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Have you ever felt warm water trickle out of a garden hose that’s been sitting in the sun? If so, then you’ve witnessed solar water heating in action. Now imagine that same water moving slowly though a system specifically designed to heat and store water – that is the essence of solar thermal water heating. People have for centuries used water heated by the sun and stored it for bathing, hand washing, cleaning clothes, heating homes and much more. The solar thermal systems used today combine the most efficient techniques for capturing the sun’s heat with modern plumbing systems to produce cost effective hot water and reduce the need for gas or electricity to heat water.
Solar thermal hot water systems vary in their details, but they all do the same basic things - gather heat in a solar collector, transfer the heat directly or indirectly to the water supply, and store the heated water until it’s used. These systems use relatively simple, time-tested technology, which is one reason they are a best bet in renewable energy. Closed loop antifreeze systems are the most popular and versatile type of solar thermal system installed worldwide. The following are the basic system components:
- one or more solar collectors
- a hot-water storage tank with an internal heat exchanger
- solar fluid (usually a solution of water and non-toxic propylene glycol anti-freeze)
- a controller, valves, gauges, insulated piping, circulation pumps, and an expansion tank
The piping loops from the collector panels to the heat exchanger and back again. This closed loop keeps the antifreeze solution (solar fluid) inside the collectors and piping at all times. Whenever the sun shines on the collectors the circulating pump comes on and the solar fluid circulates within the closed loop. The fluid gets hot inside the collectors and travels through the piping to the heat exchanger. The heat exchanger transfers the heat from the fluid to the water inside the storage tank, which stores the heated water for your use. As the fluid heats, it expands, so the expansion tank is included to relieve pressure in the system. When the sun is not shining, the circulating pump simply turns off, and the fluid stops circulating.
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1. SOLAR PHOTOVOLTAIC (PV) PANELS - An array of Solar Modules convert the sunlight into Direct Current (DC) electricity. This power is sent to the inverter.
2. INVERTER - The inverter has several important jobs:
- It converts the DC power form the solar panels into Alternating Current (AC) power, which is the standard form of power for homes and businesses.
- It matches the AC frequency to what is coming from the utility grid. Inverters must meet exacting standards in order to be approved for use.
- It 'watches' the utility grid so that it can shut down, immediately, if the utility grid shuts down. This way, if a storm or accident breaks an overhead electrical wire then your solar system will not send power into the electrical system and endanger people. Photovoltaic solar systems will only keep producing power during a power failure if you have batteries attached to the system.
- The Inverter sends the electricity to the main circuit breaker panel in the building. From there the electricity can power the building or, if there is more electricity being generated than is being used, it is fed back through the meter, back feeding the utility grid.
3. UTILITY METER – The ability to spin the meter backwards when generating excess power and forwards when requiring additional power is called Net-Metering. In Pennsylvania, utilities must offer Net-Metering to residential customers that generate electricity with systems up to 50 kilowatts (kW) in capacity and nonresidential customers with systems up to three megawatts (MW) in capacity.
4. THE UTILITY GRID - At the end of the month, if the customer uses more electricity than is generated, the customer pays the utility on the net kilowatt-hours used at the regular retail rate. If the customer generates more electricity than is used, the utility pays the customer for the net kilowatt-hours produced at the wholesale power rate.
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