ETSI TR 102 532 V1.1.1 (2009-06)

Technical Report
Environmental Engineering (EE);
The use of alternative energy solutions
in telecommunications installations

2 ETSI TR 102 532 V1.1.1 (2009-06)

Reference
DTR/EE-00004
Keywords
power supply
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3 ETSI TR 102 532 V1.1.1 (2009-06)
Contents
Intellectual Property Rights . 5
Foreword . 5
Introduction . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 7
2.2 Informative references . 7
3 Definitions, symbols and abbreviations . 8
3.1 Definitions . 8
3.2 Symbols . 11
3.3 Abbreviations . 11
4 Generator technologies . 11
4.1 Fuel cells . 12
4.1.1 Sources of Hydrogen . 12
4.1.2 On site H production . 13
4.1.3 Hydrogen storage . 13
4.1.4 Hydrogen safety . 14
4.2 Photovoltaic generators . 14
4.2.1 Traditional photovoltaic flat module for telecommunications applications . 14
4.2.2 Short term evolution of solar modules . 15
4.3 Wind Turbine Generators . 16
4.3.1 Wind Resource . 16
4.3.2 The Mechanics of Wind Turbines . 17
4.4 Micro hydro generators . 18
4.5 The Stirling machine . 19
5 Energy storage and short term power backup . 22
5.1 Batteries . 24
5.1.1 Lead-acid batteries . 27
5.1.2 Nickel-Cadmium batteries . 28
5.1.3 Nickel-Metal Hydride batteries (Ni-MH) . 29
5.1.4 Nickel-Iron batteries (Ni-Fe) . 29
5.1.5 Nickel-Zinc batteries (Ni-Zn) . 29
5.1.6 Lithium Ion batteries (Li-Ion) . 29
5.1.7 Lithium Ion Polymer batteries (LiP-Ion) . 30
5.1.8 Lithium Metal Polymer batteries (LMP) . 30
5.1.9 Sodium sulphur (Na-S) . 30
5.1.10 Sodium-metal-chloride . 30
5.2 Supercapacitors . 30
5.3 Fly wheels . 31
5.4 Super Magnetic Storage Systems (SMES) . 32
5.5 Pumped hydrostorage and compressed air . 32
5.6 Reliability of energy storage systems . 32
5.7 Safety of energy storage systems . 32
6 Power Systems . 33
6.1 Fuel cell systems . 33
6.2 Photovoltaic systems . 35
6.2.1 Off-grid connection system. 35
6.2.2 In-grid connection system . 36
6.2.3. Planning of a PV system . 38
6.3 Wind energy systems. 38
6.3.1 System design . 39
6.3.2 Installation . 40
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4 ETSI TR 102 532 V1.1.1 (2009-06)
6.4 Hydropower systems . 40
7 Hybrid systems . 41
7.1 System design . 41
7.2 Planning of a Hybrid system . 43
7.3 Selected Hybrid systems . 44
7.3.1 Wind turbine generator combined with fuel consuming generator . 44
7.3.2 Photovoltaic generator combined with fuel consuming generator . 45
7.3.3 Photovoltaic generator combined with wind generator and fuel consuming generator . 47
8 Cooling systems . 48
8.1 Geo-cooling . 48
8.1.1 Horizontal collectors . 51
8.1.2 Vertical probes . 52
8.1.3 Ground-to-air heat exchanger . 52
8.2 Free cooling . 53
8.3 Absorption machines . 56
Annex A: Bibliography . 57
History . 58

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5 ETSI TR 102 532 V1.1.1 (2009-06)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://webapp.etsi.org/IPR/home.asp).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Technical Report (TR) has been produced by ETSI Technical Committee Environmental Engineering (EE).
Introduction
In last year's thematic, as greenhouse effect and carbon footprint have been more common and well known also to
normal citizen; a lot of attention has been also pointed to the telecommunication community impact. The growing
public attention to environmental issues leads industry to work on reducing environmental impacts of their business,
also in a framework of Corporate Social Responsibility (CSR) and sustainable development.
High prices for oil and electrical energy, which are generally expected to persist, contribute to stimulate interest in new
energy sources.
