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Solar....how much wattage is enough


Matt&Jo

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8 minutes ago, Matt&Jo said:

What size genny do you use?

I use a Honda EU20i and now use a Sterling Pro Charge Ultra 60A charger. You could use a Honda EU10i, (much lighter), and use a correspondingly "smaller" charger. I always thought the EU10i could power up to a 50A charger.

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Just now, Richard10002 said:

always thought the EU10i could power up to a 50A charger.

That will very much depend on the make / quality of the charger.

Some chargers have a Pf of 0.6 whilst other (expensive ones) have a Pf of 1.0

 

The EU10 generator would struggle (maybe not even run) a 50a charger with a 0.6Pf

 

The EU10 has a continuous rating of 0.9KVa

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On 18/05/2018 at 22:03, Horace42 said:

At a guess, for starters, I would say it is linked to the size of the battery bank - and the amount of roof space available

Not so.

 

The battery bank is nobbut a store.  Your generators have to supply enough energy to replace what you use plus any lost in innefficiency.

 

N

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2 hours ago, Theo said:

Not so.

 

The battery bank is nobbut a store.  Your generators have to supply enough energy to replace what you use plus any lost in innefficiency.

 

N

Sorry but I don't know what a nobbut is - but I did say 'for starters.'

The existing battery size must have been based on something - and the size of matching solar panels to keep them charged must be in the right ball park.

The experts on these things can give the exact figures.

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1 hour ago, Horace42 said:

Sorry but I don't know what a nobbut is - but I did say 'for starters.'

The existing battery size must have been based on something - and the size of matching solar panels to keep them charged must be in the right ball park.

The experts on these things can give the exact figures.

No.

 

As Theo points out, the batteries are only a storage medium. Their size is not (directly) relevant to the amount of generating capacity you require. You need to replace your usage plus up to 20% extra, ideally on a daily basis.

 

Your battery bank needs to be at the very least twice the size of your daily usage but it could also be 5 times the size or even more, so has no relevance to the capacity of the solar charging source. 

 

Edited by WotEver
Added a tiny bit for clarity.
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10 minutes ago, Horace42 said:

Sorry but I don't know what a nobbut is - but I did say 'for starters.'

The existing battery size must have been based on something - and the size of matching solar panels to keep them charged must be in the right ball park.

The experts on these things can give the exact figures.

 

No. Keeping them charged depends wholly on how much you take OUT of them each day. And solar panels cannot replace it all, 365 days a year. In summer even small panels will greatly exceed the need, and in winter massive panels will do feck all. Panel size is NOTHING to do with battery bank size and everything to do with how many days each end of the summer you want them to still work.

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34 minutes ago, Horace42 said:

Sorry but I don't know what a nobbut is - but I did say 'for starters.'

The existing battery size must have been based on something - and the size of matching solar panels to keep them charged must be in the right ball park.

The experts on these things can give the exact figures.

Well I would use the water tank analogy.  If you have a very slow filling rate then a big tank will allow you to draw off lots of water in a hurry but it will then fill very slowly and you won't be able to do the same thing for a long time.  If you have the same tank but a much faster rate of inflow you will be able to do just the same, but do it sooner.

 

While you are off the boat the small solar panels with a huge battery bank may take a week to charge the batteries fully.  When you get on the boat and start to use the energy the huge battery bank will be depleted and will eventually go flat because the charging won't keep up with the usage.  That would be when you need to add other sources of electrical energy like your engine alternator or a suitcase generator or a bicycle with a dynamo to keep your really fit or all of the above.

 

There is no getting away from it.  Whatever the size of your battery bank if your charge sources can't keep up with the usage then it will eventually go flat.  It's just that the fully charged big bank will take longer.

 

Your sources of charge must be able to cope with at least your consumption.  The battery bank is there as a buffer to allow you to use electrical energy faster than you are generating it, but you can't do that all the time.

