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Technical Information

SI_SVBTS-TI-UEN111810 Version 1.0 1/9

ContentsAs part of the global development of telecommunications networks, Base Transceiver Stations (BTS) are also frequently constructed in Off-Grid locations or Bad-Grid locations. The Sunny Island is very well suited to ensure the electricity supply to a BTS even in such locations due to its flexibility and robustness. Off-Grid systems with Sunny Island are distinguished by the following features:

• Possibility for the supply of AC loads and DC loads in battery operation.• Optional use of 1-phase or 3-phase generators and the power distribution grid.• Selection between positive or negative grounding of the DC bus.• Flexible system design with the use of various renewable energy sources.

This document explains in detail when the use of a Sunny Island for the supply of electricity to a BTS is expedient and what is to be taken into consideration for this.

TelecommunicationUsing of Off-Grid inverters SUNNY ISLAND in Base Transceiver Stations

Technical Information Introduction

SMA Solar Technology AG 2/9

1 IntroductionThe global development of base transceiver stations is increasingly taking place in regions in which the power distribution grid often breaks down for long periods of time or where there is no access to the power distribution grid. In order to also ensure an electricity supply to BTSs in such regions, diesel generators are being installed. These require a high level of maintenance work and consume relatively high amounts of diesel fuel for low level outputs. As a result diesel generators incur high operating expenses (OPEX) and present the operators of mobile communications networks with the challenge of having to limit their Total Cost of Ownership (TCO).

Annual increase of Base Transceiver Stations from 2007 to 2012

Source: GSMA AnalysisWith electricity supplies based on Off-Grid inverters of the Sunny Island type, SMA Solar Technology AG offers a solution for hybrid battery/generator supply systems which are able to be extended flexibly through renewable energy sources. As a result the BTS operators are presented with opportunities for desirable reductions of the operating expenses.Since the Sunny Island was developed as an Off-Grid electricity supply, it is not based on the standards usual for telecommunications such as the 19" design technology. However, all requirements of the supply of electricity to BTSs are met, e.g. the positive grounding of the DC bus, the support of 1-phase or 3-phase generators or the possibility of grid-parallel operation. In addition there is a technically refined battery management and generator management and the robustness which is continually proven by the worldwide BTS electricity supplies fitted with Sunny Island inverters.

Technical Information Sunny Island Applications


2 Sunny Island ApplicationsOff-Grid inverters of the Sunny Island family enable a bi-directional DC/AC conversion and are therefore also designated as a combination of inverter and charging device or as an Inverter/Charger combi-device. Thus a rectifier as found in a grid-connected BTS is not necessary. Loads and generators can be integrated on both the AC and the DC side. The bi-directional conversion ensures that even under pure battery operation, AC loads such as air-conditioners or lighting systems are supplied. Therefore using the Sunny Island pays off especially when larger AC loads are to be supplied in the event of grid break-downs or in Off-Grid operation. All BTS components can be integrated on the DC side as normal. The use of a Sunny Island as a BTS electricity supply is also to be recommended when various renewable energy sources such as sun, wind or water are to be integrated or if flexible plant planning and modular extendibility is required.If, however, there are no AC loads to be supplied, it is recommended that a rectifier with commercially available charge controllers is installed. Even with a total load of less than 0.5 kW it would be sensible to develop a purely regenerative DC system.

3 Sunny Island for Bad-Grids or Off-GridIn addition to the elimination of the rectifier, the Sunny Island provides for use in Bad-Grids or Off-Grid the advantage of an integrated battery management and generator management system. With regular full and equalization charges, the battery management ensures a maximized battery life. The load shedding of the loads in the event of generator failures prevents a deep-discharging of the battery. The generator running time can be set flexibly based on the times of day and the battery State Of Charge (SOC).In the event of frequent and long break-downs of the power distribution grid, the use of deep-cycle batteries is recommended. Often, an additional reduction of the Total Cost of Ownership is able to be achieved if PV plants or small wind energy plants are installed per location.Various types of generators are able to be integrated through the design of 1-phase or 3-phase systems. A Sunny Island is to be installed per phase. Additionally the Sunny Island allows for the power distribution grid to be integrated in exactly the same way as a generator. The parallel use of the power distribution grid and a generator or the parallel use of 2 generators requires the application of an Automatic Transfer Switch (ATS). The Sunny Island is suitable for TN grids.

Technical Information System Design and Grounding Concept


4 System Design and Grounding Concept

Information on the grounding conceptNo. Explanation

If the standards applicable to the location demand the grounding of a PV array, it is necessary to connect the PV array via the AC side and to use a galvanically isolated PV inverter with transformer.When a diesel generator is connected to the Sunny Island the complete grounding of the neutral conductor and both protective conductors is necessary.

