Category Archives: Building Efficiency

A More Efficient Woodstove

Efficiency---still the goose that lays the golden egg...

A new woodstove in the Bruhl house. Efficiency—still the goose that lays the golden egg…

Well, our trusty 1972 Vermont Castings Defiant woodstove, a hand-me-down from a close relative, finally had to be retired. It had developed enough air leaks that it was easy to overfire, and each time it got too hot it cracked or warped a little bit more, to the point where it was becoming difficult to keep it in check and was becoming a slight safety hazard. So, we went shopping for a new one, and settled on a large Dutchwest model (Dutchwest is now owned by Vermont Castings), the 2479, a non-catalytic stove that meets the strictest EPA emissions standards.

And, since I feel that efficiency is one large key to our sustainable future,  I’m writing this post because I’m amazed at the improved efficiency of this new stove. I didn’t quite believe that the old Defiant could be topped— I burn well-seasoned hardwood, and we burn hot, clean fires. But, whereas older stoves might have been 40-50% efficient, the new ones with carefully designed secondary burn chambers are 80% or more efficient, and the result is much more heat from the wood that is burned. The difference is noticeable—the new stove brings the house up to temperature far faster than the Defiant ever did, AND does it with less wood.  Continue reading

Efficient House Design and Construction, Part 2

The Bruhl-house living room. Note the "clothes dryer"--- the rail around the woodstove. An energy-efficient method, but also a source of indoor humidity.

The Bruhl-house living room. The very-tall interior flue (barely visible on left of photo) drafts exceptionally well, and we’re very happy with the overall performance of the woodstove. Note the “clothes dryer”— the rail around the woodstove. An energy-efficient method, but also a source of indoor humidity.

(Note— This is a continuation of a post from last year, “Another Tough Cookie: Efficient House Design and Construction“.)

Ok, a longish and slightly technical post here. But, it might pertain to, say, all those people out there who live in houses. To wit—the “topic-of-the-week” between me and Mr. X seems to have revolved around indoor air quality, and the problems that arise as buildings are made more efficient and air-tight. Particularly, the air-related problems the Bruhl house is having, and what exactly the best design going forward might be to remedy those problems. And all of this was triggered last week when I picked up the latest “Energy-Smart Homes” edition of Fine Homebuilding. It contains quite a few articles about air leaks and building durability, one which includes a photograph of a house in Minnesota with the siding off and the house wrap pulled back, which reveals enormous areas of rot and mold caused by air leaks.

energy smart magazin cover

The Winter 2016 edition of “Energy-Smart Homes”; well-worth the cover price.

To catch you up if you haven’t read the post from last April, our house is fairly tight, but has no dedicated ventilation system. Adding one has been on my “to-do” list for years, but it has become more of a priority as I have come to better understand this topic. We currently have fascia and trim boards in at least three places that are rotting from the back side due to air leaks, and the photo in the magazine really made me wonder how much damage is being done that isn’t visible.

So off I went on a reading-binge. And guess what? No real surprise; it’s complicated. In some cases, really complicated. But for the sake of clarity, let me skip rather quickly to some of my preliminary conclusions, and mention the complications briefly as I go.

Ok, the short version—our house is built with stress-skin panels around a post-and-beam frame, Continue reading

Another Tough Cookie: Efficient House Design and Construction

A highly-efficient house-- the Solar House at Florida International University.

A highly-efficient house– the Solar House at Florida International University.

What makes a perfect house, in terms of energy efficiency, environmental concerns, and design and construction techniques? In the last month I’ve attended two different panel discussions on the topic, and have come away with some interesting insights. It turns out that this is an enormously complex and changing topic (like everything else!), and it also turns out that my own house, which I thought was fairly sound in these areas, might have a number of problems that I didn’t realize. It’s a big subject, but let me attempt to distill some of my realizations here:

— Air-tightness is really, really important in order to have an efficient building. It turns out that the easiest way for energy to escape from a building is if it leaks air, so highly-efficient buildings are built with a continuous “air-barrier” that is integral to the building envelope. Now, what I didn’t realize is that this barrier isn’t always a discreet item, like a layer of impermeable plastic, but is sometimes just a boundary that is sealed—say, the exterior sheathing, and then across the ceilings with gypsum board. Adhesive tapes and caulks can be used to seal seams and gaps, plastic sheeting is used in basements and under slabs, and sometimes large adhesive sheets are used that adhere to the exterior of sheathing materials. Regardless of the approach, the barrier needs to be continuous, including under the floors, because even small leaks can have large overall effects on building performance. Ideally, all mechanical air-handling systems are within this envelope, to reduce the number of potential air leaks, and to lessen the chance that negative pressure in return ducts will suck in contaminated or unconditioned air. Then, electrical outlets, fixtures, plumbing—anything at all the goes through the air barrier—must be sealed. In addition to efficiency, though, really good air barriers make houses more comfortable, AND make them more durable, because air carries moisture, and if that air goes across a temperature differential then condensation can occur within a building’s walls.

