Believe it or not, solar energy is NOT a modern invention. Actually, it has been around for thousands of years. Basically, it entails gathering energy from the Sun and converting it into a form of energy we can utilize. Today, the converted energy takes on two main forms, Solar Electric (Photovoltaic) and Solar Thermal.
Solar Electric
Solar Electric or Photovoltaic (PV) systems allow you to generate electricity by absorbing photons from the Sun's light. PV modules placed in direct sunlight are used to accept the Sun's photon particles, in turn creating energy in the form of moving electrons (direct current, DC).PV modules, or "solar panels" as they are usually called, are wired together in a series circuit (or "string"), similar to the way Christmas lights are wired. It is done this way because most inverters require quite a high voltage to allow them to work at optimal efficiency, and voltage is additive in a series circuit.
Solar panels can be mounted anywhere that sufficient sunlight hours are available. It is imperative that you mount the solar array in an area that does not have any shadows throughout the whole day. PV systems are EXTREMELY susceptible to shading issues. Referring to the previous analogy, imagine what happens when a single Christmas light bulb goes out. The whole string is knocked out. The same concept is applicable to PV modules and shadows. When even a small portion of a single module becomes shaded, there is a risk that energy production of the whole string of modules will be knocked out, severely compromising your system output (and potentially also the life expectancy of the modules!). Also, keep in mind that as the Sun moves across the sky throughout the day, shadows tend to "walk" across the roof and, therefore, should be considered during the system planning process. Remember, trees grow and solar arrays and wind towers do not--at least not in the same sense.
An Inverter is a key electronic component in Grid-tied (PV and Wind) electric systems. Inverters are devices that accept the raw DC electricity from the PV modules (or wind turbine) and instantaneously invert it into AC, or alternating current. The majority of electric systems in the United States are equipped to handle only AC and this is the type of energy you'd normally purchase from the utility company to run your home or business.The inverter(s) works in parallel with the utility company, LIPA for example. When there is sufficient sunlight to generate solar electricity, it begins to work its magic by artificially trying to raise the voltage of the power in your home (ever so slightly). If you are inside the building consuming electricity, the solar energy will be used first to power your vacuum, television, computer, etc. The moment you stop using electricity, your house voltage will rise slightly because there is decreased load. The energy will begin to flow backwards through your service panel, through the utility meter (causing it to spin backwards!), and out onto the grid where it is available for use by another utility customer, maybe your neighbor.
In New York, we have the ability to Net Meter. This is when the utility customer is credited for every unused Kilowatt Hour (kWh) generated by their renewable energy system. The customer is permitted to claim these "energy credits" free of charge whenever their system is not producing, such as at night. We like to refer to Net Metering as a 100% efficient "battery," an idealistic reference since batteries are never 100% efficient.
To maximize energy harvest, solar conversion equipment in the Northern Hemisphere must be positioned to face Solar South. For a fixed array, this is the optimal year-round Azimuth (heading) to receive maximal daily sunlight hours. This does not necessarily mean you cannot install a workable East- or West-facing system; it just means you will compromise solar capture efficiency with every degree deviation. (Don't face North.)
Tilt angle, or elevation, of the collector is important to optimize seasonal production. In the Winter, the Sun angle decreases and the days grow shorter, with the shortest amount of daylight and the lowest angle of Sun available on the Winter Solstice. Alternatively, the days leading up to the Summer Solstice progressively offer the greatest number of sunlight hours daily and have the highest Sun angles. The optimal tilt angle for a fixed, Grid-connected array is more or less equal to your latitude, which happens to be 40.7 degrees for Long Island.The ideal system setup would involve being able to follow the Sun throughout its daily path AND ALSO its seasonal position in the sky. Tracking equipment is necessary to accomplish this but generally increases the cost of the whole system. It is the most efficient system but the mechanical moving parts require periodic maintenance, adding dollars to the price tag. One who is most concerned with efficiency, for instance an Off-grid customer, will likely choose a system with a tracker.
For one who is more concerned with cost than system efficiency, such as a Grid-connected customer, a fixed array without a tracker will likely be sufficient. This type of system can harvest enough energy and will carry a significantly lower price tag. A fixed array configuration requires the least amount of maintenance and has the fastest return on investment (ROI).
Solar Thermal
Solar Thermal is the idea of extracting the Sun's thermal energy (infrared light rays) and using it to heat a liquid or a solid for the purpose of heat transfer or storage. We can directly utilize thermal energy to heat water for use in a standard home, for example. This is accomplished by passing a heat transfer fluid such as water or glycol through a solar collector which is typically mounted in direct sunlight on the roof of a home or business.There are many variations in how these systems are designed. The collectors can also be mounted on the ground or an auxiliary structure. Heat is transferred through a heat exchanger and stored in an insulated water tank for later use, like a nighttime shower. These systems are typically plumbed in series with your conventional water heater so that you can retain the ability to make hot water when the sun is not available. Already many people enjoy this investment because solar thermal systems have a very fast Return on Investment (ROI). As the price of fossil fuels continue to rise, the systems will become even more attractive. Solar Thermal is often referred to as DHW, or Domestic Hot Water.
DHW systems have the most profound impact on energy savings of all renewable technologies because solar thermal has an inherently high conversion efficiency (BTU conversion efficiency).
No comments:
Post a Comment