Location: Boulder, Colorado
SF: 4,600 SF conditioned space
Year Built: 2005
Bedrooms/Baths: 5 bedrooms; 3 full, 1 ¾, 1 ½ baths
HERS Score: Converted to post-2006 metric: -3 confirmed
Utilities: All-electric after July 2007 (natural gas-capped)

Electricity
Grid-tied 8.74 kW roof-mounted PV array (2 locations), producing ~12,586 kWh per year
Solar Thermal
(12) 4×8 roof-mounted Novan flat plate collectors provide all space, water and spa heating needs

• Very tight, super-insulated building envelope and high performance windows
• High Passive Solar Heat Gain: Lots of sun/heat absorbed by sunspace. Heat distributed throughout house via fans and ducts
• Solar Thermal Heating: Heat stored in 6,000 gallon “heat battery” tank hooked up to roof-mounted solar thermal collectors; provides domestic hot water, as well as radiant floor heating
• Cooling: Earthtubes deliver 65-75 degree F air through Energy Recovery Ventilator (ERV). Coolerado supplies whole house with super-efficient air conditioning (runs on 1/3 power used to run a hairdryer!)
• Extracurricular Amenities: Outdoor spa, steam shower
• Cloudy Cold Snap Backup Systems: 20 gallon electric water heater

• High fly ash content in all concrete
• FSC-certified wood for framing
• Recycled dairy tank for 6,000 gallon water storage tank
• Formaldehyde-free cabinets & carpet plus low-odor wood finishes
• Low-toxic, water-based floor finish & sealant-free countertops
• Low-solvent construction adhesives
• Salvaged and environmentally preferable flooring

In an effort to be as transparent as possible about the methods and materials used in our zero net energy homes, we dedicated this section to everything anyone might need to know about Solar Harvest. Scroll down to read updates, milestones, and technical documents compiled through the last five years.

• Solar Harvest technical poster
• Solar Harvest booklet details the diverse methods and materials used in building Solar Harvest
• Presentations about Solar Harvest in from various conferences and lectures

2009 Update

Closing out the third year in a row that Solar Harvest has received a letter and check for Xcel Energy’s Solar Rewards program, we can confirm Solar Harvest as an energy producer.  Although the checks are meager, the real value is the pride felt by Ecofutures, Eric, and his family, knowing that Solar Harvest surpassed expectations as a net-energy producer.

How do you calculate a homes’ net energy production? The annual zero net energy total varies daily – even hourly – because at any given time the home’s energy balance is in flux. Taking two readings at different times will result in different net-energy balance readouts. Since the final energy readout is only a snapshot in time, when that snapshot is taken has implications for how well the house looks from a zero energy perspective. What we’ve learned is that these homes produce more energy than they consume April-October. Then they use more than they make in the winter.

So, taking a meter reading in the middle of the winter makes the home’s annual energy balance look the least favorable. The fact that despite this meter-reading disadvantage Solar Harvest received a check crediting it for extra energy sent to the grid reinforces its success as a net-energy producer. Also, with the home being all-electric with no wood burning appliances, the excess kWh in the January reading are a true, one-to-one zero net energy marker: On a site basis, the home made more energy than it used.

2008 Updates

• Solar Harvest, the first three years published for the 2008 Boulder County Tour of Solar & Green Homes, this update provides findings and lessons learned to date at Solar Harvest
• Performance verification update with our live data display online here, we are proud to publish our first performance verification update demonstrating Solar Harvest’s operation as a net-energy producer
• Major specifications update (2008)
• Xcel Energy’s Solar Rewards letter and check for 2008

2007 Updates

• Advanced cooling systems, electric appliances, and additional PV installed Read why
• Energy Performance Monitor goes live!
• Xcel Energy’s Solar Rewards letter and check for 2007

2006 Updates

• Denver Post launches a cool interactive graphic online highlighting Solar Harvest’s unique construction and energy systems
• Major specifications update (2006)
• Milestones of the first year
• Line graph representing amount of energy generated since the net meter was installed in April, 2006 and a chronology of significant events in the home’s first year. Over 1,000 kWh of electricity generated & fed to the grid by October!
• Xcel Energy’s Solar Rewards letter and check for 2006

