CHAPTER 4: TECHNICAL CHARACTERISTICS OF SOLAR FARM
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CHAPTER 4: TECHNICAL CHARACTERISTICS OF SOLAR FARM
PRINCIPLE OF ELECTRICITY PRODUCTION FROM SOLAR IRRADIANCE Solar irradiance from the sun can provide an invaluable source of energy. Solar energy is normally captured by solar panels which are so designed as to produce an electric current from the heat captured from the sun irradiance. The electric current so produced is controlled by a Charge Controller which feeds a battery system which produces the Direct Current (DC) power. However, DC power is not useful for everyday life use and for industrial use, and needs to be converted to Alternating Current (AC) power. This is achieved by the use of inverters – which convert the DC power into AC power for evacuation onto the public utility power grid. The above principle of production of electricity from the sun energy is simplistically shown in the Figure 4.1 below:
Figure 4.1: Figure Showing Principle of Solar Power
PLANT DIAGRAM AND FLOW CHART Based on the above principle, a typical plant diagram/flow chart for the production of electricity from solar power can be elaborated as given in Figure 2.
Figure 4.2: Typical Plant Diagram 4.3
SOLAR PLANT COMPONENTS The solar plant will comprise of the following power‐producing components: (i)
The solar panels array
The cabling networks
The inverters, complete with computerized platform.
The step‐up transformer
The power evacuation lines
The above power‐producing components will be backed‐up and/or serviced by the following project components to offer the full spectrum of the facility. i. The Information and Welcome Centre ii. The artisanal market place. iii. The perimeter fencing iv. The mountain‐top tree barrier.
The following sub‐sections fully describe each of the above‐listed components of the solar farm, starting with the main power‐producing components. 4.4
SOLAR PANELS ARRAY The solar panel array or assembly will comprise about 62,000 modules (required to provide the 15 MW capacity) facing North ‐ which will act as solar captors. Each captor panel will be of the following dimension.
Each panel will weigh 19.1kg. The panel is provided with 6No grounding holes, 4No mounting holes and 8No drainage holes. The grounding holes allow for the passing of grounding cables; the mounting holes allow for the fixing of the panel on to its fixing frame, while the drainage holes provide for the excavation of rainwater. Each panel is made up of the following construction materials and components:
A front cover made of low‐iron tempered glass of 3.2mm thickness
A set of 60 multi‐crystalline silicon cells of dimensions 156mm x 156mm with either 2 or 3 busbars.
An anodized aluminium frame of silver colour with the necessary edge sealing made up of either silicone or tape.
A junction box with a IP65 protection degree or better.
A cable of length 1100mm of cross‐section area 4mm2.
A plug connector of type MC4 with a protection degree to standard IP 67 or equivalent
DESCRIPTION OF PV PANELS
Manufacturing Specifications The photo‐voltaic panels will be manufactured by the Chinese Yingli Green Energy Holding Company Limited which is one of the world’s largest fully vertically integrated PV manufacturers, which markets its products under the brand “Yingli Solar”. With over 4.5GW of modules installed globally, the company is the leading solar energy company built upon proven product reliability and sustainable performance.
Performance The PV panels will be made up of high efficiency, multicrystalline silicon solar cells with high transmission and textured glass which can deliver a module efficiency of up to 16.2%. Such a level of efficiency results in the minimization of the installation costs and maximizing the kWh output of the system per unit area.
The PV panels are manufactured with a tight positive power tolerance of 0W to + 5W, which ensures the production and delivery of modules at or above nameplate power thereby contributing to minimizing module mismatch losses leading to improved system yield. 4.5.3
Reliability Tests by independent laboratories prove that the PV modules:
Fully conform to certification and regulatory standards
Withstand wind loading pressure of up to 2.4kPa, confirming mechanical stability
Successfully endure ammonia and salt‐mist exposure at the highest severity level, ensuring their performance in adverse conditions. The PV panels are manufactured to international standards and conform to ISO 9001:2008, ISO 14001:2004 and BS OHSAS 18001: 2007.
Warranties From a sustainability stand point, the PV panels are covered by a 10‐year product warranty, comprising to the following criteria:
Limited power warranty 10 years at 91.2% of the minimal rated power output,
25 years at 80.7% of the minimal rated power output.
