Whole Energy Solar - Zero Energy Homes

Zero Energy Buildings

“I’d like to have enough solar panels to cover all of my electrical bills.”

We’ve heard this question a lot in the past seven years. It was 2002 when Idaho Power introduced their net metering program and Whole Energy Solar began designing and installing grid-connected solar electric systems. That was when solar became a viable option for homes and businesses with access to utility electricity. Prior to that, the use of solar electricity was limited almost exclusively to remote buildings without access to utility power.

According to Idaho Power numbers, by 2009 Whole Energy Solar had installed about 30% of all the solar energy systems on their net metering program.

“Zero Energy” – the concept of producing with solar as much electricity as a home or business consumes over the year – can be difficult, but entirely possible when combined with conservation and energy efficiency. We give below two examples of “zero energy” homes with solar electric systems designed by Whole Energy Solar. But first, it makes sense to address the importance and value of being energy efficient.

Conservation
For most existing homes and businesses, we point out that their current consumption would make it very expensive to purchase a solar electric system that covered their entire bill. It costs less and is a more efficient use of finances to examine your electrical use and find ways to conserve. It is also more satisfying for the owner and for us to install solar panels that meet a significant portion of their actual electrical needs. Conserving and becoming more efficient means that the same solar electric system will cover a larger portion of the building’s usage. Sometimes however, owners do choose to install solar first and then use that investment to motivate their quest for greater energy efficiency – replacing incandescent bulbs with CFLs, replacing old refrigerators or freezers, increasing insulation if heating or cooling with electricity, etc. Becoming more efficient over time will continue to make the solar fraction increase. With new construction done with electrical efficiency in mind, ” zero energy” is a more readily achievable goal.

How Much Solar for Zero Energy?
Since electrical usage varies widely among homes and businesses – depending on electrical appliances and actual usage – there is no single answer that can satisfy the question of how much solar. You have to look at actual electrical bills. But we can take a look at averages and give a sense of what’s possible.

The national average for a single family home’s electrical consumption is approximately 30 kWh per day. Idaho Power says their average home consumes 40 kWh per day – presumably more than the national average because of historically low electrical rates and a higher percentage of homes heating with electricity. Heating is something that requires large amounts of electricity.

The recent drop in solar prices has made the concept of zero energy buildings more accessible. The following table gives the approximate price of installed solar electric systems that would match the electrical use for three baseline home consumption averages. The estimated solar production is for typical installations with the amount of sun available in Boise, ID. (For locations with more sunshine the cost would be less; where the sun shines less, the cost would be more.)

Cost of Solar for “Zero Energy”

Electrical Use	Electrical Use (kWh/day)	Cost of Solar to Match 100% of Use	Cost after 30% Federal Tax Credit	CO 2 Offset (tons per year)
Half National Average	15	$30,500	$21,350	5.7
National Average	30	$59,000	$41,300	11.5
Idaho Power Average	40	$89,000	$62,300	15.3

Note: Businesses have an even better federal tax credit with an additional accelerated depreciation schedule that can mean the federal government pays for up to 60% of the cost of a solar energy system.

Two Examples of Homes designed for net “zero energy” electricity by Whole Energy Solar:

New Construction “Zero Energy” Home

LEED Gold home designed with many green features including passive solar design (by Rebecca F. Bundy Design for Sustainable Living www.rfbundydesign.com), Idaho’s first constructed wetland for wastewater treatment and reuse (by Whole Water Systems www.wholewater.com) and a solar electric system designed to match the owner’s target use of 24 kWh/day (by Whole Energy Solar www.WholeEnergySolar.com).

Solar Electric System (rated DC watts)

Estimated Solar

Electrical Production

(kWh per day)

CO 2 Offset

(tons per year)

6,080

24.1

9.2

Retrofit “Zero Energy” Home

Solar electric system for an existing home that was designed to produce an amount equal to the measured electrical consumption for the past year. The homeowner had a frugal electrical consumption of about half the national average.

Solar Electric System (rated DC watts)

Estimated Solar

Electrical Production

(kWh per day)

CO 2 Offset

(tons per year)

3,990

15.4

5.9

Green Building and “Zero Energy”

Green building programs like the U.S. Green Building Council’s LEED rating system give credits for installing solar electric systems that meet certain percentages of a home’s estimated electrical use. At the forefront of green building, the Living Building Challenge goes so far as to mandate that homes or buildings that aspire to their standard produce 100% of their energy and are verifiably “zero energy”. We find it inspiring to note that there are now homes among us that have taken a large step towards this lofty green goal by investing in solar energy systems intended to produce all of the electricity they use.