2005 Updates

• ENERGY STAR certificates and test results verifying Solar Harvest as the highest-rated home in Colorado
• Solar Harvest PV return on investment and payback calculation showing how many years will pass before the home’s 6.84 kW PV system “pays for itself” at 4 different rates of energy rate increase
• Building Load Summary, Domestic Load Survey and Energy Use Analysis were all tools used by engineers to predict anticipated energy use and support that Solar Harvest does not need a back-up heat system

Background

In April 2007, EcoGauge data monitoring providers outfitted Solar Harvest with temperature, energy and comfort system sensors that broadcast signals live to the web, enabling Solar Harvest to be one of the first net-zero energy homes to provide performance verification data to the public. The performance data gathered is be displayed both live on the web and in excel spreadsheets for trending and graphing.

The energy side of Solar Harvest’s data monitoring system, featured in this performance update, is centered around a web energy logger that connects to 2 “Watt Node” Pulse Output Meters by Continental Control Systems. These advanced energy-monitoring devices accurately track how much energy the PV system is producing and how much electricity the home is “buying” from or “selling” to the grid. It is using these numbers that we can most accurately judge whether Solar Harvest has met its net-zero energy goal, as featured in this update.

We are proud to announce that data collected over the past year supports what we have known is true: Solar Harvest is a net-energy producer! For the all plug loads, appliances, HVAC, spa and other electric demands, Solar Harvest used 2.19 kWh per square foot.

2008 Solar Harvest NZEH Monitored Data Result Summary

Solar Harvest produced 1,165 kWh more electricity than it consumed from September 1, 2007 – August 31, 2008*

*September 1, 2007 – August 31, 2008 was selected as the first year annual energy summary date range because this range accurately tracks energy used when the home is fully all-electric. Prior to September 1, 2007, natural gas appliances were used for cooking and clothes drying. Also, as of September 1, 2007, the supplemental 1.9 kWh PV power was fully online & producing energy.

Solar Harvest Annual Net-Energy Production Summary Table

Key Points

• As a 4,500 sf home, Solar Harvest uses 2.19 kWh/square foot for all of its energy needs including appliances, electronics, fans, and outlets
• Solar Harvest produced a surplus of 1,165 kWh
• A surplus of 1,165 kWh could have:
• Driven an all-electric car 4,369 miles (at 3.75 mi/kWh)
• Saved Eric Doub & his family 97 gallons of diesel (@ 45 mpg)
• Which means, Eric could have saved $439 worth of diesel last year!
• A surplus of 1,165 kWh sent to the grid also means:
• 3,495 kWh not produced at Xcel’s power plants for use in other homes
• 2,085 lbs CO2 avoided from being produced for use in other homes

* Add this to the CO2 emissions avoided because Solar Harvest consumed of solar energy for most of its needs throughout the course of the year, and Solar Harvest prevented 17,422 lbs of CO2 from entering the atmosphere!

2008 Solar Harvest Cooling Season Energy Results

During the month of July, 2008 Solar Harvest met the goal of being a net-energy producer. This data points out the phenomenal thermal performance of the home, and of the Coolerado Cooler, whose installation faced some initial criticism from builders and spectators of the net-zero energy home world.

Even with the Coolerado air conditioner going full time in July 2008, Solar Harvest used consumed about 660 kWh and produced 1095 kWh, for a net production of 435 kWh. That is a very powerful metric: That a 4,500 SF house, cooled to 72F, 24/7, in a heat wave with over 23 days over 90F, used only 660 kWh!

• HERS Certificate

• Articles & video/radio interviews featuring Solar Harvest
• Sign up to tour Solar Harvest
• View finished photos of Solar Harvest (Flickr)

Taking lessons from our flagship ZNE home, Solar Harvest, Ecofutures is building and retrofitting a number of new homes each year with a zero energy goal. We are regularly tracking the specifications and performance of each homes’ ZNE features for the sake of comparison and education. View the ZNE Comparison Chart.