Photo-voltaic Power

pho•to•vol•ta•ic [foh-toh-vohl-tey-ik] adjective
1. of, or pertaining to photovoltaic effect: Electricity.
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Photovoltaics (PV) is the method by which the sun's radiant energy (light) is converted into electricity by striking a charged surface of solar cells. The science is pretty staggering, so rather than repeat what can be found on any number of sources on the internet, we'll skip right to how it applies to you.

As everything in today's world strives to become more "green", or more "eco-friendly", the Solar PV market has exploded with the assistance of Federal Tax Incentives to help make the system more affordable. Solar installers have come up with dozens of ways to make the purchase more attractive, whether by amortized savings, standard term financing, monthly lease agreements, prepaid lease agreements, and even Power Plant Agreements (PPAs).

Combine our ever increasing electric rates with the fantastic weather in the San Joaquin valley, and its no wonder the region's major electric providers see some of the largest Solar PV participation in the world. Typical system payback is never more than ten years, and with a minimum lifespan of 25 years for the solar collectors, it is no wonder that people are flocking toward Solar PV systems to offset their electrical costs.

Solar PV systems consist of three major components: the racking, the module or PV Panel, and the inverter. Different people put stock into different components being "most crucial", but the truth is, the overall installation really matters more than the individual parts.

The Racking

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The racking system is basically everything that hold the modules in place. Racking Systems can be fixed, like those seen on a roof, they can be single-axis tracking, like those mounted to a pole that track the sun throughout the day, or they can be dual-axis tracking, meaning they not only track the sun across the sky each day, but they actually track the inclination to the sun each day and adjust flatten out in the summer or pitch up higher in the winter in order to maintain a more perpendicular angle in relation to the sun all year round.

Most racking systems, along with the fixed or axis tracking design, tend to incorporate rails and clips for attaching the individual panels to these rails. Axis-tracking systems also use an underlying attachment system that is substantially engineered to ensure that the torque and weight of the array isn't enough to weaken the structure in any way. Fixed arrays include "feet" that attach to the roof, typically by way of bolting directly into the truss members, and involve roofing in the penetrations to ensure for no water intrusion.

The Module

The number of module manufacturers out there is staggering these days, with the popularity of solar growing almost by the hour. The major players have actually undergone quite a retooling lately, with long-time powerhouse FirstSolar announcing its closure. Solyndra also met with the same outcome.

Solar module manufacturers come and go, and each hopes to create some market position to set itself apart from the rest. Sunpower has done a great job in distinguishing its panel by patenting its wafer cell design, moving the wiring to the back to give each cell the largest surface area possible to collect the sun's rays. This has given them a decided advantage in the current marketplace for efficiency when measured in production potential per applied area.

Other module manufacturers have sought other ways to stand apart. Today's economy of solar products currently sees Chinese products as the "affordable" way to go, with the modules competing on a price point, rather than using production efficiency.

Each method has its market, and while one may be ideal for one homeowner, another may be more attractive to another. Ultimately, almost all the modules out there today, whether made in China, in the United States, or elsewhere, all sit in a predictable 14-15% window for overall cell efficiencies.

The Inverter

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The inverter is arguably the most important individual aspect of the solar PV system.

There are two schools of thought where inverters are concerned in today's mainstream solar PV discussion. There is the tried-and-true String Inverter design, and the up-and-coming Micro-inverter design. The same basic inverter technology goes into each one, and the measured efficiencies of each one typically fall between 95-96% total efficiency, so the only true difference between the two is scale.

A String Inverter is designed to be a single, stand-alone box, responsible for converting all the solar electricity into usable AC current for your home. String inverters can be small, starting at 2,000 Watts, and scale upwards to be very large, on the low side, perhaps 100,000 Watts. String inverters have been around a long time and some are still producing power 30 years after commissioning. There are hundreds of manufacturers of string inverters today.

String inverters operate by connecting a series of solar modules into a string and connecting the positive and negative DC loop to the inverter. As string inverters get larger, they accept more strings, and potentially larger strings, as well. By this design, shade is Enemy #1 for a string inverter. Shading a portion of a panel in a string has the potential to derail the production of all the panels connected to the shaded module by the same percentage.

A Micro-Inverter is very similar to a String Inverter in every way, save one: its designed to operate on a single solar module, as opposed to the string inverter. Micro-Inverters are connected in strings (and in parallel in larger systems) to emulate the same look and feel of a traditional solar array. In fact, a micro-inverter driven solar array looks exactly like a string-driven solar array. The primary difference in a micro-inverter array is in the handling of failures and shade.

Since each module has its own inverter, only the module shaded is affected for overall system output. Likewise, an inverter failure in a micro-inverter system results in the production loss of the failed inverter, whereas a failed string inverter results in little or no electrical output from the entire array.

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