EXPORT LIMITATION

Unburden the grid

Large PV systems are installed on premises that normally have high levels of self-consumption, such as factories or dairy farms. During daytime hours and weekdays most or all of the electricity being produced will be consumed directly on site with very little being exported. Only on days such as weekends and bank holidays is there potential for all the power generated to end up exported onto the grid. To avoid issues with the grid, Distribution Network Operators (DNOs) require that no more than a pre-determined amount of electricity can ever be exported onto the grid. With export limitation, the DNO doesn’t have to worry about large amounts of surplus electricity entering the grid on weekends and bank holidays (when it is least needed).

Save costs

A major expense when installing commercial PV systems over 16A per phase can be the cost to upgrade the grid infrastructure to accommodate the increased power flowing from the array to the grid. The cables and transformers need to be able to deal with the maximum energy the PV system is going to export. Unfortunately, because of this some commercial PV systems are considered non-viable due to the high costs. With export limitation the installation owner can reduce their electricity bill with a PV installation without the extra cost of upgrading the grid infrastructure.

YOUR BENEFITS

Advantages at a glance

  • Save costs and unburden the grid

The PV installation will never export more than the allowed power onto the grid. So you do not need to include costs for upgrading the grid infrastructure and the DNO will not have to worry about an extra burden on the grid. 

  • Optimal use of generated PV power

Your customer can install the full capacity of PV that the location can support, without exceeding the DNO limitation. Produce all the PV power needed, exactly when it’s needed. During evenings, weekends and bank holidays the system will automatically limit the export power. And unlike most similar systems, the SMA export limitation system does not shut down the inverters completely, but only reduces their output power. 

  • Sophisticated yet simple system

The SMA export limitation system is incredibly clever, yet also very easy to implement. Adding the system to an installation is basically plug-and-play. Once set-up, the Cluster Controller or the Sunny Home Manager will control the export power based on data received from the SMA Energy Meter and the inverter(s). There’s no extra work for the end user. 

  • Reliable system that meets all requirements

The SMA export limitation system has been extensively tested and has proved that it meets all DNO requirements for the grid. Thanks to a fail-safe system, hard wire communication and other safety features, your customer can count on a reliable operation.

SMA EXPORT LIMITATION SYSTEM: HOW IT WORKS

The SMA export limitation system is a sophisticated yet simple to implement way of managing the amount of exported power. The system requires the SMA Cluster Controller or the Sunny Home Manager, the SMA Energy Meter and compatible SMA inverters with Speedwire/Webconnect interface.

The Active Power Feed-In Value is configured in the Cluster Controller and the Sunny Home Manager. This is the maximum amount of power the system is allowed to export onto the grid. If the balance between PV generation and self-consumption reaches a point where the system might export more than this value, then the Cluster Controller or Sunny Home Manager can tell the inverters to limit their production. It does not completely shut down the inverters, as most other systems do. With this solution the amount of generated PV power is maximized, matching exactly the local power demand plus the maximum possible export power. 

The SMA Energy Meter is a bidirectional meter that takes measurements of the grid at the point of connection. It communicates the power consumption and export values to the Cluster Controller or the Sunny Home Manager via Speedwire (Ethernet cable) every second. This meter can be used for single-phase or three-phase systems and its maximum current is 63A.

Generated PV power with SMA export limitation = local power demand + export power

  • Never generate less than you need
  • Never generate more than is allowed
  • Always generate exactly what you need and what is allowed

Comparison Cluster Controller and Sunny Home Manager

Cluster Controller Sunny Home Manager
Installation size: Max. 75 inverters Max. 12 inverters
Set up: In Cluster Controller interface In Sunny Portal
Settling time: 3 – 10 seconds 5 – 10 seconds
Reaction time Zero Export: 2.85 seconds 2.54 seconds
Connection to network router: Ethernet cable Ethernet cable
Active power export limitation: 100% of inverter nominal power 100% of inverter nominal power

Compliance with DNO requirements

DNOs require a fail-safe system, hard wire communications between the components of the export limitation system, specific power quality and operational time. The SMA export limitation system meets all DNO requirements.

RECOMMENDED PRODUCTS

CASE STUDY




A dairy farm in Bristol required a PV installation with export limitation. They wanted to place an installation of 50 kWp, while the grid was limited to 11 KVA. As SMA has solutions for both, we were very happy to work together with the installer and DNO for the installation and witness test of the system.


Regilbury Farm

Location: Bristol, England
Plant size: 50 kWp, limitation to 27% of the Maximum Rated AC Power
Witness test date: 28 October 2015
Annual yield approx: 53.2MWh annually
CO2 reduction approx: 28 tons of CO2/year
Inverters: 2 x SMA Sunny Tripower 20000TL-30
Monitoring & Control: Cluster Controller and SMA Energy Meter
Installer: Solarsense
DNO: Western Power Distribution (WPD)

Solarsense installed the PV system and added the SMA export limitation system with the Cluster Controller and the SMA Energy Meter. SMA provided Solarsense with technical support for setting up the export limitation system. Both the end user and the installer were very pleased with the results of the system. Solarsense is now looking into installing more plants with the same configuration and export limitation.

The DNO, had a long list of requirements for PV installations with export limitation.  However, they were very impressed with the SMA export limitation system with the Cluster Controller and SMA Energy Meter. 

An advantage for SMA is that we now know the issues the installers may find and the sort of tests the DNO will perform. With the information gained from this test, we are now fully prepared to support end users, installers and DNOs interested in export limitation.

NEXT STEPS

How can I find out more?

The SMA Solar Academy regularly gives webinars on SMA’s export limitation system. You can find information on this new webinar and the upcoming dates here.

Go to the Solar Academy