About Solar Power
Electricity is a vital part of our daily lives. Solar power is a non-polluting, alternative energy source that can make a major contribution to reducing greenhouse gas emissions, reducing our dependence on unstable energy sources, and providing for a sustainable future. When combined with energy conservation measures, an alternative energy system like a solar power system from Run on Sun® leads to a dramatic reduction in utility costs for the next twenty-five years.
Solar Power and Solar Energy
Although the terms are often used interchangeably, there is a difference between solar power and solar energy.
Power is the ability to perform useful work — the power rating of a solar power system reflects how much work that system can do for your home or business by powering lights, computers, HVAC equipment and so on. Power, whether from the grid or a solar power system, is measured in Watts, or more typically, in thousands of Watts, referred to as a kilowatt (kW).
Solar energy, on the other hand, reflects useful work done over a period of time. For example, if you turn on ten, old-fashioned incandescent 100 Watt light bulbs, they require 1,000 Watts of power (1 kilowatt, or 1 kW) to light them up. If you then leave those ten lights turned on for an hour, they will consume 1,000 Watt-hours (or 1 kilowatt hour, 1 kWh) of energy. Electrical bills for residential customers are generally calculated based on consumption as measured in kilowatt hours over the billing period. Commercial customers often pay for both consumption (in kWh) as well as peak power demand (peak kW). A solar power system can help to reduce both of these factors. Solar power systems are typically rated in terms of their peak DC power, as in a 4.5 kW system.
Photovoltaic Solar Cells (PV cells) and Solar Panels
All solar power systems start with a photovoltaic (PV) cell. A PV cell is a device that is able to take solar power in the form of photons and convert that energy into direct current (DC) electricity. In a solar panel, a number of solar cells are mechanically combined and wired together to produce an integrated solar panel that will have a rated power output (called the nameplate power) at a certain voltage and current. For example, a Sanyo 210 watt solar panel consists of 72 solar cells assembled into a solar panel that is 31.4 x 62.2 inches, weighs 35.3 pounds, and produces 210 watts at 41.3 volts and 5.09 amps.
Sanyo solar panel - note the individual solar cells
Solar Panel Efficiency:
Nameplate (STC) Power Versus PTC Power
All solar panels have a nameplate power rating that is printed on the panel itself – in much the same way that an incandescent light bulb has its wattage rating printed on the glass. For a solar panel, the nameplate rating is the power output of the panel under what are called Standard Test Conditions (STC). While nameplate power provides a consistent standard for all manufacturers to use, it is a poor predictor of how a solar panel will actually perform in use.
In California, all solar panels that are certified by the California Energy Commission to be used in a solar power system receiving a rebate from the local utility must also indicate their power under a second set of test conditions, known as the PTC rating (or PTC power) of the panel. Invariably these values are lower than the nameplate rating. That means that two different panels that are both nameplate rated at 210 watts, might (and likely will) have very different PTC values. Because rebates are paid based on PTC values, consumers should be certain to find out the PTC rating of the panels being proposed for their system when comparing bids.
Solar Array
In an actual system, multiple solar panels will be combined together into a solar array. Solar arrays vary greatly in size, ranging from a single solar panel to power a roadside call box to tens of thousands of solar panels producing millions of watts in a utility-scale project.
No matter how many solar panels go into the array, the DC output from the solar array must be converted to alternating current (AC) before it can be used to offset power coming from the electric utility grid.
Inverters
SMA 5000 String Inverter
Performing the conversion from DC to AC is the job of the inverter.
Inverters range from micro-inverters (that are paired with just one solar panel), to string inverters that may handle several strings of solar panels wired together, to central inverters that can handle as much as a million watts of solar power.
Modern grid-tied inverters must also be "smart" enough to shut themselves off if the grid goes down. While that might seem unfortunate, it is required for the protection of utility personnel who might need to work on power lines near where a solar power system is installed. If the solar power system continued to provide power to its portion of the grid (an energy "island") it could pose a serious safety hazard to unwary workers. Fortunately, inverters are also smart enough to turn themselves back online once the grid returns to normal operation.
The resulting clean solar power is then either used in the home or business or delivered to the electric utility through the utility meter, causing the meter to "spin backwards."
Net Metering for SolarIn a grid-tied system, power from the utility's power grid is provided at night and on cloudy days when electricity demand in the home or business exceeds the power generated by the system. During the daytime when electricity demand is less than the power generated by the solar power system, the excess electricity is delivered to the utility grid thus "spinning the meter backwards." This is the concept of "net metering" whereby the excess electricity you generate throughout the year offsets the electricity you consume. |
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A recent change to California law now requires utilities to pay owners of solar power systems for any excess energy that they produce. While most solar power system owners will not be net energy producers, this change in the law is an important step in making net metering agreements more equitable for system owners.
Interconnection Agreement & Rebate Processing for Solar Power Systems
Your utility will require an interconnection and net metering agreement. Run on Sun will handle all of the paperwork needed to get these agreements in place — all you need to do is sign. We will also handle all of the paperwork needed to get you the best rebate possible.
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