If you ask ten people what solar energy means, at least eight will describe the rectangular solar collectors they’ve seen on a roof - what’s known as an active solar system. Because of the mechanics of active systems, however, large-scale home heating project that use them have been unsuccessful, especially in the Northeast, where the least amount of sun is available at a time when the most amount of heat is needed.

Recently, there has been a growing interest in passive solar for home heating. Passive solar is actually a design tool, not an appliance like a solar collector. It depends on orienting the structure to the sun and allowing the sun to heat the interior space, and it encompasses environmental concepts that range from using vegetation for summer shade to berming the north side of a structure with earth to reduce air infiltration.
In order to use the sun’s energy wisely, one must understand its geometry and some fairly simple laws of nature.

During the winter months the sun rises late and sets early, and is low on the horizon. At its lowest point, on December 21, the sun can shine farthest into a structure—even though the length of time it shines is the shortest of the year After that, it travels in a progressively wider arc, rising higher above the horizon until June 21, our longest day, when the sun is at its zenith.

If a house is oriented to solar (true) south, the glass on the south side will admit a maximum amount of sunshine in winter, and less during the summer when the sun’s path is principally over the roof. At a latitude of 4O to 44, as it is in the northern United States, two to three times more energy will enter a passive solar house in January than in June. Nature also increases solar gain in winter by placing a blanket of white snow on the ground, which reflects even more energy into the building. In summer, energy absorbers like grass and weeds help to reduce energy entering the building.

The windows in a solar house are placed primarily on the south side, and secondarily on the east and west. North-facing glass is kept to a minimum because the north side of a building receives no direct sun, and therefore is the coldest side. All windows on the south, east, and west sides of the house are double glazed to allow the sun’s light to enter easily, yet to retard the loss of heat.

Bruce Brownell, owner of Adirondack Alternative Energy (AAE) has been designing passive solar homes for over 30 years. He has perfected a system that captures the suns warmth and saves it for use in heating the house. AAE designs are called Low Energy Requirement homes (LER), because, other than sunshine, they operate on very little auxiliary heat input. Brownell’s homes are atypical of what you might perceive to be a solar home – they do not look “solar” – typically with large amounts of south facing and large overhangs. In fact, a AAE designed home could appear as a basic shape of a house—a saltbox, for example—the interiors can range from rustic to elegant, from Colonial to contemporary. An AAE house is simple in its approach to energy conservation: it conserves the energy already available, and takes advantage of the free energy of the sun.

Everyone now understands the value of insulation, but the builder of a passive solar house must be obsessed by it. The insulation enclosing an Adirondack Alternate Energy LER house totally surrounds the exterior of the building and its foundation. In fact, because the foam boards are applied to the outside of the frame, they are the exterior. The insulation, foil-faced on both sides to reflect heat and to stop air and moisture movement, is fixed in two 2-inch layers, with the seams in each layer staggered and sealed tightly with reflective foil tape. All holes (made by nails, doors, vents, windows, etc.) in this envelope are sealed with high quality caulks and tapes on the outside: inside, foam caulking is used around window and door frames. The result is an envelope that performs with an average R value (resistance to heat moving in either direction) of 36 on all six sides of the house.

This insulation envelope also conserves the heat generated by the activities of the occupants—which can contribute as much as one-third of the house’s needs for heat. Combined with the sun’s contribution, this leaves less than one-tenth of the year’s warmth to be supplied by other means.
The insulation also creates a weather seal for the entire house. The interior is a capsule of warm weather, a microclimate that maintains a relative humidity of 45 to 50 percent all winter long. Plants thrive. There is little or no static electricity Sore throats, runny noses, and dry cracked skin are rare, because the moisture level in the air is nearly ideal for the human body. Homeowners consistently report that these comfort benefits are the best rewards of their homes. Sweeta and Richard Aulicino, whose house is in Lake George, commented about the constant humidity level of their 2,400 square-foot house: “It is a plus for our overall health. We don’t get coughs and colds here, and our skin never dries out, that is unless we travel. We can’t wait to get back to our home,” says Sweeta.

When the sun is shining on a winter’s day, the heat coming in through the windows of a passive solar house can be equivalent to having three furnaces running full blast—without a way to turn them off. Thermal storage is the means by which this excess free energy is controlled and regulated. Because thermal storage is a means of holding heat that already exists (and not, like a furnace, a way to produce more heat when you need it), it must consist of material that can absorb a lot of heat, hold it, and release it gradually. The materials that do this best are simple—brick, concrete, sand, or water. Low Energy Requirement houses use an efficient thermal storage system that combines several properties. Because the houses are super-insulated and have areas of south-facing glass equal to about one-third the area of the south walls, they need heat storage systems capable of absorbing nearly two-thirds of the solar input they receive on sunny winter days—or the houses will overheat. A typical 2,400 square foot house built by Adirondack Alternate Energy will receive about 350,000 Btus of solar energy on a sunny winter day. but during the sunny hours it only needs approximately 30,000 Btus to maintain a comfortable temperature. The heat storage system, which weighs roughly 150 to 200 tons, can store 10,000 Btus of thermal energy (heat) for each Fahrenheit degree change (100,000 Btus of heat dumped into the storage mass, in other words, will raise its temperature by one degree Fahrenheit) Because the insulated mass can hold energy for long periods, the need for additional heat during stretches of cloudy days is reduced.

