A Load Analysis for the Experimental House 0

Washer and dryer

Washer and dryer

The size of a solar power system depends on how much power you need to operate the various systems and appliances in the home. Loads can be continuous (running 24 hours a day) or intermittent.  Many large loads, such as toasters, vacuum cleaners and microwaves are seldom used or are only used for very short time periods.  On the other hand, small loads can contribute significantly to the overall load if they are a continuous draw.

Small loads that are not obvious to the homeowner, because devices and appliances appear to be shut off but are still drawing power for quick power up, are generally referred to as “phantom loads” and are easily overlooked when calculating load requirements.  These loads can be mostly eliminated by installing switch controlled outlets or a switched power bar that turns off the appliances when you are not using it.

Fridge and Aquarium

Fridge and Aquarium

Designing a solar power system that is cost effective means making some choices about the household loads that are most important to you. While a solar power system is certainly capable of operating any size of load, keeping the cost of the system reasonable requires a compromise and a consciousness of energy usage on a day-to-day basis.  For a homeowner, this means making a choice of household loads that will supply the essentials such as water and mechanical systems and then selecting the appliances and devices that are believed to be most important to a fulfilling lifestyle.  A load analysis is used to determine the amount of energy in kWh used by the chosen selection of household loads so that the appropriate size of solar and /or wind charging system can be designed for the climate conditions of the area.

The experimental house was designed to operate the necessary mechanical systems for the house, such as a jet pump to pump water from a sandpoint well and a submersible septic pump for the gray water overflow septic system, and also to operate the appliances and office and entertainment devices that were the basis of our lifestyle.

Load Analysis for the Experimental House


Rated Power (W)



Water pump 1200 0.3 0.36
Septic pump 800 0.05 0.04
Kitchen Appliances:
Fridge 404 kWh/yr As rated 1.10
Coffee Maker 900 0.25 0.23
Toaster 900 0.2 0.18
Toaster Oven 1300 0.1 0.13
Electric Frying pan 1200 0.02 0.024
Slow Cooker 110 .1 0.011
Lighting and fans:
10 lights @ 15 Watts 150 2 0.3
Ceiling fans (2 @ 12W ea.) 24 4 0.1
Office and Entertainment:
Television (27”) 100 2 0.1
VCR 30 0.5 0.015
DVD Player 30 1 0.03
Radio 2 15 0.03
Stereo 20 2 0.04
Aquarium lights 45 3 0.14
Aquarium filters 20 24 0.48
Laptop Computer 50 6 0.3
Printer 10 1 0.01
Modem and wireless router 40 4 0.16
Washer (front loading) 227 kWh/yr 0.5 * rated 0.3 1
Dryer (110 V) – seldom used 398 kWh/yr 0.1 * rated 0.1 2
Iron 1100 .05 0.05
Small Power Tools 600 .1 .06
Car Block Heater 1200 .01 .01
Battery chargers 6 2 .01
(tools, cell phones, camera, etc.)
Total AC Load: 4.31
@ 90 % inverter efficiency: 4.74

Notes:  (1) The energy rating in KWh/year is based on 416 “Normal Cycle” operations per year and includes the energy required to heat the water[29]. This is more than one load per day, which is not necessary for two people. The usage estimate has been adjusted accordingly.

(2) This energy rating in KWh/year is also based on 416 operations per year[29]. Our usage would be less based on fewer loads through the washer and we often hang the clothes to dry. Again, usage has been adjusted accordingly.

Modern inverters have efficiencies of 90 to 95 per cent. Using the lowest rated efficiency of 90%, the anticipated average daily load for the experimental house would be about 4.8 kWh.

One of the things that has made it possible to use so many normal appliances for a home that’s run completely by solar and wind power is the energy efficiency improvements that manufacturers have made for modern appliances and lighting.


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