Solar panel connection reseach. Interesting findings on YouTube

Well now, there's a thing! Helpful comments from Frank and Dave (thanks chaps) on my last post caused me to doubt my decision to connect solar panels in parallel rather than in series. Their arguments were erudite and persuasive. So wanting to delve further, I called upon my secret weapons, Rick, the smartest Engineer (with a capital E) I know, and I know a fair few, and Peter my brilliant Cambridge PhD scientist son (well I have to play the proud Dad sometimes) who has taught me so much inluding most of what I know about electronics.

Rick has never looked into Solar energy in any detail, but his knowledge of electrics and his sense of logic led him to side with me in so far as recognising that serial linking two panels with similar voltages but potentially different currents might not be advantageous. I left him to ponder.

Peter had never looked into solar power either, but he is nothing if not a quick researcher (with a good knowledge of electronics) and went off to look at a lot of graphs and interview the internet. One of his many mantras is that "Theory tells you which experiments to run" so he set out searching for people who had actually compared series and parallel solar panel connections and taken proper measurements under different conditions. What he found was very interesting.

There is a series of YouTube videos presented by a smart lady called Amy from the eltstore which I believe is in Canada. I wont go into all the detail here, but she connects up panels one way and then the other and takes readings of panel volts and amps and the amps delivered by a connected MPPT controller. If you go to Youtube and search for solar mismatch, you'll soon find her.

I was particularly interested in the mismatch topic because my intention is to add a new panel with an old one, and to some extent they will have different characteristics.

What Amy's tests clearly demonstrate is that when adding a second panel with a similar voltage, but materially different current from the first one, it is much better to connect them in parallel. All the specs and graphs i have looked at show that panel voltages are nearly always remarkably similar and stable but amps generated vary a lot with panel size and solar energy input. Furthermore, and most interestingly she demonstrates that under partial shading, series connections suffer a much larger drop in ouput than parallel. Go see for youself if you don't believe me. The videos are very good. She also does a good demo of the effects of tilting the panel in low sun, and another on the effects of temperature on panel performance.

This, as I see it, is the difference between ideal conditions and the reality of solar panels on a boat. Frank and Dave are quite correct and in ideal conditions I would follow thier advice to the letter. The ideal would indeed be for me to have two identical panels, each with their own controller, and each receiving the same amount of sunlight. The next best thing would be two identical panels connected in series to one controller and getting the same sunlight.

But that ain't gonna happen. I will have two different panels, generating different current, but closely matched voltages sharing one controller (because of expense and installation challenges), and on many occasions when we have to moor under trees or next to a wall or building, or the morco chimney casts a shadow over part of one panel, we will encounter partial shading. Unless anyone can prove Amy wrong, I'm going parallel. Having seen her videos, I might even consider getting a 150W panel rather than a 100W to add to the existing 95W.

Now I need to remeasure the roof space.

Solar expansion planning

Having decided to up our solar power on Herbie, there’s a bit of technical/ electrical planning to do, so for the record and in case it helps anyone, I thought I’d set out the considerations here.  Also, people cleverer than me might spot a flaw in my deliberations and put me straight.  Please feel free to correct me if am wrong.

Our current (gettit?) arrangement is one Kyocera 95w panel charging through an Emponi MPPT controller which is OK up to 100w but no more.  I also have a shunt type ammeter in the negative line between the controller and the batteries.  This shows we can make anything up to 6 amps when the sun is strong and in the right place.  More often we are averaging something like 3 amps.  we would like to double that by adding another 100w panel.

So if we have two panels, should we connect them in series or parallel?

I first decided series might be best, so the voltages are additive, and higher voltage in the cables means less resistance losses. Also, daisy chaining up the panels would be simple.  As I understand it, the down side is that if one panel creates more current than the other, there would be equalisation losses.

Now I’m more inclined to connect in parallel,  This way, as long as the panels generate the same or very similar voltage (much more likely), the currents are additive.

So what do I have to check in choosing a new panel?

