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Solar Electric

Solar photovoltaic (PV) modules convert sunlight directly to electricity, which can be used in many ways, both connected to a utility grid or standing alone. The price of PV modules in recent years has dropped dramatically, and can be an economically viable choice in many cases.

Photovoltaics (PV)

The solar electric panels that most folks are familiar with are technically referred to as photovoltaic or PV modules. Each module is comprised of photovoltaic cells, typically 5 or 6 inches square. The cells are commercially linked together to make weather-proof units: the solar module. Modules are then mounted and connected together electrically on the installation site to construct arrays. An array can include from a few modules to hundreds or thousands, depending on whether it is a small residential array or a large commercial array.

Converting sunshine directly into electricity is not a new technology. Alexandre-Edmond Becquerel was credited in 1839 as being the first person to discover and document the photovoltaic effect. Initially, progress on developing the technology was slow. Scientists early on recognized the enormous potential of PV and created a few experimental devices, but nothing of commercial value was produced until the 1950s. In 1954 Bell Laboratories created the first crystalline solar cell, and by 1958 solar arrays were powering American satellites and Bell Telephone remote communication stations. As the technology improved, cost went down and the percentage of power captured went up. Becquerel's apparatus converted only 1% of the available solar energy into electricity, or was 1% efficient. The first Bell cell approximated 6% efficiency, but improved to 15% by the time arrays were utilized on satellites. Today, quality commercial cells are over 20% efficient and experimental cells have attained 43.5 % efficiency and are still climbing. This trend bodes well for the future.

A Simple, Proven Technology

Modern PV cells are very simple solid-state electronic devices. They are typically made from silicon and have no moving parts. When sunlight strikes the surface of the cell, electrons are knocked loose from the nucleus of the silicon atom and are collected by wires attached to the surface of the cell. A network of wires brings this flow of electrons from each cell together to make one connection for each panel or module.  Return wires bring expired electrons back to each cell so they can be reenergized by the sun and continue to function indefinitely. This is why PV panels have a life expectancy of well over 30 years and today’s top manufacturers generally warranty them for 20 or 25 years.

Today’s commercial PV panels generically fit into one of three categories determined by the type of material utilized to create the photo-reactive base; monocrystalline, polycrystalline or thin-film.  Monocrystalline cells, as the name implies, are constructed from wafers cut from a single crystal ingot of silicon. The purity of this source makes cells of higher efficiency than the other two types, and is why monocrystalline panels, at first blush, tend to be attractive.  Polycrystalline cells are made from many smaller crystals which makes them cheaper to manufacture but approximately 3% less efficient (photo at left). The cost per unit of power produced is generally lower than monocrystalline and makes polycrystalline panels an excellent buy for many applications. Thin-film PV is the least expensive to produce but is dramatically less efficient. The big advantage of thin-film is its versatility in size, shape and physical flexibility. The photo-reactive base of thin-film can be applied commercially to a wide variety of flexible substrates including shingles, siding, awnings or metal roofing. Thin-film's primary disadvantage is it requires about twice the square footage area to produce the same amount of power as monocrystalline PV. The cost to produce all types of PV panels has been on a steady decline ever since their inception.

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Every Application is Unique

There are many variables to consider in deciding which PV panels would work best for your application. Partial shading can affect panels differently depending on the type of panel and how they are connected with other system components. Temperature affects efficiency by increasing performance as the temperature decreases due to decreased resistance (a boon to solar energy in Alaska!). Reflected sunlight, like that which bounces off of snow covered ground, can also assist in producing PV power. The combination of this reflected energy, increased efficiency at cooler temperatures, and clear spring weather makes March and April the most productive solar PV months for fixed panels throughout most of Alaska. The size of the area available for panels is very important. If space is limited you should lean toward the higher efficiency panels.

There are three different ways PV panels can be installed; dual-axis trackers, single-axis or fixed. Dual-axis trackers mechanically move the panels to follow the path of the sun. They tilt back as the sun rises in the sky and simultaneously pivot to the west as the sun crosses the sky. This tracking of the sun keeps the panels at the optimum angle for solar gain and can improve the total performance of the panels. However; the trade-off is they cost more, require additional ongoing maintenance, and can make some maintenance more difficult to perform. This is generally not the preferred option for cold climates.  Single-axis mounts only allow the array to tilt forward and back. This tilt can be either mechanically accomplished, automatically tracking the sun's height daily, or the array can be manually adjusted seasonally. This manual method is popular for pole-mounts in Alaska where the appropriate near-vertical winter angle will essentially eliminate snow accumulation, and the proper summer angle can maximize overall annual efficiency. Fixed arrays are mounted in a stationary position. They are the most common, easiest and least expensive to install, but they are the lowest performing orientation. The degree to which an array can track the sun influences whether it is mounted on a pole or attached to a structure’s roof or exterior wall.

A Versatile Source of Power

Solar PV performs very well in many applications. It can be used on-grid and off-grid, or even on a recreational vehicle. Each system is unique and has different installation and equipment requirements to maximize the power output from your investment. Systems with batteries add versatility, but cost more and require additional components, like charge controllers. Solar PV produces direct current (DC) which needs to be converted to alternating current (AC) if you intend to run standard appliances and electronics, like TVs, computers or radios. This requires a quality pure sine wave inverter if you want your electronic devises to function properly. If some of this sounds daunting or confusing, the professionals at Arctic Sun can help clear things up and provide any level of assistance you desire.

Installing solar PV, or any renewable electric source, is not rocket science, but requires a significant background in electrical science and construction techniques. It includes nuances beyond the scope of standard electrical installations and can involve high DC voltages, and the proper balancing of delicate system components. Improper installations can cause fires and/or endanger the lives of the installers and/or area residents. Even if your local codes and building authorities allow it (almost none do), the installation of a full-size residential PV system is probably not something the average handyman should undertake. A renewable energy professional can assure your system components are compatible, and balanced to produce the maximum performance possible from your equipment. They can make sure you don’t buy things you don’t really need, or miss something that is critical. They have the diagnostic equipment to fine tune the system and check for complications. Improperly installed or imbalanced equipment will at least waste your money through lost production, and at worst can cause catastrophic problems for structures and/or individuals. Make sure whoever works on your system truly understands the work they’re performing.

 

Additional solar PV detail is included in these books:
 
Solar Electricity Basics
by Dan Chiras

The future will be powered by renewables. As we transition away from finite and polluting fossil fuels, clean, reliable, and affordable renewable technologies such as solar electricity will become the mainstay of our energy supply. Solar Electricity Basics provides a clear understanding of electricity and energy. It discusses the types of solar electric system you can choose from, their components, solar site assessment, the installation of photovoltaic systems, and much more. Whether your goal …

 
Solar Electricity Handbook - 2011 Edition
by Michael Boxwell

The Solar Electricity Handbook is a simple, practical guide to using electric solar panels and designing and installing photovoltaic PV systems. Significantly updated for 2011, the latest edition assumes no previous knowledge of solar electric systems. The book explains how solar panels work and how they can be used. It explains the advantages of solar energy and the drawbacks that you need to take into account when designing a solar power system. As well as explaining the underlying principles,…

 
Photovoltaics
by Solar Energy International

"Photovoltaics: Design and Installation Manual is a solar energy training and education provider - Solar Energy International (SEI) has made available the critical information to successfully design, install and maintain PV systems. The book contains an overview of photovoltaic electricity, and a detailed description of PV system components, including PV modules, batteries, controllers and inverters. It also includes chapters on sizing photovoltaic systems, analyzing sites and installing PV syst…