Background

Due to a combination of factors there is much interest in reducing the amount of energy, and in particular fossil fuel energy ("carbon emissions") used in the industrialized countries.  The major forces driving this is the increasing concern due to climate change potential caused by burning fossil fuels, the fact that the majority of the worlds petroleum is located in unstable countries and the environmental concerns associated with drilling,  mining, and burning fossil fuels.

Unlike other topics on this site, this one is much more in the research phase, so the following description contains some speculative thoughts that will undoubtedly change as technology changes and I'm better able to find "big picture" analysis of the problem.

A brief note on "Global Warming"

While my intent for this document is to be as objective as possible, which means avoiding political or value judgments, I don't find most discussions on global warming to be particularly objective.  Up front I will admit that my bias is that I'd rather walk in the woods than watch TV, go to the mall or most of those other traditional American activities.  I'm also a business owner and investor.  In my view the problem is more due to people not being willing to think outside the box, admit their biases and attempt a rational analysis of risks and tradeoffs.  So here is my attempt at a rhetoric free description.

For those skeptical of problem of global warming (a term I think is misleading, I prefer climate instability), I can only offer this thought:  no one argues that there is more carbon dioxide in the atmosphere than at any time in any recent history (at least 100,000 years)--what they argue is whether its a problem.  While it may not turn out to be a problem, it is much more likely that it will.  The reason is that in any physical system if you change one thing, everything else will change until they system reaches equilibrium again.  In a highly complex system like the atmosphere, it is possible that these changes will somehow counteract each other (from the human perspective) and continue to provide a suitable climate for us. Unfortunately there is no reason to believe that such a fortunate outcome is any more likely than many, many other possible outcomes.  In some sense I would agree with the climate skeptics that no one knows, but in my view that should increase our urgency in doing something about it, since the outcome might be much worse than we think.

My personal guess is that the climate models are at least vaguely correct, and that the impact will be that some areas will become more habitable and others less.  This however will not be neutral, even if the affected land areas happen to be of similar size because ecosystems react to change by first going thru a collapse phase before reaching a new equilibrium.  During a change phase, those species with less stringent life requirements tend to out-compete those who live only in niche ecosystems, resulting in an overall loss of biodiversity.  While this is not necessarily negative from the human perspective, it certainly isn't positive either and carries some risk factor that we will be negatively impacted.

While humans are a highly adaptable creature, our sheer numbers will likely make the mass movement of people and agriculture from places that become less hospitable to places that are more hospitable difficult to impossible.

There is some chance (albeit not with much evidence) that the global warming and climate instability we are seeing is either a natural phenomenon or non existing.  In general those taking this viewpoint really are arguing that they are concerned that in dealing with the problem they will experience an economic loss, or loose a way of life.  Rather than look for ways to deal with the problem and preserve their way of life, they point to the fact that climate change isn't a sure bet.  In my view this is like smokers, who in spite of a preponderance of evidence that it is likely to lead to various negative health impacts, and a premature death, continue to smoke anyhow.  Its true that you might smoke and live a long time, and its true that climate change might not be a problem, but in since in both cases something is being injected into the system at a rate well beyond what history indicates is safe, and in addition neither additive is inherently positive, so expecting a positive, or even a neutral outcome would certainly appear to be nothing more than wishful thinking.

With a problem this large people tend to feel there is little they can do, but this is not the case.  If each person did a small thing, multiplied by six billion people (or depending on your viewpoint, maybe just by the one billion who have more opportunity to do something) then multiplied by a twenty year period, the impact would be huge.  While ignoring the problem is an option, it carries it's own risk factors.

My final thought is that anyone looking at the situation strictly objectively would be hard pressed not to suggest that reducing world population is likely to be as effective as any other solution, although there are so many practical, political, cultural and ethical problems in actually accomplishing this that it isn't likely.  One can only hope most of the six billion of us will individually decide this is a good idea.  In the meantime western societies can retool their economies for increased energy efficiency and use of renewable energy, giving us some time to reconsider whether our lifestyle is really making us happy or not, and whether there is a reasonable tradeoff between out current energy intensive lifestyle and the simple, but laborious lifestyles of our ancestors. 

