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The US Government has created the Residential Renewable Energy Tax Credit. This tax credit allows for a personal tax credit
for Solar Water Heating, Solar Photovoltaics, Wind, Fuel Cells, Geothermal Heat Pumps, and other Solar electric technology.

 

Solar

Standard Primer

Getting started

Before you have a solar energy system installed, there are a couple of preliminary requirements that should be considered. The most important requirement for a solar energy system is, predictably, sunlight. Although the need for sunlight may seem obvious, you should nevertheless scout out your property and make sure that you have clear access to the southern sky. The second requirement is communication with the utility company. Although not every solar energy system hooks up to the electrical grid, many of them do. Since power companies have a variety of methods for handling these additions to their system, it's important to have clear communication with your utility company before you install your system.


Grid-Tied Solar System

Putting it together

Individual solar energy systems differ according to the needs of each customer, but all systems share the same basic parts.

The most prominent feature of the solar energy system is the power source: the photovoltaic panel, which is exposed to the sun and generates an electrical current. If you want to install your system onto a horizontal surface like the ground or a flat roof, the solar panel can be secured using a ballasted mount. This option does not require drilling. Instead, the panel is fastened to a frame, which is weighed down with bricks.

Alternatively, if you have a sloping roof, your panel can be installed with a standoff mount. It's important to keep panels cool in order to ensure maximum efficiency. To avoid overheating, standoffs hold the panel slightly off the surface of the roof, leaving room for a cooling airflow. The standoffs are drilled into the roof, and flashing is added for waterproofing.

Once your photovoltaic panel generates electricity, the electrical current must undergo a few modifications before it can be tapped for ordinary use. These modifications vary according to each type of system, but there are some pieces of equipment that can be widely found among solar energy systems.

The first piece of equipment is the inverter, which turns the power generated by the solar panel into the type used in homes and businesses. Solar panels produce a direct current, but ordinary households run on alternating current. An inverter mitigates this problem by changing the DC power into AC power.

Second is the array combiner, which organizes the system by gathering its numerous wires and combining them into one.

Third, a charge controller regulates the electric current produced by the solar panels. The amount of power your solar panels produce is contingent on the amount of sunlight in the sky, so the charge controller prevents your system's batteries from overcharging. These batteries are the fourth piece of necessary equipment, and they store the energy produced by the panels.

System variations

As mentioned before, not every solar energy system hooks up to the grid; however, many of them do. There are three basic variations here: grid-tied systems, battery-based systems and grid interactive systems.

A grid-tied system does not have batteries. In this system, the inverter has a built-in charge controller and connects to the main electrical panel of the house. When the solar panel generates power, it adds its electricity to what's provided by the grid. However, there is no way to store excess power, so when the sun isn't shining the user has to rely solely on the utility company. This type of setup may have an on/off switch.

A battery-based system runs independently of the main utility grid. Here, the power runs from the solar panel to a charge controller to a battery, where it is stored in its DC state until it is needed. When this stored power is tapped, the battery charge runs through an inverter to make it ready for use.

A grid-interactive system blends the previous two models, connecting both to a battery and to the grid. The inverter can be programmed to sense when the batteries are full, at which point it draws power from them. When the battery power has been depleted, this system switches modes and draws power from the grid.

Technical Primer

A solar cell is a photovoltaic device; as the name implies, it converts light ("photo") into electricity ("volt"). The cost of a solar array may seem prohibitive, but its long-term financial advantages and environmental benefits can be attractive to people concerned with their effect on the global environment.

solar cell process

Material

Silicon is widely used for solar cells because of its atomic structure. Regular silicon lacks a charge because the number of positively charged protons (16) equals the number of negatively charged electrons; in effect, they cancel each other out. The electrons orbit the core of protons and neutrons in three different layers, with two electrons lying closest to the center, eight on the middle layer and four on the outer layer. (See illustration)

The outer layer can hold a total of eight electrons. To fill the gaps, silicon atoms join up and share electrons with one another, creating a crystalline pattern. This crystal is a stable system of interlocked atoms, with each electron fitting neatly into the overall structure.

electron place in atom

Doping

Electricity is essentially a flow of free electrons, but since the electrons in silicon fit into the crystal structure not enough of them break free to be useful. To encourage free electron flow, two silicon panels are doped.

