Three and a half years ago (in early 2008) I observed that the price of solar power modules had been dropping at a remarkably consistent 6% per year for 25 years, and that sometime before 2025 they would be cheaper than grid power in most places.

The exact year of grid parity depends a lot on where you live: sunny places with expensive electricity (think Hawaii or southern California) get there a lot sooner than cloudy places with cheap power (Seattle). For Minnesota, I estimated that sometime around 2015 a solar power system would pay for itself within the system's lifetime.

That estimate is looking pretty good, at least on the price of the solar modules (this Scientific American blog has an updated version of the graph I made in 2008). If anything, the decline in photovoltaic prices may be accelerating a little--though that could just be a short-term blip.

I'm optimistic that over the next decade solar power will become economically viable in more and more places. On a purely cost basis alone you will start seeing a substantial increase in solar power installations. That, in turn, makes me optimistic that we will manage to transition away from greenhouse-gas-emitting sources of energy in a reasonably graceful fashion.

I may be using "optimistic" in an unusual sense. There's no doubt that the earth's climate is changing, and much of the evidence now points to a faster climate change than most scientists had predicted. There's already a lot of climate change "baked in" to the atmosphere, as cabon dioxide levels have increased over 20% just in the past 50 years. What's more, moving a large fraction of energy production to solar and other renewable sources will take decades, as it's very capital intensive to build an entirely new energy infrastructure.

But I am optimistic that the long-term trends are in place to create a more sustainable energy system and eventually reduce or eliminate net emission of greenhouse gasses. It will take decades. Future historians may see the 21st century's energy revolution as just as important as the industrial revolution in the 19th century or the information revolution in the 20th.

In the meanwhile, global climate change will continue. Sea levels are likely to rise (maybe a lot), storms will get more intense, and a lot of people will have to adjust. Some cities may have to be abandoned or be put behind massive dikes like in the Netherlands (I'm looking at you, New Orleans and Miami).

But it will not be the end of civilization. We will--eventually--muddle through.

For many years, my opinion of nuclear power has been one of an uneasy truce: I've not been 100% comfortable with it, but accepted it because of the potential to generate a lot of power relatively pollution-free.

In the wake of the accident at the Fukushima power plant, I'm rediscovering some things I kind of knew before but hadn't fully appreciated:

Underappreciated Fact 1: Nuclear Power is Inherently Dangerous

Historically speaking, far more people have been killed by fossil fuel power than nuclear power. This is a fact.

But that's not because nuclear power is inherently safer. On the contrary: nuclear power has a good safety record (so far) because it is so extremely dangerous that we entomb reactors with insanely large containment structures to keep the stuff away from us even in an unthinkable disaster. Were we to build similar containment and waste-handling systems for coal-fired power plants, pollution and global warming would be non-issues.

We don't do that with coal and oil because we don't have to.

And if a containment structure is ever catastrophically breached (an event which hasn't happened yet--the Chernobyl reactor had no containment), it would likely render hundreds of square miles uninhabitable for centuries. Nothing else made by humans has that capacity.

Underappreciated Fact 2: Spent Fuel Remains a Problem

Even after decades of nuclear power, we still haven't figured out what to do with the spent fuel. Fukushima shows that in an accident the spent fuel can be almost as dangerous as the reactor itself, in its capacity to contaminate the surroundings and prevent emergency workers from fixing problems.

Here in the U.S., spent nuclear fuel is basically stockpiled at the power plant waiting for the (hypothetical) day when there's some way to recycle or dispose of it. At the Prairie Island plant here in Minnesota, they've actually run out of storage space and have had to build new storage casks. It's safe to assume that these spent fuel casks are considerably more vulnerable than the primary containment around the reactor.

Underappreciated Fact 3: In a Disaster, You May Have Other Problems

The nuclear accidents at Chernobyl and Three Mile Island happened because of internal problems, not because of a natural disaster. Fukushima, on the other hand, was caused by a combination of a magnitude-9 earthquake and a massive tsunami--an event the power plant was not designed to survive.

Nuclear reactors are engineered to withstand the most catastrophic natural disaster expected at their site. What that means in practice is that a natural disaster big enough to damage a nuclear power plant will be bigger than anything anyone expects. Normally simple things like transportation may be difficult or nearly impossible, local emergency services may be wiped out, and it could take days to get even the most basic resources to fix the problem.

If bringing a nuclear power plant under control requires something (supplies, people, expertise) which doesn't exist at the site itself, you might not be able to get it at all.

Underappreciated Fact 4: Newer Plants May be Safer, but Old Plants Rarely Die

One argument by nuclear advocates post-Fukushima has been that the Fukushima reactor and containment was an older design with known deficiencies. New plants, they argue, would never be as vulnerable.