To test how well a building is sealed, a blower-door test is used, where a fan puts negative pressure on the building, and leakage is measured in the number of air-changes per hour. Highly-efficient buildings will typically score between 1 and 3 air changes per hour (at a reference pressure of 50 Pascals), as compared to ranges of 7 and higher for conventional construction in decades past. (A good article on blower-door testing here.)

Plastic sheeting being used as an air barrier in wood-frame construction. In cold climates, air barriers are often used on the inside of buildings to prevent warm inside air from exfiltrating to the exterior, where it might cause condensation problems.

Plastic sheeting being used as an air barrier in wood-frame construction. In cold climates, air barriers are often used on the inside of buildings to prevent warm inside air from exfiltrating to the exterior, where it might cause condensation problems. Note how seams are taped, so a continuous barrier is formed.

— At any reasonable air-tightness level, mechanical ventilation is required to maintain indoor air quality, because the downside to really sealing up a house is that the indoor air quality can plummet. To compensate for this, mechanical air exchange systems are used, to vent stale indoor air outside, and draw fresh air in, and they incorporate heat exchangers to keep the incoming air as close as possible to the temperature of the outgoing air. The best of these systems measure and control for a wide variety of air-quality indicators, and will circulate air within the building, control for humidity, and/or use heat pumps to boost the temperature of the incoming air. Most systems operate automatically with efficient variable-speed fan motors, but are also activated manually at times, as when a bathroom exhaust switch is turned on. Though air exchange systems use electricity to run, the savings from reduced heating and cooling loads in a tight house generally outweigh those costs. (1 May 2015 Note: the most common names for this piece of equipment seems to be “ERV”, or Energy-Recovery Ventilator”, or “HRV”, for Heat-Recovery Ventilator. The two are slightly different. There is a good overview of these here.)

A cross-flow air-exchanger.

A mechanical ventilation system with cross-flow heat exchanger.

— There’s a “sweet spot” with regard to cost-effectiveness when it comes to designing and building highly-efficient houses. Efficiency improvements generally pay off economically, but at some point there are diminishing returns. As an example, several of the panelists discussed how going all the way to Passive House standards (a very strict standard popular in Europe) won’t always result in a monetary payback here in Vermont with its relatively severe winters, because the levels of insulation required to meet that standard here can be extreme. Economic returns can sometimes be maximized by stopping short of the highest levels of insulation and air-tightness, and spending money instead on photovoltaics and cold-climate heat pumps to make up the difference. 

— It’s easier to achieve high performance in new construction. On one hand, few improvements pay dividends faster than basic air-sealing in existing homes, as returns on investment can be extremely short. On the other hand, it is difficult to continue to completely “fix” an older home in ways that remain cost-effective. Additional efficiency, if added to a new home during the construction phase, can pay off financially, but this is not always the case with older construction. One of the panelists used an example of a “70’s ranch-house with 2×4 stud walls and R-19 fiberglass batts” as a house that could not be cost-effectively fully upgraded. Note, however, that it is possible to bring such houses up to the highest standards if financial payback isn’t a driver, and that basic weatherization or efficiency improvements could still pay off, and any resulting deficits could be closed with added PV generation and/or heat pumps.

A rough sketch of double-walled construction. This technique is often used in deep-energy retrofits, where an additional stud wall is added to the interior of older construction. Note to continuous air barrier that wraps up just behind the inner stud wall.

A rough sketch of double-walled construction. This technique is often used in deep-energy retrofits, where an additional stud wall is added to the interior of older construction, and the resulting wider wall space filled with insulation. Note the continuous air barrier that wraps up just behind the inner stud wall, and down on top of the sill plate and into the basement. Double-wall construction also helps avoid thermal bridging, which results in higher actual R-values across entire wall assemblies.

— Energy consumption of a building needs to be measured separately from its energy production in order to get a full picture. Related to this, “net-zero” is a tricky term. Here’s why—if a home has its energy needs met with PV panels on the roof, so that no additional purchased energy is required, then it is usually considered “net zero” (and has a lower HERS score). But what if those panels were in the yard, and tied to the house with net-metering? Most people would still consider this a net-zero property. But after this is gets fuzzier—what if the panels were a block away? What if they were part of a community solar array? It becomes a slippery slope—few would call a leaky old farmhouse “net-zero”, just because its electricity was produced from a community solar array three miles over (though some would indeed feel this term was valid in this case).

