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SOGERV Technical Design Specification

Authored by: K.M.Tembo, I. Gwayi University of Malawi, The Polytechnic, Malawi:

{[email protected], [email protected]}

Edited By: Peter Dauenhauer, Dr Scott Strachan University of Strathclyde, Department of Electronic and Electrical Engineering Glasgow U.K:

{[email protected], [email protected]] May 2016

1 INTRODUCTION ......................................................................................................................................... 2

2 TECHNICAL NEEDS ASSESSMENT AND DESIGN PROCESS ............................................................................ 2

3 SYSTEM SUMMARY .................................................................................................................................... 4

3.1 KANDEU SOLAR PV SYSTEMS ........................................................................................................................... 4 3.2 MANDRADE SOLAR PV SYSTEMS ...................................................................................................................... 4

4 DESIGN METHODOLOGY ............................................................................................................................ 4

4.1 LOAD ESTIMATION ......................................................................................................................................... 4 4.2 BATTERY SIZING ............................................................................................................................................ 5 4.3 PANEL SIZING ............................................................................................................................................... 6 4.4 CHARGE CONTROLLER SIZING ........................................................................................................................... 7 4.5 INVERTER SIZING ........................................................................................................................................... 8

5 DESIGNS ..................................................................................................................................................... 9

5.1 KANDEU SOLAR PV SYSTEMS ........................................................................................................................... 9 5.2 MANDRADE SOLAR PV SYSTEMS .................................................................................................................... 21

6 BILL OF QUANTITIES ................................................................................................................................. 23

7 TENDERING REQUIREMENTS AND ADDITIONAL CONSIDERATIONS .......................................................... 24

7.1 EARTHING AND LIGHTNING PROTECTION .......................................................................................................... 24 7.2 WIRING SPECIFICATIONS ............................................................................................................................... 24 7.3 LIGHTING SPECIFICATION .............................................................................................................................. 24 7.4 DISTRIBUTION BOARD DESIGN SPECIFICATION ................................................................................................... 25 7.5 STATION BATTERY HOUSING SPECIFICATION ...................................................................................................... 25 7.6 PANEL ORIENTATION .................................................................................................................................... 25 7.7 MERA ACCREDITATION ................................................................................................................................ 26 7.8 PROCUREMENT OFFICER CHECKLIST FOR ALL TENDERS ......................................................................................... 26

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1 Introduction

Electricity access is currently only 9% overall and 1% in rural areas in Malawi. The SOGERV project is

designed to directly address a goal of Sustainable Energy for All Agenda of increasing energy access

to the rural communities in Malawi. Renewable Energy Technologies (RETs) will be installed and will

bring positive contribution in rural development, poverty alleviation and development of enterprise

activities for low income people.

The Sustainable Off-Grid Electrification of Rural Villages (SOGERV) Project is funded by the Scottish

Government and runs from 2015 – 2018. The project is led by the University of Strathclyde and

partnered by Concern Universal – Malawi and WASHTED – Polytechnic. The project aims to deploy

sustainable off-grid energy projects in Chikwawa district, Southern Malawi, that provide communities

with affordable energy access. The project is targeting four villages in Chikhwawa namely Thendo,

Kandeu, Gola and Mandrade that currently lack access to electricity at homes, schools, health centres

and businesses.

The project will set up sustainable community energy suppliers to deploy appropriate RETs including

solar PV systems, solar lanterns, and efficient cook-stoves for target households, businesses, schools

and health centres. Each community energy project will establish a sustainability agreement that is

shared between district governance structures, communities, and entrepreneurs who operate the

projects. The objective is to promote development of income generating activities with renewable

energy supply and bring a positive impact on the quality of life in rural districts.

The document is structured as follows. Section 1 introduces the SOGERV project. Section 2

describes the technical needs assessment and design process undertaken. Section 3 summarizes the

systems which are specified with this design document. Section 4 explains the methodology used for

electrical system specification. Section 5 contains all of the system specific designs including the

electrical layout and any specific considerations for the location. Section 6 lists the bill of quantities

expected for the electrical system designs (it does not include any civil works). Section 7 contains

important information for the procurement process requirements as well as additional considerations

which must be adhered to in the tendering and installation process. Although all areas of the

document will be relevant for tendering, supplier should take special note of underlined text which is

meant to be directly applicable to their tendering documents.

2 Technical Needs Assessment and Design Process

The needs assessment and design process described herein is meant to inform the procurement team

at Concern Universal on the specifications for the desired solar PV Systems installed at Kandeu and

Mandrade. Suppliers for the Solar PV systems will base their tenders on this document.

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Figure 1 - Map of Project Locations

The technical needs assessment was carried out between 14th to 17th March 2016 in two target

villages of Kandeu and Mandrade. This work was carried out by WASHTED and based on the needs

and marketable solar PV-based projects as determined in the SOGERV Needs Assessment and

Market Assessment. Following the field visits, system sizing and technical designs were drafted with

assistance from the University of Strathclyde.

At each site the following activities were undertaken:

• GPS coordinates of the schools and health facilities

• Area of the buildings

• Inspection and determination of structural strength of the roofs and walls

• Determination of mobile network connectivity

• Cable lay out for lighting and PV system wiring

• Optimal electrical equipment positioning

• System security issues assessed

Global Positioning System (GPS) coordinates were collected by using Garmin Etrex 30X Model. Key

health and educational personnel interviewed. The goal of the interviews was to ensure that key

informants participate in the technical needs assessment and contribute to the process of system

design. Twenty households were interviewed to determine the strength of signal for three mobile

service providers including TNM, Airtel and MTL in the area. The team used mobile phones to verify

mobile signal availability at each household around the three selected villages. This was for the

purpose of future remote monitoring deployment.

The physical strength of the health and school walls was checked by verifying whether the walls were

built using burnt bricks or cement blocks. The strength of the roofs were physically checked to

determine whether they could withstand the panel mounting structure and by asking the staff how long

the roofs have been in existence with or without repairs. The building cross-sectional area was

measured by using a measuring tape. We measured the length, width and height (up to truss

horizontal members). Unless specifically mentioned, all the sites are suitable for solar PV installation

using the provided designs.

The sizing of the solar photovoltaic systems was conducted using two IEEE standards which govern

stand-alone PV sizing: IEEE 1013 and 1562 for lead acid batteries and solar PV array, respectively.

