Solar Panels

When first researching solar panels I identified there are three main types and in order of efficiency they are:

• Amorphous
• Polycrystalline
• Monocrystalline

With the latter being the most efficient.
Additionally, it's not recommended to purchase a panel with a black frame or black backing. Apparently black can cause a heat build-up which has the effect of degrading a panel's output.  The same can occur if the panel is fixed directly to the steel roof of the boat. 
Solar panels are made up of a matrix of silicon wafers (cells). What many people don't realise (I didn't) is that cells are manufactured in four grades. 
Class A. Cells with absolutely no defects whatsoever. No saw marks on the wafer,edge chips, P or N dopant fade, microcracks, Al paste smear or large % of wafer thickness deviation.
Class B.  These are cells that have saw marks still in the wafers (cells) that were not properly polished, have thickness deviation and colour deviation.
Class C.  Chips,breaks and microcracks. Breaks cannot be more than 1/4 of the cells total surface.
Class D.  3/4 broken cells which in effect are just pieces of wafer. Pieces are just that, pieces. They are not graded and are considered scrap for remelt or sale to micro solar appliance producers (China,Taiwan,Hong Kong) for laser cutting and use in walkway lights,etc.
There are only a small number of silicon wafer manufacturers and they tend to keep all their Class A cells to make their own panels. They usually sell their Class B, C, D to other panel manufacturers who do not manufacture their own cells. Often these panel manufacturers classify or advertise their panels as being made from Class A cells (despite being Class B or C) as they are the highest quality they can obtain.
Even more panel sellers don't advertise or inform potential purchasers of the grade of cell used in the panel. It's very much Caveat Emptor.
So the whole process of purchasing solar panels can be rather fraught with potential hazards.
In our case we have two 100 Watt monocrystalline panels connected in parallel.  This gives us a potential 200 Watts of electricity.  The panels can produce more than 12 Volts.  To regulate (control) the output from the panels a solar controller is required.  Controllers for such a small system are usually either PWM or MPPT.  A simple way of explaining the difference between the two would be to describe the PWM as momentarily stopping the transmission of electricity to the batteries when the voltage gets too high.  It might be likened to a switch which is being rapidly turned on and off to prevent the panels damaging the batteries by delivering too higher voltage.  The MPPT controller converts the additional high voltage to amperes.  So a MPPT controller allows the panel to deliver more useable electricity.  This is probably why a MPPT controller is more expensive.
Our MPPT controller delivers electricity from the panels to the domestic battery bank at 14.6V.  We have a potential 200 Watts of generating capacity so the maximum amperes should be 13.7 amps (200÷14.6).  Assume 95% efficiency and you have a theoretical capacity of 13 amps.  However on a good day we might get 10 amps from the panels.  This could probably be improved by aligning the panels to the sun (and constantly moving them to track the sun).  I have considered doing this, but the cost of installing a swivel and tilt solar panel mounting system to gain an additional 3 amps doesn’t look that financially viable.  The positive news I take from this is my eBay panels appear to be made from either Class A or B cells.  It must have been my lucky day!
If it were possible to produce the additional 3 amps for 50% of the year at an average of 8 hours daily the panels would generate an additional 4380Ah annually (((365÷2)x8)x3).  However I suspect this is wildly optimistic.  The boat alternators produce approximately 180 amps which means we wouldn’t need to run the engine for 24 hours each year to achieve 4380Ah.  Not much of a saving on such an optimistic figure! 
Where a solar panel array is useful is during the final two stages of charging the battery bank.  During the Absorption stage our batteries accept a maximum current of 10-20 amps whilst during the Float stage they accept 3-10 amps.  It therefore makes sense to use the solar panels to complete and maintain the final stages of recharging the batteries,` rather than add wear to the engine by running it to produce such a low charging requirement.
My Conclusion
If we wanted to increase our solar power production it would be cheaper to buy a third panel rather than purchase a swivel and tilt mounting system for the existing setup.