viable contracts for off-grid pv procurement

8/4/2019 Viable Contracts for Off-Grid PV Procurement

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Viable Contracts

For

Off-Grid PV Procurement


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ForewordBased on an original work by Jim Finucane and Christopher Purcell , I adapted the keydecision points that can affect the outcome of a project to provide the best solar

photovoltaic (PV) practices for Bhutan.

In simple words, I took the essence from Jim and Christopher to author a version for Bhutan.

For the non-energy specialists, it sets out an approach to project development andimplementation and provides the basic guidance on key risks and mitigating measures,which can serve as a checklist for discussions with PV and other experts.

Raaj SantoshChief Executive Officer

International Assignment Services(Independent Specialist: Super Reviewer)


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Acknowledgements

The original version of this work was prepared principally by Jim Finucane and Christopher

Purcell (Drawing on experiences and good practices from throughout the world) withguidance and assistance from a World Bank project team consisting of Anil Cabraal (WorldBank Senior Consultant), Kate Steel and Maria Hilda Rivera (The World Bank Africa EnergyUnit, AFTEG) and Bipulendu Bipul Singh (The World Bank, Energy Sector ManagementAssistance Program, ESMAP).

The observations and guidance presented in this report are based on the operationalexperience of the Jim Finucane and Christopher Purcell and other team members with PVprojects in more than 20 countries over the past 15 years in the Africa, Latin America andAsia regions.

They also draw on the reviews of a May 2010 Dar es Salaam workshop of PV experts andproject specialists, as well as from the July 2010 peer-review carried out by a group of WorldBank renewable energy specialists.


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Executive SummaryFor facilities in remote areas beyond reach of the national grid, photovoltaic (PV) systemsmay offer the most practical and least-cost way to access electricity. A PV system uses

predictable solar resources and has long been cost competitive with diesel generators andother alternatives.

If the electricity grid is not expected to arrive in the near future or if diesel fuel isunavailable or too expensive, a PV system may offer the least-cost technology for providingelectricity service.

While solar PVs have been deployed across the remote and rural areas in Bhutan to meetessential service needs of communities, its long-term sustainability has been below par , inpart due to lack of attention to proper design and provision of long-term maintenance

services.

Reliable, long-term operation requires that PV systems be well-designed and installed, usingequipment of sound quality.

Equally, if not more crucial for PV systems are the institutional arrangements that ensurethe uninterrupted recurrent funding for maintenance, repairs, component replacements,and spare parts. When any of these elements is missing, done poorly, or done in waysinappropriate to the context, system failures can result.

In past decade, technical reasons have often been cited for PV system failures. In certaincases, donor funds have been used to install multiple PV systems at the same facility.

Rather than repair components or replace batteries installed under a previous project, it hassometimes appeared easier to procure and install a new system under a new project.

But such an approach, which can only be sustained for as long as the chain of donor projectslasts, is ultimately wasteful. In such cases, rehabilitating older systems should beconsidered, along with putting in place viable long-term maintenance and fundingarrangements.

The key aim should be sustainability the reliable, cost-effective operation of a system overits design lifetime.

Any PV system presented at the design stage as the least cost solution for powering a homeor school or health clinic will only succeed as least cost if it operates over the long term.

To avoid the common pitfalls of many off-grid PV projects, a viable strategy for off-grid PVprocurement must be developed. Good practice guidance is provided on the key technicalrequirements for viable PV contracts.


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The key to success is maintenance continuity, and the basic rule is you get what you payfor.

While it is imperative that good maintenance capacities and practices be put in placetogether with viable institutional arrangements for funding post-project maintenance(including component replacements), the choice of approach depends largely onassessments of the local context.

In summary, this report offers practical operational guidance to procure PV systems in waysthat enhance cost effective supply and sustainable post-project operations.


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PV SYSTEM COMPONENTS ANDCONFIGURATIONS

In off-grid facilities, PV systems are either stand-alone or centralized configurations thatserve multiple units. The systems deliver either direct current (DC) or alternating current(AC).

The main system components are the PV panel, deep cycle battery, and charge controller; inaddition, an inverter is used in systems that deliver AC electricity.

PV Panel.