In a way, these arguments miss the point, or at best conflate two things that might be better viewed separately. Thing one—how much energy does a particular house use? And, thing two—how much of its energy needs are met with renewable power? And as for how much energy a building uses, one of the panelists held the position, and I would tend to agree, that it is best to use actual amounts of energy, measured in millions of Btu’s per year (MMBtus/yr), as this might be more meaningful than, say, a HERS score, which normalizes energy use depending on the size of the building. A tiny little house and a McMansion might have the same HERS scores, but even if they were good scores, the mansion would use far more energy. So, perhaps the sustainable goal for all of us would be to have efficient buildings that use as little energy as possible, and then to provide 100% of that energy from renewable sources.

Infrared image of a window during a blower-door test, showing clear air leakage.

Infrared image of a skylight during a blower-door test, showing clear air leakage.

The same window without the infrared camera.

The same skylight without the infrared camera.

— And finally, insulation choices matter because of their highly varying environmental impacts. This one was news to me—some insulation types have horrible environmental impacts on the production side, to the point that from an environmental perspective they can virtually never be “paid back”. In fact, two types of insulation were far, far worse than all the others. Unfortunately, they are both quite common. One is XPS, or extruded polystyrene, more commonly known as “blue board” or “pink board”. The other is ccSPF, the most common type of spray foam. Unfortunately, both of these types are common because they are extremely useful– XPS doesn’t absorb water, and can but used underground or underneath poured concrete slabs, and spray foam provides high R-values per inch, doesn’t absorb water, molds and sticks to virtually any surface, expands to fill cracks and gaps, and can actually provide structural support in some cases (good article at on this subject, “Avoiding the Global Warming Impact of Insulation“). This isn’t my field, so I’m not completely sure what the work-arounds are here, but two insulation types that came up repeatedly at the panel discussions were mineral wool and dense-pack cellulose. The cellulose in particular is probably the best all-around insulation in terms of the environment, it has low embodied energy, a low greenhouse gas footprint, and is virtually chemical-free. It must be kept dry, though, so even with air and vapor barriers it isn’t an all-around substitute. But in the words of one of the panelists, “Cellulose is a great product”.

So, all this information presents some challenges. For my own house, two big problems are apparent. First, while our house is quite tight, it does have some leaks, but I’ve always felt that it didn’t make sense to tighten it up further, only to find myself needing a mechanical ventilation system. It appears I was wrong. The leaks in some places are causing condensation problems behind some of the fascia boards, which is causing them to rot, and the overall humidity in the house is too high virtually year-round. This problem is exacerbated by our use of a propane stove and oven, which were necessary choices from our off-grid days. The combustion of propane produces water vapor, in addition to other pollutants that stay in the air. To worsen this even a bit more, “leaky” houses don’t reliably change indoor air; they only “self-ventilate” when pressure differentials are high, in the cold winter days and the hottest summer days (and in the case of the latter, when the windows tend to be open anyway). All those other days “in the middle” are probably days without enough ventilation. So, as part of my net-zero project, I think I need to work on fully tightening up the house and finish all the insulation work in the basement, and then to add a mechanical air exchanger.

The second problem here can’t really be fixed—we used a lot of pink board when we built the house; the entire basement slab sits on several inches of it, and the basement walls are insulated with it behind the stud walls. It will eventually save enough energy to pay back its environmental footprint, but I might not live to see it. So, live and learn; we all need to use what we know to do better next time.

With regard to society as a whole, it doesn’t bode well that older homes can’t be cost-effectively brought up to the highest efficiency standards, because buildings account for nearly half of the energy use in the US, and we have a heck of a lot of older buildings. As we get closer to an economy that is powered with renewable energy, we might need to decide as a society that all these homes need fixed, and support government programs that help offset the costs. There are a lot of homes out there, and it won’t be cheap, and we would need some real leadership from our politicians. Of course, this is assuming that energy prices won’t increase much. If they do, then deep-energy retrofits might indeed pay off, for virtually all buildings.

Then, too, there is that other option—a carbon tax where the proceeds are used to help increase efficiency. Interestingly, Vermont is currently considering just such a tax.

In the end, there are paths forward, but none of them are completely clear.

(See Part 2 of this post here)

 Top image credit: Junior Henry, “Energy Blues”, Flickr Creative Commons.
Air barrier: jp1958, “Wood Frame Construction”, Flickr Creative Commons.
Air exchanger: David Dodge, Green Energy Futures, Flickr Creative Commons.
Stud wall: Jenny Cestnik, “Sketch 054”, Flickr Creative Commons.
Blower door tests: Sonke Krull, Wikimedia Commons.

Bruhl Net-Zero Project– Early Results

enphase report switched

I overheard one of my students ask a classmate today, “Why are they doing so much solar in Vermont, when it’s so much cloudier here than in other parts of the country?” This was on my mind when it occurred to me that that her comment might be more meaningful if rephrased— “Since solar is working in Vermont (and Germany), where it’s relatively cloudy, imagine how it would work even better in other states?” Because, solar does work here in Vermont, and the data so far from my net-zero project is bearing witness to that fact, here in my little corner of the state.

