Rooftop Type Solar Power Plants Risk and Damage Applications

Engineering risk and damage assessment for claims department and underwriters

As of the end of 2011, 63.164,07 MW installed capacity of power plants in Turkey reached 89.736,70 MW by the end of May 2019. While licensed power plants constitute approximately 83 GW of the mentioned capacity, the total installed capacity of unlicensed solar power plants exceeded 5 GW. Especially with the commissioning of Unlicensed SPPs, which were rapidly established during the last 5 years, the share of Solar Energy in the total installed capacity became 6%. Approximately 20% of the installed Solar Power Plants are comprised of Roof-Top Solar Power Plants. Recently, Roof-Top SPPs have gained great momentum.

2. Working Principle of a Solar Power Plant

In a standard solar power plant; 700 – 800 VDC (open circuit) voltage value generated by 20 photovoltaic panels in series in each panel array is transmitted to the inverters and then to the transformer box as 370 – 460 VAC (Nikola Tesla – 1888). In the transformer box, this voltage is correlated with the hermetic type transformer through low voltage protection / measurement elements. The medium voltage (MV) value of 36 kV (36.000 V) at the transformer output, following the disconnector / metering / breaker MV cells, provides energy flow to the interconnected system. Detailed technical information is shared in the glossary section of the bulletin.

The working principle of root-top solar power plants is as explained. If preferred, energy can also be stored on accumulators. The establishment steps are as follows;

1) Establishing the load-bearing construction on the roof and correlating it with the existing construction
2) Installation of photovoltaic panels to the construction
3) DC wiring towards ground and collector panel establishment
4) Installation of inverters in a suitable location on the ground
4a) Optionally establishing batter groups in an environment isolated from atmospheric conditions
5) Bi-directional meter and transformer installation for interconnected (on grid) type systems
5a) Establishing the distribution panels for closed circuit systems (off grid)

*** In residential solar power plants it is recommended to store energy on accumulators, since the panel space is limited. Considering the limited assembly space (the amount of panels that can be installed) and investment costs, it is inefficient to meet the required energy directly from the panels. Therefore, energy should be stored on accumulators and provided during periods of low or no radiation (evening / night).

A power plant that can be assembled on the roof of a factory will be able to provide all the energy that the facility needs during the day shift. To give an example; a standard CNC machine requires an average of 15 KW power. A 1000 KW power plant on the roof-top is capable of operating approximately 60 CNC machines. It is possible to earn financial income from excess energy in both residential and industrial roof-top solar power plants, as in standard field type solar power plants. Individual energy generation has become widespread in Turkey in recent years, as in the world. The most important issue here is the bearing capacity of the building where the power plant is to be established. With this bulletin, risk and claims assessment studies of solar power plants that can be established on the roof-tops of existing companies and factories have been shared.

Photovoltaic panels installed on the roof-top of the factory building from a loss file examined by our party. Inverters and transformer box are positioned adjacent to the building façade. Since there are high voltage elements in these parts, they should be in an enclosed and locked structure. In addition, a safe means of access to the roof such as stairs etc. for ease of service and emergency response must be provided.

3. Manufacturing Technique of Root-Top Solar Power Plants

Standard solar power plants are established in open fields. By its manufacturing technique, all mechanical loads of photovoltaic panels, inverters, distribution panels, main distribution panel, transformer, medium voltage cells etc. are absorbed by ground. In roof-top solar power plants, all these loads affect the load-bearing elements of the roof.

As it is known, roofs of residences or workplaces, are designed against atmospheric effects of the region such as wind / snow etc. Apart from these, no other load is taken into account. Therefore, any extra load on the roof poses a risk. A standard photovoltaic panel (270 W) weighs 18 kg and the roof-top construction, on which a panel is to be installed, weighs approximately 15 kg. With a simple calculation, a roof-top power plant of 1000 KW capacity applies an extra 120 tons of load on the roof. Regardless of the capacity of the power plant, the loads of the panels and the wind / snow etc. to which the roof will be exposed should also be calculated during projecting phase and necessary reinforcement works should be performed. When insuring a Roof-Top SPP, it should definitely be questioned whether the building projects have been revised and whether reinforcement is made. Any project that does not pass the engineering discipline cannot be permanent.

In roof-top power plants, inverters are mounted at ground level and correlated with the cables transmitted from the roof with cable trays. In this context, they are usually installed in a closed area on the ground floor in residences and on the wall in factories in an adjacent order to the building. There should be no correlation between the electrical installations of the power plant and the existing installations of the building. Otherwise, there is a risk of electrical fire.

