Advances in Photovoltaic Technology

image: light-sensitive nanoparticle; Advances in Photovoltaic Technology

Paint-on solar cells? They’re on the way.

Advances in Photovoltaic Technology

Recent advances in material technology could soon lead to more advanced solar cells that can be painted or printed onto a surface, such as thin films and roofing materials.

 A new class of solar-sensitive nanoparticle, developed by researchers at the University of Toronto’s Edward S. Rogers Sr. Department of Electrical & Computer Engineering, outperforms current versions of light-sensitive nanoparticles.

Post-doctoral researcher Zhijun Ning and Professor Ted Sargent have led the work on colloidal quantum dots, manufactured nanoparticles that generate electricity from sunlight. Their research could “lead to cheaper and more flexible solar cells, as well as better gas sensors, infrared lasers, infrared light emitting diodes and more.”

Read more here.


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Making Roofs More Functional with BIPV-T Systems

PV roof photo: Making Roofs More Functional with BIPV-T Systems

New roof technology can provide shelter, electricity, and heat from a single roofing system.

Making Roofs More Functional with BIPV-T Systems

The days of underutilised, single-purpose roofs appear to be fading. New roof technology can provide shelter, electricity, and heat from a single roofing system.

Called a building integrated photovoltaic-thermal (BIPV-T) system, the new technology integrates painted standing-seam steel roof panels with thin-film photovoltaic panels and makes use of the sealed chamber between them for thermal energy.

BlueScope Steel and the Australian Renewable Energy Agency (ARENA) have recently installed Australia’s first prototype BIPV-T system at a home in Glebe. ARENA CEO Ivor Frischknecht said the roofing system was designed specifically for Australia’s climate and building environments to ensure the PV systems were durable and robust. The companies are developing the systems for commercial sales.

Read more here.

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What The Hell Is Community Solar?

Clean Energy Collective, Lowry facility

400 kW of clean solar power in action


Clean Energy Collective’s 400 kW facility at the old Lowry Air Force Base places a state-of-the art solar array into production where anyone with an electric bill can invest in solar electricity. It’s Denver County’s first community-owned solar array.

What The Hell Is Community Solar?

The state’s Solar Gardens legislation paved the way. More info herehere, and here. For existing buildings, and buildings undergoing renovation, this makes a lot of sense. You and I can invest in solar power without having to deal with panels on our roofs, maintenance, and so on.

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Ever Heard of Solar Gardens?

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Clean Energy Collective is a for-profit company that builds and operates medium-sized photovoltaic installations called “solar gardens.” As an electric user, you can purchase a solar panel or panels in a solar garden and receive a credit for the electricity the panels produce.

The basic idea is the same as a solar installation on your own roof, with a few advantages:

  • The PV array is located in a suitable location, free from any trees or other potential obstructions.

  • You don’t have to modify your home or business.

  • You own the panels, but don’t need to own a home, so renters can buy and support renewable power too.

  • CEC will maintain the panels, inverters, and so on for the life of the installation.

Last Saturday I joined about 30 other people at the company’s Cowdery Meadows site for a tour. This 500 kW project uses 2016 photovoltaic panels, and is located outside Boulder, near Superior, Colorado.

More info:

Clean Energy Collective

Solar Gardens Community Power

Summit Daily

solar installation, photovoltaic, renewable energy

Mke Dow of Clean Energy Collective talks with attendees at the Cowdery Meadow solar garden facility.

We Need Cheap Green Homes

A Cheap Green Home is a right-sized, energy-frugal house made from materials that represent the greenest practical choice. With a hefty budget, of course, anything is possible. A tight budget, though, demands ingenuity. And an affordable green home—the “holy grail” for homebuilding in this land of bloated plastic McMansions, is now a reality.

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This modern home built from a shipping container solves multiple problems. Factory assembly is more efficient, faster, and thus cheaper than traditional on-site construction. The foundation can be anything from a full basement to a system of posts. If you need more space, add more modules.

What is “green” anyway?

I think of “green” in terms of design elements, material choices, and methods. A green house builds in green features that are hard to retrofit later. It’s easier to site a house for passive solar gain than try to capture solar gain with renovations later. In contrast, you can add a photovoltaic system later with little hassle.

