I’ve been interested in agriculture and sustainability for a little while. When I first developed this interest I had the idea that the independent farm was under threat, and slowly disappearing. Under threat it may be, but disappearing it is not. In fact farm numbers are remarkably stable throughout the US, and have increased slightly in the last ten years.

So I was a little perturbed when GreentechMedia published a puff piece predicting the demise of rural agriculture, and advocating urban farming as the solution. I’m fully in favor of aquaponics, aeroponics, whatever-you-like-aponics and rooftop farming. And I think the food supply chain is a critical one to control and protect, and entirely worthy of strategic protection. Furthermore, the overall demand for food is growing rapidly – Norman Borlaug, Nobel laureate and thought leader of all things green, wrote in 2009 that: “In the next 50 years we have to produce more food than we have in the last 10,000 years”. Food, in all it’s dimensions, is a global-scale human problem; we need to be on it.

But this GTM guest author have to get real – the total number of farms in the US is basically unchanged over the past ten years (actual ten year growth is 1.5%). To call the ‘death of the farm’ is uninformed and wide of the mark, as you can see from this graph of farm numbers in the US since 2000[1]. Perhaps you could make a nuanced point about relative decline compared to population or economic growth, but that would still be marginal. Fundamentally, farming is in a healthy condition, despite the economic travails of the last few years.

Farms in the USA, by Region, 2000-2009

The author’s other position, is that farmers are aging, “almost sixty” on average, and about to retire en-masse. It’s true that the average principal farmer is fifty-seven, but this statistic has also barely changed in the past decade, and doesn’t seem to have driven farm closures over that period. Plus many principal farm operators employ three of four hands, and spend most of their time in front of a computer screen, or attending to business management. Again, it’s difficult to see how a single descriptive statistic or value judgment can be extended to conclude that rural farming is going out of style.

The farm lives on, as a source of food and feedstock for energy. It will have a crucial part to play in the transition to  a more sustainable and independent economy; so will cities, but primarily as destinations for sustainable, low impact lifestyles, and as centers of knowledge.

[1] Data on farm numbers comes from the National Agricultural Statistical Service, a unit of the US Dept of Agriculture.


While chatting with some friends in the Cleantech industry recently, I was reminded that good locations for Solar PV development can be counter-intuitive. We were chatting about how New Jersey is one of the better development markets, when I mentioned that New Jersey has a better solar resource, insolation, [1] than Spain. Many people think of Spain as really sunny, and the northeast US as a cloudy, dreary region with poor sun.

Now I happen to love Spain (including the autonomous regions), and can attest to several experiments with the Spanish weather. Most recently I was there in February, when we spent three wonderful, and mostly dull, days in Barcelona. Dull and wet enough to fully acclimatize ahead of our trip to Dublin. What’s the difference between Barcelona and Dublin in February? Dublin is equally wet, and a little colder.

Weather aside, a grand time was had by all, and this photo attests to the Barcelona weather.

Bari Gotic Art Gallery, on a Wet February Evening

Given the weak basis for my reasoning (which may explain why it turned out wrong), I pulled down insolation data for a dozen or so solar markets, and just for fun, Dublin too [2]. I computed annual energy generation for the default system using PV Watts 1, and also collected energy cost data for each location [3], typically using the region’s capital, or another dominant city.


Representative City Avg Energy Production (annual kwh) Energy Cost (US cents per kwh) Solar Value (Insolation X Energy Cost)
So. California Los Angeles 5 879 12.5 $735
Nor. California Sacramento 5 597 12.5 $700
Arizona Phoenix 6 468 8.5 $550
New Jersey Atlantic City 5 001 11.2 $560
Colorado Boulder 5 834 8.4 $490
Ontario Toronto 4 332 7.6 $329
Massachusetts Boston 4 975 11.8 $587
Spain Madrid 5 140 21.8 $1,121
Germany Munich 3 526 28.7 $1,012
Italy Naples 4 541 30.53 $1,386
Ireland Dublin 2 963 26.72 $792
Japan Matsumoto 4 736 17.8 $843

By this analysis, New Jersey has less insolation than Spain, though the difference is only 3%. The regions’ insolations are similar, as SEIA demonstrates.

