Solar FAQs

How Does Solar Thermal Water Heating Work?

Solar Hot Water

For solar hot water systems, flat-plate solar collectors are typically installed facing south on a rooftop.

The shallow water of a lake is usually warmer than the deep water. That's because the sunlight can heat the lake bottom in the shallow areas, which in turn, heats the water. It's nature's way of solar water heating. The sun can be used in basically the same way to heat water used in buildings and swimming pools.

Most solar water heating systems for buildings have two main parts: a solar collector and a storage tank. The most common collector is called a flat-plate collector. Mounted on the roof, it consists of a thin, flat, rectangular box with a transparent cover that faces the sun. Small tubes run through the box and carry the fluid — either water or other fluid, such as an antifreeze solution — to be heated. The tubes are attached to an absorber plate, which is painted black to absorb the heat. As heat builds up in the collector, it heats the fluid passing through the tubes.

The storage tank then holds the hot liquid. It can be just a modified water heater, but it is usually larger and very well-insulated. Systems that use fluids other than water usually heat the water by passing it through a coil of tubing in the tank, which is full of hot fluid.

Solar water heating systems can be either active or passive, but the most common are active systems. Active systems rely on pumps to move the liquid between the collector and the storage tank, while passive systems rely on gravity and the tendency for water to naturally circulate as it is heated.

Swimming pool systems are simpler. The pool's filter pump is used to pump the water through a solar collector, which is usually made of black plastic or rubber. And of course, the pool stores the hot water.

How are Solar Panels made?

Crystal Growing

The magic starts with about 250 pounds of polysilicon rocks carefully stacked in a quartz crucible. The only other ingredient is a silicon disk impregnated with a tiny amount of boron. The addition of the oron dopant ensures that the resulting crystal will bear a positive potential electrical orientation. The crucible is encased within thick walls of insulating graphite and locked inside a cylindrical furnace

As the crystal-growing furnace heats up to temperatures ranging around 2,500 degrees Fahrenheit, its silicon contents melt into a shimmering slurry. Once computerized monitors register the right temperature and atmospheric conditions, the alchemy begins. A silicon seed crystal, hung from a narrow cable attached to a rotary device atop the furnace, is slowly lowered into the melt.

The crucible starts to turn, and the seed crystal begins to rotate in the opposite direction. The silicon melt freezes onto the seed crystal, matching the seed’s crystalline structure. The crystal grows, the cable and seed slowly ascend, and the crystal elongates at a controlled width. As the growth depletes the silicon slurry, the crucible also rises.

Flash forward about 2.5 days since the crucible was charged with polysilicon: After hours of cooling to about 300 degrees Fahrenheit, the furnace hood and shaft lift away from the crucible encasement, slowly swing to one side and reveal a completed cylindrical crystal, ready to move to the second step and next production room.


A silicon crystal must change shape several times before it winds up as the precisely calibrated wafers that form the foundations of photovoltaic cells.

First, a saw cuts off the crystal’s so-called top and tail, so that a crystal of uniform width remains. Typically, wafering saws draw thin wire bearing a liquid abrasive across the crystal’s surface. (Below, a machine mounted with a giant donutlike steel blade does the cutting.) Wire saws also cut the crystal into ingots measuring 2 feet or less. Steel holders are mounted on the ends of these ingots for the next step.

Mounted ingots are placed standing on end in a rack bearing 16 at a time inside another wireslicing machine. There, wire running in a lattice configuration descends on the ingots to shear off four rounded segments, leaving flat sides. The result: The ingots now have a square crosssection, except for still-rounded corners.

The next wire saw is more intricate yet. A wire winding hundreds of times between two cylindrical drums forms a web of parallel, tightly spaced segments. As the wire unspools through the machine, ingots mounted sideways on glass and metal holders are pressed two at a time through the wire web, slicing them into the thickness of slim business cards. Each millimeter of crystal yields about 21/2 wafers. Detached from their holders, the wafers are loaded into carriers, or boats, for transport to the next step.

Solar cell production

Converting wafers into cells
At this point, a wafer is no more capable of producing electricity than a sliver of river rock. The wafer is the main building block of a PV cell, but so far its only notable characteristics are its crystal structure and positive potential orientation. All of that changes in the third, multistep, cell-production phase of PV manufacturing.

In the only phase requiring a designated clean room, a series of intricate chemical and heat treatments converts the blank, grey wafers into productive, blue cells. A so-called texture etch, for instance, removes a tiny layer of silicon, relying on the underlying crystal structure to reveal an irregular pattern of pyramids. The surface of pyramids – so small they’re invisible to the naked eye – absorbs more light.