In telecommunication the alternative energy sources, because of the high cost for Wh, are generally used in remote
areas where the public mains is unavailable.
The introduction of new components and technologies on the market has recently increased the energy efficiency of
alternative sources and in some cases, the Governments economically support the use of this alternative energy sources.
The consequence of those two facts is a better convenience in the use of this type of energy, especially considering the
continuous price increase for traditional fossil sources and electrical energy, beyond the attention that is necessary for
reducing ecological impacts.
The need for alternative energy may come also to enable telecommunication services (areas with no power grid), to
expand coverage and to deploy high data rate services (active equipment in the access network)
It becomes obvious that the use of alternative energy has to be considered with particular effort for only supplying
energy efficient ICT equipment.
One important bibliographical reference is the international document produced by ITU-T (CCITT), in 1985 [i.1]
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6 ETSI TR 102 532 V1.1.1 (2009-06)
1 Scope
Due to new power and energy context such as greenhouse effect and other environmental issues, fuel depletion and
electricity cost increase, new regulation and standards, telecom operators have to make efforts to use alternatives. The
present document covers alternative energy sources completed by current and new energy storage that can be used in
ICT. Such alternative energy sources are:
• Fuel Cells.
• Photovoltaic Generators.
• Wind Turbine Generators.
• Micro hydro generators.
• Stirling machine.
• Alternative cooling sources, e.g. geo-cooling, fresh air cooling (or free cooling), absorption machines.
The scope of the present document is to propose an overview about practical solutions for power and cooling systems
using the alternative energy sources. Interoperability of heterogeneous alternative energy sources is the key issue. The
way to ensure hybrid systems reliability and efficiency is also in the scope of the present document.
Bearing in mind the availability and the maintainability of the power plants for TLC, the present document considers:
- the principle of energy converters operating from alternative energy sources;
- the minimum set of information on energy converters;
- the main sizing parameters;
- the architecture of the power systems using the energy converters either only one type or as a combination of
two or more such devices;
- existing and new energy storage;
- cooling solutions from alternative sources (geo-cooling).
New (not traditional) solutions for cooling will be proposed and expanded in a separate document.
2 References
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific.
• For a specific reference, subsequent revisions do not apply.
• Non-specific reference may be made only to a complete document or a part thereof and only in the following
cases:
- if it is accepted that it will be possible to use all future changes of the referenced document for the
purposes of the referring document;
- for informative references.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee
their long term validity.
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7 ETSI TR 102 532 V1.1.1 (2009-06)
2.1 Normative references
The following referenced documents are indispensable for the application of the present document. For dated
references, only the edition cited applies. For non-specific references, the latest edition of the referenced document
(including any amendments) applies.
Not applicable.
2.2 Informative references
The following referenced documents are not essential to the use of the present document but they assist the user with
regard to a particular subject area. For non-specific references, the latest version of the referenced document (including
any amendments) applies.
[i.1] ITU-T (CCITT): "Handbook on Primary Sources of Energy for the Power Supply of Remote
Telecommunication Systems", 1985.
[i.2] CENELEC EN 62282-2: "Fuel cell technologies. Part 2: Fuel cell modules".
[i.3] CENELEC EN 62282-3-2: "Fuel cell technologies - Part 3-2: Stationary fuel cell power systems
- Performance test methods".
[i.4] Council Directive 87/404/EEC of 25 June 1987 on the harmonization of the laws of the Member
States relating to simple pressure vessels.
[i.5] Council Directive 90/488/EEC of 17 September 1990 amending Directive 87/404/EEC on the
harmonization of the laws of the Member States relating to simple pressure vessels.
[i.6] Council Directive 90/396/EEC of 29 June 1990 on the approximation of the laws of the Member
States relating to appliances burning gaseous fuels.
[i.7] Council directive 1999/92/EC of 25 January 1999 on minimum requirements for improving the
safety and health protection of workers potentially at risk from explosive atmospheres.
[i.8] Council directive 94/9/EC of 23 March 1994 on the approximation of the laws of the Member
States concerning equipment and protective systems intended for use in potentially explosive
atmospheres.
[i.9] Council directive 97/23/EC of 29 May 1997 on the approximation of the laws of the Member
States concerning pressure equipment.
