Solar Electricity FAQ
Q1: How long do PV systems last?
Q2: How much electricity does a photovoltaic (PV) system generate?
Q3: What does energy conversion efficiency mean?
Q4: Can I use photovoltaics (PV) to power my home?
Q5: Can I design and install a photovoltaic (PV) system myself?
Q6: How do I know if I have enough sunlight for PV?
Q7: Why should I purchase a PV system?
Q8: Are there disadvantages to using solar energy?
Q1: How long do PV systems last?
A: A well-designed and maintained PV system will operate for more than 20 years. The PV module, with no moving parts, may have an expected lifetime exceeding 30 years. Experience shows most system problems occur because of poor or sloppy installation. Failed connections, insufficient wire size, components not rated for dc application, and so on, are the main culprits. The next most common cause of problems is the failure of electronic parts other than the PV module such as the controller, inverter, and protection components. Batteries will fail quickly if they are used outside their operating specification. In most applications, batteries are fully recharged shortly after use. In many PV systems the batteries are discharged and recharged slowly, maybe over a period of days or weeks. Some batteries will fail quickly under these conditions. Be sure the batteries specified for your system are appropriate for the application.
Q2: How much electricity does a photovoltaic (PV) system generate?
A: A 14% efficient PV system in most areas of the United States will generate about 250 kilowatt-hours per square meter. A PV system rated at 1 kilowatt will produce about 2500 kilowatt-hours a year. Most PV panels are warranted to last 20 years or more (perhaps as many as 30 years) and to degrade (lose efficiency) at a rate of less than 1% per year. Under these conditions, a PV system could generate close to 50,000 kilowatt-hours of electricity over 20 years and close to 76,000 kilowatt-hours over 30 years. This means that a PV system generates more than $10,000 - $12,000 worth of electricity over 30 years. Typical PV modules have efficiencies of 14% - 16%.
Q3: What does energy conversion efficiency mean?
A: Energy conversion efficiency is an expression of the amount of energy produced in proportion to the amount of energy consumed, or available to a device. The sun produces a lot of energy in a wide light spectrum, but we have so far learned to capture only small portions of that spectrum and convert them to electricity using photovoltaics. So, today's commercial PV systems are about 7% to 17% efficient, which might seem low. Many PV systems degrade a little bit (lose efficiency) each year upon prolonged exposure to sunlight. For comparison, a typical fossil fuel generator has an efficiency of about 28%.
Q4: Can I use photovoltaics (PV) to power my home?
A: PV can be used to power your entire home's electrical systems, including lights, cooling systems, and appliances. PV systems today can be blended easily into both traditional and nontraditional homes. The most common practice is to mount modules onto a south-facing roof or wall. For an additional aesthetic appeal, some modules resemble traditional roof shingles or can be built right into glass skylights and walls. This building-integrated PV provides a dual-use building material, reduces PV system costs by using the building as the mounting or support structure, and reduces utility bills with on-site power production.
Q5: Can I design and install a photovoltaic (PV) system myself?
A: Maybe! However, unless you are very handy or experienced in home wiring, we suggest using experienced professionals to design and install anything more than the simplest application, for the following reasons:
- You might void the manufacturer's warranties.
- You might not have a functional system after spending your hard-earned money on the system.
- Electricity can be dangerous; you might get hurt.
- You might damage your home or appliances during installation.
The goal of a stand-alone system designer is to assure customer satisfaction by providing a well-designed, durable system with a 20-year life expectancy (or more). This depends on sound design, specification and procurement of quality components, good engineering and installation practices, and a consistent preventive maintenance program.
System sizing is perhaps the easiest part of achieving a durable PV power system. To determine the correct system size, you must first analyze your electricity loads. In addition to sizing the system correctly, a thorough knowledge of the availability, performance, and cost of components is the key to good system design. Price/performance trade-offs should be made and reevaluated throughout the design process. When you start your design, obtain as much information as you can about the components you might use. After studying all the issues, you can do an initial sizing of the PV system and get some ideas.
Q6: How do I know if I have enough sunlight for PV?
A: A photovoltaic (PV) system needs unobstructed access to the sun's rays for most or all of the day. Shading will severely limit the output of a PV system. Climate is not really a concern, because PV systems are relatively unaffected by severe weather. In fact, some PV modules actually work better in colder weather. Most PV modules are angled to catch the sun's rays, so any snow that collects on them usually melts quickly. There is thus enough sunlight to make solar energy systems useful and effective nearly everywhere in the United States.
Even hail won't harm most PV systems. Most homes have adequate roof space for a PV system, but you will have to size your system first to discover how much space is required. If you don't have adequate roof space, look at other options such as integrating the system into a wall or putting the system in the backyard. You could also use the system to cover a porch or patio in the backyard or mount the system on the roof or wall of a garage. Remember: an energy-efficient building requires a smaller PV system.
Q7: Why should I purchase a PV system?
A: People decide to buy solar energy systems for a variety of reasons. For example, some individuals buy solar products to preserve the Earth's finite fossil-fuel resources and to reduce air pollution. Others would rather spend their money on an energy-producing improvement to their property than send their money to a utility. Some people like the security of reducing the amount of electricity they buy from their utility, because it makes them less vulnerable to future increases in the price of electricity.
If it's designed correctly, a solar system might be able to provide power during a utility power outage, thereby adding power reliability to your home. Finally, some individuals live in areas where the cost of extending power lines to their home is more expensive than buying a solar energy system.
Q8: Are there disadvantages to using solar energy?
A: Solar energy technologies often have a higher "first cost." This means that a person is likely to pay more money up front to purchase and install a solar system. Still, in nearly all cases, the high initial cost is recovered through substantial fuel savings over the life of the product (15-30 years).