Next, wafers are moved in cartridges into long, cylindrical, ovenlike chambers in which phosphorus is diffused into a thin layer of the wafer surface. The molecular-level impregnation occurs as the wafer surface is exposed to phosphorus gas at a high heat, a step that gives the surface a negative potential electrical orientation. The combination of that layer and the boron-doped layer below creates a positive-negative, or P/N, junction – a critical partition in the functioning of a PV cell.

Coloring and Printing
The burgeoning, still-grey cells move in trays into heavy vacuum chambers where blue-purple silicon nitride is deposited onto their tops. The coating with silicon nitride – yet another member of the silicon family of materials – is designed to reduce reflection even further in the energy-dense blue end of the light spectrum. It leaves the cells with their final, dark color. Now, the cells can optimally gather photons and produce electricity. They lack, however, any mechanism to collect and forward the power. So, in a series of silkscreen- like steps, metals are printed on both sides of the cell, adding pin-stripe "fingers" and bus-bar circuitry. A functioning cell is born – only sunshine needed.

Solar panel assembly

Stringing cells into solar panels
Each phase of production depends on processes with flavors all their own. Careful control of heating and cooling dominates crystal growing. Wafering employs abrasion and cutting. Cell production concentrates on chemistry. Any factory process would be incomplete without a final assembly step, and in PV such a step is known as moduling.

At SolarWorld, module manufacturing is a highly automated process, relying on robust steel robotics to undertake the increasingly heavy lifting of assembling lightweight PV cells into modules weighing around 45 pounds apiece. Each robotic tool works within a safety fence that, by design, excludes people. First, cells are soldered together into strings of 10, using an over-under-over-under pattern of metal connectors to link the cells. Six strings are laid out to form a rectangular matrix of 60 cells. Each matrix is laminated onto glass.

To become a module, however, each laminate requires not only a frame to provide protection against weather and other impacts but also a junction box to enable connections among modules or with an inverter-bound conduit. Robots affix those, too.

Inspection and Shipping
Careful cleaning and inspection provide final touches before each module can be palletized for delivery to homes and businesses.

How does a solar photovoltaic (PV) system work?

How a PV cell makes electricity
Under the sun, a photovoltaic cell acts as a photosensitive diode that instantaneously converts light – but not heat – into electricity.

Cell Layers
A top, phosphorus-diffused silicon layer carries free electrons – un-anchored particles with negative charges. A thicker, boron doped bottom layer contains holes, or absences of electrons, that also can move freely. In effect, precise manufacturing has instilled an electronic imbalance between the two layers.

Sun Activation

Additional Resources

Many federal, state, local and utility incentives for renewable energy systems are available for residents and businesses. Some of the funding organizations have limits to how much they can fund and these opportunities can be closed literally hours from when they are announced due to large volumes of requests.

EES is happy to assist our clients to apply for these funds and also encourages everyone to keep up to date with where funding organizations are in their funding processes. Below are some of these databases and organizations to keep an eye on.

Dsire Solar

DSIRE is THE comprehensive source of information on state, local, utility and federal incentives and policies that promote renewable energy and energy efficiency. Go to the website, click on your state and see what’s available for you!

Tennessee Solar Institute

The Tennessee Solar Institute (TSI) is a center of excellence between the University of Tennessee (UT) and Oak Ridge National Laboratory (ORNL) that brings together scientists, students, policy makers, and industry partners to generate transformative changes to the field of solar-generated energy production.

VA Department of Mining, Minerals & Energy

The primary goal of the Division of Energy is to advance sustainable energy practices and behaviors. To achieve this goal, the Division of Energy works to: • increase the use of proven energy conservation practices in Virginia; • foster growth of emerging and sustainable energy industries and infrastructure; • identify applications of new and innovative energy technologies in Virginia; • advance partnerships that will enable energy efficiency and economic development opportunities; • improve the energy efficiency of commercial, institutional, and residential buildings in Virginia; and • provide energy education and outreach to Virginians to increase their ability to make informed energy choices.


The Rural Energy for America Program (REAP) provides assistance to agricultural producers and rural small businesses to complete a variety of projects. Offering both loan guarantees and grants, the REAP program helps eligible applicants install renewable energy systems such as solar panels or anaerobic digesters, make energy efficiency improvements such as installing irrigation pumps or replacing ventilation systems, and conduct energy audits and feasibility studies.

US Department of Energy

The Rural Energy for America Program (REAP) provides assistance to agricultural producers and rural small businesses to complete a variety of projects. Offering both loan guarantees and grants, the REAP program helps eligible applicants install renewable energy systems such as solar panels or anaerobic digesters, make energy efficiency improvements such as installing irrigation pumps or replacing ventilation systems, and conduct energy audits and feasibility studies.


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