Zero Energy/Carbon Neutral

There is much talk about "zero energy" homes and "carbon neutral" activities.   A zero energy house generates all the energy it needs over the course of the year, while a carbon neutral building generates no carbon.  The two are not exactly equivalent, since a zero energy house can use fossil fuel while feeding an equivalent amount of electric out onto the grid--it still generates carbon even if over time it uses no energy.  To be carbon neutral, a building cannot burn any fossil fuel at all, and as a result, all attempts at being carbon neutral use electric for all of their energy.  It would be equally valid to use a biomass based fuel that itself was generated in a carbon neutral way (for example using methane from animal waste), but given how few buildings have attempted to be carbon neutral, this does not appear to be on anyone's agenda.

Aside- Practical Details: all electric homes have some limitation due to the low energy content of electric compared with natural gas.  The main one is that electric hot water heaters are about four times slower than gas ones, and for an electric tankless hot water unit to be equivalent to a gas one, it requires its own 100amp circuit, which will require an oversized service panel.  Heat pump hot water is more efficient (2-3 times more), but has its own set of complications.  The only other issue is that many people prefer to cook on gas stoves.  Electric induction ranges may solve make most of them happy, or alternatively a market for carbon-neutral natural gas (methane) could develop.  If the later happened, it would still be possible to use gas burning fireplace inserts and stand-alone stoves, although I suspect the cost of carbon neutral gas to be much more than the current cost of fossil fuel gas.

In any carbon neutral solution, the grid is used to store excess energy for times when no renewable energy is available, which might be a daily fluctuation, weather pattern fluctuation or a seasonal one (or all of them!) Many people have attempted to do this on their own, living in "off grid" homes, but most of them use propane for cooking, hot water and sometimes refrigeration and supplemental heat, so few (if any) off-grid homes are actually carbon neutral.  As a result, the typical (keeping in mind there are only a handful) carbon neutral home is all electric, and grid connected, often using the grid for energy storage on a seasonal basis in additional to a more short term basis.  In northern climates, this means generating excess energy in the summer and buying it back in the winter.  In southern climates, the reverse would be true.

While on the small scale one can argue that it is possible to buy back renewable electric, for example by being part of a green power program, the reality is that this solution doesn't scale up beyond a small percentage of users, and in fact the only reason you can buy back reliable power is because most of it comes from easily controllable fossil fuel plants (for an in depth look at electric generation and carbon emissions, see: http://tonto.eia.doe.gov/FTPROOT/environment/co2emiss00.pdf).  Currently, the grid has no storage.  This isn't to say green power programs aren't a good idea--they are--its just all they do is put more renewable electric on the grid...they don't solve the big picture problems of building a renewable grid.

In fact, it is the grid will have to undergo a significant restructuring to handle large amounts of distributed power. Here are the issues:

1. The storage issue must be addressed. Unless there is always enough renewable generation at all times to cover the load, storage will be needed.  Current technology batteries are expensive and have relatively low energy density, although if widely deployed, they may be sufficient to cover daily fluctuations.   One solution along these lines that has been consider is using the batteries of hybrid cars as storage by converting them to "plug in hybrids" (I admit to not having done enough research to comment on this approach).  Another frequently discussed approach is using hydrogen, which to be carbon-neutral would have to come from hydrolysis of water or from a biomass source, which could then be burned in a fuel cell to make electric.  The major downside to this is that neither conversion is currently very efficient, although the fuel cell process can be efficient if there is a use for the waste heat it generates (for example to heat water, or the house itself).  In the meantime, renewable energy generation is so small that we can large quantities of it to the grid before much has to change.

