Solar power for homes is one of the most reliable means to generate electricity for the average homeowner. Since sunlight is abundant regardless of geographic location, it is one of the most practical means of generating electricity with renewable energy, at the residential level.
Solar panels (photovoltaics) are among the most common means for homeowners to generate electricity, using the energy of the sun. They can last many years and deliver a fairly stable and predictable level of power during the year.
However, the upfront installation cost can be fairly high, especially for smaller installations, such as the average size home. For large utility-scale installations the cost per installed Watt is lower due to the economics of scale. For a typical homeowner, the cost can be in the range of $7-10 per installed Watt. So, for a 1000 Watt installation (such as on your rooftop), the full cost can be $7,000-10,000. This hefty price tag can be offset by installing the panels yourself (if you know what you’re doing), government incentives (rebates), and feed-in tariffs in which you “sell” the electricity you produce to the power grid. Many jurisdictions have programs in which a homeowner can sell power to the grid, if it’s produced by a renewable source of energy (such as solar power). In some areas these rates can be very generous; as much as 80 cents/kilowatt-hour. This is usually much higher than the cost to purchase electricity from the grid. Naturally, this is an incentive which encourages people to “switch over” to renewable energy. With a payback rate of 80 cents/kilowatt-hour, it is estimated that the payback period (to recuperate the cost of initial installation) is 8-10 years.
Solar power for homes is growing in popularity, especially now with the “green revolution”. However, it is a major investment, and one which homeowners should take the time to properly evaluate. I put together a checklist of items you should investigate before purchasing a home solar power system. These items on the list are good to ask potential suppliers. This list is as complete as I can make it, but you should also do your own research based on your own particular situation, and what you are specifically looking for.
• What is the fully installed cost per Watt of (rated) power output? Are there government incentives (rebates) to help reduce the installation cost?
• How much direct sunlight do you receive in a year, in the particular area where you live? Is it very cloudy where you live? What’s the difference in electrical output between a cloudy and a sunny day for the solar panels you plan on using? Note that the electrical output during cloudy periods can be 20-30% of the output during sunny periods (direct sunlight, no clouds).
• Are there solar panels that will operate efficiently during cloudy periods? It can be better to use these type of panels if you don’t get a lot of direct sunlight, since they are designed to produce as much electricity as possible during cloudy periods. Panels that work best with direct sunlight might not work that well when there is cloud cover. This is why it may be best to use solar panels which are specifically designed for cloudy periods, especially if the area you live in does not get much direct sunlight during the year.
• What is the best area on your property to place solar panels? The more they are exposed to direct daylight (with minimal shading), the better. Rooftops are generally good for this reason. Also, if placing solar panels on your roof, it may be best to have some sort of rooftop access so that you can access them without too much difficulty, such as to clean dirt/debris, or snow off them (if applicable).
• If you plan on selling the electricity produced to the grid, can you only sell the surplus (i.e. the “excess” electricity you don’t use), or can you choose to sell the full electricity generated (as this will minimize the payback period)?
• How durable are the solar panels; meaning how long will they last? You should expect a lifespan of 20+ years. Note that Thin-Film solar panels are less expensive than silicon-based panels, but they may not last as long. Furthermore, they are less efficient. Thin-film solar panels typically have an efficiency in the range of 6-10%, whereas silicon-based solar panels have an efficiency of 10-15%. Nevertheless, as technology is constantly improving, these figures may improve over time.
• Keep in mind that the rated power of the solar panels, as given by the manufacturer, is the maximum output, given ideal conditions (i.e. direct sunlight). You want to know the actual power that will be produced by the panels, subject to the conditions in your geographic area, by accounting for the number of sunny periods, and cloudy periods (as a yearly average).
• What are the zoning bylaws for your area? Are you permitted to install solar panels? Talk to your local government about this, if you are unsure.
• Will your property taxes increase as a result of adding the extra value to your home? Talk to your local government about this, if you are unsure.
• What are the maintenance requirements, such as for the batteries (which are charged by the solar panels, and store electricity for when the sun isn’t shining), electronic equipment – such as the inverter (which changes DC power from the panels to AC power), and other components.
• You can estimate the payback period of the installation using the following formula:
Payback period, in years = (initial installation cost)/(annual return)
where, annual return = (average kilowatt-hours produced per day)x365x(payback rate per kilowatt-hour)
where, (average kilowatt-hours produced per day) = (actual power produced by the panels, in kilowatts, on average)x(average number of daylight hours per day)
Sample Calculation
The power of sunlight reaching the earth’s surface is about 1000 W/m2. If we have a rooftop solar installation with (maximum) rated efficiency of 15%, this means that the solar panels generate 150 W/m2 (maximum) in direct sunlight. However, on average the power output is lower than this. Let’s say the capacity factor is 30% during daylight hours; meaning we produce 30% of the rated power (on average). This means that we produce 45 W/m2 on average, during the year, during daylight periods.
Let’s say we have 100 m2 of solar panels installed. This translates into a rated power output of 15,000 Watts. But since the capacity factor is 30%, the actual power output is 4,500 Watts (or 4.5 kilowatts).
If we assume the average number of daylight hours per year is 10, then
(average kilowatt-hours produced per day) = 4.5×10 = 45 kilowatt-hours
If we are paid 80 cents/kilowatt-hour to supply solar power to the grid, then
annual return = 45×365x0.8 = $13,140
Let’s say we have an installation cost of $10/watt. This means the initial installation cost is $150,000 (15,000×10).
Therefore, the payback period = 150,000/13,140 = 11 years (approximately).
Here is a good website that lists suppliers of solar power, according to geographic location. You can find suppliers of solar power for homes, nearest to where you live: http://www.solarbuzz.com/