Perhaps I should start this with something of an apology. My solar array isn’t that large compared to some, just 620w, and my boat isn’t exactly 10m, it’s 10.36 according to the SSR, but perhaps the biggest misrepresentation is that it’s a catamaran. An old narrow beam catamaran, but a catamaran nonetheless. And that affords me slightly more room than an equivalent length monohull, but also brings with it it’s own challenges.

The problem

There’s a solar template that most modern catamarans follow. That is panels installed either on a hard top bimini, dinghy davits come solar arch, or both. On Jade I have neither.

I did toy the idea of building a stern mount for some panels. Random Chris’ (now Sailing Britaly) video on his solar setup was an inspiration, but I decided against it. Firstly I like the uncluttered view from my rear deck, and the ability to run and jump off the stern without worrying about banging my head. Secondly, Jade, being a Prout Snowgoose 35 from the 70s is typical of catamaran design at the time, and has narrow canoe shaped hulls. That translates into less buoyancy than more modern designs, and with 400kg of batteries and engine back there already, I was loathe to add another 60kg+ for panels and  stainless rigging.

Since I don’t have a hard top bimini the second prime panel location was out too. What I do have however, is a permanently erected cockpit tent. I could fit easily fit two 50-75w panels either side of the boom there, but it would be pointless when at anchor, as in the summer months, when not under sail, I almost always have a sunbrella fabric shade up that covers the tent and the rear deck. Keeping cool in 40c heat does more for my quality of life than the potential 50 amps the two panels might bring in.

The next option I considered and quickly dismissed was a rail mount setup on the port and starboard sides of the boat. It’s something that is popular on monohulls, though seldom seen on catamarans, but one that would have allowed me to mount two good 110w panels. The problem with that is windage. This cat is a pig to manoeuvre at the best to times and two or more essentially solid sails to the sides surely would be any help mooring in a crosswind.

The solution

I suppose the solution was staring me in the face in all the time. Just mount the panels on the coachroof. There is acres of space up there, and I already had 4x100w panels stuck there from the previous owner. The issue here was 1) the positioning of the panels, 2) having enough space to walk around the coachroof and access the base of the mast, winches, and staysail.

The original panels were mounted in such a way that adding more would be difficult. They’d have to be moved or removed. Adding to the problem was the unevenness of the coachroof, two solar vents, and two hatches.

Shading was another consideration, especially given that I have a cutter rig with roller furling stay sail. On boards like cruisersfoums, or the ‘solar on a boat’ Facebook group, people are often like “oh my god, but the shading,” it reminds me of the Simpsons “think of the children” meme. Of course they have a point, why put panels somewhere there is almost guaranteed shade. But on a boat there is almost always guarenteed shade. A boat in the northern hemisphere facing south with panels on an arch, or bimini, will at some point encounter shade from the mast and rigging. My setup is no different really. At certain angles to the sun I get some shade, at others I won’t. This is why you over-spec the array. A common practice in home installations (usually to take into account cloudy days, and winter), but seemingly less so on a boat.

The gear

Once I’d confirmed I going to mount the panels on the coach roof and live with a little shading, I had another decision to make. That was, which panels to go for. Outside of SunPower cells, the LG 365w NeonR modules are the most efficient you can get. These beasts  are 1700mm x 1016mm, and could potentially kick out up to 20amps per hour. Two of these would fill the coach roof and give me an array of over 700w which is good going on a small boat. The downside though, is the weight. The panels are nearly 19kg each, as I’m trying to cut weight not add to it, 38kg (for two panels) was more than I felt comfortable with. Additionally, taking up the whole coach roof would mean tossing my old but perfectly functional 4x100w panels, and no-one likes getting rid of perfectly good equipment.

I started to look at semi flexible panels instead. That can be something of a minefield. eBay, and Amazon are full of cheap no-brand Chinese semi flexible panels. It’s a case of pay your money and take your choice, but I wanted quality. And further more, due to the space constraints (of keeping the 4x100w) my new panels had to fit in a space of roughly 1000mm x 570mm. eBay specials at that size were limited to about 75w. The only way to get larger output panels was opt for sunpower cells. Solbian panels would fit the bill, actually, no in terms of bills they way over what I was prepared to pay.

A little looking around, and I came across Fly Solartech. Like Solbian, an Italian company (this time based in Udine), manufacturing semi-flexible fibre-glass backed panels using high efficiency Sunpower cells. The panels boast a seven layer antireflective surface with ETFE coating. The latter is important. Cheap panels often have PET coatings that yellow and haze over time in harsh sunlight. ETFE shouldn’t suffer the same problems.

fly solartech 110w solar panel

The controller was the easy part. I already knew I wanted Victron kit. It’s priced well and the bluetooth connectivity is great addition. It was actually the Bluesolar 75/15 controller I’d had my eye on, but when it came time to buy, I found that the new Smartsolar 75/15 with built in bluetooth (saving me having to buy a separate dongle) was available for around £100.

Installation

This was the tricky bit. Solar panels get hot and with heat they lose efficiency. There is a respectable body of opinion that panels should have some breathing space underneath them. In my research I didn’t find any evidence at all to suggest that this helps cool them down. I did however find anecdotal evidence that placing them directly on the coachroof could cause blistering to the paintwork or gelcoat. That being said plenty of people do it without issue.

In any case, my coachroof needs panting. It’s a job for another time, but it meant that I didn’t want to fix the panels permanently in place. Additionally, I didn’t want the heat from the panels radiating through the coach roof. My solution was to mount the panels on some 3mm PVC foam board using 3M’s DualLock. The foam board itself was then mounted to the coach roof using the same method. DualLock is expensive. Very expensive, so rather that fixing it around the permitter of the surfaces, I cut small 2cm squares and attached them at key points around the panels and the foam board. This reduces the force required to remove panels should I need to, but still holds down well enough to survive all the but the blowiest or nasty blows. It also had the added advantage of providing an air gap between both the panels and the foam board, and the foam board and the coach roof.

The results

Solar yield

One of the reasons I chose the Victron Smart solar controller was to better monitor my solar input. Unfortunately my other controller a Morningstar ProStar 30 doesn’t keep a history of solar yield. I had thought about replacing this with another Victron, but then if it works, why change it. Strangely these ProStar PWM controllers still retail for £200. I could almost buy a nice Victron Smartsolar 100/30 for that.

Anyway, the four 100 watt panels connected to the ProStar give a yield of between in 900-1200 watts. The two Fly Solartech 110w panels yield around 700 watts (conservative figure). In total that is around 150 amps a day in Mediterranean  spring/early summer. I wake up to a 50-90 ah deficit according my battery monitor, but the panels see to it that the batteries are full (as much as they are going to get anyway) in afternoon.

Oddly, I find very little difference between wiring the two new panels in series verses wiring them in parallel. My tests have shown that series has the greater potential, but shading means that parallel produces more constant results. That being said the difference is no more than 5a over the course of a day.