The PV panel or module consists of cells of thin semi-conductor material that convert

radiation from the sun into DC electricity. The panel is covered with a transparent materialthat is sealed for waterproofing and framed for easy mounting. Panels are mounted in asunny location (shade decreases performance) at a tilt, with the angle equivalent to thesites latitude or best energy capture, but not less than 15 degrees to facilitate run-off of rain, dust or snow.

Mono Crystalline, Poly Crystalline silicon and Amorphous silicon (thin film) panels certifiedto international standards with up to 25-year manufacturer warranties are generally a safechoice, although when companies go out of business or multiple mergers and sales occur,the practical viability of their warranties may come into question.

The long-term trends of declining costs and increasing conversion efficiencies for PV panelsare projected to continue. Panel costs now represent 40 % of initial installed system costs.

Deep Cycle Battery.

PV batteries, which store the energy generated by the panels, are easily the mostproblematic component of the off-grid PV system. They are also the most expensivecomponent on a life-cycle basis.

Deep-cycle, lead-acid batteries, with a life span of 5 years, are well-suited to PV systems,although they often are not available locally, which is an issue at the time of replacement.

Thus, deciding how to handle battery replacements should be tenaciously addressed duringproject preparation.

Charge Controller.

The charge controller protects the system investment and can lower life-cycle battery costs.It regulates the power from the panel to the battery, stops the charging when the battery is


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fully charged and cuts off the power from the battery to the loads when the battery isdepleted below a safe level.

Robust charge controllers with established track records that can optimize usable powerdelivered by the PV system are available using Maximum Power Point Tracking (MPPT)technology.

Inverter.

The inverter converts the batterys low -voltage DC electricity into standard AC voltageoutput, permitting the connection of a wide range of electrical appliances. If the system isused to power DC loads exclusively, an inverter is not needed.

For remote homes, stand-alone PV systems may be the most cost-effective solution to meetelectricity-service and reliability requirements.

Sustainability

Sustaining PV system operation in poor, remote communities can be problematic.

Without providing repair and maintenance, many systems become inoperative after 3 years.Reliable, long-term operation requires that PV systems be well-designed and installed, usingequipment of sound quality.

The key aim should be sustainability, which at the minimum is the reliable, cost-effectiveoperation of a system over its design lifetime. Any PV system presented at the design stageas the least-cost solution for powering a home will only succeed as least cost if it operatesover the long term.

Risk GuidanceProcurement and implementation rolloutdelays.

Design contracts with detailed technicalspecifications and strong certification,warranty, and commissioning conditions.

Standardize to as few building blocks aspossible.

Closely supervise equipment supply andinstallations.

Poor-quality, inefficient designs andequipment.

Over- or under-investment in wrongly-sizedsystems of too high or low quality.

Ensure technical system design by well-qualified PV specialists aware of current bestpractices and not linked to potentialsuppliers.

Consult with off-grid PV specialists and seekindependent review by super reviewers.


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Super reviewers think differently fromprocurement authors and can act aseffective 3 rd party quality assurance atkey points.

Source solar-resource data from websites ormaps; use month of least sunlight (worstcase model) as the design month.

Estimate system sizes usingbasic conversion ratios and estimatingfactors.

Design PV systems via an iterative process,considering:

current and near-term energy use (theintroduction of electricity may result in suchunanticipated demands as television sets + satellite receivers, video players, radio andmusic systems, computer-based distanceeducation, cell-phone charging);

best available solar resource data fromvicinity or databases that extrapolate

resources;

energy-efficient lights ( LED) and appliances(but do not set the number of lights orlighting quantity or quality too low);

Mandatory : good-quality components, usinginternational or equivalent standards forpanels, batteries, controllers, and energy-saving lights (LED);

Budget capacities to meet the recurrentcosts of maintenance, repairs, andcomponent replacements; and local O&Mcapacities, including maintenance providersat central, district, and village levels.

Lack of funds for battery replacements every4 years result in system shutdown.

Establish system ownership.

As a prudent rule of thumb, annualizedrecurrent costs should be estimated at about

15 % of the installed cost of stand-alonesystems, which would cover periodic


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replacements of major components, routinemaintenance, and repairs.

It would also include what is frequently notanticipated: support for essential tracking of system maintenance and performance,higher-level troubleshooting, andsupervision.

Failure to budget for and fund recurrentcosts is often the major factor in systemfailures.

