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What Is Photovoltaic Solar Electricity (PV), and How Does it Work In a Home?
Solar electric or photovoltaic (PV) technology converts sunlight directly into electricity. You may be more familiar with PV cells as solar cells that power watches and calculators. But PV can do much more. It can provide electricity for your home and provide the opportunity for you to take advantage of net metering.
Why use PV?
The sun generates enough clean energy in one day to provide a year’s supply of energy for your home. Why not tap into this abundant resource of clean energy? PV preserves the earth’s finite fossil-fuel resources-coal oil, natural gas-and reduces air and noise pollution associated with those energy sources. Recent technological breakthroughs, along with support from government agencies, such as net-metering, have greatly reduced the cost of PV ownership. PV system reliability and durability are outstanding - typical PV systems may last 40 years with minimal maintenance.
How does a solar electricity or “PV” system work?
Photovoltaic, also known as “PV,” produce electricity from the sun. The solar “cell” is the basic building block of PV technology. Solar cells are wired together to form a PV module.
PV systems begin with the solar module. Modules gather solar energy in the form of sunlight and convert it into direct current (DC) electricity. The more sunlight they receive, the more electricity they produce. Solar modules are the heart of the PV system. In essence, they are the power generators.
To convert DC power to alternate current (AC) power, the type of electricity used in your home, a device called an inverter is used. This type of inverter’s location can be in the basement, attic or garage. If an excess of electricity is produced through the PV system, the power will flow back through your meter for distribution back to the CFE power utility’s grid system. This is known as “net metering".
Can I "net meter" solar electricity back to CFE, Mexico’s power company? Yes.
The CFE, based on a Federal law passed in 2007, will give retail credit to solar customers who feed excess electricity back to the utility’s grid. Known as “net metering”, this utility policy is implemented by letting the homeowner’s electric meter spin backwards.
How does Net Metering work?
Thanks to Mexico’s “net metering” law, enacted in 2007, Mexican residents can now use solar power to literally turn back their CFE meter, and sell excess energy production back to their local CFE utility.
Your electric meter spins forward when electricity is flowing from CFE into your home. The meter spins backward when power is flowing from your home back to CFE. That is, if more electricity is generated through a PV system than your home requires, the excess energy flows back to CFE’s electric grid system, which turns your electric meter backwards. At the end of the month, you are billed only for net consumption - the amount of electricity consumed less the amount of electricity distributed back to CFE’s grid.
What happens if the sun doesn’t shine?
Your PV system will continue to produce electricity during cloudy weather, although the total amount will be reduced. Power will automatically be provided through CFE at night or during inclement weather.
Click here to the Insolation Maps Link and find out what´s the average value of total solar energy received in peak sun hours per day on an optimally tilted surface during
the month with the lowest solar radiation.
What does a typical PV panel look like?
A typical PV panel consists of solar cells connected electrically to form a module that can measure two to four feet wide and four to six feet long. Some solar modules look just like traditional roof shingles. Many interconnected PV modules are called an array.
Is my home right for a PV system?
A PV system needs unobstructed access to the sun’s rays for most, or all of the day, throughout the year. PV panels are relatively unaffected by changing weather. In fact, some PV cells actually work better at colder temperatures. PV modules are angled to catch the sun. To maximize the energy production of photovoltaic electricity, PV systems are installed on a southern exposed roof and mounted parallel with the roof at a 21 degree roof pitch with no shading. However, roofs that face east or west may also be acceptable. PV panels should have their surfaces exposed to the sun’s rays for most or all of the day, with minimal or no shadows from trees, chimneys or neighboring buildings between 9 AM and 4 PM.