Unfortunately, older reactors continue to be used, even decades beyond their original design lifetime. Given the cost of decommissioning an old reactor and building a new one, power plant owners have an enormous incentive to keep the old reactors running as long as possible.

It's hard to know if the margin of safety in older nuclear plants has eroded (it may take another disaster to know for sure), but it is clear that they are not being replaced by newer designs nearly as quickly as the original designers had intended.

Instead of Tony the Tiger in the tank, how about Aunt Jemima? Would it be possible to use a simple sugar syrup (about 50% water and 50% sugar) as a vehicle fuel?

Why Syrup?

One of the biggest challenges of large-scale use of biofuels is that refining the fuel is often extremely energy-intensive. Most products of biological processes are water-soluable, since biological process all take place in a water medium. Unfortunately, however, most current internal combustion engines can't run on a fuel+water mixture, so it is necessary to remove the water from the fuel as part of the process of refining the biofuel. This can take almost as much energy as is present in the fuel to begin with.

(Note that oil-based biofuels, like biodiesel, don't have this problem since the oil will naturally separate from the water. However, oil-producing plants tend to have a much lower yield of oil than sugar-producing plants have of sugar.)

So if you can build an engine capable of running efficiently on a fuel+water mixture, you can get a lot more biofuel for the amount of energy you put into growing and refining the fuel. In addition to making the biofuel much more sustainable, this also makes the economics of producing biofuels much more compelling since it's no longer necessary to buy massive amounts of fuel to separate the fuel from the water.

Once you've decided to use a fuel+water mixture, sugar becomes a much more compelling fuel choice than ethanol. Ethanol production always begins by fermenting sugar anyway (even cellulose-derived ethanol, since that uses enzymes to break the cellulose down into simple sugars), and sugar has a significantly higher energy density than ethanol. Sugar is a lot cheaper, too.

The only reasons to prefer ethanol over sugar are (a) ethanol can be used in existing engines with little or no modification, and (b) ethanol is a liquid, and sugar is a solid, and solid fuels are really hard to deal with in an internal combustion engine. But if we're designing a new engine specifically to run on a fuel+water mixture, we've already decided that compatibility with existing engines doesn't matter; and a sugar syrup is a liquid.

Sugar syrup has some other advantages: it's readily available from a wide variety of sources, it has a low freezing point and high boiling point, and the desired 50% mixture can be achieved fairly readily by removing water from certain plant saps (no need to dry it all the way to granulated sugar). You can even make the stuff at home, cheaply and easily.

Can It Be Done?

I don't know if a syrup-powered engine is possible, but I think it would be.  The challenge is that before the fuel can burn, the water has to boil completely inside the cylinder, since the water boils (even at high pressure) at a lower temperature than the ignition point of the sugar. Boiling the water takes energy and cools the gas inside the cylinder, making it harder for the fuel to ignite.

This isn't an insurmountable problem: you just have to get the cylinder that much hotter to overcome to cooling effect of the water in the mixture. The trick is to design the engine so that the energy used to boil the water can be recovered to help turn the engine. Since the role of the water in the syrup is essentially to vaporize and cool the combustion gasses, the engine has to be designed for a slightly higher volume of slightly cooler gas.

Thinking in terms of modifying an existing engine design, I would think that a diesel engine would be ideal, since it's intended to operate with very high compression and hot cylinders, and fuel which burns as a mist rather than a vapor. Somewhat higher compression (to yield a hot enough gas to ignite the syrup) may be the only change necessary.

One final note: sugar actually is used as a rocket fuel for some model rockets, typically mixed with potassium nitrate (saltpeter), but this is normally done with solid dry sugar, not syrup, since if the mixture has any water in it it becomes difficult to ignite. I did find, however, some YouTube videos of experiments with including sugar syrup in a rocket propellant.

We had our first major snowstorm of the season last night, and as I was shoveling the driveway I was thinking about different ways to remove snow.

Okay, I'll be honest--I was trying to figure out how to justify installing a snow-melting system when we have to replace our driveway in a few years. I still shovel the drive by hand, but I can foresee a time when I won't want to do that any more or will be traveling enough so I can't.

There are four basic ways to remove snow and ice from a driveway: shovel it by hand, clear it with a snowblower, melt it with a heated driveway, or hire a snowplow service. (You could look at a fifth possibility, melt it with chemicals, but that would require so much chemicals as to have serious environmental consequences. Chemicals are best used for stubborn patches of ice which are hard to remove mechanically.)

The Physics Perspective

The most obvious way to look at the problem of How to Remove Snow is to compare the energy required to melt snow vs. move it.  I measured our driveway and found that it is about 1,200 square feet (I'm going to use English rather than metric units because they're probably more familiar to my readers).