Misuse, poor maintenance, and lack of maintenance or troubleshooting skills.

Secure firm commitments for recurrentbudgets for maintenance and componentreplacements.

Outsource maintenance to local communityor an NGO to build local-service capabilities.Recruit or retain staff in remote areas.

Sudden failures due to lack of systemperformance tracking and supervision.

Fix and enforce rules for system use andmaintenance.Be clear on the scope of PV systems (e.g.,they are not for ironing, cooking, or heatingwhich consume larger energy).

Ensure user training in appropriate use andload-management practices.

Track PV system maintenance andperformance to anticipate and addressproblems before failures occur.

Organise at least 4 visits a year to conductpreventive maintenance + cleaning the

components and if necessary change thepanel tilt angle to capture more energyduring seasonal sun paths.

Closely supervise contract implementation,maintenance, and performance.


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System Design Issues and Guidance

PV panel and battery sizing .

An option sometimes considered costeffective is to slightly increase the PV panelsize, possibly to compensate for reducingbattery size, particularly as the prices of PVpanels continue to decline.

While slightly oversized panels mightaddress a concern about not fully chargingbatteries, using slightly smaller batterieswould lead to allowing a greater depth of discharge

This can be risky as not fully chargingbatteries (during inclement weather) andallowing greater depth of discharge are bothassociated with reduced durability.

Using batteries in a cycling regime outsidetheir optimal regime can sharply reducebattery life and raise operational costs.

PV panel sizing for seasonal solar radiation.

In regions with pronounced, extended rainor cloud cover seasons as in Bhutan (at least6 months when the sunlight window is small)it may be possible to design a system toavoid increasing size of PV panels.

Maximum Power Point Tracking (MPPT)technology can be used in chargecontrollers.

MPPT unlike conventional PWM controllersare most effective under these conditions: Inwinter or cloudy or hazy days when the extrapower is needed the most.

Cold weather - solar panels workbetter at cold temperatures, butwithout a MPPT you are losing mostof that. Cold weather is most likely inwinter - the time when sun hours arelow and you need the power torecharge batteries the most.

Low battery charge - the lower thestate of charge in your battery, themore current a MPPT puts into them- another time when the extra poweris needed the most.

You can have both the above conditions atthe same time as in Bhutan.

Proven MPPT controllers are manufacturedin USA.

Battery choice.

The choices are typically locally available,

Installing quality, 4-7 years deep-cycle AGM

batteries and then replacing those insystems that are still operational.


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less expensive batteries versus higher-costbut longer-life, imported deep-cyclebatteries.

Life-cycle cost analysis points toward quality,genuine, deep-cycle batteries as the firstchoice if the long-cycle life can be realized.

True AGM battery is manufactured in USA.

Engineering design margins.

A good practice though not alwaysfollowed as it increases costs is to includemargins for temperature effects, componentdegradation over time, and other causes of losses in the performance and lifetime of components and systems.

Omitting engineering margins in the urgentrush to design minimally-sized and lowest-cost PV systems will compromise systemreliability and ultimately increase life-cyclecosts.

Technical standards.

Good practice is to require that PV systemcomponents meet international standardsand to send clear requirements fordocumentation of compliance.

There should be little, if any, compromise onstandards for the main components. Itwould be a mistake to bend to localcommercial or political interests.

Procedures for accepting certifications of equipment conforming to specificationsshould be practicable (multiple choice) andbased on independent assessment of local

capabilities.


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Procurements and

Contract ManagementMany off-grid PV projects flounder at the procurement stage. Non-conformance totransparency, equal opportunity and compromises during the procurement process set thestage for subsequent low system sustainability.

The table below highlights the PV procurement problems frequently encountered andactions to avoid them.

Problem GuidanceToo few qualified bidders and high prices,associated with:

Limited, late promotion; information notwidely distributed.

Small size of contracts: No certainty onfuture flow of contracts reduces interest of potential bidders, particularly large foreignsuppliers, most of which have limitedinterest in off-grid market.

Perceived high risk of non-eligibility of PVsystem equipment and barriers to prepare

bids deters bidders, particularly foreignbidders.

Bidders lack knowledge of remote projectcommunities.

Publicize the proposed specifications earlyand often beyond traditional sites via ADBand local newspapers; network and promotewidely.