The green approach can be perplexing at times. Adding insulation enables the house to maintain a comfortable temperature with less energy. Some types of insulation, however, contribute heavily to global warming in their manufacture. You can see that it’s a balancing act, as each building has an impact on the planet. How small can we make that impact?

We can follow some standard practices:

  • Make it the the right size.
  • Make it tight.
  • Insulate.
  • Ventilate.
  • Use passive solar heating and passive cooling as much as possible.
  • Use the most durable materials you can afford.

Here are some examples of different approaches to a Green Home—cheap or not.

The “Standard” Green Home

You can build a remarkably efficient house with mostly standard design, methods, and materials. The Bircher Home in De Pere, Wisconsin, is a fine example. The house design incorporates passive solar gain and passive cooling, but looks like a conventional suburban house, apart from a small PV system and a solar thermal system.

Standard framing with 2×6 studs and cellulose insulation yields R-20 walls and R-44 roof. The house is well sealed, using foam and caulk, an infiltration barrier, and vapor barrier. A blower-door test rated the infiltration rate at 765 cfm, about half the typical rate at the time.

The result? The home uses 40% less energy than a comparable home in the area, and the $100/square foot cost, in 1999 dollars, is reasonable. You can get a normal-looking, high-performing house for not a lot of extra money.

The Advanced Green Home

The easiest way to get into a green home, if you can afford it, is to simply buy one from an innovative builder like Carter Scott. You’ll get a very green home that will perform well. And even though some of the green features, such as photovoltaics, add to the cost, you may be able to get an Energy Efficient Mortgage (EEM). This specialized mortgage increases the amount you’re able to borrow for a house that has energy-saving features that add to the up-front cost. The price? Market rate homes start at $289,900.

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Scott’s company, Transformations, builds zero energy homes in the Northeast U.S. They’re fairly small and a basic rectangular shape, with R-50 double-stud walls and R-64 roofs with spray foam and cellulose.

For heating and cooling, Scott has been using two mini-split heat pumps for the entire house. That’s a great cost savings over a furnace/AC system, and results in a simple, efficient, compact system. A photovoltaic system is sized to produce all the electricity each home needs. The homes are grid-tied, so excess electricity can feed into the energy grid.

What’s not green? His windows are cheap and they may not last long. The homes use vinyl siding, but you can go with fiber-cement siding for about $10,000 extra. Overall, Transformations is determining what works and what doesn’t in green home construction. And this approach is how we learn the most, from a production builder who tries new ideas and evaluates those ideas and the home’s performance after a year.

The Funky Green Home

The main floor of the NewenHouse.

The main floor of the NewenHouse.

Other ways to create a green home, cheap or not, I’ve covered with Jon Passi’s self-built, off-grid home, and with Sonya Newenhouse’s Passive House. Neither is actually cheap, but each is a functional and attractive way to a green, net-zero home. I can’t really evaluate how green they are from a materials standpoint, but Sonya’s house has a small footprint at about 25 feet square, so it’s definitely greener than a larger home. Jon’s home was framed with locally cut wood, which is a green choice. His house would be greener, in a way, if if were grid-tied, so his excess production could go to use and not to waste, but it’s very green as is.

Another approach is architect and builder Roald Gundersen’s “whole tree” building method. This approach uses unmilled, small-diameter, fast growing trees for the framing. Walls are often done with earth plaster, and roofs are often green. These are custom creations, but with extremely green materials choices.

A small, whole-tree building by Roald Gundersen.

A small, whole-tree building by Roald Gundersen.

roald bookend

Another of Roald Gundersen’s whole-tree structures.


Bircher home

Pretty Good House


Passi Home

99K House

Carter Scott

Seattle’s first net-zero home

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A Visit to A Zero-Energy Home

A few weeks ago I attended a class called “The Zero Energy House.” Jon Passi taught the class for the Driftless Folk School, and is the owner and builder of the zero-energy home we learned about. The house is located a few miles outside of Viroqua, Wisconsin, and was built over the last five years or so.

Jon did a bunch of the work himself, including installing the photovoltaic and solar hot water systems. He said he spent about $180,000 and the house is off-grid, so there is a fair amount of hardware included in that price.


