Home Solar Power Systems - Sizing And Planning

Sizing of home solar power systems raises a number of questions to understand the scope of your investment. Learn more here.

When contemplating a home solar energy system the first question you should ask is "What do I want this system to do?"

Will the home solar power system you build or have installed act as a backup power source only or do you expect to be able to use your home solar energy system to meet all of your energy needs including home heating, hot water, lighting and the running of all your appliances?

The size, components and cost of your system will vary greatly depending on your performance requirements. In this article we will focus on the basics of a whole house solar power system. When we refer to an "average" sized home we define that as a home of 1200 sq. feet.

Home Solar Power Systems - Questions To Consider

• Your current daily energy use (generally, your base electrical load)


• Square footage of your home


• Seasonal landscaping changes (ie tree cover) that will affect the ability of the panels to collect sunlight


• Roof size or ground area -is it large enough to accomodate the size system you need to install?


• Roof angles-will you be able to get the right tilt or angle for your panels? (If the tilt is less than the latitude of the house it will increase the size of your system)


• Will you require a tracking system rather than a fixed panel system? (Panels that move to catch the sun)


• Average amount of daily sunlight your location receives and house exposure: south, north, east or west?


• Any anticpated additions to your base electrical load (ie hot tub, addition to the house, swimming pool, extra hot water heater) additional family members


• Are you contemplating panels or solar roofing tiles? Roofing tiles generally produce less power than panel systems


• Will your system be a stand-alone (no back up power from an electric utility) or grid connected solar system (you have back up power from your electricity utility and can sell power back to them when you have excess)?

How To Calculate The Number Of Solar Panels Needed

1. Your daily average electrical consumption in watts. This information is usually available on your monthly electric bill. If you use 15kwh per day you multiple by 1000 to get your average daily usage in watts. So, 15kwh per day equals 15,000watts.


2. The average number of hours of sun your location receives every day. You can find sun maps and calculators by area on the web.


3. The watt rating of the solar panels you plan to install. (50w/100w/200watts etc)


4. How much of your electricity load you want your solar system to pick up. 100%, 75%, 50% 25%. Small systems can be expanded as long as you have enough roof or ground space.

For the purposes of this example we will assume a daily watt consumption of 15,000, 5 hours of daily peak sunlight and panels with a watt rating of 100 watts.

Step 1: Divide the daily watt hours you consume by the number of hours of sun your location receives every day. The number you end up with is the number of watts you will need to generate with your solar system every hour. Using our example divide 15,000/5 which gives you 3000 watts of energy that your system will need to provide each hour.

Step 2: Divide the hourly watt requirement (3000 in our example) by the wattage of the panels you intend to install (in this example we will use 100 watt panels). 3000/100=30. You will need 30 100watt panels in your home solar system.

Note: If you will tie your system into your local power grid there may be restricitions on the panel size (wattages) you can use. You should always engage a professional to accurately size your system and ensure it meets all utility, safety and personal requirements.

More related articles:

1. Residential solar energy - An overview


2. What are the best residential solar kits for Do it yourself


3. The top 10 questions about installing residential solar power


4. Where can I find reliable solar contractors in my area?