[i.10] CENELEC EN 62124: "Photovoltaic (PV) stand-alone systems. Design verification".
[i.11] CENELEC EN 60904-1: "Photovoltaic Devices Part 1: Measurement of Photovoltaic Current
- Voltage Characteristics".
[i.12] CENELEC EN 60904-2: "Photovoltaic devices - part 2: requirements for reference solar devices".
[i.13] CENELEC EN 62093: "Balance-of-system components for photovoltaic systems - Design
qualification natural environments".
[i.14] Council directive 2006/66/EC of the European parliament and of the council of 6 September 2006
on batteries and accumulators and waste batteries and accumulators and repealing Directive
91/157/EEC.
[i.15] CENELEC EN 50272-2: "Safety requirements for secondary batteries and battery installations
-- Part 2: Stationary batteries".
[i.16] ETSI ETS 300 132-1: "Equipment Engineering (EE); Power supply interface at the input to
telecommunications equipment; Part 1: Operated by alternating current (ac) derived from direct
current (dc) sources".
[i.17] ETSI EN 300 132-2: "Environmental Engineering (EE); Power supply interface at the input to
telecommunications equipment; Part 2: Operated by direct current (dc)".
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8 ETSI TR 102 532 V1.1.1 (2009-06)
[i.18] CENELEC EN 61427: "Secondary cells and batteries for solar photovoltaic energy systems".
[i.19] IEC 61400-1: "Wind turbines - Part 1: Design requirements".
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
Air Mass (AM): measure of distance that the direct solar beam travels through the earth atmosphere
NOTE: AM = 1,5 in standards corresponds to a sun elevation of approximately 45°.
air pollution: air with contaminants in it that prevent the air from dispersing as it normally would, and interfere with
biological processes
alternative energy: energy derived from non-fossil resource and from renewable source
NOTE: A popular term for "non-conventional" or "clean" energy as renewable.
asynchronous generator: type of electric generator that produces alternating current (AC) electricity to match an
existing power source
battery: energy storage device made up of one or more cells filled with electrolyte
NOTE: An electrolyte is a non-metallic conductor between positive and negative plates that carries electric
charges through ionic displacement.
capacity factor: amount of power a wind turbine produces over a period of time divided by the amount of power it
could have produced if it had run at its full rated capacity over that time period
Carbon Dioxide (CO2): colourless, odourless non-combustible gas present in the atmosphere
NOTE: It is formed by the combustion of carbon and carbon compounds (such as fossil fuels and biomass), by
respiration, which is a slow combustion in animals and plants, and by the gradual oxidation of organic
matter in the soil. It is a greenhouse gas that contributes to global climate change, it remains in the
atmosphere during about one century.
Carbon Monoxide (CO): colourless, odourless but poisonous combustible gas
NOTE: Carbon monoxide is produced in the incomplete combustion of carbon and carbon compounds, for
example, fossil fuels like coal and petroleum.
central power plant: large power plant that generates power for distribution to one or multiple loads
chemical energy: energy liberated in a chemical reaction, as in the combustion of fuels
constant-speed wind turbines: wind turbines that operate at a constant RPM (Revolutions Per Minute speed). They are
designed for optimal energy capture at a specific rotor diameter and at a particular wind speed
conventional fuel: fossil fuels: coal, oil, and natural gas
electric power converter: device for transforming electricity to a desired quality and quantity (voltage or current or
power or frequency)
energy converter: equipment transforming alternative energy sources (solar, wind, hydro, etc.) into electrical energy
deregulation: process of changing policies and laws of regulation in order to increase competition among suppliers of
commodities and services
downwind wind turbine: horizontal axis wind turbine in which the rotor is downwind of the tower
emission: substance or pollutant emitted as a result of a process
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9 ETSI TR 102 532 V1.1.1 (2009-06)
energy storage: process of storing or converting energy from one form to another for later use
NOTE: For example, an electrochemical storage device is a battery, an electromechanical storage device is a
flywheel.
environment: all the natural and living things around us: The earth, air, weather, plants, human and animals all make
up our environment
fossil fuels: fuels formed in the ground from the decayed remains of dead plants and animals
NOTE: It takes millions of years to form fossil fuels. Oil, natural gas, and coal are fossil fuels.
