Cost Reduction Techniques for PLC Energy Management System Programming

I received a call for help from an old client yesterday. Their factory’s energy management system costs are too high, and they hope I can help optimize it. In fact, I have encountered this issue many times. Most factories tend to choose mature solutions when implementing PLC energy management systems, but often end up paying for unnecessary features. Today, I would like to share a few tips on how to reduce costs in PLC energy systems through instruction list programming.

Factory energy management can be complex or simple. Essentially, it involves monitoring and scheduling electrical equipment to make optimal decisions based on production needs and electricity price fluctuations. Traditional solutions can easily cost over a hundred thousand, but if we understand the core logic of PLC instruction list programming, we can achieve it in a more economical way.

The Instruction List (IL) is a PLC programming method that is closer to machine language than ladder diagrams, consuming fewer resources and offering higher execution efficiency. Many engineers are accustomed to programming with ladder diagrams, which are indeed intuitive, but in energy management systems that require frequent data collection, calculations, and judgments, instruction lists can provide greater advantages. It’s like driving; an automatic transmission is easy but consumes more fuel, while a manual transmission requires skill but saves a lot of fuel.

First, let’s discuss the first tip: optimizing data collection. The foundation of an energy system is collecting power data from various electrical devices. Most engineers configure an analog input module for each measurement point, which means that for 10 measurement points, 10 modules are needed, and costs skyrocket. Using instruction lists allows for multiple points to share a single collection module:

LD     I0.0      // First collection trigger signal

MOVE   AIW0, MW10 // Move analog input value to data storage area

LD     I0.1      // Second collection trigger signal

MOVE   AIW0, MW12 // Reuse the same analog input

Through time multiplexing and clever switching control, a single analog input module can collect data from up to 8 measurement points, directly reducing hardware costs by 80%. Of course, the sampling frequency will be correspondingly lower, but for energy management systems, second-level or even minute-level data updates are completely sufficient.

The second tip is peak and valley electricity price judgment and control. Many factories adjust the operating times of electrical devices based on electricity price fluctuations. Traditional solutions often use complex PID control or fuzzy logic, but this can actually be achieved with simple instruction lists:

LD     T37      // Check current time

LT     K800     // Compare if less than 8:00

GE     K2200    // And greater than 22:00

=

MOVE   K1, LW100 // Set to low valley price period

By using simple time comparisons and logical operations, we can determine the electricity price periods. Coupled with control instructions for devices of different priorities, we can automatically reduce the operating power of non-critical devices during peak price periods. This logic written in instruction lists saves about 40% of program space compared to ladder diagrams.

The third and most cost-effective tip: use economical PLCs with instruction list programming instead of dedicated energy management controllers. Dedicated energy management controllers on the market can easily cost tens of thousands, while a small PLC with Ethernet functionality may only cost two to three thousand. The key is how to make this “small” PLC play a “big” role.

Last year, we did a case for a textile factory: using an S7-200SMART with instruction list programming, we achieved monitoring and scheduling of 12 high-energy-consuming devices in the entire factory. Through the efficient processing of instruction lists, this small PLC was able to handle energy data collection, peak and valley price control, device priority sorting, and simple report statistics simultaneously. The total system cost was less than one-third of the professional solution, but the actual energy-saving effect was nearly the same.

Of course, instruction list programming also has limitations. For example, it is difficult to implement complex graphical interfaces, and debugging can be more troublesome than ladder diagrams. However, for small and medium-sized enterprises with limited budgets, these trade-offs are worthwhile. After all, the core value of an energy management system is cost savings; if the system’s own cost is too high, it becomes counterproductive.

Finally, a small reminder: when optimizing PLC energy systems with instruction lists, be sure to pay attention to data backup. Due to the concise and efficient nature of instruction list programs, they often occupy less storage space but are also more prone to data loss due to sudden power outages. It is recommended to add a simple UPS power protection or regularly write key data to the EEPROM area. A client once lost all energy consumption statistics from the previous day after a system restart due to neglecting this point, leading the boss to mistakenly believe that the energy-saving system was ineffective.

Energy management does not have to be complex or expensive. By flexibly using instruction list programming and fully tapping the potential of ordinary PLCs, we can achieve efficient energy management systems in a more economical way. I hope these tips can provide some inspiration. Feel free to leave comments and discuss below!