Strategically phase and time procurements.Allow reasonable time of at least 3 monthsin order to comply with requirements. MostInternational bids (foreign bidders eligible)allow 3 months or more for a bidder to

present a bid proposal.

Dont pu rchase in instalments. Purchase inbulk to get benefits of discount in prices.This also will bring reputed and large foreignbidders to participate with advancedtechnologies. Phase deliveries, if bulkdeliveries are too large.

Use a web link to allow download of

complete bid documents so that prospectbidders can scrutinise their PV capacitiesprior to registration and formal purchase of bid documents.

Make it mandatory for foreign bidders towork with a local agent (preferably NGOswho work in remote communities) to

represent and install PV equipment.


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Poor-quality equipment and installations,associated with:

Not using international standards; unclearprocess for determining acceptability of alternative standards proposed by thebidder.

Unclear or inconsistent specifications.

Difficulties confirming that equipment andinstallations meet technical requirements;

lack of accredited facilities to testcomponents; expensive and time-consumingpre-shipment testing by contractedlaboratory; difficulties in determining whichlaboratories are accredited to performrequired certification.

Unclear process for acceptance of certifications and installations.

Specify multiple and if possible proven PVinternational standards.

Use qualified, independent PV professionalsfor technical design and supervision.

Use detailed specifications for equipmentand installations. State name, type andunique numbers of specifications if any tocomply.

Specify multiple and if possible proven PVinternational standards.

Set stringent requirements for documentingthat equipment conforms to specifications.

Allow multiple opportunities including

reasonable time of at least 90 days toestablish equipment eligibility.

Establish clear process for acceptingcertifications and installations with standardcommissioning checklist and forms.

Poor performance by winning firm,associated with:

Changed on-the-ground conditions.

Unforeseen logistical issues.

Poor, rushed installations, oftensubcontracted on a unit basis.

Rushed capacity building and training.

Lack of quality assurance by contractor.

Facilitate post-award contract modifications

based on changed conditions.

Bidders must work with a local agent whowill advise the prospect bidder on theground realities. In most cases this should bean entity that has experience is providingsuch services in remote areas.

Installation is a semi-skilled activity and mustbe executed by a trained member of the

local community although most NGOsprovide or facilitate this training through


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Late, inadequate supervision of installationsand maintenance in remote locations byimplementing agency.

their partners and have significant technicalhuman resources.

Provide strong supervision with professionaltechnical support for installations andmaintenance.

Procurement Method

International Competitive Bidding (ICB) is used, given the supply capabilities of PV contractsin multiple countries and that, in most cases, PV panels; true deep cycle AGM batteries,Controller and LED lamps will be imported.

A bidders conference, conducted can be an effective way to provide vital information aboutsites, distances and logistics, and organizational and environmental conditions.

Promotion and Publicity

Timely publicity increases awareness and provides an opportunity for smaller, usually localNGOs and firms that may not be individually qualified to form alliances.

Promotion should begin well before and extend beyond publication of mandatoryprocurement notices and official gazettes.

Publicity teasers can be posted on official websites and widely circulated as done thePhilippines Rural Power Project.

Targeted promotion of off-grid PV contracts covering regional and international renewableand solar energy networks can also widen the circle of potential bidders.

It is important to note that there is no restriction on the advance circulation of drafttechnical specifications and promotional information on the project concept, areas, andtimetable.

Phasing Deliveries and Scheduling

For large projects, phasing deliveries, say every 3 6 months, will accommodate thecapacities of smaller, often local NGO and firms. This should not be mistaken for notprocuring in bulk to enable discounts in price.

In many cases, phasing deliveries will also permit a good fit with the capacities of theimplementing agency to manage the tender and supervise implementation in multipleremote locations.


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Phasing deliveries also gives project managers the opportunity to steadily modify andimprove procurement details and align them with cumulative implementation experienceand lessons learned.

Procurements should be timed with an eye to the weather, local holiday seasons, andbusiness practices - conferences or events.

In many countries, it is advisable to avoid scheduling field visits for bidders conferencesduring intense rainy seasons or during major conferences or events or tender openings inearly December or closings in early January.

Bidder Criteria

To implement PV contracts, bidders must meet specific criteria, which should work as aneffective filter for deciding on their qualifications.

