Solar - again!

[guydickinson]

I've seen the recent postings about solar panels etc - but a more basic question. Recent visit to the Soton boat show where there is a discount of no VAT for a few days on Solara panels. I've been deliberating about this for ages. Is it worth the best part of £300 to have a 23 watt (allegedly 90 odd watts per day) panel with accessories to have the "leisure" battery topped up - or just run the engine from time to time?? It seems sensible but then its quite expensive! Wondered what the general opinion is (I have a 32 ft sailing boat with 2 110 batteries - one for engine, one for the rest).

 

[snowleopard]

It depends entirely on your sailing lifestyle. I would say 23w is too much for a single 110AH battery for keeping the charge up midweek while moored and nowhere near enough to keep them up while cruising. If you fit them, be sure to add a regulator if there isn't one included as there is enough power there to overcharge a battery.

 

[mandlmaunder]

Solar panels that small are a good way to keep you topped up, in the long run they will extend the life of your battery's so will return the investment in several years.
Remember that stated out put is nowhere near real life operating conditions in the UK(we are in the Caribbean and get 60-70% of optimal output 3 hours a day) so less is all you can expect.

 

[aknight]

The Solara 23W panel will generate 1.4A per hour peak (taking the rated voltage of 16.5V into account for that calculation rather than 12V). The reputable suppliers say that in northern climes you should assume a maximum of 4 hours' generation per day, and discount that by 20% for wastage in cabling, etc.

On that basis, you would expect to get approximately 4.5A of charge out of the 23W panel per day. You might hope to beat that on long, sunny, summer days. Quite a few people claim they get better performance out of their panels than the above calculation would suggest.

4.5A per day ought to be more than adequate to charge your 110A leisure battery between weekend sails, and should mean that you only need to plug into the shorepower when onboard at a marina and draining the battery more heavily for domestic purposes (or because you want to use 240V sockets). As Snowleopard says, a regulator would be advisable and you may want to check that the discount price you've been offered includes a regulator and connectors (Barden UK are selling the 23W panel alone for £278 and the full kit including regulator for £342).

Arguably you could go for a smaller panel and still feel satisfied that it charged the battery between uses. The question then is whether you feel the extra charge from the larger panel has an additional benefit, i.e it increases the extent to which you are self-sufficient on power.

The panel will also charge the battery while in use at sea, reducing the net drain, assuming the 'domestic' battery is also providing power for instruments, VHF, autohelm, etc. It probably won't make you self-sufficient for a prolonged period away from shorepower, however. You'll have to do the calculations for your own yacht, but my systems use about 2A per hour worst case, including running the tillerpilot. So the Solara panel that you have in mind would likely give you just over 2 hours' drain back while day sailing.

I use a Solara 34W panel which makes me that bit more self-sufficient (see here for more details). It all depends on what you want to achieve.

 

[[3889]]

£300 for 23w panel seems steep. 20w for less than £100 delivered, with regulator here seems a better deal - unless you suffer from an irrational fear of modern marketing channels of course. No connection though I have bought two 10w panels off another ebay seller.
I find my 20w of panels will recharge a 200ah bank to as full as it ever gets over 3 days in summer after 3 days of "normal" use.
Without knowing units / hour etc, I do know that today I can fully charge my phone in N Wales from one panel between 1630 and 1800hrs so 4 hours charge /day seems a bit pessimistic.

 

[guydickinson]

Thanks v much - and everyone!

 

[alan]

I have a Solara SM225M fitted to my deck, so not angled toward the sun. Solara say peak output should be 68W and at the rated 19.6 volts this would give a peak current of around 3.5 Amps.
On Saturday I measured the current on a nice sunny cloudless day, around mid-day with the sun around 50 degrees altitude (I am 50Km south of Rome, Italy) and I was getting 2.1 Amps. This measurement was made after the regulator and using a 45Watt car headlamp bulb as a load and with about 6 metres of cable from the panel to the regulator.
So, I would suggest that as a ball-park figure you should consider that you will actually get around 2/3 of the peak rated current, even in ideal conditions (clear day, no shadows e.t.c.).
Hope that this may help you decide if it will be worth while or not.
Incidently I am very happy with my panel (here in the Med) and it keeps my service batteries topped up and will provide for about three days at anchor with the fridge permanently on (140Ah of service batteries).

Alan.