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The approach in IEEE 1562 was altered slightly as some systems would use MPPT controllers rather

than PWM controllers as prescribed in the standard. The demand estimation approach involved

estimation based on facility space measurements and interviews with users, where appropriate.

Separate demand estimations were taken from the business model designs which were completed

concurrently to the technical designs. All assumptions on use are included within the design

specification for reference. Further research on energy-use appliances was informed by current

market offerings and desk study of potential suppliers. Further details of the design methodology are

explained in the following sections.

The technical sizing calculation uses an average daily load and minimum daily insolation as key inputs.

Key characteristics for the solar panel array, batteries, charge controllers, inverters, and cable sizing

can be calculated through the appropriate sizing calculation. Any system which had an average daily

demand of 500Wh or more would have a 24VDC nominal system voltage. All other systems are

12VDC nominal voltage. All systems would include an MPPT controller to increase the overall

efficiency of the system. The option to use 48VDC was avoided as this equipment is relatively less

available. Due to the unavailability of DC-based appliances in country, all loads are AC side with the

exception of the DC refrigerators. The power consumption of AC refrigerators was considered too

high.

3 System Summary

The systems installed in the first phase of SOGERV installations in Kandeu and Mandrade are

summarized below. The number of system is based on estimation of system costs, the available

SOGERV capital budget and the business model designed for Kandeu and Mandrade.

3.1 Kandeu Solar PV Systems

(1x) Kandeu Primary Classroom Block 24V DC / 240V AC, 340Wp, 4.9kWh

(1x) Kandeu Health Post 24V DC / 240V AC, 340Wp, 7.34kWh

(1x) Kandeu Charging Station 24V DC / 240V AC, 2.5kWp, 43.2kWh

(2x) “Large” Entrepreneur Systems 12V DC / 240V AC, 240Wp, 3.7kWh

(2x) “Small” Entrepreneur Systems 12V DC / 240V AC, 120Wp, 2.4kWh

3.2 Mandrade Solar PV Systems

(1x) Mandrade Primary Classroom Block 24V DC / 240V AC, 340Wp, 4.9kWh

(1x) Mandrade Health Centre 24V DC / 240V AC, 500Wp, 7.34kWh

(1x) Mandrade Charging Station 24V DC / 240V AC, 2.5kWp, 43.2kWh

(2x) “Large” Entrepreneur Systems 12V DC / 240V AC, 240Wp, 3.7kWh

(2x) “Small” Entrepreneur 12V DC / 240V AC, 120Wp, 2.4kWh

4 Design Methodology

4.1 Load Estimation

The watt hour per day for each appliance was calculated and summed to get the total watt hours per

day (Wh/day) for all appliances. This is also known as the daily energy requirement. Thereafter, the

maximum current draw from the system was calculated by adding the wattage for all the appliances,

which is another key input into the sizing estimations. For systems with no available structure at the

time of writing this design specification (i.e. charging stations and entrepreneur systems) demand

estimation was based on known or researched appliance ratings and expected usage patterns (e.g.

charging cycles of 12V batteries). Load estimations and assumptions are included within each system

design specification in the following sections.

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4.2 Battery Sizing

The approach for battery sizing follows IEEE Standards and has been explained previously. The main

calculations are described in this section.

The required battery type is sealed deep cycle lead-acid battery (also known as “solar”, “SLA”, or

“Maintenance-Free”). It is specifically designed to be discharged to low energy level and rapid

recharged or cycle charged and discharged day after day for years. The design team adjusted the

days of autonomy to either 3 (most systems) or 4 (health systems) days from the standard approach

(specifying between 6 and 14) due to prohibitively high cost of this level of reliability.

Nominal system voltage was set at 12V for systems with a maximum daily energy requirement of less

than 500Wh, otherwise it was set at 24V.

Then the maximum daily load in watt-hours was calculated by diving the unmodified daily energy

requirement from the demand estimation by assumed inverter losses. All systems were designed to

include an inverter and hence be fed from an AC source due to more widely available appliances

running from inverters. Inverter efficiency was assumed to be 88% for 12V based systems or 95% 24V

based systems. Larger systems were assumed to have more efficient inverters.

The maximum daily load from was calculated as shown below.

[1] Maximum Daily Load (Wh) =Unmodified Daily Energy Demand Requirement (Wh)

(1−Inverter Losses)

This can be expressed in amp-hours (Ah) by dividing [1] by the nominal voltage.

The unadjusted battery capacity was found by multiplying [1] by the days of autonomy.

A maximum Depth of Discharge (MDoD) was assumed to be 50%. A capacity adjusted for MDoD was

calculated as shown below.

[2] 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝐴𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝑓𝑜𝑟 𝑀𝐷𝑜𝐷 =𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝐷𝑎𝑖𝑙𝑦 𝐿𝑜𝑎𝑑 (𝐴ℎ)

𝑀𝐷𝑜𝐷

The capacity for End of Life (EoL) was assumed to 80%. Then the capacity for EoL was found as

shown below

[3] 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝐴𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝑓𝑜𝑟 𝐸𝑜𝐿 (𝐴ℎ) =𝑈𝑛𝑎𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 (𝐴ℎ)

𝐸𝑜𝐿

The standard takes the adjusted capacity by taking the largest adjustment due to EoL or MDOD; in this

case MDOD was relevant for all systems.

In the design for battery sizing, a minimum temperature of 20.5°C was taken from the World Bank

Solar Resource Report as the month with the lowest average temperature. This produced a

temperature correction factor of 1.048 which affect both battery life and capacity. This factor further

adjusted battery capacity as shown below

[5] Temp. adjusted 𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 (𝐴ℎ) = 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑎𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝑓𝑜𝑟 𝑀𝐷𝑜𝐷 ×

𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝐶𝑜𝑟𝑟𝑒𝑐𝑡𝑖𝑜𝑛 𝐹𝑎𝑐𝑡𝑜𝑟

The design margin for the system operation was assumed to 1.2. The design margin is typically

incorporated to account for errors in the demand estimation process and load growth. Incorporation of

this margin determines the final battery capacity requirement as shown below

[6] Final Battery Capacity Requirement (𝐴ℎ) = 𝑇𝑒𝑚𝑝. 𝑎𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 ×

𝑑𝑒𝑠𝑖𝑔𝑛 𝑚𝑎𝑟𝑔𝑖𝑛

Due to the availability of batteries at 12V and capacity of 102 Ah, most systems were assumed to use

these batteries. The larger charging stations were assumed to use 150Ah 12V batteries.

