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If you want to determine precisely how many solar panels you need, it is essential to measure the amount of energy that a solar panel can offer, and compare it with the value that you require. Considering that a normal household consumes about 8000 - 9000 kwh on a yearly basis, and the fact that a $300 solar panels of good quality can only provide about 100 - 200 watts of energy, the number of panels you need to power your entire home may be quite substantial.
Of course, depending on your needs, you might not always have to use up so much energy on a regular basis. Especially if you are an environmental enthusiast, and you know how to choose appliances that provide better functionality, while consuming less energy, you might actually be able to reduce that number to half, or even less.