When I last wrote about the project, as I was just finishing the barn panels (post: “Just in the Nick of Time“), the snow had arrived and the days were near their shortest. The snow is mostly gone now, though, the days are getting longer, and the solar production is ramping steadily up. The image above is from my March report from Enphase (the company tracks the performance of each individual invertor and panel via the internet, and sends these nifty monthly reports). The panels on the barn, according to Enphase, have offset nearly a ton of carbon emissions, and have produced well over a megawatt hour of clean, renewable power, in the month of March alone.

Enphase report from a sunny day last month-- nearly 70 kwh produced.

Enphase report from a sunny day last month– nearly 70 kwh produced.

Eventually I’ll get the whole system online, and I’ll work up the numbers for the system’s performance over the course of a whole year. But for now, it appears that my preliminary cost projections are working out as planned— the monthly savings from the project (in propane, generator fuel, electricity to charge the electric cars, and, in a side benefit, cheaper internet due to the coax we ran in with the underground power) nearly completely offset the loan payment. So it still looks like the project will pay for itself in 11 or 12 years, and then provide a large savings every month after that.

As for the net-zero aspect, my goal was to completely power the house, AND the two electric cars, with solar. I can’t quite tell on this one, but I believe we’re close to this goal. I’ll need a few more months of data—our usage for the cars will be higher in the winter months (due to using the heaters, having snow tires on, and the lower efficiency of the batteries in cold weather), while the solar production will be higher in the summer. I’m also not quite finished putting all the panels back on-line; the new ones on the barn roof are finished, but I need to reinstall all the panels we were using when we were off-grid. This should bump up the solar production another 20 or 30 percent.

So, it’s too soon for me to do a complete report, but the results so far are good. We are net-zero, we’re driving 90 miles or more every day on mostly solar power, and we’re going to save money in the long run. It’s time for everyone to jump on this bandwagon.

An Efficiency No-Brainer


shower girl

An attractive photo for an important but visually mundane topic…

This post is about water heaters, but I didn’t think a photo of a water heater would garner much attention, so I opted for the pretty-woman-in-the-shower picture. The news here is important, though, and worth attracting some attention—in the last few years heat pump technology has made two areas of household energy use dramatically more efficient. One of those areas is space heating, with the advent of affordable and highly efficient cold-climate heat pumps (also known as “ductless mini-splits”), and the other area is water heating. Heat-pump water heaters are now available that are two to three times more efficient than standard resistance-element heaters, and could save the average family $300 a year or more. As one would expect, they’re more expensive than standard models, but heating water is one of the larger energy demands in most houses, and because of this the units can pay for themselves in just just a few years. And after they’ve paid for themselves, it’s money in your pocket every month, and far better for the planet, too. Like I’ve said before, efficiency really is the goose that lays the golden egg.

There’s a short video on this Consumer Reports page that gives a good overview of these heaters. Basically, the units use heat pumps, similar to those in refrigerators or air conditioners, to pull heat from the air and put it into the water, and this takes only about a third as much energy to accomplish as creating that heat with a resistance element. Now, while these heaters are probably a wise investment for the vast majority of homeowners, there are a few factors to be aware of before deciding to make a switch. Among them:

— The heaters produce dehumidified air as they operate, which is a side benefit for most people. But, unlike a standard water heater, they need to be installed where there is access to a drain for the condensate to drip into.

— The units are a bit taller than standard water heaters, because the heat pump portion typically sits on top of the tank, so you need to have space for that. Here’s a picture of the Whirlpool model I bought as part of my current net-zero project, and you can see how it’s taller–


— Because heat pump water heaters pull heat from the surrounding air, they operate more efficiently if they have a bit of extra space around them. In most installations this isn’t a problem, but if your current water heater is in a very tiny closet, it might be an issue. Related to this, they cool the air around them as they operate. If you live in hot climates, then this can be another benefit. In colder climates, you might see less overall efficiency gains in the winter if the building has inefficient space heating, and the water heater forces that system to work harder.

— Because the price of solar PV panels has come down so dramatically, it is now cheaper to heat water with a heat-pump water heater and electricity from PV, than it is to install a thermal solar water heating system. This path to hot water requires far less maintenance, too.

— The units do make some noise, unlike standard electric water heaters. I don’t have mine installed yet, but the water heater we’re replacing is a direct-vent propane model, which has a blower fan, and I actually expect the new one to be quieter.