Specifically this must apply to the provider of PV panel as the warranty of PV panel runs upto 25 years.

The qualifications must include the financial condition of the bidder, production capabilitiesand supply experience.

The bidder should be required to list successful project experience in supply of PV Systems.

This criterion allows validation of PV panels and equipment and uncovers quality, technicaland delivery practices of the bidder during the bid evaluation process.

Installers are small NGOs or local firms that provide supervision and trained labour to installand maintain PV equipment at rural communities. They must be assessed for their capacityto implement at remote regions. This would require that installers possess the requisitetools, have trained human resources (who have been trained by a credible trainingorganisation in this field) and preferably based in remote regions where such installationsare likely to occur.

Typically installers provide for inception report, installation, commissioning, training localusers in operating the SHS, establishment of local-service capacities and after-sales services,maintenance services, record keeping and reporting.

The implementation plan will include personnel (trained credentials), schedule of transportto site, tools and equipment used for installations and whether these must be procured,timetables for inception report, delivery and installation in the communities, initialmaintenance and other services. Taken together (organization, personnel, scheduling andlogistics) these should form a whole that is practicable and capable of meeting the contractrequirements on schedule.


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Concise and unambiguous criteria ( specify type of certification with its name and uniquenumber) and forms should be included in the bid document package to reduce the risk thata bidder submits, wins, and is subsequently found not qualified. Due diligence is done onthe data and references provided by the winning bidder prior to contract award.

Viable PV Contracts.

The PV contract involves: (i) equipment supply and delivery; (ii) equipment installation andcommissioning; (iii) initial defect warranty - maintenance for 1 year.

Large tenders might attract the attention of large companies with the requisite financial andtechnical capacity. However major international PV companies focus almost exclusively onthe large and rapidly growing ON Grid-connected market.

A common scenario is that a large firm with adequate financial capability but minimal off-grid PV experience wins the contract, handles component sourcing and system integration,and subcontracts installations and maintenance to local NGOs or firms.

Good practice is usually to construct tenders of significant size to attract major internationalPV companies.

PV system packages: Standardized components.

Components should be standardized as much as possible on the sizes. Stick to one size of

panel, charge controller and battery across all facilities to facilitate interchange and lowerthe costs of installations, training, maintenance services, stocking of spares and componentreplacements, and supervision.

International Standards.

International or equivalent standards should be used for the main system components (i.e.,panels, batteries, controllers, and energy saving lights). This will strengthen the biddingdocument by reducing uncertainties for both bidders and evaluators and reduce the risk of supplying substandard equipment.

The leader in standards development for PV and the balance of system components is theInternational Electro technical Commission (IEC), which is representative of the committeesand working groups of standards agencies from most manufacturing countries.

Reference is also made to PVGAP certification, which has now been completely integratedinto IECEE-PV. However, as very few products bear the PVGAP mark and seal (only a fewmodels), this requirement is largely ineffective in practice.


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Equipment certification conforming to specifications

The bid documents should define how conformance of equipment with specifications is tobe documented.

With international standards and detailed specifications, qualification can be based onacceptable certifications by acceptable laboratories.

Thus, acceptance of equipment is based on acceptance of certifications, not on testsconducted for the project prior to shipping or after arrival in the country.

In any case the facilities to conduct the necessary tests are not available in Bhutan and atmost countries that require significant off-grid rural PV services.

The main components should be certified by laboratories with ISO 17025 accreditation toundertake the specific tests.

Panels and other components that have the Photovoltaic Global Approval Program (PV GAP)Quality Mark or the Golden Sun Quality mark issued by the China General CertificationCentre will have met this requirement.

The PV GAP Mark (www.pvgap.org) is administered by the IECEE (www.iecee.org ).

With the support of GEF and WB, China General Certification Center established andexecuted the National Certification Program for PV Products used in rural PV projectsemploying specifications (from which the charge controller PV GAP specification is derivedfrom) and named it as the Golden Sun Certification .

For details visit: http://www.cgc.org.cn/eng/news_show.asp?id=3

Note: Golden Sun = PV GAP = IEC when it comes to SHS certifications.

Guidance on International Standards for Off-Grid PV System Components.

