Whether you have decided to go off-grid, grid-tie or you just want solar energy to power some of the appliances in your home, you would still have to calculate how many solar panels you need. If you are going on the DIY Solar Power System route, calculating can be a hassle but is a necessary evil. You wouldn’t want to ruin any of the tools and materials you purchased just because your math didn’t add up, right? Don’t worry, we’ll make the process easier for you.
How Many Solar Panels Do I Need?
In order to calculate properly, here are the questions that you need to answer first. You can click on the links to jump on the part of the page for more details:
- What is my power usage?
- What is the power output of the solar panel that I want to buy?
- How many hours of sun do I get everyday?
Once these are answered, you can go ahead and calculate.
DIY Solar Power System: What is My Power Usage?
If you are going Off-Grid, it means all of the power needs in your home will rest upon the shoulders of your DIY solar power system. Everything. Therefore, the easiest way to know your power usage is by checking your previous utility bill. For best estimate, check your average monthly (it will most likely be shown in a graph in your bill), as well as your peak usage per month. An average American home uses up 901 kWh of power per month, according to the US Energy Information Administration. Are you on the average? Take note of your power usage as we will be using that for the calculation.
However, you might be opting for Hybrid Solar Power System, where you have the choice of powering up a select amount of appliances OR you can power your whole home but when the solar power gets used up, you’ll continue with getting power from the grid. Some people detach some of their appliances from the grid and plug them up to the solar power source only. If this is what you’re gunning for, here’s how to calculate your power usage:
1. Determine the power consumption of the appliances.
This information is normally located at the back of the appliance. Look for the wattage (W). (Note** If you can’t find this information and can only locate the volts (V) and ampere (A), click here to calculate the wattage.)
For example, a laptop is typically 65 Watts.
2. Estimate how long you will use this appliance.
Plain and simple, how many hours will you be using the device during the day (24-hour)? Let us assume, for example, that you use your laptop 5 hours a day.
3. Multiply power consumption against the hours of usage.
Let’s use our example above for the laptop:
65 W x 5 hours a day = 325 W-hours
4. Do the same for all appliances you intend to use with solar power, then add them up to get your daily power needs.
Let us assume that you’ll be using solar power for the following appliances:
TV: 45 W x 5 hours a day = 225 Wh
Small Air-conditioning: 500 W x 2 hours a day = 1,000 Wh (1 kWh)
5 lights: 60 W each x 5 hours x 5 bulbs = 1,500 Wh (1.5 kWh)
Laptop: 65 W x 5 hours a day = 325 Wh
Let’s add them up:
225 Wh + 1,000 Wh + 1,500 Wh + 325 Wh = 3,050 Wh or 3.05 kWh
So your power consumption would be 3.05 kWh. Let’s keep this in mind for the calculation.
DIY Solar Power System: What is the power output of the solar panel that I want to buy?
There are many different solar panels available today, but we will be focusing on one feature: the power output. Some produce 50 W, 100 W, 260 W, even 435 W. It really depends on the manufacturer. For the sake of our computation, let’s assume you will be buying 100 W solar panels.
The power output of 100 W is the amount of power the panel can produce at any given time. So in perfect conditions, you can expect a maximum of 100 W, also called the Peak Power. Plugging directly to the solar panel, this is the maximum power you can expect. However, due to power fluctuations (since we cannot count on consistent ideal conditions), we prefer to store the power collected in a battery (or sent to the grid, if you are going for Grid-Tie). Because we cannot expect continuous ideal conditions, we can expect some form of power loss (the movement of the electricity through the wires can also account for power loss). A good way to estimate the actual amount of power collected is by computing the expected output by 80%. Let’s keep this in mind for our final computation.
DIY Solar Power System: How many hours of sun do I get everyday?
At different seasons and in different areas of the globe, we receive different amount of sunlight. For instance, Norway and Iceland have 20 to 24 hours of sunlight a day for half the year (and another half in relative darkness). In the US, you can of course expect to get the most amount of sunlight during the summer months, and the minimum amount during the winter months. Check the table below for the average hours of sunlight you get in a day (Solar Radiation). We will use that number for our final computation. Let us assume that you live in New York City, with an average of 4.49 hours of sun per day.
You might say that based on experience, there are more hours of sun in a day that what is shown in the table. The number shown there is actually relative to the intensity of the sunlight. For instance, morning sunlight is only half as intense as the afternoon sun.
DIY Solar Power System: Final Computation
Now that we have all the details we need, let’s recap:
- What is my power usage? 3.05 kWh o 3,050 Wh
- What is the power output of the solar panel that I want to buy? 100 W, with an estimated output of 80%
- How many hours of sun do I get everyday? 4.49 hours
So first, let’s compute how much power each panel can give you by multiplying the maximum power output (100 W) with the estimated output percentage (80%) and the number of hours of sunlight per day:
100 W x 0.80 x 4.49 hours = 359.2 Wh
The amount of power one panel can generate and store in your battery is 359.2 Wh.
Since you need 3,050 Wh of power, let us divide this with the number we arrived above:
3,050 Wh / 359.2 Wh per panel = 8.49 panels
Let us round this number up. 8.49 panels now becomes 9 panels.
So that’s it! For this example, we will need nine pieces of 100-W solar panels.
This is the simple computation to determine how many solar panels you need when setting up your DIY Solar Panel System. Keep in mind that you should also choose a battery that is capable of storing this amount of power, else the power would just be lost.
Some additional factors to be considered when computing for the number of solar panels is the panel’s efficiency and the angle of placement. We’ll discuss this further in a different post.
Do you think investing on solar power will be worth it for you in the long run? Let us know in the comments below!