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Solar Electricity

Conservation and Efficiency

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Energy conservation and efficiency provide the foundation for a smaller, more efficient and affordable solar electric system. It is easy to get excited about photovoltaics and other renewable energy technologies, but energy conservation and efficiency measures should be considered first. Why? Because when you or a contractor sizes your system, it is based on the amount of electricity used. The less you use, the smaller, more efficient and affordable the system will be.

It is almost always cheaper to reduce energy use than to buy a larger renewable energy system. Replacing inefficient lights, appliances, equipment, and machinery can significantly reduce the size and cost of your solar electric system. Plus, the electricity savings continue for the life of the replacements.

You or a system installer can review past utility bills to determine your electrical load in order to properly size your system.

EXTRA: If interested, use Step 9: Electricity Use Worksheet to make a list of everything that uses electricity and how much. This exercise will create an awareness of what will be powered by your PV system, how electricity use changes throughout a day, month, or a season, and will help you determine ways to reduce your electrical load. The information can also be used for calculating your system size in Step 5: System Sizing.

As an example, let’s consider residential electricity use. According to the Montana Department of Environmental Quality’s Energy Saver’s Guidebook, the top three residential electricity loads in typical Montana homes are lighting (29 percent), refrigerators (18 percent), and clothes dryers (16 percent). These numbers are for homes that use natural gas for space and water heating.

Tips to Reduce the Top Three Home-Electricity Loads


Clothes Dryers


Whether for your home, farm or ranch, upgrading to efficient lighting is one of the easiest ways to save money and reduce electricity use. If using standard incandescent bulbs for lights typically turned on for 15 minutes or longer, consider replacing them with CFL bulbs (Compact Fluorescent Lamps/Lights). CFLs use 75 percent less energy and last 10 times longer than incandescent bulbs. They also produce 75 percent less heat than incandescent bulbs. This makes them safer to operate and they can cut home or building cooling costs.

CFLs cost more at the store, but they cost less to operate (the second price tag) and are cheaper overall. They will save you money when you are paying for utility electricity and may help reduce the size or number of PV panels needed for your solar electric system! Review this comparison of a 23 watt CFL and 100 watt incandescent bulb. Both provide the same level of brightness (lumens).

Add the “value” of the time it takes to replace burned-out incandescent bulbs 9 times.

CFLs can replace incandescent bulbs for most of a building’s lighting needs. They work best and are most efficient when left on for at least 15 minutes (less than that shortens their lifespan). Halogen and light emitting diodes (LEDs) are also more energy efficient than incandescent bulbs. Larger, agricultural-based buildings can be retrofitted to use T-8 fluorescent tube lighting and other efficient lights.

Other efficiency measures for the farm or ranch include modifying irrigation systems by switching from high- and medium- to low-pressure sprinkler systems and using variable speed drives for pumps, fans, and other equipment. A farm can reduce electricity use by as much as 35 percent with variable speed drives alone. If energy and water resources are a concern, planting crops with lower water requirements reduces water use and the electricity needed for pumping. Converting to drip irrigation or a linear/pivot system also saves both energy and water.

Conserve where you can and buy energy efficient fixtures, appliances, and machinery. Look for Energy Star labels and compare the bright yellow EnergyGuide labels.

The Montana Department of Environmental Quality and U.S. Department of Energy have booklets with numerous tips on how to save money and energy.

If you hire a business to conduct an energy and/or water use assessment, select one that has trained and certified employees. BPI (Building Performance Institute) and RESNET (Residential Energy Services Network) are two certification programs for homes that use the HERS (Home Energy Rating System). Your utility company may provide a free or low-cost assessment.


Energy Trust of Oregon. (2010, April). Reduce Irrigation Energy Costs. Retrieved April 30, 2011, from http://energytrust.org/library/forms/PE_BRO_Irrigation.pdf

Montana Department of Environmental Quality. (2011). Energy Savers Guidebook: Practical Ways to Save Money and Improve Comfort. Saturn Resource Management. Document Version 03.11.2011.

Sustainable Agriculture Research and Education (SARE). (2008, February). Clean Energy Farming: Cutting Costs, Improving Efficiencies, Harnessing Renewables. Retrieved April 30, 2011, from http://www.sare.org/Learning-Center/Bulletins/National-SARE-Bulletins/Clean-Energy-Farming

U.S. Environmental Protection Agency. (2011). Find Energy Star Products. Retrieved April 11, 2011, from http://www.energystar.gov/index.cfm?c=products.pr_find_es_products

U.S. Environmental Protection Agency. (2011). Light Bulbs (CFLs) for Consumers. Retrieved April 11, 2011, from http://www.energystar.gov/index.cfm?fuseaction=find_a_product.showProductGroup&pgw_code=LB