Qualifications and Certifications The manufacture of the PV panels is covered by the following qualifications and certificates: IEC 61215, IEC 61730, MCS, CE, ISO 9001:2008, ISO 14001:2004, BS OHSAS 18001:2007, SA 8000, PV Cycle. The Specification and Data Sheet enclosed at Annex 4A at the end of Chapter 4 provides additional information pertaining to conditions electrical performance, the thermal characteristics and the operating conditions of the PV panels – to which the interested reader is referred.
ASSEMBLY OF PV PANELS The assembly of the PV panels array which will be a fixed‐tilt ground‐mounted configuration, is achieved by the following methods: (i)
Tilting of the PV panels to about 20o to the horizontal to induce maximum exposure to sunlight
Bolting of the panels onto horizontal metallic I‐beams or angle‐irons placed at intervals underneath the panel assembly area.
(iii) Fixing of the top horizontal I‐beams or angle irons onto vertical metallic sections or square metallic tubes held in position by a horizontal metallic EIA Report1.doc
I‐beam at the bottom. Bracing will also be carried out if judged necessary, to produce additional structural stability. (iv) Fixing the vertical metallic struts into the ground. (v)
Each fixing hole will be 300m x 300m by 600mm deep, encased in concrete.
The photographs below show:
The appearance/look of the PV panels individually and in the arranged array system.
The horizontal supporting I‐beams
The vertical H‐section columns
The fixing holes embedded with concrete
Photographs Showing General Arrangement and Fixing of PV Panels It should be noted that he fixing height above the existing ground level will be of the order of 1.5‐1.8 metres. At this height above ground level, ease of installation will be achieved, and most importantly the PV panel array will be protected from high winds during cyclones, thereby ensuring their sustainability in the future. 4.7
FOUNDATION AND MOUNTING STRUCTURE The mounting system is a dual‐axis system with double‐supported and strutted frames for increased load resistance and weak soils. Depending on the condition on the site, up to 5 (five) standard modules can be installed horizontally or 3 (three) modules can be installed vertically. The preferred inclination angle is 20 (twenty) degrees for maximum sunshine irradiance. The foundation of the mounting system shall be screw foundation or concrete foundation. This consideration will be finalized during the detailed design stage of the project and prior to start of works on site. A typical mounting arrangement is reproduced in Figure 4.3 below
Figure 4.3: Typical Mounting Arrangement 4.8
CABLING NETWORKS Each panel or set of panels will be linked to an electrical cable as shown in the photographs below:
Photographs Showing Electrical Cable These individual cables will be entrenched as shown in the photographs above, and connect into bigger‐size cables. As the number of cables linking bigger areas of PV panels increase, it gives rise to bundles of cables which will be laid in trenches dug at 600mm depth. All cable trenches will be fitted with a 75mm thick bedding made up of either coral sand or rock sand. These cable bundles go to the Charge Controller and the Battery system for the collection of the entire DC power system of the solar power plant. A typical arrangement of such a bundle of electrical cables laid in a trench on top of the bedding is shown in the photographs below.
Photographs Showing Bundles of Electrical Cables in Trenches 4.9
DESCRIPTION OF INVERTERS The Inverters constitute the main core component of the solar plant insofar as they connect the DC power from the Charge Controller and the Battery System into the solely‐utilized AC power. A photograph of such an Inverter cabinet is reproduced below:
Photograph of a Typical Inventor
The Inverters proposed to be installed at the Bambous Solar Plant will be of the ‘Sunny Central” type whose actual ratings will be fixed at the design stage of the project. The main characteristics of the proposed inverters are listed below:
They will be up to 1 megawatt system power as standard.
Maximum yields with low system cots Note: This inverter characteristic will ensure economic advantages for the project
Full nominal power in continuous operation at ambient temperatures of up to 50o C. Note: This invertor characteristic is of utmost importance insofar as at Bambous high ambient temperatures may be experienced on extremely sunny days in summer.
Possibility of intelligent power management, via an interfacing with the appropriate software.
Adaptation to a wide range of DC input voltage for flexible use of various PV modules configurations
Perfectly adjusted for the temperature dependent behavior of PV generators
Includes all grid management functions.
