Project Participants:Tahoe Solar Designs
Pole-mount Solar PV addition
Site characteristics or focus during construction or remodel:
The structure does not enjoy ample sun on the rooftop, but the yard receives full sun for the entire day. The home is situated on a hill and the sloping backyard creates an environment where there are virtually no trees shading the panels. The grid-tied solar electric system was installed as pole-mounts in the backyard. Any amount of shade on the panels can result in a complete loss of power from the panels.
The solar PV electrical system is comprised of 16 120-watt photovoltaic panels and an inverter that is compatible with utility inter-tie. The panels are mounted on two large galvanized steel poles (8 panels on each pole), each controlled by a tracker. The tracker is a motor with a photo eye that senses where the sun is and moves the panels into the optimum position, and in this way, the panels receive direct sun through out the day. The poles were set into concrete in 6’ below ground level. The utility installed a bi-directional meter that separately displays and records the amount of energy provided by the utility and the amount of energy transferred back to the grid by the home.
The solar electricity system ties into the utility grid and relays any excess electricity produced back into the grid in lieu of utilizing batteries for energy storage. This reduces the additional cost of batteries and increases the efficiency at which the panels work. The utility credits the homeowner for any power that is provided to the grid. At the end of each month, the utility issues a bill with a summary of electricity transferred to the grid, and the amount of power provided by the utility. In the spring and summer months the homeowner typically receives a “negative bill,” but in the winter months they typically owe the utility. They participate in a program called “net metering,” which means that electricity is traded back and forth with the utility over the course of a year, and the account is settled at the end of that term. The annual bill for this home is usually around $75, but this amount includes a $54 connection fee that is charged to each customer who is connected to the utility in this manner. The system produces an average of 2,500 kilowatts per year, fairly close to the total power usage for the home.
Energy Efficiency and Renewable Energy Measures Used in Project:
The homeowners have continued to lower their energy usage over the course of time. They are in the middle of several major and minor efficiency upgrades that they believe will result in complete freedom from utility bills:
The first step in becoming more energy efficient was to replace incandescent light bulbs with compact fluorescent bulbs. Although fluorescent bulbs are more expensive than incandescent, they last considerably longer and use approximately 75% less energy for the same amount of light.
Additionally, they discovered they employed many devices that consume a “phantom load.” A phantom load occurs when a device uses energy even when off. Products that create a phantom load include microwave ovens, televisions, stereo, computers, printers, and so on that are consuming electricity 24/7. As a means of eliminating this unnecessary power drain, they purchased power strips and plugged the devices in to them, simply powering off the strips when the appliances are not in use, and flipping a switch to bring them back online.
They are also in the midst of the next phase to make their home more energy efficient. They are adding 3.5” of insulation to the exterior walls and replacing old windows with energy efficient windows and blinds.
Space and Water Heating Systems:
The final phase of the project will add solar hot water for both domestic hot water and radiant heating. Because they have forced air (using natural gas), and the fan that blows the air is the largest electricity user, they have a reasonable expectation that a solar hot water heating system will significantly reduce electricity use in the winter, as well as natural gas consumption.
Size: 2,000 sq. ft.
DESIGNER: Tahoe Solar Designs
DATE OF CONSTRUCTION: 2001
BUILDER: Tahoe Solar Designs