So, these heat-pump water heaters might not work for everyone, in every situation. If I had to generalize, though, I’d say that the vast majority of everyone out there with a standard resistance-style electric water heater could come out way ahead by switching to a heat pump model. For those people who get hot water from a fuel-oil furnace, it might enable them to turn off their furnace in the summer, when they might otherwise have to keep it running. And for people who heat water with natural gas, the units might not save enough to pay for themselves. Though, if you could switch from natural gas to heating with renewable electricity, then it would still be a big win for the planet, even if your pocketbook didn’t see a difference.

I know two people right now who have switched, and both seem to be thrilled with the performance of their new models. I’ll have ours in soon, and I’ll do a post about it in a month or so.

Copyright: choreograph / 123RF Stock Photo

Project Photos, Phase One

DSCN1167 meter sockets

The meter sockets. The one on the right is the “gross meter” to record solar input to the grid. So far my wiring has passed muster with only a few minor changes needed. A small change required here; the equipment ground in the solar meter can’t go straight to the ground rod.

Well, I think I’m roughly on track with the add-a-bunch-more-solar project (if you missed it, see post from the other week “And the Project Begins“). I gave myself a month to complete the conduit runs underground, and we finished that today; almost two-thirds of a mile of conduit. Green Mountain Power is still waiting on one easement from a neighbor (a pole on their property will need an additional stay), so they can’t pull the high voltage wire in yet. But, my part is done, so it’s on to the solar panels on the barn roof. Some photos of this portion–

DSCN1112 house box

The conduit at the house end of the run from the barn to the house. The main breaker is at the barn, so this is secondary power coming in to a 100-amp subpanel. The conduit on the right is for internet, with 500-lb strength pull cord getting pulled through as it gets put together.



All the dogs, having a good romp.



The main trench to the road; 42-inches deep. The high-voltage line will get pulled through this conduit; 7,000 volts in a single large co-axial cable, to a transformer at the barn. For this portion of the run we put the communications/internet conduit one foot above this one as we backfilled.



The goal– to get to this stake. A single pole goes here, near the road, before the run goes underground. The last few feet can’t be dug until the pole is set, and then it has to be backfilled immediately and tamped.



The deep well for the transformer (cabinet visible behind the dirt pile), and the internet conduits stubbed up in the foreground. The internet run splits from the power run at both cabinets; communications cables must be at least five feet from the high-voltage cabinets.



The view down the valley as we work. It’s been reasonably pleasant so far, but I’m definitely racing winter; a bit of snow the other evening was a reminder…


The new 225-amp load center in the barn, with the solar feed coming in at the top, the grid power coming in from the left, and the feed to the house going out toward the bottom (not all of the cables are attached in this photo).

Anyway, last night I unpacked all the invertors and racking and other parts for the solar modules on the roof, and I’ll just call that part “Phase Two”. I’ve given myself a month to get that part in place; I’ll post pictures.


And the Project Begins…


After ten years off-grid, in comes the power…

Ok, a post about the project here. We built our house ten years ago, and have powered it ever since with wind and solar. Almost. During the short, cloudy days of November and December, and other times when we get a string of stormy days, we sometimes need to run a gas-powered backup generator. For years I’ve thought about adding enough solar to completely free us from the generator and fossil fuels, but in an off-grid setup the system becomes more and more inefficient as you add more panels, because you’re adding generation that you might only need to use 5% of the time. The other 95% of the time, all that potential power goes unused (for more about this inefficiency, see my post “Not Sexy” ). But, we were very close to net-zero despite the generator use, and I wasn’t quite sure how to change the system in a way that would make economic sense.

Then we got the electric cars. Which we love. And then I started wondering about powering not just the house with solar, but the cars, too. Suddenly, the thought of tying to the grid for more efficiency began to seem like a practical path forward. Then, I realized that a number of renewable energy rebates and incentives are set to expire at the end of this year, so it seemed like a good time to push ahead with the entire grid-tie, add-more-solar plan.

So, that plan, now underway, is to bring in the grid power in from the road, underground, to the barn. Then, I’ll reverse the cable run that currently takes power from the house to the barn, and use it to bring power the other way, from the barn to the house (the barn is between the house and the road). Then, I’ll add 10,000 watts of panels to the barn roof, and grid-tie them with Enphase micro-inverters. The current PV system, with the inverter in the basement, will stay largely intact, but will become a fairly robust PV and battery backup system for those times every year when the grid power goes down.

That’s the very short version, anyway. Oh, and then we’ll replace the propane hot water heater with a new, highly efficient electric heat pump water heater, which will virtually eliminate the propane bill.

If all goes well, monthly cash flow should about even out. We’ll pay for the home-improvement loan, but we’ll be able to mostly quit buying propane (we’ll still keep the propane range-top, for now), we won’t have to buy fuel for the generator, and we can charge the cars here and save the money that we normally reimburse my wife’s place of work. On the practical side, I can also quit fueling and maintaining the generator, and can quit climbing up on the scaffolding next to the barn all winter to rake the snow off the solar panels.

