Engineering solutions provider BMG’s electromechanical specialists has extended its solutions service to include solar inverters and drives, which are designed to enhance the efficiency of photovoltaic (PV) systems.

“PV modules – which use daylight to generate electricity – are gaining popularity globally as a form of renewable energy that is clean, emission-free, sustainable, safe and cost efficient. Through the use of environment-friendly PV technology to generate electrical power, companies in South Africa are finding effective solutions to combat the country’s grave electricity crisis,” claims BMG electromechanical division electronics manager Mick Baugh.

He says the benefits of using eco-friendly solar-powered pumps for irrigation, animal farming and community water supply, include an uninterrupted water supply during the day and independence from the unreliable grid. In addition, advanced PV systems require minimal maintenance, which is an important advantage in remote areas where servicing is difficult.

“Solar pump systems, which are particularly popular in remote areas where electricity is unavailable, require a solar inverter to convert direct current (dc) generated by solar panels into alternating current (ac) for use in industrial, commercial and residential applications,” he says.

Baugh adds that a key differentiator in the selection of the correct inverter, is its ability to run the motor pump at the optimal working voltage and power ratings, to ensure solar panels deliver the highest possible power in various irradiation and ambient temperature conditions.

“For optimum performance of the PV pump system, we believe it is critical for users to fully understand the control strategy of the system and to consider factors such as where to install the drive, condensation issues, the temperature range and the back-up supply.”

Control Strategy

Simpler solar-powered drives for pumping applications operate as under-voltage regulators, lowering the pump speed and thereby reducing the absorbed power when the dc voltage reaches a minimum voltage set-point. This simple control mode negatively impacts performance of the PV modules, since they operate at a non-optimal voltage.

In advanced controllers, the drive works to obtain the maximum power from solar panels by keeping the dc voltage at the optimum point. Drives that operate at a constant ac voltage must be selected depending on the electrical characteristics of the installed PV system and should optimise the hydraulic efficiency of the pump.

Baugh recommends the use of Finnish-made Vacon solar-powered drives that feature maximum power point tracking control to ensure an optimal operation voltage for PV modules in pump applications. These highly-efficient controllers provide extended running hours, with an earlier start and later stop.

Consequently, more water is pumped per watt peak of installed PV modules, leading to reduced investment costs and a quicker payback period. Such controllers detect instantaneous irradiance or temperature variations and omit local maximums, which are generated in partial shading conditions or from degraded modules in the PV array.

Outdoor Installations

Conventional solar pump inverters are usually installed in cabinets along with various supporting components. Baugh says this is not recommended because cabinets need to be ventilated to avoid overheating. Moreover, airflow though the cabinet needs to be filtered to avoid dust collection and filters must be periodically cleaned and replaced, which increases risks and adds to maintenance costs.

The Vacon IP66 drive solutions for outdoor installations, which BMG supplies, consist of a small enclosure, which is separated from the drive, to house the mains switch and surge protection device. The Vacon IP66 drive can be installed outdoors without any reliability risk and does not require maintenance, as there are no filters to clean or replace. Drives can be mounted in the same structure as the PV modules, taking advantage of their shading to avoid overheating.

This ground-level system is fitted with light-emitting diodes to visualise various operating conditions of the drive. A display panel provides further detailed information of the drive, such as running speed and MWh readings.

Condensation

In conventional solar-powered pumping installations, intermittent operation and internal temperature changes promote cyclical condensation-evaporation processes inside of the drive.

When installed inside a cabinet, such installations are sensitive to internal condensation and require temperature-controlled heaters. This can be a problem in solar-powered pumping systems because an ac grid is not normally available on remote sites.

Conversely, the BMG-supplied Vacon IP66 drives and Nema 4X enclosures are well-protected against water and dust ingress. A specially designed Gore vent prevents condensation, without the need for a heater.