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Starting signal

Equipotentialbonding busbar

Batterytemperature

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Batterycurrentsensor

Battery PV

AC/DCconverter

DC-Loads

AC-Loads

Sunny WebBox(optional)

PV

DC-supplied contactor

LegendPhase conductor (L)Neutral conductor (N)Protective conductor (PE)

Positive conductorNegative conductor

Communication cableControl cableMeasuring cable

Small windturbine system

Small windturbine system

Technical Information Communication Options


Combination of the Sunny Island with renewable energy sources• AC coupling and DC coupling for the integration of small wind energy plants and PV plants are freely

selectable.• Energy sources should feed-in as near as possible to the load and in conformance with their load profile,

e.g. a PV plant for the supply of electricity to an air-conditioner should be coupled into the AC side.• AC-coupled PV inverters must be controllable via the frequency. For this, the "OFF-Grid" operating mode

is to be activated in PV inverters from SMA Solar Technology AG.• The Smart Load for Sunny Island lends itself to the integration of uncontrollable renewable energy sources.

5 Communication OptionsThe connection of a Sunny WebBox to the RS485 interface of the Sunny Island enables the detection of failure statuses and the monitoring of system parameters, e.g. the battery State of Health (SOH) or the generator running times. This data gives information on energy flows and the state of charge of the batteries and enables analysis of the system behavior and evaluation of the energy yield. Via registration of the plant in the Sunny Portal, additional event tables as well as various diagram presentations and report functions are available.Use of the Sunny WebBox with access to Sunny Portal is also recommended in order that the Sunny Island System can be integrated into a Network Operation Center (NOC). Thus the status of the BTS electricity supply can be monitored at a glance via internet access. The presentation of data in the Sunny Portal can be configured to individual requirements.Several modems can be used with the Sunny WebBox in order to enable a connection e.g. viaGSM (Global System for Mobile Communications) or DSL (Digital Subscriber Line). If 2 up to 4 Sunny Islands are interconnected to form a Cluster, the Sunny WebBox only communicates with one of the Sunny Islands, the master of the Cluster. An internal communications bus connects all slaves and up to 4 DC coupled Sunny Island Chargers with the Sunny Island master. Further AC-coupled SMA products can be integrated via an RS485 bus.

The integration of a BTS in the DC bus of an Off-Grid system requires positive grounding of the battery. Since all Off-Grid inverters of the Sunny Island family have a transformer and thus insulate DC and AC galvanically from each other, this grounding is easily possible.When a charge controller such as the Sunny Island Charger is used on the DC side or transformerless PV inverters are used on the AC side it is to be observed that no grounding of the positive or negative poles of the PV array is allowed.

No. Explanation

Technical Information Selection of the Sunny Island


6 Selection of the Sunny IslandFor a hybrid generator / battery supply system it is economically essential that the diesel generator runs for as short as possible and at the optimum operating point. Above all the generator output is therefore to be considered to ensure that it operates as closely as possible to the nominal power of the generator during battery charging. A further aspect is the continuous power of the AC loads to be supplied during battery operation.

Combination of Generator and Sunny IslandThe following table gives recommendations as to which Sunny Island is suitable for which generators.

Depending on how continuously the AC loads are to be supplied and depending on the estimated generator runtime the dimensioning can deviate from the recommendations in the table.

Dimensioning of the GeneratorIf the generator power is lower than the power of the Sunny Island, the maximum charge current must be lowered via a parameter setting in the Sunny Island in order to avoid a generator overload. The efficiency of the operation is not impaired by this, however a portion of the Sunny Island power for the charging of the battery remains unused. In order to use this power, additional renewable energy sources can be integrated for charging the battery.If the output power of the generator is greater than the input power of the Sunny Island, the generator must be able to align its output power to that of a load. The generator can thus be much larger than given in the above table. However, in relation to the economic efficiency it is to be observed that for diesel generators, consumption per kilowatt-hour greatly increases the closer it runs to no-load operation. The diesel generator should largely serve as a battery charger and otherwise be disconnected.

DC voltage Generator type Generator power Sunny Island used

Continuous AC power in battery operation

+24 V 1-phase 1 kVA … 5 kVA 1 x SI 2224 2.2 kW+24 V 1-phase 3 kVA … 8 kVA 2 x SI 2224 4.4 kW+24 V 3-phase 5 kVA … 15 kVA 3 x SI 2224 6.6 kW− 48 V / +48 V 1-phase 3 kVA … 10 kVA 1 x SI 5048 5 kW− 48 V / +48 V 1-phase 9 kVA … 20 kVA 2 x SI 5048 10 kW− 48 V / +48 V 3-phase 5 kVA … 30 kVA 3 x SI 5048 15 kW

Technical Information Integration of renewable energy sources


Integration of the DC loadsThe requirements of the DC loads to be supplied have very little influence on the efficiency of operation. It is to be observed that the runtime of the generator and the number of starts per day lay within a sensible range. This range varies greatly depending on the type of integrated energy sources and the AC loads. Therefore the determination of an optimum based on the overall energy requirement and the battery capacity is recommended. For this, the following extremes are usual:

• 2 generator starts per day without the use of renewable energy sources• No generator runtime during full supply via renewable energy sources

The upper limit for the DC continuous load is to be selected so that enough power for battery charging is available.

