Putting Pellets Away

Meeting thermal needs with biomass requires system designers to consider a storage solution that works for the customer, the site and the delivery company.
By Tim Portz | August 21, 2015

Almost unanimously, pellet delivery companies would prefer their eventual customers install as much storage as they possibly can when deploying a pellet-heat system. Many pellet systems are installed by companies that will later service those systems and deliver pellets, and their opinions on storage options make it clear that being able to store a high percentage of annual usage offers numerous advantages.

Customers with greater storage capacity will enjoy a lower price per delivered ton. “We always try to steer people toward larger storage spaces,” says Morton Bailey, president of Lyme Green Heat. “We realize that larger storage solutions increase the installed costs of the total system, but by offering a discount on volume, our customers can pay back the difference over time.” Bailey points out that customers who opt for larger storage solutions have the ability to protect themselves from price fluctuations and have to think about resupply less often.

The advantage is shared by the pellet delivery companies that service these customers. “When you get into a more rural area where the road might present some challenges during the heating season, we recommend people get enough storage that they’ll only need maybe one delivery during the season,” says Chip Straub, general manager at Vermont Renewable Fuels. While the ideal storage situation for both consumers and delivery companies would be a system that can hold exactly one year of supply, this condition is rare, particularly in residential environments. Constrained by price, available space and aesthetic requirements, system engineers and installers instead work to minimize the number of required deliveries within a given year. “The industry is pretty straightforward on the amount of storage capacity someone needs,” Straub says. “You want to size your storage so that you’ll only need to fill three to four times per season.” A typical residential pellet customer in the Northeast will likely consume around 10 tons of pellets per season, making three tons of storage capacity a common solution.

Complicating matters, however is an aging housing stock throughout the Northeast. “The challenge has always been headroom, at least in Vermont,” says Straub. “We have basements, but some of those basements are under six feet tall and some of them are even under five feet tall. So that is always a challenge when a customer is trying to decide on options for bulk storage.”

Fortunately for Straub, Bailey and their industry colleagues, a broad range of solutions has emerged that make adequate pellet storage possible, regardless of the challenges and complexities of the installation.

Outdoor Silos
When available space is not an issue, in some instances, outdoor silos offer system engineers and end users a cost-effective means to store an entire season’s supply of wood pellets. “Almost all of our commercial stuff is exterior storage, mostly because of the size of storage and the annual usage,” Straub says. “We have customers that have 30-ton silos, 50-ton silos, all the way up to 100-ton silos.”

Co-opted from the grain bins that dot the countryside in rural America, silos are either built from galvanized steel sections on-site or delivered in one finished unit. “The exterior silos are the least expensive, but they are also the least appreciated,” says Dave Frank, cofounder of Sunwood Biomass, a Vermont-based biomass heating engineering and installation company.  “They are so unbelievably functional, and so affordable.”

 Silos can be scaled to satisfy the annual supply for all residential applications and the vast majority of commercial installations. Frank says silos have tremendous advantages when it comes time to deliver a new load of pellets, a transaction that he believes doesn’t get enough consideration in some plans. “Pellet delivery companies can blow product into the silo, or they can use an auger to move pellets in as well,” he says. 

Above all else, silos allow system owners to buy in bulk and drive down the delivered costs of their pellets. Bailey and Lyme Green Heat have been delivering bulk loads of pellets for seven years, and try to configure customers’ storage solutions to match neatly with the delivery vehicle fleet. “If you really want to save money, you’re going to design your solution so that we can show up with our 28-ton tractor trailer and deliver a full load of fuel,” he says.

The enthusiasm within the ranks of system designers for silos is beginning to catch the attention of some of agriculture’s largest grain silo manufacturers. Charles Sukup, president of family-owned Sukup Manufacturing Co. in Sheffield, Iowa, is seeing inquiries and quote requests coming in from “all-over.” While its bread and butter is grain storage and grain handling, Sukup isn’t surprised by the growing opportunities with wood pellets. “Pellets are similar to corn in that you need a good bin to maintain the low moisture content,” he says. “Our bins and conveying systems are very suited to that task.”

Despite the many advantages offered by outdoor silos,  they simply aren’t feasible for many installations. Residential customers balk at the idea of having a large bin or silo next to their home. ‘We’re OK with satellite antennas and swimming pools, but we aren’t OK with outdoor silos,” Straub says.

Metal, Fabric Indoor Bins
Residential and commercial customers who can’t or won’t deploy outdoor storage must find space inside their home or facility to deploy any number of hard- or soft-sided bins in the marketplace.
Hard-sided bins are largely built of sheet metal and offer a rigid, water-tight storage option for system operators. “Sheet metal bins are totally sealed, and work better in a damp environment,” Straub says. “They are completely caulked and air-sealed all the way around.”

System designers admit that hard-sided, indoor bins bring with them installation challenges. “The big challenge for metal bins is construction time,” Straub says. “They are a giant Erector set. It usually takes two men who know what they are doing eight to 10 hours to put one up.” And while Straub and his team have had some luck cutting down hard-sided bins to accommodate available space, this only increases installation time and costs.

Fabric, or soft-sided silos were developed to offer indoor storage at lower costs, with far less installation time. In Straub’s experience, a fabric bin can be installed in about half the time of a sheet metal bin, around two and a half hours for a two-person team.