Doping is a process by which foreign atoms are added to the silicon crystal, disrupting its neat order. Phosphorus and boron are popular chemicals for doping; phosphorous has five electrons in its outer layer (compared to silicon's four), which leaves one electron out of the crystal grid. Boron, on the other hand, has only three electrons in its outer layer, effectively creating a hole where an electron could go. Phosphorus-doped silicon is called n-silicon (n stands for negative) because of its extra electrons. Boron doping creates p-silicon, or positive silicon.

Junction

The doped panels are still electrically neutral (despite their misleading names) because the foreign chemicals have brought in an equal number of protons and electrons, maintaining the balance. However, when the panels come together this equilibrium is disrupted near where they join. Extra electrons from the n-silicon jump to the p-silicon to fill the holes in the p-side's crystal.

Since the electrons on the n-side have jumped ship, the n-side is left with more protons than electrons near the junction, creating a positive charge. The converse is true on the p-side. This static charge creates a barrier between the two sides of the cell, making it difficult for more electrons to cross over. (See illustration)

junction

Sunlight

Sunshine is comprised of photons, little particles with a lot of energy. When a photon with the right amount of energy hits an electron, it can knock the electron free from its atomic orbit. This is much more likely to happen on the n-side, where there are electrons that are left out of the interlocked crystal. However, it happens on a smaller scale on the p-side too.

Barrier Crossing

The static barrier is strong, but it isn't impenetrable. If a free electron can work up a high enough velocity, it can break through to the other side. This isn't likely to happen on the n-side, because there's a bigger crowd of free electrons and it's difficult for one to work up enough energy to break through. However, there are so few free electrons on the p-side that they're better equipped to work up the speed to cross over and join the crowded n-side.

Flow

With the n-side getting more and more crowded with free electrons, a highly conductive wire provides them the opportunity to spill outside of the solar cell. The overflow of free electrons keeps getting bigger, which pushes the crowd farther along the wire until they reach a load.

Reunion

Once the electrons have powered the load, they keep going along the wire until they get back to the p-side of the solar cell. Some electrons break through the barrier to the n-side; others fill the gaps in the boron-doped p-silicon.

Cost Effectiveness of Solar Power

Solar power is still more expensive than power from the utility grid. If you calculate the amount of electricity you should be able to produce with a solar cell over its 30-plus year lifespan, then divide that number by the initial cost of installation, the cost per kilowatt hour of a solar cell is about 30 cents. The power grid, on the other hand, sells electricity at a rate of about four cents per kilowatt hour.

Moreover, the solar cell is unlikely to meet all of your electricity needs, which means you'll still need to be hooked up to the utility grid. This can also work to your advantage, because when your solar cell is producing more than you need you can pour your extra electricity into the grid and effectively turn your meter back. This is a more efficient option than storing the extra energy in a battery.

If the cost seems prohibitive, consider the redeeming benefits of solar energy. First, it's clean energy. It doesn't produce any greenhouse gases or other environment-damaging byproducts. Second, solar energy users are protected from inflation in energy cost. Once the initial installation is paid for, the cost of maintaining a solar cell is minimal. If inflation continues to affect energy costs, as it almost certainly will, electricity from the utility grid will become more expensive and the solar array will eventually pay for itself.
Third, since solar energy is clean, there are government incentives in place to encourage people to use it. One incentive is subsidies; another is the exchange of renewable energy credits.

Companies are only allowed to put so many harmful gases into the atmosphere. That amount is regulated through a credit system. When a company runs out of credits, it can essentially buy more by paying a person with a solar array. While this is environmentally questionable, since it allows polluters to put more toxins into the air, the system is intended to make solar energy an attractive alternative energy option.

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