PHOTOVOLTAIC INSTALLATION GUIDELINES

Transcription

1 PHOTOVOLTAIC INSTALLATION GUIDELINES A guide to PV system design & installation A publication by Malta Intelligent Energy Management Agency Supported by Intelligent Energy Europe

2 Photovoltaic Installation Guidelines A Guide to PV System Design and Installation Prepared by Malta Intelligent Energy Management Agency Disclaimer The sole responsibility for the content of this publication lies with the authors. It does not necessarily reflect the opinion of the European Union. Neither the EACI nor the European Commission are responsible for any use that may be made of the information contained therein.

3 Foreword These guidelines have been prepared by the Malta Intelligent Energy Management Agency (MIEMA) for use by installers of PV systems in Malta. The Agency has been set up with the support of the Intelligent Energy Europe (IEE) programme and a number of public institutions, namely the Malta Tourism Authority, the Ministry of Finance, the Economy & Investment, the Ministry for Resources & Rural Affairs and Fondazzjoni Temi Zammit. Its aim is to promote a more intelligent use of energy resources.

4 Table of Contents Foreword Introduction Basic principles to follow Steps to follow to design an efficient PV system Steps to follow when installing a PV system System design guidelines Different system design options No battery backup systems Battery backup systems Mounting options Roof mount Shade configuration Building-integrated PV array (BIPV) System output estimation Different parameters affecting the output Estimation of the system output Supplier and system qualifications Pre-engineered systems Warranties System installation guidelines General Recommendations Materials recommendations Equipment recommendations Design and installation recommendations First stage: preparation Second stage: design Third stage: installation...17

5 1 Introduction Photovoltaic (PV) and solar water heater (SWH) technologies, as renewable energy sources (RES), present different advantages over more traditional energy generation technologies, and are more adaptive in particular applications. Photovoltaic systems are fuel-free, generate no noise and harmful emissions, and are relatively safe and reliable. They require minimal maintenance, and are very flexible technologies that provide energy to specific customized fields and applications. The Malta Intelligent Energy Management Agency (MIEMA), as Malta s first energy agency, focuses its activities on the achievement of a better use of energy resources, and in developing renewable sources in the country, thanks to the support of the Intelligent Energy Europe (IEE) Programme. As a result, the aim of this publication is to provide a technical information resource to those installing photovoltaic (PV) systems in Malta, as a list of guidelines for installers. This guide represents the current state-of-the-art in PV systems, both in design and in installation, and will therefore continue to be improved and updated online in the future. If you have any suggestion about further information or corrections on the subject, please do not hesitate to send your suggestions by to MIEMA (info@miema.org). Malta Intelligent Energy Management Agency 5

6 2 Basic principles to follow Thanks to a residential PV generating system, a homeowner is able to produce all or part of his/her daily electrical energy demand on his/her roof, exchanging daytime excess electricity for future needs (i.e. night-time demand). If the solar unit cannot produce for the entire house, the electricity is simply drawn from the utility, since the house remains completely connected to the electric network at all times. The system can also integrate a battery backup or uninterruptible power supply (UPS) in order to operate specific circuits in the house, during a utility outage. Concerning the technical design of the system, it is advisable for an installer to work with experienced and well-established firms that suggest pre-engineering packaged solutions. After the whole design has been chosen, attention to installation is very important: in fact, studies have proved that 10-20% of new PV plants experience installation problems that generate a significant loss of performance of the power unit. This document is therefore outlining the criteria that describe a quality system and key design and installation considerations that should be met to achieve the best results. 2.1 Steps to follow to design an efficient PV system 1. Select a packaged system that matches the demand of the owner. Customer concern for a system may include a reduction in the monthly electricity bill, environmental concern, desire for backup power, etc. So size and orient the PV array to provide the expected electrical power and energy. 2. Check if the roof area or other installation site is able to meet the demands of the desired system size. 3. Specify sunlight and weather resistant materials for all equipment that is to be set outdoors. 4. Choose the array to minimize shading from foliage, vent pipes, TV antennas and anything that can reduce the general performance of the system. 5. Design the system in compliance with all applicable building and electrical conventions. 6. Design the electrical system in order to minimize electrical losses due to wiring, fuses, switches and inverters. 7. Properly house and manage the battery system, should batteries be required. 8. Check that the design meets local utility interconnection requirements. 2.2 Steps to follow when installing a PV system 1. Ensure that the roof area or any other installation site is capable of handling the desired system size. Malta Intelligent Energy Management Agency 6

