While the claim may be that this type of panel has superior shade resistance, the results can be very different.

smaller cell size
: The smaller the cell size, the less shading it requires to be 100% shaded. The same amount of shade that completely covers a small cell might only cover ¼ of a larger cell. Larger cells are better for shade resistance.

solar cells shaded
: If just one cell is 100% hard shaded, the output from that series string of cells will be zero, or close to zero.

: Silicon solar cells consume power as well as produce power. If a cell is shaded, it will consume power from the other cells in the series string, resulting in diminished output and heating up of the shaded cell.

solar panels in parallel
: If several series strings of cells are connected in parallel without the installation of blocking diodes, the power from good strings will feed into a shaded string resulting in diminished panel output and the chance of cells burning.

blocking diodes
: Blocking diodes prevent back-feeding in parallel circuits, but reduce voltage output by 0.7v.

: By-Pass diodes prevent cell burning ("Hot-spots") and do not consume any power or diminish panel output.

: The more cells and electrical connections there are on a panel, the more output-reducing series and shunt resistance the panel will exhibit, and the more chance of a connection failure, particularly if the panel is flexed.

solar cells in series
For best results, look for a panel with large, high efficiency cells, in one series string, with by-pass diodes protecting any string of 50w or greater.

blocking diode drawing
Blocking diodes must be installed on circuits or panels connected in parallel.

An essential component in the installation of solar panels on your vessel is a solar charge controller or regulator. This will regulate the voltage and current coming from your solar panels going to your battery. Most solar panels are 16-25 volts, so if there is no voltage regulation the batteries will be damaged from overcharging. Bear in mind that a fully charged 12v battery is around 12.7 volts at rest, but needs around 14.2 to 14.8 volts under charge. A solar panel has to put out at least that much voltage to be of any benefit, but if the panel voltage is not controlled and reduced it will cause serious battery damage.

Another point to keep in mind: solar panels provide power best when cool, under a clear sky, and in full sun; in other words in perfect conditions. But one can't count on that type of weather day after day, so solar panels have to be built to provide that extra voltage for when the sun is low in the sky, there is cloud cover, high temperatures, or heavy haze to ensure your solar output is not compromised. The truth is a 100 watt panel rated at per industry Standard Test Condition (STC) of 77oF and 1Kw/sq m irradiance will put out less watts when its surface temperature is 100oF degrees and when only 800 w/sq m irradiance is available, i.e. when it is in non-standard conditions.

So this is where the right solar charge controller can help. There are basically two types – PWM (Pulse Width Modulation) and MPPT (Maximum Power Point Tracking).

In Defense of Lithium Ion Batteries
Yes, it's true; thermal runaway can and does happen in Valve Regulated Lead Acid (VLRA) Absorbed Glass Mat (AGM) batteries, and is not a new phenomenon afflicting Lithium Ion batteries alone. A Google search of "Thermal Runaway in AGM Batteries" will reveal enough technical papers on the subject to keep even the most techno-savvy occupied for a long while, and will save me trying to explain the why's and wherefore's here. The simple fact is that, given the right conditions, an AGM battery can, and will, start a self-perpetuating internal heating process (thermal runaway) that can end in catastrophic failure with the possibility of fire and explosion. So why is there so much negative publicity and bad karma surrounding Lithium Ion batteries, when AGM's are prone to much the same maladies?

IRS Form 5695 2015 Pg 1IRS Form 5695 2015 Pg 2

The US Federal Government offers a solar energy tax credit, applicable to your second home, i.e. your boat! As long as there is a head and galley onboard and it is docked in the United States, your vessel qualifies. This tax credit, extended to December 31, 2019, is a 30% credit on qualified expenditures to purchase and install solar panels, with no maximum limit for equipment placed in service after 2008. In the last few years, we hear at different boat shows the success stories from boat owners getting that 30% tax credit. This credit can be retroactive – as long as the solar system was placed into service after January 1, 2006.

Check out this updated link to the Dept of Energy's website that gives a simplified description of the energy tax credit: Want to see how simple the actual IRS form is to fill out: Your state government may also have a solar tax credit. It may be worth investigating.

Life has become so much easier for so many people since they took advantage of this tax credit. If you want solar power on your boat, it may have just become more affordable. There is still time to plan and implement your solar power project, but I wouldn't suggest waiting too much longer – December 31, 2019 will be here before you know it! Contact us at about your marine solar system.

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