Fabric silo solutions, like their steel and hard-sided cousins, have roots in agriculture. German fabric silo manufacturer A.B.S. has been manufacturing fabric silos for over 30 years. The company’s founder, Adolf Lesk, established the company in 1983 to service operations that needed an indoor solution for animal feed and grain. Since the company’s founding, A.B.S. has sold over 60,000 fabric silos. “Our fabric silos are easy to adapt to room dimensions,” says Maren Oberland, an international sales representative at A.B.S. “When you have a room with difficult dimensions, we can adapt the silo to these unique dimensions. Our technicians regularly talk to our customers and help them determine the right silo for their situation.” This flexibility is well-received by North American system designers, and A.B.S. has a number of distribution agreements in place.

One performance characteristic unique to fabric silos like those manufactured by A.B.S. is that they allow operators to physically move the walls and sloped floors to keep pellets flowing through the system. Installers, however, are split on whether this is an advantage. Bailey sees it as an advantage. “A fabric bin, you can actually push on the walls and keep working pellets through the system. If the bin has the proper angle of repose and the pellets are being funneled out of it properly, you’ll get to a point where there is an inverted cone,” he says.  “You literally push on the corners, and they all fall into the center. In doing that, you keep the fines and dust working through the system.”

For Frank, this kind of tinkering runs counter to what he thinks his customer’s want. “We’ve come so far with automation in pellet systems,” he says. “Most of our systems require no more intervention than ash removal once every four weeks. We’re that close to oil and gas solutions for reliability, and then you introduce a small thing like someone having to kick the bottom of a bag.”

Still, Frank finds it hard to argue with the economics of fabric silos. “In some projects, the low cost and speed of deployment make bags the solution that ultimately gets chosen,” he says. And noting that when deployed in a commercial environment with maintenance staff already in place, “dealing with the required maintenance is not an issue.”

Considering Conveyance
With indoor and outdoor, hard-sided or soft-sided storage solutions systems, designers and operators must consider pellet conveyance when making their final decisions. Quite simply, pellets must be able to move efficiently into the storage solution from a delivery truck as well as out of the storage solution into the pellet appliance. Pellets are either moved mechanically with augers or pneumatically with suction. Each conveyance option brings with it advantages and challenges.

Tim Heutz, president of Heutz Premium Pellet Systems, a system installer and pellet delivery company based in Lewiston, Maine, spends a great deal of time thinking about the “fill” when designing a new system. “We would like to see the straightest route and the shortest route possible,” Heutz says. While his truck is capable of delivering pellets pneumatically at distances of around 100 feet, he works to avoid that whenever possible. “A common problem is the storage unit is placed where there is a long run or lots of turns during the fill,” he says. “This can cause a lot of pellet degradation.”

Heutz prefers that the distance pellets travel from a delivery truck to a house is less than 60 feet, and, if possible, that 60 feet would include the distance pellets travel once inside the building. For Heutz, longer fill distances, particularly if there are several corners, introduce a risk of subpar system performance as pellets tend to degrade and break down when moved long distances.  “These long fills cause questions of reliability in the overall solution, when actually it’s just a matter of the fill not being thought out,” he says.

Augers can move pellets at almost any distance, but for the most part, they must be engineered with straight runs only. Any turn the system has to make must be broad, and any existing walls and infrastructure have to make way for an auger. “Everything must get out of the augers way,” Frank says. “That can be challenging.”

Sites Dictate
Engineers, installers and delivery companies all agree that for the most part, the unique realities of each project ultimately will decide which storage option will be deployed. A commercial location may have an annual usage that makes the capacity of an outdoor silo the most attractive solution, but out of the question because the site is being historically preserved. A residential project may opt for a fabric solution because the basement was hand dug over 100 years ago into stone and rubble, and a fabric silo is the only thing that will fit.

Frank points to the infancy of the industry, noting that collectively, he and his industry colleagues are working up the learning curve. “There are some guys out there who are pretty good and everyone is getting better, but right now I would say that people aren’t giving enough up-front attention to pellet storage,” he says. Frank continues by looking upstream to the cadre of architects and developers more accustomed to fossil fuel heating solutions. “They’ve not had to give much thought to fuel storage because of our fossil fuel laziness. It’s getting better, though,” he says.

Heutz, too, cites the industry’s infancy for some of the challenges. That and system designers interest in providing the lowest-cost option in an effort to win a job. “I think some designers think, ‘If I do it this way it’ll save costs and I’ll get the job.’ But in the long run, if the customer is not happy, you’ve done a disservice not only to yourself, but to the whole industry,” he says.

System designers feel the burden to design the right system falls squarely on their shoulders. ““I don’t know if the customer is informed enough to be making those decisions,” Bailey says. “I think it comes back to the installing contractor and the decisions they are making.”

This is intuitive as customers don’t want systems, they want heat and regardless of the fuel used, they rely on professionals to install something that works. The good news is each successful system installation creates new fans of pellet systems, and not just end users. More and more architects and developers are thinking about pellet systems to satisfy heat loads at their projects. Better still, Frank says, is that the practice of engaging with pellet system engineers early is on the rise and the results are very promising.  “The ones who have, have knocked it out of the park.”

Author: Tim Portz
Executive Editor, Biomass Magazine
[email protected]