Energy Methods

The College uses energy to heat, cool, and ventilate buildings, to run electronic equipment, to cook meals, heat water for showers, and much more. This energy comes from electricity, heavy oil fuel, natural gas, and solar panels.

  • Central Systems

    Many buildings on campus – especially the large ones towards the geographic center – are heated and cooled using central systems like the central heating plant and central chiller. Smaller buildings, especially those on the outskirts of campus often have independent heating and cooling systems that are a lot like normal residential boilers and air conditioners (only larger).

    Central Heating Plant and Cogeneration

    The central heating plant provides steam for heat and hot water to many buildings on campus. It has the ability to burn either natural gas or heavy fuel oil, a thick liquid biproduct of gasoline refinement. Greenhouse gases and other emissions from heating the campus (and generating electricity) are much lower when a high percentage of natural gas is burned.

    Cogeneration is the use of a primary energy source to produce more than one useful form of energy. In Williams’ case, the primary energy source is heavy fuel oil or natural gas, and it is used to generate both electricity and steam that heats campus buildings. More of the primary fuel is needed to generate the combined electricity and heat, as a higher pressure of steam is necessary to drive the generator than to heat the campus. However, the combination is more efficient than generating either electricity or heat alone, as the waste heat from the electricity generation is used to heat buildings. Electricity is only cogenerated during the heating season when the plant is on.

    Central Chiller

    The central chiller uses electricity to chill water, which is then piped to buildings on the north side of campus for air conditioning during the summer months. Some of the larger buildings on campus (such as Jesup and the Science Center) have independent chillers that cool those buildings. These large central chilling systems are generally more efficient than smaller air conditioning units.

  • In 2004, Williams installed our first solar array on top of Morley Science Center. Since then, we have installed a number of other arrays - ground-mounted and roof-mounted at the Library Shelving Facility, at Weston Fieldon top of Sawyer Libraryon and around the Class of 1966 Environmental Center, and on The Log.  All these arrays are connected to the power grid.

    Energy Production Tracking

    Solar Photovoltaic (PV)

    How it works

    Technology

    Solar panels, also known as photovoltaics (PV) are made of at least two layers of semi-conductor materials. One layer has a positive charge, and the other has a negative charge. When light hits the top semi-conductor layer, a portion of the energy is absorbed, freeing electrons from the negative layer to flow through an external circuit and back in to the positive layer. This flow of electrons creates electric current. Individual solar panels can be connected to increase the power output, creating a solar array.

    Snapshot from pv animation
    Click to view a short animation.

    A more detailed explanation of how solar panels work can be viewed at UnderstandSolar.com

    Sizing

    The size of a solar panel or array of solar panels is usually given in kilowatts. The number of kilowatts is the maximum generating capacity of the panel or array. For example, the 7.2 kilowatt array on the roof of Morley Science Center can generate 7.2 kilowatts of electricity under ideal conditions.

    Usage of electricity is often described in kilowatt hours. The output of a solar panel in kilowatt hours is the output at any given time period multiplied by the amount of time. If a 7.2 kilowatt array were producing at peak for eight hours, it would have generated 57.6 kilowatt hours of electricity. However, it would be highly unusual for a solar panel to produce at maximum capacity for eight hours. The most output the Williams array has given in a 24 hour period has been around 50 kilowatt hours.

    How conditions affect output

    The more sunlight a solar panel is exposed to, the more electricity it will generate, up to its maximum capacity. Any shading on a solar panel from nearby trees or buildings will decrease the amount of electricity generated, as will snow cover in the winter. Solar panels also work most efficiently when light from the sun hits them at 90°, which is why solar panels are sometimes tilted to the south (in the northern hemisphere).  The degree of the tilt determines what part of the year the solar panels are optimized for: the greater the slant, the more the panels are optimized for production during the fall, spring, and winter when the sun is low in the sky.  To work well, solar electric systems need unobstructed light from the sun during most daylight hours for most of the year. A good site has no shading where the solar panels will be installed, either from vegetation, nearby buildings, or other parts of the building on which they are installed.

    You can see the affects of weather conditions on the electricity output of the panels in a series of timelapse movies of the Morley PV array

    Advantages and Disadvantages

    Solar photovoltaic systems are generally reliable, well tested and low maintenance.  They’re quiet and less visually intrusive than many other sources of renewable energy, and can generally be designed to meet a wide variety of electrical requirements. In locations that don’t already have a power supply, an off-grid solar electric system may be more cost effective than running power lines.

