What type of solar panels?

[Rivers & creeks]

We need to boost our charging capacity for the summer. We spend six weeks travelling each summer, mostly at anchor. I run the super quiet genny for an hour a day to heat the calorifier and put 25ah into the 420ah domestic bank - obviously not enough to 24 hours of levy usage. If we don't motor for a few days we get so low the fridge low voltage cuts out so we need to make more juice.

It's a ketch so there are shadow lines everywhere and no gantry to fix panels. A few questions to help please:

1. Do I have to use amorphous panels to stop shadows killing the output?
2. Are any other panel types tolerant of a shadow?
3. Am I right in guessing that you get about half the quoted output? E.g. A 60w panel will in reality give about 3ah?
4. Any recommendations for specific panel deals?

Thanks!

 

[cimo]

hello LK

1. No.
2. all types are subject to effects of shading. Ask for & compare the I-V curves for each panel you are considering. some claim to be more tolerant, but then you may well find their overall performance is less, relative to other "less tolerant" models.
3. Averaged over a days daylight hours, half output delivered is a good figure to work with.
4. no, sorry.

If I may, I believe you are asking the wrong questions though. First step in this process is to determine you overall power budget, and develop a system that will provide for your requirements. You say 25ah of charging/day isn't emough. Do you have a feel for what would be? Of course, establishing a power budget would also include reducing consumption where possible.

Nigel Calder's(?) boat maintenance book, covers this subject in great detail, well worth the money.

 

[Rivers & creeks]

Yes we've done a rough audit, the fridge is the biggest culprit at 40ah; lighting is all LED and comes to 12ah; iPads and other charging 10ah; water pumps and loo 8ah; other incidentals 10ah. All told its 80ah and the sensible figure to take out of the domestic bank is 220ah. If I put 25ah in each day we can last 4 days before a good solid overnight marina shorepower charge. We'd like to stretch that to 7 or 8 days meaning we need about 30ah of solar.

 

[Mistroma]

Good advice from cimo. I can give you some real data collected last season cruising from Scotland, Cornwall, Brittany to Rias.

I was ill before leaving and ran out of time so didn't connect the panel for a week after we left Scotland and (cold & foggy so not a great loss). I simply tied the panel on the coach-roof with 4mm2 cable back to regulator. It's a 65W BP rigid mono-crystalline panel and output is completely killed by even a small shadow. I still managed to average 18Ah/day over the season with 25Ah and even 30Ah produced each day at height of summer.

Shade tolerant panels seemed to be very expensive, I only paid £100 for the BP panel (new on eBay). I intend to fit another 60W panel (poss. 2x40W) and tie them down beside the original panel. Using 2-3 panels helps as they aren't always shaded at same time and this seemed more cost effective than buying shade resistant panels.

Where are you currently located?

I hope that this helps.

Just read your latest post. Sounds as if your setup is very similar to mine 450Ah domestic bank with usage about 70-80Ah/day. Might be better to assume you will often work batteries between 80-50% and not 100%-50%. Bad news is that this only gives you 126Ah to play with.

 

[Rivers & creeks]

Just read your latest post. Sounds as if your setup is very similar to mine 450Ah domestic bank with usage about 70-80Ah/day. Might be better to assume you will often work batteries between 80-50% and not 100%-50%. Bad news is that this only gives you 126Ah to play with.

Thanks, some very useful data. Just to say maths wise that 50% capacity of 420ah is 210ah not 126ah.

I like your idea of several smaller panels so that at least one is shadow free.

 

[Mistroma]

Sorry, not explaining myself clearly enough. If you cycle between 100% and 50% you have 210Ah capacity. However, if away from a marina for any length on time you will usually cycle between 80% and 50% which only gives 126Ah capacity from a 420Ah bank.

It sounds as if you might have a Honda genny and I have one as well. The problem is that I don't like to run it for hours and hours to get back to 100% so tend to stop at 85% at most when at anchor. So available capacity is much reduced.

Everything with batteries works against you. Take out 80Ah in a day and you need to put back about 100Ah with flooded batteries. Use a lot of Amps and capacity drops. Sip Amps. form battery and you end up putting twice as much back (because self-discharge loses as much as you are using when only drawing a fraction of an amp). And so on. I've never found anything about batteries and charging that's a virtuous circle, always a visious one where you lose out.

Oh well, that's life.

 

[William_H]

Quote" Am I right in thinking a 60w panel will give on 3ah" I think you have got your temrs confused here. Yes a 60w panel will give 3 amps that is because they usually produce 20 v open circuit so 20 v into 60w is 3 amps. Multiply that by 6hours of useful charge each day and you get 18 ah (Amp hours) per day A fiddle of description but they all do it. It means 3 amps max into a 12v system. Unless you fit a MPPT regulator which may give a bit more current.
I think the choice of panel will be dictated by mounting and location. Separate panels would give more immunity to individual shadows. (but more chance of finding a shadow).
If you can find a location for it the PV panels for houses will give the most power for your buck. They are however often 40 v output and 200 watts good for a 24v system but need to be fed into an MPPT regulator for a 12v system. ie 40 v in 14 v out.

Ultimately however i think for a few holidays each year your present generator system might be best. Solar is good for unattended boats or like me ones with no generator.
Something like this amp meter with AH recording might be a big help in your battery management. I have bought one but it has not arrived yet so i can't guarantee its worth but i am optimistic. I will post when it arrives and has been tested.
http://www.ebay.com/itm/DC-120V-200...nt-/170901497030?ssPageName=ADME:L:OC:AU:3160 good luck olewill

 

[Graham_Wright]

I have seen several banks on guard rails. Although concerned about spray damage, this does seem to be a good location. They were all top hung and had stays at the bottom to vary the angle.