fuel: any material that can be consumed to be converted into energy
gearbox: protective casing for a system of gears
generator: device for converting any energy resource into electrical energy
geothermal: heat that comes from within the Earth
geothermal heating/cooling: method of heating and cooling a building using underground thermal conditions
geothermal power: electricity generated from naturally occurring geological heat sources
green credit: new way to purchase renewable electric generation that divides the generation into two separate products:
the commodity energy and the renewable attributes
NOTE: The green credit represents the renewable attributes of a single megawatt of renewable energy. Also
known as green tags, renewable energy credits, or renewable energy certificates.
green power: popular term for energy produced from non-pollutant or renewable energy resources
greenfield: site on which a power plant has not previously existed
grid: common term referring to an electricity transmission and distribution system
gust: sudden brief increase in the speed of the wind
horizontal-axis wind turbines: turbines on which the axis of the rotor's rotation is parallel to the wind stream and the
ground
hybrid system: power systems combining two or more energy conversion devices, or two or more fuels for the same
device, that when integrated, overcome limitations inherent in either
NOTE: In the present document we define that at least one source is from alternative "renewable" energy source.
inverter: equipment that can convert direct current into alternative current
mean power output (of a wind turbine): average power output of a wind energy conversion system at any given mean
wind speed
mean wind speed: average wind speed over a specified time period and height above the ground
mechanical energy: energy possessed by an object due to its motion (kinetic energy) or its potential energy
median wind speed: wind speed with 50 % probability of occurring
nacelle: cover for the gearbox, drive train, and generator of a wind turbine
natural gas: hydrocarbon gas obtained from underground sources, often in association with petroleum and coal
deposits
NOTE: It generally contains a high percentage of methane, varying amounts of ethane, and inert gases. Natural
gas is used as a heating fuel and for electricity generation.
peak wind speed: maximum instantaneous wind speed that occurs within a specific period of time
photovoltaic: application of solar cells for energy by converting sunlight directly into electricity
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10 ETSI TR 102 532 V1.1.1 (2009-06)
power quality: stability of frequency and voltage and lack of electrical noise on the power grid
prevailing wind direction: direction from which the wind predominantly blows as a result of the seasons, high and low
pressure zones, the tilt of the earth on its axis, and the rotation of the earth
recycling: process of converting into new products materials that are no longer useful as they were originally designed
renewable energy: energy derived from resources that are regenerative or that cannot be depleted
NOTE: Types of renewable energy resources include wind, solar, biomass, geothermal and moving water.
rotor: blades and other rotating components of a system (e.g. rotor of a wind energy conversion turbine in the
alternative energy sources field)
solar energy: electromagnetic energy transmitted from the sun (solar radiation)
solid fuels: any fuel that is in solid form, such as wood, peat, lignite, coal, and manufactured fuels such as pulverized
coal, coke, charcoal briquettes, and pellets
step-up gearbox: gearbox that increases turbine electricity production in stages by increasing the number of generator
revolutions produced by the rotor revolutions
sustainable energy: energy that takes into account present needs while not compromising the availability of energy or a
healthy environment in the future
trade wind: consistent system of prevailing winds occupying most of the tropics
NOTE: They constitute the major component of the general circulation of the atmosphere. Trade winds blow
northeasterly in the Northern Hemisphere and southeasterly in the Southern Hemisphere. The trades, as
they are sometimes called, are the most persistent wind system on earth.
turbine: term used for a wind energy conversion device that produces electricity
NOTE: see also "Wind Turbine".
turbulence: swirling motion of the atmosphere that interrupts the flow of wind
variable-speed wind turbines: turbines in which the rotor speed increases and decreases with changing wind speeds
NOTE: Sophisticated power control systems are required on variable speed turbines to insure that their power
maintains a constant frequency compatible with the grid.
vertical axis wind turbines: turbines on which the axis of the rotor's rotation is perpendicular to the ground
Watt-peak (Wp): unit used to express the maximum power produced (or provided) by a photovoltaic module for solar
radiation of 1 000 W/m for a standard spectrum and temperature
wind energy: power generated by converting the mechanical energy of the wind into electrical energy through the use
of a wind generator
wind farm: piece of land on which wind turbines are sited for the purpose of electricity generation
wind (turbine) generator: system that converts kinetic energy in the wind into electrical energy
NOTE: See IEC 61400-1 [i.19].