7 2. If the PV is roof-mounted, check that the roof is able to support the additional weight of the PV system. Improve or consolidate the roof structure if necessary. 3. Properly seal any roof penetrations with roofing industry approved sealing methods. 4. Install equipment according to providers specifications, using installation requirements and procedures from the manufacturers' specifications. 5. Ground the system parts to reduce the threat of shock hazards and induced surges. 6. Check for proper PV system operation by following the checkout procedures on the PV System Installation Checklist. 7. Ensure that the design meets local utility interconnection requirements. Malta Intelligent Energy Management Agency 7

8 3 System design guidelines 3.1 Different system design options When you design a PV system at a residence, you have two main electrical options: you design a system that interacts with the utility power grid and have no battery backup capacity, or a system that interacts with and integrates a battery backup. Figure 1 represents the general configuration of a PV residential system. Figure 1 General configuration of a PV residential system No battery backup systems This system is able to generate electricity only when the utility is available: if an outage occurs, the system is designed to shut down until utility power is restored. Different components of the system: PV Cell: electronic device that converts the solar energy into electricity, through the production of photons under the influence of sunlight. PV Module: serial assemblage of many PV Cells, protected by a coating material, to allow the use of the panels outside. The average area of a PV Module is between 1 and 5 square metres. PV Array: a collection of many PV Modules. Often sets of four or more modules are framed or linked by struts in what is called a panel, which is typically around 10 square metres in area. This allows some assembly and wiring operations to be done on the ground if called for by the installation instructions. Balance of System equipment (BOS): BOS includes mounting and wiring systems used to integrate the PV modules into the structural and electrical systems of the residence. The wiring system integrates a switch for the DC and AC sides of the DC/AC inverter, a ground- Malta Intelligent Energy Management Agency 8

9 fault protector, and an electrical overload protector for the PV modules. Currently, most systems include a combiner board, since most panes require fusing. Sometimes, the inverter integrates this fusing and combining function. DC/AC inverter: as PV modules generate DC power, the system has to integrate a convertor to transform the power into standard AC electricity that could be used by the house s devices. Metering: the system includes meters to provide information about the general performance. Some meters provide an indication of the home energy usage too. Utility switch: switch to control the use of the utility power. Figure 2 General scheme of a system with no battery backup Battery backup systems This type of system includes electricity storage in the form of a battery to keep critical load circuits in the house, in the case that a utility outage occurs. And as these outages are not exceptional cases in Malta, this kind of system can be very useful on the island. If an outage occurs, the unit disconnects from the electricity network and powers specific circuits in the house. These critical load circuits are wired from a sub-panel separated from the rest of the electrical circuits. If the outage occurs during the day, the PV array is able to assist the battery in supplying the house loads. If the outage occurs at night, only the battery supplies the load. The amount of time critical loads can operate depends on the amount of power they consume and the energy stored in the battery system. A typical backup battery system can provide about 8kWh of energy storage at an 8-hour discharge rate. In other words, the battery will operate a 1-kW load the average usage for a home for 8 hours. Additional components of the battery backup system: Batteries Battery charge controller Sub-panel for critical load circuits Malta Intelligent Energy Management Agency 9

10 Figure 3 Grid-Interactive PV System with a battery backup 3.2 Mounting options The first point to focus on is the way the PV array will be set on the house. There are several ways to install a PV array at a residence, depending on many parameters: The configuration of the house (roof, trees, buildings around, etc.) The array area you want to install (given the fact that generally, 1m² of PV array represents an electric capacity of around 100W). Access to the system, which could require an area of up to 20% of the total mounting area Roof mount The best and easiest place to put the PV array is usually on the roof of the building, the place most exposed to the sun. In this case, the PV array may be mounted above and parallel to the roof surface, without forgetting to keep a standoff of several inches for cooling purposes. Generally, for Maltese flat roofs, a separate structure has to be mounted to set an optimal tilt angle with the PV array. Figure 4 PV arrays without (left) and with (right) a separate structure Malta Intelligent Energy Management Agency 10

11 Important issues to consider in the case of a roof mounting: Support brackets: particular attention must be paid to the roof structure and the sealing of the roof penetrations. Generally, one support bracket is used for 100W of PV panels. In the case of a new construction, it is advisable to consult the architect to ensure proper coordination between the contractor laying the roof membrane and the PV array installer. Weight capacity: in the case of old buildings such as farmhouses and houses of character, masonry roofs are usually designed near the limit of their weight-bearing capacity. Particular attention must therefore be paid to the roof structure, to check if it could handle the additional weight of the PV system or whether some form of reinforcement might be necessary Shade configuration An alternative solution to roof mounting is to create a shade structure with the PV array: the structure can act as a patio cover or a deck shade. This configuration can include both small and large PV arrays, depending on the space available. Overall, this option will probably cost somewhat more than roof mounting, due to the structural works needed, but it is a good way to make use of the PV panels while saving on roof space. Figure 5 A Patio Cover with PV modules Before this option is chosen, the main issues to consider are: The angle of the system: it is necessary to check that the angle used for the patio cover matches the PV array requirements. Wind loads: some improvement may be necessary, compared with classic patio covers, to face the possible additional wind loads. Weight of the PV array: particular attention must be paid to the weight of the whole system, to check if it matches the structural limits of the shade support structure. Aesthetic aspect: module wiring, if visible from underneath, must be set in order to keep the installation aesthetically pleasing. Malta Intelligent Energy Management Agency 11