System Component Equipment Standards and GuidancePanelsUse IEC standards or Golden Suncertification.

IEC 61215 Ed. 2.0 : Crystalline siliconterrestrial photovoltaic modules - Designqualification and type approval.

Golden Sun certification BatteriesUse IEC standards or PV GAP or Golden Suncertification.

IEC 61427 Ed. 2.0 : Secondary cells andbatteries for solar photovoltaic energysystems - General requirements andmethods of test.

PV GAP, PVRS 5ALead -acid batteries forsolar photovoltaic energy systems General
http://www.iecee.org/http://www.cgc.org.cn/eng/news_show.asp?id=3http://www.cgc.org.cn/eng/news_show.asp?id=3http://www.cgc.org.cn/eng/news_show.asp?id=3http://www.cgc.org.cn/eng/news_show.asp?id=3http://www.iecee.org/


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requirements and methods of test formodified automotive batteries.

Golden Sun certification Charge ControllersUse IEC standards or PV GAP or Golden Suncertification.

IEC 62509 Ed.1 : Battery charge controllersfor photovoltaic systems - Performance andfunctioning.

PV GAP, PVRS 6ACharge controllers forphotovoltaic stand-alone systems with anominal voltage below 50V accepted foruse in the IECEE PV scheme.

Golden Sun certification Energy-efficient LED lamps

Use ELI or PV GAP or IEC standards.

Accept Efficient Lighting Initiative standards(www.efficientlighting.net ) for low watt LEDlamps.

PV GAP, PVRS 7ALighting systems withfluorescent lamps for photovoltaic stand-alone systems with a nominal voltage below24 V.

IEC 60969 Ed 2: Self ballasted lamps forgeneral lighting purposes - Performance

Requirements.

Balance of System components and minorequipment (battery Enclosures / Boxes,panel mounting structures, switches, cablingand wiring, breakers and fuses and fuseholders)

Use IEC standards .

IEC 60669-1: Switches for household andsimilar fixed-electrical installations. Part 1:General requirements.

IEC 60227-1-4: Polyvinyl chloride insulatedcables of rated voltage up to and including450 V/750 V-Parts 1-4: Generalrequirements.

For battery enclosure and mountingstructure, require declaration of compliancewith the specifications and drawings andprovision of detailed drawings.

Solar Home System

Use IEC standards or Golden Suncertification.

Project Specification Certifiable.

IEC 62124-2004: PV stand-alone systemsDesign verification.

Golden Sun certification .
http://www.efficientlighting.net/http://www.efficientlighting.net/http://www.efficientlighting.net/http://www.efficientlighting.net/


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Warranties

The typical range of component performance warranties are as follows:

1. PV panels: 20 years to 80 % of original specified output.

2. Charge Controller: 3 5 years.

3. Batteries: 3 5 years.

4. LED Lights: 3-5 years.

The basic requirements for equipment performance would cover the following:

There would be a specified 1 2 year defect liability period on quality of equipmentand installation following acceptance, during which any omissions or faults would beattended to without cost to the purchaser.

Should a stipulated portion (e.g., 10 %) of any class of equipment fail within thespecified period, that whole class of equipment would be replaced by suitablecompliant equipment without cost to the purchaser.

Any failure of system components during their respective warranty periods, throughno act of negligence on the part of the user, would mean prompt on-site repair orreplacement, free of charge, by the contractor.

Equipment certification conforming to specifications

Some purchasers may wish to arrange for samples from winning bidders or pre-shipmentinspection of equipment by an independent, contracted inspection agency to ensure thatthe equipment to be shipped is, in fact, the certified equipment offered in the bid.

The main components of PV systems PV modules, controller and batteries arecommoditized , and there is seldom value in requesting samples from winning bidders or

visiting factories to inspect production.

Blueprint Installations

A useful first step is for the supplier to complete a series of pilot or blueprint installations ,hopefully in a relatively accessible location, which can be closely inspected by all keystakeholders together with technical PV specialists.

The purpose is for the contractor and implementing agency to reach agreement that theblueprint installations indeed meet all requirements prior to the start of a large, rapid

rollout of multiple installations. The blueprint installations are used as benchmarks for


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acceptance of future installations, as well as for training both installers and inspectors of installations.

