Solar panel advice - to keep batteries topped up please?

[sixknots]

Hello there I am new to this forum & was hoping for a bit of advice?

I have just bought a CR310 which will live on a pile mooring on the Hamble

As she won't be connected to shore power I was thinking I'd better have something fitted to keep the batteries topped up when not on board.

Does anyone have experience with solar panels on the South Coast?
- Are they up to the job of keeping the battery topped up when I'm not on board?
- Can anyone recommend suitable solar panels to do the job: what size/how many do I need?

If possible I'd rather avoid a wind generator due to cost/noise/danger of blades but I'd also be interested in any views that say I'm mad going for solar in the UK and need a wind generator instead.

I'll only be using it to keep the battery topped up - primarily so I can make sure the boat starts when I go to her. I'm not planning any long-distance, bluewater cruising or to have long periods without using the engine or the ability to top up the batteries by staying overnight in a marina etc.

Thanks for your help!

Simon

 

[wrr]

The answer depends on your battery capacity. I keep two 110 ah batteries topped up with a 30 watt panel and voltage regulator. The rated output is rarely achieved as the panel is laid flat and because of cloud cover, shadows etc. However it is adequate to keep the batteries fully charged all year round.

 

[The Dogs Pollacks Brother]

My last boat was a small fishing boat and we only had one battery...a big ole' lorry battery used to start the engine and power the sounder, radio, lights ect. We fitted a simple 5W jobby from Maplins and just had crock clips straight to the battery terminals. This was enough to compensate for any natural discharge (if you leave a battery long enough it goes flat does'nt it!) and served us well for 2 seasons on a swinging mooring. Of course this would NOT charge a battery so if you need that you must think bigger.
We now have a much larger boat with a twin battery set up and have a bilge pump fitted to operate while we are away from the boat. We now have a 40W panel with a regulator (from Sunstore web shop) which is absolutely fantastic. It always gives us a fully charge battery, even in the winter months in darkest Wales! One of the best £60 we have spent on the old girl!

 

[ghostlymoron]

These people are a good source of knowledge as well as reasonably priced suppliers. Size of panel depends on the size of your batteries. There MPP controllers are good as well. Suggest you give them a ring. Poly crystalline panels are better on a boat as they can be mounted on curved surfaces and walked on although they are more expensive and not so efficient as monocrystalline.
http://www.sunstore.co.uk/search.php?mode=search&page=1

 

[johnalison]

Our 36w panel does a good job of keeping about 200Ah of batteries topped up during the winter and had a useful effect when we are on the move. If you want to keep everything going, fridge, autopilot etc, you will need much more.

 

[Mistroma]

The answer depends on your battery capacity. I keep two 110 ah batteries topped up with a 30 watt panel and voltage regulator. The rated output is rarely achieved as the panel is laid flat and because of cloud cover, shadows etc. However it is adequate to keep the batteries fully charged all year round.

A lot depends on your battery type as well. I worked out that my 450Ah Trojan T105s would just about get by on solar. They have an unusually high self-discharge rate but low winter temps. obviously slow that down. The boat in near Vigo and 65W was bare min. for worst part of the year. Of course output jumps hugely in summer.

AGM batteries would probably get away with a smaller panel and ordinary leisure type would not be quite as bad as mine. Assuming OP is on South coast somewhere, I imagine that your suggestion of around 15W/100Ah would be OK for an average leisure battery during winter.

If I find time, I might check the figures for South coast in winter.
Quick calculation forecasts min. output in December of around 1.3Ah for a 30W panel lying flat and unshaded somewhere around Bournemouth.
So that's 0.65% of a 200Ah bank's capacity per day from a 30W panel. Sounds enough to keep it charged.
This site is very useful for working out approx. output http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php

 

[BarryH]

I have a 20w panel connected to a 100amp/hr battery. Its always fully charged when I go to the boat. My useage is small. I have no inboard. It just runs the echo/log and the internal lights (led) and the nav lights occasionally. Not had any issues with the panel or the controller, a cheapo Maplins jobby.

 

[VicS]

Like Barry above I use a small solar panel to keep a small battery topped up.

I find that even a 5 watt panel is sufficient for a 60Ah battery

Id expect 10 watts to be adequate for 120 Ah and proportionally larger perhaps for larger batteries.

In fact with only an outboard engine, like Barry, to supply any more power my 5 watt panel is my principle charging source

Up to a 10 watt panel no regulator will be necessary if feeding a battery bigger than 100Ah.


Normally engine start batteries are adequately charged by the engine, even if used infrequently, and solar panels are used for the house battery.


Whichever I would definitely recommend solar.

 

[ghostlymoron]

I think 10w is a bit light for a 120ahr battery but it depends how much juice your using. An MPP controller is a good investment at a tenner. The first thing is to do an energy audit on your system. Everything follows from that.