12 Maintenance: a simplified array access for maintenance has to be settled with the system Building-integrated PV array (BIPV) Introduced commercially in the 1990s, Building-Integrated Photovoltaic (BIPV) modules are becoming popular abroad in the construction of new buildings, replacing conventional materials in parts of the roof, skylights or even facades. In the case of flat roofs like ours, a thin film solar cell integrated to a flexible polymer roofing membrane may be installed. In new buildings, the initial cost can be offset more easily, as the owner/developer will save on the traditional building materials and labour costs. This factor is making BIPV one of the fastest growing segments of the PV industry. Even existing buildings may be retrofitted with BIPV modules. Facades of old buildings may get a new modern look (MEPA permitting), when such modules are mounted over the existing structure, whereas transparent or translucent PV modules can replace glass in windows or skylights. Figure 6 Example of a BIPV building: the CIS Tower in Manchester clad in PV panels 3.3 System output estimation Different parameters affecting the output Many factors affect the output of a solar power system. For example, the output is produced in proportion to the intensity of the solar radiation striking the PV array, but this solar intensity fluctuates throughout the day, as well as day to day, month to month, etc. As a result, it is essential to know and to study the influence of these factors on the final output to have realistic expectations of the electricity production, and of the economic benefits generated by such a system. Standard Test Conditions (STC): to compare the different products efficiencies, solar panels are tested in specific test conditions recreated in factories, called the STC. This consists in: a Malta Intelligent Energy Management Agency 12

13 temperature of 25 C, a solar irradiance of 1000W/m² (often considered as peak sunlight intensity, corresponding to clear summer noon time intensity), and solar spectrum as filtered by passing through 1.5 thickness of atmosphere (ASTM Standard Spectrum). These parameters are obviously different in the real situation, changing the final output of the system. Furthermore, modules have a production tolerance of +/-5% of the rating, which means that the module can produce 95W and be called a 100W-module : as a result, it is better to use the low end of the power output spectrum at a starting point (95W for a 100Wmodule). Temperature: when a solar module heats up, its efficiency decreases. And as the PV array is made to stay under the sun, the influence of the temperature has to be taken into account in the estimation of the system output. Generally, the typical reduction factor concerning temperature is around 89%. So the 100W-module has a real capacity of 95x0.89=85W under full sunlight conditions. Dirt/dust: the accumulation of dust on the PV array can reduce the output of the system, especially in Malta where the air can be very dusty. As a result, we must take into account a reduction factor of 93%. So the 100W-module, with eventual dust on its PV array, can generate a capacity of about 85x0.93=79W. Mismatch/wiring losses: an eventual module mismatch, and also the resistance in the system wiring, can generate some losses of power in the system. Even paying particular attention to this factor, it is very difficult to reduce these losses to less than 3% of the total capacity. DC/AC conversion: during the conversion process from DC power to common household AC power, some power is lost into the inverter. Generally, we consider that the efficiency of the inverter used in residential PV power systems, and of the wires from the rooftop array down to the inverter, is about 90% Estimation of the system output During an entire day, the power output will change because of the variation of the angle of sunlight striking the solar module during the course of that day. Thus, in order to carry out an estimation of the electrical output of the PV power output, many parameters have to be taken into account: Pitch of the PV array: obviously, the angle between the PV array and the roof will affect the general output of the system. Malta Intelligent Energy Management Agency 13