If we get a heavy snowfall of a foot, which translates to an inch of equivalent rainfall (Minnesota's snow tends to have one inch of rainfall equivalent for every 8-15 inches of snow), that's about 6,000 pounds of ice on the driveway which needs to be melted (which will yield about 750 gallons of water, if you're keeping track).  It takes 144 BTU to melt a pound of ice, so it will take about 850,000 BTU to melt all the snow.

In addition to melting the snow, you also have to heat the driveway itself. If there's three inches of brick over the 1,200 square foot driveway, that's about 40,000 pounds of brick. In the worst-case scenario, that brick needs to be warmed by about 100 degrees F, which will take about another 900,000 BTU. Normally a snow-melting installation includes a layer of insulation underneath the driveway, so we don't need to heat the ground underneath the driveway. In total, then, we need about 1.75 million BTU to melt a foot of snow from the driveway on a very cold day.

Calculating the energy it takes to move the snow isn't quite as straightforward since it depends on whether you push the snow (with a plow), lift the snow (with a shovel), or launch the snow (with a snowblower). Hard-to-measure factors like friction and ice adhering to the surface can matter a lot. The simplest case is the snowblower, which essentially fires the snow out a chute. If we assume that the snowblower shoots the snow out fast enough to launch it about 30 feet straight up, then it will take about 300 BTU to clear all the snow.

This is a rather lopsided result: it takes about 5,800 times as much energy to melt the snow as to clear it with a snowblower. This is not a helpful result in my quest to justify a snow melting system. It's not the end of the story, though: a snowblower turns out to be much less efficient.

It turns out to be fairly easy to convert chemical energy from natural gas into heat. Our on-demand hot water heater (which would likely be pressed into service to drive any snow-melting system) claims to be 98% efficient, and the required plumbing would have only minimal loss, so over 90% of the energy of the natural gas would be available to heat the driveway. Delivering our 1.75 million BTU to the driveway will require just a little over 1.75 million BTU of natural gas.

Small gasoline engines, like the ones used to drive snowblowers, are not very efficient. Only about 10% of the energy content of the gasoline is actually converted into mechanical energy in the driveshaft of the engine. What's more, the snowblower has a lot of internal friction, idle time, and other losses. It's probably reasonable to assume that only 10% of the output of the engine actually gets converted into flying snow. Realistically, then, it probably takes about 30,000 BTU of gasoline (or about 1/8 of a gallon) to clear the driveway.

Even accounting for the relative efficiency of melting vs. moving snow, it still takes 58 times more energy to melt the snow. This is still not a helpful result, but there's one more wrinkle: a foot of snow on a very cold day is a worst-case scenario for the snow melting system, and melting less snow on a warmer day leads to a direct reduction in the energy required. The snowblower, on the other hand, is likely to use about the same two cups of gasoline no matter how little snow fell or how warm the weather, because most of the energy is going into friction and the important factor is how long it takes to walk the machine across the entire driveway. With only an inch of snow on a warmish sunny day, the snow-melt system might require only 2-3 times as much energy as the snowblower.

The Fuel Perspective

Another way to look at the problem is to estimate the amount of fuel consumed by the different ways to remove snow. For our foot of snow, the snow-melt system will consume about 18 therms of natural gas, or about $13 of gas at recent prices from our gas company. The two cups of gasoline the snowblower consumes is about $0.30 of fuel these days.

The amount of gasoline consumed by the snowplowing service is harder to estimate because they likely burn more gas getting to and from our driveway than they use in actually clearing the snow. Plow services tend to drive big four-wheel-drive trucks which get poor mileage (especially with a giant plow rig attached to the front), so it seems reasonable to assume they burn about 1/2 gallon (or $1.20) getting to and from each client on the route.

Finally, when I shovel the driveway by hand, it takes me about an hour and burns 720 calories according to government exercise tables. That's about three candy bars, which cost about a dollar each at the convenience store, so about $3 worth of "fuel" is required.

Here, too, there's a slight wrinkle. Our geothermal system uses waste heat to warm a storage tank for hot water, and this heat could be available for use in a snow-melt system. This could give us the first 25,000 BTU or so for free each time we run the heated driveway--not very helpful for the foot of snow on a subzero day, but a significant factor in the case where we're trying to remove a small amount of snow or ice on a warmer day. This low-use scenario could wind up costing $0.50 or less.

The Time and Money Perspective

Finally, we can look at the problem from the perspective of how much time and money it takes to clean the driveway. Right now I spend about an hour shoveling the driveway every time we have a significant snowfall, and for bigger storms this sometimes needs to be done twice or more. As already established, this costs about $3 worth of candy bars.

Clearing the driveway with a snowblower takes about a half-hour, and about $0.30 worth of fuel each time. This may seem like a no-brainer (replacing $3 of Snickers with $0.30 of unleaded and taking half the time), but the snowblower itself will cost about $500 and last perhaps five years. If I have to clear the driveway ten times a season, it's clear that buying the snowblower is the most important expense, adding about $10 to the cost of each snowfall.

