the state, transformed from the chemical energy in the oil, first to heat, then to mechanical energy, then to electricity, then put to work in our homes and businesses.

How often do we stop to appreciate how much easier our lives are because we have learned how to transform energy to suit our needs? The next time you're riding that stationary bike (consuming about 40 watts) or climbing the stairs (about 100 watts) think about what life would be like without electrical energy.