wind power plant: group of wind turbines interconnected to a common utility system
wind resource assessment: process of characterizing the wind resource and its energy potential for a specific site or
geographical area
wind speed: rate of flow of wind when it blows undisturbed by obstacles
NOTE: Expressed in m/s.
wind speed frequency curve: curve that indicates the number of hours per year that specific wind speeds occur
wind speed profile: profile of wind speed changes at different heights above the surface of the ground or water
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wind turbine: wind energy conversion device that produces electricity
wind turbine rated capacity: power that a wind turbine can produce at its rated wind speed
wind velocity: wind speed and direction in an undisturbed flow
3.2 Symbols
For the purposes of the present document, the following symbols apply:
Wh watt-hours
Wp watt peak
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
AC Alternating Current
AFC Alkaline Fuel Cell
AM Air Mass
BB BroadBand
BMS Battery Management System
CPV Concentrating PhotoVoltaic
DC Direct Current
DMFC Direct Methanol Fuel Cell
EV Electrical Vehicle
FC Fuel Cell
GaAs Gallium Arsenide
HYP HYdro-Power
LA Lead Acid
LVBD Low Voltage Battery Disconnector
MCFC Molten Carbonate Fuel Cell
MPPT Maximum Power Point Tracker
MTBF Mean Time Between Failure
MTTR Mean Time To Repair
PAFC Phosphoric Acid Fuel Cell
PCM Phase Change Material
PEM Proton Exchange Membrane
PEMFC Proton Exchange Membrane Fuel Cell
PTFE PolyTetraFluoroEthylene
PV Photovoltaic
PVG Photovoltaic Generator
RPM Round Per Minute
SC Super Capacitor
SMES Super Magnetic Energy Systems
SoC State of Charge
SOFC Solid Oxide Fuel Cell
TLC Telecommunication
VRLA Valve Regulated Lead Acid
WTG Wind Turbine Generator
4 Generator technologies
This part of the present document describes the alternative energy generation technologies that can be considered as a
power source for telecommunication applications.
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4.1 Fuel cells
A fuel cell is an electrochemical reactor used to convert the chemical energy (reduction and oxidation) contained in an
external fuel into electrical energy (Direct Current output power) characterized by a continuous supply of reactants and
flowing out of reaction products. The fuel cell can operate without interruptions as long as the necessary flows are
maintained.
The fuel cell reactor is composed of sets of positive and negative electrodes, an electrolyte between them (e.g. salt
diluted in water or polymer) and a separator (e.g. PEM) to avoid leakage or cross-over of fuel (e.g. H or methanol)
directly towards the oxidizing agent (e.g. air) without producing useful electrons in external circuit.
Elementary fuel cell voltage are very low (0,1 V to 1 V in open circuit) and several cells are mounted in serial
arrangement (stack) to obtain practical voltage for powering telecom equipment. The current is dependant of the plate
surface.
There are various types of fuel cells available as showed in the following table.
Table 1: Types of Fuel Cells
FC type PEMFC AFC DMFC PAFC MCFC SOFC
Proton
Molten
Exchange Alkaline Fuel Direct Methanol Phosphoric Acid
Solid Oxide
Name Carbonate Fuel
Membrane Fuel Cell Fuel Cell Fuel Cell Fuel Cell
Cell
Cell
Polymer Polymer
Molten Li CO
2 3
membrane membrane
ZrO and Y O
Electrolyte KOH solution Phosphoric acid and K CO in
2 2 3
2 3
protons protons
LiAlO2 matrix
conductive conductive
Ions in
2-
+ - + + 2-
CO
H OH H H O
electrolyte
Temperature 700 ℃ to
40 ℃ to 80 ℃ 60 ℃ to 80 ℃ 60 ℃ to 100 ℃ 180 ℃ to 220 ℃ 600 ℃ to 660 ℃
In operation 1 000 ℃
H (pure or H (pure or from
bio-gas and bio-gas and
2 2
H
Fuel Methanol
natural gas natural gas)
from reformer) reformer)
O (pure)
Oxidant Air Air Air Air Air
System
30 % to 50 % 60 % 20 % to 30 % 40 % 45 % 55 % to 60 %
efficiency
Transport, Cogeneration,
Cogeneration,
Portable Centralized
Portable Centralized
Applications equipment, Spatial Cogeneration electricity
equipment electricity
Cogeneration, production
production
Back-up Transport
Developing Mature
Small series Used Small series Small series Small series
progress technology
The most used in TLC applications are the PEM fuel cells based on a polymer electrolyte in the form of a thin,
permeable sheet. Efficiency of the commercial systems is greater than 35 %, and operating temperature is about 40 °C
to 80 °C. Cells stack outputs generally range from 50 watt to 250 kW. The higher the operating temperature the less
degraded on the hydrogen has to be. PEM fuel cells can provide the solid-state backup power solutions.