While my premise was wrong, I stand-by the underlying point, that New Jersey has a great solar resource, and intuition about good solar locations is subject to bias (BTW, McKinsey recently published a good piece on behavioral strategy and bias). It’s easy to see why we might be biased to think of Spain as sunny, and the northeast US as dull, even though they are almost equal.

In addition to insolation, I encourage people to consider regional energy price disparities; this is where intuition can really be turned on its head. For instance, the economic value of the solar radiation in Atlantic City is greater than in Phoenix (the higher energy value in New Jersey makes up for the greater insolation in Arizona). The same is true of Dublin versus Los Angeles, and Spain beats New Jersey by a wide margin on economics[4].

My verdict on Spain vs. New Jersey? I’m going to call this one a draw. I will continue to develop solar in New Jersey, and go on vacation to Spain, and not the other way around. And I will always check with PV Watts.

[1] Solar resource is typically measured in insolation, a build up of Incident Solar Radiation; it measures the sunlight that falls on a square meter of land over one year.

[2] The PV Watts 1 default system is 4.0 kwdc, with a 77% de-rate factor, an azimuth of 180 0 degree, fixed-tilt, and the optimal tilt for the location (generally the optimal tilt in degrees is equal to the latitude). I used PV Watts 1 because it has international data.

[3] Price data was accessed on March 22, 2010, and derived from the following sources:

[4] Consumer prices are a very crude proxy for solar analysis, but they are a general indicator of how much energy is worth. They don’t reflect price distortions, time-of-use considerations, policy preferences or available incentives.

Towards the end of 2008 my friend, Ted Horton, who blogs at NorCal PV, invited me to make some 2009 predictions for the US Solar PV industry. He does this every year, reaching out to a group of respected solar professionals, and puts a composition on his blog.

I offered a few predictions, from the blindingly obvious (utilities will get into the solar business), to the obscure (major recall of solar panels). A more fanciful prediction was that 50% of the U.S. (by population) would be open for  meaningful commercial PV development by the end of 2009; at the beginning of the year I estimated that 20% of the U.S. qualified.

At that time New York was opening up (LIPA), and Pennsylvania was taking steps to structure a solar market. As the year progressed, the growth opportunities came more slowly than anticipated (Pennsylvania), and often with more hair (Arizona). And we saw some markets close or encounter instability (Connecticut, Massachusetts, Oregon).

When Ted recently asked for some 2010 predictions, I decided to go back and tot-up the numbers, convinced I had undershot. After some number-crunching, I was surprised to find 50% of the U.S. actually was open for business by the end of 2009, including utility projects. If you just count commercial projects, the number is 32%, though that is still 50% growth on the 2008 year-end figure.

I’m posting a table of the data elsewhere, and here are a few principals I used in determining which markets are open:

  • In general, “open for business” means there is a competitive market, where developers and customers can work on commercially reasonable terms toward widespread deployment; demonstration projects and pilots do not count. Almost every state permits solar development – that, in itself does not mean a market is open.
  • Open also requires that projects are currently being developed as of year-end 2009 (speculative land-assessment doesn’t count). This also means that new projects can be developed, so states with funding holdups, such as Connecticut and Oregon, don’t count.
  • I skipped the residential segment; it is not my area of practice, and there are too many marginal calls.
  • For the commercial segment, “open” means a transparent and substantial incentive program supporting behind-the-meter projects.  It should permit PPAs and be broadly available. Basically, it should be a competitive free-for-all, with customers, developers and installers mixing and mingling.
  • For the utility segment, “open” requires large scale projects under development, intended to supply the grid. These projects are dependent on more complex factors so the “widespread” requirement isn’t appropriate.

Comments or questions on how I categorized the markets are welcome.

Here is a table showing the populations (source US Census website, 2/14/10) and how I categorized states to compute the percentages for the companion post, “The Glass is Half-full”.  I categorized the markets by state based on my day-to-day knowledge of PV markets in the U.S..