In Turkey, there is no difference between unlicensed field type power plants and roof-top power plants on the basis of regulation. As of only 2018, the relevant regulations were updated in order to transmit the excess energy produced in roof-top solar power plants below 10 KW to the grid and to earn financial income.

All equipment used in the design and installation of the PV system is established in accordance with the following Turkish Standards (TS), International Electro-technical Commission (IEC, EN, HD, ISO) Standards.

 
4. Risk and Claims Assessment

Standard residential roofs are manufactured on wooden columns and beams, and factory roofs on steel construction. The most important design criterion in roof-top solar power plants is to transfer the load evenly on the carrier elements. It is obvious that the loads directly affecting the roof coverings will not be stable. Therefore, the load-bearing construction of the panels must be socketed with the existing construction of the roof.

Issues to be taken into account in terms of static in project design;

In the establishment of roof-top SPPs, primarily the extra self-load (dead load) on the roof should be taken into consideration. In addition to the weight (self-load) of the roof-top SPP application to be made on the existing structure, additional snow load and wind load may occur due to the change of structure form.
Snow load calculations for buildings in Turkey are usually made according to TS-498 standard. Although TS-498 includes calculation criteria according to the atmospheric conditions of the region in snow load and wind load calculations, it also recommends using the meteorological data of the application area.

Another important issue for solar power plants is the construction design and the angle of the panels. If the grade of the roof-top SPP to be established is parallel to the roof grade (that is, it will be fixed directly to the roof cover with construction), the correct application of TS-498 will be sufficient. However, if there will be a difference between the grades of roof and panels, the application of TS-498 alone will not be sufficient in terms of snow load and wind load.

Grade difference between solar panels and roof

 

In an application as shown in the image above, solar power panels will function as a snow collector / catcher on the roof and allow the snow load to affect the building above the region calculations. Since the snow load calculation of single grade roofs is taken into account in the design of TS-498, the wind accumulation effect is not included in the calculations. Application of Euro Code – 1 Standard for Solar Power Plants with different grade values that are classified as special construction class will prevent probable problems.

Since additional wind load will occur in solar power plants designed with a grade value different from the roof grade, additional wind load calculations should be made in the roof design.

It is important to choose the correct standard according to the Solar Power Plant criteria planned during the design phase and to apply this standard. In the application phase, it is necessary to pay attention to frequently encountered construction application faults and to transfer the projects to the field correctly.

Considering our past claims experiences, although it is a simple problem that can be overcome by regular inspection and follow-up, frequently encountered construction application faults, when not taken into account, causes damages to the power plants with the effect of snow / wind load much below the design load. Especially if the construction joints do not correspond to each other, the holes drilled later on the construction narrow the construction section and weaken the bolt connection.

 
In a claim file we have examined, as can be seen in the image on the above, the load carrying part of the photovoltaic panels is directly correlated with the roof cladding. As is known, roof claddings are made of sheets with an average thickness of 2-3 mm. An installation made like this poses a great risk against snow / wind load and threatens the structural integrity of the roof.

Air circulation is important for photovoltaic panels. As the temperature of the panel increases, the internal resistance of the panel increases, extra heat is generated and panel efficiency decreases. As is known, high resistance in any electrical circuit causes a short circuit, and sudden temperature increases are the most important factors that trigger a fire. Although no structural element that will create a fire load is used in a standard roof covering, roof mounted photovoltaic panels are considered as fire loads for the roof.

The most important point here is that the panels continuously generate power while under the sun. In a standard electrical circuit, the voltage in the current can be cut off by turning off the input switchgear. However, it is not possible to reduce the circuit voltage to zero in photovoltaic panels by their working principle.

In this context, even if the inverter line is disconnected, there is voltage present in both panels and DC cables. Such case scenarios should be studied during the project design phase of the power plant. Especially emergency response units such as fire brigade should be trained in photovoltaic panels and their effects.

The intervention method is extremely important in a fire incident in a photovoltaic system under continuous power. Photovoltaic panels contain toxic substances, and smoke / toxic gases that spread to the atmosphere during a fire is a threat to safety of the individual.

During the fire extinguishing, it is absolutely necessary to perform extinguishing and cooling with foam. In extinguishing works with water; it is known that the water layer will be extra conductive and will fuel the fire. As the panel surfaces will be covered with foam in extinguishing with foam, the contact with sunlight will be prevented and the voltage level in the panels will be reduced.

Other risk factors for roof-top power plants are electrical leakages, reverse currents and grounding resistances. There are an average of 80.000 cable connection points in a 1000 KW (1 MW) power plant, with two cable connections in each panel. In case of a loose, non-contact that may occur at any node point, the DC current generated in the panels will reach every point of the building through construction. This can cause arcing, fire and electrical injuries. In order to prevent such situations, both the panels and the construction should be correlated with the grounding line and residual current relays should be implemented in inverter distribution panels.

