Basic solar panel question from a complete numpty

[Homer J]

Dear All

If anyone has the energy to answer this post I'd be very grateful. I would like to get a solar panel to charge the batteries but am mechanically and electrically challenged

What do I need to buy to top up two domestic batteries?

A solar panel of course, but a regulator (not entirely sure what it does), something to prevent overcharging and also how do I connect everything.

Also while I am confessing to this ineptitude how can I fit a 12v outlet at the helm? There is already power to existing instruments, can I take a feed off them or does it need a separate supply from the panel or elsewhere.

Any replies (in simpleton English) would be most appreciated.

 

[TQA]

Before anyone can give an informed answer you need to tell us the capacity of the batteries in amp hours. Often on a sticker on the battery and should be something like 105 ah.

Then we need to know how many amp hours you take out of the batteries on a daily or weekly basis. A list of items and the number of hours they are switched on is a starting point.

 

[lpdsn]

A basic regulator will just limit the maximum voltage output by the regulator. Solar panels typically produce something near 20V (you can check the values for the specific panel you buy). The regulator typically limits this to 14.4V to avoid overcharging of your batteries. They do nothing to increase the current output at 14.4V.

Fancier MPPT regulators will manage the panel to optimise the power that it produces (basically trying to get the best combination of Volts & Amps) and will also bump up the available output current at the output voltage to get as much power out as it can. They're more expensive, so it is a trade-off.

So it depends what you mean by top-up. Are you just trying to ensure the batteries are fully charged if you leave the boat for a while, or are you trying to keep them charged whilst you're on board and running things such as the fridge?

Circuits are pretty simple. You'll want to make sure that there's no risk of a short-circuit of your batteries. And that the wiring is sized for the loads you expect.

In terms of 12V outlet. The way I've done it is to put all the DC sockets on a separate fused and switched circuit (i.e. cigarette lighters, USB charging etc.) You also want to make sure what you have at the helm is suitably waterproof if exposed to the elements. There should be an IP rating, which it is easy to check against the scale on-line.

 

[William_H]

The question of solar is like the question "how long is a piece of string?" The answer to that being as long as you need.
Two domestic batteries implies a dual system with 1,2,both, off switch. Just how much topping off of the batteries do you want? Typical is a small panel which simply aids in maintaining the battery charge while the boat is unattended. A 10 watt panel might do this job. In fact 2 x 10watt panels one for each battery might be better. Or you use 1 panel and 2 small diodes at each pos terminal (in lieu of fuses). This means that battery system is left turned off when you leave the boat. At 10 watts and a reasonable sized battery it is OK to not use a controller. The controller is there to stop over charge. The 10w panel will at best pump in .5 amp which will not harm a fully charged decent battery. Don't be alarmed at the 20 v a solar panel produces. This is a max no load voltage and immediately reduces to the battery voltage when you connect it to the battery.
You would need to fit fuses for each solar panel wire to the pos of the batteries.
You biggest problem may then be to find a place to mount the panels. On a cabin top is one option. I fit mine on bungees over the sail cover on the boom. I disconnect and remove when I go sailing.
When you answer this question of mounting then you realise that this is the most limiting factor in solar power. Solar panels and regulator (for higher power panels) are not so expensive and if you have enough panels (power) you can run a lot of electrics indefinitely on solar. But where do you mount them on a boat? Panel power is directly proportional to size.
I hope this answers some questions. olewill

 

[VicS]

Dear All

If anyone has the energy to answer this post I'd be very grateful. I would like to get a solar panel to charge the batteries but am mechanically and electrically challenged

What do I need to buy to top up two domestic batteries?

A solar panel of course, but a regulator (not entirely sure what it does), something to prevent overcharging and also how do I connect everything.

Also while I am confessing to this ineptitude how can I fit a 12v outlet at the helm? There is already power to existing instruments, can I take a feed off them or does it need a separate supply from the panel or elsewhere.

Any replies (in simpleton English) would be most appreciated.

The most basic type of controller simply disconnects the solar panel from the battery once the volts have risen to something like 14.4 volts and reconnects when the battery volts have fallen to some lower figure (13.7 or thereabouts).

The next step up in sophistication is what is known as a "pulse width modulated" controller (PWM for short) It controls the charging by breaking it into a series of pulses, of decreasing duration, as the battery approaches full charge. Unlike the simple controller it does not disconnect entirely but in effect reduces the average current to maintain the battery at full charge.

The next step up from PWM is what is known as " Maximum power point tracking" ( MPPT for short). This type of controller manages the current drawn from the solar panel in order to keep it operating at its optimum output. This is usually with about 16 volts at the panel terminals. The MPPT controller then uses electronic wizardry to convert the extra volts into extra current into the battery. This type of controller really only comes into its own with fairly large solar panels.

You will be able to obtain a PWM controller with two outputs for the two batteries if they are not combined into one bank. MPPT controllers only come with a single output. They are probably combined into a single bank therefore a single output controller should be adequate.

As far as your 12 volt socket at the helm goes the most sensible thing to do is to run a separate fused supply from the main distribution panel. If you connect it to the instrument supply you will limit its usefulness to low current equipment only.
Difficult to be more precise without knowing a lot of details of your present electrical system

Wiring for 12 volt circuits is always much heavier that it would be for the same current at 240 volts. This reason is to limit volts drop in the wiring to an acceptable level. It does not matter if you lose a volt, say, when you have 240 of them but it does matter if you only have 12 of them to start with. Current and cable run length have to be taken into consideration when calculating gauge of wiring for 12 volt circuits.

