Your Solar System’s Output

Your solar system has been installed and as part of the overall process you have been informed in regards to how much the system will produce on average per day, per month and per year. In fact this information would have probably played a role in you making a decision to go down the solar road in the first place, especially if you are the proud owner of a commercial solar system.

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The Process

Now the performance of your solar array makes certain assumptions and one of these is that the solar panels are clean. Remember the output of your system is directly related to how much light strikes the surface of your array and is converted into DC electricity and then passed to your inverter(s) which converts this energy into AC that services your electrical loads.

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Dirt Is Bad

If there is a layer of dirt covering your array this reduces the actual amount of light that the solar panels can process and this reduces the amount of energy available to service your loads which is obviously not a desirable outcome.

So how much can dirt influence the output of your solar system, 15 to 30% for moderate dust conditions according to the National Renewable Energy Laboratory https://www.nrel.gov/pv/assets/pdfs/2015_pvmrw_105_weber.pdf and losses up to 100% possible, if cementation occurs.

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The Numbers Don’t Lie

So I will assume a moderate level of soiling, 25% reduction in overall output we will look at a domestic system of 5 kW, 5000 watts, location Melbourne, Victoria, Australia.

This system on average will produce:

•  5 x 3.6 kWh = 18 kWh/day
•  So 6,570 kWh/year. 
• If we attach a value of $0.25/kWh that equates to $1642./year. 
• If we reduce this figure by 25% now the system saves $1,231/year 
• a drop of $411/year.

Now if this was a commercial system of 100 kW the figures would be as follows:

• Produces 131,400 kWh/year
• If we attach a value of $0.25/kWh that equates to $32,850./year saving.
• If we reduce this figure by 25% now the system saves $24,637.5/year 
• A drop of $8,212/year 

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Comparison Charts

LOSS PER YEAR

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Note; the above figures assume a fixed price of electricity at $0.25/ kWh and all solar produced is consumed on site.

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LOSS PER 10 YEARS

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Not All Locations Are The Same

The amount of general soiling a solar system will experience depends on many factors:

• Amount of bird activity in the area
• Some locations are naturally more dusty than others
• Coastal and bay side systems more prone to salt build-up
• Systems near ongoing building works experience higher levels of soiling
• Areas of high pollen count

Now rain can play a role in cleaning panels but sometimes it can create a detrimental effect if the precipitation is light and combines with high pollen count, natural floating dust and or particulate matter from bushfires so it cannot be relied upon to maintain a dust free surface.

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Cleaning And Maintenance

Implementing a regular cleaning schedule not only ensures optimum system performance but also allows the opportunity for suitably qualified personnel to make a visual check of the system in general.

In fact sometimes panel cleaning schedules can coincide with a full system maintenance ( see our System Maintenance Blog) but at the very least the person conducting the cleaning can visually flag any obvious issues with the system if this is the case.

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Conclusion

The importance of maintaining a regular cleaning schedule for your solar system is obvious. To maintain optimum efficiency the panels must be dust and detritus free and relying on natural rainfall can be problematic at best. The system owner must practice due diligence in regards to prudent cost benefit analysis, weighing up the cost of the cleaning process versus the losses if cleaning is not undertaken. In addition, the fact that as part of the cleaning process a visual inspection of the solar array occurs, potential or existing issues can be identified and reported.