Tag Archives for energy

Mass balance analysis of algal biodiesel

Physorg.com reports on a recent paper in which the authors analyze the sustainability of algal biodiesel from a mass balance perspective. The paper, Bioresource Tech. 102, 1185, essentially highlights one of the tradeoffs with algal biodiesel. The low tech route of large containment ponds limits the total output of dry biomass per hectare, as evidenced by the author’s computation that even 11 square miles of algae ponds, at a growth rate of 50 g of bone-dry biomass per square meter per day, would only be sufficient to replace 0.1% of the US consumption of diesel.

Of course, there are many ways to increase the output per hectare. One of these are vertical tubes, or bioreactors, for algae growth. The issue with this approach is that it is capital intensive, requiring not only the tubes, but cooling systems to prevent algae death from overheating and requires higher overhead, since the tubes must be scrubbed occasionally to reduce fouling.

If I were to be looking at this area for technology breakthroughs, I’d be looking at people applying anti-fouling or other surface chemistry applications to reduce the maintenance costs, or clever engineers designing passive cooling systems for these reactors. I can imagine a system where the bioreactors were built to exchange heat with an HVAC system in cooler environments, or with their own ground-sourced heat pump in warmer times. The cost of the cooling is a major barrier and it would be a win to spread that cost around amongst several different systems.

Limitless solar?

One of the things I have been almost continuously talking about in the realm of renewable energy is the need to diversify our sources of energy. Another is the need to beware of people who preach that there is One True Solution. It was thus with great interest that I read about an upcoming paper in the Proceedings of the IEEE.

In this paper, Derek Abbott of the University of Adelaide argues that solar, and in particular, solar thermal, is the Ultimate Answer to the world’s energy problems.  In fact, according to Physorg, he claims that solar thermal can last us for “the next billion years.”

Despite this claim, the quoted numbers in the article and the conclusions are actually pretty reasonable in general. Solar thermal is the most cost-efficient (although certainly not the most space efficient) renewable technology in terms of energy yield.  However, stating that solar thermal by itself is sufficient for the next “billion” years is rather unreasonable.

Either Abbott presumes that the rate of growth of energy usage on the planet will slow down to nearly nothing or that we will eventually fill near-Earth space with solar collectors and ship either hydrogen or microwaves back down to Earth. No other possibility can justify his statement. As I calculated some time back, at modest growth rates, there is a much-closer horizon of about 500 years before we start running up against the limits of solar power.

There are also other issues in the article that should be addressed. The first is the cost, both capital and variable, of transmission lines in his scenario. If, as he suggests, we convert 8% of the desert land in the world to energy production, we are faced with the challenge of either building transmission lines to the hinterlands, which are on average about 30% efficient, or according to his scenario, generating hydrogen, liquefying it, and shipping it. I don’t know the efficiencies of electrolysis of water, or of hydrogen liquefaction, but in any case, there are three lossy steps here, before that hydrogen is either burned or passed through a fuel cell to make electricity.

Don’t get me wrong: in large part I agree with Dr. Abbott. Both my numbers and his point to the same conclusion – that solar must be a part of any renewable future. My primary concern about this article and others like it is that they will serve to skew the funding and research environment in renewable energy the same way that the biofuel craze has. We have a good way to go before we can replace fossil fuels in their entirety and it seems clear to me that as we transition away from a fossil fuel energy monoculture, we would do well to avoid another one.

Notes from my Renewable Energy talk

As promised, you can click through here and get a list of resources that I used in putting together my talk and that you might find helpful in general. I appreciate the great audience that I had – everyone was really engaged in the subject and I’m glad that so many of you got a lot out of it.

There are a couple of points I want to reiterate. First is that I think that true wealth can only be measured in Joules, the unit of energy, and that access to energy is a key human rights issue. I also think that the current and coming energy crisis can be solved by breaking both design and technology constraints on our production and use of energy. Of these, I think that the design constraints are going to be hardest to solve.

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Does the blame fall on biofuels

In the alternative energy circles, a recent Science magazine online article published by a group from Minnesota has been making a lot of waves in the media. This article from the Seattle Times is typical of the coverage. There are a couple of issues with both the article and the coverage of the article that I’d to point out.