The number of series batteries for system was found by:

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[7a] 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑆𝑒𝑟𝑖𝑒𝑠 𝐵𝑎𝑡𝑡𝑒𝑟𝑖𝑒𝑠 =𝑆𝑦𝑠𝑡𝑒𝑚 𝑉𝑜𝑙𝑡𝑎𝑔𝑒

𝑆𝑒𝑙𝑒𝑐𝑡𝑒𝑑 𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝑉𝑜𝑙𝑡𝑎𝑔𝑒

The number of parallel batteries for system was found by:

[7b] 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑃𝑎𝑟𝑎𝑙𝑙𝑒𝑙 𝑆𝑡𝑟𝑖𝑛𝑔𝑠 =𝐹𝑖𝑛𝑎𝑙 𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑅𝑒𝑞𝑢𝑖𝑟𝑒𝑚𝑒𝑛𝑡 (𝐴ℎ)

𝑆𝑒𝑙𝑒𝑐𝑡𝑒𝑑 𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 (𝑒𝑖𝑡ℎ𝑒𝑟 102𝐴ℎ 𝑜𝑟 150𝐴ℎ)

The total number of batteries for system was found by:

[7c] 𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑎𝑡𝑡𝑒𝑟𝑖𝑒𝑠 = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑆𝑒𝑟𝑖𝑒𝑠 𝐵𝑎𝑡𝑡𝑒𝑟𝑖𝑒𝑠 × 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑃𝑎𝑟𝑎𝑙𝑙𝑒𝑙 𝑆𝑡𝑟𝑖𝑛𝑔𝑠

12V 102Ah batteries were selected for design estimation, as these are common size and known to be

widely available in Malawi. A 12V 150Ah battery was chosen specifically for the charging station. It

was assumed that batteries would be wired such that nominal voltages meet the required level.

Hence, the total installed battery capacity per system is:

4.3 Panel Sizing

The PV panel sizing must account for system losses, the level of resource, and dynamic effects in

order to ensure the batteries are charged sufficiently and load demand is met. The methodology for

sizing the system is described in this section.

The assumed system losses are calculated using the efficiencies of the components shown in the

table. These values are all within the typical ranges provided by the standards, and agreed to by the

design engineers as quite reasonable for the context.

Parameter Value

Parasitic Load Controller 0.99

Coulombic Effect of Battery 0.90

Wire Losses 0.95

Module Mismatch Losses 0.95

Module Aging 0.90

Dust/Dirt 0.90

Table 1: Component Efficiency

Total system losses was therefore calculated as follows:

[8] 𝑆𝑦𝑠𝑡𝑒𝑚 𝐿𝑜𝑠𝑠𝑒𝑠 = 1 − ∏ 𝑐𝑜𝑚𝑝𝑒𝑛𝑒𝑛𝑡 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑖𝑒𝑠

This was 0.349 for all systems.

The Peak Sun Hours (5.07) for the design was obtained from the World Bank Malawi Solar Modeling

Report1 for Nsanje District worst month of July, which we assume has a similar solar resource to the

neighbouring Chikhwawa District.

The array to load ratio was assumed to be 1:1.3. The array to load ratio represents an oversizing

margin on the generation capability to account for load growth, errors in estimation, and to allow for full

charging of the system following the worst case scenario (all days of autonomy are used). This value

is within the recommended range defined by the Standard which allows for a range of 1.1 to 1.4.

A number of PV modules were considered for each system as shown in the table below.

Characteristics of the modules were based off of manufacturer specifications from known brands

available in Malawi.

Maximum Power (Pmax)

Open Circuit Voltage (Voc)

Maximum Power Point Voltage

(Vmmp)

Short Circuit Current (Isc)

Maximum Power Point

Current

10 22.40 17.40 0.63 0.58

20 22.40 17.40 1.23 1.15

70 22.40 17.40 4.30 4.02

85 22.40 17.40 5.22 4.89

1 http://documents.worldbank.org/curated/en/2015/07/24758967/solar-resource-mapping-malawi-solar-modeling-

report

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120 22.60 17.60 7.26 6.82

125 22.60 17.80 7.43 7.02

250 37.47 30.34 8.76 8.24

300 45.10 35.68 8.99 8.41

315 45.75 36.81 9.12 8.56

Table 2: PV Modules considered

The Maximum daily load from [1] must be supplied by the chosen set of panels incorporating any total

system losses [8] and the available resource (sun) and the array to load ratio. Thus the equality shown

below must be adhered to.

[9] 𝐷𝑎𝑖𝑙𝑦 𝐺𝑒𝑛𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑅𝑒𝑞𝑢𝑖𝑟𝑒𝑚𝑒𝑛𝑡 (𝑊ℎ) = 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑑𝑎𝑖𝑙𝑦 𝑙𝑜𝑎𝑑 (𝑊ℎ) ×

𝐴𝑟𝑟𝑎𝑦 𝑡𝑜 𝐿𝑜𝑎𝑑 𝑅𝑎𝑡𝑖𝑜 ÷ 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦

The Array Charging Current is found by:

[10] 𝐴𝑟𝑟𝑎𝑦 𝐶ℎ𝑎𝑟𝑔𝑖𝑛𝑔 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴) = 𝐷𝑎𝑖𝑙𝑦 𝐺𝑒𝑛𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑅𝑒𝑞𝑢𝑖𝑟𝑒𝑚𝑒𝑛𝑡 (𝑊ℎ) ÷

(𝑆𝑠𝑦𝑠𝑡𝑒𝑚 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 × 𝑃𝑒𝑎𝑘 𝑆𝑢𝑛 𝐻𝑜𝑢𝑟𝑠)

The number of series connected PV modules was calculated as:

[11] 𝑁𝑜. 𝑆𝑒𝑟𝑖𝑒𝑠 𝑐𝑜𝑛𝑛𝑒𝑐𝑡𝑒𝑑 𝑝𝑎𝑛𝑒𝑙𝑠 = 𝑁𝑜𝑚𝑖𝑛𝑎𝑙 𝑆𝑦𝑠𝑡𝑒𝑚 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 ÷ 𝑁𝑜𝑚𝑖𝑛𝑎𝑙 𝑚𝑜𝑑𝑢𝑙𝑒 𝑣𝑜𝑙𝑡𝑎𝑔𝑒

The number of parallel connected PV module strings was calculated as:

