Getting to Zero


Inside this Article

Hardisky Home After Retrofit Photo
The Hardisky home—after its renewable energy retrofit.
Hardisky Home Before Retrofit Photo
The Hardisky home—before its renewable energy retrofit.
Hardisky PV System Photo
The generation from 40 solar-electric modules offsets the home’s electricity use.
Hardisky SHW System Photo
Eight solar hot water collectors supply the home’s hot water and some supplemental space heating.
Hardisky PV System Inverters Photo
Two Fronius grid-tied inverters make up the balance of the home’s photovoltaic system.
Hardisky SHW Balance of System Photo
The balance of system components of the solar hot water system.
Hardisky SHW Area Heater Photo
The solar fan-coil unit in the basement, which serves to supplement the home’s space-heating system.
Hardisky SHW Heat Pump Photo
A high-efficiency heat pump replaced the old furnace, providing space heating and cooling.
Hardisky Whole Home Photo
With the combined output of the solar hot water and PV systems, the Hardisky home should be able to reach its annual net-zero energy goals.
Hardisky Home After Retrofit Photo
Hardisky Home Before Retrofit Photo
Hardisky PV System Photo
Hardisky SHW System Photo
Hardisky PV System Inverters Photo
Hardisky SHW Balance of System Photo
Hardisky SHW Area Heater Photo
Hardisky SHW Heat Pump Photo
Hardisky Whole Home Photo

A net-zero-energy home is an ambitious goal for a newcomer to renewable energy, but that didn’t stop Tom Hardisky. Last spring, after years of exploring various options, the wildlife biologist retrofitted his 1991 ranch home in Pennsylvania with solar-electric, solar hot water, and heat pump systems that should offset 100% of his household energy needs. Home Power spoke to Tom about his project, motivations, and lessons learned, as well as the process of selecting a system designer and the challenges of navigating all of the available incentives.

Home Power: What sparked your interest in renewable energy?

Tom Hardisky: When I was in grade school some 30 years ago, my science teacher broke the disturbing news: We will someday run out of fossil fuel. She said that our generation was charged with finding a lasting energy solution without further tapping into our dwindling energy resources. I realized then that by being dependent on a nonrenewable energy supply, we were moving down a disastrous path.

HP: So, after all those years, what motivated you to move forward with this project now?

Tom: The time was right as far as incentives. In addition, electricity rate caps began expiring at the beginning of 2010 for Pennsylvania electric utility companies. My electric company, Pennsylvania Power and Light, is gradually increasing electric rates. For average PP&L customers, that translates into an increase of approximately 30% in 2010. I anticipate never-ending rate increases—I thought there would be no better time to do this.

The major financial incentive for my retrofit was the Pennsylvania Sunshine Program rebate, which provided 35% of the cost of my PV system. The only stipulation is that it could not exceed 10 kW. The combined effect of PV, solar hot water, and heat pump financial incentives actually broadened my vision. I ended up maximizing PV module coverage on my roof and investing in solar hot water and heat pump systems.

Income from solar RE credits (SRECs) was an important incentive as well. I have a five-year contract with Sol Systems LLC that pays me $280 per solar-produced megawatt-hour.

In addition, the heat pump qualified for a $400 rebate through my local electric company’s E-power Program. And, when I file federal income taxes next year, I will be able to take advantage of an available tax credit. An after-rebate 30% federal tax credit will be an important source of investment return.

HP: What made you decide to go for net-zero energy for your home?

Tom: I’m a conservationist by nature and profession, so an energy-independent home was logical and always my dream. I wanted an RE system that would meet all of my energy needs, including home heating, hot water, and electricity. I thought maybe I could set an example for other homeowners and help us move toward that lasting renewable solution proposed by my grade-school teacher.

HP: Once you got serious about the idea, what steps did you take?

Tom: When a PV installation short course was offered by the Honesdale, Pennsylvania-based Sustainable Energy Education Development Support, I jumped at the opportunity to learn more—and possibly complete most of the installation myself. The real value in taking the course was a good education in solar energy system basics—terminology, components, and designs. By the end of the three-day workshop, I realized that having basic plumbing and home wiring skills was not enough for me to take on such a project. This was no weekend project. If I wanted a well-designed, high-quality RE system, I needed professional help.

HP: How did you choose a system designer to work with?

Tom: At a local Go Green Expo, I spoke to several RE installers. Most installers were very new to the business. Their level of experience seemed to be reflected in the quality of their expo displays and their answers to basic questions, such as, ”What renewable energy system options are available?” I found that the most knowledgeable professionals had well-organized, attractive exhibits with informative literature. Designers who placed most of their emphasis on educating me rather than selling their products and services were the type of people I wanted to do business with. Installers who provided free site visits and solar analyses were on my preferred list.

