another solar panel question!

brokethebox said:
I'm wishing to put a solar panel on board just to cover the use of an electrical bilge pump. Does anyone have an idea of the size of panel I'd need? I've just got a little rule pump, and she's a timber boat in a mud berth.
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It depends entirely on how much water gets in and therefore how long the pump needs to run for each day. For example, a 30s run at 5A every hour is 12 minutes x 5A = 1Ah per day. I'd have thought 30W would be fine for that.
 
Yes it is a valid question but not easily answered. In practice you could buy a 10w or even 5w and connect it to a battery without a regulator. It may be fine but you may fancy a bit more power and a regulator. It is o you really up to you and also depends ona suitable place to fit the panel. good luck olewill
 
I think all these solar panel questions are easily answered by, 'fit the largest your boat and pocket will accommodate'.
 
Thanks all, my back of envelope sums came to a 5w one too so I'm glad.
Does anyone know how efficient they are compared to their spec?

And what difference does a regulator make as opposed to a maplin bought panel?

I chuckled at tge pockets, doesnt boating mean or pockets are permanently empty? we're six months back from a nine month trip to.Antarctica and I'm still penniless!
 
oldvarnish said:
I think all these solar panel questions are easily answered by, 'fit the largest your boat and pocket will accommodate'.
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I'd agree with that. Also, the little Maplin/Halfords things strike me as pretty expensive for what they are, and unlikely to be able to do much more than replace the normal self-discharge of a decent sized lead acid battery in winter. Better to do the job properly once, to my mind. You'll enjoy the benefits of a decent solar system long after you've forgotten the pain in the wallet.

I fitted a couple of 20w panels to Jissel and they easily keep up with our needs at anchor in the summer, provided we don't use the cold box (a 6amp peltier efect one, so not too surprising). In winter, I no longer bother to hook up the charger when I spend a weekend on board as the batteries are fully charged by the time I get down the next time, even if it's the following weekend (swinging mooring, so no mains). The controller I have charges the starter battery until it burps, then turns its attention to the domestic one, so I'm pretty much guaranteed a fully charged starter, no matter what. You'd be amazed what that does to your peace of mind!

Overall, a rule of thumb I was given was to expect 25% of your install PV capacity, so I can expect 10 AH a day from my 40w on average, but I reckon I'd be lucky to get 1/4 of that in winter - even less on those dreary dark December days. If you get 1/2 AH a day from a 5w panel then, I reckon you'd be doing well.

One thing that tends not to be considered in the fianancial equation is battery life. My panels & controller cost me little more than a 125AH battery. Keeping the batteries charged means they last longer so, over the lifetime of a PV installation, it could easily pay for itself in battery replacement costs, especially on a mooring away from mains power.
 
Anyone who thinks a solar panel will a) produce it's nominal output and b) do it for 8hrs a day, obviously also believes in the tooth fairy as well.

Assuming the SMALLEST Rule pump (250 gph which is no longer made) as the 500gph
Start up 2.8 amps continuous run 1.9 amps. Say 4' in every hour, usage in the region of 4ah/day.
Solar panel producing 40% of nominal output for 3/24 day (sun seldom shines in winter so I'm being over-optimisitic).
The closest standard panel at which I come out is a 40 watt one.

Someone comes on this board asking a genuine question and all you do is pull his leg!!!
 
nimbusgb said:
All the above assumes the panel is delivering at full capacity. In the UK in winter that is optimistic! :)
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That's why I suggested quite a big panel. On a grey autumn day my 100W of panels produce 100 - 200mA.

My boat came with (a) a 30W panel and (b) a small Rule pump - I think it's a 25S. because the sump in the bilge is small and the discharge pipe is quite long, the pump cycles continuously in auto - the sump level fall caused by filling the discharge is very nearly the difference between on and off. Not having learned this, I bought the boat and left her in a marina with the pump on auto over the winter. When I went back after four weeks the battery was completely flat, showing that 4A for 10 seconds every 5 minutes is more than a 30W panel can supply in a UK winter. Should be OK, though, if the pump isn't short-cycling.
 
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brokethebox said:
Thanks all -I'm learning every time I log on!

Stemar you say they look expensive at maplin/Halford - does anyone have any recommendations of where to buy?

J
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My information will be out of date but Nostrodamus had a very good offer for high quality gear in the last couple of months, I'd suggest contacting him.

I'm sure he won't object to me mentioning that he learnt the hard way that "economising" on a solar power system is doomed to disappoint and that it's best to use genuine commercial expertise rather than well-intentioned, frequently poorly researched, amateur advice.
 
brokethebox said:
Thanks all -I'm learning every time I log on!

Stemar you say they look expensive at maplin/Halford - does anyone have any recommendations of where to buy?

J
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I got my kit at Sunstore, who have a 5w panel for £12 http://www.sunstore.co.uk/12v-Solar-Panels-c-286/. You'd have to add some wire & stuff, but the Halfrauds & Maplin kit is nearly £40. Theirs may be semiflexible, but that isn't clear, and I can't see the advantage if they are. From memory, the rigid panels are more efficient and tend to have a longer life - unless you tread on them!

Prices have gone up a bit, but you can still get the same kit I bought, two 20w rigid panels & a duobattery controller for change from £120, including UK shipping. I made a frame from pop-riveted angle aluminium, and the whole job would be less than £150, which I appreciate is a lot more than you were thinking of spending, but would do far more than just keep a pump running when you aren't on board - imagine being able to stay at anchor indefinitely without running the engine!

I used two 20s because the only place for them was on the hatch garage, forward of the spray hood, which means one will quite often be shaded by the boom, and one shaded 20w panel and one unshaded will produce more output than a single 40w panel with the same shade.
 
A related question, if I may..?

I see that sunstore and others suggest fixing their semi-flexible panels to the desk using SikaFlex or something similar. Do people find that this is adequate, or is it better to screw them down..?
 
PatrickB02 said:
I see that sunstore and others suggest fixing their semi-flexible panels to the desk using SikaFlex or something similar. Do people find that this is adequate, or is it better to screw them down..?
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Mine are held down with velcro. There is absolutely No Freaking Way I would use anything as permanent as Sikaflex.
 
JumbleDuck said:
Mine are held down with velcro. There is absolutely No Freaking Way I would use anything as permanent as Sikaflex.
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They wouldn't be there long in Gosport!

I'd use a (not too) removable Sika or bolt them down if I had easy access to the underside. After all, the only time I can imagine wanting to remove them is at the end of their life. My panels are rigid & mounted on a riveted ally frame riveted to the hatch garage. Not impossible to remove, but at least a scrote would need tools. They're also postcoded with a Dremel, so easily identifiable. Not sure how you'd do that with a flexible one.
 
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