Power Quality Issues Caused by Distributed Generation

Posted on 11th October 202323rd March 2024 by Bertie Bezuidenhout

To mitigate the effects of Load-Shedding, many homeowners have decided to install PV Solar Energy systems. And, as I said before, they are more worried about how much it would cost than the quality of the products. If they can pay the lowest possible price for the entire installation, they are happy and do not care so much about what they get.

During the early stages of Load-Shedding, someone from our neighborhood asked me for advice regarding a PV system, but when I gave him a rough estimate of what it would cost, including the cost of a well-engineered design, I could see that the price was far more important than the quality of the system. Those advertising in the newspaper say that something the with same output would cost far less. Not long after he had his PV system installed, he told me that their washing machine had broken down and that they were compelled to replace it. I did respond since I knew what the cause of it was.

As in many other countries, PV systems with microgrids has become an unavoidable choice. This, in turn, bring along new challenges for utility companies. Naturally, if those employed by the utility companies are awake, knowledgeable, and experienced, they can proactively conduct power quality monitoring exercises. With the ever-increasing expansion of renewable energy systems, the most important power quality challenges that is brought about, is the harmonic distortion which affect the voltage and current quality at the point of common coupling (PCC), and negatively affects the loads.

We are all aware that there is a wide variety of inverter models are available on the market with new ones added constantly. Consequently, the harmonics delivered to the main power grid will thus vary according to inverter types and their control strategies. Utility companies therefore must have the knowledge, skills, and instrumentation to investigate the impact of these components that accompany the renewable (embedded / distributed) generation.

The technical consequences of distributed generation are dependent on the size of the system and its location in relation to the main power generation grid. These influences are reverse power flow, overvoltage along distribution feeders, voltage / current harmonics, phase unbalances, power losses, voltage control disturbances, low power factor, and Electromagnetic interference problem.

To overcome these effects, grid measurements, data analysis, and system modelling are needed for different parameters of grid and electricity generated by the renewable energy suppliers to find solutions and to make this resource more reliable.

Power quality parameters such as inrush current, power factor, total harmonic disturbance (THD), and frequency fluctuation should be recorded and studied regularly.

Inrush Current is a small predictable difference between distributed generating station’s voltage and utility grid voltage which can produce transient inrush currents. This can cause a temporary voltage sag at the neighboring buses, nuisance trips, thermal stress of the power components and several other problems.

With Under Voltage / Overvoltage, the grid connected distributed generating systems only inject active power into the utility grid, which may change the value of reactive power that flow in the system.

Output power fluctuation is one of the main factors that may cause severe operating problems for the utility network. This occurs because of variations in solar irradiance caused by the movement of clouds and may continue for minutes or hours. This may cause power swings, voltage flickers and fluctuations of over / under voltage.

Power factor often decreases to unacceptable levels due to high-powered distributed generation which sits on lightly loaded short distribution lines.

Current and voltage harmonic distortion, voltage and current distortions is generated by nonlinear loads such as power inverters that are used in solar systems where the currents flowing through the impedances of the grid affecting the voltage nodes. Harmonics produced under such circumstances can cause series and parallel resonances, overheating in transformers and capacitor banks, and false operation of protection devices that may reduce the reliability of power systems. A total harmonic distortion voltage (THDu) value of between 5% and 8% indicates significant harmonic distortion. Some equipment malfunctions may thus occur. The acceptable current and voltage harmonic level generated in the microgrid was specified by the IEEE standards 519 and 1547 and IEC-61000-3 standard, and this should not exceed a THDu of more than 8%.

Frequency fluctuation is an important factor in power quality. Any change between the produced and the consumed power may lead to frequency fluctuation. Small sized solar systems may cause frequency fluctuation to be insignificant compared with other renewable energy-based resources. However, this issue may become more severe by increasing the penetration levels of solar systems. Large enough frequency fluctuation may change the winding speed in motors and may damage generators.