Population (million) Commercial
% Open
% Open
% Open
United States 307.0 32% 43% 50%

Open Y/N


Open Y/N


Open Y/N

United States 307.0 NA NA NA
Alabama 4.7 N N N
Alaska 0.7 N N N
Arizona 6.6 N N N
Arkansas 2.9 N N N
California 37.0 Y Y Y
Colorado 5.0 Y Y Y
Connecticut 3.5 N N N
Delaware 0.9 N N N
District of Columbia 0.6 N N N
Florida 18.5 Y Y Y
Georgia 9.8 N N N
Hawaii 1.3 N N N
Idaho 1.5 N N N
Illinois 12.9 N N N
Indiana 6.4 N N N
Iowa 3.0 N N N
Kansas 2.8 N N N
Kentucky 4.3 N N N
Louisiana 4.5 N N N
Maine 1.3 N N N
Maryland 5.7 Y N Y
Massachusetts 6.6 Y Y Y
Michigan 10.0 N N N
Minnesota 5.3 N N N
Mississippi 3.0 N N N
Missouri 6.0 N N N
Montana 1.0 N N N
Nebraska 1.8 N N N
Nevada 2.6 N Y Y
New Hampshire 1.3 N N N
New Jersey 8.7 Y Y Y
New Mexico 2.0 N N N
New York 19.5 N Y Y
North Carolina 9.4 N Y Y
North Dakota 0.6 N N N
Ohio 11.5 N N N
Oklahoma 3.7 N N N
Oregon 3.8 Y N Y
Pennsylvania 12.6 Y N Y
Rhode Island 1.1 N N N
South Carolina 4.6 N N N
South Dakota 0.8 N N N
Tennessee 6.3 N N N
Texas 24.8 N Y Y
Utah 2.8 N N N
Vermont 0.6 N Y Y
Virginia 7.9 N N N
Washington 6.7 N N N
West Virginia 1.8 N N N
Wisconsin 5.7 N N N
Wyoming 0.5 N N N

Last week the Energy Information Administration released their 2008 Year in Review. There is a ton of data in the 118 page report, which may explain the year they take to compile and publish it.

From a clean energy perspective, there are lots of data on how renewables are growing, and how they compare on overall capacity, new capacity, energy generated, and so on. Overall, energy consumed in the US dropped by ~1% from 2007. The EIA attributed the decrease to a slow real growth rate, 0.4%, combined with the coolest year of the decade. At the same time supply of power, measured by peak summer capacity increased by 1.5%, exceeding 1 terawatt for the first time (1,010,171 MW to be exact).

So…. demand decreases, while supply increases…. and theory tells you that normally price would decrease. The Law of Supply and Demand, right? Well, not so fast. Electricity prices actually increased in 2008, and not by a little. They grew by a huge 6.7%, with some even huger outliers; commercial prices in Alaska and Hawaii increased by 25-30%, and 15 states had an increase of 10% or more.

The numbers behind the numbers are fuel costs; 2008 was a dreadful year for fuel costs, with average costs up by 27%. So perhaps we should count ourselves lucky to get away with ‘just’ a 6.7% cost increase for delivered electricity. Instead of the Law of Supply and Demand, over time, Regulation and Price Elasticity are the correct price setting frameworks:

  • In regulated markets, fuel adjustments are approved by regulators to ensure fuel costs are passed along to consumers.
  • In unregulated markets, contracts are reset regularly, and these resets allow providers to adjust price; customers can fix prices for up to three years, but it is common to choose short time-frames, often just one month. As energy is inelastic (demand is unresponsive to price changes) most of the fuel costs are passed along to customers, with little change in the amount consumed.

While the price increase during a bad recession stinks, there isn’t anything new in this. We know that the price-at-the-plug is heavily influenced by fuel costs, and this is just more evidence. It serves as a reminder though, that over-dependence on fossil-fuels exposes us to volatile fuel costs.

The corollary is to expect cost decreases in 2009 and 2010 based on cheaper fuels. That’s what I thought, but preliminary data for 2009 actually shows a 2% increase, with fuel costs mixed.

There were a few other tidbits that were either new or interesting to me:

  • The first nuclear reactor to be built in the US since the mid-80s is underway, the completion of a reactor #2 at Watts Bar in Tennessee (which was halted in 1988).
  • Solar is the fastest growing generation type; 2009-2012 planned additions are over 1,900 MW, a 360% increase on  2008. (And the 1,900 MW looks like a conservative number to me).
  • Energy generated by wind increased by 60%, to over 55 terawatt hours.
  • Speaking of terawatts, the US fleet grew to 1 terawatt. Over half of the added capacity in 2008 was wind, so perhaps the billionth trillionth watt was a renewable one!
  • And finally, I have to recommend Chris Nelder’s humorous angle take on the EIA’s draft Five Year Outlook.

