Climbing the Energy Everest

The Ups & Downs of

Creating a Net Zero-Energy Home by Mel Tyree

carbon free

Living plants rely on solar energy as their primary energy source, so why not a house? In July 2000, my wife Charleen and I set our sights on building a net zero-energy home. Our goal was to demonstrate that you can operate a comfortable, modern home—even in a climate-challenged location—without burning anything.

The Tyrees' barn was designed to perfectly accommodate a 10 KW PV array.

The Tyrees' barn was designed to perfectly accommodate a 10 KW PV array.

At the start of the project, I was inexperienced in building design. But I had spent much of my career in biophysics immersed in numbers and calculations, working to quantify the exchange of energy and matter between sunlight, the environment, and plants. When I began running energy systems design calculations for our new home, I was amazed by how well my years of seemingly unrelated research had prepared me for the journey ahead. Along the way, we had to overcome some unique regulatory and technical challenges, but, in the end, patience and determination gave way to a carbon-neutral home that derives 100% of its energy from the sun and wind.

The motivation to build our zero-emission home came from the desire to reduce our contribution to global warming and pollution. That meant eliminating our home's dependency on all conventional fuels. Homes with solar- and wind-electric systems commonly rely on natural gas, propane, heating oil or firewood for cooking, as well as water and space heating. We wanted to prove that it is possible to live in a home that offsets 100% of its energy with renewable, nonpolluting sources.

The first step was to find a location for our new home. Over several months, we came across four suitable properties in our home state of Vermont, but our potential neighbors were opposed to the notion of having a wind turbine in their backyard. Eventually we widened our search to the North Country of New York, where we found a beautiful, affordable property that met our needs—102 acres of forest and pasture, in Ellenburg, just north of Adirondack Park at 44.9° north latitude.

New York state's net-metering law for residential RE systems allowed excess energy credits to be carried forward to the end of the annual billing cycle and supported property tax exemptions for the systems' value. In addition, the New York State Energy Research and Development Authority carbon free

Erecting the tower—10 feet at a time. Final section—120 feet up. Hoisting the rotor.

(NYSERDA) offered generous financial incentives for both PV and wind systems. Based on some initial conversations, neighborhood support for wind generators seemed positive. I also learned that the town of Ellenburg has no zoning regulations that prevent erecting a 120-foot tower for the wind genny. Our project's future looked bright. We closed on the property in October 2003 and were on our way.

Our Big Picture Energy Plan

Offsetting 100% of our energy needs would be no small feat given the cold, cloudy winters and humid summers in Ellenburg, which sits about six miles from the Canadian border. Key to our plan was a ground-source electric heat pump for space heating and cooling (see "Get Pumped" sidebar). Producing the electricity needed to run our heat pump—an estimated 7,400 kilowatt-hours per year—would require substantial RE generation capacity. And while our heat pump is also designed to assist in domestic water heating, we'd still need to generate about 3,000 KWH annually for our tank-style, backup electric water heater. Even though using energy-efficient appliances and lighting would help keep the remainder of our loads to a minimum, our annual electrical load still came close to 17,000 KWH.

Because net-metering eligibility in New York limits the size of residential PV systems to 10 KW, we planned to add a 10 KW wind turbine to the 10 KW PV array. Based on our site's solar and wind resources, this hybrid system was projected to offset 100% of our home's energy use. Ice storms can cause extended power failures in our area, so we wanted a grid-tied PV system with battery backup, which would supply electricity for the critical loads: an emergency backup oil furnace, well pump, refrigerator, some lights, and a microwave.

Working the System

Our plan was to install wind and PV systems prior to building the house, and we didn't want to waste any time. Within days of closing on the property, we contracted Sustainable Energy Developments Inc. (SED) of Ontario, New York, to install a 10 KW Bergey wind generator on a 120-foot tower. But, in all the excitement, we overlooked a few critical details. Apparently, our local power company, New York State

Even just the rotor assembly of the 10 KW Bergey is big and heavy.

Even just the rotor assembly of the 10 KW Bergey is big and heavy.

carbon free

Electric & Gas Corp. (NYSEG), was not very supportive of on-site residential power generation. Even more sobering, at that time, was that New York's residential net-metering legislation for wind systems was not as favorable as it was for PV systems. We would be credited only 4.2 cents per KWH for excess energy our wind turbine produced but would have to pay 17 cents per KWH for this "premium" electricity when we needed to buy it back from the utility.

Another hurdle came when we discovered that the state's property tax exemption for solar- and wind-electric systems was voluntary, and that our local tax authority was one of the few in the state that had opted out of the program. Based on the full-retail value of our planned RE systems, the associated property tax payment would amount to $3,000 per year. By the numbers, our project made little economic sense. But we weren't going to give up that easily.