Hiring a snowplow service is the most expensive option, but it takes me zero time to clear the driveway. We used to hire a service until about 10 years ago, and back then they charged a minimum of $30 every time it snowed with a surcharge for more than three inches of snow. Today it would probably cost $40-$50 for every snowfall, and our foot of snow could cost as much as $75 with surcharges.

The snow-melt system actually starts to look compelling from a time and money perspective. Like the snowplow service, it requires zero effort for snow removal, but the deep snow on a cold day will only cost about $13 in natural gas. I haven't priced the cost of installing the system, but my guess is that it would add between $2,000 and $5,000 to the cost of replacing the driveway (which will have to be done anyway in a few years). Considering that we already have a water heater capable of driving the system, we could well come in at the low end of the range.

The installation price of a snow-melt system is steep, but it should last for the life of the driveway or longer. Over 25 years, the $5,000 spent on the system will cost only $200/year, or $20 for each snowfall if we need it ten times per season. So (rounding off a little), a heavy snowfall will cost about $35 in fuel plus capital expense to melt the snow, as compared to $50-$75 for a plowing service. A light snowfall would cost only about $20 to melt (essentially just the amortized cost of installation), but $40-$50 for a service.

Concluding Thoughts

There's no question that moving snow takes much less energy than trying to melt it, and the cheapest, most efficient way to clean up after a snowstorm is to shovel by hand. I'm happy to keep doing this, but She Who Puts Up With Me has zero interest in hand-clearing our driveway.

At some point, I might not want to keep shoveling, or my business travel schedule may make it likely that I won't be in town when the snow flies. When that time comes, we can hire a service, buy a snowblower, or install a snow-melt system.

Buying a snowblower is the cheapest option, but also the least convenient--it will still require someone to spend a half-hour in the cold and blowing snow. I don't think She Who Puts Up With Me will be too excited about this, though it's still better than hand-shoveling.

That leaves hiring a service or going with the heated driveway.

If we have to choose between those options, the snow-melt system is substantially cheaper, as long as we anticipate using the service for a number of years. If we expect to need a service for only a few years (maybe we expect my travel schedule to change, or move to a different house), then the capital expense of the snow-melt system makes it more expensive.

All this is still dreaming at this point: the time to make a decision about a heated driveway is when we replace the driveway. Our current driveway is 25 years old and in poor shape, so it could be replaced at any time. On the other hand, after the geothermal system this year we're not eager to embark on another major home-improvement project for a couple years.

It's been three months since our geothermal system was installed.  We've made it through the hottest part of the summer, and proved that a heat pump sized for a Minnesota winter does a bang-up job with air conditioning in the summer.

So far we've discovered only one problem: the sinkhole.

When the contractors buried the plumbing for the loop field, they basically excavated a trench about ten feet wide, twenty feet long, and six feet deep.  That's about 45 cubic yards of material removed.  At the bottom of this pit, they connected the six deep wells to a manifold and a pair of pipes which run under the garage into the utility room.  These pipes circulate the antifreeze solution which transfers heat between the ground and the house.

After all the plumbing was done, the geothermal company just pushed the 45 yards of material back into the hole.  They made no attempt to level the ground, nor did we expect them to.  On the contrary, they made it very clear that they would leave the yard a complete mess and it was our responsibility to fix the landscaping.

A week or so after the geothermal guys left, the landscapers arrived.  They used a bobcat to level and grade the ground and plant grass seed on top.

Now, we had a dry spring and summer and for a while things looked pretty good.  If you've had experience with excavation, though, you can probably see where this is going.

A certain amount of settling is always expected when you dig a hole and refill it.  That's because the granules of dirt, sand, and clay don't just drop back into the same compacted configuration they had been before.  Instead, they're fluffed up a little, and it takes some time to unfluff.  A good soaking rain helps, since the water suspends and lubricates the particles.

This August, we got that rain.  When we got that rain, the ground above the excavation settled.  And collapsed into a big sinkhole.

My best guess is that when they pushed all that material back into the hole, they accidentally left a sizable void in one of the corners of the excavation.  This is easy to do when the dirt is dry and lumpy like it was this past spring.  The void sat there quite happily for a couple months, until we got enough rain to actually soak all the way down to the underground air pocket.

Once the water reached the void, it collapsed and created our sinkhole.

The sinkhole is about a cubic yard in volume, which is to say, big enough to look ugly and alarming, but not big enough to actually be dangerous.  Fortunately it's not in a place visible from outside our yard, so I don't feel like it has to be dealt with this instant to keep the neighborhood looking good.

