Frequently Asked Questions - All FAQs

Your site must have clear, unobstructed access to the sun. Buildings, trees or other vegetation should not shade your site. South-facing roof exposure is best, but roofs facing east and west may be OK. If a rooftop is not available, your PV system can also be mounted on the ground.

A small PV system can use as little as 50 square feet. A larger system, to meet the needs of a typical household, would use between 300 to 600 square feet. As a rule of thumb, 100 square feet of PV area produces 1 kilowatt of electricity.

As you may know, solar panels come in many sizes. There are two basic types, photovoltaic and solar heating. Photovoltaic panels have solar cells that produce electricity. Solar heating panels can be made to heat either liquids such as water, or air. Most of my comments will refer to the photovoltaic or solar electric panels.The photovoltaic panels are more properly called modules by the solar electric industry. Most of the photovoltaic modules have a glass front called a superstrate) that provides protection from the elements (rain, etc.) while allowing sunshine to reach the solar cells. The solar cells are attached to the superstrate with a clear plastic that is in the form of a plastic sheet before the solar cells are laminated (stuck to) the glass by a combination of heat and pressure while a vacuum is applied to the assembly to minimize any bubbles in the plastic.

While this is in theory a simple process, it becomes more difficult the larger the photovoltaic module. This difficulty tends to limit the size of photovoltaic modules.

In general, the larger a photovoltaic module, the lower the cost per square foot, up until the maximum practical size is reached. There are some other considerations when considering the size of a photovoltaic module for any particular application (power plant, home, cabin, remote telecommunications site, etc.).

1. The size limits shipping options. Large modules must be shipped by special truck in special packing. Smaller modules can be shipped by UPS or the mail. Optimum size depends of the total system size and how to best ship the modules. 2.
2. Generally, the larger the module, the lower the installation costs due to a few number of wiring connections, mounting bolts, etc.
3. In many areas where there is a high chance of hail stones, smaller modules are used because the damage of a single hail stone is limited to the module it hits. A single large hail stone can cause $200 of replacement damage for a small module, while the same hail stone hitting a large module may cause $4,000 of damage. With a large number of smaller modules, the system will usually continue to operate at a lower level of output when a few modules are damaged. With one large module, the system will most likely fail completely. This is important in some applications such as telecommunications.
4. The weight per module can be very important during assembly. Most modules are of a size and weight that two persons can lift and install on the mounting frame. Larger modules become expensive to install.
5. Some applications only require a few small modules. Any solar panel that is larger than needed is wasting money. This is one reason while there is a wide range of module sizes.
6. Some applications require a voltage that is not generally available from a large module. In this case the system designer needs to select a combination of smaller modules that when wired together will have the required voltage and power.  Generally the person designing a solar system needs to select the panels that will accomplish the desired performance at the lowest installed price, while considering the impact of failures and the problems of the various sizes of modules.

Please see these articles for detailed explanations of how Photovoltaic (PV) technology works:

• AZ Dept. of Commerce "Bright Ideas" Report on Photovoltaics - Introduction
• Solar for Consumers - Electrical Generation - PV & Thermal Solar

http://www.nrel.gov/rredc

This article explains in some detail how solar water heaters work.

This graphic summarizes how photovoltaic cells work.

Approaches to passive solar are contained within concepts of thermal mass design; thermal skin design; composite design; with direct gain; indirect gain; and isolated gain approaches for heating and thermal sinks and diurnal dispersal techniques for cooling. Please refer to the website section titled Solar Architecture for a tutorial on the variety of approaches and strategies for passive heating and cooling.

There are a variety of passive system solar buildings throughout the State of Arizona., and some are identified in the website section titled Solar in Arizona. Additionally, contact statewide solar organizations like the Arizona Solar Energy Association (Regional Director in your region), and/or local solar architects (listed in the website section - Products and Services) for locations of buildings incorporating passive design in your area. See this article