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Microgrid Shelter: ensuring stable, reliable off-grid load supply in remote locationsby Lorenzo Caldera and Maura Sinico, Siemens, and Stefano Nassuato, FIAMM Energy Solutions

Microgrids are an interesting alternative wherever a stand-alone grid is feasible or even necessary for reasons of infrastructure, security of supply, or geography.

Especially in remote locations where human maintenance activities are limited and have high cost impacts, one of the current technological challenges is to have very flexible infrastructures both in terms of operations and logistics. Here it is fundamental to have an off-grid system which guarantees energy production/storage and which can be monitored remotely. This is where Microgrid Shelter prototype comes into play.

The system developed is built up by different elements, all included in a twenty foot compact shelter comprising: a sodium nickel chloride (NaNiCl2) storage technology; small renewable plants (photovoltaics and wind turbine); a diesel generator and a control center. The basic approach of the Microgrid Shelter is to maximise power production coming from renewable energy stored or supplied by an electrochemical storage system, ensuring off-grid stable and reliable load supply. The diesel generator

guarantees black-start functionality and power generation in emergency conditions, while the control center monitors the whole system performance.

Thanks to its modularity, the system can be easily customised according to specific requirements related to unit sizes and energy mix, representing a reliable, environmentally friendly and cost-effective microgrid system.

The system architecture

The Microgrid Shelter is built up of the following elements:

l Renewable generation: two photovoltaic plants of 5 kWp each; one wind turbine of 10 kW.

l Energy storage: two electrochemical storage systems of 30 kW and capacity of 90 kWh each.

l Traditional generation: one diesel generator of 30 kVA and 750 ℓ tank.

l Electrical loads: base power 2,5 kW, peak power 5,5 kW at 400 V AC and 2 kW at 24 V DC (loads are in islands, not connected to the main national grid).

Although the number and size of the units were indicated by the customer, the system has been developed as a flexible prototype which can be customised both in terms of size and elements that can be installed depending on usage or environmental constraints.

All generation units that are part of the system (PV plants, storage, wind turbine) are conneted to a direct current bus at 690 V DC (DC bus) through Sinamics S120 converters.

Siemens Sinamics converters S120, usually used as drives for motion control, have been used in an innovative way. Managed by a dedicated control unit (CU), thanks to a firmware upgrade for bidirectional power flow management, converters allow the interfacing of static generation unit (battery and PV) as well as rotating machine. The CU also handles the AC/DC converter in order to support the island grid, maintaining required voltage and frequency.

The brain of the entire Microgrid Shelter, which co-ordinates the different units and converters, is realised through a PLC Siemens IM 151-8. The PLC acts as a control system supplying loads while maximising renewable generation. The basic approach of the control system is in fact to use the renewable energy (solar and wind) as a primary energy source, exploiting storage units to integrate the green production. On the other hand, the diesel generator has been included to guarantee charging functions for the storage system in case the charge level drops below a certain level or for black-starts/emergency conditions.

The innovation of this project stands in the central intelligence provided by the interaction between the control units and the PLC. This interaction makes possible the balance of the energy flow inside the DC bus according to the availability of the renewable generation, the needs of the loads, and the state of charge of the storage system.

The whole system has been developed compacting hardware (the converter, the Fig. 1: Microgrid Shelter layout.

For enquiries, please contact us on:Tel: +27 11 894- 8341Fax: +27 11 918-1072Email: sales@allbro.comwww.allbro.com

Established in 1978 Allbro is a South African company with more than 600 employees. Allbro supplies key components that are used in almost every locally made transformer. With the acquisition of ABB York in 2011 Allbro also became a leading supplier of non-metalic enclosures to the industrial and residential contracting trade. Brands like York, Okari, Enlec, Utilec are well known in the South African market and are all solely manufactured by Allbro in South Africa. Local manufacture to international standards means that products are suited to the local environment, are of the highest quality and are readily available.

