The Beach's home is a 1000 sq. ft. home in the Denver metro area. It has an asphalt shingle hip roof, the front side of which faces south with a slope of about 22 degrees. Starfire Energy designed and installed a 1.6 kW solar electricity array for its south facing roof. The Beach's use an average of about 6.5 kWh of electricity each day. Accounting for the mild shading from the nearby trees, this installation is projected to produce about 80% of the household's annual electricity consumption each year. The Beach's plan to add insulation and upgrade some electrical appliances to reduce their electricity usage. Once those improvements are complete, their photovoltaic installation should produce as much electricity as they use each year. The photo (click on it to see a larger image) shows the photovoltaic installation just after it was installed in October 2007.

Starfire Energy monitor's this array's performance via a web connection. Web monitoring of solar electric system production isn't necessary and most people do not have it installed on their systems, but we find it useful to demonstrate system performance to people who are interested in solar electric systems. It also helps to satisfy our "inner geek". We can install this type of monitoring on new or existing solar electric systems. The plot to the right (click on it for a larger image) shows the system's daily energy production for the past week. On a sunny day in December, the array can produce 3.5 - 4.0 kWh of electricity. In March, that increases to 8.5-9.0 kWh. In the winter, snow covering the array can reduce its production to nearly zero, but it melts off quickly when the sun starts shining again. A snowfall of up to 2" will usually melt off after one day of sunshine.

Starfire Energy can also install equipment to monitor a how much electricity a home draws from the grid and how much electricity it sends to the grid. The plot to the right (click it to see a larger image) shows the following data for the Beach's home today:

• DC solar power produced by the solar array (red line)
• AC solar power produced by the inverter (blue line)
• Solar power sent to the grid (green line)
• Utility power consumed from the grid (orange line)

The difference between the DC solar power and the AC solar power is due to power losses in the inverter. The difference between the AC solar power and the solar power sent to the grid is due to loads in the home consuming solar electricity. The regular up-and-down cycles in the power from the grid at night are from their refrigerator's compressor cycling on and off. In the winter months, an increase is seen at about 4:30am when the programmable thermostat turns on their furnace to warm the house before they wake up. Large spikes in consumption from the grid (power consumption in excess of 2 kW) are generally from running an electric clothes drier. In the summer, the Beach's use a solar clothes drier (one of the most common forms of solar power, also known as a clothesline) to largely eliminate that electricity usage.

Since the Beach's home is grid-tied and net-metered, their solar electric system runs the meter backwards when it produces more electricity than they use that day. The plot to the right (click on it for a larger image) shows the amounts of utility electricity taken from the grid (red bar) and solar electricity sent to the grid (blue bar) each day for the past week. On days when the blue bar is larger than the red bar, their system produced more electricity than they used that day. When that happens, their electric meter reading is smaller at the end of the day than it was at the beginning of the day. If their electric meter reading at the end of the year is smaller than it was at the beginning of the year, Xcel will pay them for the net production at the wholesale electricity price (about half of the retail electricity price).