More on solar electric

More on solar electric

By Dan Slattery

More on Solar Electric

Although there are monetary incentives for investing in solar power available through ComEd and the state of Illinois, the following point cannot be emphasized strongly enough—you must capacitate your existing structure (home, office, etc.) for maximum energy efficiency, first and foremost.

This means replacing your light bulbs with high-efficiency compact fluorescent lighting, replacing your appliances with thoseavailable on the market today, such as the “Energy Star” series.

If these preliminary needs are not met, it is akin to heating your house with the windows wide open. In northern Illinois, the average homeowner’s electrical consumption is approximately 750 KWH (kilowatt hours) per month.

You must first bring your energy usage down to around 300-500 KWH/mo. to gain effective usage of solar and/or wind power.

In order to accomplish this, you must calculate what is called a “load profile analysis.”

This “load profile analysis” is what will determine the type and capacity of system you need to replace your dependence on the grid. It consists of (a) all the loads that the system will be required to power, (b) the length of time each load will be “on” during an average day, and (c) the average number of days per week that the load will be used. This information is then tabulated and turned into the “average daily watt/hour consumption.”

Another factor that must enter the equations in your analysis is what’s called “phantom loads.” These are things like your VCRs and televisions with “instant-on” features. This is because the power supplies in these items are always “on” whether they’re in use at the time or not. Also, things like cordless phones that have a “plug-in” power supply that is always running. The wattage on these items is usually printed right on the “plug-in” power supply itself. VCRs, TVs and other appliances always have a sticker or tag attached to the bottom, back or inside of the appliance indicating its power consumption rating. One example of a load profile is as follows:


AC Qty. Wattage Hrs/Day Days/Week Avg.

Appliance Watt/Hrs/Day

Light 2 60 8 7 960

Toaster 1 900 .25 5 161


Motor 1 720 6 7 4320

Total AC Watt/Hrs/Day – 5441 (5.44 KW Hr/day)

DC Qty. Wattage Hrs/Day Days/Week Avg.

Appliance Watt/Hrs/Day

Light 1 60 1 5 42.86

Total DC Watt/Hrs/Day – 42.86

(Stand-alone systems multiply by 1.35 to correct for battery & system inefficiency) (57.86)

(or .058 KW/Hrs/Day)

Largest combined load – 5441 + 57.86 = 5498.86 W/Hrs/Day

Or, 5.5 kilowatt hours per day. This is just an example. The more frugal you are with your energy use, the less it will cost you in the short and long term.

There are two basic types of solar electric systems—“stand-alone” and “grip-tie.” A stand-alone system enables you to produce and provide your own power for your own needs, independent of the grid. Stand-alone systems, however, almost always need battery back-up. Therefore, since the batteries act as a “load” on the system (via charging), the overall efficiency of these systems is compromised by a multiplication factor of 1.35.

On the other hand, a “grid-tie” system does not necessarily need battery back-up. This increases the overall efficiency of the system, and at the same time, allows you to sell any excess power you generate back to the grid (or ComEd, in our case).

I strongly recommend grid-tie systems for the following reasons: (a) You’re selling “green power” back to the grid, and if enough people do so, eliminating or curbing air, water and land pollution through the use of fossil-fuel electricity production and associated nuclear waste; (b) The utility companies are giving us more incentives than ever before to take advantage of producing our own power and selling it back to them.

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