The electrical characteristics of fuel cells and their performance tests are described in EN 62282-2 [i.2] and
EN 62282-3-2 [i.3].
4.1.1 Sources of Hydrogen
PEM fuel cells use hydrogen as a fuel. Hydrogen for fuel cells can be produced in large central locations and delivered
in gaseous, liquid or solid (metal hydride) state in tanks, by pipeline, or can be produced at the fuel cell site using an
onsite reformer.
Hydrogen high pressure cylinders tanks are typically used in situations where the fuel cell needs to run for a short
period of time (approximately 8 hours).
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4.1.2 On site H production
Reforming
There are many types of reforming, each with its own strengths and weaknesses. Steam reforming is often selected for
projects because of its ability to provide high efficiency use of valuable fuel inputs. Fuel processors have been
developed for a variety of common fuels including methanol (a liquid used as windshield washer and many other
common products but highly toxic). Extended run fuel cell systems allow supporting back-up requirements of days
versus hours by using compact and convenient liquid fuels.
Electrolyser
In some cases it is possible to produce hydrogen directly on site using a photovoltaic system to electrolyze water
(reduction of costs may be achieved in combination with wind and/or grid).
In that case, hydrogen has to be stored in hydrogen storage (see clause 4.1.3) for next use. The H is still converting in
electricity through a fuel cell or a motor+alternator.
This is a solution for interseasonal storage. Even with an efficiency of only 25 % of the H electrolyser + storage +
generator. It can be demonstrated an important gain when producing H with the wasted excess of energy of PV when
battery are charged. The major problem is cost and reliability of this very complex solution.
4.1.3 Hydrogen storage
Hydrogen can be stored in many ways: gas, liquid, in solid hydride.
High pressure storage
Commonly H is compressed in steel or composite tanks and held at pressures up to 70 MPa.
Most backup power fuel cell systems will use compressed hydrogen as a fuel source located near the fuel cell system.
The most typical hydrogen cylinder is often referred to as a "T-cylinder B50", it is approximately 152 cm high and
25 cm wide and holds about 8,5 cubic meters of gas. Multiple tanks are connected together as needed. Each tank weighs
approximately 70 kg. An array of four to six tanks contains enough hydrogen to operate a typical 5 kW fuel cell for nine
hours at full load. Cylinders are typically pressurized to approximately 200 bar, but the pressure is regulated down to
low pressure at the hydrogen tank enclosure to ensure maximum safety and code compliance.
Each T-cylinder stores enough hydrogen to deliver approximately 10 kWh of regulated AC or DC electricity from a fuel
cell system. Hydrogen is typically stored outdoors, but can also be located indoors in certain building types if the right
safety and ventilation procedures are followed. Suppliers can offer outdoor enclosures or can also recommend approved
hydrogen storage options for specific applications.
Liquid storage
H is liquefied at -252 °C. Liquefying is energy intensive, but liquid hydrogen has three times the amount of energy as
an equal weight of gasoline.
Hydride solid storage
Hydrogen can also be stored in metal hydrides - granular metal that absorbs hydrogen. These tanks are comparatively
heavy.
Similar, but lighter, are carbon nanotubes, and other carbon absorption techniques still in the experimental stage.
Hydrogen can also be stored in chemical hydrides by way of chemical bonds. Chemical hydrides typically allow
hydrogen to be stored in conventional tanks that only release hydrogen when a certain catalyst is present, making them
very safe for transportation.
