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Export Limiter | How it works

Since California’s duck cure incident export limiter becomes a top topic in the power generation and distribution industry. This creates an increase in demand for export limiters around the world as more and more utility companies and state electricity boards restricting the amount of power exported in the grid.



In this blog, I will give a brief description about export limiters and how it works. I have installed more than 200 export limiters in solar power plants and successfully synchronize more than 100 generators with solar power plants with export limiters.


Content Table



What is an export limiting device?

In many countries, state electricity companies have limits on the power exported to the grid from a small grid-tied power plant. In these countries, export limiting devices are used to limit the amount of power exported from a small power generation plant to the grid coupled with the plant.


Exporting electricity power from grid-tied small power plants to the grid, affect the stability of the grid. Because these small power plants are not very stable and didn’t produce power at constant magnitude throughout the days. And this leads to change in load on gird power plants.


Thermal power plants produce most of the power available in the grid and these type of power plants works efficiently on peak load and continuous operation. Exporting too much to the grid will directly affect the efficiency of these power plants.


What is an export control device in solar?

In solar, export control devices are used to control the power generation of a grid-tied solar power plant. So that, amount of electricity power exported from solar power plant to grid can be controlled as per the state electricity rules.


ZED Advance is one of the most powerful export control devices available.

Export Control devices are also known as export limiters.


A grid-tied solar power plant starts exporting power to the grid if the power requirement is lower than the power generation. An export limiter measures the load requirement [Via Current Transformer and Multifunction meter] and controls the power generation of the grid-tied solar power plant.


If the load requirement is lower than the power generation, the export limiters ramp down the power generation. And if power generation is equal to or lower than the load requirement, the export limiter won’t alter any change in power generation.


If the load increase from lower than solar power generation to higher than power generation. The export limiter will ramp up the power generation of the solar power plants.


What is a grid-tied inverter with a limiter?

Grid-tied inverters don’t come with an export limiter. Hence a separate limiter is required to buy. Limiters control the power generation of the inverter so that it didn’t produce excess power. The grid-tied inverter has the communication protocol called MODUS. Hence limiter communicates with the inverter via MODBUS.


This protocol of communication isn’t good are Ethernet communication protocol. It takes time to established communication in MODUS and hence required more skilled tech engineers. To check the compatibility of any grid-tied inverter with an export limiter, its MODBUS mapping is required.


ZED Advance can communicate with more than 17 different makes of grid-tied solar inverters, learn more.

How does an export limiter work?

Export limiter required current transformer at the coupling point of grid and load. This current transformer feedback the load requirement to a multifunction meter.


This multifunction meter will converter this analogue feedback into a digital signal. Export limiter received this digital signal from multifunction meter via LAN cable. You can also use the existing current transformer and meter, if available.


Note: not all multifunction meters are compatible with an export limiter. Please make sure that the available multifunction meter is tested with the export limiter.

Export limiter uses this load feedback and controls the firing angle of the grid-tied inverter’s thyristors via LAN cable. If the load demand is less than the solar power generation export limiter will ramp down the output power of the solar inverter.


And if the load demand is rising from below the solar power generation to above it. The export limiter will ramp up the output power of the solar inverter.


Gird-tied solar inverters take almost 1 minute to ramp up and ramp down their power generation. Hence, a minimum of 5% of the load is needed to keep on the grid so that no power can be exported.


This load sharing can be achieved via setting the setpoints of an export limiter.


Best grid-tied inverters with the limiter.

To keep the price of solar inverters low, every available solar inverter in the world is still using Modbus as a communication protocol for their inverter. And the problem with the Modbus interface is that it is not a plug and play type communication system.


Hence Modbus mapping of the inverter is required to check the compatibility of the inverter with the limiter. On the basis of ease of communication, commissioning of the limiter and backup support from inverter manufacturers following inverters are the best solar inverters with limiters.


#1 SMA: In terms of tech support and ease of communication with the external control devices, SMA is the most favourable grid-tied solar inverter. It has a wide range of grid-tied solar inverters and is easily available. SMA is the best inverter for the Generator-Solar Hybrid system.


#2 FRONIUS: Fronius is the second-best option for the generator-solar hybrid system. And the reason why it is in the second position is due to the lack of tech support. Many times during the commissioning of a controller, Fronius inverters shows errors and it required tech support to short these issues.


And due to poor tech supports, sometimes it takes days to get the right information from them. Hence increase the commissioning time.


ZED Advance is a 4 in one controller for solar power plants. Click here to know more.

#3 DELTA AND ABB: Both Delta and ABB are on third positioning. Because their tech support is far much poorer than Fronius. Two same model numbers of these makes of inverter sometimes required two different settings to communicate with the controller. And it becomes very confusing for the tech engineer to established network communication with them.


It has been seen that both Delta and ABB make solar inverters take more time in stabilising network communication with an external controller.


#4 SUNGROW AND GROWATT: Both Sungrow and Growatt have slow response times. These inverters take more time to ramp up and ramp down power. And that’s why these solar inverters are not the best option for mid (above 100kW) and large size (above 500kW) generator solar hybrid systems.


The reason why these inverters are at number 4 is that these inverters are easily available and establishing network communication with them is not very time-consuming.


#5 SOLIS AND POLYCAB: Both Solis and Polycab have the same electronics. Hence what is valid for one, will be valid to others too. The response rate of these inverters is low too and they take more time to establish network communication with an external controller.


ZED Advance is compatible with all above mentioned solar inverters and 12 others too. Click here to know more.

Key features to buy ZED Advance?

  1. With ZED Advance you can go Solar without Net Metering or Gross Metering.

  2. With ZED Advance you can Syn your Generator with your Gird connected Solar power plant

  3. With ZED Advance you can monitor your PV plant, Generator and Grid.

  4. With ZED Advance you can use your Grid-tie PV plant even in Power cuts.

  5. ZED Advance is compatible with 17 plus makes of Solar inverters.

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Guest
Dec 08, 2021

Hi

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