 

[Homer J]

Dear All
Many thanks for the replies which were very useful. I'm always amazed how generously people give their time and advice. Thanks again. We

 

[johnalison]

I fitted a 12v cable to the cockpit, with a cigar-lighter socket, for general use. I think this is preferable to tapping off the instrument supply, which might not take the wattage for some applications. I don't use my socket much, but it will take the H/H GPS, a powerful lamp, the iPad etc.

 

[BarneysDad]

I got 80 watts worth ( 4 x 20w panels ) from http://www.selectsolar.co.uk/cat/165/choosing-a-solar-panel -- they have a programme set up where you can add the consumption of each piece of equipment on your boat. Then it tells you what wattage you'll need. I don't have a fridge or TV. Just the basic - VHF, nav hardware, lights, FM radio, USB phone chargers. My electrician hints that I'm over paneled but I always have well topped up batts even over the dark days of winter.

Siting of the panels is important as they want a clear view of the sun & sky. That's hard to achieve as the sun seems to keep moving across the sky. I notice on other yachts ppl are haphazard abt siting. Avoid directly under booms, tilted at angles which only catch a few hours of direct light; ropes, bits of canvas laid over them.

Don't be frightened of them. Hope this helps.

 

[Stemar]

Don't be frightened of them. Hope this helps.

Good advice all round, but hat's the best bit

My advice would be to go for the biggest panels you can fit on your boat and in your budget. There's no such thing as too much power (there is, but you won't be getting close!) Position is important - in clear sun and angled to be facing the sun at all times is what you want, but is, shall we say, challenging on a boat, especially a small one.

Two smaller panels are better than one as a small shadow on a panel can drop its output dramatically. With two panels, a shadow on one won't affect the other. My two 20w panels are mounted on the hatch garage as that's the only place they could go without risking being stepped on. They're under the boom, which really isn't ideal, but they're enough to provide our needs at anchor in summer (LED lighting, water pump, no fridge)

You'll need a controller. The different types have been described above. I have a PWM controller that has two outputs and it's set up so it charges the engine battery first then turns its attention to the domestic one. My reasoning is that it's more important to be able to start the engine than turn a light on, plus, it's rare for the engine battery to run low, so charging doesn't take long. If you do it the other way round, the engine battery might not get a look in.

As for the 12v outlet, a lot depends on what you want to do with it. Running a tiller pilot needs a lot more power than charging your phone. As has been said, it needs to be fused and, preferably, switched. Try to avoid just running it from the battery isolator switch; it's all to easy to add one, then another, then another, until suddenly you've got a load of spaghetti and a Bolognese of in line fuses with no idea which wire does what. Use multi-strand wire, not domestic wiring cable. The vibration from the boat's engine can work-harden solid wire, causing fractures. Tinned wire doesn't corrode like plain copper, but is more expensive.

Here's my thought process:

1. What do I need to plug in - how many amps / watts? (amps = watts/12)
2. How thick a wire do I need? buy something with a suitable rating - go up a size rather than down.
3. Where can I get my power from, considering the expected current draw?
4. Do I need an extra fuse? In line fuses are simple to fit, not so simple to remember where they are or what they do 5 years down the line
5. Where can I run the wire? Keep it out of the bilges, away from anything that gets hot or moves, including all the junk in your lockers. Fix it every foot or so, so it can't escape or vibrate.
6. Do I need to allow for the length of the wire? (More than 10 m of twin wire, add 50% to the rating)
7. Where should the socket go? (Out of the way of errant lines, feet & elbows, and that includes the wire you'll be plugging in)
8. What sort of socket do I need? (Assume it needs to be at least splash/rain proof.)

One final thought. Get yourself a digital multimeter and learn how to use it. It doesn't have to be expensive, but you'll be glad to have it when you throw a switch and nothing happens.

 

[Richard.C]

I think all cigar light sockets are rated to 10 amps only so you could install wiring to suit that and be done. If you want more than 10 amps I think you should be looking at a different type plug & socket.

 

[PaulRainbow]

I think all cigar light sockets are rated to 10 amps only so you could install wiring to suit that and be done. If you want more than 10 amps I think you should be looking at a different type plug & socket.

12v sockets of the fag lighter variety go up to 20a, depending on the model.

 

[Homer J]

I would need the external 12v for running an iPad and pumping up a dinghy. Would 10apms be sufficient?

 

[ex-Gladys]

I would need the external 12v for running an iPad and pumping up a dinghy. Would 10apms be sufficient?

Depends which pump.. I have a Bravo pump, which draws a lot more than 10 Amps. The warning says don't use it without the engine running, and that's with a CAR! It has croc clips to attach direct to the battery

 

[RichardS]

I would need the external 12v for running an iPad and pumping up a dinghy. Would 10apms be sufficient?

We have an electric inflation pump which comes supplied with a car cigarette socket plug and standard. If yours has that plug then it will, almost by definition, be fine at 10A.

Richard

 

[nemodreams]

Many cigar sockets of 'marine' grade that have 10 amp stamped on them - will melt at 5 amps ! Be careful if anything is actually pulling more than 5 amps constant ! There is some serious rubbish around !

My high pressure inflator pulls significant amps - it basically wanted to be croc clipped to the battery direct. I had to wire separate high ampage panel mount socket, with its own 25 amp supply via an inline car type fuse.
I used these - series 5 Buccaneer -
http://uk.rs-online.com/web/p/industrial-automation-circular-connectors/3444021/
plus the panel socket.

 

[Homer J]

Blimey - why does everything have to be so complicated! Not only does the word 'boat' (or aeroplane - I have experience here too) make it miles more expensive but also so much more complicated.

However, a big thanks to all those who have tried to answer my questions
jeez.