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Shining a Light on Solar Panels: The Basics

How do solar panels work – Live in an area with plentiful sunshine? Want to reduce your electric bill and decrease your carbon footprint? Then you may be thinking of installing solar panels. That’s great. But first, why not learn a little about the technology, rather than shopping blindly or relying on a solar-panel salesperson who may have his commission rather than your best interests at heart?

How do Solar Panels Work?

Most of the solar cells used for generation of home power are of two types: photoelectric and solar thermal. Photoelectric (also called photovoltaic) cells convert sunlight directly into electricity, while solar thermal technology employs the sun to create electricity indirectly. This article will deal exclusively with photoelectric solar cells, which are growing in popularity due to their dependability.

The Costs of Solar Panel

Solar panels are expensive if purchased out of the box and installed professionally. However, you can save a significant amount by building your own solar panels from scratch, or by purchasing a kit, and installing the panels yourself. As with any amateur project, there is a certain amount of trial and error, but the Internet is full of enthusiastic hobbyists. Some have pictures of homemade solar cells, while kits are available from a number of places.

The cost of installing solar panels varies greatly depending on your location–and the benefits vary, too, depending on the amount of exposure they will have to the sun. However, there are potential tax breaks and incentives. Find Solar offers a handy solar-panel-system cost calculator to help you estimate the cost of buying, installing and operating a solar panel array. The calculator also factors in tax incentives available to you based on your location.

Solar Panel Benefits

The environmental benefits of using solar cells versus other methods for generating electricity is enormous.

Over its 35-year expected life, a 10Kw system will provide the equivalent CO2 reduction as planting 1450 trees. (Based on typical utility pollution, it will prevent emissions of 963,125 lbs. of carbon dioxide, 4,237 lbs. of sulfur dioxide, and 1,364 lbs. of nitrogen oxides.) It will produce 575,000 kilowatt hours of electricity, as much as would be generated by burning 583,000 lbs. of coal.

AC/DC: Batteries, Not the Band

The electricity produced by your solar cells must be stored in deep-cycle batteries for nighttime and cloudy-day use. Batteries have a shorter lifespan than the panels themselves and have to be replaced when they can no longer hold an adequate charge. Of the various types of batteries available, nickel-cadmium are the best (although more expensive to buy) because they have a longer operating life. For an additional boost to your battery’s lifespan, install a charge controller, which prevents overcharging and excessive draining. For safety, batteries must be kept in a non-metallic enclosure with adequate ventilation.

Most household appliances are built to run on AC (alternating current), while electricity that comes from your battery will be DC (direct current). You will need an inverter that converts DC to AC. Most of the other necessary hardware is identical to that used in a regular AC home-electric system: junction boxes, wiring, grounding, and over-current protection devices, outlets, etc.

The National Electrical Code includes a section that covers installing photoelectric cells. Be sure to follow all local building codes for electric installation as well. It also makes sense to use a licensed electrician with some prior DC-power installation experience.

Practical Issues

There are many practical issues to consider in the use of solar cells. For example, determining how many solar cells you will need to create enough electricity to power your home.  “A typical 2 kW (or 2000 watt) system that consists of 12 solar modules will typically generate 2000 kW [hours] of electricity per year with some variables.” It is also important to correctly orient your cells so they have maximum sun exposure year round.

Snow Covered Solar Panels
Snow Covered Solar Panels photo by Mike Weston

Are there disadvantages to using solar panels? One significant caveat is that they do not work when covered with five inches of snow! When it snows, one must carefully clear the panels to avoid damaging them. Placing panels on the side of the house instead of the roof can mitigate this disadvantage. Still, it is important to consider how the system will function during a January ice storm; having a wood-stocked fireplace, backup propane system and candles at the ready would be wise.

Solar Cells Basics

Internet hobbyists have built basic solar cells at home. They are extraordinarily useful for understanding basic physics at play. Building a simple solar cell is easy, beginning with a thin sheet of copper, a bottle of water, salt and a heat source. After cooking the copper, one scrubs it lightly, then halves it. The top of the water bottle is cut off, salt is mixed into the water, and the two pieces of copper are placed on opposite sides of the bottle. A multimeter can be attached by alligator clips to each of the halves of copper to observe the electrical current.

In this simple solar cell, light strikes the modified copper. Some of the photons that strike the first piece of copper excite electrons and–voila!–they jump through the salted water to the other side, reaching the second piece of copper. A multimeter (also known as a volt/ohm meter or VOM) will show the electrical current that flows from one piece of copper to the other.

The Science Behind It

A photoelectric solar cell works when photons of light strike the solar cell and are converted into electricity. Typically, the material inside a solar cell is silicon or another semiconductor material. When light strikes the solar cell’s surface, photons in the light excite electrons in the silicon. (A ray of light contains a great many photons, tiny quanta of light akin to small particles.) An electric current is then produced, which can be used for household appliances or stored in a battery.

Photoelectric Cell Drawing
Photoelectric Cell Drawing

Electrical engineers have a common schema called an “N-P junction” (figure 29, from a 1941 patent to R. Oh, the first for a solar cell). The “N” zone is a semiconductor material like silicon, doped with a negative impurity; the “P” zone is doped with a positive impurity. Alternatively, one could just as easily create a solar cell based on a “P-N junction”; the two layers would be flipped, with the “P” layer on top and the “N” on the bottom.

The “N-P” schemata (or “P-N” as the case may be) represents a useful conceptual diagram that electrical engineers use to show an electrical phenomenon. They equally apply to technologies created back in the 1940s as to those of today.

The solar cells silicon is produced in a way that improves its capacity for conducting electrical current. Two silicon wafers are placed next to each other, separated only by a junction. One of the silicon wafers (or layers) is ‘doped’ with the negative material, while the other is doped with positive material. Such a design facilitates the creation of an electrical current.

Promising Breakthroughs

Recent breakthroughs promise to improve the output of solar cells. Scientists at MIT have developed a solar cell that increases power by a factor of over 40. The new technology employs ‘organic solar concentrators’ to increase power conversion.

Nobel Prize-winner Alan Heeger, Professor of Physics at the University of California at Santa Barbara, announced that his team had increased the efficiency of solar cells (neither exclusively solar thermal nor photoelectric) by as much as 5.1 percent. Their technique employs alkanedithiols as agents to improve the solar cell’s power-generation capacity and is expected to be market-ready within a couple of years.

Given the technology’s far-reaching environmental benefits, recent scientific improvements and the inevitable cost reductions associated with wide adoption, solar power represents a clean, efficient and cost-effective way to reduce both pollution and our dependence upon limited oil, gas and coal resources.

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