"The more I find out, the less I know."


The Dorkmobile

Tuesday - November 11, 2008 11:55 AM

Inspired by a combination of high gas prices and a desire to get more consistent exercise, this summer I bought a recumbent tricycle and cargo trailer for my commute to work.

Trike.png

Since June, my goal has been to ride to work at least two or three times every week, about a 16.5 mile round trip. I'm pleased to say that I've put over 900 miles on the trike so far (including a few longer rides for fun), and I've saved about two tanks of gas in the minivan.

I'm not going to pay for the fancy trike through gas savings alone--at least not this decade--but I've found that riding to work has a number of side-benefits aside from the obvious health and environmental ones.

The biggest is that riding the trike is straight-out fun. More fun than driving a car, naturally, but also more fun than riding a bike. The recumbent seat position is much more comfortable than a bike seat (which hurts my butt, and also puts a lot of pressure on my wrists and shoulders), and the low-to-the-ground arrangement gives a palpable feeling of speed like riding a go-kart.

I've also found that the trike gets a lot more reaction from other people. Where a bicycle is common and even a nuisance to some drivers, the trike with trailer is a real novelty. I get lots of kids who wave at me as I zoom by, and cars give me a lot of space (and often wave, too).

Now that winter is setting in, you might think that riding season is over. Not if I can help it!

Within the next week or so, I should be receiving a velokit, basically a tent with windshield for the trike, allowing me to continue riding even on cold mornings. With a trike, slippery roads are not nearly the problem that they are on a bicycle (you can't wipe out on an icy patch).

At the same time I'm doing some upgrades of the drivetrain, switching to all-internal hubs (where the gears are inside the wheel, keeping them from being exposed to rain, snow, sand, etc.). Combined with the velokit, The Dorkmobile will be complete, letting me ride in all but the worst winter weather in comfort and looking like a total geek.


Posted at 11:55 AM | Permalink |

I have no energy!

Wednesday - August 13, 2008 02:38 PM

I just discovered that in my transition to the new version of iBlog, my entire "Energy" category disappeared.

It looks like the only way to get it back is to recover the entries by hand, a task I'm not likely to complete for a while. In the meanwhile, here is a link to the old energy category page.


Posted at 02:38 PM | Permalink |

The Magic Year

Sunday - April 27, 2008 02:49 PM

It's always dangerous to extrapolate current trends far into the future, but I've been doing it anyway for solar energy. I got my hands on a data set of the average price of photovoltaic modules over the past 25+ years (in constant 2006 dollars), thanks to Robert Margolis at NREL.

Keeping in mind that the data shows the prices of the PV modules only (not installation), the trend is remarkable: on average, the real price per watt of photovoltaic modules over the past 25 years has tracked almost perfectly to a curve which drops by half every 10.5 years (or about 6% per year). There are a few blips here and there--corresponding to supply and demand fluctuations--but the simple 6% annual drop in prices explains 96% of the variation in PV module cost over two and a half decades.

PV-ModulePrice.png

Given recent advances in photovoltaic technology, there's no reason to believe the trend won't continue for a while longer. It may even accelerate at some point.

At this point, it's natural to ask when solar panels will be cheaper than power from the electric company. You have to make some assumptions about the long term interest rate, how long the modules will last, and the relative cost of installation, and I came up with the answer that solar and grid power will be at parity somewhere between 2020 and 2025.

That's not the whole story, though, since it's reasonable to assume that the cost of electricity will increase faster than inflation for the foreseeable future. That means that while the cost of solar power is going down every year, the savings will go up--and the savings will continue to increase even after the solar panels are bought and paid for.

So in reality, it makes financial sense to install a photovoltaic system while it's still somewhat more expensive than grid power, since over the life of the system the savings will continue to increase. The Magic Year--the year when a brand-new photovoltaic system will pay for itself over its lifetime--depends on the assumptions you use about the inflation rate for electricity, the real interest rate, the life of the system, and so forth.

The Magic Year is 2015
The Magic Year is 2015 using these assumptions:

  • The installed price of a photovoltaic system will be twice the price of the modules alone
  • The price of the modules will continue to follow the historical curve
  • Grid power today costs $0.10/kWh (about the price I'm paying now)
  • The real inflation rate for grid power will be 3% (i.e. grid power will increase on average by 3% more than the inflation rate)
  • The long-term real interest rate will be 3.5% (i.e. the interest rate will be 3.5 percentage points above the inflation rate)
  • One watt of PV capacity will generate one kilowatt-hour of electricity per year (about the factor for Minnesota)
  • The system will last 30 years
  • After 30 years, the photovoltaic system will have no residual value (i.e. it will need to be completely replaced)

PV-MagicYear.png

I used a Net Present Value (NPV) calculation, the standard way to figure the current value of future cash flow or savings. If the NPV is negative, then the system costs more to install than it saves over its lifetime; conversely, a positive NPV means the system pays for itself. The breakeven point (NPV = 0) is the Magic Year.

Your Magic Year may be different than mine. For example, in the California desert where grid power is more expensive and a photovoltaic system produces more power over a year, the Magic Year could be as early as 2007 (using the same interest rate and inflation assumptions). In Seattle, where hydro power is still cheap and it's cloudy all the time, the Magic Year could be 2025 or later.

