How Many Solar Panels Does It Take to Make One Kilowatt? Calculating the Number of Panels Required for Your Home Energy Needs

Converting to solar power is an environmentally-friendly alternative energy option that has been getting more attention in recent years. But how many solar panels would a residential home need, and how many solar panels does it take to make one kilowatt?

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Everyone's lifestyle is different and so is the amount of energy they consume. Consumption depends on the type of appliances you own and how often they're used. So when it comes to 'getting off the grid', you need to determine a realistic energy consumption sufficient for your energy needs and lifestyle.

Solar Arrays

A solar array is an interconnected system of smaller photovoltaic (PV) modules called PV cells, or solar cells. These cells, when connected in series (one after another), can charge a bank of batteries that will store the energy until needed. A device called an inverter is placed between the batteries and the final load, converting this energy into electricity that can be used to power your lights and appliances.

Each solar array has a specific rating. Some are 50 W, 80 W or 120 W, which means how much power it can output under ideal sunny conditions. As you can see, the panels are measured in Watts yet the energy needs of most appliances are measured in kiloWatts. Therefore, a number of these solar arrays are required in order to meet typical daily energy needs.

How Much Power Do You Need?

Electrical power is measured in Watts and energy consumption is measured in kiloWatt hours (kWh). A kiloWatt hour is simply:

The amount of electricity used (1000 Watts = 1 kiloWatts), in kiloWatts

    multiplied by

The number of hours the energy is used.

Usually the calculation states the time period such as one day, one month or one year.

For example: if a 100 W light bulb is on for 10 hours a day then:

100/1000 (kilowatt) x 10 (hours) = 1 kWh per day.

In one month, that same 100 W light bulb, turned on for 10 hours a day will consume:

100/1000 (kiloWatt) x 10 (hours) x 30 days = 30 kWh hours per month.

Your electrical bill will usually show how many kWh all of your electrical devices used over the last billing period (usually around 30 days).

Determine Your Energy Requirements

Before converting to solar power, look at your electricity bills from the last year, and determine your energy usage. Some of us will use more energy in the summer when the air-conditioner is running. Others, who live in colder climates, may use more electricity in the winter, when the nights are cold and long. Make a good estimate at how much power you'll need per day. If you don't have your utility bills, then here are some average numbers to get you started** (important note: these can vary widely, depending on the type & brand of light or appliance you purchase. Numbers are shown for illustrative purposes only):

  • 16 W bulb (on for 10 hours) - 4.8 kWh/month (57.6 kWh/year)
  • 100 W bulb (on for 10 hours) - 30 kWh/month (360 kWh/year)
  • Refrigerator - 36.7 kWh/month (440 kWh/year)
  • Dishwasher - 41 kWh/month (492 kWh/year)
  • Clothes Washer - 24.9 kWh/month (299 kWh/year)
  • Electric Clothes Dryer - 74.7 kWh/month (896 kWh/year)
  • Stove & Oven (self-cleaning) - 61.25 kWh/month (735 kWh/year)

** Source: Natural Resources Canada

Will Solar Power Work In My Location?

Solar panels will work anywhere there is sun. That said, however, some locations are better than others. Here are some of the more important factors you need to take into account:

  • Location. Southern locations receive more direct sunlight than northern locations.

  • Season. In the northern hemisphere, daylight hours are longer in summer and, once the batteries are fully charged, the excess electricity will be wasted. In winter, the days are shorter and there may not be enough sunlight to recharge the batteries for the night-time requirements.

  • Climate. Solar arrays are most efficient in bright, direct sunlight. Efficienty can be dramatically and significantly reduced if the sky is overcast. If snow collects on the panel, the array will stop produce electricity until the snow melts or it is manually cleared.

  • Obstacles. Anything that blocks sunlight from falling on the panels will reduce the efficiency of the arrays. This includes shadows, leaves, dust and other debris. The panels can quickly become inefficient when obstructed from receiving full, direct sunlight.

How Many Solar Arrays Will I Need?

The answer to this question depends on your lifestyle and energy consumption. As a rough calculation, if you require 3.85 kWh per day, then you'll require the following number of solar panels:

    3.85 kWh (per day) divided by 7 hours of sunlight (per day)
    = 0.55 kW from the solar array

If you have a 120 W panel, one of the largest units available today, then you'll need:

    0.55 (kW) divided by 120/1000 (kW)
    = 4.6 panels

This is a rough calculation but it shows that under ideal conditions, you'll need more than one solar panel to meet a typical lifestyle. This is assuming the following:

  • Your roof is large enough to accommodate 5 panels (since you can't really have "4.6" panels).

  • The panels receive direct sunlight for at least 7 hours a day.

  • There are no obstacles in front of the arrays.

  • The panels are kept clean.

It's hard to know how many solar panels you would need, as it depends on so many factors. However, the above calculations can provide you with a good starting point to see if solar power is a viable option for your home energy needs.