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SUSTAINABLE DESIGN CENTER    STRATEGIES & TECHNIQUES

Sustainable Design Insights & Rules-of-Thumb —
just enough data to make you dangerous...

RULE OF THUMB: Photovoltaic Sizing & Costs

Photovoltaic Array Sizing and Costs – for 1 KW of PV

• Area required: ~ 100 SF
• Annual energy produced: ~ 1000 kwh (993 kwh in Seattle, 1040 kwh in Portland, 1750 kwh in Las Vegas)
• Installed cost : ~ $10,000 (This is a conservative number. $7500/KW is not uncommon and that cost can be cut in half in some areas because of incentives from state government, federal government and utilities)

To help commit these to memory, note that the numbers increase by one order of magnitude.

INSIGHT: Interpreting Statistics

A stat today isn’t the same as a stat yesterday. So be careful when you say a building will save “only” 33 percent, as the new ASHRAE standards are much tougher to beat by large percentages than are previous standards.

One of PAE's recent LEED buildings, for example, would be 45% better than the old standard (ASHRAE 90.1 -1999) but is 33% better than the tougher new standard (ASHRAE 90.1 -2004).

To put that in perspective:

• In LEED 2.0 projects were awarded all 10 energy efficiency points for being 60% better than ASHRAE standards at the time (90.1 -1999)

• In LEED 2.2 projects were awarded all 10 points, out of 100, for being “only” 42% better than the much tougher new ASHRAE standards (90.1 -2004)

• LEED 3.0 brought about even more changes, placing greater emphasis on energy efficiency by providing 19 (out of 110) possible points in this category.