Solar Panels are installed to generate electricity by using sunlight. Solar panels work best when there’s no shade cast upon them. In fact, the shadow effect falls on even simply a part of one solar panel in your solar array will probably compromise the output of the full system.
The shadow effect occurs when a photovoltaic system does not receive the same amount of incident irradiation level throughout the system due to obstacles. In these conditions, the cells receiving a lower level of irradiance can absorb power instead of producing it. Bypass diodes are used to reduce the impact of shadowing effect and to protect the mono or poly solar panels. A single diode solar cell model is built from datasheet values and the parameters are used to obtain the panel with irradiance for each cell as a variable. Bypass diodes are used across every 10 cells in the panel and shadowing effect on this system is studied. A maximum power point tracking system using the perturb and observe algorithm and a buck converter are also added to the system. The simulation results show that the model derived is accurate. When the irradiance level is changed, the percentage increase in the maximum power point (MPP) is almost equal to the percentage increase in the incident irradiance level on the panel. Additionally, when bypass diodes are added to the system, higher values of MPP can be obtained during a partial shadow. However, they also introduce multiple local MPP into the system and this cause the maximum power point tracking (MPPT) algorithm to get stuck at a local maximum instead of the global maximum in some cases.
What are main problems faced due to the shadow effect?
How the shadow effect on one out of 36 cells in a small PV module can reduce power output by over 75%.
Hence the foremost problem due to shadowing is the reduced power generation.
Reduction in Power Generated
Shadowing impacts the desired power expected to be generated by a Solar panel. This disheartened the owners of the panel. However, if the proper installation is done, such a problem doesn’t arise.
Approving Net Meters
A very common problem faced due to shadowing is getting the net meter bills approved by the Electricity Board. In the case shadowing arises, the Electricity department doesn’t approve the net meters creating a huge problem for installers.
Panel Voltage consistently lower than expected
Given that we know PV voltage SHOULD stay consistently high, what can we do if we see an unexpectedly low panel-side voltage?
The first thing to do would be to physically inspect the panels (if it’s safe to do so) and make sure there isn’t some obvious obstruction. Mould can build up along the bottom edge of a row of flat panels when water isn’t able to drain properly, which reduces the output of the entire array.
If everything looks normal after a visual inspection, check the outdoor terminal connections – these will usually be MC4 connectors which can be separated using an inexpensive specialist tool (or without one – though with greater difficulty). It’s important to make and break these connections only when the panel is under no load – this means either covering the panel to exclude light, or working very early or very late in the day. When the MC4 connector is open it can be visually inspected and any corrosion or oxides cleaned away by spraying the male and female terminals with a Switch or Contact Cleaner. Check the indoor connections too – but not during the day.
The next level of panel testing uses a thermal camera – but don’t worry, although this requires more specialised test equipment, it is available quite affordably as a mobile phone accessory. Or try calling around solar installers, or electricians. They use them to fault-find on distribution boards. As long as the panel is still connected in the circuit, any resistance to the flow of electricity will show up as heat.
What are the factors causes shading?
The shadow effect, typically caused because of clouds, environmental obstructions such as trees or nearby buildings, self-shading between panels in parallel rows, dirt, dust and different other trash like bird droppings, etc. These shading effects are also static as a result of the position of the obstruction or in some cases dynamic, as an example, a shadow cast by moving clouds.
How to tackle the shadow effect?
Although the performance and therefore the return on investment (ROI) from a solar power system can be severely affected by shading – especially shading that occurs regularly due to an object that casts a shadow at the same time every day as the sun passes through the sky – there are a number of ways to avoid or mitigate these effects.
Positioning of PV solar systems
Before installing a solar PV system you must do a careful analysis of the site considering all time of the day for all seasons of the year to avoid shade. A nearby growing tree or building that may come up in future also need to be considered before finalizing the location for PV System.
Site your solar panel array where there will be no regular the shadow effect
This is the first and most obvious step to making sure your system does not suffer the consequences of being partially shaded. It is extremely important to consider all times of day for all seasons of the year when working out whether some nearby object might cast a shadow onto your roof. A solar system installer should be able to tell you if shading will be a problem using a range of mapping tools.
Solar system owners should also be vigilant in making sure that there are no nearby trees which might grow tall enough to eventually cause shading issues. Solar system lifespans are typically expected to be 25+ years, during which time trees have plenty of time to grow.
Clouds are another source of potential shading. Clouds passing through the sky during the day may also result in fluctuations in system output, but these are basically unavoidable. Amorphous silicon solar cells are said to be better at handling shading than crystalline silicon solar panels, but generally speaking the relatively low overall efficiency of amorphous panels means that crystalline modules are generally a better choice.
There are some other technologies under development that may offer high efficiencies even in inclement weather, such as ‘super black’ solar cells, but most of these are still either expensive or not yet commercially available.
Use the MPPT Solar Inverter
Maximum Power Point Tracking (MPP Tracking or MPPT) is a technology that now comes standard in most quality inverters. An inverter equipped with an MPP Tracker (or several of them) is able squeeze the most usable energy possible out of a string of solar panels (even when shaded) by adjusting the voltage to always suit the inverter’s preferred input range. In a nutshell, an MPP Tracker helps to minimise output losses associated with partial shading and other panel output mismatches. Inverters without MPPT capability simply lose the output from the weaker string once it passes below the required output threshold.
Related MPPT Solar Inverter Products
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Get a system with power optimisers
If the shading on your roof is not extensive (‘near shading’), then power optimisers might be the right option for you. These devices get around the problem of partial shading by eliminating the need for or importance of strings in the first place. The power optimisers essentially allow every solar panel in a system to operate independently, so that overall system energy production is not disproportionately affected by just one or two shaded panels.
The main downside to these technologies is that they tend to be a bit more expensive than a system with a standard system containing a central string inverter, so there’s no need to splash out on them in instances where shading is not an issue.
Now a day panel manufacturers are providing bypass diodes for the entire panels so that if one panel gets shaded it will not affect the performance of the entire array, but if we use bypass diodes for each cell of the solar panel, the power output from the solar panels isn’t dropped at zero simply because one single cell is shaded. Here the shaded cells are merely bypassed and not allowed to impact the output of the whole panel. The power output of the panel might reduce, however, it won’t be directly based on the power output of the lowest performing cell.
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