One of the most important criteria that must be planned before establishing a solar power plant on the roof of any facility is the existing energy infrastructure of the facility. If the existing infrastructure is neglected and insufficient, it will pose a problem for the extra loads that will occur after the installation of the power plant. Especially the existing electricity / data cables of the lighting / air conditioning systems located on the roof sections should be distributed over a single line as much as possible and taken into cable trays. Within this context, it is important to establish photovoltaic panel cables at the furthest points from the existing lines.

Below are images of a fire incident occurred in the roof-top solar power plant of a facility examined by our party. The fire incident occurred as a result of a short circuit in the electrical installations on the ceiling of the facility. With the spread of the fire, the roof section caught fire and caused damages to the panels. As can be seen, existing risk factors in the operation can directly affect solar power plants.

 

Another important risk factor in roof-top or ground-mounted solar power plants is inverters. Since there is radiation in the atmosphere during evening / night, the panels are constantly powered and this power is correlated to the inverters. Since the amount of energy during these hours is not in the amount to be transmitted to the interconnected system (network), inverters are in standby mode with a little load. Therefore, it is important that inverters are well-maintained and can be monitored continuously. All power plants are equipped with automation (scada) systems. These systems must be constantly monitored by expert operators and necessary actions must be taken in case of warnings by the system.

 

In the inverter records shown above; peak or zero generation situations can be seen. In such and similar situations, the automation system alerts the user / operator. Lack of control or ignoring system warnings is a major risk factor. In a claim file examined by our party; the fire started in the inverter as a result of the short circuit caused by the defect in the inverter, spread to the panels in the roof-top power plant in short amount time and caused the building to be completely burnt along with the power plant.

Above are the drone and satellite images of the fire incident caused by the inverter and the total loss building and power plant

Establishing a solar power plant on the roof of any residential or industrial building can also damage the roof insulation. It is an expected situation that rain / snow water will penetrate into the building as a result of deformation of the roof coverings during the assembly activities or the sections opened in the coverings for fixing not being insulated properly.

Risk of hail is another factor that should be taken into account in roof-top solar power plants. Since the possibility of hail is higher in cities, roof-top plants are considerably under a higher risk than field type plants.

 

5. Conclusion & Evaluation

Our research and claims experiences regarding roof-top solar power plants have been explained in detail. The prominent issues in risk and claims management for roof-top SPPs are as follows;

• Solar power plants that are planned to be built later on the roof of an existing building should be handled by experts of the subject and existing risks and conjoined risks to be created by new equipment should be identified by conducting a feasibility study.

• Prominent risk factors in Roof-Top SPPs; damage to the building on which the SPP is installed due to structural risks and possible fire that will occur in the SPP being effective at the plant along with the building. It is necessary to process the established SPP to the static projects of the building to prevent structural risks, and to select the material of the building roof with appropriate properties to prevent a probable fire from spreading to the building. While the reinforced concrete terrace roof offers the most appropriate situation, sandwich panels with petroleum-derived insulation materials used in building roofs and facades constitute the most risky situations.

• The electrical installations of the roof-top solar power plant should be separated from the existing installations of the building.

• The medium voltage transformer to which the energy produced in the power plant is correlated must be separate. Associating the structure with the transformer causes overcapacity problems in peak generations.

• Sufficient air gap should be left between the PV panels and the roof covering for fresh air circulation. Otherwise, the panels may overheat and get damaged or cause a fire.

• It is recommended to control the automation (scada) system instantaneously. Automation systems alarm and notify users in case of a possible malfunction and out of tolerance power values.

• Daily / weekly / monthly and annual periodic checks of the power plant are important. Atmospheric effects of temperature / precipitation / humidity etc. especially effective in seasonal changes on the installations should be examined.

• In this context, it is recommended to examine the roof-top solar power plants in more detail than standard solar power plants in terms of mechanical and electrical titles in the process of transferring the risk to the policy. Field type solar power plants are generally installed on open fields and the possibility of intervention in case of possible damage is easier than the roof-top. Any damage that may occur in the roof-top power plant reveals the concept of conjoined risk regarding the residence or factory it is installed on.