 

[macd]

As to type of panel, I've had four different makes of semi-flexible, and all have suffered UV degradation and partial delamination, sometimes in as little as three years (mostly spent in sunnier climes than UK). Personally, I wouldn't touch them again.

Rigid panels definitely offer more watts per £ and in my experience last for aeons without significant loss of output. Granted, they are often trickier to fit.

There was a recent thread concerning the respective merits of wiring panels in series or parallel, and their respective influence on shadow effects, which might interest the OP.

 

[vyv_cox]

I agree macd's comments, although my semi-flexible is still producing some power, despite some delamination, after 15 years. I have used a flexible panel and found it a real nuisance, we seemed to be forever untieing it to move it somewhere else. I think in your situation I would go for rigid panels that swing out from the guardwires, despite their nuisance factor. On a ketch it should be possible to mount them well astern to avoid the damage that occurs when they are midships.

 

[geem]

I have a couple of roving 40 watt solar panels that clip to the top guardwire and are supported at the bottom by a pole that adjusts the angle to the sun. it is simply a notched pole that locates on the bottom guard wire. My panels have being doing this since 2004 and have suffered no damage including an atlantic crossing and back where they were permanently clipped to the davits. They give better output than the 64 watt panels permanaelty fixed to the deck as these ones cant be angled to the sun.

 

[Oscarpop]

Just ordered a couple of 100w flexible ones through Barden that are made by Solbian.

They are made with zips attached so that you can zip them on to the top of the bimini. When the bimini is not in use, you simply unzip them and store them flat under a berth.

It should sort our storage and mounting issues.

 

[noelex]

Before looking at solar I would optimise your generator charging.
25A is lower than 420ahrs of batteries can accept when reasonably discharged.

Is your battery charger small, or its acceptance voltage set too low?

 

[Rivers & creeks]

Battery charger is small at 25ah - it was fine when the bank was 210ah but we doubled it this winter because of lack of capacity. It really needs a 40ah charger but if I could put 50ah of solar charge in each day that would solve the problem in a silent way!

 

[Boo2]

So is anyone going to be brave and say who is a good UK supplier of any particular brand of Solar Panels that works well in our application ? I had a quick look on eBay and saw these : http://www.ebay.co.uk/itm/150W-Sola...5?pt=LH_DefaultDomain_205&hash=item43b75e20ef but I have no idea whether they're any good or not. I would be mounting them from the guard wires as several posters above since there's nowhere else to put them on Sunrunner, is this type bash-proof enough for boat use ? And who makes suitable support props doe anyone know ?

I did my calcs as follows : 150W / 20 V * 6h = 45Ah / day, more than I currently need but I am thinking of installing a fridge, and it would be really nice not to need to run the engine on a trip just for batteries, Any comments on my calcs ?

If there's a "standard" supplier for all this stuff then I'd be interested to know who it is ?

Thanks,

Boo2

 

[geem]

So is anyone going to be brave and say who is a good UK supplier of any particular brand of Solar Panels that works well in our application ? I had a quick look on eBay and saw these : http://www.ebay.co.uk/itm/150W-Sola...5?pt=LH_DefaultDomain_205&hash=item43b75e20ef but I have no idea whether they're any good or not. I would be mounting them from the guard wires as several posters above since there's nowhere else to put them on Sunrunner, is this type bash-proof enough for boat use ? And who makes suitable support props doe anyone know ?

I did my calcs as follows : 150W / 20 V * 6h = 45Ah / day, more than I currently need but I am thinking of installing a fridge, and it would be really nice not to need to run the engine on a trip just for batteries, Any comments on my calcs ?

If there's a "standard" supplier for all this stuff then I'd be interested to know who it is ?

Thanks,

Boo2

I would halve your predicted output per hour. You're may be able to all more than 6hours of Sun per day in summer but you will unlikely get this kind of output in winter. My solar panels are rated at 200watts. In summer I get upto about 7 amps typically in bright sunshine but more normally about 4 or 5 amps due to poor sun angle and shadows. In the Caribbean I got upto 13 amps by angling all the panels to the sun.
In heavy rain/dull conditions we still get 2 amps

 

[ghostlymoron]

I think that if you're going to use a fridge (why would you in a UK summer?) you're going to have to plaster the boat with PV panels or run the engine or uprate the alternator. You run the risk of spending more time managing the generation plant than sailing. Increasing battery capacity is futile unless you have adequate generation facilities.

 

[geem]

Under normal uk weather conditions 128w of solar keeps us fully charged. This is with a fridge, led lights, electric autopilot and no other form of charging. For summer holidays we would take two extra 40 watt roving panels to clip on the guard wires. We never use the engine to charge

 

[VicMallows]

Under normal uk weather conditions 128w of solar keeps us fully charged.

I think you have made the most important point of all ... USEAGE. There is no point comparing the requirements of someone who reads by LED light whilst warm in their sleeping bag with a family who watch TV with the eber on full blast.

FWIW, I find 80w (nominal) of solar more than adequate in UK . My biggest user is either the computer or the heater or both, depending on season.....and I have a gas fridge. But that tells us nothing useful for YOUR particular situation.

 

[JensK]

On eBay, I just bought a 60 W foldable solar panel, made of 3 x 20 W stiff panels which can be unfolded to one large panel with legs to support it. It is quite cheap. I believe it can be moved around easily on the boat according to the sun. No experience with it yet, though.
Best regards JensK