14 Figure 7 Pitch of the PV array affects the electricity generation Direction of the roof: particular attention has to be paid to the direction of the roof, or of the support of the PV array. In collaboration with the Institute for Electric Power Conversion of the University of Malta, MIEMA has conducted studies to estimate the energy output that might be expected from a classical PV system in Malta. For further details of such studies, kindly send an to MIEMA (info@miema.org). 3.4 Supplier and system qualifications Pre-engineered systems When designing a PV system, particular attention needs to be paid to the compatibility and specification of its different components, to avoid problems of size and layout matching. Unless the installer is familiar with the technology to check if the system integrator is competent, it is much safer to choose a supplier that provides pre-engineered systems Warranties In addition to a standard warranty, a PV system can be provided with different kinds of guarantees. These are generally the following: Product warranties: most components of the PV system have a product warranty, provided by their manufacturers. However, the life expectancies of the different components are generally very different: for example, if PV modules generally have a warranty of 20 years, inverters sometimes have a one-year warranty. This aspect must be taken into account when considering the global cost of the system and its longevity. System warranties: some warranties certify the life expectancy of the entire system for five years or more and take into account potential operational issues. For instance, some warranties certify the performance of the PV system. Malta Intelligent Energy Management Agency 14

15 Annual energy performance warranties: although very few systems are provided with such warranties, an energy performance warranty ensures that the system will generate a specific amount of energy every year, guaranteeing a consistent performance. This is particularly helpful to ensure that the customer does benefit from savings on his/her electricity bill. In such cases, a metering installation is necessary to verify the system power output. Malta Intelligent Energy Management Agency 15

16 4 System installation guidelines 4.1 General Recommendations This section provides a list of general recommendations to help the installer to choose the right materials, equipment and installation methods in order to set up a system that would be effective for many years Materials recommendations Use sunlight/uv resistant materials. Use appropriate roofing membranes and/or synthetic rubber roofing compounds when necessary. Materials have to withstand the high temperatures they are exposed to during the summer months in Malta. Isolate dissimilar metals (such as steel and aluminum) from one another using insulating washers, etc. Aluminum and concrete materials should not be placed in direct contact with each other. Stainless steel is preferred for fasteners Equipment recommendations All electrical equipment should be listed for the voltage and current ratings necessary for the application. All required over-current protection should be included in the system, with access for maintenance. All electrical terminations should be tightened and secured. Installation of the mounting equipment should be made according to the manufacturers specifications. Roof penetrations should be appropriately sealed using a method that does not impact the roof warranty. Between 9:00 am and 4:00 pm, the PV array should be free of shade. Even small obstructions such as vent pipes should be shifted in order to maximize the performance of the system. Malta Intelligent Energy Management Agency 16

17 4.2 Design and installation recommendations First stage: preparation In order to design the system to maximize the efficiency of the PV array, the first stage is a preliminary study of the residence s consumption. The most important preparatory steps are the following: Contact the Malta Resources Authority (MRA) to obtain information about PVs in Malta, such as grants, standards, etc. Get past electricity bills of the house and carry out a basic energy audit to find ways to reduce the electricity consumption (contact MIEMA for assistance). Choose the size of the PV system based on the budget, the available mounting area, and the energy reduction cost. Determine the physical size and dimensions of the PV array and all its components. This step is very important to know where and how the PV array is going to be mounted Second stage: design Design the system by going through the following steps: Determine where to place the PV array (roof or elsewhere). Choose the pre-engineered system package that contains the desired options, and the best supplier system warranty if this applies. Select system options making sure the equipment meets the guidelines of local incentive programmes, when these are available (check with MRA). Contact Enemalta to get the required documents for net metering. Choose the location for the PV array on roof plan (or wherever it is to be mounted). Determine the ideal location on the roof, taking into account the different obstructions (plumbing, etc.) which may need to be relocated. Measure the distance between each component of the system, and draw a diagram representing the whole design of the PV system Third stage: installation Finally, the last stage is the installation of the PV system. The main recommendations to focus on are the following: Check whether MEPA permits are required. Malta Intelligent Energy Management Agency 17

18 Check that all the equipment was provided and no evident damages are present. Review installation instructions for each component of the system. Calculate the approximate length of wire runs from the PV Array to combiner and inverter. Check capacity of PV array circuits, in order to determine the minimum wire size for current flow. This may need to be enlarged to reduce voltage drop. Size PV array wiring such that the maximum voltage drop at full power from the PV array to the inverter is no more than 3%. If an array combiner bow is set between the PV modules and the inverter, spread this voltage loss between the PV array-to-combiner wiring and the combiner-to-inverter wiring. Determine the length of wire between the inverter and the main service panel. Check if the panel is correctly sized to receive the PV breaker or whether it must be upgraded. When installing the PV array, install the roof mounts according to the manufacturer s directions. Before setting the PV modules on the structure, check the open circuit voltage and short circuit current of each module. To reduce installation time, use plug connectors to connect panels together. Do not use more attachment points or roof penetrations than specified in the drawings. Run properly sized wires between all the different components of the system. Check if all PV circuits are operating properly. Malta Intelligent Energy Management Agency 18