2. The grid is not designed for distributed generation.  Currently the grid is essentially a mesh of tree-like structures: large amount of power are moved on big lines to substations and from there is it distributed on trunk lines, which are then divided into branch lines.  A branch line only has to carry the average amount of power needed by the customers it serves, a number that is typically much smaller than the maximum each can use because at any given moment most people are using only a very small amount of their maximum.  When this assumption stops being true, like during a summer heat wave when everyone turns on air conditioners, the grid occasionally fails.  If every building were to generate solar electric, the reverse situation can occur (for example on a sunny summer day in Seattle when everyone is at the beach!) causing the grid to carry more than its maximum amount of power--only backwards!  There are, of course, multiple solutions: store it locally, convert it to hydrogen, install bigger wires, etc.

3. If we're going to move large quantities of electric between regions seasonally, we will undoubtedly need many more high power transmission lines.  Most (all?) northern communities are unable to generate enough electric for their daily winter use.  Since no one likes these things, some effort will have to into installing this capacity in an environmental and community sensitive way.

4. The grid has losses--about 7-10% of the generated power is lost, so for a home to be zero-energy, it must generate enough extra to cover these losses.  Since the grid currently moves power one way, I would assume that moving it two ways (eg once on generation, and then a second time to buy it back), would involve twice the loss.

This is not to say the problem isn't solvable, just that the solution will require rethinking how our power grid works in addition to adding voluminous amounts of renewable capacity (including conservation!).  For a more in-depth view (and slightly different as well), the American Solar Energy Society published a big picture solution to getting to carbon neutral at  http://www.ases.org/climatechange/climate_change.pdf

My short version would be: 

1. We need to look at every possible renewable energy technology.  Unfortunately even renewable energy has environmental impact, so we must be careful to understand what that is before deploying them on the grand scale.

2. At regular intervals, review each renewable technology, deploying and researching the ones that make the most sense at the time. The reason is that at this point, no single renewable technology appears to be able to solve the entire problem.  Since the technology behind them is not mature, one can expect many improvements over the next 20-50 years.  Funding needs to be based on performance potential, not short term economic potential. Our current policy makes no sense: we throw money at whatever the current panacea of the moment appears to be (say hydrogen or ethanol), but its all motivated by short term profit alone, not potential or clear thinking.  By providing random incentives, we allow the current short term thinking of the US financial markets to dictate our national energy policy.  It becomes up to the private sector whether to fund research, manufacture products or purchase them. Instead we must be looking for the best economic policy that makes an efficient transition to renewables with the least amount of pain.

3. Finding out what the best scale is to deploy the renewable generation.  We know that distributing the generation is likely to lead to improved reliability, but we also know that homeowners are notoriously bad at maintenance.  The cost of retrofitting the grid for distributed generation must also be considered.  If power plant scale turns out to be too big, then we need to know if millions of distributed generation points is too small.

The ASES study is the most logical approach I've seen so far, but is not an outline that many environmentalists will find completely satisfying because it only addresses the issue of atmospheric carbon.  At issue is the other environmental costs of renewable energy, in particular what is the environmental cost of deploying renewable energy on undeveloped land that is still a functioning ecosystem supporting biodiversity and providing respite from the onslaught of development.  We've already dammed most rivers, so now we look toward covering thousands of square miles of land with wind farms and thousands more with concentrating solar power plants.  These technologies certainly solve the carbon problem, but unless their use is limited to already developed land, those of us who value natural spaces will find these solutions a very bitter pill to swallow.

Biofuels are a promising approach, in particular those based on agriculture or wood waste, but like every other solution, an investigation into the negative environmental effects of the massive use of biofuels needs to be done, especially given that our entire agricultural system is currently heavily petroleum based.  Any massive change in the way biomass moves thru the ecosystems could result in serious consequences.

Finally, no discussion of climate change can ignore the issue of nuclear power, since it is effectively a zero carbon alternative.  In my view, nuclear power has never even approached living up to its promise of "energy too cheap to meter".  Not only are the power plants expensive and complex, but the issue of nuclear waste has found no decent solution after thirty years or so of looking for one.  The fact that the "waste" is actually so physically hot (not to mention radioactively hot) that it must be stored in water to keep it cool, indicates that these plants are not at all efficient.  From the waste perspective, the only reasonable solution is a breeder that actually uses all its fuel...although I have never seen such a reactor described: the breeder still produces high level waste--just less of it, and with generally shorter lifetimes. Unfortunately the breeder (as well as all reactors) use the exact same fuel (U235 & PU239) that is used in bombs, so for many people the possibility of nuclear proliferation makes breeders only more dangerous than the standard reactor.