Home Energy Efficiency and PV
An energy efficient home means you can install less PV. Every dollar on energy efficiency in the home saves $20 on your PV electric panels. To become energy efficient in the home, use compact fluorescent light bulbs, which use 75% less energy than the equivalent incandescent. A 15 watt compact fluorescent will produce as much light as a 60 watt incandescent. Also look for energy saving appliances (clothes washers, refrigerators, room A/C, dishwashers. Refrigerators before 1990 are power hogs! The CFE even has a loan program to buy energy efficient refrigerators, to help you become more energy efficient in the home.
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How does shading affect my PV system?
Proper placement of your Photo Voltaic (PV) system is critical to the success of the PV systems output. Having even one cell in a PV module in the shade, especially during the best sun hours of the day, can decrease the output for the entire module and possibly the entire system.
Since the shaded cell is not producing any moving electrons, it acts like an open circuit to the entire string. This is similar to having one Christmas tree light burned out in a string of lights. No current can flow!
When looking to place your PV system, please watch for any type of shading. Shading can include trees, chimneys, TV antennas / satellite dishes, bovodas of the house.
Step 1- Review your roof for good access to the sun. Does the area for PV system receive full sunlight with no shading?
Step 2- If you have 100% of sunlight on a south facing roof, you have an ideal roof for PV, although east and west facing roofs are very good also. If there is shading on your roof, consult with a person trained on PV.
Can my home accommodate a PV system?
The amount of space needed by a PV system is based on the output of the PV system and the type of PV system installed. Most residential systems require as little as 50 square feet (for a small “starter” system) up to as much as 1,000 square feet for larger systems. A typical two-kilowatt system could occupy approximately 200 square feet (20 square meters). If your location limits the physical size of your system, you may want to install a system that uses more efficient PV modules. Greater efficiency means that the module uses less surface area to convert sunlight into a given amount of electric power.
How much PV will I need?
As a starting point, you might consider how much of your present electricity needs you would like to meet with your PV system. For example, suppose that you would like to meet 50 percent of your electricity needs with your PV system. You could work with your PV provider to examine past electric bills and determine the size of the PV system needed to achieve that goal.
You can contact CFE and request the total electricity usage, measured in kilowatt-hours, for your household over the last 12 months (or consult your electric bills if you save them.). Ask your PV provider how much your new PV system will produce on an annual basis (also measured in kilowatt-hours) and compare that number to your annual electric demand to get an idea of how much you will save.
Calculating Electricity Bill Savings for a Net-Metered PV system
Energy From the PV System
Determine the size of your PV system in kilowatts (KW). This value represents the "kW of PV" input for the equations below.
Based on Central Mexico’s geographic location, and an estimated average of 5.4 hours per day of prime sunshine, the "Energy Production Factor" is 1,971.
To estimate the annual energy produced by your system, use the following equation:
Energy from the PV system = (kW of PV ) x (Energy Production Factor) = kWh/year
Divide this number by twelve if you want to determine your estimated monthly energy reduction.
How much does a PV system cost?
The total cost of a PV system includes the PV system and installation. Your PV system’s cost will depend on a number of factors, including system size and the energy efficiency of your home, whether the home is under construction and whether the PV is integrated into the roof or mounted on top of an existing roof. The cost also varies depending on the PV system rating, size, manufacturer, retailer and installer. Small-scaled PV systems with built-in inverters that produce about 600 watts of power per hour may cost about $7,200. These small systems will offset only a small fraction of your electricity bill. A 1.5 or 2-kilowatt system that will offset the needs of a moderately energy-efficiency home may cost $10-12 per watt ($15,000-$20,000), plus installation. At the high end, a 2.5 to 5-kilowatt system that will completely offset the energy needs of many larger conventional homes may cost ($25,000-$50,000). These prices of course, are just rough estimates, and your costs will depend on your system's configuration, your equipment options and other factors.
In addition, you can take advantage of:
- Net Metering- Homeowners can use solar power to run their CFE meter backwards and sell excess energy production back to the CFE;
- Depreciation- Businesses, including home business, can depreciate 100% of their solar investment in the first year after installation, according to the new Mexican Tax code
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