Adirondack Alternate Energy has named its thermal storage system a Heat Energy Battery because it stores heat in much the way an automobile battery stores electricity, whether that heat originally comes from the sun, a person’s body, appliances in the house, or a woodstove.
The main component of the thermal storage is located under the entire first floor of the house, which can be either the basement or the ground floor level. Adirondack Alternate Energy commonly uses sand 4 feet deep as the storage medium, but stone dust, mine tailings or concrete also have been deployed with equal success.

A second component of the thermal storage system is its vertical mass. Located near the center of the house, this masonry or concrete chimney reaches from the foundation to the roof. Within it are the air circulation shafts, which pick up hot air near the peak of the house and transport it through the vertical mass to the sand bed below. If a woodburning stove is used to supplement the heat, the stove flue is also installed within the vertical mass. Between the horizontal and vertical masses is a large space where a squirrel cage fan pushes heated air collected at the top of the house through a grid of metal piping embedded in the sand mass. When the temperature in the house is warmer than the temperature in the sand mass, as it would be on a sunny day, the air passing through the pipes in the storage bed warms the walls of those pipes, which in turn, warms the sand. The air, now cooler, goes back into the house through registers along the perimeter walls creating a loop of air through the house. The same loop of air warms the house when its temperature is lower than that of the sand mass. The house air circulated by the fans absorbs the stored heat from the sand storage and releases it to the house through the registers.

The system operates on a twenty four hour cycle, accepting heat from all sources during the day, and releasing that heat at night.
Indoor temperatures, which in most houses range from 66° to 74°F throughout the winter months, are regulated by the interaction of the heat storage and air handling systems, and the sources of heat in the house. The radiation of heat through the structural concrete slab and flooring that covers the storage mass keeps the floors warm and comfortable.
The temperature balance engineered into each house is a departure from “traditional’ passive solar design. For instance, the amount of south-facing glass is less, to reduce excessive heat loss through the windows. The storage volume, much larger than it would be in that “traditional” passive solar house, is designed to moderate temperatures, in cooperation with the superior insulation envelope and the air circulation system, as well as to store heat for use during average periods of sunless skies.

The Heat Energy Battery is therefore the temperature equalizer for an Adirondack Alternate Energy house. It will decrease the building’s need for auxiliary energy. More important, it will regulate temperature swings and keep temperatures even throughout the house. It can be engineered for any style of house, and virtually eliminates the need for expensive devices such as automatic venting or insulated shades or shutters.
On a sub-zero blustery winter night, stored energy and heat from the activities of the family inside will keep a Low Energy Requirement House at about 60 F But 70T is more comfortable for most people, so you may need a way to add 10 degrees or so to the air temperature of the house. Most homeowners choose airtight wood- stoves as their supplementary heat. During a cold, icy winter in the northeast, an airtight woodstove may burn one to one and a half cords of seasoned hardwood to keep a 2,400 square foot house warm for the entire season. The Aulicino’s have installed a heat exchanger into the air column that taps into the hot water tank, which operates on propane. Because low-powered fans move the house air constantly, it can be warmed as it passes over the coils. If it has been sunny all day, there may be no need for supplemental heat. The system is so efficient that they only use 400 gallons of propane to heat their 4,000 sf home for the year!

The appliances in most of Adirondack Alternate Energy’s houses are electric, because the combustion byproducts given off by gas stoves and hot water heaters are undesirable in spaces where air movement is so tightly controlled. Because the appliances are also secondary sources of heat, owners of these houses quickly learn to balance laundry washing and drying or bread baking against cloudy days.

It’s these type of behavioral changes that are, perhaps, the greatest benefit to living in a solar home. Because they are dependent on the sun for their warmth, the occupants learn to respect the value of energy in all its forms. While it requires more thought during the designing of the house, ultimately a solar house offers benefits beyond the simple satisfaction of home ownership. What is the value of cheerful rooms filled with light? Of ending the personal fear we have all felt whenever our nation’s energy supplies are threatened? Can any homeowner truly evaluate lifetime savings in fuel costs or the rewards of peace of mind? And the biggest question of all…why aren’t we doing more of this?