Given the choice of nuclear power, covering thousands of square miles of land with wind farms, and/or much of southern Arizona with concentrating solar plants, most environmentalists will probably pick "use less power", but of course that may not be one of the choices offered.  Difficult choices like this will probably be the key battles over the next twenty years.  One can only hope that thru a combination of technology improvements, proper economic stimulus, and social change that we will be able to find a solution that is acceptable to the majority of people.

There are many other schemes to achieve carbon neutrality, including planting trees, burying carbon etc.  While they may or may not be able to get carbon out of the atmosphere, these solutions don't address the fundamental issue: that by using fossil fuels, we're consuming very old solar energy that is not replaceable in any reasonable time frame.  To achieve true carbon neutrality we will have to stop using fossil fuels virtually completely. (note: the only scheme for burying carbon that could make sense would be if the carbon comes from biomass. This is essential using plants to remove carbon and then storing it somehow.  Personally I'm pretty skeptical storage will work, unless there is some way to lock it up chemically, and even then you have to think about the natural geologic processes that might chemically unbind the carbon.) 

Zero Energy Theoretical Case Study

The following is an theoretical analysis of various approaches to building a zero energy house (or at least as close as you can get) without complete reliance on the grid for energy storage.  Obviously if you could rely completely on the grid, then you could just keeping putting up PV panels until you generated the amount of electric you needed for the year.  As previously mentioned, this ignores the fact that at the time you need grid electric, there may be no renewable electric available. 

For this analysis, I looked at a 2 story, 2000SF house with about 15% of its wall in glass because these are pretty typical numbers for new houses.  In order to make the analysis easy, I made a lot of simplifying assumptions, but since I was looking for relative comparisons, they shouldn't matter.  I also assumed that the climate was Seattle (4400 degree days, very little winter solar), the location was urban (so wind & wood aren't possible), and that the residents were a small family, which was already made some effort to conserve electric & hot water.

Note: this analysis uses a lot of energy terminology, most of which is described in the  energy units section.  If you want to better understand the entire energy picture, I recommend you read the entire energy section.

I started by assuming the house was built to typical energy code levels (note: in many places you're allowed to build even worse than this). I then looked at various things I could do to use less energy: a combination of conservation and generation.  I assumed R-19 in the walls, R-30 in the ceiling & floor, U.4 windows, and an air leakage rate of .5ACH as the base case.

The base case house uses 40 million BTUs (11800kwh) of heat energy, another 4 million (1200kwh) in hot water, and 5500kwh of electric (19 million BTUs).  The total is 63mBTU (18,500kwh).

The first step was to look at doing everything that could be done relatively cheaply.  By moving to energy-star appliances, putting TV/DVD etc on plug strips so you can actually turn them off and using mostly compact fluorescent lights, you can easily knock off 1/3 of your electric usage.  For somewhere between $3-5 thousand, the house could have been built super-insulated as well (R30 walls, R48 ceiling/floor, U.34 windows, ,35ACH). By picking energy-star washers & dishwashers that are also water-efficient, using PEX home run plumbing and low flow shower head, you can save another 25% off your hot water usage.  So without doing anything expensive, the house now looks like this:

Improvement 1 uses 29 million BTUs of heat (8400kwh), another 3 million (880kwh) in hot water, and 3600kwh of electric (12 million BTUs).  The total is 44mBTU (12,900kwh).  Nearly 1/3 less!