• The insurance product to be included during insuring phase of the roof-top power plant is of particular importance. It is seen that in cases of damages that occur due to reasons unrelated to the installation and operation of the power plant, the carrier elements of the roof are also subjected to claim in addition to the material damages to the plant components. In terms of clarifying the concept of such interrelated material damages, in policies that provide coverage alone for roof-top solar power plants; it should be emphasized that in case of a possible damage, only the system components provided with coverage can be subjected to the policy. Or, while providing roof-top SPP coverage, building fire insurance policy must be made necessary. In addition; if there is a party to the roof-top SPP installation contract, it should be stipulated that subrogation will not be a matter of discussion unless coinsurance is made with the party. !!!

• In structures covered by insurance products other than the coverages designed specifically for roof-top power plants; after the components of the building are damaged as a result of the damage in the power plant, all the damages are claimed from the package policies. It will also be useful to state that power plant system components that do not constitute the subject of the policy and are not included in the sum insured, cannot be subjected to claim in case of damages. This will make the process easier to manage.

• The biggest problem that directly affect the downtime period in claims regarding possible financial losses is the supply period of the spare parts. Especially in areas where central inverter is used, all generation stops in case of a possible damage. All of the inverter brands are of foreign origin. Manufacturer companies do not have spare parts in their stocks, parts are supplied form abroad in case of damage. Supply periods of parts may be extended in cases such as a pandemic or public holidays.

• Repair periods may be extended due to negative situations that have been / may be experienced in the past between the Insured and the manufacturer. In addition, minimum amount of spare parts should be kept ready in order not to increase the downtime. (For example, 1% of the total number of panels is backed up, or 1 spare inverter is backed up if the system is a string inverter one)

• Physical examination possibilities of roof-top power plants are more limited compared to field type power plants. Visual physical examination is difficult because of the less service space between roof-top panels. Hence, it is recommended to perform periodic examinations with a drone to detect possible hail etc. damages.

• Even if there is no evidence of physical damage, measurements should be performed periodically (twice a year) with a thermal camera to detect the internal defects of photovoltaic panels.

• Flexion / buckling may occur in photovoltaic panels as a result of atmospheric effects (snowfall, hail etc.) or structural deformations that may occur in the construction. In this case, micro cracks occur in the panel cells and their generation capacity decreases. Electroluminescence test gives positive results for proximate cause analysis of micro cracks.

• Determining the electrical load of the plant is an important element for determining the necessary improvements or measures to be taken. In addition to the Scada system; electrical parameters such as voltage / current / resistance etc. should be measured and recorded with clamp type multi-meters, earth megger or solar measurement devices daily / weekly / monthly periods. In case of a possible damage, these records are important in order to determine the cause of the damage.

• In order to determine the root cause of damages that may arise from the lines or equipment of energy providers, monitoring and recording should be made with medium voltage energy analyzers. This is the most important step of root cause detection and subrogation analysis.

• In the selection of equipment to be used in solar power plants such as photovoltaic panels / inverters / transformers / medium voltage cells; it should be taken into account that the manufacturer or distributor companies from which they will be supplied have product liability policies. When subrogation is determined according to the detected root cause, it is important for the companies doing the insured work to compensate the losses.

• Similarly, companies that will carry out the manufacturing must have professional liability policies. Therefore, liability policies should be sought in all companies involved in the process including project design / product supply / manufacturing / operation.

• It is recommended to make a contract between the owner of the roof-top solar power plant and the owner of the building in order to avoid any unfavorable legal processes between the parties.

• In accordance with the relevant articles (1435 and 1446) of the Turkish Commercial Code regarding the obligation to give notice, the insurers should receive confirmation in writing from the claimant regarding all technical issues of the system to be insured.

• It is recommended that the above-mentioned issues be taken into account at a minimum before providing cover for roof-top solar power plants.

 None of the parties, including the fire brigade, have sufficient experience for the newly implemented roof-top solar power plant projects. As intervention and access to the roof will always be difficult due to the height, a bad scenario should be operated in every case of damage based on the current conditions of the fire department. The best example of conjoined risk and conjoined damage will be roof-top SPPs. Since the root cause will always be “from the power plant towards to the others “root cause and subrogation determination is the most important step in roof-top SPP damages, not counting the exceptions. Unless preliminary preparation and a sustainable strategy are prepared in this vitally critical issue, the damage and its consequences will cause the most damage to all parties.

 Optimization is important so that the goals and results can match. Knowing that there are serious problems in compliance with the building standards and legal requirements in Turkey, we must admit that a project that is disconnected form engineering science will never be correct. In addition, different types of construction are active in each region throughout the country. We see that each power plant will be a boutique manufacturing for unstable existing structures.

 As a big deficiency; the biggest risk is that fire brigade, EPDK (Energy Market Regulatory Authority), energy providers or relevant ministries (Energy – Industry), cannot create standards together for the same subject. First of all, harmony between the authorities is expected. Unfortunately, since the situation will not change in the near future, we will see manufacturing and structuring as if it is correct, appropriate, real.

