S265S   09 0901
Reference Sheet II01-28 Internet Search Techniques
Google search results for these search terms:
effect of clouds on solar cells
Below are the first three Web pages appearing on the search results for the above search terms. None of these pages gave us any useful information about what type of solar cell performs best in cloudy conditions.

#1 in the Search-Results List
Solar panels hold a wealth of benefits, both for individuals and for the world at large. Economically, solar panels promise to lower the cost of electrical power. Environmentally, solar panels can give us cleaner power, sustainable power that will not require further damage to the environment. Solar power can reach remote areas. It can carry education, or urgently needed medical information.

The effects of clouds on a solar panel, though, might diminish those and other promising benefits.

The effects of clouds on a solar panel might make it far less efficient in certain parts of the world and at certain seasons.

For that reason, people who are considering solar panels for their homes are often heard to ask: will clouds affect my solar panels?

#2 in the Search-Results List
There is an increasing trend of more photovoltaic (PV) grid connected systems. Possible technical
problems raised are quality and stability of the electrical distribution system when more PV units are
grid connected, and the islanding effect. Electrical power quality of grid connected systems depend on
various factors. They are solar intensity variation due to amount of and movement of clouds, shading
of PV arrays, electrical characteristic of arrays, inverter characteristics and electrical loads, etc. Studies
on effects of moving clouds on electrical outputs of PV grid connected systems were done overseas
about 10 years ago.

#3 in the Search-Results List
Amorphous - Amorphous solar panels are also referred
to as "thin film" solar panels. This type of solar cell uses
layers of semiconductor that are only a few micrometers
thick (about 1/100th the thickness of a human hair). This
lowers the material cost but makes it even less efficient
than the other types of silicon. However, because it is so
thin this type of cell has the advantage that it can be
placed on a wide variety of flexible materials in order to
make things like solar shingles or roof tiles. Because they
can be put on to flexible backings they have proven very
valuable in certain types of applications where flexibility is
more critical than power. For example, these types of
solar panels are often used in portable products such as
solar backpacks and solar bags. Overall efficiency on
average is about 5-6%.
Google search results for these search terms:
solar amorphous crystalline cloudy OR "low light"
Below are the first three Web pages appearing on the search results for the above search terms. All three pages gave us information about which type of solar cell performs best in low light, namely amorphous silicon cells perform better than crystalline silicon cells..

#1 in the Search-Results List
18W amorphous solar panel
1. Works in all weather conditions, including low light and cloudy conditions. 2. Ideal for deep cycle or multipl...

#2 in the Search-Results List
Why amorphous panels perform well in low light
Multi-crystalline panel operating voltage is between 14 - 18 volts. If the voltage falls below 13.5 volts charging voltage, the battery cannot be charged because of back emf. Energy produced is dissipated by the controller, ie wasted.
Amorphous panel have peak operating voltage of 62 volts. As voltage drops in low light the voltage output it is still well above 13.5 volt. Energy produced can still charge the batteries.
Solar panel efficiency itself should not be the indicator when choosing panels. More important is the total useful power produced.

#3 in the Search-Results List
1. Crystalline Silicon PV Module: There are 2 types of crystalline silicon (c-Si) are used PV modules. Mono crystalline and poly crystalline. Conversion efficiencies of crystalline pv modules averages about 10-15%. Downside is  poor effeicieny in low light conditions and are not shadow reststant. Dust and dirt deposits reduces efficiency considerably.
 
2. Amorphous Silicon PV Module: Amorphous silicon (a-Si) PV module or thin-film silicon PV module absorbs light more effectively than crystalline silicon PV module, so it can be made thinner. However it's efficiency is low at between 6 - 8%. Production cost is lower. Amorphous panels are usually twice the size of crystalline panels for the same wattage. Because of it's higher efficiency in low light and being shadow resistant actual power production is higher than crystalline panels.
 
3. Hybrid Silicon PV Module: This combines the advantages of the above two types of panels (c-SI) and (a-SI). By surrounding mono crystalline silicon with thin layers of amorphous silicon we increase the mono crystalline panels to lower light levels and indirect light. Hybrid silicon PV module has highest conversion efficiency at around 17%.

Which Solar Panel

For most people price is always the single most crucial factor.
From cheapest to most expensive
1. Amorphous
2. Multi-crystalline
3. Mono-crystalline
4. Copper indium

Amorphous panels are cheaper to manufacture and to compemsate for lower efficiency the panels are twice the size of similar capacity multi-crystalline panels but half the price.
If space is a problem such as on boats and caravans then mono-crystalline panels are the way to go.
If not then amorphous panels should be the choice as the same 20 year warranty is offered.

Advantages of Amorphous Panels
Multi Amorphous panels are reputed to work in low light. The reason for this is clear when you consider that the BD40 amorphous panel has peak operating voltage of 62 volts.  As voltage drops in low light it is still above 13.5 volt charging voltage of your 12 volt battery bank.

With a multi-crystalline panel it's operating voltage is from 14 - 18 volts. If the voltage falls below 13.5 volts the battery cannot be charged. Energy produced will be dissipated by the controller.

Amorphous panels are shadow resistant meaning that power production is not cut-off if a shadow falls over the panel.
The glass surface is smooth. Dirt and grime forming are easily washed off. Bird droppings will not cut-off power production.

As amorphous panels work well in indirect light it's efficiency could be increased with reflected light.

MPPT Controllers
These are essentially Dc to Dc converters. If a solar panel produces 2 amps at 20 volts ie 40 watts feeding this current directly into the battery results in only 2 amps X 12 volts  that is 24 watts. 16 watts is "lost", An MPPT controller converts the current to 3.3 amps at 12 volts (40 watts) before feeding it into the battery.