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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, will 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 this is for a new installation, such as a cottage, then here are some average numbers to get you started^**:

• 16 W bulb (on 10 hours) – 4.8 kWh/month (57.6 kWh/year)
• 100 W bulb (on 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)

• e 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 and can be reduced by 50% 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 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