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Successful long term operation

PV systems are expected to have a long life time successfully producing electricity at, or close to, their original output level for at least 20 years. It will take a few years for the PV system to generate the amount of energy used in its construction. Only after this point is reached is the system having a positive impact on climate change or oil depletion.

While the majority of PV systems operate well for many years, this is not always the case. A design that does not make it sufficiently easy for the occupants to check system performance will allow minor problem to persist and may significantly reduce energy production. Some systems may be wrongly installed and operate below expected performance for years before this is picked uPp. Others may develop minor problems which are not corrected, dramatically reducing energy production.

When large numbers of small systems are installed in new urban developments and then left with ordinary householders to operate with no professional back-up there are particular risks that poor performance may not be picked up. PV UP-SCALE has focussed on large scale urban developments and has been able to look at the lessons learnt from the larger developments installed in the past and how those lessons are being applied by the developers and builders installing PV on developments today.

Developers today are likely to have very limited knowledge and experience with PV. If PV systems are then passed on to householders with no knowledge of PV, no direct contact with the PV installers and no servicing and maintenance plan the opportunities for problems to be missed and energy production to be reduced are multiple.

This is particularly important for PV because it is not always obvious whether or not a PV system is operating as it should. PV systems operate silently and without movement. If a grid connected system has tripped out power is still available from the grid. The only way to tell if the system is working is to look out for warning lights or keep an eye on metering or monitoring data. If the operators do not know how to interpret this data problems may go undetected.

Information about the PV system will also need to be passed on if the building occupants change. The PV system is expected to last for over 20 years and occupants are likely to change in this time.

PV UP-SCALE has developed best practice guidance on how to ensure systems are designed, commissioned, handed over and maintained so that they are most likely to be kept in good operating order.

The recommendations particularly apply to the design and installation of PV systems in groups of houses or where PV systems are installed in buildings with no specific connection to renewable energy or electricity generation. In these situations extra care is needed to ensure the occupants are able to successfully operate the PV system on a long term basis.

With buildings such as schools or care homes it is important to make sure someone at the building “takes ownership” of the PV. For example at one site in Kirklees there was a fault showing on the display panel because one of the inverters was down however it was not noticed or reported for some time. An operator’s handbook was available however there had been personnel changes since the system was installed and no maintenance personnel reside on-site.

The situation is different if someone has made an individual decision to purchase and install a PV system. In that case they can be expected to have some understanding of the system, the quantity of electricity expected to be produced, the guarantees available and contact information for the supplier in the event of problems. But issues may still arise in later years if the house is sold. Providing maintenance information and contact points in a study format is still recommended.

The projects which have reported the greatest ease of operation and lack of problems have been systems operated by professional utility personnel. For example the NieuwSloten project in the Netherlands. Here the PV system is owned and operated by the utility NUON. The householders own the houses, but not the PV system. The electricity generated is used within the district but is not linked directly to the house on which it is mounted. Three different system concepts were considered for this project:
a. 1 system per house: 100 individual systems
b. 1 system per block of houses: 6 systems
c. 1 system per district: a single 250 kWp system.

Option c was chosen in order to minimize the costs of inverters, installation and maintenance. The system is monitored online. In order to ensure the safe operation of the installation and be able to follow it at a distance, three indicators are placed in all switchboards (DC- over voltage protection (varistors), DC- isolation control of the invertors, and a smoke alarm). The system has been trouble free to operate and has not involved utility personnel in extra work.

In Gleisdorf in Austria a number of PV systems were installed as part of a municipal programme. The PV Power plant installed on the roof of the Utility Company has been working very reliably and there have been very few problems reported. Service activities are carried out by the employees of the utility company. Function control is checked monthly and once a year the modules are cleaned. In the winter the surface of the PV modules is kept free of snow. The expected annual yield of 9000 kWh has been exceeded to 9500 kWh.

However projects where utilities are responsible for operating individual systems on houses have had more mixed results. For example the Nieuwland project in the Netherlands had an experimental Performance Guarantee & Maintenance System, but after some years this did not work out. In general the maintenance system was not stimulating a high performance of PV, as REMU collected the problems and did once a year some maintenance. Maintenance had to be done both regarding the roof integration which had some problems, and also regarding the technical quality and performance of the PV. During 2003-2007 maintenance was done on a minimum level; and the Performance Ratio went down quite a bit. The tenants have some understanding of PV as the communication by REMU and the Municipality from 1997 to 2000 was excellent. Nevertheless if a system was not or badly functioning, nobody notices unless the roof is leaking.

There have also been some problems where ownership of utilities has changed and the sense of ownership of the PV projects has faded.

During the design stage the designers need to consider how the performance of the system will be checked. A visual display is needed so that occupants can see whether or not the system is operating correctly. Simpler systems may just have an operating light and a fault light. More complex displays also provide energy production data. Energy production data can tell you if the system is operating as it should, however this is only effective if you have some idea how much energy should be being produced! Providing feedback to occupants on energy use and energy provided by the PV system can result in extra energy savings and is recommended.

The display needs to be in a location where it will be seen by the person responsible for ensuring correct performance. The display must give information in a way that can be understood by the operator. If displays are not sufficiently clear problems may not be picked up and no incentive to save energy is provided.

A connection to a remote monitoring service may also be provided. Some systems have a simple warning light system on site and more comprehensive data collection and display system available else where via a remote monitoring system. The correct solution will vary depending on the type of system and who has responsibility for operating it. There are commercial solutions offered in Europe that provide remote monitoring, yield and performance check (error detection routines), with the aim of reducing costs by optimizing energy yields and system maintenance. By making use of advanced Information Technologies and satellite solar radiation data, the user can be informed quickly of the PV system malfunctions.

