SOLAR PROJECT
Nevada's First Net-Metered Photovoltaic Tract Home Uses
ENERCHRON®!
The first total electric bill for this home in the month of October 1997 (16 days of billing, no PV input), was only $11.00!
When reviewing this site what is of prime importance to remember is the approach which was taken in the design of this home. The success of this project is based on implementing all of the variables which would create the foundation for a sustainable design.
For this site, a rooftop photovoltaic system made sense due to site location.
Please keep in mind that in different locations, which may have the resources of wind or water, those types of electricity generators should also be considered. The house is intended to demonstrate how much can be accomplished toward energy efficiency and the use of solar energy, and the enhancement of occupant comfort, under circumstances in which the
sitting and orientation do not "classically" support passive solar, and according to financial conditions appropriate to those who must live within tract home budgets, including no air conditioning.
The house appears to be a remarkable success in achieving all goals. Of particular note is that each measure made to improve efficiency has also enhanced the quality and the livability of the house for the owner/client.
The coating used for the house, both exterior and interior, is a full spectrum energy repelling coating
(ENERCHRON® V40, by Helios Energy Products, Inc.), to further promote summer cooling and winter heating, especially with the large exposed west-facing surface, as well as to enhance interior lighting and
day lighting efficiency.
To reduce maintenance costs, a thicker coating (6 mils DFT) was applied than the tract-builder standard.
The house has an elongated plan, with the main axis oriented east-west, precluding useful coupling of passive solar gain to the house interior, but maximizing the view toward the Sierra mountains, a situation that is very
typical of the Minden/Gardnerville area.
The decision was therefore made to slide the garage around to the south end of the house, to protect that end from excessive summer heating, and to provide a roof surface which could be adapted to a south-facing slope.
The immediately striking aspect of that decision is that one is not greeted by a huge garage instead of a house front.
It looks like a house, not a garage. A window was installed in the south side of the garage to warm it passively in the winter, helping to reduce heat loss from the house into the garage.
The envelope has been upgraded (a tract builder option) to 2x6 studs with R-19 insulation.
The under floor insulation is R-19, and the (blown-in) attic insulation is in excess of R-30.
The garage is fully insulated, including an insulated garage door, to prevent heat-buildup at the south end of the
house and to enhance the usability of the garage interior.
Low-e glazing was selected to enhance thermal efficiency for both summer and
winter. Additionally, a low-cost owner decision was to install radiant barrier material below all attic ceiling surfaces, in both the house and the garage, for improved summer comfort and efficiency.
Additional soffit vents were provided to enhance the movement of air through the attic. When it was noticed that the builder framed over the attic exhaust vent at one end, the owner added a solar-powered attic fan at the peak in the center, to further promote cooling/ventilation in summer months.
To enhance heating efficiency in the winter, a sealed fireplace alternative with 100% outside air intake was selected.
Interior Design, Day lighting and Electric Lighting
The open plan of the interior promotes air distribution to provide for distribution of heat gains which results in temperature consistency. Ceiling
fans in the living room and both bedrooms provide for cooling comfort through air movement. The interior was designed to promote
day lighting, so that the heating impact of electric lights would not be needed during daylight hours.
Window shading was selected to control sun-glare and heat-gain on the east and west sides of the
house and to provide enhanced thermal efficiency during hot and cold seasons, but with sufficient translucence and controllability to allow for bright interiors.
The ENERCHRON® V40 coating on the interior enhances reflective efficiency, promoting improved distribution of
day lighting throughout the interior, while also enhancing brightness at lower electric lighting levels (wattage).
Incandescent-colored fluorescent and compact fluorescent lights were used throughout, all with electronic ballasting for instant-on and flicker-free operation.
The fluorescent pendant lamps hanging above both dining areas, originally stock items from Home Depot, were specially adapted for this home by
the Lutron Company to demonstrate full fluorescent dimming capability.
The compact fluorescent down lighting in the kitchen and over the fireplace wall are from the Iris lighting line and are courtesy of Cooper Lighting for this home.
The down lights will shortly be retrofitted with dimming ballasts for full proportional dimming control, demonstrating dimming capability of compact fluorescents now on the market.
The only fully interior room without access to daylight was
day lit anyway by the installation of a
Solatube®, bringing sunlight from a roof reflector into the bathroom. The security light mounted over the garage is photovoltaic powered, to provide security even during power outages.
Rooftop Photovoltaic System Rationale, Description and Metering
All thermal needs for the house are met by on-site combustion of natural
gas, so that electricity is used only where it is absolutely essential, for lighting, electric motors, and electric appliances.
With the selection of very energy efficient appliances and motors, and all fluorescent lighting, it is anticipated that the house electricity needs could be met on an annualized basis by a rooftop (PV) solar electric system with a capacity of somewhere between 1 and 1.5 kilowatts (1,000 to 1,500 watts).
Nevada recently passed, and the Governor signed, a "net metering" law, which permits homeowners to bring the power from their own rooftop solar electric generators directly into the house on their own side of the meter, thereby displacing electricity effectively at the full retail value of each displaced kWh.
Any excess power generated over a long averaged period (in this case, one year), however, would not require any payment to the homeowner by the utility.
The economic rationale, therefore, is to select a somewhat undersized rooftop system, where the averaged power output over a year is somewhat less than total homeowner need, so that all rooftop generated power produces effective cost-reductions for the homeowner.
In this case, it suggests the less than 1 kW size that is installed on the garage roof of the house.
(That was, fortuitously, also all of the area with appropriate slope and orientation available for mounting the PV system.)
The PV system is the Sunslate system of PV roof tiles.
The area of approximately 100 square feet is rated at about 800 watts of output
capacity under full sun.
The cells are polycrystalline cells by
Solarex, assembled into the tiles and installed by Atlantis. An inverter is used to change the DC output from the PV system to 110 volt AC for the house.
The metering and interconnection to the grid has been provided courtesy of Sierra Pacific Power, which has cooperated in an exemplary way throughout this project.
To help really understand what the PV system is doing, and its benefits to both the homeowner and the utility, Sierra Pacific has installed metering with 15-minute accumulated sampling intervals that will show:
(1) Electric power output from the rooftop PV system;
(2) Net flow of power to the house from the utility;
(3) Net flow of power to the utility from the house rooftop.
Usage of natural gas for all other purposes will also be monitored, to provide a total energy consumption appraisal of the house design features.