 

[Mistroma]

I think 10w is a bit light for a 120ahr battery but it depends how much juice your using. An MPP controller is a good investment at a tenner. The first thing is to do an energy audit on your system. Everything follows from that.

Drifting a bit from OPs original question and I contributed by following on from another comment about output during the winter.

OP said he just wanted to keep batteries charged on a mooring when nobody on the boat. So only usage of interest is self-discharge rate (plus anything left on 100% of time e.g.Alarm). I should have looked at output from April-October.

Going back to my Bournemouth example, average daily output for a 10W panel would be around:
2.9 Ah/day in April, peak at ~3.7Ah/day in June and around 2.2Ah/day in September.

On that basis, even a 5W panel should easily keep a 100A leisure battery topped up over the summer (even with some shading).

Of course OP might appreciate more power (who wouldn't) and not have shorepower when laid up and a much larger panel would be required. I'd also say that it's unlikely that OP would always leave his batteries fully charged when leaving the boat. So that should really be factored in. I'd guess that 10W /100Ah would be a better minumum size for his very limited requirements.

 

[William_H]

Or to approach the problem from a another angle. You need to decide the biggest panel you can or are prepared to mount on the boat facing south and tilted toward the midday sun. The cost will also dictate your purchase.
A 10w panel will give useful charge maintenance and can be connected to a decent sized battery without using a regulator. I would suggest that be your starting point. You need to decide if the panel is to be permanently mounted or removed for sailing.
I have used a small panel for many years as only power source. It clamps with bungees around the mainsail cover and is removed for sailing. That is however on a swing mooring.
Really if you visit and run the engine better than every 3 weeks you should not have a problem with battery discharge although a solar panel can take away some concern when you hit the starter switch. good luck olewill

 

[Stemar]

Another vote for SunStore. I ordered two panels and only received one. I emailed them and the second one arrived next day with an apology.

If you can mount your panels where they won't be shaded, a single panel's fine, but I didn't have that luxury, they had to go under the boom, so I got two 20w panels rather than one 40w, as a small shadow has a disproportionate effect on the whole panel. This means I should get more out of one 20w in full sun (if we ever get any!) and one with a shadow on it than from a single 40w with the same shadow. I got rigid panels as they're half the price of the semiflexible, walk-on-able ones and I've heard a number of stories of premature failure from the semis - maybe thay aren't really as walk-on-able as they'd have us believe!

As for the controller, Sunstore do one that can manage the charge to two battery banks, with options to charge equally, part charge one then do both, fully charge one then switch to the other. From memory it's about £25. I expect to be enjoying the benefits from it long after I've forgotten that it cost 2-3 times the cost of a cheap controller.

 

[johnalison]

I suspect that most people on moorings will want to compensate for the self-discharge, plus top up from a weekend's use, assuming that motoring back to the mooring has not achieved this. It is probably going to be necessary to be a little generous in one's calculations. I would expect my 36w panel to give me about 30 Ah during 5 days off the boat, in a good week.

 

[VicS]

FWIW before I fitted my 5 watt panel I used to have to take the battery home for recharging once or twice during the summer.

Since fitting it I have not had to do that at all.

Mine current panel is a semiflexible Spectralite panel from Seateach http://www.seateach.com/SpectraLite-Solar-Panels.htm

 

[maej]

I am in a similar situation with a 34 footer on a swinging mooring in the Solent. I have 2 * 110 Ah domestic a 1 * 105 Ah engine. The longest I tend to leave my boat unattended is 5 weeks, though usually only 3 weeks so self discharge is fairly limted for me. If you will be leaving your boat for longer then self-discharge will obviously be more of a concern for you.

So far the (new in December) engine battery has never failed to start my elderly bukh even when it struggles to start in the freezing conditions. Even the old decrepid battery was ok in warmer weather, so I'm inclined to suggest your engine battery will be ok without solar assistance. Having said that I am still considering a small panel just to compensate for self discharge on the engine battery, probably 5 watts and mounted in a convenient but less than ideal locaiton for power generation, just in case I have to leave the boat for a few months unexpectedly, so perhaps this is something you could also consider.

I have fitted some panels that can recharge my domestic bank over a week or so while I'm away so that my domestic bank is always full when I arrive, whatever state I left them in. I did this because I don't visit marinas often enough to rely on shore power each time. An alternative with this arrangement is to use a VSR to route the charge to the engine battery whenever it drops a bit, but I haven't done this.

 

[RASilcock]

Have used flexi solar for 30 years on various yachts,however there appear to be lots of cowboys making & selling them now.I bought a 70w. GBSOL panel from MEI Portsmouth £400 & it failed after a year,research showed others had same problem.All I got back was the usual second hand car dealer woffle so be carefull.Rieaa.

 

[chutty98]

I also use 20w setup and suits my needs just fine throughout summer and winter but as others have said it depends on your usage. I'd say mine is fairly average but also have no inboard. I went for this 20w solar kit which was nice and easy easy to setup too.