Configuration advice for East/West Systems

**spoonwzd** · April 14, 2018, 8:06am

Hi everyone. I’m looking for advice on how to best forecast my system.

I live in the UK and have two 3.54kW PV strings mounted on each roof of my house. Each string has its own 3.68kW SolarEdge inverter with the total / combined export limited to 5kW by a Modbus meter.

My house roofs face South-East @ 130° (-50° azimuth) and North-West @ 310° (130° azimuth) with a roof pitch angle of 40°.

My attempts so far to get accurate prediction results from the Solcast API have not been successful. Can anyone advise how I best forecast my system generation?

Thanks in advance.

**PowerWeather** · April 15, 2018, 10:00pm

I have two solar arrays too and managed to get a suitable generation prediction by making a separate API call for each array then combine the two results by adding them together. You can then cap the resultant output at any given time point to be no more than your inverter’s max output ie. 5kW in your case

**spoonwzd** · April 16, 2018, 5:15pm

Thanks for your response.

This was my first thought, but estimations for my West-facing array yield similar results.

For example, my two identical arrays are defined as follows:

longitude=-3.488382&latitude=50.719087&capacity=3540&tilt=38&azimuth=-50&install_date=20180218
longitude=-3.488382&latitude=50.719087&capacity=3540&tilt=38&azimuth=130&install_date=20180218

However the reported results for the West (130° azimuth) array are almost identical compared to the East:

|PeriodEnd|Period|PvEstimate -50|PvEstimate 130|
|---|---|---|---|
|2018-04-17T06:00:00Z|PT30M|16.43825066|16.43825014|
|2018-04-17T06:30:00Z|PT30M|49.31475197|49.31475042|
|2018-04-17T07:00:00Z|PT30M|89.49714246|89.49713965|
|2018-04-17T07:30:00Z|PT30M|176.8366418|167.0847934|
|2018-04-17T08:00:00Z|PT30M|262.3412938|254.6402824|
|2018-04-17T08:30:00Z|PT30M|348.0293369|342.034646|
|2018-04-17T09:00:00Z|PT30M|426.5635467|422.7020385|
|2018-04-17T09:30:00Z|PT30M|504.8681253|502.4454471|
|2018-04-17T10:00:00Z|PT30M|586.7211594|584.3696133|
|2018-04-17T10:30:00Z|PT30M|653.8480583|653.6352857|
|2018-04-17T11:00:00Z|PT30M|714.3058111|715.8328025|
|2018-04-17T11:30:00Z|PT30M|761.6465648|764.810698|
|2018-04-17T12:00:00Z|PT30M|799.19648|804.0011122|
|2018-04-17T12:30:00Z|PT30M|820.8422197|826.9923692|
|2018-04-17T13:00:00Z|PT30M|823.1789313|831.0167414|
|2018-04-17T13:30:00Z|PT30M|813.9759663|827.6384117|
|2018-04-17T14:00:00Z|PT30M|786.6997708|797.3182033|
|2018-04-17T14:30:00Z|PT30M|741.048414|753.3133264|
|2018-04-17T15:00:00Z|PT30M|679.1397541|692.9365227|
|2018-04-17T15:30:00Z|PT30M|604.3635104|619.4803521|
|2018-04-17T16:00:00Z|PT30M|516.2408869|532.4232454|
|2018-04-17T16:30:00Z|PT30M|427.3509175|445.361508|
|2018-04-17T17:00:00Z|PT30M|324.4969317|343.9153821|
|2018-04-17T17:30:00Z|PT30M|220.6341996|242.9619809|
|2018-04-17T18:00:00Z|PT30M|116.163239|129.7340401|
|2018-04-17T18:30:00Z|PT30M|58.45570211|68.79884594|
|2018-04-17T19:00:00Z|PT30M|20.09119525|20.09119462|

in reality the West array hardly generates anything until mid-late morning when the sun is higher is the sly, but Solcast reckons it will perform similarly to the East array.

Have I got something wrong?

**spoonwzd** · April 16, 2018, 5:42pm

The answer is: Yes! My azimuth is back to front. #facepalm

Should be -130 for my East and 50 for my West!

**siliconrob** · April 17, 2018, 2:16pm

Thank you for this question, I am sure others will experience this problem as well.

azimuth range -180 to 180

Power API

The angle (degrees) from true north that the PV system is facing, if tilted. Must be between -180 and 180. An azimuth of 0 means the system is facing true north. Positive values are anticlockwise, so azimuth=-90 for an east-facing system, and azimuth=135 for a southwest-facing system. Default value is 0 (north-facing) in the southern hemisphere, 180 (south-facing) in the northern hemisphere.

The world map demo is a way for you to experiment with some of the optional parameters that the API supports

World Map Demo

The optional parameters are underneath the world map

**spoonwzd** · April 16, 2018, 8:04pm

Yes, I typically decided to read the FAQ more closely after my first post!

As you highlighted, it says East is -90, but the world map you linked to says the opposite:

Which is correct?

**siliconrob** · April 17, 2018, 12:16am

You are right about it being opposite, the demo labels have been corrected. Thank you for pointing this out.

**spoonwzd** · April 17, 2018, 7:15am

Now East and West are displayed in the wrong order. I’m not sure my OCD can cope with this

**darren** · April 17, 2018, 8:14am

Anti-clockwise rotation in the form of a range slider doesn’t translate as nicely as I’d like either, thanks for the feedback. We’ll have a think how this might be better visualized in a UI control.