Voltage is the main thing.  Panels specs should quote  the open circuit voltage Voc, typically about 21.5 volts and a maximum power point voltage Vmpp typically between 17.5 and 18 volts.  For parallel connection a pair of panels need to have these values as similar as possible.  Our current panel has a Vmpp of about 17.6v which I have checked with a voltmeter to be sure it hasn’t deteriorated in this respect.  I’m not sure but I suspect panels deteriorate more in amps than volts.

Type of cell is another issues. Monocrystalline or polycrystalline.  Poly is cheaper, mono is a bit more efficient so panels are a bit smaller for the same output.  They also tend to look a bit nicer. This is where you have to consider space on the roof.  I haven’t made a final decision on this yet, although the difference of up to £50 spread over ten years isn’t a lot. The narrower the panel, the less chance of tangling with Herbie’s centre ropes.

The panel frame is a bit of a consideration, but most of them are ok.  I just need to check the side of the frame is deep enough to take the screws for my tilting stands. 30mm plus is ideal.

Quality.  This is a tough one.  Panels come in a variety of prices for similar specs.  How do you avoid getting inferior quality without paying too much?  My gut feeling is that most panels are OK irrespective of price, but for something I want to work well over many years, I’ll stick to suppliers I think are reputable.  Our last one came from Midsummer Energy, not the cheapest but still reasonable and they are more than just box shifters.  I’ll probably stick with them.  Bits of cable and plugs etc I’ll source from ebay I think where they are a lot cheaper.  Little bits like that can soon add up.

Controller.  I’m going to have to buy an uprated one as the Emponi won’t take 200w.  Choosing MPPT is important, dearer but much more efficient.  Google it if you don’t know why.  Size matters too.  I want to fit the new one in place of the old and space is tight just there. Some of these controllers are at least twice the size of others.  And then there is cost.  Some come with more bels and whistles like remote monitoring etc.  I just want one that is efficient, has the right overload etc protections and from a good manufacturer.  Victron (well known in boat electrics) do a good small 15A MPPT controller for about £80.  That’ll do nicely.

Connections – how best to wire up in parallel.  I am pleased to discover than using the industry standard weatherproof MC4 connections, you can get natty branch connectors to plug two cables into one, which is what you need.  Lots of videos on YouTube show how to do it.

Cables.  Cables get hot and waste power if they are too thin.  They could even catch fire. I checked our existing cables. They are 4mm squared which will be OK to carry the increased current. Phew! I didn't want to have to take the boat ceiling down again for a new run of cable.  I need to check the cables between the controller and the batteries and the fuse too.

So I’ve done my homework.  If you can spot any flaws or omissions I’d be glad to hear about it.  I’m reckoning the panel, plugs, cable, controller, new tilting frames (see previous post) are going to add up to in the region of £300+.

A new solar panel frame plan

I’m astonished to look back at old posts and find that it is seven years since we fitted our solar panel on Herbie.  Perhaps that roof corrosion cause by the magnetic panel frame feet is a bit more forgiveable after all.  Anyhow it looks like I’ll complete the roof repair and repaint before too long so it’s time to think about what comes next.  More solar, that’s what.   I can’t remember what I paid for our existing solar panel but I’m sure that prices have dropped by something like half since then.  So we’ll be getting a second panel soon.

My ingenious two way tilting panel frame has done pretty good service. 

It does what it says on the tin (sorry, aluminium), but it’s a bit less sturdy than I would like, and it can get it’s knickers (or knees at any rate) in a twist during the folding and unfolding, so I’m thinking of a stouter and simpler design.  Hunting round the web I found some that work like this.

Basically three bits of aluminium angle at each end of the solar panel. The prop piece can be placed where you like using the holes and screws attached to plastic knobs, and when you lay the panel flat, the screws secure the panel flat using the end holes.   As you can see, you can tilt the panel either way to face the sun. (Our own measures show that titling the panel makes quite a difference in the amps generated a lot of the time.  You can buy frames  like this for £50 a pair (for one panel) plus carriage. It might seem dear, but if you cost up all the bits and pieces and include their labour and profit, it’s not unreasonable.

