Solar shadowing – reducing the losses is like partially unblocking a water pipe. Partially solar shadowing reduces the losses proportionally. Nevertheless, except in extreme clouding, quality modules produce some output. During daylight it’s rare to have zero output.
Solar Shadowing – reducing the losses – bypass diodes partially assist
Most 12-volt solar modules have 60 cells. Each cell is connected in a string. A totally shadowed cell produces no current. Blocking one affects all. Basic modules supply the current of the least producing cell.
To limit this, a good quality module has three strings. Each such string has 20 cells and each string has a so-called ‘diode’. If activated, it carries current from unshaded strings. This assists, but is not a perfect solution. With only one cell shaded, output is slashed one-third. Worse, diodes are not reliable. One diode failing will prevent associated strings working.
A typical bypass diode. Pic: Original source unknown.
The diodes have a second purpose. If some cells are shaded or dirty, remaining cells ‘see’ them as a load. They feed them power, but diodes preclude that.
The ideal is a diode across each cell. Doing so, however, is costly. Worse, diodes fail more often than cells. Reliability is reduced.
Avoid solar modules with less than three diodes. (Diodes are inside the module connection boxes).
Solar Shadowing – reducing the losses – the more effective ways
In basic systems, the lowest cell output limits the overall output. With multiple modules, shadowing one limits output of all. The loss is confined to the area shaded.
Power optimisers attach to existing solar modules. They maximise energy. Power optimisers also eliminate power mismatch. They decrease shadowing losses. Such optimisers can be built into solar modules. Or fitted separately. The concept works well.
The optimisers use technology proven in RV and home solar regulators etc. They work like a car’s torque converter. They ‘juggle’ volts and amps to optimise watts.
A conventional solar system combines module dc outputs. It feeds them to a central inverter. The micro-inverter concept is similar. Each module has a small inverter inbuilt. Regardless of partial shadowing that inverter converts output to 110-230 volts ac. It does so even if current varies.
Pic: Enphase micro-inverter
A micro-inverter cannot compensate shadowing. It can, however, confine loss to the shadowed module. This enables solar’s use where partial shadowing is unavoidable.
Micro-inversion has a possible downside. It may affect people seeking to build their own stand-alone solar systems. The inverters run at high voltages. In some countries (including Australia) such work has to be done by certified electricians.
Solar Shadowing – reducing the losses
Our books cover shadowing issues in depth. Solar That Really Works! is for cabins and RVs. Solar Success is for homes and properties. Our books also cover legal issues. Caravan & Motorhome Electrics covers RV solar and general electrics. All are available in digital or print form. You can download our digital versions right now. Click on the books’ title (above). Print versions are stocked by all Jaycar stores. You can also buy them (from anywhere) from booktopia.com.au/