The design also needs to allow for easy access for maintenance. Access to individual properties for maintenance or repairs can be an issue; locating inverters in communal areas is one way around this problem in apartment or flats buildings.

At the end of the Commissioning and Handover stage the completed systems should be handed over to the eventual occupants in full working order, commissioned and grid connected.

During commissioning it is important to check correct operation and administrative set up including:
• PV system output – ideally this should be compared to expected output although this will require knowledge of irradiance levels. Alternative methods such as comparing the outputs of different strings can also be used. Appropriate monitoring methods are described in the standard IEC 61724 (Photovoltaic system performance monitoring - Guidelines for measurement, data exchange and analysis), although currently work is being done at an international level in order to modernise the existing guidelines and better adapt them to the latest PV systems.
• Grid connection – Ensure export tariff agreed and contracts signed if needed
• Ensure electrical commissioning has taken place according to applicable regulations and permission to grid connect given.
• Visual display – check working correctly and understood by operator.
• Monitoring system – check working correctly.
• Responsibility for checking performance may need to be specifically allocated.
• Arrange insurance.

Clear operating and maintenance instructions must be provided including:
• Operation and maintenance leaflets in a sturdy format.
• Information about expected power and yields.
• A point of contact that can reliably answer any queries and organize maintenance.

At some new housing estates, developers have been keen to include PV to boost their green image but have not given sufficient thought to explaining the systems to the occupants. The new occupants may have no knowledge of PV before moving into their new house and no particular interest in the system so long as it works. Correct operation needs to be checked and commissioning done by the developer or their representatives. In addition all the paperwork needs to be complete, especially any paper work regarding grid connection. This can be very complicated and should not be left for private householders to complete. In some countries the paper work for connecting a small PV system is similar to that for connecting a large generator!

Once the systems are handed over the owners tend to be left to organise maintenance and operation by themselves. PV systems are low maintenance and easy to operate. Unfortunately this is sometimes interpreted as meaning they need no one to keep an eye on them. They may be good but nothing is perfect or lasts forever without some assistance. A maintenance plan is needed which includes consideration of:
• Who will be responsible for keeping an eye on the system? Do they understand how they visual display works? Do they know how much energy they are expecting to be generated and how to check it?
• Who can they contact in the event of problems or queries? Providing the telephone number of the standard utility helpdesk is not sufficient if the person answering the call is not going to be able to answer the query.
• How to transfer information in the event of personnel changes/sale of the house.

It is also beneficial to consider how to foster a sense of pride in the sustainable aspects of the area or building. The visibility of PV can be very useful here. For example in La Darnaise, the first renewable powered district in France PV is considered the flagship of the project. The social impact of this visible element of the urban regeneration is considered to be very valuable.

Groups of houses occupied by social housing tenants can be very successful but it does require some care and forethought. The housing association can keep an eye on the condition of the PV systems, act as a central contact in case of queries or problems and organize maintenance and repairs.

Housing Association tenants need to know something about their PV systems. In Kirklees the housing associations prepared leaflets and the installers explained the systems when they were installed. The systems have been particularly successful at estates with a stable population and involved tenant representatives. Follow up can be done during a monitoring programme, for example at the Fernside solar village in Kirklees monitoring is done manually with a project officer visiting the houses on a monthly basis and noting meter readings. At the same time they can answer questions or concerns. At other estates the tenants have changed fairly frequently leading to a poor understanding of energy issues with those tenants who were not there when the system was first installed. A tenant information sheet is now included in all new tenant packs.


Fernside solar village in Kirklees, photo D Munro

People have to have a reason or incentive to maintain their interest in the performance of anything they own. If there is no reason to keep an eye in something it will eventually fall into disrepair. If the financial value of the electricity generated is low and there is no inconvenience suffered if the system is not working, and no pride in the sustainability of the building the result is likely to be poor performance in the long term. Financial incentives linked to generation, such as enhanced feed-in tariffs, provide an incentive for an owner to check performance occasionally and take action if problems are noticed.

One possibility for ensuring the successful long term operation of PV systems is to use an Energy Service Company (EsCos) to operate and maintain a group of systems. This has not yet been tried at many locations and there is limited data available but it is seen as a way forward for some situations. The company would have a commercial incentive to maximise energy production and responsibility for holding information on the systems. Checking performance and organizing maintenance would be part of their role.

The PV demonstration programme on municipal buildings in Barcelona has not yet found a successful model for maintenance. The possibility of using an EsCo is now being considered. At the moment maintenance of energy installations in public buildings is done by the General Services departments at the district level. The existing work load of these services, together with the special characteristics of PV installations compared to conventional electrical ones has led to problems with the maintenance of the PV systems. Energy Services Companies are already being introduced for the management and maintenance of Solar Thermal Systems, a more developed market than PV in Barcelona.

The most risky time in a project, when there is the most likelihood of failing to do something, leading on to later problems, is when responsibility for the PV system is being passed from one person to the next. For example if systems are handed over to occupants without proper commissioning and information transfer or during changeover of occupants when information can easily be lost. If these risk points are considered when setting up a project it should be possible to keep PV systems operating successfully for many years.

Further information can be found in the case studies.
• Case studies with examples of utility involvement in the operation of systems include: Gleisdorf in Austria, Nieuw Sloten and Nieuwland in the Netherlands and Jvosai Town in Japan.
• Case studies with private developers include Kirklees and Barrow in the UK, and Hauts de Feuilly and Lyon-Confluence in France.
* Case studies with Housing Association experience in operating PV system include: Kirklees in the UK, La Darnaise in France, Gleisdorf in Austria and Nieuw Sloten and Nieuwland in the Netherlands.

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