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"Key technical due diligence parameters, vendor selection process and Inspection criteria of Solar PV Module for Solar Projects"

King Abdullah City for Atomic and Renewable Energy (K∙A∙CARE) announces its plan to launch the Machine-Assisted Cleaning Solutions (MACS) project.

In case of DC system design, why are fuses mandatory on both poles in ungrounded system & in grounded system only on ungrounded pole?

We all are well aware about the functioning of the PvSyst software. We generally use this to simulate the generation of solar PV plants at various locations. For that we have to consider some losses also and in this article we will get some information about the various losses which need to be considered while preparing PvSyst file and also how to optimize these losses:

1. Near Shading: This is basically shading loss due to lesser inter row distances (pitch) of two consecutive solar module rows, as per pvsyst this can further categorize into two subcategories:
a. Irradiance losses: Due to lesser space, in between two consecutive rows some amount of irradiance in the morning and evening will not collected by solar cells so termed as irradiance loss formerly called "Linear shading losses”.

b. Electrical losses: How you form the strings on structures whether I or U, based on that "according to string" minimal amount of loss present in the system.

Depend on the tilt of the structures this can be max up to 2.5%.

2. IAM factor on global: The incidence effect (the designated term is IAM, for "Incidence Angle Modifier") corresponds to the decrease of the irradiance really reaching the PV cells's surface, with respect to irradiance under normal incidence, due to reflexions increasing with the incidence angle. This will be calculated by Pvsyst itself as this is module dependent. Done many pvsyst simulation and found this shall not be more than 3%.

3. Soiling loss factor: We have no measurement device which can measure the soil/dust/bird dropping at site, generally considered as max up to 2% but can be further reduced up to 0.5% if we can reduce the time cycle for module cleaning.

4. PV loss due to irradiance level & PV loss due to temperature: Both the losses are dependent on .PAN file of module manufacturer and also completely dependent on the site meteo data, shall be calculated by pvsyst internal simulation.

5. Module quality loss: This loss refers positive and negative Wp tolerances of modules. Following cases shall be considered while choosing solar modules:

a. If both tolerances are present means positive and negative(i.e+-5Wp) then this will add loss in the system so that generation become less.
b. If only positive tolerances will be present then generation will be more so gain of max up to +0.4%.

6. LID - Light induced degradation: LID occurs when oxygen impurities in the silicon wafers react with the doped (p type) boron or gallium in the first few hours/weeks of illumination of cell. The effect can reduce cell efficiency from 2 to 4% right of the bat. Better to get the confirmation from module manufacturer for first year degradation of solar modules so as to LID loss.

7. Module array mismatch loss: Mismatch losses are function of production electrical uniformity and binning thereof. If module comes with bin class then surely this will be less say 1% otherwise more if electrical characteristics(Current/Voltage) are different in comparison with each other modules.

8. Ohmic wiring loss: As the name implies this loss is due to cables selection, representing the loss on DC side in between module to inverter through DC cables. This shall not be more than 2%@STC, superior solar designing while selecting right size of DC cables can reduced further up to 1% depend on the shape of land and contract also.

9. Inverter Loss during operation: This loss completely dependent on the .OND file of inverter manufacturer. While selecting inverters through efficiency we can know the loss figure.

10. Auxiliary losses: As the name implies auxiliary means various loads are present in solar plant which will take power for running at day time as well as night time. This loss shall be in between 0.7% to 1% depend on the size of the plant.

11. System unavailability: During O&M contract this loss shall be finalized based on mutual understanding in between client and O&M company, this loss shall be in between 0.5% to 1% depend on the size of the plant.

12. AC ohmic loss: Representing the loss on AC side in between inverter to evacuation through AC cables. This shall not be more than 0.5% at full load.

13. External transfo loss: Basically this loss refers to inverter transformer loss, max considered up to 1.1%.

By Amit Upadhyay. Amit is a solar energy enthusiast and is currently Deputy Manager-Design & Engineering at Mahindra Susten.