Here's a view of Jon Passi's zero energy home showing the front door, the sun room, and the solar thermal system to the left.

Here’s a view of Jon Passi’s zero energy home showing the front door, the sun room, and the solar thermal system to the left.


Jon built his home mostly conventionally, with poured basement walls, two inches of foam insulation below the slab, two inches of foam insulation on the exterior, and three inches of foam insulation on the interior. The solar hot water system feeds into a preheating tank, and then into a radiant heat system in the slab. There’s also a propane-fueled water heater, a small inline pump, and a backup boiler for baseboard radiators that Jon installed on the main floor and upper floor. The backup boiler system has never been used, but Jon said he installed it in case he wants to leave for an extended time during the winter sometime in the future. Jon reports that the radiant heat in the slab does an excellent job of controlling moisture in the basement, and I can attest that it was clean, dry, and warm on a rainy October day.

On top of this relatively standard basement, Jon built the framing with locally milled lumber. However, he said he would not do so again, as the lumber was not uniform in size, so he ended up milling every piece to size. You can imagine how time-consuming that was. The walls are insulated to about R-30 with open-cell spray foam, and the ceiling is insulated to R-50 with cellulose. Jon used Hardyplank siding and has been very happy with its durability and low maintenance requirements.

Heat comes from solar gain in the sunroom, and a woodstove on the main floor, in addition to the solar thermal heat in the basement slab. As for electricity, Jon installed a 3 kW photovoltaic system, with panels installed on the roof and on a ground mount. He said he really would need only about 1 kW for his needs.

Here's a view of the ground-mount PV on the left, the solar thermal system farther on, and the recycled windmill in the distance.

Here’s a view of the ground-mount PV on the left, the solar thermal system farther on, and the recycled windmill in the distance.

Water comes from a well located 100 feet or so from the house, up a small hill. The windmill is an old model, perhaps 100 years old, and was refurbished and sold to Jon by an Amish man who specializes in old windmills. It feeds into a concrete cistern, which will be full in just six hours on a windy day. The cost for the windmill and cistern were around $8000, and Jon reports that they work well and he’s happy with them.

My impressions

Two main ideas are sticking with me about Jon’s house: how normal it seems, and how feasible the whole project seems. I think most of us could pull this off.

Jon’s house looks utterly normal inside and out, with just a couple clues that it’s not. When you enter the main floor, you might notice the thick walls; the window sills seem to be about 12-15” deep. And as you walk around to the back of the house, you’ll see the photovoltaic panels and the solar hot water system. That’s about it.

Jon’s house, at about 2,500 square feet, seems oversized for one person. But it’s a more flexible size than a tiny home of 500 square feet, and is roomy enough to easily accommodate a family. And it seems that most families could handle this house just fine, as long as one person is willing to learn how to run the PV, solar thermal, and electrical systems. A smaller house would be cheaper to build and easier to heat, but this one may be easier to sell for use as a full-time home.

The main floor houses the woodstove, kitchen and dining area, and sunroom. The sunroom can be opened up and closed off with glass-paned French doors. I have had a similar space in one of my previous homes, and can attest that a properly designed sunroom can provide a great amount of free heat in cold, sunny weather. Without doors to completely close off the space, though, the sunroom will drain heat from the rest of the house after the sun sets.

The kitchen is the heart of the main floor.

The kitchen is the heart of the main floor.

The built-in dining table anchors the kitchen area; french doors to the sunroom are visible beyond.

The built-in dining table anchors the kitchen area; french doors to the sunroom are visible beyond.


The sunroom, with thermal-pane windows, warms up nicely on sunny winter days.

The second-floor has a bathroom and a couple large bedrooms, with a large open area that Jon uses like a living room.

The second floor houses two bedrooms, a bathroom, and this living area.

The second floor houses two bedrooms, a bathroom, and this living area.

I like the solar thermal-radiant floor heat system, as the basement was quite comfortable. In warm weather you can simply shut it down and let the concrete mass cool. In cold weather the system can provide a substantial amount of heat, then automatically store it in the slab. I wonder about the cost, though, and its effectiveness in warming the second floor of the house. I also wonder if it would be cost-effective to install a loop for a wood boiler. It would be a redundant system, but would be functional when it’s cloudy. That’s a discussion for another day.

