How Much Solar Power? Determining How Many Watts Your House Needs

View of Solar Panel
View of Solar Panel | Image by Flickr

If you’ve decided to add a system of photovoltaic solar panels to your home or business or established that it is time to expand an existing system, the next question is: How much wattage I need

[19459002?] For this to find out, you should know how much power you consume (or how you plan to consume, for new construction or additions that will require a lot of power – as a woodworking shop or a hot tub), and how much sunlight you receive throughout the year.

Assuming that you have been at your site for at least a year (so you get a good feel for your electrical needs for each season), takes every electricity bill, and write down the number of kilowatt hours (kW-h) which were invoiced and the number of days in the cycle. Then divide the number of kw-h by the number of billing days, the average kw-hours a day. To make things easier, some people just assume 30 days for each billing cycle (and not all of the energy companies to report the billing days). That’s how much kw-hr, your system will need to generate each day to meet your power needs. Once you have done this for the value of the bills throughout the year, you will know your average daily consumption and your peak consumption. You can choose the size of your system based on both value. If you use the average value (and assuming your utility allows you to back to sell them power, you should definitely check this first!), Then take a few days you extra power and sell it back to the energy and some days you purchasing power, but in the course of a year, your net electric bill must be close to $ 0. If you use the peak number, then you have to sell power back to the power company almost every day, but your system will be more than when the system dimensioned based on the average power cost.

Now, to get the power from solar panels you need, you must know how many hours of direct sunlight that will receive your system. If you have been at your location for several years, you would have a good idea how many hours of direct sunlight receive your building, either seasonal or average throughout the year. One way to determine how many hours of sunlight you receive is for a day to take comments several times on whether the portion of your roof where the solar panels are installed sunlit. If you do this every day for a year, you’ll get a good idea of ​​how many hours of sunlight your solar panel on a seasonal basis. There are a number of problems with this approach: it is very time-consuming because it is necessary to take measurements during the day, nearly every day; there will be some days when you just can not take the measurements (you’re out of town, work and can not go to the house to the roof, clouds obscuring the sun, etc. must be observed.); and unless you have a solar panel system that follows the sun, the sunshine hours getting your roof is not the same as the hours of direct sunlight as much of that light will not come at right angles to your roof throughout the year.

Another way to increase the number of hours of direct sunlight you receive is estimated to assume a value or use a rule-of-thumb. Often five hours of direct sunlight on average expected for the year. Although this is a fairly generally accepted, you might end up disappointed if your solar system generates less power than you expect because you have fewer average hours of sunlight than this.

A third method is to look at an average regional value. The Florida Solar Energy Center presented a study in August 2004 on the ACEEE 2004 Summer Study on Energy Efficiency in buildings called “geographic variation in the potential of Rooftop Residential Photovoltaic Electric Power production in the United States.” This study simulated the generation of a 2 kilowatt (kW) system for photovoltaic roof 236 sites in the United States. Depending on location, they found that these 2 kW system on the roof between 5 and 8.5 kw-hr would generate on average per day during the year.

Using the general rule-of-a 2-kw system receiving direct sunlight for five hours a day would be expected to generate 10 kw-hours on average each day throughout the year. The study of Florida, the same system would be expected to generate only five -. 8.5 kw-hours a day throughout the year

How you proceed depends on your goals. If your goals are to offset your electricity costs, it is one of the approaches will provide an estimate of the number of hours of direct sunlight you receive. However, if your goal is to become energy independent, then the use of the results of the simulation Florida, a more conservative value that would provide more chance of a system sized for your needs. Take the results of the simulation and a few of your own observations (if you have a lot of tall evergreen trees on the south side of your house that a majority of the winter sun, etc. Block) and you should be able to estimate number hours of direct sunlight you receive.

For example, if you decided to average current consumption value used and you 600 kw-hours use per month and your billing company does not report the number of days in the billing cycle (assume 30 days per month) than you consume 20 kw-hour electricity (600 kw-h divided by 30 days a month). About 3.5 hours of direct sunlight per day using the Florida simulation data and assuming you live in western Kentucky, you will receive (from the graphical estimating a value of 7.0 kw-h divided by 2 kw – study is based on a 2 kW system). Then your system should be sized to approximately 5700 watts.

Source: by Daniel Peplinski


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