Many solar designers often ask me which are the key parameters based one which we can select the solar inverter. Here are some important parameters (Technical Aspects) that need to be compared before finalization of any make of solar grid tied inverters.

First of all as per site climate if the irradiation graph is parabolic curve (radiation vs. time) rather than Central/Monolithic, inverter shall be used in comparison with Modular type Inverters.

Basic Parameters (Protection) Provided By Inverter Manufacturer:

DC Overvoltage, AC Overvoltage, DC Fuses, AC Short Circuit, DC Short Circuit, Frequency Out of Voltage, Voltage out of range, DC inverse Polarity, Ground Fault, Negative Grounding(GFDI), Insulation monitoring, HVRT, LVRT, Anti Islanding, AC output Breaker.

These all are the basic protection provided by inverter manufacturers but out of above the following two, Insulation Monitoring Relay & AC Output Breaker Type need to be confirmed from our end.

1) Output Breaker Type: Some manufacturers provide MCCB in place of ACB. So do speak to your manufacturer and please confirm this point from manufacturer itself.

2) Insulation Monitoring Relay: Inverter is equipped with Insulation Monitoring Relay but please confirm the make of this relay. To save cost some manufacturers provide simple ABB etc. make relay in place of Bender relay which is more sensitive for insulation failure.

Apart from these, the below technical aspects are very important to freeze solar inverter for your upcoming solar projects:

1) Maximum Efficiency: Higher Efficiency will affect Higher generation

2) Auxiliary Consumption: Lower auxiliary consumption will result in a higher generation. This auxiliary consumption is divided into three sub categories which are:

The number of fans that are provided with inverter to cool inverter and the consumption of it. If VFD is with FAN then surely you will save some amount of generation.

When inverter is running in the daytime, the IGBT cards need some aux power, this is called Control Circuit Consumption. Some manufacturers directly take this consumption from the DC Bus of the inverter and this extra power is not included in provided max efficiency of the inverter. So this again must be verified from the manufacturer.

At the night time, inverter will be in sleep mode but will continue to draw some amount of power from grid. This is called Standby Consumption.

3) Output Voltage: Due to Higher output voltage you can save some amount of cable runs from inverter to transformer so as to reduce cost.

4) Fresh Air Requirement(m3/h): This is required as low as possible to avoid any extra filtration unit for cooling purpose.

5) MPPT Voltage Range: Window of MPPT voltage should be wide enough(550-950V). Many manufacturers provide 600-850V window. In this case at higher temperature (at noon) series voltage will be reduced to say 580V as voltage is indirectly proportional to temperature. To avoid losing a fare amount of generation, this parameter must be carefully looked into.

6) Temperature Derating : Check with inverter manufacturer the graph of temp vs. output KVA of inverter. This will help you understand when your output KVA will start derating and at which temp. Some manufacturers might say that the output of inverter is 990KVA. But from 25deg C onwards, the output KVA will derate to say 900KVA upto 50deg C.

7) Shut off temperature: At which temp inverter will shut off. This indicates the max temp rating upto which inverter will provide some amount of output in terms of KVA.

8) Power Factor (0.8 lead to 0.8 lag) & Reactive Power Compensation: Generally inverter is fixed at unity power factor but this shall be adjusted as per grid situations manually. It can also sometimes sense the grid and be automatically adjusted. This is a very important aspect. If inverter feeds reactive power to the grid, you will loose some amount of active power generated. Also if in the signed copy of the PPA, government authorities have specified the details of reactive power generated at the project, directly feeding to grid can cause some amount of penalty resulting in further losses. Also note as inverter is directly connected to the transformer it accordingly senses power factor at this level only. But at grid main meter power factor will be different in comparison with at trafo level because in between both (inverter trafo & main meter at grid), cable capacitance and trafo inductance is not included. For sensing power factor at main meter some manufacturers provide reactive power controllers which are connected directly in between inverter to main meter via RS485 cable to sense actual power factor of the plant for better reactive power compensation.

By Amit Upadhyay. Amit is a solar energy enthusiast and is currently Deputy Manager-Design & Engineering at Mahindra Susten.

