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Tillerman
Tillerman

Posted: Sun May 08, 2016 9:01pm

Post Subject: Solar Power

Hi, I'm hoping you may be able to help me. I have aquired two 2.75 watt solar panels off a house. I want to put them on my boat so I can be pretty much free from the marina electrical hook up. My boat has three 110amp 12 volt leisure batteries, which I will increase. I believe I need a charge controller also. But, are the panels that go on a house different to those that go on a boat? I'm somewhat confused over this. Hope you can help, Chris

Tony-B
Tony-B

Posted: Mon May 09, 2016 8:00am

Post Subject: Solar Power

First of all to clarify things for other readers. The batteries will be 110 Amp hours, not 110 amps (a very common mistake), they can produce thousands of amps if allowed. There is no way solar panels off a house will be rated at 2.75 Watts. The whole house installation of several panels may be rated at 2.75 Kw (that's 2750 Watts) so it is more likely that your panels are rated at 275 Watts. If they are 2.75 Watts they will be very small and may be connected directly to your battery bank but there is no way they will do more than just keep make up for the batteries self discharge rate. Assuming they are 275W then you will need to put a controller between panels and batteries. As you want to avoid shoreline use invest in a reputable MTTP controller rather than the cheaper PWM ones. An MPPT controller will provide up to 30% more charge in less that ideal conditions when compared with PWM ones. Still assuming 275W panels, each panel can in theory produce about 20 amps a 13 volts but are unlikely to do so in the UK so ideally you will need a 40 amp controller but you may get away with a 20 or 30 amp one BUT at midday in mid summer you are likely to reduce the charging current to some degree. I have no idea what the maximum voltage of your panels are, I think some house panels can be rated at over 30 volts but others at less than 20 volts. An MPPT controller will usually be rated for at least 100 Volts so connect the panels in series (that is pos on one panel to neg on the other) so you can use thinner cables between panels and controller as they will be running at a maxim,um of 60 volts but only 20 amps or less. The controller will reduce the voltage to suit then battery bank and up the current by a proportional amount.

Tillerman
Tillerman

Posted: Tue May 10, 2016 12:44am

Post Subject: Solar Power

Tony -B Thank you for your kind assistance. The information you have supplied is very helpful and will allow me to proceed. Apologies for the (.) They are 275 per panel. Not to sure why I put the dot in between. Someone must have put brandy in my tea. Could you recommend a good charge controller? Also I was thinking of taking the battery bank up to six. Many thanks, Chris

Tony-B
Tony-B

Posted: Tue May 10, 2016 8:07am

Post Subject: Solar Power

I do not recommend equipment unless I have tested it myself or have read good user feedback. The problem with MPPT controllers are that a certain well known "auction" site seems to have been supplied items that were not as described so buy brand names or from well established and known suppliers although you will pay more. Outback, Morning Star and Stecca are well known brands. AS far as the batteries are concerned I just hope that you have done a power audit and charging calculations although the charging calculations are difficult for solar because of its variable nature. If your batteries keep going flat because you never recharge them enough then fitting more batteries will not solve the issue, you will just destroy more batteries. If the batteries go flat because they can not hold enough electricity for your needs then fitting more will solve the problem AS LONG AS you charge them enough each day. I very much doubt that you will have enough solar to supply your needs in the depths of winter but probably will in high summer providing you are not doing things like trying to use electricity for cooking or heating. An example power audit and charging calculations can be found on the web and in the maintenance notes on my website (TB-Training.co.uk). With batteries and charging there are so many variables all they will do is ensure your battery bank size, charging regime and power use are roughly in balance. I would suggest that to ensure you keep your batteries well charged, do not waste diesel fuel & engine running hours yet maximise the battery's life that you install some kind of battery monitoring device. I would suggest an ammeter and voltmeter plus bit of learning or an ammeter and Smartguage. Meters that basically count Amp hours in and out are prone to encouraging far too many boaters to destroy their batteries by lack of charging but they do also give accurate amp and voltage readings that can be used.

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