We became frequent faces at city council and school board meetings, grabbing anyone and everyone's ear whenever we could to make our case for reversing the property tax policy. For all our effort, we did persuade the local tax assessor to add a new stipulation that the property taxes for each new system would not exceed $227 per year—versus the $3,000 we had originally projected. Other good news was that the New York state legislature was on board to approve a bill that restructured the net-metering rules for wind energy. According to these rules, which went into effect in 2006, we would get full retail value for excess energy produced in any given year, provided that the energy credits were used within the same 12-month period. With the dollars-and-cents side of things looking more promising, we decided to proceed with our project.

Wrangling the Wind

Due to all of the regulatory hurdles, it wasn't until August 2005 that the Bergey wind generator was up and spinning. The actual wind turbine installation went very smoothly. SED did a fantastic job assembling the tower, turbine, and balance of system components. However, we couldn't find an appropriately sized crane within any reasonable distance from the site to lift a pre-assembled tower. The resulting section-by-section installation of the tower using rigging and a gin pole turned out to be one of the highlights of the project for me.

Anyone with long-term experience with home-scale wind systems will tell you that the technology isn't for the fainthearted, and my experience mirrors this seasoned perspective. Compared to low-maintenance PV modules, which have no moving parts and typically carry 25-year warranties, wind turbines are inherently reliant on rotating parts that are exposed to some of the harshest conditions imaginable. Turbines have a tough job to do and, over time, can fail. While our wind turbine installation went without a hitch, some technical issues with the system still lay ahead.

Not all wind turbines, inverters, and their use together in a given system will produce similar results when it comes to producing energy. In our system, on days where wind speeds

Get Pumped

The ground-source heat pump that heats and cools our home—and supplements domestic water heating—is our biggest load, consuming almost half of the electricity our RE systems generate. This amount might sound high, but it's actually quite low because of the high efficiency of the heat pump and its ability to take advantage of ground temperature. If we burned carbon-fuel (like oil or natural gas), the heating load would account for 72% of our home's total energy consumption.

Since our goal was to reduce our carbon footprint to zero, fossil-fueled appliances were out. Electric resistance heating would have been an option, but ground-source heat pumps deliver heat with less energy input. A ground-source heat pump takes advantage of the relatively constant temperature below frost level in the ground—transferring ground heat to the home in the winter and the home's heat to the ground in the summer. These systems put out a lot more heat energy than the amount of electric they consume (300% plus), even on the coldest of winter nights. In our system, for every 4.3 KWH of energy sent to the house, the compressor consumes just 1 KWH for an overall efficiency of 330%. (For more on heat pumps, see "Heat from the Earth—A Heat Pump Primer" in HP98.)

Hot Air Out:

Heat Exchanger:

Refrigerant to potable water and air


Heat Exchanger:

Groundwater to refrigerant

Heat Exchanger:

Groundwater to refrigerant

150 ft. Between Wells-

Water Flow Through Aquifer:

Heated by earth


Hot Air Out:

Heat Exchanger:

Refrigerant to potable water and air


Dump Well:

220 ft. deep

150 ft. Between Wells-

Water Flow Through Aquifer:

Heated by earth

Pump carbon free tech specs


System type: Grid-tied, solar- and wind-electric with battery backup

Location: Ellenburg, New York

Solar resource: 4.3 average daily peak sun-hours

Average annual PV system production: 10,400 AC KWH

Wind resource: 12 to 13 mph average wind speed

Average annual wind system production: 8,800 AC KWH

Utility electricity offset: 100% plus

PV System

Array: Five subarrays of 16 modules each, four modules per series string, 70.4 Vmp, 10 KW STC total

Array installation: UniRac SolarMount racks on south-facing roof, 45° tilt

Array combiner box: Five OutBack PSPV with four 15 A breakers each

Batteries: 36 Rolls Surrette KS-21, 2 VDC nominal, 1,000 AH at 20-hour rate, flooded lead-acid

Battery bank: Three series strings, 3,000 AH total at 24 VDC nominal

Charge controllers: Five OutBack MX60, 60 A, MPPT, 70.4 Vmp input, 24 VDC nominal output

Inverters: Two Xantrex Series 2 SW4024 inverters with Grid Tie Interfaces (GTIs), 4 KW each, 8 KW total, 24 VDC nominal input, 120/240 VAC output

System performance metering: Two form 12S AC KWH meters

Wind System

Turbine: Bergey Excel-S

Rotor diameter: 23 ft.

Rated energy output: 10,800 DC KWH/month at 12 mph (5.4 m/s)

Tower: Bergey XLG37 guyed-lattice, 120 feet

Inverter: Xantrex GridTek 10, 10 KW, batteryless grid-tie, 240 VAC output

System performance metering: AC

KWH meter repeatedly exceed 28 mph, our Xantrex GridTek 10 inverter spends much of its time in standby mode. The turbine's power output increases as blade speed increases to 300 rpm—where the nominal maximum output of 10 KW is produced. In winds exceeding 28 mph, the turbine's rpm continues to slowly increase. At 420 rpm (12.4 KW output), the inverter goes into standby mode to protect it from being overloaded. The inverter is designed to stay in standby for five minutes before turning on again. It will attempt to go back online regardless of how fast the blades are spinning.