[12] 𝑁𝑜. 𝑃𝑎𝑟𝑎𝑙𝑙𝑒𝑙 𝑠𝑡𝑟𝑖𝑛𝑔𝑠 = 𝐴𝑟𝑟𝑎𝑦 𝐶ℎ𝑎𝑟𝑔𝑖𝑛𝑔 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴) ÷ 𝑃𝑒𝑎𝑘𝑀𝑜𝑑𝑢𝑙𝑒 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐼𝑀𝑃𝑃)

The total number of array modules was calculated as:

[13] 𝑇𝑜𝑡𝑎𝑙 𝑁𝑜. 𝐴𝑟𝑟𝑎𝑦 𝑀𝑜𝑑𝑢𝑙𝑒𝑠 = 𝑁𝑜. 𝑆𝑒𝑟𝑖𝑒𝑠 𝑐𝑜𝑛𝑛𝑒𝑐𝑡𝑒𝑑 𝑝𝑎𝑛𝑒𝑙𝑠 × 𝑁𝑜. 𝑃𝑎𝑟𝑎𝑙𝑙𝑒𝑙 𝑐𝑜𝑛𝑛𝑒𝑐𝑡𝑒𝑑 𝑠𝑡𝑟𝑖𝑛𝑔𝑠

The final PV array size in Watts-peak was:

[14] 𝐹𝑖𝑛𝑎𝑙 𝐴𝑟𝑟𝑎𝑦 𝑆𝑖𝑧𝑒 (𝑊𝑝) = 𝐴𝑐𝑡𝑢𝑎𝑙 𝑁𝑜. 𝑜𝑓𝑀𝑜𝑑𝑢𝑙𝑒𝑠 𝑥 𝑃𝑀𝑎𝑥

The PV design approach deviated from the Standard approach since SOGERV systems will use a

maximum power point tracker (MPPT) controller rather than a PWM controller as expected in the

Standard. The Standard sizing methodology is based on average daily load in Amp-hours and not

wattage, which is more suitable when using MPPT.

4.4 Charge Controller Sizing

Charge controllers must operate within specific voltage, amp or watt ranges to ensure the safe

charging conditions. Most charge controllers will control both the input and output charging currents.

A variety of charge controllers were considered for each system as shown in the table below.

Manufacturer Model type Compatible System Voltage

Max Input Voltage

Max operating power (W)

STECA Solarix MPPT 2010 MPPT 12V, 24V 75 125/250

STECA Solarix MPPT 1010 MPPT 12V, 24V 100 250/500

Morningstar SunSaver MPPT MPPT 12V, 24V 75 200/400

Morningstar Prostar MPPT-25 MPPT 12V, 24V 120 350/700

Morningstar Prostar MPPT-40 MPPT 12V, 24V 120 550/1100

Morningstar Tristar MPPT-30 MPPT 12V, 24V, 48V 150 400/800/1600



Victron Easy solar 24/1600/40 MPPT 24 100 1400

Victron MPPT 100/15 MPPT 12V, 24V 100 400

Victron Bluestar MPPT 150/100 MPPT 2V, 24V, 48V 145 2900

Table 3: Charge controllers considered and characteristics

The design minimized the overall number of charge controllers on each system. A 10% safety margin

was added to all relevant input and parameters to select the model. Since it is assumed that 24V

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equipment is more readily available, it was further assumed that all charge controllers would operate

on 24V for the larger system and 12V for smaller systems. Finally, as all systems have loads on the

AC side, the inverter size is most relevant for constraints due to load characteristics. Thus, the

requirements for the charge controller we determined as follows.

[16] 𝑀𝑎𝑥 𝑂𝑝𝑒𝑟𝑎𝑡𝑖𝑛𝑔 𝑃𝑜𝑤𝑒𝑟 = 𝑃𝑀𝑎𝑥 × 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑃𝑎𝑛𝑒𝑙𝑠 × 1.1

𝑀𝑎𝑥 𝑃𝑉 𝑂𝑝𝑒𝑛 𝐶𝑖𝑟𝑐𝑢𝑖𝑡 𝑉 = 𝑃𝑎𝑛𝑒𝑙 𝑉𝑂𝐶 × 𝑁𝑜. 𝑃𝑎𝑛𝑒𝑙𝑠 𝑐𝑜𝑛𝑛𝑒𝑐𝑡𝑒𝑑 𝑖𝑛 𝑆𝑒𝑟𝑖𝑒𝑠 × 1.1

𝑀𝑎𝑥 𝐶ℎ𝑎𝑟𝑔𝑖𝑛𝑔 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 = 𝐼𝑆𝐶 × 𝑁𝑜. 𝑃𝑎𝑛𝑒𝑙𝑠 𝑐𝑜𝑛𝑛𝑒𝑐𝑡𝑒𝑑 𝑖𝑛 𝑃𝑎𝑟𝑎𝑙𝑙𝑒𝑙 × 1.1

For most systems there are multiple options for controller with a very straightforward configuration. In

the case of the charging station, multiple charge controllers are needed which adds an additional

constraint. All charge controller selections are specified within the individual system designs.

4.5 Inverter Sizing

For all systems, load is supplied on the AC side. With PV systems this requires the conversion of the

native DC to AC through an inverter. Although high quality inverters provide electrical protection

against overuse, a safety margin 30% was used in the design to increase the rating of the inverter to

avoid damage. In the demand estimation, it was assumed that loads could potentially be connected all

at once. Although it is unlikely that this will be the case, the maximum running power can be

determined as follows:

[17] 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑅𝑢𝑛𝑛𝑖𝑛𝑔 𝑃𝑜𝑤𝑒𝑟 (𝑊) = ∑(𝐼𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙 𝑎𝑝𝑝𝑙𝑖𝑎𝑛𝑐𝑒 𝑊 𝑟𝑎𝑡𝑖𝑛𝑔) ÷

𝑖𝑛𝑣𝑒𝑟𝑡𝑒𝑟 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦

The requirements for the inverter are:

[18] 𝑀𝑖𝑛. 𝐼𝑛𝑣𝑒𝑟𝑡𝑒𝑟 𝑅𝑎𝑡𝑖𝑛𝑔 (𝑊) = 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑅𝑢𝑛𝑛𝑖𝑛𝑔 𝑃𝑜𝑤𝑒𝑟 × 1.3

9

5 Designs

5.1 Kandeu Solar PV Systems

5.1.1 (1x) Kandeu Primary School Classroom Block – 24V DC / 240V AC, 340Wp / 4.9kWh (204Ah)

Load estimation

Load

Description Qty

Load

Voltage

(V)

Load

Current

(A)