My main question in living with this house would be cooling. Sleeping in hot and especially humid weather is pretty sketchy for me. The bedrooms are upstairs, and I wonder if the windows can provide enough cross-ventilation. Fans can help a lot, but when it’s wicked hot out they’re just not enough. Maybe a mini-split system system would work to just cool the sleeping areas at bedtime. I’ve seen systems that draw only 900 watts or so in cooling mode, but more in heating mode. If that draws too much power from the PV system, I suppose I could sleep in the basement.

Diagram of a ductless mini-split heat pump system. Creative Commons photo courtesy of

Diagram of a ductless mini-split heat pump system. Creative Commons photo courtesy of

The main ideas to remember with this house are these:

  • A superinsulated and methodically air sealed house can look conventional yet work very well for creating a net-zero home.
  • Superinsulating, air sealing, and passive solar design make heating the home much easier.
  • The solar thermal and photovoltaic systems are more complex to manage than grid power, but it’s not that complex; just about anyone can learn how to run the systems in this house.
  • Jon learned it all when he decided to build his own house! “I had no idea you could even run an entire house off solar ’til I did it, and the same with solar hot water. The alt-energy stuff still amazes me, because I used to think the kind of house I now live in was an impossibility, or that it only was for super-rich people.”

What would Jon do differently?

After living in a house, there are bound to be some features that could be tweaked. Jon said that he would make a few changes, as well, if he were to build again.

“I’d put a masonry stove in it to heat it, and I’d probably make it underground, or semi-underground, plus I’d put the well farther up the hill so I’d have better, free water pressure. I bought lots of lumber for the house from the Amish, because I wanted to use local wood, but I had to re-mill every bit of it, so I would probably not use local sawmill wood next time. I guess, other than that, I would probably do lots of things the same,” Jon said.

And now for another viewpoint

Jon’s house is efficient, comfortable, off-grid, self-built, peaceful, and livable. And since technology is changing year by year, and as more and more people are building zero-energy homes, I think it’s helpful to evaluate how the systems work. You’ll find different points of view, even amongst building science professionals, so many questions still don’t have definitive answers. But I’m going to include a couple of links that make me think about the options.

I still don’t know if the solar thermal/radiant heat idea is efficient or a good idea. The consensus online at Green Building Advisor is that a radiant slab is overkill in a superinsulated house; is that true with solar thermal heating it? What about the idea that circulating pumps are too inefficient so off-grid homes don’t use radiant heat?

What if Jon had built without the solar thermal and radiant heat, and instead had used a mini-split system with extra PV to power it? He would also have cooling with this system. His backup system is a boiler and radiators, fed by propane. Could he eliminate that, as well? What would heat the house if he were gone for two months in the winter, and it was cloudy for days at a time? I think one or two propane-fueled direct vent heaters would cost much less than the boiler setup, and would be fine as a backup.

Well, in Jon’s case, he’s already at the mercy of the sun god, as he needs the sun for power and for hot water. That’s why he has a wood stove for heat, as well.

Solar Thermal Is Dead

Heating A Tight, Well-insulated Home

Will One Radiant Floor Heat Two Stories?

My tentative conclusion after reading all these is that solar thermal and the radiant heating are not optimal. A better solution would be more PV and a mini-split system.

And finally, I’m waiting for interior photos and will post them when I get them.

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Where Are the Neighborhood PV Systems?

I recently visited an off-grid, net-zero home out in the boonies of Vernon County, Wisconsin. The owner/builder, Jon, installed a 3 kWh photovoltaic system, and created a useable, comfortable home. It would have cost $10,000, he said, to hook up to the grid, so he skipped it.

It got me thinking, though. PVs are about $1/watt right now, thanks to massive excess production capacity, especially in China. The installed price will vary but should be $5-6/watt. If demand is less than supply, as is the case right now with PV panels, we should see low prices for a time, then production capacity (supply) diminish to meet demand. Now would be the perfect time for Jon, for example, to buy PV panels, hook up to the grid, and start selling electricity. Plus, there are still federal tax credits for these systems.

