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When planning a stand-alone residential system a careful
analysis of the household loads needs to be made. We typically tell customers
to go room by room through the house, garage and outbuildings and list each
fixture and appliance to be operated and how many hours per day each will be
turned on. If you have not done so, go back and read the guidelines in
Renewable Energy Fundamentals. Electricity is measured in Watts or
Kilowatts (1000 Watts). A 100 watt incandescent light bulb draws 100 watt hours
of electricity per hour. In 10 hours that 100 watt bulb will draw 1000 watt
hours (100 X 10 = 1000) or 1 Kilowatt. If we substitute a high efficiency 27
watt compact fluorescent bulb which produces the same amount of light, we will
now draw 27 watts per hour or 270 watt hours (.27 Kilowatts) in 10 hours. You
will save 73% of the energy consumed for lighting by converting the 100 watt
bulb to a 27 watt bulb. Similarly, a new Maytag high-efficiency refrigerator
will consume only 1400 to 1500 watt hours (1.4 Kw.-1.5 Kw.) of power whereas a
standard refrigerator manufactured in the mid 1990s will consume almost 6 times
that amount of power. In the case of both the light bulb and the refrigerator
it is cheaper to go out and buy the newer, high efficiency version than to buy
the renewable energy equipment required to run the low efficiency version of
the appliance. We cannot stress how important it is to plan for maximum
appliance efficiency when planning your renewable energy project.
Battery Sizing Worksheet (pdf format)
Your load analysis for your den may look something like this;
2 overhead light bulbs at 15 watts each X 4 hours per day. Total load 120 watt
hours per day.
2 end table lamps at 15 watts each X 2 hours per day. Total load 60 watt hours
per day.
A 17 inch color television at 70 watts X 4 hours per day. Total load 280 watt
hours per day.
A stereo with CD player at 25 watts X 2.5 hours per day. Total load 62.5 watt
hours per day.
Your total daily power consumption for the den is going to be the sum of all of
these totals or 522.5 watt hours per day.
Now we can go from room to room and list each appliance in this
manner and when we are through we will have an accurate load evaluation for the
entire home. Don’t forget the garage and any outbuildings that will need to be
supplied. If there is a water pump, don’t forget to calculate that in as well.
Click on Load Evaluation Form (pdf format)
and print it out to make this part of the project easier. Also you will find
some samples of how much power various appliances consume by clicking on
Power Consumption Tables.
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