Device

Power (W)

Total

Power

(W)

Daily

Usage

(Hrs/day)

Weekly

Usage

(days/week)

Avg. Energy

(AC) Watt

hours /day

Internal

lights 16 240 0.03 6 96 3 7 288

External

lights 2 240 0.05 11 22 11 7 242

TV 1 240 0.15 35 35 3 7 105

Total Power Rating 153 Average Daily AC

Energy Demand 635

Circuit ratings

MCB

Rating CCT

Load

Description Qty

Device

Power

(W)

Load

Voltage

(V)

Cct

Current

(A)

Cumulative

Power (W)

Cct

Current

Rating

(A)

Cct

Power

Rating

(W)

5A LGT/CCT1 Internal lights 8 6 240 0.2 48.00 0.2 48.00

5A LGT/CCT2 Internal lights 8 6 240 0.2 48.00

0.3 70.00 External lights 2 11 240 0.09 22.00

10A PWR/CCT1 TV 1 35 240 0.15 35.00 0.15 35.00

Total Current Rating 0.64

Total Power Rating 153.00

Technical specification

Parameter Value

Nominal System Voltage 24V DC

Average Daily Energy Requirement 635 Wh/day

PV module specification (4x) 85Wp Polycrystalline panels

Total Array Size 340 Wp

Panel Configuration 2 parallel strings; each consisting of 2 series modules

Station Batteries (4x) 12V 102Ah Deep Cycle, Sealed Lead Acid Maintenance Free/Gel Batteries. 50% DOD

(An equivalent configuration proposed by supplier will be considered)

Total Battery Capacity 204Ah (at nominal system voltage)

Total Energy Storage 4.9 kWh

Battery Configuration 2 parallel strings; each consisting of 2 series batteries

Charge Controller specification (1x) MPPT Charge Controller

Operating Power: 330W (min) - 500W (max)

Open Circuit V. (min): 30V

Module current / Load Current (min): 20A

Low Voltage Disconnect

Preferred Models: Morningstar PS-MPPT-25, Victron Bluestar MPPT 100/30, Steca Solarix MPPT 2010 or equivalent

Charge Controller configuration As per the circuit diagram

Inverter specification Input 24V DC

Minimum Peak Power output rating: 200Watts

Pure Sine Wave 230VAC 50Hz Output

Onboard Low-voltage disconnect (18.4V)

Inverter Configuration As per the circuit diagram

10

Electrical layout diagram

KANDEU SCHOOL CLASSROOM BLOCK CIRCUIT ARRAGEMENT FOR CONTROL OF AC LOADS

7.1

5 M

ETER

S

9.5 METERS 9.5 METERS

BATTERY BANK

ONE GANG SWITCH

TWO GANG SWITCH

INV INVERTER

CHARGE CONTROLLER

PANEL

LOW ENERGY LGT FITTING

DISTRIBUTION BOARD

DOUBLE SOCKET

Lighting circuits: 1.5MM2 STRANDED SINGLE CORE COPPER CABLE, 600/1000 V

Small power circuits (socket outlets): 2.5MM2 STRANDED SINGLE CORE

COPPER CABLE, 600/1000 V

See C

ontro

l Arran

gemen

t

DOOR

INVCC

CC

LGT/CCT 1

PWR/CCT 1

RATING OF PROTECTIVE DEVICE

LGT/CCT 1 -5ALGT/CCT 2 -5APWR/CCT 1 – 10ATo Battery – x 30A DP DC MCBFrom PV – x 32A DP DC MCBFrom Battery – x 30A DP DC MCBAC loads – x 10A SP MCB (SPARE)

Distribution Circuit Voltage: 230 V AC @ 50 Hz)

DC Generation Voltage 24V

CC

INV

AC LOADS

6mm2

10mm2

10mm2

10mm2

LOW ENERGY EXTERNAL LGT FITTING (IP54 rating)

LGT/CCT 2

Control Arrangement

ROOM 1 ROOM 2

FRONT

REAR

Sw1 controlling room 2 lightsSw2 controlling both external lights

Sw controlling room 1 lights

32A

32A

25A 25A

10mm2

10mm2 10mm2 1.5mm2 – LGT/CCT1

5A

2.5mm2 – PWR/CCT1

10A

1.5mm2 – LGT/CCT2

5A

AC DB

11

Control panel wiring arrangement

Additional Specifications

Isolators on DC side must be suitable for DC operation.

MCBs on AC side must be Type B

MCBs must comply with BS EN 61009-1

AC power circuits should be protected by 30mA RCBO device.

In order to restrict access to the electrical system components, a barrier (brick wall with locked

door) will need to be constructed around the batteries, charge controller, distribution board

within the classroom block. The current diagrams have not do not show the room which will be

built. The room should have sufficient accessibility to maintain the equipment and have proper

ventilation. Suppliers should explicitly plan to design and construct this component at each

school.

12

5.1.2 (1x) Kandeu Health Post – 24V DC / 240V AC, 340Wp / 7.34kWh (306Ah)

Load estimation

Load Description

Qty Load

Voltage (V)

Load Current

(A)

Device Power

(W)

Total Power

(W)

Daily Usage (Hrs/day)

Weekly Usage

(days/week)

Avg. Energy

(DC) Watt hours /day

Avg. Energy

(AC) Watt hours /day

Internal lights

4 240 0.03 6 24 3 7 72

External lights

2 240 0.05 11 22 11 7 242

Phone Charging

1 240 0.01 3 3 3 7 9

Microscope 1 240 0.13 30 30 3 7 90

Refrigerator 1 24 4.17 100 100 1.9 7 190

Total Power Rating 179 Average Daily DC Energy

Demand 190

Average Daily AC Energy

Demand 413

Average Total Daily

Energy Demand 603

Circuit ratings

MCB Rating

CCT Load

Description Qty

Device Power

(W)

Load Voltage

(V)

Load Current

(A)

Cumulative Power (W)

Cct Current

Rating (A)

Cct Power Rating (W)