Even better would be a neighborhood PV system. In a new development just being built, it seems like it would make sense to put those rooftops to work with PVs on every home, all grid-tied. The PV system could be owned by all homeowners together, and maintained by the association. The PV system would be a valuable asset that’s part of the house, and the homeowners get the benefits of PV power with little hassle.

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I’ve also read about this project in Ithaca, New York, where a housing co-op added panels to their existing development, and self-financed the project. In this case, the PV project generates 55% of the electricity needed. I think it would be great to have developments and neighborhoods that generate a surplus.

For that to happen, it’s important that every state adopt net-metering, so that homeowners and developers are adequately rewarded for their investment. This idea is essentially a distributed power system that requires little maintenance and produces no pollution. An added benefit: the utility companies will need to build fewer new power plants in the future.

Where else is this happening? I have seen few examples besides these two.

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More On Passive Houses, LEED-Certified Homes, and Net-Zero Buildings

Are high performance homes viable and appropriate for the mass market? Do they provide what their builders advertise? Are they worth the effort, or is it more greenwashing?

Why do I ask that? According to a 2005 report by the U.S. Energy Information Administration, buildings consume 48 percent of the energy—and over 70 percent of the electricity—used in this country every year. I think that’s a result of cheap energy for so long, but things are changing. “Energy independence” is a new theme, but it’s going to be challenging in the land of oversized McMansions.

Let's hope the time for these is past.

Let’s hope the time for these is past.

We’ve been accustomed to low standards for new construction and for remodeling for so long because of cheap energy. What if, during the housing boom of the last 15 years, homeowners and builders had emphasized energy efficiency instead of flashy items? I’m thinking of things like adding massive amounts of insulation, sealing the house against air leakage, and upgrading windows, rather than Viking ranges and granite countertops and showers with multiple jets, not to mention excessive square footage.

I’m not opposed to those elements (with the exception of excessive square footage), but I do think that more rigorous standards for energy and resource efficiency are more important. We must build structures that are more sustainable, energy efficient, and resource efficient first, and then add the other elements. Simply raising the minimum standards for housing is a huge first step.

Is the Passive House standard appropriate?

In my last post I explored Passive Houses. I like the Passive House standard because it’s about designing efficiency into the home with a heavily insulated, nearly airtight envelope. It’s so well insulated that the incidental heat produced by bodies and appliances can provide all the heat needed in some climates. Even in colder climates Passive Houses dispense with a standard HVAC system in favor of a heat- or energy-recovery ventilator and a small backup heater.

The Passive House standard is defined by results, not by methods. There are three benchmarks to hit: for air-tightness, for heating, and for overall energy use. There are some principles to follow as well, such as eliminating thermal bridging, and superinsulating, but they’re a means to an end. The three benchmarks are tough to achieve, though, so you tend to see the same methods employed to reach the standards.

A Passive House in Austria shows the typical simplicity of the design.

A Passive House in Austria shows the typical simplicity of the design.

A Passive House is quite simple but not easy, and the house either hits the target or it fails to. Thousands have been built in Europe and more are underway in the U.S., where the standards are under review because of the energy load required for dehumidification. We may see the standards tweaked to address regional differences such as high humidity.

In any case, Passive Houses have shown that it’s possible to drastically cut energy use in a home—up to around 90% in some cases compared to a standard American home with a HERS rating of 100—with building design, rather than additional hardware. Passive vs. active techniques, essentially.

Other standards for improved homes exist, as well. The U.S. Environmental Protection Agency runs the Energy Star program, which requires homes to use at least 15% less energy than a home built to the 2004 International Residential code standard, which results in a HERS score of 85 or better. That’s better than nothing, but doesn’t seem very ambitious. A Passive House should score in the range of 20-30. A net-zero home scores at 0.

LEED takes a different approach

The LEED for Homes standard, in contrast to Passive House, addresses a variety of factors in building an environmentally friendly home. This standard, from the U.S. Green Building Council, aims to “promote the transformation of the mainstream homebuilding industry toward more sustainable practices. LEED for Homes is targeting the top 25% of new homes with best practice environmental features.” The standard will be updated in 2013.

