DIY Solar Power System: How Many Solar Panels Do I Need?

DIY Solar Power System: How Many Solar Panels Do I Need?

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.

 

DIY Solar Power System

 

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:

  1. What is my power usage?
  2. What is the power output of the solar panel that I want to buy?
  3. 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.

 

Related:

DIY Home Solar Systems: Should You Build Your Own?

Grid-tie Vs. Off-Grid Solar Power System: Which Should You Choose?

 

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.

DIY Solar Power System - Amount of Sun Per Day Per City in the US

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:

  1. What is my power usage? 3.05 kWh o 3,050 Wh
  2. What is the power output of the solar panel that I want to buy? 100 W, with an estimated output of 80%
  3. 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!

DIY Solar Power System: How Many Solar Panels Do I Need?

4 thoughts on “DIY Solar Power System: How Many Solar Panels Do I Need?

  1. Reply
    Win Bill - May 29, 2017

    Going off so the grid has always been my father’s dream. We just don’t know where to find the right quality of solar panels. We live in New York and sun is pretty good around here. However solar panels are still very expensive as an investment so we will probably just use hybrid style for now. Going completely off the grid might seem to be too perfect of an idea for now.

    1. Reply
      SuperSolarMan - May 31, 2017

      Hi Win! I also think that going hybrid first is better than going off grid immediately. You have to test the waters first, understand how solar energy works for you. You don’t need to shell out tens of thousands of dollars at the onset — there are providers that allow you to pay it off by installment. There are several good installers in New York, you can get a free quote here.

      Cheers to Solar Power!

  2. Reply
    Simon - June 2, 2017

    A DIY solar system sounds right up my street, this really does accomplish a huge step in becoming self sufficient.

    I talked to an estate agent during our last home sale and he said there are complications within the small print regarding stipulations on the ownership of the house roof to those who have opted for solar power to be installed by the large companies in association with the main grid, turning my attention towards the DIY route, then you are not tied into any contracts.

    Would you consider going hybrid first rather than jumping off grid straight away, just in case your energy calculations fail to be correct?
    Very interesting topic, I think there will be a surge in people opting to go the DIY route for solar energy, thanks for the info,
    Simon.

    1. Reply
      SuperSolarMan - June 5, 2017

      I would recommend going hybrid first to get your feet wet. You will be able to get a lot of info on DIY Solar Power online, but the best lesson you will get by experiencing first hand. When you are already “experienced” with solar power, that is the time to consider whether going completely off-grid will work for you.

      Thanks for dropping by!

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