Then, after fifteen years the system should be paid for. After that—virtually free utilities and transportation energy, for decades.

That’s the rough outline, anyway. There’s actually a lot more to it, but I’ll discuss the details as they come along. Until then, I’ve got plenty to do…


Not Sexy

La Bastilla Ecolodge cropped

Off-grid or grid-tied—that is the question. La Bastilla Ecolodge, Nicaragua. Hmmm, there’s no ice there…

Something’s become more and more apparent to me lately as I ponder our off-grid setup—being grid-tied is inherently more efficient than being off-grid. I know, nothing too sexy here with this technical point, but it’s an important realization, and it has implications for the larger systems that nations need to be working toward.

In my case, as I add generation to approach net-zero, each additional kilowatt of capacity will be needed less and less. Some numbers to illustrate—we are off-grid, and have about 3 kw of solar PV installed in two large arrays. On a sunny day in the summer, when the days are long and the sun is high, the system can produce over 20 kwh’s of power. We tend to use about 7 kwh a day, which means that in the summer we’re often making about three times the amount that we use or can effectively store. The batteries tend to be full by 10:30 in the morning on such days, and then the panels do very little for the rest of the day. In December, however, it’s quite the opposite, with much shorter days and a lower sun angle. At that time of year we only average about 4 or 5 kwh’s of generation each day, which is a bit shy of what we need, and so we run the gas-powered generator off and on, especially in November and December. Usually by mid-January the skies are clearer and the days start lengthening a bit, and we start breaking even again, and continue that way for the next ten months.

So, our house is close to net-zero, but I’d like to completely eliminate those hours where we need to run the gas-powered generator. If I added 2 more kw’s of PV capacity, I’d probably get really close. BUT—that investment (probably $4,000 if I did it myself) would only be needed for about two months a year. Thus, for about 80% of the year it would just sit there essentially unused, which would equate to hundreds of kwh’s of uncollected, and therefore lost, power. In short, the closer I approach being fully net-zero in the off-grid setup, the less efficient the total system becomes. Needless to say, this isn’t good—in addition to the expense, everything has environmental costs when produced, even technology that we need more of like solar PV, so it seems like it would be a case of not using our resources wisely.

If our house was grid-tied (which it never has been, due to the potential expense, because we’re something like 1,500 feet from the power lines), the story would be dramatically different. All those hundreds of kwh’s that I currently am forced to waste would flow into the grid, which would enable to power company to generate less. At other times, when our demand exceeded our production, I would draw these “banked” hours back from the grid. This is actually another of those win/win/win situations. It would be more efficient—it would keep my solar production from being wasted, the losses incurred by transforming power to and from a chemical state in the batteries would be avoided, and when generation is required, it would be done by the power company’s much-more-efficient stationary natural gas plants, or by grid-scale wind or hydro.

Yet another win/win---power companies on both the Canadian and U.S. sides of Niagara Falls generate 4.4 gigawatts of hydroelectric power, without destroying the beauty of the falls.

Yet another win/win situation—power companies on both the Canadian and U.S. sides of Niagara Falls use the river to generate 4.4 gigawatts of hydroelectric power, without destroying the beauty of the falls. This is the equivalent of about four nuclear power plants.

The power company benefits as well—peak solar hours often overlap with peak grid demand, so grid-tied solar inputs tend to reduce peak demand on the grid. The opposite tends to be true when grid-tied homes are pulling from the grid, say, in the middle of the night to charge EV’s, during times of very low demand. The net effect is that grid-tied systems help level the grid. Many power companies, like Green Mountain Power (GMP) here in Vermont, seem to be embracing distributed generation for another reason—taking the long view, they seem to recognize that the role of power companies is and will be changing, away from the old idea of generating power and distributing it in one direction for a single price, and to the model of the power company as a manager of a complex grid that buys power from many sources and distributes it, as needed, in all directions, perhaps with time-of-use (TOU) pricing. (See earlier post “Cloudy Day Pause” for more about how grids might function in the future.)

Remarkably, being grid-tied would probably be a better choice even if I had to use a power company, like some in the Midwest, that rely nearly 100% on coal. Being grid-tied does not change the total amount of fossil fuel that is burned—the companies burn less when grid-tied homes are feeding power in, and then burn more later, when such homes are pulling power out.