LEED for Homes, which requires independent, third-party verification, focuses on eight areas: indoor air/environment, site development, site selection, water savings, materials selection, energy efficiency, resident awareness of a home’s performance, and innovation. By following the LEED for Homes approach to these factors, you can build a home that:

  • provides a healthy indoor environment with few pollutants and abundant fresh air
  • minimizes water use
  • uses more sustainable materials and uses them efficiently, minimizing waste
  • minimizes energy use
  • is sited and built so as to minimize its environmental impact, and to have efficient access to needed services, businesses, etc.
  • costs less to operate and is sustainable over the long term.

The U.S.G.B.C. has targeted the standards to the top 25% of new homes, but other groups are applying them in the mass market. This is a fantastic idea!

Habitat for Humanity in Kent County, Michigan, has committed to the LEED Gold standard of certification. That’s not as good as Passive House standards for energy use, but it is impressive, especially since Habitat homes are meant to be affordable. (I have not seen a cost/square foot or sales prices for their projects, but have asked for that information. I’ll post it when I see it.)

This page at their site provides a good summary of LEED standards with some research done by the Alliance for Environmental Sustainability. The AES reports that annual savings on electric, heat, and water should total at least $1000 per home. Other Habitat groups around the country are taking the same approach, including LEED townhomes in St. Paul, Minnesota, which I think is a great option, as not everyone wants or needs their own yard and accompanying maintenance. Plus, townhomes can be built to a higher density, making better use of buildable lots, with the potential of preserving existing open space.

I’m encouraged to see the progress LEED, Passive House, and other sustainable techniques are making in improving housing in the U.S. And while no standard can be perfect in every situation, it seems to me that the ideal house project would use the performance standards of the Passive House, and the sustainability criteria of LEED.

Next I’ll have a look at net-zero homes.

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Passive Houses, LEED standards, and Net-Zero Buildings: are They Viable for the Mass Market?

According to a 2005 report by the U.S. Energy Information Administration, buildings consume 48 percent of the energy—and over 70 percent of the electricity—used in the United States every year. This is why drastically improving our buildings’ energy usage is so important.

Passive Houses are one way to do that. I have visited half the Passive Houses in Wisconsin. One of the two. And so lately I’ve been reading about the Passive House standard, LEED standards, and net-zero energy buildings, trying to sort out these different approaches to building science. They all point more or less in the same direction—higher performance buildings—but with different methods.

Visiting the NewenHouse

I visited Sonya Newenhouse’s certified Passive House in Viroqua, Wisconsin, in late May of this year, and again yesterday. All I can say is, “Finally!” It’s a small and efficient house that works very well, yet doesn’t seem like a cave. It’s a 25’ x 25’ square with 968 square feet on two stories, without a basement. Yes, it’s less than half the size of the average American home, but it does have a semi-attached “stuga” or cabin, which is really a three-season porch with a loft and storage space, including a root cellar. And though it’s not a mandatory element, it’s the most charming space of the whole project, so I think it adds great value to the home.

The NewenHouse front facade, as seen from Hickory Street.

The NewenHouse front facade, as seen from Hickory Street.

A view of the east facade, with the main entry porch and stuga.

A view of the east facade, with the main entry porch and stuga.

The stuga provides three-season living with a small woodstove and storm/screen window system.

The stuga provides three-season living with a small woodstove and storm/screen window system.

Sonya in the garden.

Sonya in the garden.

Besides living in the house, Sonya built the home, which she calls the NewenHouse, as a prototype for “superinsulated, sustainable kit homes for people who want to live lightly on the earth.” That description comes from the flyer Sonya provided when I toured the house. There’s more info here at Sonya’s blog.
These scarlet runner beans aren't necessary for shade in high summer, but do help prevent solar gain in late summer and early fall.

These scarlet runner beans aren’t necessary for shade in high summer, but do help prevent solar gain in late summer and early fall.