5A AC LGT/CCT1 Internal lights

4 6 240 0.10 24.00 0.10 24.00

5A AC LGT/CCT2 External

lights 2 11 240 0.09 22.00 0.09 22.00

10A AC PWR/CCT1

Phone Charging

1 3 240 0.01 3.00 0.14 33.00

Microscope 1 30 240 0.13 30.00

10A DC DC PWR/CCT1

Refrigerator 1 100 24 4.17 100.00 4.17 100.00



Note: DC refrigerator should be connected via a fused connection unit (and not a standard

socket). The fused connection unit must be switched, double Pole, 13A, with neon & front flex

outlet


Parameter Value



PV Modules Specification (4x) 85Wp Polycrystalline panels

Voc=22.4V, Vmpp =17.4V, Isc=5.22A, Impp=4.89A

Total Array Size 340Wp

Array Configuration 2 parallel strings; each consisting of 2 series modules

Batteries Specification (6x) 12V 102Ah Deep Cycle, Sealed Lead Acid Maintenance Free/Gel Batteries, 50% DOD


Total Battery Capacity 306Ah

Total Energy Storage 7.34kWh

Number of Batteries 6


Charge Controller Specification (1x) MPPT Charge Controller





13

Preferred Models: Morningstar PS-MPPT-25, Victron Bluestar MPPT 100/30, Steca Solarix MPPT 2010 or equivalent

Inverter Specification Minimum Peak Power output rating: 300Watts




KANDEU HEALTH POST CIRCUIT ARRAGEMENT FOR CONTROL OF AC LOADS

9.0 METERS

8.7

ME

TERS

HEIGHT = 2.54 METERS

INV CC

LGT/CCT1

LGT/CCT2

BATTERY BANK

THREE GANG SWITCH

INV INVERTER

CHARGE CONTROLLER

PANEL

ROOM ENERGY SAVER BULB

CONTROL BOARD

CC





CIRCUIT VOLTAGES

SECURITY ENERGY SAVER BULB IN WELL

GLASS FITTING

PWR/CCT 1

DOUBLE SOCKET




DOOR

CC

INV

AC LOADS

6mm2

6mm2

6mm2

10mm2

Control Arrangement

32A

25A

25A 25A

10mm2

6mm2 6mm2

5A

10A

5A

ACDB

1.5mm2 – LGT/CCT1

2.5mm2 – PWR/CCT1

1.5mm2 – LGT/CCT2

One gang controlling open area lightsOne gang controlling room lights

One gang controlling both external lights

DC

FR

IDG

E

DC

PW

R/

CC

T 1

DC DB

DC LOADS

15A4mm2 – DC PWR/CCT1

25A

6mm2


14






5.1.3 (1x) Kandeu Charging Station 24V DC / 240V AC, 2.5kWp, 43.2kWh (1800Ah)

Load estimation

Load

Description Qty

Load

Voltage

(V)

Load

Current

(A)

Device

Power

(W)

Total

Power

(W)

Daily

Usage

(Hrs/day)

Weekly

Usage

(days/week)

Avg. Energy

(AC) Watt

hours /day

Internal lights 5 240 0.03 6 30 5 7 150

External lights 2 240 0.05 11 22 11 7 242

USB charging

hub 2 240 .33 78 156 3 7 468

Miscellaneous

Usage (e.g.

computer)

2 240 .13 30 60 4 7 240

4.5 Ah battery

charging 6 240 .08 20 120 8 7 960

12Ah battery

charging 6 240 .14 33.6 201.6 6 7 1209.6

24Ah battery

charging 4 240 .14 33.6 134.4 8 7 1075.2

50Ah battery

charging 3 240 .25 60 180 6 7 1080


Energy Demand 5424.8

Circuit ratings

15

MCB

Rating CCT

Load

Description Qty

Device

Power

(W)

Load

Voltage

(V)

Cct

Current

(A)

Cumulative

Power (W)

Cct

Current

Rating

(A)

Cct

Power

Rating

(W)

5A LGT/CCT1 Internal lights 5 6 240 0.03 30.00 .13 30.00

5A LGT/CCT2 External lights 2 11 240 0.05 22.00 .09 22.00

10A USB/CCT3

USB Charging 2 78 240 0.33 156.00

.775 186.00 Miscellaneous

Usage 1 30 240 0.13 30.00

10A PWR/CCT4 Miscellaneous

Usage 1 30 240 0.13 30.00 .13 30.00

10A CRG/CCT5 4.8AH Bat

Charging 6 20 240 0.08 120.00 .50 120.00

10A CRG/CCT6 12Ah & 20Ah

Charging 12 33.6 240 0.14 403.20 1.68 403.20

10A CRG/CCT7 50Ah

Charging 3 60 240 0.25 180.00 .75 180.00




Parameter Value


Average Daily Energy Requirement 5424.8Wh/day

PV modules (10x) 250Wp Polycrystalline panels


Total Array Size 2500W

Panel Configuration

Station Batteries (24x) 12V 150Ah Deep Cycle, Sealed Lead Acid AGM/Gel Batteries. 50% DOD





Charge Controller specification Required: (3x) Morningstar Tristar MPPT-60

Charge Controller configuration As per the charging station circuit diagram

Inverter specification

Input 24V DC




Inverter Configuration As per the charging station circuit diagram

5A 12V Battery Charger Specification

Preferred: (5x) RS Pro 12V 5 Lead Acid Battery Charger

Multistage charger (bulk, absorption, float)

Input: 240VAC 50Hz

Output current (bulk charge): 4.5-5.5A

16

Automatic shutdown

Reverse polarity, short circuit protection

2.8A 12V Battery Charger Specification

Preferred: (10x) TecMate OmptiMate 12V 2.8A Lead Acid Battery Charger

Multistage charger (bulk, absorption, float)

Input: 240VAC 50Hz

Output current (bulk charge): 2.8A-3.2A

Automatic shutdown

Reverse polarity, short circuit protection

1A 18V Battery Charger Specification

18V DC 1 Amp power supply

Input power plug: UK 3 Pin Mains Plug

Output: DC 18V 1 Amp

Input: 230VAC, 50Hz

Max Power Output: 20W

Output connector: DC 5.5mm plug

12V Household battery specification

(15x) x 12Ah SLA MF 12V Battery



USB charging bank specification

(2x) 10 port USB charging station

(or equivalent to 20 total charging ports)

Input: 230VAC 50Hz

Output: minimum 1A charging per port, maximum 2.4A per port

over-heat, over-current, over-charging protection, auto-shutoff after full charge

Maximum 150W concurrent load demand for all charging ports


18







5.1.4 (2x) “Large” Entrepreneur Systems 12V DC / 240V AC, 240Wp, 3.7kWh (306Ah)

Load estimation

Load

Description Qty

Load

Voltage

(V)

Load

Current

(A)

Device

Power

(W)

Total

Power

(W)