HP: Why did you decide to work with the designer you ultimately selected?

Tom: Because of the questions they asked me. The best question they asked was, “What are your energy and overall project objectives?” The K.C. Larson staff also answered all of my technical questions, and they were very receptive to allowing me to reduce costs by completing some project tasks on my own.

HP: What modifications did you make to your home prior to installation?

Tom: My existing asphalt shingle roof was 18 years old but in good repair. However, the installers asked me to consider having a standing-seam metal roof installed because it would last the life of the PV system. They also asked me to specify a light color to decrease heat buildup during the summer months.

Prior to the roof installation, I relocated the plumbing roof vent pipes and exhaust ducts from the south side of the roof to the north side. That left the entire south-facing roof free of obstacles, maximizing roof space for the PV array.

The installer also recommended that I replace my 18-year-old electric water heater, so I installed a new, more efficient, 50-gallon water heater to minimize the chance of future problems. I also sealed air leaks. I installed new basement windows with a much higher R-value, insulated the attic with fiberglass blanket insulation, and caulked and added 2-inch foam insulation along the perimeter of the basement to decrease heat loss and air infiltration. 

Since the system was installed, I’ve identified additional sources of heat loss as well—namely basement doors, the electric service entrance, and other unsealed foundation wall openings/cracks. I’m in the process of completing these improvements. 

HP: Did you make lifestyle or energy use adjustments?

Tom: Although I made no major lifestyle changes, I am now much more conscious of my use of energy. Turning off unnecessary lighting was always a routine. However, soon after project completion, I found myself trying to figure out why my house used 6 to 8 kWh overnight—even when the heating or air conditioning was not running. I discovered that the outside security lighting was responsible for about 5 kWh each night.

My habits with respect to hot water usage have changed. During the warm months, I produce much more hot water than I can use. I used to wash my white clothes in warm water. Now, I always use hot water. When I need a bucket of water for cleaning or rinsing, I reach for the hot water faucet.

HP: What was the home’s initial energy profile, and how did it change?

Tom: Prior to my solar system installation, I had an 18-year-old electric water heater, no central air-conditioning, and forced-air oil heat. Annual heating oil charges were about $880, and my annual electric bill exceeded $900. My annual electric consumption over the past two years averaged 5,344 kWh.

The new heat pump provides central air-conditioning that I did not have before, and I now have a much more efficient electric water heater and electric forced-air heat. Since I did away with the old furnace, I no longer need heating oil.

Overall, my electric consumption increased by 21% since system installation, primarily because of the new electric heat pump, but during the first three months of operation, I had a monthly electric bill of $8.45—the minimum base distribution charge from the electric company.

HP: Do the systems need maintenance?

Tom: Thus far, there has been minimal system maintenance. Because of excess hot water production, I cover five of the eight solar collectors and close down half of the solar thermal system during the summer months. All eight panels will be in operation during the spring, fall, and winter. The maintenance work entails moving panel covers and closing a few ball valves. I’ll periodically change filters in my air exchanger, and that’s about it for the year.

HP: What did you learn from the installation process?

Tom: Never underestimate the effects of shading. During the design phase, the folks at K.C. Larson asked me to take my chimney down to the roofline since I had removed the fuel-oil-fired furnace. Although I did not need the existing chimney, I balked. The slight shading that my chimney temporarily casts on my PV modules in the morning seemed insignificant. However, as the sun path changed, I noticed some solar energy loss. Considering the cumulative impact of this partial shading, I decided to lower my chimney to eliminate any shading issues but still leave Saint Nicholas with suitable access. 

HP: Your goal is to produce more energy than you use. Do you think you’ll be able to achieve your net-zero target?

Tom: Energy use during the winter months will greatly influence my net-zero status. 

The PVWatts calculator estimates my PV system’s annual production at 9,750 kWh. If my energy consumption does not increase by more than 82% of last year (5,344 kWh), I should reach net zero.

With my solar hot water system and more efficient home heating and cooling, I am confident that my systems will produce more energy than I use annually.

HP: Tom did not set out initially to design a net-zero home, so how did the project evolve to that level?

Keevin: The possibility of a net-zero status arose during the final design of the solar thermal system, but after the PV system design was complete. The roof was to be completely covered with PV modules and all of the available ground space was slated for the thermal collectors. After Tom approved the solar thermal and heat pump designs, it was then I knew the home could be very close to net-zero.

K.C. Larson’s Keevin Larson discusses the energy systems for Tom’s net-zero home.

HP: How do all of the systems work together to achieve the net-zero goal?