The house design and execution are a mix of clean, European design and a bit of funky recycling. The kitchen cabinets are attractive but not high-end. The floor is a smooth concrete on the main floor, and mid-grade ash upstairs. The interior doors, light fixtures, and some plumbing pieces are recycled. Sonya said she has minimized the use of toxic materials, such as VOCs. The windows, wall system, exterior doors, and insulation package, however, are high-end. These are the parts that must be well sorted out to meet Passive House standards.

Passive House standards

Those standards are rigorous, and certified houses must achieve specific results:

  • airtight building shell with 0.6 or fewer air changes per hour
  • annual heat requirement less than 4.75 kBtu/square foot/year
  • primary energy (heating, hot water, and electricity) use less than 38.1 kBtu/square foot/year.

So what does it take to meet those standards? Passive Houses use a specific approach to achieving energy efficiency and using only 10-20% of the energy of an average American home. Here are the design principles:

Consistent with Passive House standards, here are some important features of the NewenHouse:

  • 16” thick double-wall system with dense-pack cellulose insulation
  • R-54 insulation under the slab and R-90 in the attic
  • no furnace or central air conditioning system
  • heat-recovery ventilator
  • solar hot-water system
  • triple-pane windows
  • 968 square feet.
16" thick walls make for useful windowsills.

16″ thick walls make for useful windowsills.

When you build to Passive House standards, a 400-watt heater helps to replace a furnace.

When you build to Passive House standards, a 400-watt heater helps to replace a furnace.

The heat-recovery ventilator fits into a 2nd-floor closet.

The heat-recovery ventilator fits into a 2nd-floor closet.

Here's a view of most of the main floor.

Here’s a view of most of the main floor.

Does it work?

And how is the house performing? We had a mild winter, and Sonya reported low electric bills and a comfortable house. Not surprising, given that the Passive House standard originated in Germany and Scandinavia. But what about the hot weather performance? We’ve had a wicked hot summer here in western Wisconsin, as has most of the country. Sonya reported that the house is about 5-20 degrees cooler than the outside temperature, which is sometimes higher than she would like. Shutters or awnings of some sort would definitely help, as would exterior solar screens, especially for windows on the west facade.

Sonya emphasized that the outside temperature isn’t the predominant factor with the indoor temp—it’s the sunshine. In the winter, with an outdoor temperature of around 0 degrees Fahrenheit, and sunshine, the house stays comfortable. But in spring, for example, with an outdoor temperature of around 40 degrees Fahrenheit and cloudy skies, the house may need some backup heat after a few days. In the summer, the design and orientation minimize solar gain, and I think the challenge will be humidity in a humid climate.

The Passive House standard is focused on a tight, extremely well insulated building and minimizing the heating load. It doesn’t address water consumption, use of sustainable materials, siting, embodied energy, and so on, but LEED standards cover that. So in contrast to the LEED standard, for example, which awards points for various inputs, the Passive House standard is defined by results. And it does work. Thousands of Passive Houses have been built in Europe, and I can attest to the charm of Sonya’s house. I would live there myself.

How it performs over time is another question, but the Passive House standard does indicate that the house will require little heating or cooling, and it has fewer components that will break down and require replacement over the years, such as a furnace or air conditioner. Photovoltaics and solar water heaters, both of which are installed on this home, are simple systems and should endure at least as well as “normal” components.

Designing a Passive House

As for the method, the designer must factor in the climate at the home site to determine the heating and cooling loads, and the requirements for insulation. The software package, the Passive House Planning Package, lets the designer enter all the specifications and then calculates the necessary wall thickness, insulation, and all the rest. The process is deliberate, exacting, and eschews guesswork. If you want to add a window on the north wall, the program will calculate the effect on the entire structure. Ignore a couple details and your new house may not qualify for Passive House certification.

What’s wrong with Passive Houses? One of the frequent dings against the Passive House standard is the cost over standard building techniques. Of course, if it were easy and could be done for no cost it already would be. And the current building standards in the U.S. have a lot of room for improvement, as well, so the basic home built in this country is likely underbuilt and underinsulated. Just think if our building codes encouraged less square footage but 20% greater energy efficiency.

Anyway, if you want a certified Passive House, or the performance required at that standard, you must follow the requirements, and some of those requirements are expensive when compared to a standard house. The thick walls, insulation package, meticulous air sealing, and elimination of thermal bridging can add significant cost up front, especially if the builder is not experienced with Passive House building methods.