Saving for the Magic Year
There are a lot of assumptions and an uncomfortable amount of extrapolation which go into calculating the Magic Year, but it seems reasonable to assume that 2015 will be the year to install a photovoltaic system here in Minnesota (give or take a couple years). She Who Puts Up With Me and I have decided to run with this assumption, and start putting aside some money every month with the idea of saving enough by 2015 to install a PV system big enough to bring our net electrical consumption to zero. We're also putting aside enough to pay for a major upgrade of our heating and air conditioning system at the same time--which might include switching to a geothermal heat pump.

In the meanwhile, we'll keep burning firewood in the winter--the stove has now paid for itself with gas savings--and doing smaller energy upgrades along the way like windows and lighting. 2015 is only seven years away, and by then we hope to have our net home energy use down to zero.


Posted at 02:49 PM | Permalink |

Questions to Ask About Alternative Energy

Tuesday - October 30, 2007 02:50 PM

If you follow alternative energy news (where I define "alternative" as anything not derived ultimately from fossil fuels), you get deluged with announcements about promising new technologies, each of which seems to be poised on the brink of ending all our problems.

Most of this is hooey. There's a lot of money flowing into energy technology these days--for good reason--and so there's a lot of incentive to hype any new invention which might somehow conceivably be pressed into service for energy production.

Since most of the stuff you read about will never produce a single watt of power, it's important to keep some perspective on exciting new developments. Here's my list of questions you should ask about any new energy technology:

Has the technology been demonstrated outside the lab?
A lot of hype gets expended on technologies which exist only in the lab, and sometimes only on paper. There's a huge gap between a lab experiment showing that geewhizium-doped buckyballs can extract energy from cellulose and actually throwing your grass clippings into your household Mr. Power box and getting electricity out. Most promising technologies never make it out of the lab environment for a variety of reasons: poor operating reliability, sensitivity to common environmental conditions, short operating life, and so on. If a technology has actually been shown to work in real-world operating conditions, that's a huge step forward; otherwise, it may be interesting, but probably irrelevant.

Does the technology produce net positive energy over its lifetime?
Surprisingly, many of the technologies promoted as future energy sources don't actually produce energy by the time you subtract all the inputs. Biofuels, in particular, are controversial in this respect: some calculations show that corn ethanol actually contains less energy than it takes to produce by the time you add up the energy required to plant, harvest, transport, ferment, and especially distill the stuff. The fact that the calculation is even close shows that this is probably not a promising source of energy. Hydrogen fusion is a great example of an energy source which is easy to demonstrate, but has yet to demonstrate net positive energy output.

For a long time, photovoltaic solar cells had the same problem, in that it took more energy to produce a solar cell than the cell could reasonably produce in its lifetime--though manufacturing efficiency for solar cells has long since improved to the point where this is no longer the case.

Other technologies, like wind, hydroelectric, biomass (i.e. burning wood), and nuclear are unambiguously energy-positive.

Can the technology scale?
Humans consume a staggering amount of energy, around 5x10^20 joules per year, about five-sixths of which comes from burning fossil fuels. That's approximately the equivalent of 140 trillion watts of installed photovoltaic capacity. So any technology which is going to eliminate our dependence on fossil fuels has to be able to get big. Really big.

Our global economy has an astonishing capacity to build manufacturing capacity in a hurry: just look at how much infrastructure we''ve built over the past hundred years dedicated to things like refining petroleum, building cars, and processing foodstuffs. So I'm not worried so much about being able to manufacture energy infrastructure as long as the raw materials are plentiful. The kinds of things which can prevent a technology from scaling up are:

Limited resource: Some energy resources, like hydroelectric, geothermal, tides, and (to a lesser extent) wind only occur in a useful form in particular times and places; and while these can be very useful resources, they can't provide energy everywhere its needed. In some cases, the total global resource may be insufficient to replace more than a small fraction of our fossil fuel usage. Waste-to-energy schemes are inherently limited by the amount of trash available.

Limited materials: I've seen some proposed technologies which rely on exotic materials (platinum catalysts, etc.) which may not exist in enough abundance on the surface of the Earth to meet our energy needs. Fortunately, most alternative energy ideas use fairly commonplace raw materials, though there is some question about the availability of uranium for nuclear power (but see this rebuttal).

Limited area: The earth has a finite amount of area, and the space available for power generation for certain applications can be limited by the application (for example, the roof area of a car limits the amount of solar energy it can collect). For biofuels, which are essentially solar-to-liquid fuel, some calculations suggest that the current technology would require more arable land than currently exists in order to replace our fuel needs, though this could change with higher yielding crops and different growing techniques.

Environmental impact: Most alternative energy sources are fairly clean, but some present real problems. Nuclear, in particular, poses some tough disposal issues which haven't yet been solved even for our current level of production. It's not clear how we would deal with the waste produced if we ramped up to using nuclear power for the bulk of our energy needs.

Technologies which can't scale to the 10^20 Joule/year range are inherently destined to be niche energy sources. In my view, the only alternative energy source which has been proven to be scalable to global proportions is photovoltaics: with current technology, the entire global energy demand could be met by covering an area smaller than the U.S. desert southwest in solar cells. Of course, in practice the solar collectors would be spread out across the globe, and a large fraction (perhaps all) of the required collector area could be on rooftops and other currently unusable areas.


Posted at 02:50 PM | Permalink |


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