Keevin: The air-to-air heat pump system puts out twice as much heat energy as the electricity put into it. Since the PV system generates electricity, it helps offset the heat pump’s use during the air-conditioning mode. The heat pump system also contains a backup electric resistance heating element, which is energized if the heat pump cannot provide the needed home-heating capacity. This is when the space-heating mode of the solar thermal system can help supplement the home’s space-heating needs. The less the heating element is energized, the more savings.

HP: What process did you use to design the solar hot water system?

Keevin: We installed a similar but smaller system in early 2009 for another client. This system had five thermal collectors and two 105-gallon solar storage tanks. This system proved the concept of heating the basement mass during the daytime, allowing the heat to radiate up to the first floor during the day and into the evening hours. But that other project’s basement has much more heat loss than Tom’s basement, so this system will retain a warm temperature within the confines of the basement for a much longer period of time. In other words, fewer Btu of heat are required due to less heat loss and outside infiltration.

HP: How does the SHW hydronic design optimize efficiency?

Keevin: If the basement temperature is 60°F or above and the temperature in the solar storage tank is at least 75°F, the hydronic heater can still heat the basement with solar. The heater can be advantageous due to the quick delivery of the heat—it raises the space temperature instantly, and this heated air rises up to the first floor. 

HP: What savings does the heat-pump system offer over the old oil-fueled furnace?

Keevin: Tom’s furnace used, on average, 355 gallons of No. 2 fuel oil each year. At an average of about $2.25 per gallon, a furnace with 80% efficiency would cost $20.39 per 1 million Btu. If utility electricity cost $0.11 per kWh, the cost to run his heat pump would be about $16.12 per 1 million Btu—a 21% savings.

When the weather gets really cold, below the 35ºF effective capability of the heat pump, the backup electric resistance heat will kick in. This, by definition, has a lower coefficient of performance, and uses more energy. Since it’s electric, the PV system will offset at least a portion of that. But considering completed and future weatherization upgrades, the comparative amount of heating the home will require is still unknown. 


Tom Hardisky (disky at lives on a 13-acre farm in rural Pennsylvania. He is a wildlife research biologist for the Pennsylvania Game Commission. He has bachelor’s degrees in biology and wildlife science, as well as a master’s degree in wildlife ecology.

K.C. Larson •

Pennsylvania Sunshine Program • • State incentives

Sol Systems • • RECs

System Component Manufacturers:

Schüco USA • • PV modules, SHW collectors

Fronius • • Inverters

Goodman • • Heat pump

Rheem • • Storage tanks

Comments (4)

Bill Daugherty's picture

Tom and/or Kevin:

Can you please tell me what product was used for the disconnect devices shown next to the PV electric meters in the schematic for this PV system?

I got a quote for a battery / grid tied system from a pretty good sized PV contractor here in NC. I want to back feed the main panel just as you have shown, but the tech support person at Outback (inverter manufacturer that I contacted) just glazes over and basically tells me I have to transfer all circuits that I want to back up to the inverter integral load center.

When the grid power goes out, how does this system prevent feeding 240 volts back into the grid?

Thanks in advance for your feedback.

PS, I'm surprised this is the first comment.

Bill in NC

Justine Sanchez's picture

Hi Bill,
Thanks for your comment. In the case of this particular system, there are no batteries and it is a simple grid-tied inverter that when the grid goes down, it ceases to function at all. In order to obtain it's UL1741 listing inverter manufacturers build these inverters so that they do not "island" i.e. they have to shut down (within a very short time frame) when the grid power goes that when utility workers are out there fixing the cause of the black out they will not get shocked by someone's grid-tied PV system.

The system you are describing for your home is a different case. In your situation you will have a dedicated load center that will be fed off of a battery-based inverter output circuit that is isolated from the grid during an outage. The Outback tech support person is correct, any circuits that you want to power during a utility outage have to be connected to this dedicated load center. I encourage you to check out some of our past articles on this topic:

Justine Sanchez
Home Power Magazine

Bill Daugherty's picture


Many thanks.
I understand how a battery system is typically wired with just a few circuits fed from the dedicated load center. I just e-mailed you a schematic that feeds a single 40 or 50A circuit from the dedicated load center to the main service panel, back feeding through a breaker interlocked with the main breaker to make the main panel hot, while isolating the Grid IN circuit on the inverter with a second manual transfer switch (60A panel with interlocked main breaker and generator breaker). I'd appreciate any feedback.

I did not see a way to add an attachment to a comment.

Thanks again,




I just heard back from a PV design consultant that indicated that the schematic that I emailed to you works. Because of the way the 2 panels with interlocked main / gen breakers are arranged it is not possible for the PV/Gen system to ever feed current to the grid when the grid is down.

Bill NC

Justine Sanchez's picture

Hi Bill,
I just emailed you some comments on your drawing as well. Good luck with your project!

Justine Sanchez
Home Power Magazine

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