It’s a simple principle but I plan to make something a bit different in that in the ones I have seen  the top piece is a length of angle that sits under the solar panel, whereas I plan to rivet a flat bar to the side of the panel frame, but deeper so as to make room for drilling the holes.  Making my own reduces the cost considerably of course, and it’ll be more bespoke to my solar panel sizes and be a bit of fun to make.  Making two pairs, one for the old panel and one for the new makes economic sense as postage for the aluminium costs no more for two lots, saving £15.  The best price for the aluminium, in case anyone wants to get some, seems to be at aluminiumwarehouse.co.uk where they will also cut pieces to your required length for a small charge.  Not a bad idea as the full lengths of stock angle are and unweildy 2.5 metres.

My idea is to have the bottom rail and the upright in 50x25mm angle for rigidity and as I said the top piece as a flat bar rivetted to the side of panel frame, but much deeper to allow for drilling the adjustment holes.  All 3mm thick, which should be plenty strong enough.

This time I won’t be using magnetic feet, which as we now know are prone to rust unless you buy prohibitively expensive ones.  I’ve been looking at adjustable furniture feet, the sort you find on steel desk legs, which I think I will glue to the roof.  People seem to recommend the adhesive/sealant Sikaflex for this sort of job, so I’ll give that a go.  Various screwed knobs can be found on ebay.  You have to shop around for this stuff if you don’t want the costs to run away. The building ought to be easy, mainly a matter of drilling holes, which in aluminium is simple.

So that’s the plan for the frames.  There is still time for someone to point out any flaws before I order the stuff.  Next post I’ll tell you my thinking on the solar electrics.

Roof painting –be patient, work quickly

Sounds like an oxymoron doesn’t it?  Let me explain. 

The paint on a boat roof has a hard time, sun, rain, frost, lying snow, poles, planks, solar panels etc all take their toll.  I reckon the paint on the roof is lucky to last half as long as that on the cabin sides.  Herbie’s roof is no exception, suffering particularly where it comes into contact with roof “furniture”  Even a bag of coal left on the roof over the winter caused a lot of paint damage and resultant rusting because of the film of rain water that lingered under the bag.  Repairing and painting the whole roof in one go is nigh on impossible unless the boat can be taken indoors for a week, so I’ve been doing it in sections.  Learning more and more as I go.

I’ve talked to a few people who “mean to get round to doing their roof one of these days, but it all seems a bit daunting”.  I also spoke to someone who was quoted £1000 for having it done professionally. So for the record and in case it helps or inspires anyone to have a go, here is how I’ve been doing it. 

I suppose the first thing to say is that just patching over little bits of damage is only a stop gap at best.  New paint never matches the old. In an ideal world you would take the whole roof back to bare metal and start again, but I don’t think you can do that out of doors unless you have loads of time and fantastically lucky weather. The better way is to repair/ make good  damaged patches and then repaint a whole section of the roof at one go.  Then it’ll look OK.  Two years ago(?) I repaired and repainted a 20cm wide strip along either side of the roof  to fix a lot of small scars and wotnot  caused by boat hooks, gangplank, autumn leaves etc.  You can just make it out in the second photo below. Then last autumn I repaired the section where the coal bag had lain.  I wish now I had done that better because the repaint still bears the unevenness caused by pitting in the rust.  Then a couple of months ago I had a go at the central section of the roof, around the stove chimney, where there was a fair bit of corrosion.  That time I used filler to even the surface and got a much better finish.

So now I move on to a ten foot section towards the rear of the roof which includes where the solar panel has lain.  The magnetic feet of my fancy titling panel frame are the main culprits here.  Ordinary magnets rust like crazy and attack the roof at the same time.  A lesson learned!

