Solar Panels – everything you need to know!

Posted by Sammy on June 17th, 2019

What kind of panel should I fit?
This question is a bit of a red herring –in reality the question should be ‘How much space do I have?’

There is now a whole taxonomy of solar panels comprising three generations and various species within each generation. The academic drive is to make panels that are more environmentally friendly, both to make and to dispose of, and to reduce the cost per Watt. But this has resulted in a much poorer conversion efficiency (the amount of electrical power you get per Watt of solar power in) which is not helpful to sailors with a small area available to mount the panels. Because of this let’s eliminate from this discussion the third generation organic panels however creditable the motives for developing them. Similarly, second generation Amorphous panels have, in my opinion, little to recommend them: although they are cheaper to manufacture the cost per Watt by the time time they sit on the shelf in the shop is two or three times the cost per Watt of the first generation crystalline panels. Their only obvious advantage is their tolerance to shading. So back to the first generation: crystalline panels come in mono- or poly-crystalline species but they only differ slightly in cost per Watt and efficiency.

Added to the mix is the flexibility aspect, flexible panels require a bit of clever manufacture and this is passed on in higher prices. If you want a little more detail on the three generations of panel read my article in PBO January 2015, which is available from the reprint service. So does this mean the default starting point for any installation is a rigid, crystalline panel? In short: yes!
What are the costs? This is a quick survey carried out in November 2015 across a small number of reputable suppliers. Two things leapt out at me when I did this: firstly if you use panels destined for household solar energy installations their cost is really low, below £1/Watt so it would be feasible to outfit your yacht with these and if the frames eventually get corroded earlier than you might hope you could afford to ditch them and replace them. Their output voltage is typically around 30V so you need a regulator which will handle that voltage but I shall seriously look at these as replacements when I eventually need them. Secondly, in general I was surprised at just how much the cost of panels has fallen since the original of this article was published in PBO Summer 2011, and how much choice of manufacturer there now is. Here are a few pointers but shop around and you’ll probably be able to beat these numbers.

Where should I put my panels?
If you’re just fitting a small panel to top up batteries on a mooring buy a cheap rigid panel and find places on your boat where you can tilt it to catch the sun’s rays for the majority of the day. We do this during the winter in Greece where we strap an old 15W amorphous panel to the coachroof and it works well for us. It’s not heavy and a crystalline panel would be smaller and thus lighter. Choose a spot that isn’t shaded for the majority of the day and this technique should serve you well. Do the sums. I have heard of people whose batteries have been damaged by a constant high power being applied to an already charged battery even through a regulator. My rule of thumb for trickle charging is a panel Wattage about 10% of the battery’s stated Amp-hours –but anyone else’s guess is just as good.

If you spend more time on board and need to get the best from your panels, mono- or polycrystalline panels will give more power from the same space –we replaced our 75W bank of amorphous panels with 200W of monocrystalline panels in the same area. But with higher efficiency comes higher sensitivity to poor mounting conditions, so if you want the best from your panels you need to do your utmost to ensure they are not shaded, and also that they are tilted as close to a right-angle to the sun as possible. For this reason, liveaboards usually mount theirs on gantries at the stern or on the pushpit.

Read more at https://www.pbo.co.uk/expert-advice/solar-panels-everything-you-need-to-know-24455#hGYxeRt1kYQxcS0K.99