Solar panels and 24volt system

[All_at_Sea]

Hello, l hope you are all nicely tucked up in some exotic location. We too will be joining you from June this year, but first l must sort out a dilemma. I have a 24v system, 2 batteries in series for aux and two for the engine,anchor combo. I was told at the boat show that in order to get a 24v charge l would need two panels in tandem so twice the expense. However l was thinking that the batteries are actually 12v individually so could l charge them as a 12v system or do l have to buy two of everything?

I do have a diesel generator on board but want to be a bit more independent than that so l am looking at windcharger and solar to provide about 40-50 amps a day. Is this realistic in the Med?

 

[JerryHawkins]

We have a 24v system and have your dilema. 24v is a double-edged sword - all the cables can be smaller than for 12v for the same power, but 24v kit is generally more expensive - get to know your local lorry parts places!

There are some solar panels for 24v systems, but normally, you would need 2 x 12v panels in series to be able to charge a 24v bank. However, to get the same power you would have 2 smaller panels instead of one large one. Problem is that 2 smaller ones still cost more than one large one, but not twice as much. The advantage is that it may be easier to fit 2 smaller panels than one larger one and if one panel gets damaged it is cheaper to replace a smaller one than a larger one!

 

[grumpygit]

There is a way of doing what you ask but honestly it would not be worth the cost to modify your existing battery/charging circuits and the pitfalls that might occur. If you would like me to take you further through it with more detail please send a PM.

Two panels of the wattage you require in series with one 24volt regulator/blocking diode plus the wiring and waterproof joint or box will be all you require.
It also is not just the cable sizes but more importantly being 24volt gives you half the amperes for the same wattage used . (apply Ohms Law )

I personally think more vessels should be 24volt and half the consumption to service loads. Most modern electronics are rated upto 32volts and things like pumps, water makers, alternators and starters are at similar if not at the same price. Even phone chargers for cig lighters are rated for 12/24volt systems these days.
Yes, an extra battery per bank or solar panel will be required but I think the costs are well worth the improvement to the system.
You do not have to buy solar panels from marine dealers, there is plenty of domestic/industrial suppliers out there so you can shop around for a good deal. Kyocera Polycrystalline Panels are a good panel and will do the job for you.

I cannot answer about a wind generator as I don't use one but same principal of a 24volt unit would be best. IMO the Solar panels would be more efficient in the Med. (more sun than wind )

 

[Gumpy]

You cant reliably charge them as two 12v systems as they will never get the same charge level.

This lot
http://www.energyenv.co.uk/SolarModulesMain.asp
have done solar for one of our members on a 24v system using 24v panels, unfortunately they have a minimum order on panels as 24v ones are not so common.

 

[castlevar]

I have a 24volt system have two koycera panels 160watt each
wish i had fitted larger they are really great keeps everything working and koycera have 25 year guarantee faulty panel last year replaced both panels no charge to me.

 

[petulantchild]

I agree with the previous posts in that you cannot reasonably charge two 12 volt batteries efficiently. I have a 24 v system and have messed around with the panels in series and parallel to get the best from them. In my experience, having tried 12v and a 12 to 24 converter and parallel at 24v, both through a regulator, I get more amps at 24v. The converter takes some power and costs about as much as a small panel anyway. Make sure that both panels are rated the same or you will end up taking the smaller panel's rated output. A mistake I made because I was trying to fill certain sized gaps with different sized panels. IMO 24v from 2 12v panels in parallel will suit your needs.

 

[tkomarine]

We are 24v and have recently got 24v panels from www.marlec.co.uk they are very helpful. I purchased one last year which has been good and have another on order now. The make is 'Sunware' Speak to Teresa.

 

[Anonymous]

You will need either two 12V panels in series or one 24V panel. Yes, you can easily get your 50Ah per day with large enough panels -- we have two large 12V panels that push out 15A for most of the day; between 100 to 150 Ah at 12V = 50 -75Ah at 24V equivalent power. Ours are BIG panels, tho', 185W each. Be careful about the nominal rating of these panels. With my Solara panels 185W is the maximum possible output with the best angle of inclination and is calculated by taking Volts X Amps at the panel itself. You will lose a surprising amount in the wiring (resistive drop) and to get the charge into the battery you will need more than 27.2V across the battery, so you need to do the sums on that basis.

I installed my panels flat, on top of a very rigid bimini structure that we have, mounted on two teak bearers that are held onto the stainless bimini tubing with stainless U bolts. I argued that with such large panels it would be impracticable to point them to the sun and second (and more important) you really only need solar at anchor or moorings and you keep swinging anyway. In the Med in the summer flat is, I think, best unless you can sit there pointing them all the time. If you are into maths, you can see for yourself the effect of the angle of inclination; the reduction in power is the cosine of the angle of inclination. But once the sun starts to get much below 45 degrees the path through the atmosphere has attenuated it so much that you are beyond the region of fast charging (will still run a fridge until 7pm but not much more).

The biggest caution for you if you buy two 12V panels is that you must not let any part of either panel be shaded by rigging, boom, cockpit structures,... These panels are made up of elements connected in series (like a lot of little batteries) and if any element goes dark, it stops the flow of current. Many designs include a diode across each element internally (and you need a diode across each array) but losing the voltage of one or two elements has a devastating effect on the charge rate into the battery. I have two 12V panels in parallel (because I have a 12V system) and that means that I seldom drop below 8A to 10A (at 12V) charging.

As for wind, we have never had it. In the Med most people find solar best. I am told that in the Caribbean it is the other way round. Wind can make a noise and in any case you try to anchor in sheltered spots! Also, the sailing is not very good in the Med. Most of us motor for long periods so the need for wind generation to run the nav kit is not really an issue except at night.

Finally, consider some kind of battery monitoring system. I have the BEP but quite honestly the 'fuel gauge' part of it is pretty useless as the charging conditions change so much (temperatures and rates) according to whether the charge is coming from our engine alternator (80A), our battery charger (80A) or our solars (8A to 15A). I now find that the digital voltmeter part of the BEP tells me all I need to know about battery state and the current monitor tells me exactly what rate I am charging or discharging at. The BEP has a bilge pump monitor built in which is very useful. I can tell how long the bilge pump has run for and how many cycles. Very reassuring particularly on long motor passages.

 

[LadyInBed]

I am interested in getting a 24v panel.
What make / type of panel(s) did they supply?
Was it one panel or two connected in series?
What was the Wattage?