Size Matters

• 
• 

In recent months, announcements of new biomass-to-power projects have flooded renewable energy news. These ventures range from the construction of a giant 100-megawatt (MW) wood-powered plant, to building 25 small 4-MW wood and agricultural-waste-fired plants. Presumably, different parts of the world have different needs and demands when it comes to electricity-but is one size more economical than the other?

In August, Denmark-based Babcock and Wilcox Vølund A/S, a subsidiary of U.S.-based Babcock and Wilcox Power Generation Group Inc., announced that it had reached an agreement with Italy-based Advanced Renewable Energy Ltd. to supply up to 25 small biomass plants over the next 10 years, all of which will be built in Italy.

In addressing its plan to build multiple plants, Ryan Cornell, company spokesman, says the main impetus was to meet customer needs. "These are the types of plants [our customers] were looking for, so we are licensing a design that fits their needs," he says. "There are several reasons why they wanted to go with the smaller plants instead of larger, centrally localized plants, some of that has to do with essentially the size of the region where they are building."

All 25 plants will be built in two regions in southern Italy-Calabria and Sicily. "The towns are small there, so you are looking at building a small plant to serve a town of 1,000 to 5,000 people. They don't need a gigantic plant to serve these towns-the electrical grid isn't developed in the same way it is in the United States. It is small and limited, so we are trying to provide electricity to these small regions separately rather than to a large region."

Cornell says another reason for small-scale plant development in this particular area is that the Italian government encourages the development of small biomass plants to support the local forestry industry. "They essentially have large tracks of forest land there, and they are trying to provide a market for the waste products that are generated," he says. "It is more economical this way. Instead of building one plant 100 miles away and then trucking the wood and biomass in, the plant is built nearby and the biomass has to be hauled only 10 miles."

Cornell says local, small-scale development reduces transportation costs and helps generate more jobs for the local people.

In summary, Cornell says in this case, the market is different than it is in the United States. "These are smaller towns with smaller power needs," he says. "Considering the grid infrastructure, it makes sense to keep it small rather than taxing the grid with power output from one large plant."

Other companies such as Québec, Canada-based Sanimax and Ontario–based StormFisher Biogas also favor small, local facilities to utilize continuous waste streams. With plans to invest more than $160 million, the companies recently announced a joint venture to construct eight biogas plants in the Midwest over a period of time, which has yet to be determined.

Sanimax annually collects more than 1 million tons of animal and food byproducts, vegetable oils, and hides and skins and transforms them into useable products for industries worldwide, including feed companies, chemical manufacturers, tanneries, soap producers and pet food manufacturers.

StormFisher Biogas, a renewable energy company that builds, owns and operates biogas plants across North America, works with the food processing and agricultural industries to process organic byproducts into electricity and natural gas. In the next five years, the company plans to develop 18 plants across North America. The first three plants will be built in Ontario and are expected to be on line in 2009. Each of the plants will process about 100,000 tons of organic byproducts annually and generate 2.6 MW of electricity, enough to power approximately 2,600 homes.

Is Bigger Better?
Good things don't always come in small packages, according to Peter Flynn, pool chair in Management for the Engineers Department of Mechanical Engineering University of Alberta at Edmonton, Canada. Flynn has spent nearly a decade studying the burning of biomass-agricultural and wood waste-in standard power plants instead of coal. He has also been involved in numerous research projects to determine the economics of different plant scales.

Flynn says building multiple small power plants in a region is an economic disaster. "The mantra that has come out of my work is that capital efficiency trumps transportation," he says. "Talking about ethanol and power generation-everybody who has modeled power generation has come up with an economy of scale that says, when you double the size of a plant you will have a 62 percent increase in capital costs," Flynn says. "This is for a 100 percent increase of capacity."

He has also found that small power plants are not as thermally efficient as large plants. "A 200 MW power plant will turn 30 [percent] to 39 percent of the thermal energy in the biomass into electricity," Flynn says, considering a 200 MW plant to be large. "A 25 MW plant will turn 20 percent into electricity, or maybe 25 percent into electricity. It's losing more heat per unit of capacity, and this is because the surface area per unit of biomass is bigger."

Flynn conducted a study with other researchers for the British Columbia government to determine the plant economics of using surplus trees killed by mountain pine beetles as a feedstock to generate electricity. "We found that if a plant was built at 300 MWs, generated power could be sold for 7 cents per kilowatt hour. If it is built at 100 MWs, power could be sold for 12 cents per kilowatt hour-having it bigger made it cheaper per unit of power output."

Although larger facilities cost more to build, more power and efficiency would be generated, which would outweigh the higher construction costs, Flynn says. "This is an economy of scale," he says. "This is why we build big refineries and coal-fired plants, and all the same stuff is true for ethanol."

A common misconception in the biomass industry is that biomass cannot be economically transported great distances because its energy content isn't high enough, Flynn says. "That is absolutely wrong," he says. "I can tell you six studies from Europe, the U.S. and Canada-highly detailed studies-have said this isn't true."

Even the cost of fuel doesn't make that much difference, Flynn says. "When you look at the cost of trucking something, the biggest cost of driving a car is the depreciating value of the car," he says. "So when fuel increases, it has a small impact. When you look at trucking costs, a quarter or maybe a third of that cost is fuel. So, if I have a 50 percent increase in fuel cost, it's not a big deal."

Flynn says he conducted a highly detailed study in a mixed farming county in Alberta, Canada, to determine whether it would be more economical to install anaerobic digesters on individual farms or to build one large, centralized plant. The study looked at the cost of trucking the manure to the centralized plant and then transporting the leftover liquid back to the farms where it would be spread on the land as fertilizer. "Unquestionably, it was more economical to have a centralized plant, much like the people in Denmark have, which is a heavy dairy industry country," he says.

Other Factors
Should the size of the community affect the size of a plant? In some cases, but not usually, Flynn says. "If you have district heating, where you capture waste heat from a power plant and use that, then the economics of distributed plants changes a bit because you can't ship low-quality heat long distances," he says. In North America, where district heat is rarely used, it's irrelevant, Flynn says. There is a reason why there are no small coal-fired power plants for each small town in North America. "It's expensive, and while it may promote rural living, the economics are not there," he says.

Another issue to consider is the staffing needs for a large number of plants. "Staffing for a 500 MW plant is nearly the same as it is for a 50 MW plant," Flynn says. "You have to have a person in the control room no matter what the size. Having more plants means more workers, raising costs considerably."

Flynn says companies that build multiple smaller power plants and receive government subsidies are generally less profitable and are a waste of taxpayer dollars.
The technology utilized at a biomass power plant also affects the economics of plant size. "Many technologies are expensive and require a large plant to be economical," Flynn says. "For example, Fischer-Tropsch Synthesis is a very capital intensive process."

Other studies have shown that large biomass power plants may have less of a negative affect on the environment. Research conducted by Patricia Thornley of the Tyndall Centre for Climate Change Research at the University of Manchester, United Kingdom, showed that smaller facilities generally produce higher levels of emissions per unit of electrical output than larger ones. In addition, gasification processes facilitate a reduction in emissions for large plants.

As the world continues to look for ways to create cleaner, less expensive power, it is critical to consider logistics such as the size of biomass power plants, Flynn says. "All of this doesn't matter if we are talking about a half of a percent of a country's energy mix," he says. "But when you start talking about 25 percent of a country's energy from renewable energy-we better get this right. If we get it wrong, the consequences could be enormous."

Anna Austin is a Biomass Magazine staff writer. Reach her at [email protected] or (701) 738-4968.