Next, I looked at adding some passive solar (I'm assuming the site isn't shaded by something) and upping the insulation a bit more.  I changed the walls to R50 (about 1 foot thick), reduced the air infiltration down to .2 ACH, and made all the windows that don't face south triple glaze U.2.  Again the cost is not high.  Depending on how you assume the R30 walls were built in the last case, moving to R50 could be a very small added cost.  The extra air tightening costs a bunch of cans of spray foam and two days labor: maybe $500.  The triple glaze U.2 windows are a bit of a problem because there are a very limited number of manufactures that make them, although obviously if people started ordering them more manufactures would make them.  The price premium is only around 10%.  For passive solar, I assumed just 7% of floor area in south facing glass, and no added thermal mass.  Note that the additional cost of this kind of passive solar is zero!

Improvement 2 uses 20 million BTUs of heat, but gets 10 million of them from passive solar leaving 10 million used (2930kwh), still uses 3 million BTUs of hot water (880kwh), and 3600kwh of electric (12 million BTU).  The total is 25mBTU ( 7400kwh).  This is now less than half of what we started out using, at an up front cost of $6-9 thousand.

At this point, further reduction in energy use becomes harder.  The easiest thing is to install PV, which in the northwest will generate most of its power in 6 months of April thru October.  Each kw of capacity installed generates 1000-1100 (or so) kwh of electric in a year and costs about $7 thousand.  Since electric usage is typically similar throughout the year, a 2kw system would easily meet all the daily electric needs during the sunny period, but that still leaves 1500kwh or so that has to be imported during the dark months.

If you increase the insulation levels to extreme (R80 walls & ceiling, R50 floor, and keeping the same windows & air infiltration levels, you save another 3 million BTU of heat loss--about 15%, but its not clear exactly how you'd build such a house.  The walls and ceiling would have to be more than 20 inches thick unless heavy use of polyiso board, and given that the newer CFC free polyiso is only about R6 per inch, you're still looking at 13" or so of insulation!  If you were able to do this, it is not worth going any further unless you can improve the windows (now accounting for 40% of the loss) and air infiltration (now accounting for 30% of the loss).

Another option is to increase the amount of passive solar by putting more windows on the south side.  Doing so is likely to require the house have some thermal mass, and due to the extra windows results in higher nighttime and cloudy day heat loss, which would suggest that movable high insulating shades be used over at least half the glass area (something that's not likely to go over well with most homeowners at this point in time).  As a rule of thumb you can use up to 15% of the floor area in south facing glass, and doing so would double the amount of captured solar.  This adds an additional 10mBTU to the building, but cost 6mBTU in additional heat loss thru the windows.

In climates with winter sun, solar thermal could make a big difference, but there is so little solar energy here in the winter that its not effective here.  Alternatively we could try to store excess heat in the summer, but because there is almost no solar for 3 months, the storage requirements are large.

Rather than go into more arcane possibilities, it suffices to say that getting down to zero carbon is not easy.  What is easy however is that the energy use of homes could be cut by more than half for very low cost.

For someone wishing to be a zero carbon emitter, the house can't use any fossil fuel.  That means that the hot water backup must be electric, cooking must be electric and the dryers must be electric.  In the case of backup heat, the only reasonably efficient system is a geothermal heat pump which typically moves 3 BTUs of heat into a building for every BTU is consumes.  The downside is that they are typically expensive to install.

Conclusion: while we still need to look at zero energy homes, what we need to do is start building every single building with very high levels of insulation, buy energy efficient appliance and lighting while also looking to see if we can make small lifestyle changes that reduce energy use.

No discussion of carbon emissions is complete without looking at travel.  Once you live in a reasonably efficient house, it is very easy to use more energy (and carbon) in transportation, and if the  house is very efficient transportation will dominate your carbon footprint.  For example the house described as "improvement 2", above would require about 200 gallons of gasoline for supplemental energy (ignoring conversion efficiency).  For a  30 miles per gallon (better than average) car, that 200 gallons only brings you 6000 miles --less than half of what the average American drives!  For someone who flies, you also have to account for the airplane's approximate 50 miles per gallon per passenger average-- a 3000 mile cross country flight uses 60 gallons of gas per pasenger!