7 Integration of renewable energy sourcesThe Sunny Island can be combined with renewable energy sources depending on the location. The renewable energy sources can be integrated either on the AC side or DC side via appropriate converters. When integrating generators or loads on the DC side a battery current sensor must also be integrated in order that the Sunny Island battery management correctly measures the charge current of the battery. Renewable energy sources can be integrated optimally with SMA inverters on the AC side.During the selection between AC coupling and DC coupling, orientation towards the requirement of the loads is recommended for a maximum yield. If for example an air-conditioner is to be supplied, it is preferable to integrate a PV plant on the AC side, since in the event of large amounts of sunshine an increase in cooling is required and the air-conditioner has an AC connection.The power rating of the generators that are coupled via charge controllers or Off-Grid inverters is freely selectable within certain limits. In order to avoid over-dimensioning of the energy sources the maximum charge current after deduction of the typical load current should not be exceeded wherever possible:

• As an upper limit the energy sources to be connected should not be able to provide more than twice the power of the Sunny Island.

• A lower limit is only valid in systems without a generator. In these systems a charge current of at least 10 A should be achievable for peak times based on a nominal capacity each of 100 Ah.

Technical Information Approaches for the design of a BTS electricity supply


8 Approaches for the design of a BTS electricity supplyThere are 2 approaches for the design of a BTS electricity supply. The first is the classic design of an Off-Grid system based on renewable energy sources. In the process the system is cost-efficiently designed depending on the location-specific availability of renewable energy sources. A generator is optional, serves at most as fall-back level and therefore has a low runtime. Maintenance work and diesel consumption are accordingly low. This approach is particularly suitable for larger off-grid systems with local peculiarities, since the design can be specifically optimized for the local conditions.For the supply of electricity to BTSs, however, a standard system that is transferrable to several locations is normally designed that is also be economical even with limited space for PV modules and in grid parallel operation. Furthermore, operators of BTSs expect an amortization period of within 4 years.Thus, for off-grid BTS locations, the approach is currently chosen often assuming an operation of 24 hours per day 7 days per week with 1 or 2 generators to optimize the Total Cost of Ownership. Here, as opposed to the classic design as an off-grid system the reduction of diesel consumption and the maintenance intervals is decisive.The implementation of a generator / hybrid supply system can improve the Total Cost of Ownership, in that a battery takes over the supply of the loads and the generator only charges the battery 1 or 2 times per day for a few hours. Thus the generator runtime and maintenance work necessary are greatly reduced and at the same time its efficiency and lifetime increase. Because of these cost savings, as opposed to the continuous generator operation there is in most cases a lower Total Cost of Ownership, although the battery must be replaced frequently due to the large operational demands.A pure generator / battery hybrid supply system without renewable energy sources normally transfers the complete nominal capacity daily, e.g. with a 2-time electric discharge down to an SOC of 40%. The permanently high energy output causes a considerable quantity of waste heat. Alongside the high currents, the temperature increase acts above all as an accelerating factor of the battery aging. Therefore it is worthwhile to always integrate a portion of renewable energy sources, which can perform a daily conservation charge during running supply through a BTS. Thus the high operational demands and warming of the battery significantly lower and the battery lifetime is increased. To use the generator for the float charge of the battery would be very inefficient since the fuel consumption per kilowatt hour is very high in no-load operation.In a Sunny Island System the large variety of power classes of PV inverters and wind turbine inverters allows for the coupled renewable energy sources to be varied location-specifically without having to completely change the system design. This makes the solution very flexible and modularly adjustable. At the same time the Sunny Island functions as system manager and enables all operating modes mentioned.

Technical Information References


9 ReferencesCesme in Turkey

Photo source: Girasolar

Mugla in Turkey

Photo source: Girasolar

Croatia

Photo source: EnergyPLUS

PV plant: Solartracker with Sunny Boy 3000; peak output 3.2 kWp

Wind turbine: Proven small wind turbine system with Windy Boy 6000A; power 6 kW

Off-grid system: 1 x Sunny Island 5048Battery: Battery type OpzV;

Battery capacity 1 500 AhLoad: BTS

PV plant: 3 x Sunny Mini Central 6000A; peak output 17.88 kWp

Wind turbine: 3 x Windy Boy 5000A; power 15 kW

Off-grid system: 6 x Sunny Island 5048Battery: Battery type OpzV;

Battery capacity 3 000 AhLoads: BTS and a restaurant

PV plant: Sunny Boy 3300 and charge controller; peak output 11.5 kWp

Off-grid system: 1 x Sunny Island 5048 with generator

Battery: Battery type OpzV; Battery capacity 2 900 Ah

Load: BTS

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