    The initial costs for PV systems have been decreasing rapidly due to ongoing research into their materials and production methods as well as legislation that provides financial incentives.  Like several other sources of renewable energy, solar power is a variable energy source.  Solar panels can’t produce electricity at night or during periods of dense cloud cover, so a solar electric system must either have batteries for storing electricity or a backup source (such as a connection to the grid).  All solar panels used at Williams are connected to the grid.

    Solar Thermal

    On campus Collectors

    In 2018 solar thermal collectors were installed on Poker Flats coop housing in order to help heat hot water for the residents.

    How it works

    Click on the image to view a short animation about how evacuated tube solar collectors work.

    Solar thermal systems convert sunlight to heat that can be used for space heating, space cooling, and domestic hot water.  The core of these systems is the solar collectors. There are several different kinds of solar collectors, the most common of which are flat plate and evacuated tube. Solar collectors convert the sun's energy most efficiently when the sun’s rays hit them at a ninety degree angle. In the United States, the sun is always in the southern part of the sky and is higher in the summer and lower in the winter. That means that solar collectors are most effective when they’re installed facing south and tilted towards the south. The degree of the tilt determines what part of the year the solar panels are optimized for: the greater the slant, the more the panels are optimized for production during the fall, spring, and winter when the sun is low in the sky.

    Collectors

    Evacuated Tube Collectors
    Closeup of evacuated tube solar collectors

    Evacuated tube collectors feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and a metal absorber tube attached to a fin. The fin's coating absorbs solar energy but inhibits radiative heat loss. The tubes are manufactured with a vacuum between the outer and inner tubes, which eliminates conductive and convective heat loss and helps them achieve very high temperatures.

    The inner copper tube is filled with a non-toxic liquid. As the liquid absorbs heat from the copper pipe, it evaporates and rises to the top of the copper heat pipe. A larger portion of copper at the top of the heat pipe is the condenser. It either surrounds or is mounted inside a pipe through which a heat transfer fluid (generally water or antifreeze) flows. As the heat transfer fluid flows, the condenser loses heat to the fluid, and the gas inside the heat pipe condenses and flows back to the bottom of the heat pipe as a liquid. The heat transfer fluid is then pumped to a heat exchanger inside the building, where the heat is taken out of the transfer fluid and put in to the domestic water supply or heating system.

    Flat Plate Collectors
    Flate plate solar collectors 

    Glazed flat-plate collectors are insulated and weatherproof boxes containing a dark absorber plate under one or more glass or plastic covers. Unglazed collectors, typically used for solar pool heating, have a dark absorber plate made of metal or polymer, without a cover or enclosure. This type of collector is by far the most common.

    With both types, small tubes run through the box and carry a fluid (either water or an antifreeze solution). As the sunlight hits the dark absorber plate, it heats up and transfers heat to the fluid passing through the tubes.

  • How it works

    Wind Speed and Power Generation

    Power output of a wind turbine rises as the cube of wind speed. Wind turbines operate within a narrow range of wind speeds - if the wind is too slow, the turbine won't turn, and if it's too fast, the turbine will shed the wind rather than risk damage to the turbine. Wind speeds of over 6.5 meters per second are typically necessary for economic wind energy generation.

    Horizontal axis wind turbines at Searsburg, Vermont. (Photo courtesy of

    Several factors can affect the amount of power a turbine can generate. Wind speeds increase as height above the ground increases - this is the main reason why commercial scale wind turbines have increased in height over the past twenty years. Wind energy production is negatively affected by roughness of terrain and the resulting turbulence - another reason that wind turbines have increased in height.

    The wind in any given location does not blow constantly, at the same speed, or from the same direction. The seasonal and daily variations can be to a certain extent absorbed by the electrical grid, but as the percentage of wind power on the grid increases, the variability will have to be managed.

    Wind Turbines
    Vertical axis wind turbine.

    Modern wind turbines come in a variety of styles and sizes, depending on their intended use. The most common style is the horizontal axis turbine, where the axis of the blades is parallel to the ground. Less common are vertical axis turbines, where the axis of the blades is perpendicular to the ground.

    Turbines range in size from small turbines (50 watt - 250 kilowatt) designed for residences, boats, and off-grid applications to large scale commercial turbines - anywhere from 250 kilowatts to 3.5 or 5 megawatts. The "nameplate" capacity of a turbine such as quoted above refers to the maximum theoretical production of the turbine.

  • testing