Solar Systems
You might be asking - "Why go solar?"
- A Photovoltaic (PV) solar system reduces, or can completely eliminate, the amount of electricity you have to purchase from your utility or electric service provider.
- A PV system can save you money on your electricity bill and act as a hedge against future price increases.
- The electricity generated by your PV system is clean, renewable and reliable.
- You are doing your part every minute of every solar day as you help your community by reducing the electricity demand and providing additional electricity for "the grid" when you generate more than you use during the peak hours of the day (noon to 6), when this demand is at its highest.
Solar Facts - How Solar Works
You've probably been hearing about the "solar revolution" for the last 20 years -- the idea that one day we will all use free electricity from the sun. This is a seductive promise: On a bright, sunny day, the sun shines approximately 1,000 watts of energy per square meter of the planet's surface, and if we could collect all of that energy we could easily power our homes and offices for free.
PV tiles and other forms of solar energy work by converting some of the energy in sunlight into a clean form of electricity. The PV cells consist of a positive and a negative slice of silicon placed under a thin slice of glass. As the photons of the sunlight beat down onto the PV cell they knock the neutrons off the silicon. The negatively charged free electrons are attracted to the silicon but are trapped by the magnetic field that is formed from the opposing fields. Small wires on the silicon catch these electrons and when connected in a circuit an electric current is formed.
This reaction gives Direct Current (DC) electricity, and it must be passed through an inverter to be converted into the Alternating Current (AC) used in our homes and businesses to power electrical items. A small portion of the power generated is lost in the process as the inverter is 95% efficient and there is loss through the cabling connecting the system together that must be accounted for.
General Sizing for Solar Power
In sizing an electric system using solar power, the first two factors we consider are the levels (insolation values) from your area and the daily power consumption of your electrical loads. Orientation of a solar array is best at true south. True south is slightly different than a magnetic reference or compass south. The more an array is situated off of true south, the less the total insolation value. A quick way to determine solar south is to divide the span of time between sunrise and sunset in half. The position of the sun at the resulting time would be true solar south.
The angle of the solar array can be anywhere from your latitude plus 15 degrees to latitude minus 15 degrees for a yearly fixed mount position. Your latitude offers the best year-round position. By biasing the array "latitude plus 15 degrees" you will get slightly more insolation during winter months. A "latitude minus 15 degrees" will bias the array to summer months.
What is insolation?
Insolation, or sunlight intensity, is measured in equivalent full sun hours. One hour of maximum, or 100% sunshine received by a solar panel, equals one equivalent full sun hour. Even though the sun may be above the horizon for 14 hours a day, this may only result in six hours of equivalent full sun.
There are two main reasons. One is reflection due to a high angle of the sun in relationship to your solar array. The second is also due to the high angle and the amount of the earth's atmosphere the light is passing through. When the sun is straight overhead the light is passing through the least amount of atmosphere. Early or late in the day the sunlight is passing through much more of the atmosphere due to its position in the sky. Sun tracking (trackers) devices are available and can help reduce reflectance, but cannot help with the increased atmosphere in the sun's path.
Because of these factors the most productive hours of sunlight are from 9am to 3pm around solar noon (solar south). This is different than 12 noon. Before and after these times power is being produced but at much lower levels. When Renova sizes solar panels for a solar power system, we take these equivalent full sun hour figures per day and average them over a given period.
In most locations in the United States winter produces the least sunlight because of shorter days and increased cloud cover, as well as the sun's lower position in the sky. Usually, we work with a yearly average, a June - July average when insolation is highest, and a December - January average when insolation is lowest.
The diagram above illustrates the path of the sun over varying seasons. When selecting a site for your solar power panels, a spot that is clear of shade from a minimum of 10am to 2pm on December 21st is optimum. Even a limb from a deciduous tree will substantially reduce power output.
Many solar sites are quite uncomplicated in terms of shading and aspect. You may already have a good idea of where the sun appears in the morning and disappears in the evening, as well as how low it swings in the winter sky. If your site is partially shaded, it may be necessary to determine exactly where the best placement of solar panels will be. We will perform a more sophisticated site analysis when we meet.
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