By Susan Kraemer

Globally, most of the high DNI needed for CSP is in high inland deserts - which also have the best resources for mining for metals.

In the mining industry, re-deployable diesel generator sets are commonly used to supply electricity. These are modular and scalable sets of gigantic generators, operating 24/7, fueled by diesel, that are moved to a new site when a mine is finished.

As CSP moves into the mining market, it must compete effectively with these huge generator sets in supplying base load power that is movable, because the need for that off-grid energy ends once the mine is depleted. For smaller operations, that might be in just ten years.

Amortising capital cost

While it’s easy for CSP to compete with diesel on fuel prices, the higher capital costs of CSP do make it a heavier lift, at least initially.

According to Tom Georgis at SolarReserve, the solution to recovering those initial costs and spreading them out over a longer term is re-deployability.

Inspired by his experience with power barges that are readily deployable wherever power is needed, Georgis is working with engineering teams at Solar Reserve and RocketDyne to re-engineer their power tower CSP plants for the mining industry.

“A concept we’ve been developing is this “M” class, a smaller version of our utility-scale CSP with molten salt storage,” he tells CSP Today. “It’s still early stages, but we recognize that there’s a need for this type of re-deployable technology within the mining sector.”

The “M” class power tower CSP plant would be customized to meet the needs of small mining operations, in 20-30MW units with storage, providing 24/7 base load power in off-grid locations, and designed so they can be disassembled and moved to a new site after ten years.

A possible lease arrangement

Unlike the more familiar power purchase contract with a utility, SolarReserve could move to a leasing model. Lease lengths would have to be flexible as well as long term, because unpredictability is a given in the mining industry; not just in supplies but in demand.

“The situation changes from year to year,” explains Bill Moeller, CEO of Utah’s 60 year old firm Clifton Mining. “A mine has a certain amount of reserves. Based on those reserves and metal prices; you can estimate how long one is going to run."

"But suppose the price drops after ten years? Metal prices go up and down all the time. If you’re caught in a marginal situation; you can’t afford to run, you’ve got to shut down. That happened to us. We shut down for quite a few years; but not because we ran out of ore.”

Because of the uncertainty of the metals market, predicting how long power will be needed is difficult, so the suppliers of diesel generator sets are flexible. Sometimes a mine needs additional generation too. “Whenever we’re through, or if they need to be upgraded,” Moeller explains; “we can turn the last one in and get a bigger one.”

Financial feasibility

But while uncertainty is one problem, the certainty of paying more every year for diesel is worse. As Moeller puts it: “We don’t have any choice. We know diesel is going to get more expensive. I think everybody would be happy to switch to solar. It doesn’t have any pollution. But the thing is, what would it cost?”

With diesel prices at $300 to $500 a megawatt hour, SolarReserve can beat the fuel prices now. But that means a longer time frame to recover the capital costs, like a 25-year utility contract.

“Our technology is more expensive upfront,” Georgis says. “But the high cost of the diesel gen set is the fuel, whereas we have zero fuel cost. When you combine them together we are much more cost effective, but the M class still has to be financed, and if it’s a shorter mine life, and a shorter PPA of maybe only 10 years, then it does become more challenging to make the economics work.”

A re-deployable model based on the power barge idea would mean getting perhaps three ten year PPA contracts out of the re-deployable plant, smoothing out the initial capital expense.

The advantage of CSP: storage

“Most mines run 24/7,” says Georgis. “The actual mining operations are very capital intensive, so it just makes economic sense to have multiple shifts running day and night.”

This is a key point about mining for the CSP industry. Mines need extremely reliable power, continuously.

“If the power shuts down for any reason then the mining operations stop, but it doesn’t mean you can turn it back on five minutes later,” he explains. “It can take a long time to bring up all of the machinery and get it back up online and operating; just like a power plant. It’s much more efficient to run 24/7; not stopping and starting.”

This is the biggest concern chaining the mining industry to more expensive diesel.

“The opportunity costs of foregone mining production are substantial, favouring lower risk conventional generation over renewable energy, which may pose reliability and intermittency concerns,” says Reg Howard-Smith, chief executive of the Chamber of Minerals and Energy of Western Australia.

SolarReserve would include a small auxiliary salt heater run on diesel to offer a backup in case of a power shortfall due to maintenance or extended winter weather, to bring the salt temperature back up to the 560 C needed. This option would be used well under 10 percent of the time to heat the salt and produce power.

The sales target is small mines in more isolated regions like Western Australia; that need about 30MW of energy, but need it day and night, and need to be able to move it after the mine is depleted.

Nearly everything re-deployable

Although their “M” class design is still underway, Georgis believes that only the storage tanks might turn out to not be re-deployable. The tanks are carbon steel and stainless steel and the base is a concrete pad. The molten salt could be redeployed.

The very high-precision heliostats are engineered to last 30 years, and he foresees no problem transporting them.

“That glass, with the reflectivity we require, is extremely durable in very harsh conditions, so that’s not one of our concerns,” he says. “And steam turbines are already moved around, because there’s an active market for second-hand steam turbines.”

“We’d have to look at the steam generation system and the piping; whether or not that could be disassembled and reassembled,” he adds. “We have engineering work to do but we definitely have resources working on it and we’re progressing the design and the concept.”

Preexisting infrastructure enables re-deployment

It might seem incredible to imagine uprooting and transporting a CSP plant, even disassembled, but the mining industry routinely operates on a much larger-than-life size scale. Clifton Mining, for example, uses several 250MW diesel generators, and runs its mining equipment on 440 volts.

“The biggest draw is processing the ore, and the second is underground ventilation,” says one Australian mining industry insider. At their off-grid sites, diesel also powers “a small town” of office buildings.

The extraction itself is done by huge heavy vehicles and machines powered with petrol. As a result, there is a huge infrastructure already, with roads capable of supporting convoys of gigantic mining machinery.

One of the prime regions for CSP-powered mining that SolarReserve is targeting is Western Australia, where they would be able to simply piggyback on that gigantic infrastructure system already in place, bringing the disassembled CSP plant in from sea on existing roads that the mining industry uses to transport metals out to the coast for export.

“Western Australia has excellent renewable energy resources, particularly solar resources, in the state’s primary mining regions such as the Pilbara, Mid-West and Goldfields,” says Howard-Smith.

“The development of scalable, transportable and more cost competitive CSP technologies in the future has the potential to make CSP very competitive.”

To comment on this article, write to the author Susan Kraemer.