A number of inverters will be required for the 15mW production plant. They will be enclosed in a building fitted with corridors which will provide easy and ready access to the inverter units. All the inverters will be connected to a customized computer platform or programmable logical controller (PLC) – which will allow for the optimal monitoring and control of the solar plant. The Specification and Data Sheet of the proposed inverter is enclosed at Annex 4B at the end of Chapter 4 – to which the reader is referred, should he be interested in having information on technical data, such as Input DC, Output AC, efficiency, protective devices, general data and other features. 4.10
FEATURES OF STEP‐UP TRANSFORMER The power output from the inverter, of rating 22kV will require step‐up to 66kV for connection to the public grid at the CEB sub‐station at La Chaumiere. For this purpose a step‐up transformer, which will be housed in a building, at the end of the farm, will be installed. The transformer will be supplied by Schneider Electric.
Its technical features, specifications and data are provided in the Specification and Data Sheet enclosed at Annex 4C at the end of the Chapter. The transformer room will be constructed on the flat part of the site at its northern top. This position will allow for the shortest route of the power excavation line. At this position, the housing building will also require basic standard strip footing and separate column‐base foundations. Depending on site conditions, however, such standard foundation may be modified to shallow bases and ground beams as required. 4.11
POWER EVACUATION LINE From the step‐up transformer, the 66kV power line will be connected to the CEB La Chaumiere sub‐station, through a 66kV power line which will run from the transformer room at the site to the CEB sub‐station, over a total distance of 3.9km. The alignment of the evacuation line is as shown on the context plan enclosed at Annex 1B at the end of Chapter 1 entitled “Project Particulars” The alignment of the power evacuation line will run across bare lands, forest lands and unhabituated areas, without therefore bearing any environmental impact on any human receptor.
INFORMATION AND WELCOME CENTRE The Information and Welcome Centre will be housed in a building of about 30 square metres in size. It will (i)
Provide space for visitors while on a visiting tour of the solar farm installations.
Accommodate training facilities at the site, in the form of lecture room, fitted with all the necessary accessories and appliances, where lectures on the operation and benefits of the green renewable energy concept of the solar farm will be presented.
The building is located towards the western portion of the site, within close distance to the main entrance gate and the parking area. This means that the visitors will not have to walk long distances on their visit to the solar farm. The centre will be used for visit and educational purposes, in line with the Government’s policy of Maurice Ile Durable (MID) concept, and create awareness and education among school and college children and the mauritian population at large. The layout and front‐elevation of the Information and Welcome Centre are enclosed at Annex 4D at the end of Chapter.
ARTISANAL MARKET PLACE The project finally incorporates the setting‐up of an artisanal market place – which will constitute an open‐air sheltered space where hand‐made materials representing the solar farm will be displayed for sale, after having been manufactured by the local women entrepreneurs of the Médine and Bambous Villages. This artisanal market place will occupy an area of about 100m2 – which will be open but covered, and put at the disposal of the interested local population. The targeted artisanal products can be:
Hats with the logo of the solar farm
Paintings showing the general installations of the solar farm
Carvings related to the solar farm
Tee‐shirts with any interesting feature of the solar farm.
The intrinsic purpose of this artisanal market place as envisaged by the promoter will be the social link with the local population, and the gender empowerment potential afforded by the project, insofar as the women entrepreneurs of the local population will be targetted. This is considered to be an enhancement opportunity offered by the solar farm project. 4.14
PERIMETER FENCING It is envisaged to provide fencing all along the site boundary to keep the site safe from intruders but more importantly from stray animals which can damage the cells. The perimeter fencing will thus be erected to provide site security against vandalism and animals finding their way into the site‐premises. At this point in the project procurement cycle, it is envisaged to place a galvanized‐ pole supported chain‐link fencing around the periphery of the project site. A photograph of the typical chain‐link fencing proposed is reproduced below:
Photograph of Chain‐Link Fencing
MOUNTAIN‐TOP TREE BARRIER It is proposed to install all along the boundary of the site along the mountain‐top a tree barrier which will consist of our row of Eucalyptus trees and one row of Ficus tree, planted in a staggered fashion. The purpose of this double line tree barrier is described below: (i)
It will provide stabilization of the mountain‐top area overlooking the solar farm, through its root penetration action.
It will act as protection against accidental rolling of any boulder along the mountain slope – which can cause damage to the solar panels
It will provide some shade along the mountain‐top area of the site.
It will induce an environment of naturally landscaped area, which will produce in‐turn a positive visual impact. The positioning and alignment of the trees barrier along the southern (mountain‐top) boundary of the site are shown in the site layout plan enclosed at Annex 4E at the end of Chapter 4.