Last week was a good week for CleanTech interest events in the Boston area. On Tuesday night there was the PEHub event at Bingham McCutchen’s office, which drew a great crowd, on Friday morning you could have listened to the Chairman of FERC speak at The Restructuring Roundtable at Foley Hoag’s downtown office, and on Friday evening the MIT Energy Club hosted a solar social which was good fun. That left the MIT Energy Initiative’s Thursday afternoon colloquium, featuring Tony Hayward, the CEO of BP, as “Most Infuriating Event of the Week”.  It was enough to convince me to post my first blog entry.

Mr. Hayward’s 45 minute speech (prepared remarks available here), was mostly a position paper leading up to why shale-gas should be a cornerstone of US Energy Policy. And given BP’s foresight to heavily invest in shale-gas, he all but patted himself on the back. He also undermined, in one way or another, other policy tools that might deter support for shale-gas, littering his speech with the usual anti-renewable red herrings, including intermittency (I’ll deal with this in a later post), power density (I’m taking that on here), and existing track record and scalability (I’ll also deal with those in a later post).

Power Density 101 – Conventional Power is Good, Renewables are Bad

Power density is the power-generating capacity of a given area of land.[1] Mr. Hayward for instance, during Q&A, compared a 10,000 bpd oil-well to a biofuel operation of comparable power production – he thinks you need to cultivate 100,000 acres of feedstock to generate the equivalent fuel. I don’t know much about biofuels, but on the subject of renewable power vs. conventional power, which he also alluded to, I think Solar[2] compares well.

This issue also came to mind recently when I read Ecogeek’s comments on a paper (they attributed to The Nature Conservancy) which describes an impending land-use crisis from renewable energy development. The paper in question estimates that 73,000 square miles will be developed for renewable energy use in the next 20 years, which would make renewable energy the biggest land-use category over that period. For their paper they used the footprint of the power plant itself, and added allowances for mining and waste storage (supplemental data on power density calculations here).

On footprint alone, Solar, and other renewables, do look weak compared to conventional base-load power plants. But conventional power plants have severe second-order land-use impacts, that Solar and other renewables avoid.

Power Density 201 – Not So Fast…

Let’s take Vermont Yankee as an example, a 620 megawatt nuclear facility in Brattleboro, Vermont, which generates about 35% of Vermont’s energy. It sits on 120 acres next to the Connecticut River; on a crude measure of power density it achieves 5.3 megawatts per acre – pretty good compared to the accepted metric of 100 kilowatts (DC) / 75 kilowatts (AC)[3] per acre that fixed-tilt crystalline Solar achieves.[4] The 120 acres includes on-site waste storage and some administration buildings, but doesn’t include off-site activities like mining, manufacturing and fuel processing.

So initially Solar looks pretty bad, but things take a different turn when you look at the impacted land area outside the power plant’s “footprint” (you can check out Vermont Yankee’s footprint on pages 3-6 and 3-7 of this report). Outside of the footprint, nuclear facilities are surrounded by three zones of reduced but non-zero impact. The first zone, the Exclusion Zone (EZ), allows essentially no land-use or habitation, and in Vermont Yankee’s case it looks like an area of about 1,000 acres. The second is the Emergency Evacuation Zone (EEZ), a 5 mile radius, (approx. 75 square miles or 50,000 acres); this area is considered to be at a heightened risk of contamination in case of a mishap, and as long as the nuclear plant is commissioned it is overshadowed by fear of fallout. The final zone is the Emergency Planning Zone (EPZ), a fifty mile radius, and approx 75,000 square miles of impacted area. When Three-Mile Island had its near-meltdown, the Emergency Evacuation Area was called-into action; Chernobyl’s exclusion zone, the so-called” Zone of Alienation” is over 1,100 square miles (that’s 700,000 acres).

