Grid Interactive System Performance Data

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Inverter Performance Graphs


The 'Quoted' figures are those that were supplied by the system installer before the system was installed. These figures assume ideal exposure to the sun at the angles my system is set up for. As can be seen from the graphs below, there is some shading around the middle of the year, and the system doesn't appear to be functioning as well as it might around midday at other times of the year. Most of the actual figures fall a fair way short of those originally quoted.

  


This graph shows the maximum power (kWh) obtained on cloudless days at various times of the year with the different panel configurations. Basically, there doesn't appear to be much difference between Panel Config 1 & 2, but quite an improvement can be seen with the third configuration.

 

Each vertical column represents an incrament of 0.1 kWh. As can be seen, there were 3 days for the year when the system only produced 0.1 or 0.2 kWh for the day. The highest single day for the year was 7.2 kWh, with a few more days following closely behind.

 

Power Production graphs for selected days

The traces on the following graphs are composed of vertical lines plotted each minute extending from the minimum to maximum power produced in that minute. Note the 'grass' at either end of the days when the inverter is on but not doing anything particularly useful - even consuming more than it's producing for part of the time. (ie The SunPower meter is going backwards).

Abbreviations used in text accompanying graphs

CRP

 Carport Roof mounted Panels

HRP

 House Roof mounted Panels

 

This is an example of a suuny day, close to the Winter solstice, when daily irradiation is at its lowest and shading at its highest.

08:15 - 09:15 : Shading of all panels receding - first CRP, then HRP.
09:30 - 10:45 : Dips caused by shading from neighbour's TV antenna to some CRPs. Still a small amount of shading from antenna elements after that.
14:30 - 14:35 : Shading of CRPs.
15:25 - 15:30 : Shading of lower group of 3 HRPs. Bypass diodes on these panels effectively isolate them from the other 6 panels in the series string, allowing the others to produce some power.
15:55 - 16:00 : Shading of next group of 3 panels further up house-roof. The remaining exposed panels can't produce significant amounts of power.

08:15 - 09:20 : Shading of all panels receding.
15:10 - 16:00 : Similar to above graph.
16:00 : Short dip in graph caused by inverter making significant changes to it's maximum power point tracking voltage and current.
Fine sunny day with no cloud.

10:40 - 13:40 : MPP (Maximum Power Point) tracking on Inverter apparently not working correctly, resulting in reduced output power. During this period the current rises from around 8.1 to the inverters maximum of 9.0 Amps, and the MPP Voltage falls from around 130 to 75 Volts, before rising to around 110 volts around 11:30 and falling back to around 75 Volts around 13:00. At around 13:40 the current drops to just under 8.0 Amps and the voltage rises to around 130 Volts. The humps didn't appear in the above graphs because the maximum current produced at that time of the year was under 8.0 Amps.Click here to see the one minute graphs for Power, Voltage and Current.
An example of a basically suuny day (apart from the intermittent cloud after 4pm), close to the Summer solstice, when daily irradiation should be at its highest and shading at its lowest. Hump in the middle of the day follows a similar pattern to the above graph. Click here to see the one minute graphs for Power, Voltage and Current.


 

Power produced under various weather conditions

Note : This is a VERY rough guide. A lot of factors influence these values- The time of the year, which determines the irradiation (amount of light) reaching the panels and is related to the number of daylight hours in a day and the angle of which the light will be hitting the panels, the temperature of the panels, and the variability of the weather.

Conditions Power produced if conditions persist all day Instantaneous Power in the middle of the day (approx)
Dark Sky, constant rain -0.2* to 0.3 kWh 100 Watts max
Overcast but light sky, little or no rain around 1.5 kWh 100 to 300 Watts
Bright Sunny Days 4 to 7.1 kWh 800-950 Watts

* Because the inverter actually draws some power, on a couple of days when the sky was quite dark, the inverter was consuming more power than it was generating. These readings were taken from the SunPower meter.


Graph of Daily Electricity Production vs Consumption

The first graph shows electricity production from the solar grid-interactive system (above the zero mark on the y-axis) and household power consumption (below zero on the y-axis) on a daily basis for the first 4 months of the system's operation. Days when the grid-interactive system was not fully functioning can be seen by the red mark on that day. The system had a few more bad days between the 15th and 31st of December, but has been working well since. The second graph shares the same time scale as the first and shows (a) via the blue columns and scale on the left hand side whether more power was produced (above zero on the y-axis) or consumed (below zero) on a daily basis and (b) via the orange line and scale on the right had side a running total of the daily figures.


Page Last Updated : 22/05/02