How We Make Power

To understand emissions, understand how electricity is made.

Spin a turbine that's hooked to a generator and you get electricity. How do you spin a turbine? For most electric utilities there are three good ways: boil water and use the expanding steam to spin the turbine, pass lots of water through a turbine to make it spin, or burn fuel and let the rapidly expanding gases spin the turbine.

Is one way better than another? While some methods are certainly more efficient, less costly or more environmentally friendly, we believe the key to providing reliable electricity to hundreds of thousands of people and businesses is to have all three ways of spinning a turbine available 24 hours a day, 365 days a year.

How to boil water

A steam-turbine-powered generator is one of the most reliable ways to generate electricity because so many different fuels can be used to boil the water to make steam. Steam turbines provide 80% of the electrical generation for PSNH. The steam to drive them comes from burning coal, gas or oil. Some steam turbine plants are "dual fuel" and can switch back and forth from oil to natural gas.

Burning oil, coal or natural gas results in air emissions of sulfur dioxide, carbon dioxide, carbon monoxide and, in the case of coal, minute levels of mercury. Fortunately, there are several ways that PSNH works to lower emissions.

Fuel Diversity

There are some who want utilities to switch entirely to natural gas to reduce sulfur, carbon monoxide and mercury emissions. But switching to one fuel would put utilities at the mercy of fluctuating prices, lack of availability and the large capital expense it would take to create new plants and convert older ones.

In recent years, PSNH has increased the use of natural gas. But using a diverse range of fuels lets PSNH produce power reliably, affordably with concern for emissions and fuel availability.

Water over the dam.

The turbines in hydroelectric power plants are spun by water-or more accurately, they're powered by gravity as water flows downhill past the turbine blades. Efficient, reliable and affordable, hydroelectric plants provide clean electric power at low cost. Unfortunately, they must be located near a river or below a dam and they are limited in the relative amount of power they can produce. For example, PSNH's Newington Oil/Gas power plant produces 409 megawatts of power while its nine hydroelectric plants have a combined output of only 69 megawatts. Hydroelectric power comprises 5% of PSNH's total electrical output.

In addition to adding to diversity, hydroelectric power plants can also "store" energy simply by holding lots of water behind the dam above the power plant. If additional power is needed rapidly on a high-use day, operators simply open the dam to create additional power.

While hydro power produces no emissions and they are an important part of PSNH's overall power output, they can have environmental effects to wildlife and water. Couple that with the limited supply of water, the large cost of building hydro plants and their relatively small power output, building new hydro-plants to reduce air emissions is unlikely.

Kick in the afterburners.

The turbine in a jet-fueled power plant is remarkably similar to the jet engine in an airplane in that they both use the expansion of burning fuel to spin a turbine. But like their cousins in the air, combustion turbines are expensive to run and not very efficient. What they're best at is providing large amounts of power almost instantaneously. This makes them ideal for use as backup when a large plant is unexpectedly shut down for repairs, or a heat wave dramatically increases electricity requirements. Though they comprise 15% of PSNH's total electrical output capability, jet-fueled power plants are never turned on unless other plants can't keep up with demand.