A Marine Solar Panel, or a
Wind Charger?

The case for fitting a marine solar panel or two on your sailboat can be overwhelming...
'Fit 'em and forget 'em' goes the sales pitch.
'Free power from the sun' claim the advertisements.
"It's a miracle" say I, fully in agreement with all except for the 'free' bit, remembering what it cost to buy two 85watt solar panels for Alacazam.

But was it money well spent?

Yes, definitely, but only because Alacazam was cruising in the West Indies at the time, where there's no shortage of sunshine.

In these tropical regions you can generally rely on 10 hours of it every day which means I could expect around 60A from the solar panels over this period.

Similarly, when we were cruising in the Mediterranean our marine solar panels were great contributors to the inward flow of amps.

But when we return to the UK? Sadly no. Not even in the summer months. 

Here a windcharger will be much more productive - and cost effective - than a marine solar panel.

Factors Affecting the Performance of a Marine Solar Panel

A number of factors affect their performance, or from another point of view, just one - the sun:

  • Angle of incidence of the sun's rays - This of course depends on season and latitude. At the equator the sun is high in the sky for much of the day, so excellent performance can be expected. In high latitudes, with the sun low in the sky, performance will be much reduced;
  • Period of exposure - At the equator, cloud cover accepted, you can feel entitled to 12 hours of it. At high latitudes in the summer, rather more but less intense. But in these latitudes in the winter, you shouldn't expect much from your solar panels at all;
  • Temperature - As temperature rises output falls. Output is normally quoted at 25°C. In the sun-drenched tropics their surface temperature could easily be double that, and were it not for the cooling trade winds, their output would be seriously impaired;
  • Cloud cover - Less is best. No surprises there.

The Technology behind a Solar Panel

A photovoltaic (PV) solar cell consist of two layers of silicon-based laminates constructed as a 'semiconductor' in which one of the layers is electrically positive and the other negative. When subjected to the sun's rays, the photovoltaic activity between the two produces an electrical current.

The principle's not new, having been unearthed by the French scientist Henri Becquerel (1852 - 1908), who also won the Nobel Prize for bringing radioactivity to the world's attention.

Solar panels are made up of a number of photovoltaic cells, of which there are three main types:~

  • Monocrystalline rigid panels;
  • Polycrystalline rigid panels;
  • Amorphous silicon flexible panels

Monocrystalline panels are constructed of small individual photovoltaic cells, and have an efficiency rating of 15%.

These will outperform polycrystalline panels which are constructed of larger PV cells and are rated at 13%.

Both types are considerably more efficient than the flexible amorphous silicon panels which are rated at a rather disappointing 6%.

But flexible panels shouldn't be discounted; after all you can fix them to a non-rigid surface - on a bimini, a curved coachroof or even around a sailcover - where you otherwise couldn't harvest any energy from the sun at all.

Clearly the larger the marine solar panel array the more energy it will harvest. A good quality monocrystalline panel will be rated by the manufacture at around 120watt per square metre.

boat solar panels and windcharger on Alacazam's stainless steelgantryTwo 85w marine solar panels and a windcharger on Alacazam's gantry...

Often you'll see rigid panels mounted on pivoting clamps that can be adjusted to be perpendicular to the sun's rays. This will clearly maximise their performance, providing they are regularly adjusted to keep pace with the sun's movement - a degree of discipline that I sadly lack, so mine stay fixed flat on the stern gantry as shown here.

Note that the radar and the windcharger are located outboard so as to reduce as far as practicable to extent of any shadows cast on the solar panels.

But there are days when the sun chooses not to put much of an appearance at all, so like most cruising sailors, our green energy set-up includes both wind and sun charging methods.

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