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Tampilkan postingan dengan label solar thermal. Tampilkan semua postingan
Tampilkan postingan dengan label solar thermal. Tampilkan semua postingan

Selasa, 14 Juni 2011

Marrying Gas and Renewables

A Turkish developer recently announced that it would build a new power plant using technology from GE that matches wind and solar generation to the output of a highly responsive natural gas turbine, all integrated in one package with the hardware and software to mesh its output with the grid. GE is apparently calling this scheme IRCC, for "integrated renewables combined cycle", adding yet another acronym to our growing list of energy choices. This development looks interesting from a technical perspective, but also for what it suggests about GE's view of the future market for generating equipment and power delivery.

The International Energy Agency's "Golden Age of Natural Gas" scenario remains a question mark, rather than a certainty, but if gas is to serve as the key fuel for bridging between our high-emission present and the low-emission future, then we're likely to see more installations like the one in Turkey emphasizing the synergies between gas and renewables, rather than the tough competition gas is giving renewables in some markets. The IRCC--not to be confused with an IGCC or the IPCC--is interesting because it goes well beyond the idea of using gas-fired power plants to back up the naturally variable output of wind farms and utility-scale solar arrays.

The IRCC concept is built around a new combined cycle gas turbine, the Flex-Efficiency 50, with an impressive capability to ramp up and down, as needed, with minimal loss of either efficiency or emissions performance. And thanks to the energy technology portfolio the company has built up over the last decade, GE is able to offer one-stop shopping with GE wind turbines and a solar thermal generating module from eSolar, in which GE has recently invested. The gas turbine/solar thermal hybridization looks especially useful in maximizing plant efficiency and incorporating solar thermal power into the grid at the lowest possible cost, by avoiding the expense of an extra steam turbine and generator. If all this works as advertised, the grid operator shouldn't know or care whether the power being dispatched was generated using wind, sun, or gas.

Before you confuse this posting for a GE ad, I should note that at least in the configuration chosen for the Turkish site most of the power from this integrated plant would still be generated by the gas turbine, which has 10 times the peak output of the concentrated solar power module and more than 20 times the rated power of the small wind farm tied into it. By the time you account for the capability of the gas turbine to run 24/7 when necessary, compared to typical capacity factors of 25-40% for wind and up to 25% for solar, the proportion of the IRCC's annual megawatt-hours generated from gas could exceed 95%. Nor is GE the only firm bringing turbines like this to market. So it's an impressive step, though more of an incremental than revolutionary one. However, with its inherent flexibility, I wouldn't be surprised if this type of gas turbine could effectively integrate a much larger quantity of renewable generation on the grid outside the IRCC's fence, particularly after the operating experience of the first few installations has been absorbed.

GE's timing in introducing its IRCC concept could prove especially apt. Not only does the Flex-Efficiency turbine look useful for helping to meet California's aggressive new 33% renewable electricity target, but the 50-cycle version featured in GE's marketing materials--likely minus the solar thermal module--could be just what Germany needs, now that its government has begun to come to grips with the quantity of new fossil generation that's going to be required to make up for the post-Fukushima accelerated retirement of its nuclear power plants.

Kamis, 24 Maret 2011

Renewable Energy: Horses for Courses

It has become nearly impossible to keep track of all the major wind and solar projects underway at any point in time. Considering that I can recall when a month's worth of project announcements could be counted on the fingers of one hand, that's a sign of the tremendous progress in renewable energy over the last decade. Today, the projects that I notice tend to involve either novel technologies, or companies or locations in which I'm interested, such as the new rooftop solar thermal installation on the convention center of St. Paul, Minnesota, not far from where my in-laws live. I probably wouldn't have even paid attention to this one, if the eye-popping price tag hadn't included a cool million in federal stimulus funding. As I read on, it quickly became clear from the figures included in the news story that it requires more imagination than I possess to view this project as a good investment for taxpayers.

In putting the project's $2 million cost into perspective it's important to understand the distinction between solar thermal collectors and solar photovoltaic panels (PV). The former capture and transfer heat, while the latter turn sunlight into electricity, which is much more valuable. A 1 Megawatt (MW) PV installation would cost quite a lot more than $2 million, but that doesn't make this installation's price a bargain. Assessing that depends on the annual energy savings and resulting avoided fuel purchases. From the project description and the emissions reductions cited in the article it was possible to work out the expected annual energy savings involved, which appeared to have been something of a mystery to the facility spokesperson quoted. A MW of solar thermal equates to 3.4 million BTUs per hour, although the River Centre's rooftop clearly wouldn't generate that on a 24/7 basis even in a much sunnier location than the Twin Cities. However, the 900,000 pounds a year of avoided CO2 are unambiguous. At 117 lb. CO2 per million BTUs of pipeline gas, that equates to saving 7.7 billion BTUs of gas a year. And at last year's average commercial natural gas price for the state, that works out to an annual avoided cost of $58,000.

When I convert that stream of future energy savings into its net present value over 25 years, even with fairly generous assumptions on the cost of capital and future natural gas inflation, it is worth about what the convention center alone paid for it, or around $1 million, ignoring the impact of the two years it apparently took to build it. So in the parlance of corporate project evaluation, the federal officials who approved the RiverCentre's solar roof for that stimulus grant destroyed about a million dollars of taxpayer value when they decided to fund a solar thermal project in such a northern location with relatively low annual peak-sun hours. What were they thinking?

Well, the DOE official present at the facility's unveiling offered a clue by means of a hockey quote--always a good call in Minnesota. "We want to be where the puck is going to be, not where it is now." I would translate that as their funding of this project constituting an investment in bringing down the cost of future solar installations. Unfortunately, that would be much more credible if the installation in question involved leading-edge thin film or multi-junction concentrating PV technology, for which performance and cost have been improving steadily, if not quite in Moore's Law fashion. But this is solar hot water. The thermodynamics and heat-transfer considerations for such an application haven't changed since I was in engineering school, even if the packaging has improved. There's only so much heat to be captured and transferred, especially in a place with an average January temperature of 22°F.

When I'm critical of projects such as this one, it's not out of a sense that all renewable energy is impractical or ineffective. Renewables are earning a place in our energy mix, and they will become even more important in the years ahead. However, because they depend on harnessing diffuse energy sources in real time, rather than disgorging geologically stored energy in the manner of fossil fuels, it matters greatly where we put them. That's why I've been relentless in my criticism of Germany's overly-generous feed-in tariffs, and I see rooftop solar thermal in St. Paul in much the same light. Installing renewable energy devices in locations with poor resources, particularly using taxpayer money--or in this case money borrowed on the taxpayers' behalf--reinforces all the worst stereotypes about renewable energy as a boondoggle. The British have an expression that seems apt here, "horses for courses": run the right horse for each racecourse. If someone wants to bet their own money on rooftop solar in Minnesota, they do so with my blessing. But where my tax money is involved--and perhaps I'm especially sensitive about that this time of the year--I insist that it be done someplace that affords the technology a decent chance of earning an economic return, rather than just feel-good, PR value.