NCSU Solar House Design

The NCSU Solar House was built incorporating readily available solar and energy efficient technologies to serve three primary purposes:


  • Demonstration – To demonstrate how solar and energy efficient technologies can be effectively incorporated into an attractive, livable and affordable house of traditional design and materials typical of the region.
  • Education – To serve as an educational resource and laboratory for students, clubs, professional organizations and the general public; to educate the public on the benefits of living in a solar and energy efficient house.
  • Research – To build a fully instrumented solar research facility to evaluate the performance of various passive and energy efficient technologies and to serve as a research laboratory for graduate students in engineering, architecture, interior design and other related disciplines.


Key Features

  • A centrally located SUNSPACE collects, stores and distributes solar energy for heating of the house.
  • Two TROMBE WALLS collect, store and distribute solar energy to the adjacent rooms.
  • An active SOLAR HOT WATER HEATING system provides for most of the hot water needs of the house.
  • A roof-mounted PHOTOVOLTAIC (PV) System (rated at 5.4 KWh DC) generates electricity from the sun.
  • Two Solar LIGHT TUBES provide natural daylighting to portions of the house.
  • A WATER SOURCE, GEOTHERMAL HEAT PUMP coupled to a horizontal, closed-loop heat exchanger in the backyard provides cooling and additional heating to the house.
  • EARTH BERMING for the 1st story North and West walls reduces winter heat loss and summer heat gain.
  • Natural and man-made architectural devices provide shading to the South side of the house in the summer.
  • ENERGY EFFICIENT appliances and lighting reduce energy usage of the house.


House Data

  • 1700 sq ft in the main living space with an additional 320 sq ft in the Sunspace.
  • 3 Bedrooms, 2 bathrooms, kitchen, living/dining room, den, utility room, Sunspace and a conference room.
  • 232 sq ft of glazing (glass) on the South wall of the Sunspace. 128 sq ft of glazing on the Trombe walls (combined).
  • 29 sq ft of direct solar gain windows.


Living /Dining Room

  • French doors can be used to control the flow of air between this space and the Sunspace.
  • Open stairwell on the northwest corner allows air from the Sunspace that has released its energy to the house to sink and return to the Sunspace through the lower level French Doors.
  • 14” Solar Lighting fixture (equipped with dimmer and fluorescent light bulb) provides natural light.
  • Fluorescent lights throughout the house use approximately 75% less energy than incandescent bulbs.
  • North wall windows are small and have operable insulating shutters to minimize heat loss.
  • The Fireplace draws combustion air from the attic and can be used to provide additional heat as needed.



  • Remodeled in 2008; uses wood from North Carolina for the cabinets and granite from Mount Airy for the countertops.
  • Energy-Star rated appliances.
  • Interior window can be opened to control heated air flow from the Sunspace.


Master Bedroom suite

  • 10” Solar Lighting fixture (equipped with fluorescent light bulb) provides natural light to the closet.
  • Casement windows seal better than double-hung windows; double pane windows lose less heat than single pane windows.
  • Plantation shutters minimize heat loss in winter and heat gain in the summer.
  • No windows on the East wall to reduce heat loss.
  • Ceiling fan moves air to increase comfort and allow for a higher thermostat setting in the summer.
  • Attic access has a second sealed door above the pull-down stairs to reduce heat loss through this opening.



  • The Sunspace provides 85% of the energy used to heat the house. The living spaces of the house wrap around the sunspace in a “U” shape to connect to the main source of passive heat.
  • Sunlight comes through the windows (glazing) in the winter and is converted to infrared wavelengths (heat) by the brick, tile and concrete (thermal mass). Three square feet of thermal mass are provided for each square foot of glazing. Medium to dark surfaces are used to enhance the heat absorption capability of the thermal mass.
  • Heat is transferred by conduction through the bricks. This process takes several hours, providing heat to the house in the evening when it is needed most. The slow process of heat transfer into and out of the thermal mass also serves to stabilize temperatures in the house.
  • Heat is also transferred by hot air that enters the house from the Sunspace through the open upper level French Doors. The air releases its energy to the cooler house, becomes denser and sinks down the Northwest stairwell and returns to the sunspace through the lower level French Doors for reheating (Natural Convection).
  • French Doors are typically left open throughout the year except for the hottest summer months. These doors are weather-stripped with spring bronze material to allow the Sunspace to be sealed off from the rest of the house if necessary.
  • In the summer, the upper level windows are shaded by a 38” overhang; the lower level windows are shaded by a Kiwi plant that grows on the attached trellis. Additional shading can be provided by remote controlled shades on all Sunspace windows.
  • A whole house attic fan removes additional heat from the Sunspace and provides additional ventilation in the summer when used in conjunction with the lower level vent windows.
  • The Thermal Storage Floor provides additional heat removal capability to the Sunspace. It consists of a hollow core, precast concrete material filled with small rocks that is located between the upper and lower levels. This floor is connected to the top of the Sunspace via ducting that runs through the attic and inside the North wall of the house. Heat is drawn from the top of the Sunspace using small fans and is delivered to the rock-filled hollow core concrete which removes the heat as the air returns to the Sunspace.



  • Domestic Solar Hot Water Heater would provide about 65-70% of the hot water needs of a family living in the house
    • The remaining energy required comes from electric heaters in the hot water tank.
    • This system uses Glycol (anti-freeze) to transfer solar heat between the collector on the roof and the water in the tank. A heat exchanger is located within the tank. Use of glycol ensures that the fluid within the collector on the roof will not freeze in cold weather, preventing damage to the collector.
  • A water-source geothermal heat pump provides cooling and additional heating to the house. It is coupled to a horizontal, closed-loop heat exchanger buried 4 feet deep in the backyard. The water in this cast-iron piping exchanges heat with the ground (which remains at moderate temperatures at that depth throughout the year) as needed for efficient operation of the heat pump. Electricity to run the heat pump costs about $150 total for the winter heating season and about $300 total for the summer cooling season.


Utility Room

  • Inverter converts DC power from the solar PV panels into AC power for use in the house and for connection to the utility power grid.
  • This is the location for the storage batteries for the previous PV array that was installed from 1992-2008.



  • South facing roof slope of 35 degrees optimizes the annual solar collection of roof mounted collectors (slope matches latitude).
  • The 38” roof overhang and the trellis with Kiwi plant provide summer shading to the Sunspace and Trombe walls.
  • The single panel on the side roof is for the solar hot water heater, the large array on the center roof is the Photovoltaic array.
  • Deciduous plants on the South side provide shade in the summer while allowing sunlight through in the winter.
  • Water Catch barrel collects water from gutters on the house. Pump is used to deliver the collected water to the garden through a hose.
  • Solar powered motion sensing LED and Halogen security lights are used on the exterior of the house. The cell charges the system’s battery by day and the battery powers the light at night. Batteries are large enough to support two weeks of operation without sunlight.
  • Trombe walls
    • Two 12” thick Trombe walls collect, store and transfer solar heat to the two bedrooms on the lower level. One wall has a concrete block thermal mass, the other wall uses brick for the thermal mass.
    • High and low vents on the East (brick) Trombe wall allow for a natural convection flow of heated air from the exterior of the thermal mass into the room.
    • Interior surfaces of Trombe walls should be left uncovered to maximize radiant heat transfer.
    • Windows in the center of the Trombe walls reduce heating effectiveness but provide natural lighting to the rooms and a visual connection with the outdoors.