Allbro spesialises in:

Plastics - Injection MouldingGlass Reinforced Polyester (GRP)Compression Moulding Toolmaking

* Injection Moulding Line in our Botchabelo Operation

* Excellent toolmaking capabilities

* Dough Moulding Compound (DMC)

* Sheet Moulding Compound (SMC)

Enclosures for :

• General purpose• Metering• Power Distribution• Consumer Units• Industrial Instumentation

Switchgear Accessories:

• Hinges• Locks• Accessories

Insulators:

• Low Voltage - 1000V• Medium Voltage - 3.3 kv - 11 kv• High Voltage - 15kv - 33 kv

Transformer Equipment:

• Bushings• Tap Switches• Magnetic oil Gauges• Buchholz Relays• Thermometers• Pressure Relief Valves

Designed and Manufactured in South AfricaSince 1978

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Fig. 2: Microgrid Shelter architecture.

Fig. 3: Microgrid Shelter switchgear.

power and auxiliary circuit, the control system) into one switchgear. This small size enables the system to fit with standard size containers (20 foot), facilitating transportation and delivery also in remote locations while a remote supervision via IEC 60870-5-104 protocol can be offered. The supervision is done thanks to Siemens Sicam CMIC RTU (remote terminal unit).

Renewable generation

The system includes two photovoltaic plants of 5 kWp installed out of the shelter (close or on top of the roof depending on customer needs/environmental conditions) and a wind turbine of 10 kW.

The wind turbine is installed on a traditional lattice tower 18 m high and the rotor blade is 6 m in length.

The brain of the Microgr id Shel ter (CU and PLC) manages the renewable units at the maximum power available, disconnecting them from the system when the storage level reaches its highest capacity.

Energy storage

The electrochemical energy storage is based on Sodium Nickel Chloride (NaNiCl2) technology which offers high energy density, which is completely recyclable and which works at an internal temperature of around 300°C, providing performances that are insensitive to the external temperature into a wide range (-30°C up to +60°C).

Once activated, this battery doesn’t need a cooling system but just some power to stay at the right temperature if inactive, overcoming the main drawback of other storage technologies that have high auxiliary consumption for cooling needs.

The energy storage is divided in two branches of four modules with approximately 30 and 90 kWh. One branch is used to manage the system and the other as a backup.

The brain of the Microgrid Shelter uses the storage to maintain stable the voltage in the DC bus, managing the whole system's energy flows. For this reason, the system's is regulated to maintain the battery state of charge in an average range in order to guarantee the reserve up and down of energy. Batteries’ rack and batteries’ management system (BMS) are located in a dedicated room inside the shelter.

Traditional generation

The traditional diesel generator of 30 kVA is connected directly to the AC side of the system. The unit has been installed to guarantee the energy storage recharge in case

the state of charge drops below a certain limit; the black start and batteries warm-up during the first start of the microgrid shelter. Finally, the diesel generator is also used in emergency conditions to supply loads directly.

The diesel generator and the fuel tank of 750 ℓ are placed in a dedicated room inside the shelter.

Conclusion and future developments

The Microgrid Shelter is an innovative system engineered to be modular and easily customised. The use of more than one energy source allows a higher stability of the power supply, while renewable sources combined with energy storage allows the system to maintain the desired power output

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and overcome the main drawbacks of the

renewable generation in terms of availability

of the primary energy source and fluctuating

power output.

The Microgrid Shelter is the right answer to

feed loads in remote environments where

there the is no electrical grid available, where

maintenance activities costs are high or where

Fig. 4: Microgrid Shelter wind turbine.

Fig. 5: Microgrid Shelter energy storage.

Fig. 6: Microgrid Shelter diesel generator.

the electrical loads are not permanent and therefore building a fixed infrastructure is not justified. Customisable according to customer needs, the system can be monitored remotely and operates stand-alone minimising human workforce efforts and related costs.

Contact Rodney Swartz, Siemens, Tel 011 652-2306, rodney.swartz@siemens.com