Now, while being grid-tied is more efficient when viewed system-wide, what would happen if everyone was grid-tied, in a future situation where fossil fuels might be nearly totally phased out? It’s easy enough to see how the grid can work as a virtual (and unlimited) “battery” for a small proportion of customers, but where is the upper limit? The short version—we’re not quite sure. One thing is for sure, though—U.S. power companies are nowhere close to this limit. In Vermont the electric utilities are currently allowed by law to have up to 4% of their generation from grid-tied systems, but that number was established somewhat arbitrarily in years past, and the legislature is currently expected to soon raise it to 15%, a move that is being welcomed by most of the power companies. A better case study of high RE penetration would be the situation in Germany, though it’s complicated enough that the topic really warrants its own post. Short version—their solar feed-in is around 35% on sunny days, and due to vagaries in the international coal market (coal has become cheaper due to plentiful supplies of natural gas in the U.S.) it has caused disruption in the business models of German power companies, which has had economic costs and, as of yet, fewer than expected CO2 reductions (see Economist article, “How to Lose Half a Trillion Euros“. I personally think The Economist is quite one-sided in this article, but that, again, would probably be a whole other post.) Eventually grids worldwide will need to move toward 100% RE generation as we phase out fossil fuels, and much of this will be distributed generation from point sources. But, 1) we’re not even close enough to worry about it now, at least in the U.S., and 2) power companies will change their business models over time. Indeed, companies like GMP have already started. Fortunately, moving to a smarter grid isn’t an all-or-nothing propostion, but rather evolutionary change over time. (Again, previous post “Cloudy Day Pause” discusses some of this in more detail).

So, back to where I started—it isn’t sexy, but the higher efficiency of grid-tied systems is an important point as we work out our workable vision of the future. We’ll eventually need a smart, flexible grid that efficiently connects renewable generation from million of sources to millions of destinations. In the much shorter term for me, tying to the grid might be the easiest, if not the cheapest, way to achieve net-zero. Much to ponder…

Top image by La Bastilla Ecolodge/Creative Commons at, image has been cropped.
Niagara Falls image credit: pierdelune / 123RF Stock Photo

Net-Zero is Possible

An interior view of Middlebury College's 2013 Solar Decathlon entry, a net-zero house.

An interior view of Middlebury College’s 2013 Solar Decathlon entry, a net-zero house.

Until this past summer, I had more or less assumed that a net-zero house, one that didn’t use any fossil fuel to function, could really only be achieved in some ridiculously expensive research and development setting. That may have been true a decade ago, but it isn’t true now. A combination of technical advances and cost reductions has now put a net-zero house within the reach of nearly everyone. Even better, net-zero can be achieved in most buildings in stages, and are investments that are likely to outperform the market in today’s investment climate. The result is a win-win-win situation.

First, what exactly is “net-zero”? There isn’t a hard-and-fast definition, but, in general, net-zero buildings create as much energy as they consume. They typically combine highly efficient construction and appliances with some form of renewable energy generation, usually on-site. But, this can be done in different ways, and sometimes with different goals in mind, and the result is a wide variety of net-zero terms, as delineated in this list from a designer in Waitsfield, VT (his house is in the list below)—

“Net-zero carbon, net-zero cost, net-zero source, net-zero site, near net-zero, net-zero ready…there are many terms used to describe a certain category of buildings that are referred to as “net-zero energy buildings” (or NZEBs).”

In the last six months I have seen or heard about no less than six examples of net-zero buildings, and the variety of approaches in these buildings will give you some sense of the term, I think. (Some of these details are from memory, so forgive me out there if I get something wrong).

Building #1— Kim Quirk is the owner of Enfield Energy Emporium in Enfield, CT, an architectural firm, and she bought and renovated this house and has turned it into a net-zero office space and living quarters. I saw her presentation about this at Solarfest this past summer, and if I recall, the house was originally built in the mid-19th century, and was mostly gutted when she bought it. She had the basement foamed, and did a deep-energy retrofit that included increasing the thickness of the exterior walls and filling them with cellulose insulation. She added a 5kw PV system in the yard, which is net-metered. And here’s the unusual part—for heating, she dug a huge hole under her driveway, about 10 x 12 feet by 10 feet deep, lined the sides with a liner and foam, filled it with sand, water, and tubing, and then buried it. (My rough calculations—about 60 tons of insulated mass). This thermal mass is a huge “Thermos” that can store an entire summer’s worth of heat gathered by a largish array of evacuated-tube thermal collectors. So all summer long they run and pump hot water through this thermal mass (pics here), which brings the temperature up to something like 180 degrees. In the winter another set of tubing pulls the heat out, where it’s radiated into the house in a system of low-temperature (90 degree F) baseboard heat. An interesting approach. One of her goals was zero-combustion in addition to net-zero, and from her talk this summer it sounded as if the building was on its way to achieving her design goals.

Building #2— Architect Bill Maclay’s Dartt House, in Waitsfield, VT. I saw Bill give a presentation about this building last week at Renewable Energy Vermont’s Expo in Burlington. This is another older structure, renovated in much the same way as Kim Quirk’s house. It is actually two or three net-zero projects together—a building that serves as an office, and an adjoining building that he been turned into two apartments. Unlike Kim Quirk’s solar-heated thermal mass method, these buildings use air-to-air heat pumps for both heat and cooling, all powered by a combination of larger PV arrays—one 17kw array that serves as the roof of a carport (last pic on this page), smaller arrays to the rear of the house, and another large net-metered array that is off-site.

