Solar panels

[Kate89]

Hi everyone, sorry I've got more beginner questions...

 

Just looking into solar panels for the boat, we're planning to live aboard and won't have plugin/shore power for the foreseeable future so need to be self-sufficient in that respect. Does anyone successfully run a small fridge without a generator?

 

I was hoping that we'd be able to cope without a generator but I don't know if I'm overestimating solar power. We'd be running a fridge, multiple LED lights, and occasionally chargers for phones and laptops (not planning on having a TV).

 

Any advice on number or type of solar panels would be greatly appreciated.

[Peter-Bullfinch]

Our fridge runs successfully on 2x100w solar but only from late March to late October. We use cold parts of the boat in winter to keep food fresh but we aren't permanent live aboards

[GoodGurl]

solar wont be much good in winter so you will need to run the engine or get a genny

[Kate89]

Our fridge runs successfully on 2x100w solar but only from late March to late October. We use cold parts of the boat in winter to keep food fresh but we aren't permanent live aboards

 

solar wont be much good in winter so you will need to run the engine or get a genny

 

That was my thought... our current neighbours beg to differ and insist that they run their fridge and lighting and a couple of hours of TV off of their solar power and a couple of hours of the engine being on, I need to ask them what their secret is.

Excuse my lack of battery knowledge... but we currently have 3 brand new batteries, one starter and two leisure, is there any benefit in getting a 3rd leisure battery so it allows you to effectively have a bigger 'store' of power?

[Arthur Brown]

http://www.victronenergy.com/upload/documents/Book-EN-EnergyUnlimited.pdf

 

is a free download book on the topic of power management. All the details can be found there and lots more besides.

 

Your solar panels will make their rated power for three months in the peak of summer, for three months in winter the panels will make about 8% of their rated power, the months in between will provide between 8 and 100% of their rated power. LOTS of panels is good.

 

Otherwise. you need to run the engine for a reasonable period each day and for a whole day at the weekend, or run a generator for a similar period.

 

A good understanding of your electrical installation helps, as does a means of determining the battery state of charge.

[Kate89]

http://www.victronenergy.com/upload/documents/Book-EN-EnergyUnlimited.pdf

 

is a free download book on the topic of power management. All the details can be found there and lots more besides.

 

Your solar panels will make their rated power for three months in the peak of summer, for three months in winter the panels will make about 8% of their rated power, the months in between will provide between 8 and 100% of their rated power. LOTS of panels is good.

 

Otherwise. you need to run the engine for a reasonable period each day and for a whole day at the weekend, or run a generator for a similar period.

 

A good understanding of your electrical installation helps, as does a means of determining the battery state of charge.

Excellent thank you for the link, plenty of bedtime reading for me there!

[Arthur Brown]

Remember that this is a web forum, there is much knowledge and wisdom here but you need some understanding to be able to sort out what advice is relevant to your questions.

 

Enjoy the read! The author is a boater and part of Victron.

[Sea Dog]

Excuse my lack of battery knowledge... but we currently have 3 brand new batteries, one starter and two leisure, is there any benefit in getting a 3rd leisure battery so it allows you to effectively have a bigger 'store' of power?

Although it seems so, it's really not that simple. There is an advantage with increased capacity, of course, but a bigger bucket takes longer to fill. Batteries fill to about 80% pretty quickly, but the final 20% takes a lot of time. The bigger the battery bank, the larger the final 20%. So, you need to have enough capacity such that you can do all you need to do between charges without draining your bank below 60% (otherwise you'll shorten their life significantly) but simply adding more might be counter-productive.

[peterboat]

Hi Kate,

I have nearly 1KW of solar 1500 ah of full traction batteries and still run the gennie for 3 hours a day in winter. Batteries that are allowed to run down soon die they have to be charged up to full on a very regular basis if not you will be lucky to get a year out of them.

I have lived onboard without shore power for 12 years it is an art so ask good questions and use the tinternet in all forms for help

[spadefoot]

Hi Kate,

I have nearly 1KW of solar 1500 ah of full traction batteries and still run the gennie for 3 hours a day in winter. Batteries that are allowed to run down soon die they have to be charged up to full on a very regular basis if not you will be lucky to get a year out of them.

I have lived onboard without shore power for 12 years it is an art so ask good questions and use the tinternet in all forms for help

You must have a much larger power usage than me, or a much smaller alternator.

My engine gets a couple of hours every other day, and 5 or 6 hours once a week or so.

Fridge, water pump, a few led lights. 240amp alternator. cheap batteries.

Washing gets done and things get charged whilst engine is running.

