Ways to cut the cost of CPV maintenance
Compared to flat-plate PV, CPV maintenance is a relatively costly affair. But system developers and component manufacturers are working to change the picture.
A GTM Research ‘Roadmap for CPV Technology’ presentation dated October 2011 contains a telling data point related to annual operations and maintenance (O&M) costs. In a table on levelised cost of energy (LCOE) assumptions, the O&M cost stays the same until 2020.
A footnote points out that “it is likely that CPV systems would be able to lower O&M annual costs for future systems.”
But it is clear that three years ago, when the CPV industry was still firing the hopes of now-vanished players such as GreenVolts, Isofotón and SolFocus, O&M costs were seen as a minor item given the expectations for volume growth and module efficiency for the sector.
Alas, that volume growth never happened. And as crystalline-silicon (c-Si) PV costs have plummeted in recent years, it has become more important than ever for CPV to seek cost reductions elsewhere. So reducing the cost of O&M is now very much on the agenda.
It needs to be, because right now the costs for CPV O&M are clearly higher than for traditional PV, particularly when it comes to high-concentration (HCPV) modules. A big part of this is due to the need to keep the solar cells firmly focused on the sun.
Unlike standard PV, which can still work in the absence of a tracker, with CPV a deviation beyond 0.1º off the angle of the sun can start to have a significant impact on CPV performance.
Because of this, Maria Lahuerta, marketing director at the tracker manufacturer Exosun, says that in CPV it pays to think of trackers as being just as important as inverters: if they fail, production stops.
Exosun, which is beginning to deliver trackers to major CPV players such as Abengoa and Soitec, has a number of simple tricks up its sleeve to help boost tracker reliability. One is to rely on quality components.
It buys German motors rather than Chinese ones, reasoning that the extra cost will be repaid through improved operations.
Another straightforward measure is to make sure the components that might break and need replacement, such as the motors, are all located at the base of the tracking structure so they can be reached quickly and easily, without the need for a crane or ladder.
This means that if there is a failure, the downtime can be minimised and production can resume as quickly as possible.
CPV trackers also need to be more robust than single-axis PV versions, says Lahuerta, because if they bend or buckle even a small amount under the weight of the system or the action of wind then there is a chance the cells will wander off-focus.
Finally, to correct any small inaccuracies in targeting there needs to be some way the tracker re-set itself if it goes off-centre. One method is to have sensors that keep the panel pointed directly at the sun.
Another is for the tracker to gently move the panels back and forth along their axes until it hits upon the point at which the maximum output is achieved.
With all of this the tracker can account for about a fifth of the total system cost for CPV, according to 2009 figures from Concentrix Solar (now Soitec).
And although field data is still lacking, Exosun believes the maintenance costs for CPV trackers could be roughly double those for single-axis PV arrays. Clearly, though, this will vary greatly depending on factors such as location and O&M scheduling.
Soitec, for example, is aiming to reduce tracker O&M costs through the preventive and corrective maintenance of moving parts.
Francis Taroni, senior vice president of industrial operations, also points out that it is now best practice to establish operational control centres on site that are linked to supervisory control and data acquisition (SCADA) systems.
These “can be interconnected to tracker system control management from Soitec to ensure full SCADA capabilities,” he says.
Beyond trackers, another challenge for CPV O&M is keeping systems clean, particularly in areas such as the Middle East where there is plenty of dust and sand in the air.
But for many other tasks, such as balance-of-plant maintenance, site security and vegetation management, the O&M load is “similar or the same as for conventional PV power plants,” Taroni says.
And in one area at least, CPV can claim to have it easier than traditional PV. With technology originally designed for use in outer space, the solar cells used in CPV are likely much more durable than c-Si.
According to Dr Gerhard Strobl, director of business development at the cell maker Azur Space Solar Power, accelerated lifetime testing of the company’s solar cells suggests they may be able to last 100 years.
So even if you spend more time and effort cleaning them and keeping them pointed in the right direction, you will not have to worry about replacing them in a hurry.