Solar Power Panels – How To Know How Many You Need
Posted on 2009 under solar cost, solar power for homes, solar power residential | 1 Comment29 Jan
So, that’s really great! You’ve decided that you want solar power for homes. You’ve looked at a few solar power panels and pictured them in or on your house or business … but how can you tell exactly how many solar power panels will you need? Here’s how to determine exactly how much wattage you’ll need, specifically tailored for your home individually.
Start by establishing how much energy your home consumes. You cannot know the exact amount of solar power panels that you’ll need until you have accurately made that calculation.
Do this by digging out your old utility bills and have a good look a them. Establish your monthly average energy usage, ideally over the course of a full year to account of the changes in the seasons. Take note of the total amount of kilowatts per hour (kw/hr) your home consumes.
To get the average kw/hr your home requires, simply divide the total kw/hr by the total number of days in the billing period you’re looking at. Most utility company billing periods are for 30 days.
By doing that you will know how many kw/hr your solar power for homes system will require each day to meet your solar energy needs. Do this for the whole year and you’ll know both your average daily usage and times in which your consumption is likely going to peak. This is essential information for sizing up how many watts your home needs.
It is important to confirm that your utility company is willing to buy back any excess solar power your solar power for homes system produces. While it is rare indeed for an electricity company to actually pay you for the extra electricity you supply them, most are happy to buy back power up to the extent of your current bill. After that, they will take it but have an agreement that they won’t pay you for it. You need to check out where your local company stands on this matter.
If you are someone who is choosing to not go fully off-grid (which is perfectly reasonable by the way!) and you haven’t invested in any batteries to store the extra solar power, then some days you’ll be selling your solar energy to the utility company. In the U.S., by law electric companies have to pay you whatever rate you would pay them. On other days, you don’t produce enough solar power for homes and you may be buying energy from them. Either way, over the duration of a full year, you want to aim at having your energy bill end up around the zero mark. In other words, you want to have just the right amount of solar power panels, not too many and not to few.
Energy companies rarely (if ever) offer to give you money if you over-supply them. So do not build a solar power for homes system that will produce more solar energy than you could ever possibly use. You want the system to generate just enough to keep your bills at zero.
To establish exactly how many watts of solar power panels you need, you have to work out how many hours of direct sunlight that your solar power for homes system will receive. Effectively, how many hours of direct sunlight does your home soak up on average over the course of the year?
There is several ways to work this out. The ‘hard way’ is to take time daily to notice for how long the sun shines on the part of your roof where you are thinking of installing your solar power panels. As you are unlikely to want to keep this up for a whole year, this way is probably impractical.
If your solar power for homes system has tracking system, (a built in ability to move and track the sun) the number of hours of sunlight your roof receives will not be the same as the number of hours of direct sunlight. Your calculations will be different because the sun’s light hits the solar power panels from many different angles (not only when it’s coming in at right angles to your roof).
Generally speaking, most houses enjoy roughly 5 hours direct sunlight on average throughout the year. This is a rough approximation, so don’t get upset with me if it turns out you get less energy than this article suggested! (You could always go back to taking daily readings if you want!)
If you live in the U.S. and you want to get a far more accurate assessment, look for your local average regional value. In August 2004, the Florida Solar Energy Center presented a study entitled “Geographic Variation in Potential of Rooftop Residential Photovoltaic Electric Power Production in the United States” in which they tested power generation of a 2 kilowatt solar power for homes system all around the U.S.A. They took readings in more than 200 locations throughout the U.S. The research showed that on average a 2 kw rooftop system would harness between 5 and 8.5 kw/hr per day throughout the year.
So taking the low end of the scale, a 2-kw system would experience 5 hours per day of sunshine. Therefore, that 2-kw system could expect to enjoy 10 kw/hr of solar power per day on average across the period of the whole year.
Consider how you were planning to use the solar power for homes. Were you wanting to go completely off-grid? That will create greater demands on your solar power for homes system. Also, be aware of any potential problems such as tall trees blocking your sunlight to the solar power panels.
If your average power consumption were to be 600 kw/hr per month and you establish that your electricity company has a billing period of 30 days per month, then you can know that your daily energy consumption is 20 kw/hr per day (i.e. 600 kw/hr divided by 30 days per month).
Using the Florida simulation data found in the graphic entitled, “Geographic Variation of PV Power Production Around the U.S.”, we can see for example that the southernmost tip of Florida has an estimated value of 7.5 kw/hr based on the use of a 2kw rooftop PV system. Therefore, we can know that people living in Southern Florida receive an approximate average of 3.5 hours of direct sunlight per day.
If you know your home is currently using 20kw of electricity per day (aka 20,000 watts), then, given that you know you receive an average of 3.5 hours per day of sunlight from which to produce your total solar energy needs, then the solar power for homes system you would need to incorporate roughly 5,700 watts of solar power panels to deliver the amount of energy your home typically consumes every day.
Now don’t delay. Nothing speaks louder than action. Go source and purchase those solar power panels today!
from Sam Deane,
your solar power for homes guide,
at www dot go solar power for homes dot com
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by TropicalMonkey, on June 21 2009 @ 11:17 pm
I guess the units are not really accurate in this article. Note the usage such as kW/h and “If you know your home is currently using 20kw of electricity per day (aka 20,000 watts)”