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4.1.4 Hydrogen safety
Like all good fuels, hydrogen contains a lot of energy. Considering applicable European Directives and standards,
hydrogen can be handled safely when guidelines for its safe storage, handling and use are observed. Hydrogen's
combustion properties imply the same caution required when using any fuel, as well as care to address the properties
unique to hydrogen. Some of hydrogen's special properties actually may provide safety benefits compared to gasoline or
other fuels. The hydrogen industry makes, distributes, stores and handles hydrogen nationwide and has compiled an
exemplary safety record.
Main references:
• Industrial gas:
- directive 87/404/EEC [i.4] and its amendment 90/488/EEC [i.5];
- directive 90/396/EC [i.6];
- directive 1999/92/EC (ATEX) [i.7] and directive 94/9/EC [i.8];
- directive 97/23/EC [i.9].
• Hydrogen:
- Local law and regulation on industrial gas and storage.
4.2 Photovoltaic generators
4.2.1 Traditional photovoltaic flat module for telecommunications
applications
Photovoltaic (PV) technology permits the transformation of solar energy directly into electric energy. Solar energy to
electric energy conversion takes place within solar cells, which can be amorphous, polycrystalline or monocrystalline,
according to their structure. In most cases they are made of silicon. In particular a solar cell is a semiconductor device
that converts photons from the sun into electricity. This conversion is called the photovoltaic effect, discovered by
Bequerel in 1839.
A photovoltaic module is the basic element of each photovoltaic system. It consists of many solar cells, which are
electrically connected and placed between glass and tedlar plate, and framed by an (usually) aluminium frame.
According to the solar cell technology it is possible to distinguish between monocrystalline, polycrystalline and thin
film amorphous solar modules. Most commercial crystalline modules consist of 36 or 72 cells. The typical crystalline
modules power ranges from a few W to up to 300 W/module with a voltage range from 12 V up to more than 100 V
DC. The most important module parameters include a short circuit current, an open circuit voltage and a nominal
voltage at 1 000 W/m2 solar radiation. Module parameters are measured at standard test conditions (STC) - solar

radiation 1 000 W/m2, air mass (AM) 1,5 and temperature 25 °C. The documents [i.10], [i.11] and [i.12] give more
information about photovoltaic module's characteristics.
A number of solar-modules and other components (batteries, charge regulators, inverters etc.) can form large
photovoltaic systems.
Advantages and drawbacks
The advantages of PV include:
• Complementarities with other energy sources, both conventional and renewable.
• Flexibility in terms of implementation. PV systems can be integrated into telecommunication sites.
• Low and simple maintenance.
• Production of electricity without greenhouse gas emissions.
• Long operating life (up to 25 years).
ETSI
15 ETSI TR 102 532 V1.1.1 (2009-06)
Drawbacks include:
• Low efficiency (7 % to 14 %).
• High costs.
• Possibility of vandalism.
A PV system can deliver electrical energy to a specific appliance consumption or for commercial production in case of
electric grid connection.
4.2.2 Short term evolution of solar modules
Reducing cost of PV and improving efficiency are the 2 challenges for the next years. About silicon, after using
electronic quality waste, a dedicated industrial process will be favourable to cost decrease, more over other thin film
technologies using less material will also be in favour of low cost. The table hereafter shows technologies trends for the
next years.
Table 2: PV's technologies trends
Technology Advantages Drawback Market
availability
Thin layer Low cost and cheaper than efficiency lower than In production since end of
CiGS η = 14 % to 15 % silicon, monocristal silicon, 2007
CdTe η = 12 % to 15 % Sun spectra matched Longtime stability had to be
semiconductors confirmed
III-V semiconductors Worldwide efficiency record Need concentration and In production by the end
multi-junction under
η = 40,7 % in lab, η = 35 % tracking equipment, of 2008
concentration in production, More expensive than silicon
η = 35 % @ 500 sun Thin layers

4.2.3 Photovoltaic Concentrators
A promising approach to lower the cost of electricity generated by solar photovoltaic systems is to use lenses or mirrors
to focus, or "concentrate", sunlight from a large area onto a small solar cell receiver. This system is suitable for
converting direct solar rad
...