Root cause determination in insurance practice is an indispensable part of the claims management process. Associating any event with the law is possible only by putting forward the root cause in the most clear and objective way. Associating the events with a rule of law without determining the root cause and making coverage interpretations causes the emergence of interpretative counter theses in the claims management process, thus prolonging the file process or accepting artificial results that are known to be incorrect. In some cases, the lawsuits are lost and the possibilities of subrogation cannot be evaluated because the root cause cannot be clearly determined or the determined root cause cannot be conveyed with an appropriate insurance and legal language. Decision makers want to be able to anticipate this risk, if they cannot, they always abstain from proceeding with a lawsuit.

Since conjoined risks in Roof-Top SPP damages are important factors that make the events complex, revealing the root cause of any incident based on the data obtained is possible through scientific analysis with experts, focusing on scientific, unchangeable results that will satisfy all parties within the process and in a way that will not allow interpretation. Thus, uncertainty, which is the biggest problem for decision makers, is out of the equation.

With this bulletin, risk and claims management studies of solar power plants that can be built on roofs of existing companies and facilities have been shared.

Glossary:

A large number of components are used in solar power plants in order to convert solar energy into electrical energy. These components are shown respectively in the image below.

Photovoltaic Cell>Photovoltaic Panel>Panel Array>Inverter>Distribution Panel Measuring Panel>Transformer>Transmission Line>Subscribers

 
 Photovoltaic Cell: The smallest building block of the system. Sunlight reaching the photovoltaic cell stimulates the semiconductor components (emitter / base) inside the cell and provide electron exchange. The charge / current carried by the freed electrons creates voltage by potential difference and thus, electrical energy.

 
 Photovoltaic Panel / Module: The power generated in response to the voltage / current produced in a single cell is around 4 watts. Since no power can be supplied to any system with such a low power value, a module is created by connecting an average of 40 – 60 cells in series and in parallel. The current generated in photovoltaic panels is direct current – (DC).

Direct current / DC; is the constant flow of electrical charges from higher to lower potential. In alternating current / AC; the direction and intensity can change according to the need. Efficient transmission of energy is possible with alternating current.

 
 Cell Array: Photovoltaic cells are generally divided into 3 in the form of groups consisting of 20 connected in series and these three groups are connected to each other in series, thus forming a module array. In the junction box on the back of the modules, there is a blocking diode for each of the three groups. Diodes are circuit elements that transmit electric current in one direction, they prevent current that can be transmitted to the panel from the inverter and ensures that energy distribution inside the panel is equal.

 
 Panel Array: In order to utilize the energy generated in each module efficiently, an average of 14-20 modules are connected in series with each other. In panels in series; the voltage value of each panel is added up, while the total current value remains constant as the maximum current value that can be produced by a panel. Therefore, the current generated in the panels in each series is transmitted to the inverter over all other panels in the series.

 
 Inverter: 700-800 VDC open-circuit voltage value from each array inverted to 3 phase 380 – 460 VAC levels with the voltage and frequency regulating component within the inverter. On average, 120 – 180 PV panels (6-8 arrays) can be connected to an inverter and 30 – 40 KW energy can be generated. (There are power plants where 500 KW inverters are also used based on the project)

Energy parameters can be read and recorded via the internal user interface on the interface on the inverter. In addition, all inverters in the power plant communicate with each other via RS232 / 485 and ethernet cables.

 

 Distribution Panel: 3-phase AC energy generated in each inverter is linked to thermal mechanical switches for short circuit / over-current protection within the field distribution panels, which are generally located close to inverters. In addition, there are residual current devices for residual current protection and surge arresters for lightning protection in the panel. An average of 4 – 6 inverters can be connected to a panel and the collected energy is transferred to the transformer box with underground cables after NH-type fuses.

 
 Measuring Panel: The energy obtained from all inverters in the power plant is transmitted to the main distribution panel in the transformer box. Breakers and energy analyzer / electrometer are located within the main distribution panel. 3-phase 380 – 460 VAC energy is recorded in this panel and transmitted to the medium voltage (MV) transformer.

 
 Transformer: 3-phase 380 – 460 VAC low voltage value is increased to 30 – 36 kV (36.000 V) with medium voltage (MV) transformer in order to transfer the energy generated in the power plant to the transmission line efficiently and is transferred to the transmission line via medium voltage breaker cells.

 

Technical Terms:

References:

– Ekol Sigorta Ekspertiz Hiz. Ltd. Şti. Risk ve Hasar Arşivi

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