This is the point where I should show you a photo of the damage, but stupidly I forgot to take one.  Sorry folks I’ll do that next time when I attack similar damage under the feet of the roof box.  By the way, another big lesson is revealing itself here.  The best way to keep your roof in good nick is not to store anything on it!

So, to the process.  This is where the patience comes in.  Even if you are repairing and repainting a tiny area, you need several days to do it, because of paint drying times.  Yes you can claim to be working whilst spending twenty three hours a day watching paint dry. That means at least four consecutive days with suitable weather, no rain (especially in the mornings), not too hot, not too cold, not too windy, not too dusty.  Flippin’ ‘eck!  Does that exist? Well last weekend it looked promising so I had a go.

If you already know how to suck eggs, you can either stop here or read on and tell me what I’m doing wrong

Day one. Sand off the rusty patches, feathering them out as best you can so as to help with a smooth finish later. Your patches will now be twice the size of the original damaged area. I used a nice little palm sander, only thirteen quid from Wickes, and ideal for this job. While you’re at it lightly sand over the whole area to be repainted, I expect you’ll find little nicks in the paint here and there.  Treat them just the same as the bigger patches.The sanding also helps get rid of any accumulated grime etc. on the “sound” paint. Wash it all off with clean water and over the exposed metal patches  brush a coat of Fertan rust converter, which is easy to apply and is happy in the wet.  Total time taken, about a couple minutes per patch.  No more than an hour for the whole day’s work.

Day two.  Areas of rust converted by the Fertan will have turned black. Wash off them off, lightly sand the patches again and when the roof has dried, mix up some filler.  I used Isopon which sets really fast so you have to mix smallish bits at a time. Smooth the filler over the pitted area and beyond the edges of the exposed area.  Each patch will now be three times the area of the original damage!  You can sand the Isopon after only an hour drying out.  It sands very easily.  You should end up with a smooth surface right across the patch, extending it still further to blend in with the roof surface.  Sand harder at the edges to feather out. At this point I brought out the little hand held Dyson and sucked up what dust I could before washing the whole area off again. If the weather is right, the roof dries in minutes. (If it steams, stop right there, it’s too hot to paint). When dry, brush on some good metal primer, again extending beyond the prepared patch and feathering out as best you can. That’s all you can do today, most paints need sixteen hours between coats. Again only about an hours work.

Day three.  This depends a bit on how many days you can spare in total.  Another coat of primer would be good.  I didn’t have that much time, so after sanding down and washing yet again, it was on with a coat of some high build undercoat.  By now the patches over smallish areas of damage seem enormous.  Here I do have a couple of photos.

Some of those smaller patches cover an area where the damage was only a few millimetres across.  Yet again, less than an hours work today.

Day four. Another undercoat would be a very good idea, but I didn’t have any days left.  Now you might say just leave it for another time then, but undercoats and primers are pretty porous and it’s not a great idea to leave them exposed to the weather for long for the damp will get in. So I pressed on. Out comes the old sander again – last chance to get a smooth surface before the top coats. Feathering out still further.  It can seem a bit daft slapping on all that paint then sanding half it it back off, but that’s what you have to do.  Then, a final light sanding over the whole area to get it clean and smooth, a quick vacuum if you have one, and a good rinse with clean water.  When that is dry, a final wash with a white spirit soaked rag to remove any grease and you’re ready for the top coat. Getting it all really clean is vital. Work so far today, about an half hour. 

Now the first top coat of, in my case, raddle paint.  Four inch brush, well stirred paint and work as fast as you can to keep a wet edge, working the paint in then quickly laying off the paint side to side right across the roof. I was cursing the met office because half way down we got a short light shower of rain. I stopped and waited for an hour.  It dried off and looked ok.  Better to start off against a touch dry edge than a half dry sticky one.  That ten foot section took about twenty minutes. Here and there the paint “grinned” a bit (showed through). Ignore that and keep going, never go back over sticky paint, the second coat will sort out all that.

So that’s where I stopped because we had to go home.  That single top coat will hold out the weather till I resume sometime soon, but I will have to sand and wash again first.

