The challenges of integrating renewable energy sources into off-grid power systems

The challenges

Integrating a large amount of renewable energy can affect the stability and performance of an off-grid power system. When integrating renewable energy sources into a remote system, you must consider the following impacts:

• Decreased availability of short-circuit current
• Decreased reactive power generation capacity (var.)
• Decreased rotating energy reserve

Short-circuit current level

Most renewable energy systems generate much less current during a short-circuit than a diesel generator. This decreased fault level can produce the following effects:

• The overcurrent protection components (circuit-breaker and fuse) might be delayed or become completely inoperative
• Protection coordination can be compromised
• Incident energy can increase during an arc flash event
• Voltage regulation can be affected
• Voltage distortion can increase, affecting power supply quality

Reactive power generation capacity (var.)

Renewable energy sources can be greatly limited in reactive power (var.), reducing the ability to start motors and magnetize transformers.

Rotating energy reserve

Integrating renewable energy sources generally leads to a significant decrease in the available rotating energy reserve, since diesel-powered generators are not designed to operate at low-load levels and some will have to be shut down. As a result, power system blackout could occur more often and frequency stability could be greatly affected.

Power generation and the power system load must be equal at all times to prevent blackout and frequency variations. It is also very difficult to control power output for wind turbines or solar panels, which depend directly on the renewable energy source.

Possible solutions

Solutions can differ depending on whether the power system is for a community or for an industrial or mining site, because the needs and nature of the loads are very different. The following solutions can be considered to reduce the impacts associated with integrating renewable energy sources:

• Integrate a synchronous condenser to increase the fault level, regulate the voltage and provide reactive power.
• Oversize the inverter of renewable power systems to increase the fault level.
• Implement an energy source control strategy combined with active load management to ensure system stability.
• Use modern protection relays, integrating new technologies and ensuring rapid and selective elimination of small amplitude faults.
• Eliminate large rating fuses that are not compatible with renewable energy sources.
• Integrate a power storage system with adequate performance and autonomy to ensure power system stability and service continuity.

In conclusion

Developing new technologies that include power storage systems and evolving control systems will make it easier to integrate massive amounts of renewable energy into off-grid systems and will eventually eliminate having to generate power from fossil fuels. BBA’s expertise in off-grid power systems can help make integrating renewable energy sources harmonious.