RecommendationsBhutan has unique topography and climatic conditions which include high altitudes, lowatmospheric pressure, extreme temperature variations, cloud cover for almost 180 + days ina year, excessive rainfall during summer and heavy snow fall in winter at higher altitudes,etc.

In summer months it rains excessively and in winter it snows. In between Bhutan is coveredwith clouds. During spring and autumn there is medium to weak sunlight.

One way of balancing these topographic and climatic variables is to employ a chargecontroller that uses Maximum Power Point Tracking (MPPT) technology to harvestadditional 30% of energy in a given small sunlight window to recharge the batteries.

Another way to enhance would be to deploy PV panels with above average powerconversion efficiencies of crystalline silicon solar cells in modules.

MPPT Charge Controller

Maximum Power Point Tracking is microprocessor controlled. The charge controller looks at

the output of the PV panels, and compares it to the battery voltage. It then figures out whatis the best power that the panel can put out to charge the battery. It takes the panel voltageoutput and converts it to the best voltage (Step down Voltage to increase Current - Amps) toget maximum current (Amps) into the battery. It is Amps into the battery that counts. Thinkof it as a solar booster.

A conventional charge controller would not execute the above step optimizing. It simplypasses on the panel current using the battery setting voltage. So even if the panel can givemore current (Amp s) during high sunlight levels, the conventional controller wouldnt

know, which means the battery recharge would still be slow, implying the window of opportunity to quickly recharge the battery is lost during maximum sunlight.

Most modern MPPT's are around 93-97% efficient in the conversion. You typically get a 20to 45% power gain in winter and 10-15% in summer or more. Actual gain can vary widelydepending on weather, temperature, battery state of charge, and other factors.

MPPT's are most effective under these conditions:

In winter and during cloudy or hazy or days - when the extra power is needed the most.


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1. Cold weather - solar panels work better at cold temperatures, but without a MPPTyou are losing most of that. Cold weather is most likely in winter - the time when sunhours are low and you need the power to recharge batteries the most.

2. Low battery charge - the lower the state of charge in your battery, the more current

(Amps) a MPPT puts into them unlike the conventional charge controllers - anothertime when the extra power is needed the most.

3. You can have both of the above conditions at the same time.

Power Conversion Efficiencies

Power conversion efficiencies of PV modules play an important role in weak sunlightconditions. Weak sunlight occurs commonly during winter but it can also occur duringsummer when the region has excessive rainfall as in Bhutan.

Monthly Averaged Insolation Incident On A Horizontal Surface (kWh/m 2/day)

Lat 27.5Lon 90.433

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecAnnualAverage

22-yearAverage

3.91 4.37 4.79 5.43 5.47 5.19 4.92 4.66 4.38 4.53 4.13 3.82 4.63

Monthly Averaged Daylight Hours (hours)

Lat 27.5Lon 90.433

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Average 10.6 11.2 12.0 12.8 13.5 13.8 13.7 13.1 12.3 11.5 10.8 10.4

Although the above table shows an insolation of 5.47 kWh/m 2/day during summer, this datawhich is derived from a satellite doesnt factor the rainfall occurring during summer atBhutan implying that cumulative summer insolation data can be misleading.

Consequently, the sunlight window is either weak or shortened, implying sunlight is partiallylost to recharge the batteries in full. (A common reason for battery failure due toconsecutive deep discharges)

In winter the same applies except that it is excessive snow in higher regions and weakinsolation at lower regions.

It is in conditions such as above that a PV module of higher conversion efficiency becomesvital to keep the solar home systems balanced.


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System Components Factored to meet Bhutan conditions.

PV Panel.

PV panel with must be deployed. Moduleabove average power conversion efficienciesefficiencies range between 15% to 20%.

Charge Controller

Maximum Power Point Tracking (MPPT) Charge Controller - 10 Amps, 12 V must bedeployed factoring near growth in usage. MPPT charge controllers cost more thanconventional (PWM) controllers.

Panel and Battery Sizing

Table 1: Panel Size Without change in Scope (Load).

ESTIMATED DAILY ENERGY REQUIREMENTS AND PV SYSTEM SIZE

Appliance Units(no.)