But if the inverter tries to reconnect when the turbine is spinning faster than 460 rpm, it goes offline and stays that way until I notice it and do a manual reset. At times, there may be hours or days of lost production if I'm traveling or don't notice that the inverter is offline. This issue isn't unique to my unit: Testing at the National Renewable Energy Laboratory (NREL) documented this behavior back in 2002. Because I only recently added anemometers to the tower for measuring wind speed, I can't yet be certain how much energy production is lost due to this issue, but I estimate between 8% and 15%.

Considering what was to follow, the inverter performance issue was minor. In February 2006, the wind generator threw a blade. This caused the turbine to vibrate so violently that it broke the pivot point connecting the turbine mount to the tower and the turbine fell—my $23,000 wind generator was toast. Fortunately, the 1,100-pound turbine did not hit any guy wires on its way down—otherwise it could have taken down the tower with

carbon free

carbon free

Ready to be wired: A bank of 36, 2-volt cells can provide about 60 KWH hours of backup electricity.

it. A batch of defective blades was the cause of the failure. The system sat idle for almost six months until we received a new turbine in August 2006. The five-year warranty covered all the costs, and Bergey generously compensated us for the value of our lost electrical production—above and beyond the warranty terms.

Harnessing the Sun

In the spring of 2005, while we waited for our replacement wind turbine to arrive, construction of a new barn was underway. The barn faces toward true south with 1,000 square feet of roof area for our 10 KW PV array. We contracted Vermont Solar Engineering to design and install a grid-tied solar-electric system with about 60 KWH (at 80% depth of discharge) of battery backup for critical loads. An array of 80 BP Solar 125-watt modules would feed five OutBack MX60 charge controllers. But before we got very far into the project, we hit a few more regulatory stumbling blocks.

NYSEG rules did not allow both a wind and a PV net-metered system on the same residential line. A call to NYSERDA confirmed this, but they said they were in the process of redrafting rules. NYSERDA contacted all power companies in New York and found that Niagara Mohawk would allow that combination. This gave the NYSERDA the leverage they needed to rule that all New York power companies must follow the policy allowed by Niagara Mohawk.

That good news came with caveats, though. Due to the state's 10 KW cap on residential net-metered PV systems, NYSEG would not approve the use of more than 10 KW of rated inverter capacity. This restricted our inverter choices and ultimately resulted in a less-than-optimal system. To meet code, we ended up undersizing the inverter capacity to 8 KW and selecting older-model Xantrex SW inverters. It was a clear case of poor regulations dragging technology down with them, as a variety of more efficient battery-based inverters are currently on the market.

Setting aside the regulatory walls we hit, our PV system has been operating without a serious glitch since November 2006. We were pleased with the job Vermont Solar did on our installation, and they promptly corrected a couple of minor problems.

Hitting Zero

At long last, the day came to break ground for our new home. After nearly four years working through the regulatory and technical issues related to the power systems, building the house went surprisingly smooth, taking only about four months. By January 2008, we were moved into our new two-story home. The home features all the modern conveniences and amenities, as well as low-E windows, low-toxicity materials, and energy-efficient electric appliances.

Although the up-front costs of our home's energy systems tacked on an extra 40% to the cost, the investment was well worth it. NYSERDA provided a 50% rebate on the installed cost of both systems, and we were able to take advantage of state and federal tax credits, which lowered our initial system costs significantly. In the long run, as utility rates continue to climb, the cost to operate the home will be far less than a conventional home that depends on fossil fuels. Over the past nine years, the price of electrical energy has been increasing at 3.7% annually and fuel oil has increased 14.6% per year. Taking this into account, I've calculated that our initial return on investment is about 5.4% per year and increases each year as the projected cost of energy goes up. This results in an estimated financial payback period of 10 to 11 years.

While there were definitely some frustrating phases during the project, our solar-electric and wind systems have been operating smoothly for more than a year. I'm proud to say that we've reached an actual production of 19,000 KWH, and are offsetting more than 100% of the energy required to heat, cool, and power our new home, without relying on any fossil fuels or wood. Despite the problems, I wouldn't hesitate to tackle the project again.


Mel Tyree ([email protected]) is a university professor who likes to build scientific equipment and tinker with electronics. As a public service, he compiles and posts information about small wind turbines on a University of Alberta Web page, called the Small Wind Information Exchange Program (

Sustainable Energy Developments Inc. • 585-265-2384 • www.sed-net.comWind power equipment and installation

Vermont Solar LLC • 800-286-1252 • • Solar-electric equipment and installation

Small Wind Info:

AWEA Small Wind Listserve •

SWIEP • or http://tech.groups. • Consumer reporting group on wind systems

System Components:

Bergey • • Wind turbine

BP Solar • • PV modules

OutBack Power Systems • • Charge controllers

Surrette • • Batteries UniRac • • PV mounts

Xantrex Technology Inc. • • Inverters rfrSr

Ready to be wired: A bank of 36, 2-volt cells can provide about 60 KWH hours of backup electricity.

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