Solar panels

[tarik]

Evening all,


I am an absolute novice re solar. I have two 12v batteries and would like to arrange a solar charging system.

Do I need 2x 20watt solar panels ( potential fitting problems) or preferably 1x 40 watt.

What does the Team suggest?


As always many thanks for all replies.



David

 

[Kelpie]

Impossible to answer without knowing how much current draw you are expecting to keep up with. If it is just to trickle charge the batteries so that they don't gradually go flat whilst you are away from the boat, then a very small panel hard wired in will do the job.
If you want something more substantial, to cope with actual usage, you will probably need to include a charge controller, but they can be had for about £10 so a small price to pay not to fry your batteries. You can get controllers which will send current to two separate batteries, by the way.

I've recently installed a system with a 50w panel and a 20A dual-battery charge controller. Total price was about £100. I could have got a much smaller charge controller at slightly less cost, but I may in future add more panels, and the 20A should see me right up to about 250w total, if I ever decide I need that much power.

 

[charles_reed]

Evening all,


I am an absolute novice re solar. I have two 12v batteries and would like to arrange a solar charging system.

Do I need 2x 20watt solar panels ( potential fitting problems) or preferably 1x 40 watt.

What does the Team suggest?


As always many thanks for all replies.



David

As you don't explain what you hope to achieve with your solar panels it's difficult to comment, apart from saying that your proposed 40 watts would probably be adequate to keep the batteries topped up whilst the boat is not being used.
For full-time liveaboard, in UK, hoping to be free of external power-sources x10 that capacity is probably necessary.
The limiting factor on most monohulls is finding sufficient mounting area.
The only way (apart from trial & error) to arrive at a power budget - your average usage in 24 hours - and then see what capacity of solar panels you need - assume you get 40% of stated wattage for 6-hrs/day.
My budget is 60-80 AH and during the months of June and July in Greek waters my 330watts of PV panels allow me to stay @ anchor almost indefinitely - in March and October they're inadequate.

 

[vyv_cox]

I have a 38 watt panel on deck aft of the mast that I originally installed in Wales and used for many years there and in Holland. It did little more than keep batteries charged when the boat was unoccupied. I never saw more than about 1.8 amps from it, barely enough to run the plotter when on board. I did have a sophisticated controller that charged two battery banks and the price of these is now about half what it was then. Google Sunworks.

 

[AndrewB]

I'm assuming you want to trickle charge your two batteries, and you are essentially asking us whether it is best to use one solar panel or two to do it. Note that as well as the solar panel you are going to need to fit a charge controller (regulator) to make sure the batteries don't get over-charged. These are often supplied with the solar panel.

The answer then depends on how your two batteries are configured:

(1) If the two batteries are not connected to one another, then to keep them independently charged from one solar panel is going to require a special split charge controller - readily available but extra expense. Otherwise two solar panels each separately charging a battery, each with their own normal charge controller.

(2) If the two batteries are normally connected in parallel, i.e. you have 12v system aboard, then it would be simplest and cheapest to have just one 40w panel, though 2 x 20w panels usually can be connected together to do the same job. Either way only one charge controller is needed.

(3) If the two batteries are normally connected in series, i.e. you have 24v system aboard, then I'm not sure but I believe it is possible to connect two solar panels in series to charge them, and this is preferable to trying to uprate the voltage from a single panel. You would need a special 24v charge controller.

 

[duncan99210]

Irrespective of why you're fittting the panel and what your demand for electricity is, I think it is a good idea to fit two smaller panels rather than one larger one. This is because of shadows, which affect the output. By having two panels the chances of having full output from at least one of the panels is improved.

 

[bobgarrett]

As others have said it all depends on what you expect from them and your style of sailing.
We recently changed from weekending and so never needing anything beyond the engine and marina supply to a six month passage to and from the Baltic. I thought about our use carefully and realised that the power we'd get from even large solar panels per day could be gleaned from running the engine for a very short period; so why spend a fortune on panels, regulators and mounting. Then we felt that running the engine while at anchor and on long sailing legs was noisy and unnecessary.
In conclusion we reduced power needs by replacing all lights with LEDs, fitted a good solar regulator (in case we go for more solar panels later) and a solar panel a bit less than 0.5 sqm in size for about £100. This we hung from the safety lines at the side or stern depending where the sun was. It reduced our net power use by up to a couple of amps meaning that only once did we need to run the engine just for charging.

 

[LadyInBed]

First Q(s) to answer is where do you intend to fit them (two are more versatile than one) and what area (L and B) can you accommodate.
I would say that if you can accommodate higher wattage pannels than you calculate you require, it won't go amiss.
Solar o/p is seldom if ever its max rated, better to have spare capacity than insufficient.