Watts(W)

Use(hrs./day)

Watt(hrs. /day)

LED Lamp 3 3 5 45LED Night Lamp 2 0.5 8 8Radio / Music / Video Player 1 15 0 0TV 1 50 0 0Laptop 1 40 0 0Other - Phone Charger, etc. 1 30 2 60

Sub Total (Wh) 113

Margin near term growth in usage 0.25 28.25

Energy demand (per day) 141.25

Margin technical losses 0.5 70.625

Gross energy use (Wh/day) 211.875

Full Sun-Hours - Winter 3.82

PV system Panel size (Wp) 55


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Upon review you will find that I have maintained the current load as specified in the tender.I have assumed 1 unit of 30 W adapters that will charge a mobile phone in about 2 hours.

I have introduced usage options for a television set, radio and a laptop computer that has aZero (0) in usage column.

Margin near term growth in usage means usage could increase once electricity isintroduced. It also means that since I have retained the tender data, I needed a factor forincreased light usage in winter, when daylight hours fall to only 10.4 hours.

Keep in mind that lights are used post dusk and pre-dawn in rural communities. The tenderdata assumes 4 hours post dusk and 1 hour pre-dawn. It may not be sufficient.

Table 1.1: Battery Size Without change in Scope (Load).

BATTERY SIZE Volts 12

Number of Days of Battery Autonomy 5

Design Factor 1.5

Total Daily Load (Ah) 11.7708333

Battery Capacity (Ah) 88

I have retained the battery days of autonomy at 5 although for Bhutan it should be 6 ormore. Likewise I have assumed the indoor ambient temperature in higher altitudes duringwinter to be above 9 degrees centigrade and hence used a design factor of 1.5 although forBhutan it should be 1.6.

If I had increased the value of design factors in my calculations, it would have increased thecost of battery to unviable levels given the scope of solar application.

However, I assumed the SHS will be using a MPPT charge controller to harvest more solarenergy to recharge the batteries quicker and therefore w ouldnt need excess backup to

discourage deep discharge. A MPPT charge controller reduces the size of the battery toreasonable levels in addition to making the PV system efficient.


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Please use the accompanying spr eadsheet to model and conduct what if analysis . Keepthe watts 2nd column constant.

If I introduce Television viewing for only 4 hours every day, the size of the panel with itsbattery would change.

Likewise the capacity of the charge controller would also change implying the capacity tohandle a larger load from 7 Amps (that it currently states) to 10 Amps.

I recommended a 10 Amps charge controller to factor load growth (Only TV) so that thecharge controller can be retained when Television viewing is initiated at a future date. Anyload in addition to TV viewing would require a 20 A charge controller.

Table 2: Panel Size With change in Scope (Load)

ESTIMATED DAILY ENERGY REQUIREMENTS AND PV SYSTEM SIZE

Appliance Units(no.)

Watts(W)

Use(hrs./day)

Watt(hrs. /day)

LED Lamp 3 3 5 45LED Night Lamp 2 0.5 8 8Radio / Music / Video Player 1 15 0 0TV 1 50 4 200Laptop 1 40 0 0Other - Phone Charger, etc. 1 30 2 60

Sub Total (Wh) 313

Margin near term growth in usage 0.25 78.25

Energy demand (per day) 391.25

Margin technical losses 0.5 195.625

Gross energy use (Wh/day) 586.875

Full Sun-Hours - Winter 3.82

PV system Panel size (Wp) 154


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Table 2.1: Battery Size With change in Scope (Load)

BATTERYSIZE

Volts 12

Number of Days of Battery Autonomy 5

DesignFactor

1.5

Total Daily Load (Ah) 32.6041667

Battery Capacity (Ah) 245

You notice that if a beneficiary views television for 4 hours a day, the size of the PV paneland battery change to 154 W and 245 Ah against 55 W and 88 Ah for the current scope -(lights + mobile phone charging).

Conclusion

This brings us to the most important question in deploying PV systems: The Scope of SolarHome Systems. You will notice that the scope (including anticipated load growth) for a solarsystem must be known or set in prior unlike margin growth in usage which can be factoredwithin the scope during design calculations.

Scope of a SHS is the most important data prior to initiating a PV project (especially forthose who receive electricity for the first time) which ironically is explained in the last page.

The accompanying spreadsheet provides scenarios to model the scope. Once we have thescope frozen, everything else is computation.

viable contracts for off-grid pv procurement

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