Right now, I'm thinking that the time to deal with the sinkhole will be in the spring, after we've had a complete freeze-thaw cycle and I can be fairly confident that the excavation is mostly done settling.  I would hate to fill it all in, just to have it sink again.

If I had thought of it at the time, I should have taken the garden hose and run it into the rough-filled pit the geothermal guys left before the landscapers arrived. That would have at least uncovered the void and prevented the dramatic sinkhole, even if the ground would still have settled after being regraded.

Update: A few hours after I wrote this entry, I discovered that I was a little too sanguine about the need to immediately fill in the sinkholes. The sinkholes are trapping runoff which would normally flow downhill and away from the house, and with heavy enough rain some of the water is making it into our basement. Not much, but enough to make me want to go get a couple yards of sand and rough-grade the sinkholes before the next big storm.

High Speed Rail, which generally means trains running faster than 110 MPH, is hot again these days.  There's money in the economic stimulus package, the beginnings of a plan in California, and just this week, a five-part series on National Public Radio.

I am a big fan of the idea. Personally, I would love to be able to hop on a train in Minneapolis and be in Chicago three hours later without the hassle of airports.  Or, even better, an overnight sleeper to San Francisco (currently a two-day trip by rail). For me, this would be a service worth paying a premium over an airline ticket, given how miserable air travel is these days.

But....the cost of actually building and operating a single high speed rail line will be substantial; and the cost of building a national network of superfast trains will be astronomical--though no more astronomical than the cost of other national infrastructure like the interstate highway system, power grid, or airspace system.

Fans of fast trains hope that once one regional network is built, the benefits will be so obvious that other regions will demand their own networks, eventually creating a national system.  Opponents charge (probably correctly) that high speed passenger rail service will inevitably operate at a loss and require government subsidies (though the highway and airspace systems also require considerable government care and feeding).

Public Rails and Private Trains

Government is good at building gigantic infrastructure projects, but not at figuring out how to make the most efficient use of the infrastructure once built.  Competitive markets, on the other hand, are great at figuring out what customers want, but no private enterprise could possibly afford to build a high speed rail network--and forget about the idea of two competing sets of tracks.

My idea is to have government build and maintain the high speed rail lines, but private companies own and operate the trains.  Any company which could meet appropriate technical requirements would be allowed to operate high speed trains and pay a fee for the privilege.

This is similar to the way the highways and airspace systems work today, where government builds and maintains the infrastructure but private companies set schedules, pricing, and routes.  It's almost the exact opposite of how Amtrak currently works, since Amtrak has a quasi-governmental monopoly on interstate passenger rail, but has to negotiate with private companies to use most of the tracks its trains run on.

There would be technical issues to work out--for example, traffic control, and how to allocate the most desirable time slots on heavily-traveled routes.  But we have decades of experience solving similar problems in the national airspace system.

In exchange for solving these (minor) issues, a high-speed rail system would gain several advantages:

1. Taxpayers would not have to pay for the trains, just the tracks.  This might not sound like big savings, but over the lifetime of the system it's substantial.
2. The government would be out of the business of setting fares and routes, and the free market can figure out how to deliver service at the lowest price.
3. Riders would have the choice of several different services--for example, a cheap train with lots of stops and crowded cars, or a more expensive and comfortable train.
4. This would create space for innovative new services--for example, same-day freight service--which a government-run system would never attempt.
5. With competing services and innovation, the odds are much greater that the high speed line would be used at maximum capacity, increasing the economic benefit and the system's ability to pay for itself.

Personally, I've never understood why railroads have to own and maintain their own tracks.  The public-private hybrid we use for other transportation modes seems to work much better, and were it not for the historical accident of how the railroads were built in the first place 150 years ago, I don't see why anyone would follow that model today.

Our new geothermal heat pump system is installed and operational (you can read about our initial research, and the decision to go ahead). All that remains at this point is to clean up the mess.

We have replaced our traditional furnaces, air conditioners, and water heater with a new system consisting of two geothermal heat pumps, a backup gas-fired furnace, a hot water storage tank, and a gas-fired on-demand hot water heater. The geothermal heat pumps both heat and cool the house using the soil under our yard as a gigantic heat sink (which is several times as efficient as a traditional furnace or air conditioner), and use waste heat to heat the water in the hot water storage tank. The on-demand hot water heater kicks in if the water in the tank isn't hot enough, and the gas-fired backup furnace is used on really cold days or when the power company turns off the heat pumps to manage the power grid in the winter.

First, a Rude Surprise

Recall that there are three financial incentives for installing this system:

• A $150/ton rebate from our electric company, Xcel energy, for new geothermal systems
• A "dual-fuel" electric rate which gives us cheaper electricity for the geothermal system if we have a gas backup and let the power company shut off the geothermal to manage the power grid, and
• A 30% federal tax credit

Of these, the $150/ton geothermal rebate from Xcel is relatively small (heat pump capacity, like air conditioner capacity, is measured in "tons." Our system is six tons total).  The dual-fuel rate is the one which really makes the system work financially, since that makes the geothermal significantly cheaper to operate than natural gas, even in years when natural gas is cheap.