Now, skipping the off-site impacts, including extraction, manufacturing, waste management/recycling and transmission (all of which would probably look worse for nuclear than Solar), lets compare Solar’s power density against the Exclusion Zone and the Emergency Excavation Zone, land areas which are permanently and definably impacted by the presence of a neighboring nuclear power plant.

At 1,000 acres, the Exclusion Zone achieves 650 kilowatts per acre. But the result for the Emergency Evacuation Zone is distinctly worse, only 11 kilowatts per acre. In comparison, fixed-tilt photovoltaic solar in Southern Vermont, tilted at 40 degrees, achieves a power density of about 75 kilowatts per acre. A 620 megawatt Solar plant requires only 13 square miles, versus ~2 square miles for the Nuclear Exclusion Zone and ~75 square miles for the Emergency Evacuation Zone. By the latter comparison, Solar has six times the power density as the nuclear plant.

While typically power density is the measure in question, you could make an argument that this analysis should be extended to reflect capacity factor, accounting for Solar’s “intermittency”. Intermittency is another red herring, but let’s look at it that way, a measure you might call Energy Density.[5] Nuclear power plants typically have 90-95% capacity factors, while Solar is typically 20-25% (and more like 18% in southern Vermont). Even if you give nuclear the benefit of the doubt on that one, you’re still looking at Solar, in Vermont, having about one and a half times the Energy Density of a recently upgraded nuclear power plant. Even a thin-film Solar power plant, with it’s decreased efficiency compared to crystalline silicon,[6] would still have energy density equal to the nuclear plant.

And nothing against Vermont Yankee – pretty much any nuclear plant in the US is going to look bad on this comparison; as long as you count the impacted neighboring land. Coal plants are going to look even worse, when you consider that their particulate pollution isn’t contained to a convenient 5-mile radius.

Power Density, you might say, is in the eye of the beholder, but there’s plenty to say in favor of renewables. Ultimately it might depend on how you feel about living or working in the shadow of a thirty-seven year old nuclear power plant. And we should remember that all power plants have some land-use impact, and you have to pick your poison.

November 4, 2009


1.                  The harsh realities of energy, prepared remarks by Tony Hayward, delivered at MIT on 29 October, 2009; http://www.bp.com/genericarticle.do?categoryId=98&contentId=7057586

2.                  Energy Sprawl or Energy Efficiency: Climate Policy Impacts on Natural Habitat for the United States of America; Robert I. McDonald, Joseph Fargione, Joe Kiesecker, William M. Miller, Jimmie Powell;  http://www.plosone.org/article/info:doi/10.1371/journal.pone.0006802

[1] For liquid fuels, energy density is the key metric, and it is computed differently: it is the energy contained in a given volume, typically measured in mmbTu per gallon in the US.

[2] For simplicity I’ll refer to “Solar” – apologies to the solar thermal folks.

[3] For ease of comparison I’ll state all power ratings in Alternating Current (AC); photovoltaic solar is more commonly rated in Direct Current (DC) and suffers approx. 25% loss when inverted to AC

[4] That’s a good figure for an economically optimized ground-mounted installation. Roof mounted installations tend to have shallower tilts, and hence considerably more power density. Roof mounted installations also avoid consuming land, so from a land-use perspective have even higher power densities.  Here are some rough figures to show that a density of 75,000 watts AC is reasonable:

Assumption 1: say, 180W module, 1,310 mm x 990 mm, 13.5% nominal efficiency

Assumption 2: tilted at 40 degrees, with 6.5 ft row spacing to eliminate shading… ~1,000 modules per acre = 180,000 watts (DC)

Assumption 3: allow 30% loss for difficult grades, shading setbacks, access roads and the like… = 130,000 watts (DC)

Assumption 4: allow 25% inversion loss, = 97,500 watts (AC)

[5] As a quick primer for those of you who aren’t engineers, power is a unit of capacity (like speed, measured in miles per hour) and energy is a unit of power over time (like how many miles you’ve driven in the past two hours). As nuclear power plants typically run about 90-95% of the time, and Solar runs about 20-25% of the time, the distinction is materiel.

[6] Thin-film solar panels use a lower-efficiency photovoltaic materiel and are heavier; they have the advantage of being cheaper per watt, but are 8-11% efficient, versus the 14-17% of crystilline silicon.