Daily

Usage

(Hrs/day)

Weekly

Usage

(days/week)

Avg. Energy

(AC) Watt

hours /day

Internal lights 2 240 0.03 6 12 5 7 150

Phone

charging 15 240 0.01 3 45 6 7 270


Energy Demand 330

Circuit ratings

MCB

Rating CCT

Load

Description Qty

Device

Power

(W)

Load

Voltage

(V)

Cct

Current

(A)

Cumulative

Power (W)

Cct

Current

Rating

(A)

Cct

Power

Rating

(W)


10A PWR/CCT2 Phone

Charging 15 3 240 0.01 45.00 .19 45.00

Total Current Rating .24



Parameter Value

19


Average Daily Energy Requirement

330 Wh/day




Panel Configuration






Charge Controller specification

(1x) MPPT Charge Controller





Preferred Models: Morningstar PS-MPPT-25, Victron Bluestar MPPT 100/30 or equivalent

Charge Controller configuration

As per panel configuration above


Input 12V DC



Onboard Low-voltage disconnect (10.5.4V)


Additional Notes

Structural layouts not known, but assumed to be 1 or 2 room building capable of supporting roof

mounted solar PV system. This will be clarified at a later date. Supplier may need to adjust design to

installations requirements when this is known.





5.1.5 (2x) “Small” Entrepreneur Systems 12VDC / 240V AC, 120Wp, 2.4kWh (204Ah)

Load estimation

Load

Description Qty

Load

Voltage

(V)

Load

Current

(A)

Device

Power

(W)

Total

Power

(W)

Daily

Usage

(Hrs/day)

Weekly

Usage

(days/week)

Avg. Energy

(AC) Watt

hours /day

Internal lights 2 240 0.03 6 12 5 7 60

Hair Trimmer 2 240 0.08 20 40 3 7 120

20


Energy Demand 180

Circuit ratings

MCB

Rating CCT

Load

Description Qty

Device

Power

(W)

Load

Voltage

(V)

Cct

Current

(A)

Cumulative

Power (W)

Cct

Current

Rating

(A)

Cct

Power

Rating

(W)


10A PWR/CCT2 Hair Trimming 2 20 240 0.08 40.00 .17 40.00

Total Current Rating .22



Parameter Value


Average Daily Energy Requirement

180 Wh/day



Total Array Size 120 W

Panel Configuration






Charge Controller specification

(1x) MPPT Charge Controller





Preferred Models: STECA Solarix MPPT 2010, Morningstar Sun Saver MPPT, Victron Bluestar Charge Controller MPPT 75/15 or equivalent

Charge Controller configuration

As per panel configuration above


Input 12V DC



Onboard Low-voltage disconnect (10.5.4V)


21

Additional Notes

Structural layouts not known, but assumed to be 1 or 2 room building capable of supporting roof

mounted solar PV system. This will be clarified at a later date. Supplier may need to adjust design to

installations requirements when this is known.





5.2 Mandrade Solar PV Systems

5.2.1 (1x) Mandrade Primary Classroom Block - 340Wp / 4.9kWh (204Ah)

System is equivalent to the Kandeu Primary School Block. Refer to section 5.1.1 for all designs.

5.2.2 (1x) Mandrade Health Centre – 24V DC / 240V AC, 500Wp / 7.34kWh (306Ah)

Load estimation

Load Description

Qty Load

Voltage (V)

Load Current

(A)

Device Power

(W)

Total Power

(W)

Daily Usage

(Hrs/day)

Weekly Usage

(days/week)

Avg. Energy

(DC) Watt hours /day

Avg. Energy (AC) Watt hours /day

Internal lights

10 240 0.03 6 60 3 7 180

External lights

2 240 0.05 11 22 11 7 242

Phone Charging

1 240 0.01 3 3 3 7 9

Microscope 1 240 0.13 30 30 3 7 90

Refrigerator 1 24 4.17 100 100 1.9 7 190

Total Power

Rating 215

Average Daily DC Energy Demand

190

Average Daily AC Energy

Demand 521

Average Total Daily

Energy Demand 711

Circuit ratings

MCB Rating

CCT Load

Description Qty

Device Power

(W)

Load Voltage

(V)

Load Current

(A)

Cumulative Power (W)

Cct Current Rating (A)

Cct Power Rating (W)

5A AC LGT/CCT1 Internal lights 10 6 240 0.25 60.00 0.25 60.00

5A AC LGT/CCT2 External

lights 2 11 240 0.09 22.00 0.09 22.00

10A AC PWR/CCT1

Phone Charging

1 3 240 0.01 3.00 0.14 33.00

Microscope 1 30 240 0.13 30.00

10A DC PWR/CCT2

Refrigerator 1 100 24 4.17 100.00 4.17 100.00



Note: DC refrigerator should be connected via a fused connection unit (and not a standard

socket). The fused connection unit must be switched, double Pole, 13A, with neon & front flex

outlet


Parameter Value



22

PV Modules Specification (2x) 250Wp Polycrystalline panels



Number of Modules 2

Array Configuration 2 parallel strings; each consisting of 1 series modules

Batteries Specification (6x) 12V 102Ah Deep Cycle, Sealed Lead Acid Maintenance Free/Gel Batteries (An equivalent configuration proposed by supplier will be considered)

Total Battery Capacity 306Ah

Total Energy Storage 7.34kWh

Number of Batteries 6


Charge Controller Specification (1x) MPPT Charge Controller





Preferred Models: Morning Star PS-MPPT-40, Morningstar Tristar MMPT-30, Victron Bluestar MPPT 100/30, or equivalent

Inverter Specification Input 24V DC





23

MANDRADE HEALTH POST CIRCUIT ARRAGEMENT FOR CONTROL OF AC LOADS

5.4 METER

S

7

12.3 METERS

INCC

LGT/CCT1

LGT/CCT2

PWR/CCT1

BATTERY BANK

ONE GANG SWITCH

TWO GANG SWITCH

INV INVERTER

CHARGE CONTROLLER

PANEL

ROOM ENERGY SAVER BULB

CONTROL BOARD

DOUBLE SOCKET

CC





CIRCUIT VOLTAGESSECURITY LIGHTS ENERGY SAVER BULB IN WELL GLASS

FITTING




DOOR

One gang controlling central area and corridor lights

One gang controlling both external lights

One gang controlling room lightOne gang controlling adjacent room light

DC

FR

IDG

E

DC PWR/CCT 1

CC

INV

AC LOADS

6mm2

10mm2

10mm2

16mm2

Control Arrangement

32A

32A

25A 25A

16mm2

10mm2 10mm2

5A

10A

5A

ACDB

1.5mm2 – LGT/CCT1

2.5mm2 – PWR/CCT1

1.5mm2 – LGT/CCT2

DC DB

DC LOADS

15A4mm2 – DC PWR/CCT1

25A

6mm2


Refer to control wiring arrangement for 5.1.2 Kandeu Health Post – 24V DC / 240V AC, 340Wp /

7.34kWh (306Ah).