And though a Passive House does require some expensive components, such as triple-pane windows that may be more challenging to find in this country, it also eliminates the normal heating and cooling systems—a hefty cost saving. And you can also choose to use recycled and low-cost components and save money where those components don’t affect performance. Over time, a Passive House should cost much less to live in, though it seems that the payback time for whatever extra cost you incur would be variable.

Furthermore, the software package and standardization of design principles should make the project more efficient and thus cheaper too. I can definitely see that a builder who has built 10 Passive Houses—and has flattened the learning curve—will be able to streamline the entire building process, making it fast, efficient, and relatively economical. It’s the “custom” or non-standard projects that are slow and expensive, as designer and builder work to sort out every detail. Sonya’s kits for Passive Houses promise the speed and efficiency of most other production homes, when built by an experienced Passive House contractor. As for criticism, the developer of the Passive House concept has heard it all.

My impression of the NewenHouse

I can appreciate some of the critiques too. I’m sure it can be difficult to build a nice-looking home to the Passive House standard, in an extreme climate, that is not a basic box. But it seems to me that homes in the most extreme climates have the most to gain from those standards. Here’s one example.

And the more Passive Houses are built in the U.S., the better the designs will become. The NewenHouse is a pretty basic box, but with some nice-looking details, and I think it’s an attractive-looking house. According to Sonya, the NewenHouse cost about $175 per square foot, excluding the price of the land, but including the solar photovoltaic and solar hot water systems. I’m sure some elements of the house could be cheaper, and some could be “nicer,” or higher quality, but I think Sonya’s choices strike an appropriate balance. Most buyers of Passive Houses, especially in kit form, are not also considering a standard McMansion, I suspect, so higher building performance wins out over two-story foyers and master suites.

I think the NewenHouse, though small for many families, offers a good example of an efficient, attractive, and pretty standard-looking home that could be built anywhere. And while $175 per square foot is fairly expensive, this is a prototype so future iterations should come in cheaper, and the Passive House standards, by design, really front-load costs to avoid them later.

Does a Passive House work in milder and warmer climates?

And what about a Passive House in different climates? The jury is out on Passive Houses in hot climates. The data is just not there yet, but it’s coming. As with the northern U.S. and Canada, the potential for energy savings in just the Southern U.S. states, and desert Southwest, is massive. We need to know how well a Passive House handles high heat and high humidity, since the standards do focus on creating an airtight shell and minimizing heating load.

As for homes in mild climates, where there isn’t much heating or cooling needed, does this standard make sense? In college I lived in Santa Barbara, California. I can’t recall ever needing heat, but the high temps did reach to around 90 degrees Fahrenheit a few times. That’s a pretty dry climate, too, so we didn’t deal with much humidity. That seems like a climate where the Passive House standards don’t justify their cost. There’s little heating load, there’s a small but possibly growing need for cooling, and if you have the windows open 350 days per year, a tight envelope is money wasted.

It seems to me that the best strategy, in a mild and dry climate, would be to have plenty of insulation in the roof to resist increasing temps in hot and sunny weather, coupled with moderate insulation in the walls. Again, the wall insulation would resist temperature swings, but a simple 2×6 wall with cellulose insulation can achieve an R-20 value. That seems like plenty. And insulation is cheap and doesn’t need maintenance.

So if I were creating an energy-efficient house in a mild climate, I would use the most efficient appliances and lighting. Most rooms would have windows on two or more sides for good cross ventilation, and I would open windows and use fans to keep the rooms comfortable. Maybe this view is too simplistic, but sealing a house to the Passive House standard, then keeping the windows open most of the time, sounds absurd.

Managing humidity is another story. How do you do that without an energy-hungry air-conditioning unit? From what I’ve read, the Passive House standards don’t address it, so I’ll have to look into it further. A Passive House is clearly an improvement over a standard American home, and obviously is more challenging to build. If you live in a warm and/or humid climate, is the Passive House standard the one you want, or should you focus on LEED standards, or something else?

Ok, that’s a long post, so I’ll end it there, and get to LEED and net-zero in the future.

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