We calculated that, given the cost of replacing our old furnaces (which had to be done anyway) and taking advantage of all the financial incentives, the geothermal system would pay for itself in about nine years.  That's not bad, considering that the heat pumps have a ten-year warranty and the loop field (the underground heat exchange wells which account for about half the project cost) should last pretty much forever.

Shortly after we committed to the project and paid for 50% of the system up front, we heard from our tax advisors that we might not actually be able to take advantage of the full geothermal tax credit. The problem is that the tax credit is nonrefundable, meaning that if it reduces your tax liability below zero then you don't get the difference back.  At the time we were planning the system, it was still unclear if the credit would be refundable or not; and now that it's not, we don't know if we will have enough tax liability in 2009 to get the full value of the incentive.

We re-ran the numbers without the federal tax credit, and it turns out that without it the system will pay for itself in 18 years instead of nine.  That's not great, but it's not terrible either, especially considering the nonfinancial benefits (helping the environment, etc.).

The System

The system we had installed is one of the more complicated (and therefore more expensive) residential geothermal systems out there.  We had to work around two major limitations in our home: an addition with a completely separate furnace and air conditioner (and no practical way to tie the ductwork together into a single system), and a relatively cramped utility room. Our system consists of:

1. The geothermal loop field, which is six parallel wells drilled to a depth of 180 feet in the front yard, each with a loop of pipe filled with antifreeze solution.  A buried manifold connects the six loops to a pair of pipes which go underneath the garage into the utility room.
2. A 2-ton heat pump for the addition, which uses antifreeze pumped through the loop field as a heat source or sink and an air conditioning-style compressor to heat or cool air. Some waste heat is pumped into the hot water storage tank through a pair of water pipes.
3. A 4-ton heat pump for the main house, which pumps its refrigerant through a heat exchanger in the gas backup furnace to heat or cool the house. It also pumps waste heat into the hot water storage tank.
4. A gas backup furnace, which also serves as the forced air blower for the main part of the house.
5. A hot water storage tank, which is warmed up to about 110 degrees when the heat pumps are running (and stays cold when they're not).
6. An on-demand hot water heater, which runs when the hot water in the storage tank isn't hot enough.
7. A motley assortment of pipes, pumps, wires, fuseboxes, relays, etc.

Together, all this gear replaces everything which had been in our mechanical room except the water softener.  It looks like the inside of Captain Nemo's submarine.

The Installation

The project took about two weeks to complete, though 90% of the work was finished in the first week.  Drilling the loop field and replacing our old mechanical systems happened in parallel, with our new hot water heater and gas backup furnace operational after the first full day of work.  This meant that we wouldn't have to be without heat or hot water, though fortunately the weather has been nice enough that the heat hasn't been necessary.

In order to be fully operational, after the equipment was in place and the loop field completed, the loop field had to be connected to the heat pumps and filled (it took about 125 gallons of an antifreeze mixture.  I'm told this fluid should never have to be replaced, unless the system has to be drained for some reason).  Then we had to wait for Xcel Energy to install a second electric meter, since the "dual fuel" rate requires that the geothermal system be separately metered from the rest of the house.

Once all that was done, we ran into a series of minor problems: the wrong part for a control relay, a burned out switch, and finally, after everything was running properly, the technicians accidentally left one of the heat pumps in a test mode, requiring another visit to reset it for normal functioning.

All told, the installation went about as well as can be expected for a project of this magnitude.

Living with Geothermal

The weather has been very pleasant lately, and we haven't used our new system much yet. It was a little cool the first evening the geothermal was on, so we ran it for a few hours to take the chill off.

Some things take getting used to in transitioning from traditional heat and air conditioning to geothermal. The biggest change is that unlike a gas furnace, which normally cycles on and off, a geothermal system is most efficient when it operates continuously in its lowest stage.

That means that it no longer makes sense to turn the heat down at night and when we're not at home during the day.  We had saved a significant amount on our heating bill by turning the heat way down at night, but now that strategy will actually cost us money by forcing the geothermal system to run in a less efficient mode to catch up--or worse, the system might switch to the gas backup furnace, negating the efficiency of geothermal entirely.

Getting the most out of geothermal will mean making only very gradual changes to the temperature in the house.  The name of the game is to try to keep it running in the lowest stage possible, and avoid running the gas backup at all.  We'll have to experiment with it when we get into the next heating season to see what works, but I'm guessing that we can turn down the heat modestly during the work week, as long as we are careful to raise it only gradually on the weekend.  The wood stove will be helpful, since it will give us a way to add more heating capacity without losing the benefit of the geothermal.