Our house, under construction in 2004. Timber-frame construction with R-40 walls and R-60 roof panels.

Our house, under construction in 2004. Timber-frame construction with R-25 walls and R-32 roof panels.

Building #3— Oddly enough—our house. Technically a “near-net-zero building” as it is now, as we still use propane for hot water. But we’re on our way to net-zero, via yet a third approach—using sustainably-gathered biomass for heat. In our case, cordwood. Our house is off-grid, with a 3kw PV system and a 1kw wind turbine. With the addition of a bit more PV and solar hot water, we should get all the way to net-zero. Even as is, the building uses only a fraction of the fossil fuel that most Americans use. The house also has a fair amount of passive-solar design features—it is oriented to the south, and most windows and living areas are on that side of the building, and closets and utility areas are on the north. The site is shielded to the north by hills and trees, and open to the south. The building has performed admirably—on sunny days in the winter I can leave home for work with the house at 63 degrees, and come home to a house that is well above 70, all with no heat on, even if outside temps are in the 20’s. We typically use about 2 1/2 cords of wood per winter for heat, which we burn in a single wood stove on the main floor of the open-floor-plan design.

Building #4— Well, “buildings”, plural. A company called Vermod is making net-zero single-wide modular homes to address the need for efficient low-cost housing in the state. With 12-inch-thick walls and triple-pane windows, and a 6kw PV system on the roof, Continue reading

Cree Bulbs for the Bruhl’s

Cree bulb cropped

Want to know how a government policy can effect real change? Here’s an example—I have been meaning to start switching over to LED bulbs in the house, even more so since I read a piece last summer by Marc Gunther about the newest generation of LED bulbs (“A Better Light Bulb. Again“). We’ve purchased a few LED bulbs in the last year for specific applications (in one case, some pendulum lights where we needed lots of light output but limited heat), but those bulbs have been expensive, costing up to $35 each. Then, a month ago while walking through Home Depot I saw the Cree bulbs, that were referenced in the article, selling for $9 apiece. That’s still expensive, but not so expensive that I wouldn’t consider buying a few at a time and replacing the compact fluorescent (CFL) bulbs that we currently use in the house. But, I didn’t buy any then, because I wanted to compare energy usage among the different brands of LED bulbs, as I suspected that they weren’t all equally efficient.

Fast-forward to last weekend, when I was again walking through Home Depot and saw the bulbs, but this time for $4.98 apiece, a much lower price than I expected. This turned out to be due to a promotion by Efficiency Vermont, a program funded in part by the state, that is underwriting the cost of the bulbs. At this price I bought eight bulbs instead of just a few, and took them home to try them out. I like them. They are bright, they have a warm tone, they come on instantly, they should last nearly forever, and, as my son and I accidentally dropped one and it didn’t break, they seem to be quite a bit tougher than the curlicue CFLs. But here’s the biggest bonus—the new bulbs use only 9.5 watts apiece, and we were replacing CFL’s that were rated at 13, 18, 20, and 26 watts. In the case of the first three the light output seemed the same or better, and was close even in the case of the 26-watt CFL (marketed as a 100w replacement). So, in one fell swoop we reduced our energy use for these eight bulbs by at least 50%, and possibly more, even over the CFLs, which are already many times more efficient than the old incandescents. That’s substantial.


Some of the replaced bubs, which we gave away for reuse.

Then, it struck me that this remarkable incentive program wouldn’t last forever, so I stopped back by Home Depot after work the other day and bought 25 more bulbs, enough to finish replacing nearly every bulb in the house. Lighting accounts for about 20% of electrical use in the average American home, and I suspect it’s an even higher proportion in our off-grid setup. In winter months we don’t currently make quite enough solar power to get by (relying occasionally on the gas-powered generator), and if the new bulbs help reduce this energy gap, then it will result in a direct savings in burning fossil fuel. A good deal.

So back to where I started, this is a good case of supply and demand principles at work. The government underwrote an incentive, and that incentive increased demand for the bulbs, and energy was saved as a result. (And judging from the near-empty racks of bulbs at the store, I wasn’t the only one who has been swayed by the low prices into purchasing more). So, a public thank-you to Efficiency Vermont, and another public thank-you to some forward-thinking legislators who set up and voted to fund the state’s efficiency programs. Demand for bulbs like these will eventually reduce their costs, and the products will stand on their own merit. The same is true for electric vehicle incentives, and a whole host of other efficiency incentives I can think of. This is money well spent, it is smart policy, and it is part of that “better path forward”. In a world where real change sometimes seems hard to achieve, here’s a program that works.