solar panel advice for ignoramus

[Neil McFarlane]

Hello, I have just bought a boat and am looking for advice about solar panels.

 

The boat has a starter battery and one leisure battery which are currently connected. I'm assuming that it may be better to disconnect the two battries so that the starter battery doesn't get discharged accidentally by running my laptop and other equipment.

 

I want to know what I need to power my laptop. If I get a solar panel, should this be routed to charge the leisure battery which I should then use to power the laptop? Or is it better to connect the panel directly to the laptop (with a regulator/inverter), or some combination of both?

 

And what size solar panel would keep the leisure battery discharging when powering the laptop (assuming I'm drawing from the leisure battery and not directly from the solar panel and assuming sunny conditions on a midsummer's day (I know winter will be a different story)?

 

I realise answers will need to be approximate, but it's a typical-sized laptop and I'm just looking for a rough idea and better understanding of how things work. I've read around but am still a little confused.

 

Thanks in advance!

 

 

Edited June 15, 2020 by Neil McFarlane

[Tony Brooks]

Before anyone can give you a sensible answer we need to know more about the charging system. If you have two batteries and they are designated start & leisure (domestic or service) batteries then there may well be some form of charge splitting between the two batteries. This will not be the case if it has two alternators but with just two batteries I think there will only be one alternator. The charge splitting could be some form of relay, diodes or a big switch marked 1, 2, both, off or similar. It is even possible that with just two batteries they may be connected as one large bank so any chance of some photos so we can work out what you have. We need to see how the batteries are wired and any large switches you have. 

 

Then there is a question about the type of boat. One with just two batteries may be a smallish GRP cruiser and if so roof space may limit the amount of solar you can fit.

 

In my view the solar installation should be as large as you can fit (sounds like a live-a-board boat) on the boat or that you can afford. remember that in winter the output will be very low. You must use a solar controller to protect the batteries and never try to connect solar direct to the laptop. In any case the laptop input voltage and solar output voltage is likely to be different. i think you need a 12V car type laptop power supply.

 

PS the course notes on tb-training.co.uk may help you understand the boat's systems.

 

Edited June 15, 2020 by Tony Brooks

[manicpb]

Relative ignoramus myself but I've recently added a 100w solar panel to my newly purchased boat. 100w with the current weather and long days is kicking out more than enough power for several hours telly/DVDs, radio on almost all day and the lights/water pumps/etc. Winter will obviously be a different story altogether!

 

Inverters, if not already installed, can be a pricey outlay so (as stated above) a 12v car charger is the cheapest and convenient solution.

 

100w panel plus a decent solar controller should be in the region of £175-£250. If your looking at kits, ensure the controller is of some quality (you will find lots for under £200 but the controller may be poor). You want to read what your solar panel is producing, what the battery is holding and if you wire it up right what load the boats using (not essential but helpful). A controller that displays red/amber/green LEDs makes for a guessing game as to what state your batteries are in.

 

Edit*

Of course if you can afford and have room 200w or more is better. I've just shared my experience of 100w to give you guide on usage and price.

Edited June 15, 2020 by manicpb

[Alan de Enfield]

If you are going for 100w panel you will need a 10amp MPPT controller (a good one is about £80-£90)

If you go for a 200w panel you will need a 20 amp MPPT controller (a good one is about £130-£140)

 

This is a good website to price things up (I have bought from them on several occasions and am a 'satisfied customer'.

 

https://www.bimblesolar.com/about_us

 

You buy an 'everything you need kit' this is one example for a 175 watt system

 

https://www.bimblesolar.com/12v-175w-mppt-kit-abs

£265 complete (+ postage)

[Neil McFarlane]

Still a bit confused - do you use the solar panel to charge the leisure battery and then run everything from that battery? If so and it's a sunny day, presumably the solar supplies enough to the leisure battery, the leisure battery supplies enough to the laptop and therefore never discharges, and you can stay switched on theoretically forever as long as the sun is shining? Or do you use the solar to run appliances directly, or some combination of both? (e.g. some of the power goes directly to the appliance and if there is an excess, the rest goes to charging the leisure battery?)

[Alan de Enfield]

12 minutes ago, Neil McFarlane said:

Still a bit confused - do you use the solar panel to charge the leisure battery and then run everything from that battery? If so and it's a sunny day, presumably the solar supplies enough to the leisure battery, the leisure battery supplies enough to the laptop and therefore never discharges, and you can stay switched on theoretically forever as long as the sun is shining?

In principle - Yes.

 

As long as you are using less than you are putting back in.

If you are taking out 100Ah per day and only putting back in (say) 90Ah then you are slowly flattening your battery(s)

Cloudy days, raining days, Spring, Autumn and Winter will all mean that you panel output is VERY much reduced. 

In Winter time you will commonly only get 1% or 2% of your Summer output so you cannot plan your life around Solar power - you need a secondary source of power generation for around half of the year.

 

You need to learn to live with the limitations and weather.

Edited June 15, 2020 by Alan de Enfield

[The Welsh Cruiser]

8 minutes ago, Neil McFarlane said:

Still a bit confused - do you use the solar panel to charge the leisure battery and then run everything from that battery? If so and it's a sunny day, presumably the solar supplies enough to the leisure battery, the leisure battery supplies enough to the laptop and therefore never discharges, and you can stay switched on theoretically forever as long as the sun is shining? Or do you use the solar to run appliances directly, or some combination of both? (e.g. some of the power goes directly to the appliance and if there is an excess, the rest goes to charging the leisure battery?)

The solar goes to the battery until it's fully charged. The controller stops the battery from being overcharged, potentially damaging it. Your laptop will draw from the battery but as long as the power in from the panel at least equals the power to the laptop, the battery will remain fully charged.

 

By the way don't feel overwhelmed by all this. I was at first and wrecked a couple of sets of batteries because I didn't understand the topic. 7 years on, I've a fair understanding. It shouldn't take that long really but there you go. My advice is to do a lot of reading on the subject, might even save you having to replace expensive batteries.   

[Neil McFarlane]

OK, understand a bit better now - thanks!

[Tony Brooks]

55 minutes ago, Neil McFarlane said:

Still a bit confused - do you use the solar panel to charge the leisure battery and then run everything from that battery? If so and it's a sunny day, presumably the solar supplies enough to the leisure battery, the leisure battery supplies enough to the laptop and therefore never discharges, and you can stay switched on theoretically forever as long as the sun is shining? Or do you use the solar to run appliances directly, or some combination of both? (e.g. some of the power goes directly to the appliance and if there is an excess, the rest goes to charging the leisure battery?)

Most solar controllers have a solar load output that will allow you to run certain things directly off the solar but at your stage of knowledge and as its boat related its best to stick with solar charges the battery and the battery supplies the electricity you need. As I said above don't try to run anything directly from the solar.

 

Note what Alan said about if the solar output is equal to or greater than the electricity you are using the solar will supply it via the batteries. If the solar output is less than the load then the batteries make p the difference but you start to discharge them. if the solar output is greater than the load then the load will be supplied and any excess charges the batteries.