[Arthur Brown]

In my opinion! Keep the battery set that you have, get used to life on battery power. You should get 2 years out of a battery (set) but first time you may not. The only simple direct reading State of Charge monitor is the Smartgauge. Other meters exist but none so simple to read simple rested voltage readings are the cheapest battery indicators but usually take some interpreting.

 

Remember that for BSS your batteries need to be secured properly so you cannot just add a battery without adding a securing point for it

Edited December 5, 2016 by Arthur Brown

[Wanderer Vagabond]

You must have a much larger power usage than me, or a much smaller alternator.

My engine gets a couple of hours every other day, and 5 or 6 hours once a week or so.

Fridge, water pump, a few led lights. 240amp alternator. cheap batteries.

Washing gets done and things get charged whilst engine is running.

We run our engine for about two and a half hours every day which seems to keep the batteries topped up but I'm sure that our domestic alternator is a lot less powerful than yours, I think all we've got is about 70amp!

[MoominPapa]

The bigger the battery bank, the larger the final 20%.

 

No. Doubling the size of the battery bank doubles the current in the final stage as well as doubling the amount of charge to be put back, so the effects cancel out. A bigger battery bank needs longer in the first stage, where the charge current it limited by the output of the charger or alternator. Once the charge current starts to drop, the time to full charged is the same no matter what size it is.

 

MP.

[MtB]

 

 

That was my thought... our current neighbours beg to differ and insist that they run their fridge and lighting and a couple of hours of TV off of their solar power and a couple of hours of the engine being on, I need to ask them what their secret is.

 

 

There's their secret, right there!

[Sea Dog]

No. Doubling the size of the battery bank doubles the current in the final stage as well as doubling the amount of charge to be put back, so the effects cancel out. A bigger battery bank needs longer in the first stage, where the charge current it limited by the output of the charger or alternator. Once the charge current starts to drop, the time to full charged is the same no matter what size it is.

 

MP.

So, as an example, adding an extra battery to my 440Ah bank making it 550Ah would not increase my charging times in any significant way (since the first 80% is relatively quick anyway)?

[WotEver]

So, as an example, adding an extra battery to my 440Ah bank making it 550Ah would not increase my charging times in any significant way (since the first 80% is relatively quick anyway)?

That is correct. Once the batteries are demanding less than the charger's maximum output the charging time is dictated by the battery chemistry. 20 batteries will charge in the same time as 1 battery when they're in absorption.

[MoominPapa]

So, as an example, adding an extra battery to my 440Ah bank making it 550Ah would not increase my charging times in any significant way (since the first 80% is relatively quick anyway)?

It would increase the time of the first phase, when the alternator is flat-out, by 20%. The phase where the battery voltage reaches the limit and the current is reducing would be the same length.

 

MP.

[Sea Dog]

It would increase the time of the first phase, when the alternator is flat-out, by 20%. The phase where the battery voltage reaches the limit and the current is reducing would be the same length.

 

MP.

We'll I'll go to the foot of our stairs! I have been labouring under a misapprehension. The first phase isn't much of an issue with my 175a alternator either as it's always down to half that in a few minutes.

[MoominPapa]

We'll I'll go to the foot of our stairs! I have been labouring under a misapprehension. The first phase isn't much of an issue with my 175a alternator either as it's always down to half that in a few minutes.

Think of it like this. The existing batteries have reached 14.4v terminal voltage (or whatever the alternator is set for). You attach another battery and the alternator reacts by increasing the current to get the terminal voltage back to 14.4v. The existing batteries are still at 14.4v terminal voltage: nothing has changed for them, they have no way of determining that another battery has been connected. Therefore there's no possible mechanism by which the charge time can be increased.

 

The bigger your battery bank, the more energy you can extract from your alternator during the long constant voltage phase, so the number of amp-hours in the bank will go up faster during that phase The time to fully charge will not change though, that's controlled by the time to reach constant voltage, and by the characteristics of the batteries once constant voltage is reached.

 

Cheers,

 

MP.

[GoodGurl]

 

 

That was my thought... our current neighbours beg to differ and insist that they run their fridge and lighting and a couple of hours of TV off of their solar power and a couple of hours of the engine being on, I need to ask them what their secret is.

Excuse my lack of battery knowledge... but we currently have 3 brand new batteries, one starter and two leisure, is there any benefit in getting a 3rd leisure battery so it allows you to effectively have a bigger 'store' of power?

its the engine thats keeping the batts topped up, i have 1KW of solar and 2v full traction batteries and i need to run the genny for 2hrs a day