Solar Performance Parameters Simplified

Industry Insights

Solar projects installation base has been increasing by leap and bounds across the globe.

Organisations has started sitting up and taking notice of the service activity of these projects and realizing how important that this function is.

It is stated that solar projects hardly have any moving parts in the projects and hence the need of maintenance is negligible.

If anybody believes this they are in a fool’s paradise.

Just like any equipment, these installations need proper monitoring, up keep and maintenance.

The solar project O&M function is around 4 years old in India and the exponential rise in projects base has taken many by surprise. Many organisations were not geared up to meet these challenges. Many companies just draw up a PM schedule and try following it just because “something needs to be done”. These schedules are not drawn up with any systematic methodology nor does one understand that these frequencies of PM need to be changed according to the conditions.

It is just like medical check-ups that we human beings undertake; depending on the health conditions, check-up frequency and medicine dosage changes.

To many, the only activity in a solar installation is “just module cleaning and de-weeding” (even one of my bosses in the solar industry had thought so).

The first step is to evaluate whether these installations are performing as what is expected; the starting point to draw up methods of doing course correction

This is just an effort to explain the some of the major parameters with which one can evaluate the performance of the installation.

1.      Grid availability (GA)

This is the ratio of the actual grid availability to expected grid availability.

This is a major factor which affects the generation since without the availability of the grid, the solar projects cannot produce power and export the power.

2.      Plant availability (PA).

This measures the percentage of sunlight hours when the plant was ready to produce. All components of the system should be available for effectively converting the solar radiation to electricity. This is actually calculated by getting the individual availability of components (not often followed by many).

Ex. Inverter Availability = [hours with inverter production > 0] / [hours with irradiance > 100W/m2].

Plant Availability = weighted average of all components availability

This directly affects the LCOE ( levelised cost of energy).

3.      Yield.

This is the energy production per unit of plant capacity (Kwh/kw)

4.      PR (performance ratio).

This is the percentage of the received sunlight energy converted into electricity by the plant. When the project is envisaged, the design would calculate the energy production, taking into consideration the radiation, conversion efficiency of modules, efficiency of inverters, various losses in the system and weather related aspects. This (PV Syst) gives the expected generation.

Radiation is measured using pyranometers installed at site. For large installations there is a requirement of more number of pyranometer to be installed.

The actual generation is what is measured in the meter at the point of injection to the grid.

Pit falls:

a)     At design stage the expected generation is calculated depending on the various parameters. When doing the construction, many a time these may be altered and hence the expected generation may vary from the design generation. To get this new expected generation, one needs to calculate the expected generation with the as-built details. (Many companies may not follow the method of documenting the as-built drawing and recalculating the generation based on the as-built project).

b)     The solar radiation do vary and the amount of radiation expected (design stage) will vary from the actual received radiation. This does affect the energy delivered. The Service department cannot be held responsible for this radiation difference. However one needs to know whether the generation difference is due to solar radiation or due to any other factor.

c)      For this we need to have a measurement parameter which is devoid of the variations solar radiation (OPR)

5.      IPR (investment Performance ratio).

This Measures performance of the asset (or fund) from a financial perspective. This gives information whether the investor needs are fulfilled. This is driven by plant performance as well as weather conditions. IPR = [actual energy production] / [reference energy production]

6.      WPR – Weather Performance Ratio

This measures the performance of the weather conditions. Weather conditions are monitored by the climate station (consisting of pyronometers, temperature sensors, wind mast, humidity sensors etc). This is driven by variance between actual weather and long-term weather average. WPR = [actual insolation] / [reference insolation]

7.      OPR – Operating Performance Ratio

This measures performance of the power plant itself, given actual weather conditions. This factor compares actual plant PR to reference plant PR – ideally it is 100%. OPR = [actual energy production] / [expected energy production with actual weather]

Now the question is how often should one monitor these parameters? It is advisable that these are monitored on a daily basis and corrective actions taken.

Monitoring these parameters is the first step to effectively identifying and correcting the issues (other than breakdown repair).

Monitoring and evaluating the breakdown frequency, leads to identifying problematic areas and taking suitable measures to correct the recurrence of such problems.

Understanding these parameters and their inter relationships leads to a better evaluation of the asset functioning. The simple task is to now, identifying the problematic areas and attack them systematically.

Trust me, this brings in big rewards. Just think of a fleet of projects with performance crossing the expectation consistently by 7% to 9%. (This is not a dream, but something which has been achieved over a fleet of projects of 200Mw spread across countries by my team)

This is a first step to moving from preventive maintenance to predictive maintenance and effectively increasing ones profitability and stake holder’s confidence.


Author: Mr. Radhakrishnan (RK) Mundoli, Renewable Energy Operations Specialist, Solar Project Execution, Solar Asset Management, Solar Business Consultant

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Thursday, 19 July 2018 04:59