5.2.3 (1x) Mandrade Charging Station 24V DC / 240V AC, 2.5kWp, 43.2kWh (1800Ah)

System is equivalent to the Kandeu Charging station See section 5.1.3

5.2.4 (2x) “Large” Entrepreneur Systems 12V DC / 240V AC, 240Wp, 3.7kWh (306Ah)

System is equivalent to the Kandeu Large Entrepreneur systems See section 5.1.4

5.2.5 (2x) “Small” Entrepreneur Systems 12VDC / 240V AC, 120Wp, 2.4kWh (204Ah)

System is equivalent to the Kandeu Small Entrepreneur systems See section 5.1.5

6 Bill of Quantities

Refer to spreadsheet and provide and detailed bill of quantities

24

7 Tendering Requirements and Additional Considerations

The specification contained within should be used as guidance for the systems designed and delivered

by suppliers. The ultimate responsibility of the adequacy of all the technical design decisions is held

by the supplier; if the supplier arrives at a different size than specified, a clear justification should be

provided for a change in the design approach.

7.1 Earthing and Lightning Protection

Several methodologies are acceptable. The design team prefers that the approach has supplier

input. Thus, a proposal for the earthing approach taken to ensure health, safety and level of

protection is required. As opposed to other elements in the proposal, supplier are expected to both

design and install this element. The approach should be both appropriate for the systems installed and

provide a sufficient level of protection, meeting any relevant national (MERA) standards.

Suppliers are required to provide a detailed earthing and lightning protection scheme within the

tendering document. Different approaches for different systems can be proposed if deemed

advisable. This approach should justify the appropriateness for the systems as well as the level

of protection provided such that the procurement team can evaluate. Specific mention should be

made within the tendering document. It is expected that further discussion and agreement on the

exact approach occur after selection.

7.2 Wiring Specifications

The cables used for wiring the solar PV system must be selected to ensure that they can withstand the

environmental, voltage and current conditions at which they may be expected to operate. The PV

system is comprised of AC and DC cable sections i.e. the DC cable section include PV array to Charge

Controller, Charge Controller to Battery Bank, Battery Bank to Inverter and Charge Controller to DC

Distribution Board; while the AC cable section is consistent with the system connected to AC side of

the inverter. These cable sections are specified according to the IET Wiring Regulations BS 7671.

The specified cable sizes and MCB/Isolator ratings are indicative. It is the responsibility of the

contractor to ensure the cables sizes and MCB/Isolator ratings are in accordance with the PV module

and battery specifications used by the contractor and the load estimations provided herein. Where

there are any differences to the cable sizes and MCB/Isolator ratings indicated in these preliminary

designs, the contractor should highlight these and provide full and detailed justification for these

changes.

The recommended IET (Wiring Regulations 17th Edition) approach to cable sizing is summarized as:

1. Determine the design current Ib

2. Select the rating of the protection on based on the calculated Ib

3. Select the relevant rating factors (see tables in IET wiring regs 17th Editions).

4. Divide In by relevant rating factors to give tabulated cable current-carrying capacity It.

5. Choose a cable size to suit It from IET tables.

6. Check voltage drop (max 3% allowed for lighting and 5% for power).

7. Check for thermal constraints.

Suppliers are required to acknowledge their ability to meet the wiring specification according to

this section. Specific mention should be made within the tendering document.

Suppliers are required to estimate their cabling length requirements. Specific mention should be

made within the tendering document.

7.3 Lighting Specification

External lighting on all systems must either meet the IP54 standard (or greater) or be installed within a

dust and water tight enclosure that prevents damage from weather effects. All proposed lighting

https://en.wikipedia.org/wiki/IP_Code

25

elements (indoor and outdoor) must be supplied and installed with a corresponding fixture (i.e. Edison

screw, etc.)

Suppliers are required to acknowledge their ability to meet the lighting specification according to

this section. Specific mention should be made within the tendering document.

7.4 Distribution Board Design Specification

The distribution board will be installed as follows to ensure minimal cable runs, safe installation, and

space for remote monitoring equipment that will be installed at a later date. A high quality of

workmanship is expected as demonstrated in the photograph below.

Suppliers are required to acknowledge their ability to deliver the distribution board design

according to this section. Specific mention should be made within the tendering document.

7.5 Station Battery Housing specification

If no sturdy platform exists, a battery housing must be constructed to support the batteries. Batteries

should be ventilated and raised off the ground a minimum of 5cm. Structure should be made from

Steel.

Suppliers are required to acknowledge their ability to construct the station battery housing

according to this section. Specific mention should be made within the tendering document.

7.6 Panel orientation and connections

All panels will be mounted at 18 degrees North Facing (+/- 2 degrees) to maximize the energy harvest.

Any mounting structures, roof or ground will need to be designed accordingly.

Since the orientation of the structures are not known, the supplier will be responsible for determination

of this and design of a suitable mechanical works.

MC Type 4 connectors should be used to wire the PV panels in the required series parallel

arrangement. Please see the example provided below showing 2 parallel strings with 2 panels in

series.

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Suppliers are required to acknowledge design responsibility for design and installation of the

mounting structure for the panels. Specific mention should be made within the tendering

document.

7.7 MERA Accreditation

Supplier must have current accreditation by the Malawi Energy Regulatory Authority (MERA) to design

and install electrical systems.

Suppliers are required to provide evidence of their accreditation within the tendering document.

7.8 Procurement officer checklist for all tenders

Supplier company and experience profile

Evidence of MERA accreditation, check against MERA confirmed

Proposed Timeline of installation

Bids for supply, design, and installation of all solar PV systems including specified per system

should be broken down with quantities and costs within the “SOGERV Tendering Document”

Supplier compliance with specifications 7.1 to 7.7

Supplier should include the “design specification for earthing and lightning protection”

document

Suppliers should explicitly explain any part of the bid which they will not be able to supply

along with a clear justification.

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