Introduction to Load Analysis
I've been putting it off, but it's time to attack electricity 101. In doing a load analysis, we are primarily interested in POWER and TIME. This means Watts X Hours. If we are dealing with more power and/or time, we may use KiloWatts X Hours. 3000 WattHours = 3 kWHours.
Note that this is exactly the unit your electric bill is in (if you get one.) Also, it can be helpful to distinguish between POWER and ENERGY. Power x Time = Energy. For example an engine can be very powerful but doesn't use much energy if it only runs for a minute.
A quick and easy load analysis can be done by looking at an electric bill. You may find energy usage from 5 kWHour to 30kWHour per day, depending on the type of electric appliances used. If you are interested in lowering your electric bill, it will pay to look into more efficient lights and appliances. If you are looking to meet all or most of your needs with a solar electric system, you will almost certainly have to eliminate huge loads like electric water heaters and ovens. Tools and pumps are not a problem because they are not on for long periods of time.
An average solar-powered home with "all the modern conveniences" is designed for about 4kWHour / Day to keep system costs within budget. The average Grid-connected American home uses 20-30kWHour / Day. So it isn't generally practically to take an average home and convert it to off-grid. Electric heating devices, forced air blowers, inefficient refrigerators, and phantom loads just add up to too much daily energy loss. But, Grid-intertie solar electric systems on normal homes can still be very practical due to the backup function of the grid. With current state subsidies, any size of system makes sense - large or small.
You may require far less or far more power than "average." It is essential to do your own detailed load analysis.
VOLTS X AMPS = WATTS
It is possible to examine all your appliances and multiply the Amps on the nameplate times 120 Volts to get the Watts for each appliance. A saw rated at 12 Amps, for example, will draw 1440 Watts. Some items are rated in Watts already, like light bulbs, hair dryers or microwave ovens.
It's not necessary to tear apart the house to do this, but doing a few calculations like this will give you a better feel for what's going on as you use your system later. A good anaysis can be done using values published by others - see COMMON LOADS.
GO TO LOAD LIST - SAMPLE
GO TO LOAD LIST - BLANK to do your own analysis.
Next page: Common Loads