So that’s four days to do less than five hours work.  Each time I chose to do the work mid morning, after any dew has gone and leaving plenty of drying time before the evening damp descends, and  hopefully before any sun makes the roof too hot to work on.

On the other hand, also this weekend I went from this:

to this:

in about five minutes.  Yes I just screwed on the front panel I had painted indoors at home.  I think it has worked out OK.  Herbie looks instantly smarter.

Finished paint plus a hidden gem on the Avon

Here’s my finished (all bar a coat of varnish) cratch mullion.  True to form the masking tape had bled here and there because of the grain of the wood, but nothing a tiny dab of white with an artists brush wouldn’t cover.  I’ll fix it to the boat next time we’re there, then you’ll be able to recognise us when you see us coming.

Now then, this hidden gem.  Yesterday we went to Offenham (near Evesham) on the Avon to join in my big bruvver’s 80th birthday bash.  Little did we know he had arranged a treat for a group of us in between lunch and the afternoon festivities he took us for a walk down his road, Boat Lane, which as you might guess leads to the river.  Only about a hundred and fifty yards from his house he led us into the little Boat Lane (micro) Brewery where the proprietors were ready to welcome us with a tasting session and a tour.  Well what a cracker it is!  The owner/brewer is a a true artist with the recipes and the brewing process is meticulously carried out to produce some quite outstanding and interesting beers.  I suppose these days you would refer to their stuff as Craft beers. On sampling one of two draft beers on offer  I was pleased that I was right when I suggested it was made with cascade hops.  Anything made with cascade is invariably delicious to me, even if it is an American hop. Due to issues of scale, they sell chiefly in bottles at the moment, but they do have a small amount of draft beer too.  They are already selling all they can make and over the next year or two the scale is bound to grow.  As well as superb bitters and stouts, they do a range of really nice beers and stouts with added fruit flavours,  - oranges, mango, raspberry, ooh I can’t remember the rest but all really good (hic). We came away with a few bottles of the Offenham Orange.

One thing I learned during the tour was how HMRC calculates the alcohol duty the brewer needs to pay.  I imagined that they came round with the old hydrometer to measure the specific gravity of the beer.  That would of course indicate the alcoholic strength but not of course measure the quantity being made.  What in fact they do is require the malt sellers to record how much malt ( and presumably other sugar producing grains) is supplied to the brewer then apply a calculation to estimate how much alcohol that would make.  Simple really.

Boat lane brewery is open to the public on most days and if you moor your boat at the Bridge Inn (where perversely there is no bridge, but an old chain ferry) on the Avon it’s only a couple of minutes walk.  Highly recommended. You can find them on facebook where a number of customers rave about their wares.

While you’re in Offenham take a stroll down the main street past the thatched cottages and marvel at the village maypole, which at 64 feet is the tallest in England.  It is painted nearly as nicely as Herbie’s new cratch front.

Banbury Canal Day revived

The formerly cancelled Banbury Canal Day has been un-cancelled.  A planned building extension across the canal was supposed to be started by now, but for some reason or other it hasn’t, so as former attendees, we got a letter from Banbury Council saying they were reinstating the canal day to take place on October 1st and inviting us to apply for a place.  Well Banbury is practically Herbie’s home town at the moment so, if we’re spared, we’ll probably put in an appearance.

Meanwhile, my cratch front panel is progressing.  Two days ago –all masked up over the white base so that the white borders will reveal later:

Today after two coats of the greys:

The grey paint didn’t want to sit well on top of the white gloss despite rubbing down first but I managed to persuade it in the end although at the expense of an ultra smooth finish.  I doubt the brush marks will show at normal viewing distance.  As you can see, any precision is in the masking and not in the painting.  Tomorrow morning one more coat of the greys and then the big reveal when I pull off the masking tape.  I am mentally prepared for the inevitable bits of bleeding under the tape as long as there’s not too much of it. hopefully a little dab of white here and there will make good.  Then I think a couple of coats of clear varnish will finish the job.