Disclaimer: The views above are strictly those of the author and do not reflect those of any other organisation or individual or this publication.

Electrical power generated by solar Photo-Voltaic (PV) is one of the best options for sustainable energy requirements but the variability and unpredictability inherent to solar create a threat to grid reliability due to balancing challenge in load and generation. Variability of power represents the change of generation output due to unscheduled fluctuations of solar radiation patterns. Large unscheduled changes in solar power generation are called ramp events which hamper the penetration of variable power in the existing grid. The variability in PV power is not a major issue with small-scale systems, but a large scale grid-connected system needs sufficient statistical analysis to model the power fluctuations to assess the reliability of the system. The variability can be quantified as a measure of dispersion in variable renewable power generation. Though there are different ways to quantify variability, the simplest way to measure variability is using the normalized squared deviation about mean of the actual generation for some time blocks. 

To accommodate variability, the short-term and long-term forecasting became an important tool in asset management, operations and maintenance of PV solar generation. The recent developments of deep learning algorithms in ANN (Artificial Neural Network) based methodologies using NWP (Numerical Weather Prediction) models have created a huge scope in forecasting the solar power generations with acceptable error margins. Since there are computational issues like the uncertainty in the initial value vector of NWP, proper availability of learning vectors in DNN (Deep Neural Network) and choice of proper architecture of DNN, forecasting can be viewed as statistical prediction rather than a problem with deterministic solutions. Thus from an analytical viewpoint, forecasting can be regarded as the temporal evolution of probability distributions associated with variables required in predicting the solar power generation. Predictability can be viewed as the ability to forecast the solar power generation with sufficient accuracy such that penalty due to error-deviation is very small; and predictability can be measured using probability.

Variability of actual solar power generation is the characteristics of solar plant whereas the predictability refers the property of proper forecast models. A good forecast model is that which captures the genuine patterns in the historical data, but does not replicate past events that will not occur again. Though there is a common belief that the high variability of power generation reduces predictability, the predictability of good forecast is independent of variability. If predictability depends on the variability of the solar generation, then either there is some issues in the basic architecture of the forecast model or the forecast system is not running in its full potential.       

-By Abhik Kumar Das, del2infinity Energy Consulting

The recent proliferation of solar installations across the U.S. means balance-of-systems (BoS) components (everything other than the panels and inverters) are coming under wider scrutiny during risk-mitigation inspections.

Lower solar Feed in Tariffs has required developers to look at cost effective solutions to meet project IRR requirements. Trackers are increasingly being preferred by many IPPs, as good trackers are the only Bankable way to meet the IRR target. Decision to be made is which Tracker technology is suitable in terms of cost but at same time, will last for 25 years. Simply compromising on the structure integrity to arrive at lower cost is not prudent.

To fly a plane around the world on solar energy alone was considered almost impossible until Solar Impulse took to the skies last year, setting a new record for the longest non-stop flight*. 

Converting sunlight directly into electricity, the photovoltaic (PV) solar panel industry has dominated the solar generation market recently because of its astounding price drops. Prices have fallen 99 percent in the past quarter century and over 80 percent since 2008 alone. This has also helped to slow the growth of the “other” form of solar, concentrating solar thermal power (CSP), which uses sunlight to heat water and uses the steam to drive a turbine and generator.

Meyer Burger develops solar technology - from wafers to solar PV systems - with the aim of promoting the widespread use of photovoltaic energy and making solar power a first-choice source of renewable energy.

Scientists in South Korea have made ultra-thin photovoltaics flexible enough to wrap around the average pencil. The bendy solar cells could power wearable electronics like fitness trackers and smart glasses. The researchers report the results in the journal Applied Physics Letters, from AIP Publishing.

 

Copper-indium-gallium-selenide (CIGSe) solar cells have the highest efficiency of polycrystalline thin-film solar cells. The four elements comprising CIGSe are vapour-deposited onto a substrate together to form a very thin layer of tiny chalcopyrite crystals.

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