Calculating Daily Energy Consumption

Example 1: (Converting to 100% Solar Grid Tie from Grid Use Only)

Starting from the monthly electric bill...      
1. Record the Electric Bill Monthly Consumption. 660kwh __________ Monthly Consumption
2. Divide Monthly Bill by Number of Days in Month = Daily Consumption 660 / 30 = 22 kwh __________ Daily Consumption
3. Divide Daily Consumption by number of Sun Hours at your location.* 22 kwh / 5.5 hours = 4000 Watts __________ Hourly Consumption by Sun-Hours
4. Hourly Consumption by Sun-Hours / Efficiency Correction Factor. ** 4000 Watts / 0.69 = 5797 Watts __________ Hourly Consumption by Sun-Hours (Corrected)
5. Hourly Consumption by Sun-Hours (Corrected) Divided by Size of Solar Panel Chosen. 5797 Watts / 175 Watt Panel = 33.12 Panels [32 or 34 Panels]*** __________ Each 175 Watt Panels
       
* 5.5 Sun Hours might be your Annual Average. Winter Months will be shorter and summer months will be longer. For Grid-Tie it might be ok to use Annual Average, but for Off-Grid (not Metered Electricity) one should use the Winter Sun Hours to prevent a shortage of power in the winter.
** 0.69 Correction factor includes Inverter Efficiency 0.94 x Battery Efficiency 0.90 x Panel Efficiency 0.82.
*** 32 Panels can be reduced by lowering the electrical consumption of the House. For every dollar in a lower electric consumption, you will save $5-10 in the cost of Solar Panels and other equipment.

 

Supporting Documents

Item Description Link

Web Link

Sandia National Laboratories PV System General Sizing Tool

http://www.sandia.gov/pv/docs/Wkshts1-5.html

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