It’s the first question that anyone thinking of going solar asks: how many panels do I need for my roof? Here's how you can calculate that.
Every home is different, and the performance solar panels will be affected by the tilt of your roof, your home location, and even the direction your home faces, so it is always best to speak to an expert or a solar installer to get a full reading on how many panels you will need. However, it is still possible to get a rough idea.
Your energy usage
When asking how many solar panels you will need, first you need to know what your current home power usage is. If you have a recent energy bill lying around you should find this figure on there. Energy usage is sometimes given for the year -- divide this by 365 to calculate your average daily use.
For example, say your yearly use is 4,000 kilowatt hours (kWh). Simply divide this by 365 (days per year) to get an average daily usage of 10.9kWh.
Remember that this is an average and give plenty of room for cloudy days and winter. We’ll use 15kWh to give a buffer.
Measuring the sunlight
Next we need to figure out how much sunlight your home gets. This is easier said than done, and for this we will have to call in the experts. Contact a solar installer or local solar authority to get some information on the sunlight measurements in your area.
Let’s say your home receives a solid 6 hours of sunlight per day, which is a reasonable average accounting for the movement of the sun and possible shade from trees or other structures. So now we divide your daily usage by the amount of hours of sunlight.
15kWh/6 = 2.5kw needed every hours
We now multiply our kilowatt hours by 1,000, which converts the figure into watts, rather than kilowatts (this makes subsequent calculations easier).
2.5 X 1,000 = 2,500 watts
So your solar panel system needs to produce 2,500 watts of energy per hour to power your home. Simple, wasn’t it?
Solar panels are rated for the amount of watts they produce. Let’s say you want to buy 200-watt solar panels, it’s easy enough to work out that you will need 13 panels to cover your 2,500 watts per hour.
200 watt panels X 13 = 2,600 watts per hour.