We've had a couple of months to investigate installing a geothermal heat pump system for our home, and now it's Decision Time.

This whole process started back in January when our old, conventional furnace went kaput on one of the coldest nights of the year.  It was past its expected life expectancy, so we started researching geothermal.  A geothermal heat pump uses the ground under the house as a gigantic heat sink, pumping heat underground in the summer (when the air conditioning runs), and pumping heat out in the winter (when it acts as a furnace).  This takes considerably less energy than conventional heating and cooling.

Financially speaking, a geothermal system costs more upfront, but less to operate.  The payback time is long enough that most people would be (understandably) reluctant to install one without some sort of financial incentive.  Fortunately, there are incentives aplenty:

• The Fiscal Stimulus Package offers a 30% rebate to new EnergyStar rated geothermal installations from the federal government.
• Xcel Energy, our power company, offers a special "dual fuel" electric rate: if we have a conventional backup and let them turn off the electric heat pump occasionally to manage demand, they cut the electric rate in half.
• Xcel also offers a rebate of $150/ton for installing a new geothermal heat pump system.

Doing the Research; Running the Numbers

Going into this process, we were helped by the fact that my parents installed a geothermal system a little over a year ago.  They've been generally happy with it, but had some issues (more on that later), and they were able to provide some hard numbers.  We figured it would cost about $25,000 to replace our furnace.

We identified several local geothermal contractors and invited them to our home to inspect the existing system and offer ideas and bids.  The contractors we did invite represented a cross-section of major heat pump brands, and all passed our initial screen of good histories on Angie's List.  We did not talk to the installer my parents hired, after hearing some of their negative comments and seeing other customers' complaints.

Our home presents a couple of unique problems for this installation.  First, we actually have two furnaces, separated by about 30 feet.  One is for the main part of the house, and the other is for an addition built before we moved in.  Ideally, we would want to replace both units with a single heat pump and tie the ductwork together, since a second heat pump adds considerable cost to the system.  There also isn't very much room around either of the existing furnaces for new equipment, making it difficult to find room for a conventional gas backup furnace (and without that special electric rate, the numbers don't make sense).

None of the contractors we spoke to thought it was feasible to put in only a single heat pump to replace the two furnaces: there just is not enough room to run the needed ductwork without cutting through bearing walls.

The space constraints also knocked out one of the manufacturers, which simply didn't have any way to give us both the heat pump and the gas backup in the space we have available.

We settled on a system from a local WaterFurnace contractor with many years of experience, and which could show us examples of how they'd handled similar problems for other customers.  The total cost will be about $40,000, and this will include two heat pumps, a natural gas backup furnace, a hot water holding tank, a desuperheater to use waste geothermal heat to preheat domestic hot water, and a whole-house on demand gas water heater.  The cost is split approximately one-third for equipment, one-third for drilling the geothermal wells, and one-third for installation and other components.

This will be a six ton system total (heat pumps, like air conditioners, are measured in "tons" of capacity), with four tons serving the main part of the house, and two tons serving the addition.  Only the main part of the house will get the backup gas furnace, but that will be sufficient to keep the addition warm (though not totally toasty).

Given that the total cost will be so much higher than we expected, we went back and did a more careful analysis of the payback.  Working in our favor is that we are also getting a new water heater in the bargain (which we would probably need in a few years anyway), so we can count the avoided cost of a new water heater towards the geothermal system.

After figuring out the various rebates and backing out the cost of two new furnaces, two air conditioners, and a new water heater, we estimate that the geothermal system will cost about $11,000 more than replacing everything with the conventional equivalents (after rebates).  It will save us about $900/year in heating costs, and $250/year in hot water (since the hot water will be essentially "free" when the geothermal system is running), and pay for itself in ten years.

I didn't figure in any air conditioning savings, since last summer we barely ran our A/C at all.  However, if we do have a hot summer, the savings will increase very quickly because the efficiency improvement for geothermal air conditioning is even more dramatic than for geothermal heat.  This could easily be hundreds of dollars more in savings.

So the numbers still make sense--the system will pay for itself before the warranty runs out.

That said, this will be a financial strain.  First, we have to pay for the whole system in one big lump, whereas if we were to replace our furnaces, hot water heater, etc., as they failed, we would be spreading the cost out over several years.  Second, we don't get the federal rebate (well over $10,000) until we get our 2009 tax refund sometime in 2010.  That means that it will be over a year between the time we spend the money and when we get that part of the money back.

Finally, the $40,000 number doesn't include relandscaping the front yard.  Drilling the wells will leave the yard a mess, and we're going to have to spend some money getting it repaired and cleaned up.  We had been planning to do a some significant landscaping within the next few years, so this will also get moved up to this spring.

