Understanding Photovoltaic (PV) Solar Systems

Sustainable Future sells, designs, and installs solar electric (photovoltaic) systems to generate electricity for your home or business. Our customers enjoy lower utility bills and the knowledge that they are reducing pollution and fossil fuel consumption every time the sun shines. The major system types are listed below.

Grid-Tied

With a grid-tied solar system, you can use power provided by your solar system and the local electric utility. Grid-tied systems are popular for several reasons. First, you can install a solar system that fits your budget, even if it doesn't generate as much power as your home or business is using. Any extra electricity that you need is provided by the grid. In addition, if it's a sunny day and you aren't using much power, you can feed any excess electricity generated by your panels back out to the grid. The utilities are glad to see systems such as these because they help reduce peak demands on hot sunny summer days. Many local utilities (including TVA) will buy the green power you produce at attractive rates.

Another reason for the popularity of grid-tied systems is that no large banks of batteries for backup power are needed, thus reducing the cost and complexity of the system. The only drawback to purely grid-tied solar systems is that if the power goes out on the grid, your power will go down as well, to allow workers to safety repair the line.
However, if power outages are minimal in your area, you won't be without power very often.

Grid-Tied with Battery Backup

If you're considering a grid-tied solar system but want the ability to power critical appliances during a power outage, then a battery backup may be for you. The advantage of these systems is that if there is an outage on the utility grid, you will still be able to draw power from your backup batteries. It's generally not practical to use a battery backup system to keep a power-hungry air-conditioning unit going during a power outage, but items such as fans and energy-efficient refrigerators are often realistic.

Stand-Alone/Off Grid System

In some remote areas, connecting a solar system to the utility grid can be cost-prohibitive or impractical. These customers generally consider an off-grid system, where the solar panels are used to charge a large bank of batteries and these batteries are then used to power all appliances in the home. Off Grid systems involve additional components and must be carefully designed around expected energy needs. Many off grid homes also use backup generators for additional power when necessary.

How to choose the system that's right for you

If you're interested in a solar system, you'll want to consider the following.

• Grid-tied or off grid? If you're in a remote area, you may need an off-grid system. If power is locally available, a grid-tied system without battery back up will be the less expensive option.

• Where should I put the panels? Take a look at your building and property. Good locations are typically an unshaded, south-facing roof, or another open area of the property where some south-facing panels can be installed. A solar site analysis is a good investment to help you choose the best place and will be an excellent opportunity to discuss the advantages of different types and sizes of systems.

• How will the panels be mounted? Choices include roof-mounted systems, pole mounted systems, and ground-mounted systems. Roof-mounted systems can be slightly less expensive than a pole mounted system; however they can be less efficient if your roof does not point directly south at the proper angle. Complex roof lines can also cause undesirable shading.

• Do the panels need to be tilted at an angle? Ideally, yes. However, if you prefer the look of flush-mounted panels on your roof, this can be done with a small decrease in efficiency. A solar site analysis can tell you how much efficiency you will lose by not mounting them at the best angle. If efficiency is of primary importance, we suggest tilting the panels at latitude and installing a pole-mounted array where you can seasonally adjust the angle of the panels to the sun.

• What happens at night or when it's cloudy? With a grid-tied system, you'll just use power from the grid at night. For off-grid systems, you'll need a battery backup or generator.

• What size system do I need? This depends upon how much power you are using, and your budget. Customers with grid-tied systems can choose to generate anywhere from a tiny percentage of their overall energy use to ALL of their energy use, based upon their budget. We recommend making your home as efficient as possible - that way you need a less expensive solar system. Your energy use habits have a huge effect on your power bill. Consider the following two examples: The "Green" family of four uses 300 kilowatt hours of electricity per month. They have energy efficient appliances, excellent insulation, solar hot water, and use a wood stove for heat in the winter. To maintain their home using only renewable energy, they spend about $25,000 for a PV system. The "Brown" family lives in the same size home with many air leaks, no insulation, lots of inefficient appliances, and an outdated heat pump. They may spend ten times the amount that the "Green" family spent to create a net zero energy home.