Tildy Bayar, Associate Editor, Renewable Energy World
June 17, 2013 | 1 Comments
LONDON -- A new kind of tracking system, in combination with system-wide savings, could substantially reduce balance of system costs, claims one company.
Reduction in balance of system (BOS) costs is the holy grail of solar project development. Tracking the Sun, an annual PV cost-tracking report produced by the U.S. Department of Energy's Lawrence Berkeley National Laboratory (LBNL), found that non-module costs represent a sizable fraction of the installed price of PV systems in the US – in 2011, US$4.90/W for commercial systems of 100 kW or more, while utility-sector PV systems >2000 kW averaged $3.40/W. Continuing deep reduction in the price of solar panels will require concerted emphasis on lowering the portion of non-module costs, the report concludes.
California company Inspired Solar Technologies (IST) claims its dual-axis backtracking system can significantly reduce LCOE and achieve up to 90 percent more energy yield per unit of land. IST says its tracker system yields 38-45 percent over fixed mount systems, and its array design saves 20-25 percent from tighter packing; the balance of cost reductions comes from reduced power losses and reduced parasitic demand, it says.
Founder and CEO Ken Oosting believes his company has found the answer in a combination of system-wide improvements – some large and some small – that leverage each other. "The key to achieving the breakthrough was patient optimisation of a large number of parameters," he says.
The IST ArrayBot features a dual-axis backtracking design. Dual-axis trackers typically use a motor, often a stepper motor, which offers an advantage for very small and precise angular changes. Unusually for a tracking system, IST's uses hydraulics, which are more generally associated with large-scale movement. While passive hydraulic systems are often used in single-axis tracking, IST's is active, driving the tracker.
In Oosting's former incarnation as a robotics fellow at the Georgia Institute of Technology, he worked on feedforward control to produce smooth input to move robot arms. "That work had implications for how we control a hydraulic unit," he says, "not because of stability, but to get efficiency and improved reliability and maintenance metrics out of it."
The ArrayBot uses a feedforward motion control system that pre-calculates pointing vectors, joint angles and rate of change to give a fluid flow demand for the hydraulic pump, which tells precisely how fast to run the single motor per tracker. Pointing vectors are calculated for each day. If there are weather changes the system can adapt during the day, says Oosting; the calculations are done overnight so the day's range is known. If there are heavy winds the motor speed can be adjusted.
IST says it has recorded pointing vector accuracy (continuous movement, rather than incremental) at better than 0.004 degrees. While accuracy varies between updates in most tracked solutions, Oosting says, "Our smooth movement means our accuracy remains high at all times."
IST joins a growing renewables sector trend for taking proven components from other industries, such as automotive. "Our components are all well known and have a good track record serving in industry and harsh environments," Oosting says.
One issue sometimes seen with hydraulics is fluid leaks and/or fires. The ArrayBot uses a non-toxic, biodegradable hydraulic fluid, eliminating the danger. "We had to pull in the experts and make sure we got the right seals, pumps, hoses etc," says Oosting. "Our fluid has a great operating range for temperature and is easy-cleanup, but it's not particularly cheap" – in fact it's quite a bit more expensive than standard hydraulic fluids, he says. "But when you think about the fluid as a component of the tracker it's a very small percentage of the overall expense. It avoids environmental issues for customers and additional O&M costs."
Each tracker holds a 540 m³ array capable of supporting 300 standard sized solar panels. IST claims the form factor of its solution allows for a smaller footprint, tighter solar plant layout and correspondingly improved land use. The standard kW/ha measurement is 5-5.5 acres (around 2 ha)/MW. "Our numbers run between three and four acres (1-1.6 ha)/MW, and in some cases we can go below three acres (1 ha)/MW," says Oosting.
A small footprint makes the ArrayBot a good option for integration with wind farms, he says. "Most other options require a lot of flat land; we don't. On our demonstration site we're on a knoll at the peak of a hilly area." He also suggests placing the array "in landfills, even in flood plains because we can mount the inverters up on the post."
Other Cost Reductions
"We found a way to reduce the number of components in the array frame by about 300 – I won't give away the secrets to that," Oosting says. "We have fewer moving parts per MWh than even single-axis trackers. We have substantially fewer electric motors than any dual-axis or single-axis tracking system that we're aware of."
Manufacturing costs are another significant vector. Oosting says the company has worked closely with different vendors - "Timkin, cylinder manufacturers" – in order to verify that the ArrayBot's components could be easily and cheaply manufactured. "One problem you can run into in designing something that's really innovative like this," he says, "'is a great idea that looks good on paper but nobody can make it. In the solar industry a lot of ideas out there look good, but will they ever be commercially available?"
The system's passive energy consumption is "less than that of a 40 W light bulb during the majority of operations. Given our 100 kW per tracker capacity, I think this puts us squarely at the bottom of the chart for parasitic energy use," says Oosting.
Operations and maintenance
IST projects its O&M costs to be less than fixed systems, a surprising claim, due to several features. First, the company plans to offer a robotic cleaning solution. "Our technology is particularly suited for automatic cleaning because we have 300 panels in one array. You can't afford to put a robotic cleaner on an individual array with 30 panels," Oosting says.
Second, the system is low to the ground. "Electric motors, especially in dual axis, tend to be up in the air and not very easy to get to. Ours is right at ground level and has just one electric motor per 300 panels," he continues.
There is an incremental O&M expense for motion (backtracking typically causes motion loss of around 2 percent), but Oosting says this may be outweighed by the reduced cleaning and maintenance costs. The array can be tilted during rainstorms to facilitate passive cleaning, and is exposed to less dust and debris from the ground because, when in stow, it is 9 metres off the ground.
Financing depends on bankability, "and ours is going to improve with time just like everybody else's," says Oosting. He should know: he has taken 10 previous companies to market. "As with any new technology, you have a long-term vision for where you want to go. We had to get through the market acceptance and build our installed base - but this will be reality as we go forward," he says with quiet assurance.
"There are market forces that are beyond our control – things like Solyndra were very unfortunate for all of us in the solar industry, and the problems the panel manufacturers are having too," he continues. "Big-picture market things are unpredictable, but we have to adapt within that market."
Lead image: The ArrayBot uses a feedforward motion control system that pre-calculates pointing vectors. Via Inspired Solar Technologies