How to Buy Solar Panels

Are you thinking about buying a solar panel system but don't know where to start? You came to the right place!

SEI PV Design Manual
A Really Great Read

Before we dive in to the specifics of solar panels (a.k.a. PV modules, solar electric panels), let us remind you that energy efficiency and conservation are the best ways to reduce your energy foot print and your electrical bill (see our Energy Efficiency and Your Home article). Please actively explore and incorporate all avenues of efficiency before pursuing a home solar panel system. That being said, solar power is an exciting clean-energy option that is becoming more and more popular. Solar electricity is a fascinating topic. To really feed your curiosity, we highly recommend the book Photovoltaics: Design & Install Manual.

What shapes, sizes and types do solar panels come in?

Solar panels vary in length and width and are often about 2 inches thick. They are generally about 30 pounds or less, but the larger solar panels can be cumbersome to carry onto the roof. We carry a wide selection of solar panels for home use: framed, foldable, and rollable.

  • Framed solar panels are the industry standards. They are the most cost effective and applicable for most home solar panels applications.
  • Foldable solar panels are lightweight (less than 5 pounds) and can fold up and fit easily in a backpack.
  • Flexible (or rollable) solar panels are also lightweight but bulkier than the foldable panels. Many people use these rollable solar panels on boats because they are durable and can be easily stowed after use.

Generally thin-film laminate type of solar panels (foldable & flexible) are more expensive per watt and require more square footage to produce the same wattage of an equally sized framed module.

What size solar panels do I need for my home and how many?

The number of solar panels you will need depends primarily upon the amount of electricity you are trying to produce and the insolation in your area. Solar insolation can be thought of as the number of hours in the day that the solar panel will produce its rated output. This is not equivalent to the number of daylight hours. Read more about insolation in our How To section and get an idea of the insolation in your area: Solar Insolation Map - USA.

You'll find solar panels in a variety of wattages. Watts are the main measure of a solar panel, along with nominal voltage. For a rough idea of how many watts of solar panels you will need for your home, start by dividing your electrical usage (in watt-hours per day) by the solar insolation in your area. Bump that number up by 30-50% (to cover system inefficiencies) and you'll have an idea of the number of watts of solar panels total you will need. If that number is more than 1000 watts, you are talking about $4K to $8K or more for the solar electric system. (Could we take this opportunity to mention the importance of energy efficiency again?!) If you could still use a little help with the math, please give us a call and tell us how much electricity you are trying to produce (in kwh/month or watt-hours/ day) and your location, and we'll help get you started.

What types of solar panels are there?

Most solar panels can be classified as monocrystalline, polycrystalline or amorphous. This is based on the silicon structure that comprises the cell. It's not quite as complicated as it sounds. Basically a 100 watt monocrystalline solar panel should have the same output as a 100 watt polycrystalline solar panel and a 100 watt amorphous solar panel. The main difference is the amount of area which the solar panel occupies. Because the monocrystalline structure is more efficient than amorphous (and only very slighlty more so than polycrystalline) in turning sunlight into electricity, the amorphous solar panel of the same wattage will be physically larger. By the way, when talking about efficiency of solar panels, keep in mind that solar panel efficiency is still only about 13-18% efficient in turning sunlight into electricity. Often amorphous solar panels are less expensive than the crystalline panels. If space is not an issue, then an amorphous panel could be a great option. Additionally, amorphous solar panels perform better than crystalline solar panels in very hot temperatures and are also slightly more tolerant of partial shading.

Solar Energy for Home Heating & Cooling

Please keep in mind that solar panels produce electricity, and should not be used to produce electricity for heating or cooling sources. If heating is your main issue, be sure to check out Solar Air Heaters and Solar Water Heaters. Solar air heating and solar water heating are examples of solar thermal technologies which produce heat, but not electricity (and are much more cost effective than solar panels). While solar electric panels are not an economically feasible choice to power your air conditioning, a solar panel can power an attic fan that can help reduce the amount of time you use your AC.

Locating your Panels - Very Important!

A key factor in the effective use of solar electricity is proper placement of the solar panels. Make sure to locate the panels where they will receive full sunlight between the hours of 10 am and 3 pm. Be sure that the solar panels will not be shaded by shadows from tree branches, chimneys, other structures, etc. Once again - NO SHADE! You will be mounting the solar panels on the roof, the ground or a pole. For more information on the proper placement solar electric panels, please checkout the How To for Solar Panel Mounting article.

How Long will Solar Panels Last?

Solar panels use the sun's light to generate electricity. They generate electricity during sunny daylight hours and can be used in a system with batteries so that the electricity can be used at other times as well. Also known as Photovoltaic (PV) modules, solar panels are the main component of a solar electric system. Along with an inverter, mounting system, batteries and Solar Charge Controllers, solar panels can produce electricity to power the energy efficient appliances and lights and appliances in most households. Solar panels themselves generally last over 25 years, and require little maintenance. Many of the first solar panels produced in the 50s are still in use today. Many of the solar panels have a 20 year warranty or more. A common warranty states that the panels will produce at least 80% of their rated power after 20 years.

What else will I Need with a Solar Panel?

In addition to the solar panel mounting hardware, there are additional components that you will need for a safe installation. If you plan on using just one solar panel in a battery based system (an off-grid system), you will need a solar charge controller and overcurrent protection to protect each major component of your system: solar panels, solar charge controller, deep cycle batteries, and inverter. If you plan on using more solar panels in your system, you will also need to safely wire the photovoltaic solar panels together and to the charge controller. An easy and safe way to do this is by using MC (multi contact) connectors. These connectors connect to the cables coming from the solar panel and can be cut in half to expose bare wire. Combiner & pass-through boxes are used to collect the bare ends of the wire from multiple solar panels; then from the combiner box you can run just one set of wires to the solar charge controller. For each series string of solar panels, you will need an appropriate sized breaker.

That's a lot of components to figure out! If after reading all this you are a little confused but even more excited about solar energy, what's next? Well, you can read more about solar panel systems. Also, our AltE U offers in-person workshops in Massachusetts and Ohio, as well as free education online videos. If you are considering installing your own solar electric system or installing PV (photovoltaic panels) as a business, be sure to check out our series of three classes beginning with our Basic Photovoltaic and Site Assessment class.

Of course, you can call our expert solar staff at altE, Monday through Friday, with any questions you may have about buying solar panels.

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