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 Interactive Energy Calculators
Our calculators help you understand energy production and consumption in a whole new way. Use them to develop a personal profile of your own energy use.

Carbon Pollution Calculator

Electric Power Pollution Calculator
PV System Economics
Solar Water Heating
What's a Watt?

Photovoltaic System Economics

Are you thinking about putting a photovoltaic (solar electric) array on top of your house and disconnecting your electric company? Or, of staying attached to the grid and selling electricity back to them? This worksheet does a simple, "back of the envelope" calculation of PV system economics (please do a more careful sizing before you buy something!), and can help you understand the various tradeoffs that may be involved in using this increasingly popular renewable energy technology.

Enter information about your electricity consumption, your cost of service, and your local sunshine, and the spreadsheet will help you predict the effectiveness of installing a photovoltaic system. You can click on the "?" button in any table entry for more explanation and help.

Electric Utility Photovoltaic System
Electric Consumption (KWH/Month)
Average Full Sunlight/Day (hours)
Grid Attachment Cost
PV System Peak Wattage Requirement (dc)
Electricity Cost ($/KWH)
PV System cost per peak watt ($$)
PV System Yearly Expense
PV System Lifetime (years)
Displaced Grid Electricity Cost ($$)
PV System Cost ($$)

Two other things to consider: An increasing cost of electricity, at percent per year, will increase the present value of your future grid-supplied electric consumption, while the time value of money, at percent per year, decreases it, as well as the present value of yearly PV operating expenses.

You will probably conclude that disconnecting the electric company isn't in order. On the other hand, most people could live comfortably with much less electricity than they currently use. Today, a reasonably priced PV system can supply a families' electricity if they use it efficiently, and if the electric grid isn't near, PV generated electricity may be the cheapest power source.

More information on PV:

The PV economics calculator is sponsored by the Texas State Energy Conservation Office (SECO). The calculator can also be accessed at Martindale's Calculators On-Line Center, along with other energy calculators.

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