Does Efficiency Really Save When Installing a PV System?

| 3/9/2009 4:15:00 PM

Tags: energy efficiency, solar panels, Dan Chiras,

Several readers have questioned the validity of my assertion that energy efficiency can dramatically reduce the initial cost of a solar electric system. In my blog Making Solar Electricity Affordable, I noted that each dollar invested in efficiency could save $3 to $5 in initial costs. The reason for this is that it is much cheaper to save energy than to generate it with a photovoltaic (PV) system.

To illustrate my point, I’ve included a table from a book I am publishing later this year entitled Power from the Sun. It’s an introduction to solar electricity that’s being be published by New Society Publishers. This data was provided to me courtesy Kurt Nelson, an experienced PV installer and teacher.

In Table 1, I list four energy efficiency measures and how much they’ll save a homeowner in watt-hours (column 4). Column 5 shows the cost of each measure.


Table 1: The Cost of Energy Measures and Energy Savings

Efficiency Measure  New Consumption  Old Consumption  Energy Savings  Cost to Implement 

New Refrigerator

1,300 Wh/day

2,200 Wh/day

900 Wh/day


New Chest Freezer

900 Wh/day

1,800 Wh/day

900 Wh/day


Six 18-Watt CFLs

432 Wh/day
(@4 hrs/day)

1,800 Wh/day
(six 75-watt
@ 4 hrs/day)

1,368 Wh/day


Eliminate Phantom Loads
via Power Strip


384 Wh/day

384 Wh/day


Table 2 lists the daily and annual savings in kWh and the total cost of the improvements. It also lists the annual savings and the cost of the system. As you can see, the return on investment is 5.5 percent. These measures will save about 1,296 kWh of electricity per year. These changes cost nearly $1,700.


Dan Bossenbroek_1
3/9/2009 9:38:13 PM

Great article. It's interesting that those results can be achieved by using lower cost effective measures like replacing refrigerators and freezers. I'm sure the ratio of the cost of PV vs energy saving measures would be even higher if you had included a programable thermostat, low flow shower heads, weatherizing windows and adding insulation.

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