Avoiding the Pitfalls

Part of making the numbers work is making sure we actually can claim all the rebates and incentives for this project.  My parents discovered this the hard way, when they went to do their 2008 taxes and learned that the model of heat pump they installed wasn't EnergyStar rated and therefore not eligible for the federal rebate.  The rebate in 2008 was limited to $3,000, so they weren't counting on it to the same extent that we are, but it was a rude surprise nevertheless and a warning for our project.

I've verified that both of the heat pumps we'll be installing qualify for the federal rebate, but we still need to contact Excel and make sure we have all our ducks in a row for both of their programs.

I also expect that there will be some as-yet-unknown gotchas.  We don't yet know where all our utility lines are, so we don't know where the wells can be drilled and where the connection to the house will have to go.  There's the chance that something will turn out to be unsuitable and put the kabosh on the whole project.

The Plan

If all goes well we'll probably have our new system installed by the end of May.  We need to get a permit for drilling the wells, and plan where everything will go.  Drilling will be in early May, with the mechanicals shortly thereafter.

A year ago my parents replaced their relatively new natural gas furnace with a geothermal system (or for the purists, a Ground Source Heat Pump, GSHP). They wanted to save energy and the environment, and saw this as a way to cut way back on their carbon footprint. They combined this with "windsource" electric service (which, at least in theory, supplies your electricity from wind farms at a slightly higher cost) in order to reduce their CO2 emissions from heating their home to effectively zero.

A geothermal (GSHP) system uses a heat pump (essentially a refrigerator which can be run in reverse) to extract heat from the ground in the winter, heating the house and cooling the ground. In the summer it runs the other way, extracting heat from the house to cool the house and warm the ground. A series of water-filled coils, the ground loop, act as a heat exchanger and turn the ground under the yard into a giant heat sink. The net result is heating and cooling 3-5 times as efficient as a traditional furnace.

My parents are happy with their system, but I had a hard time seeing how it made financial sense. Even with the higher efficiency, drilling a bunch of deep wells for the ground loop is a very expensive proposition, and natural gas is quite a bit cheaper than electricity.

Nevertheless, we decided that when the time came to replace our own furnace we would at least investigate geothermal.

That time came this winter, when the main furnace in our house (we have two) died on a cold night. It's 25 years old and past its expected lifetime, and when the technician looked at it his first question was whether we actually wanted to spend any money fixing it. We got it working again (at least for now) for a couple hundred dollars, and immediately started researching replacement options.

And so began the first chapter of Our Geothermal Adventure.

The Energy Equation

My first step was to call Dad and get some hard numbers from him about his geothermal system. Fortunately he keeps good records of utility bills, and was able to give me actual electricity and natural gas usage both pre- and post-geothermal. I could match those records against the records I kept of our bills from the same month to see how their heating costs compare to ours (answer: my parents' house uses about the same amount of heat as ours).

A little analysis showed that in my parents' home, the geothermal system heats their house for about a third as much energy as natural gas. This is as expected. However, at the rate we pay for electricity (about $0.11/kWh right now), electricity is two to three times as expensive as natural gas per BTU.

So in a year when gas is cheap (like this year), geothermal would cost about the same, and when gas is expensive we might save a third of our heating bill. That hardly seemed like enough of a difference to justify the huge upfront costs of the GSHP.

We decided to keep exploring anyway, since the environmental positives were appealing, even if the financial equation wasn't coming together.

Excelobama To The Rescue

About that time we learned that a geothermal tax credit was in the 2009 Stimulus Bill, as it was then going through congress. That would mean that the feds would pick up nearly a third of the cost of our installation if we decided to go down that route.

Then, at the first meeting with a geothermal salesperson, we learned that our local power company, Excel Energy, has a special "dual fuel" rate for people who heat with electricity (including geothermal) but have a fossil-fuel powered backup. The deal is that you let Excel turn off your electric heat as needed (an hour at a time, up to 24 hours over the course of the season) and they cut your electric rate in half for the power used for heating. This lets the power company better manage their load during the peak of heating season, and the backup furnace runs only a tiny fraction of the time.

The combination of these two factors--the Obama rebate and the Excel price cut--changed the math radically. Even compared to a year with cheap natural gas, our heating bill would be cut in half. If gas goes back to $1.50/therm (as it did after Katrina), we save 75% or more. And with the feds picking up 30% of the upfront cost, the payback for going geothermal got much faster.

In fact, when you look at the price difference between a geothermal system and a conventional furnace (remember, we have to replace the furnace anyway), we figure the geothermal will pay for itself within 7-10 years. That's actually before the warranty runs out from some manufacturers.

So it looks like we'll be getting a new geothermal system this summer. And this article can only end with....

To Be Continued....