First, let me tackle the article. While no one will argue that corn ethanol is an extremely poor choice for a biofuel feedstock, it is also inarguable that the article focused on current biofuel technology. This implicitly assumes that all new biofuels will be roughly equally bad for the environment. Clearly, this is not the case, since algal-derived biodiesel and similar biomass-derived fuels will not contribute equally to global warming through the destruction of ecosystems. The article also assumed by implication that biofuels are the primary driver behind conversion of ecosystems to cropland. Past data would indicate that this is almost certainly not the case, since slash-and-burn was prevalent in the Amazon basin well before biofuels become a cause celebre. The issues around land use in the developing world would exist with or without biofuels contributing, since there is rarely an incentive for the governments who control these lands to preserve them. Rain forests do not yield significant economic benefit to those who live near them. All the biofuel boom has done is exacerbate the situation. Hopefully, this will bring attention to dealing with the root causes of the destruction of these ecosystems – namely, food security and poverty.

The media has been largely guilty of indulging in shrill hachet jobs on the nascent biofuel industry based on this article. I am certainly not implying that the authors of the Science report intended this; rather, I think that the natural tendency to want to take potshots at large targets is to blame here. Nevertheless, I think its important that people interested in short term energy development continue to work on capturing energy from biomass. With any luck, we’ll solve both the petroleum problem and the disappearing ecosystems problem at the same time.

Upgrading from an oil furnace to a heat pump

Last fall, when I was at MRS, the 40 year old oil furnace that had heated our home finally died. The diagnosis: cracked heat exchanger. We’d discussed this possibility a few times, trying out some scenarios. At the time of the incident, our current thinking was either a high-efficiency oil furnace capable of burning biodiesel or a heat pump. The folks at McNutt Service Group, the contractor we decided to work with, quoted us around $4000 for the oil furnace and about $6300 for the heat pump. The heat pump we had selected was a slightly above-average Trane model (16 SEER, 9.0 HSPF), which (along with the new air-handling system) we felt would give us the best deal in terms of efficiency and cost. After much debate, we decided to go with the heat pump for a variety of reasons. the most salient of these was the operating cost. I ran some rough numbers and estimated that over a 20 year lifespan of each unit, I should save around $6000 using the heat pump, based on a 3% per year increase in the cost of heating oil and a 1.5% increase in the cost of a kWh of electricity.

After receiving my first electrical bill that included a full month of the heat pump, I realize I may have underestimated the savings. The amount had only increased by about $35. At first, I thought that this month might have been warmer than usual, and in fact there were some warm days in the month. There were also several nights of temperatures in the teens. The National Weather Service’s climate data page did not indicate that the highs and lows during the month were excessive in either way (average temperatures 3-5 degrees above normal in December and a roughly equal number of days above and below in January.) With that, I was reasonably satisfied that the bill represented a typical January bill. A quick check back through my financial records showed me that from Oct. 2006 to Oct. 2007, I’d spent $766 on heating oil.

Going back to my spreadsheet, I plugged those differences in. Still not trusting the $35 number, I assumed that over the 6 month “winter” period, I’d average $50 more a month, for a total of $300. This number I assume is the cost of heating with electricity. Plugging in the growth rates I mentioned earlier, I set about determining my time to payback over an oil furnace. It’s less than 5 years to save the $2300 difference between the two units. But this really isn’t a good comparison – the new oil furnace would be much more efficient than the ancient Lennox furnace we had. The oil furnace we were quoted on was 90% efficient. Though I don’t have the numbers for certain, I’m estimating that the old furnace was no more than 70% efficient. Using that to adjust the cost of fuel oil, I recomputed the time to payback and got 7 years. Still, not bad at all. Assuming the growth numbers hold, I’ll save around $9000 (in today’s dollars) over the lifetime of the heat pump. And this doesn’t even count the savings in the summer of the 16 SEER heat pump over the old 11 SEER air conditioning unit that came with the house.

Bottom line for us was that the heat pump is looking to be a very good investment. And if folks like Nanosolar make it ultra cost-effective to put photovoltaics on every roof, the heat pump will be an even better decision.

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