POA solar irradiance estimation

[riating]

We have an installed Solar PV system on a shopping mall. The solar modules are installed at varying tilts on different sections of the mall. We do have a Solar PV sensor based weather station at one of our sub systems.

I already have done a PVsyst based simulation for the individual sub-systems to get a value of Solar irradiation.

Need to understand if I could use the actual reading from the single weather station at this site. I understand that for each of the subsystems the temperature and air values will be different. But please advise what is the best source to evaluate the most accurate solar irradiation values

 

[jaggedben]

What are you trying to do? Evaluate the performance of the installation?

 

[riating]

Yes the intent is to get a more accurate assessment of the PR for each of the subsystems.

Secondly it will help me calculate better when the inverter output is suppressed due to reduced load

 

[solarken]

Yes the intent is to get a more accurate assessment of the PR for each of the subsystems.

Secondly it will help me calculate better when the inverter output is suppressed due to reduced load

Is this a zero export or off grid system? Is that why the inverter would curtail production?

 

[jaggedben]

My gut feeling is that for your purposes the weather data from the one subsystem will be fine.

 

[ggunn]

Yes the intent is to get a more accurate assessment of the PR for each of the subsystems.

Secondly it will help me calculate better when the inverter output is suppressed due to reduced load

Is this a grid tied system with standard inverters? If so, unless you have export limiting hardware in place, the output of the PV system does not change when the building load changes.

 

[riating]

Yes these inverters are grid tied and we also have export limitation in place.

 

[AlbertL57]

For a system with multiple orientations/tilts, I'd suggest a pyranometer measuring global horizontal irradiance. With that, you can calculate a weather-adjusted "expected production" figure for any date and time by adjusting the estimated production numbers from PVSyst using the ratio of the actual to predicted irradiance.

 

[riating]

At one of our plant the system is divided into 04 sections with each one at different tilt and orientation. At this site we have one silicon pyranomter installed.

Is it possible to use the measured POA for one of the sub-system and correct it and use it for the other sub-systems. The hope is that these irradiance values will be better than the reference value from the TMY file.

Please provide help with the calculations needed to make this correction. Thank you

 

[AlbertL57]

We have an installed Solar PV system on a shopping mall. The solar modules are installed at varying tilts on different sections of the mall. We do have a Solar PV sensor based weather station at one of our sub systems.

I already have done a PVsyst based simulation for the individual sub-systems to get a value of Solar irradiation.

Need to understand if I could use the actual reading from the single weather station at this site. I understand that for each of the subsystems the temperature and air values will be different. But please advise what is the best source to evaluate the most accurate solar irradiation values

Very interesting topic. Probably the most valuable single measurement for your application would be global horizontal irradiance (GHI) , measured with a pyranometer. From that value, the expected POA irradiance for any array azimuth-tilt can be calculated. I think it's much more difficult to convert a POA measurement to another azimuth-tilt.

 

[jaggedben]

Very interesting topic. Probably the most valuable single measurement for your application would be global horizontal irradiance (GHI) , measured with a pyranometer. From that value, the expected POA irradiance for any array azimuth-tilt can be calculated. I think it's much more difficult to convert a POA measurement to another azimuth-tilt.

If it's possible to estimate POA from GHI then it must be possible to go the other way, and the resulting estimated GHI would (I think) be more useful than the TMY file for evaluating the performace of colocated arrays at different orientations.

 

[BillK-AZ]

I suggest calling NREL (see https://www.nrel.gov/grid/staff.html), they may have already a tool or approach for this need and they are generally helpful. The basic question you are asking is 'Based on GHI of x kWh/m², air temperature of T, tilt/azimuth, etc. what would be the expected PV output of a specific PV array?

This has been done already, systems monitored by Also Energy that I watch show a predicted output by inverter when the system includes a pyranometer and temperature sensors.