Although there may be more solution available to moderate the impact caused by distributed generation, one suggestion is to switch off some or all the PV panels when flowing current is under the critical value, or rather divert the power to charging a battery bank. A second suggestion is the use of passive or active filters.

When new solar farms are proposed for connection to the municipal distribution network where this is perhaps far more critical, neither solution are compulsory, as far as I understand. I recently saw a proposal for a grid-tie solar farm without batteries nor active passive or active filters. But, as I said earlier on, utility companies need employees who are awake, knowledgeable, and experienced to know what to look for. Alternatively, utility companies can contract a company, us, to regularly conduct power quality monitoring exercises on their behalf.

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Is Solar Energy a Subset of Electrical Engineering

Posted on 6th October 202330th October 2023 by Bertie Bezuidenhout

In recent times, I have attended several seminars and that makes me wonder whether the entire process of Solar Energy Systems installation has anything to do with Electrical Engineering, or is it perhaps closer to something like tree cutting where there are so many claiming to be “experts” in that field.

Almost daily, we receive a note of someone saying that they are tree-fellers. On the radio, I hear CCTV installers are “experts” in Solar Energy Systems or perhaps companies selling totally unrelated products advertising that they also sell PV Modules.

Listening to questions posed at these seminars, I begin to doubt that Solar Energy Systems have any relationship to Electrical Engineering, or the placement of the PV Modules have anything to do with Mechanical Engineering. When I read or hear about fires where Solar Energy Systems were installed, I truly begin to doubt that.

It should not be that difficult to connect the wires together or tighten a bolt, or is it? People tend to think that hot connections on wiring circuits are only caused by a screw that is not tightened. How about a situation where the screw is over-tightened. Yes, that also causes hot connections. How about the bolts fastening the PV Modules. Yes, if the bolts are not tightened to the correct torque, the PV Modules will become loose and cause severe damage, perhaps even electrically induced fires. If not tightened to the correct torque, the bolts will undo itself with vibration caused by wind or it will break if it was over-tightened.

Who is at fault? There are perhaps many parties, but I will start blaming those who do not do a due diligence when it comes to appointing the “installers”. Do they, the homeowner or company, insist on having a proper design being done. Read more – https://agulhascorp.com/designing-solar-energy-systems/ of what we do. Do the homeowner or company ask the right questions to ascertain whether the person or company that they are about to appoint have sufficient experience in Electrical and Mechanical Engineering.

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Engineering Solar Systems

Posted on 24th September 202330th October 2023 by Bertie Bezuidenhout

Some noises have started to arise that unannounced inspections of rooftop solar panel installations need to be conducted to counteract heightened work health and safety risks as demand soars.

With the surge in demand and the appearance of fly-by-night installers, this may have some merits.

Businesses that sell, design, and install solar systems have a duty to provide and maintain a working environment that is safe.

Those thinking of “becoming energy independent” may be tempted to settle for affordable solutions and installers, without verifying credentials, which may prove a very expensive decision.

The installation and management of solar PV systems is a complex and highly skilled undertaking, installed on top of your most expensive asset. It is therefore important to ensure that the electrician can provide you with a CoC, which confirms that they complied with the rules and regulations in place to ensure safe installation.

Scientifically Based Designs and Calculations

What is even more important is that the design of a Solar Energy Systems are not as simple as calculating the roof space, dividing that space by the area of Photovoltaic (PV) Modules, assuming it would produce 100% – or even a certain percentage – for the entire day and then base the rating of the system on that.

Power Quality Monitor

Under normal circumstances, we install a Power Quality Monitor to record the power consumption over a specified period – read more on why this is important. Based on the results I obtained with this instrument, we then know what the peak demand for that period is and whether there are other important aspects that must be considered, which could ultimately affect the performance of the Solar Energy – or Uninterruptible Power Supply (UPS) – systems, and in particular the Inverters.