 

N

Edited by Theo
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11 minutes ago, Theo said:

Well I would use the water tank analogy.  If you have a very slow filling rate then a big tank will allow you to draw off lots of water in a hurry but it will then fill very slowly and you won't be able to do the same thing for a long time.  If you have the same tank but a much faster rate of inflow you will be able to do just the same, but do it sooner.

 

While you are off the boat the small solar panels with a huge battery bank may take a week to charge the batteries fully.  When you get on the boat and start to use the energy the huge battery bank will be depleted and will eventually go flat because the charging won't keep up with the usage.  That would be when you need to add other sources of electrical energy like your engine alternator or a suitcase generator or a bicycle with a dynamo to keep your really fit or all of the above.

 

There is no getting away from it.  Whatever the size of your battery bank if your charge sources can't keep up with the usage then it will eventually go flat.  It's just that the fully charged big bank will take longer.

 

Your sources of charge must be able to cope with at least your consumption.  The battery bank is there as a buffer to allow you to use electrical energy faster than you are generating it, but you can't do that all the time.

 

N

Obviously from what you and Mike say you must be the experts on this, and I am but a novice. I hope the OP learns something from my ignorance.

I just wonder how the OP has managed without solar panels. The battery buffer must have been large enough to provide all the power during periods of no-charge - and the power source must have been adequate to have surplus power (over and above the direct load) to fully charge the batteries when running.

The analogy of a water tank is great - except that whatever size tank and whatever charging source (rain instead of sun)  you can never overfill it.  Excess rain goes to waste. Which doesn't matter if the tank holds enough water for all your needs when it is not raining. And so with an erratic source of sun the batteries should be sized to provide all the power necessary and gather as much power as possible....and save it for a rainy day!

 

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14 minutes ago, Horace42 said:

I just wonder how the OP has managed without solar panels.

OP hasn’t managed. He didn’t own the boat when he started this thread, hence his question. 

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19 hours ago, WotEver said:

OP hasn’t managed. He didn’t own the boat when he started this thread, hence his question. 

The previous owner then! - somewhere along the line - the batteries must have been about the right size.

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1 hour ago, Horace42 said:

The previous owner then! - somewhere along the line - the batteries must have been about the right size.

Not nessecererly.

 

The previous owner might have sould the boat cos he was so fed up with the electrics.

 

N

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1 hour ago, Horace42 said:

The previous owner then! - somewhere along the line - the batteries must have been about the right size.

But as three of us have been telling you, the size of the bank is irrelevant to the size of his generation. Maybe the previous owner was on shore power, maybe he got fed up with his batteries going flat, who knows?

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16 hours ago, WotEver said:

But as three of us have been telling you, the size of the bank is irrelevant to the size of his generation. Maybe the previous owner was on shore power, maybe he got fed up with his batteries going flat, who knows?

 It is not me seeking guidance. Telling me I am wrong does nothing to solve the problem for the OP.  

 In my opinion, I say the batteries matter - they are an essential part of the energy supply/demand system - and cannot be ignored in the energy balance equation - if as you say the size is irrelevant - then leave them out - see how you get on.

But as I said - looking at the batteries was for starters (and roof space) - and if the solar panel is sized to keep them fully charged under all load conditions then that is fine. Problem solved.

I do not dispute there is a need to do a consumption audit - everything using power - with a diversity factor to cater for essential/non-essential items for controlling demand - with a solar panel large enough to drive the largest item - at whatever time of the year - a microwave oven in the Winter perhaps.

From what has been said by others,  if I was looking for a solar panel I would go for a control system that enabled extra panels to be easily added if more power was required - and definitely a battery bank large enough to store the surplus power in days of good sunshine.

Apart from technical nit-picking the most useful feedback here to the OP would be from  experienced users - with pointers dealing with different makes and suppliers - and what practical factors to consider in how to get the most benefit from them.

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10 minutes ago, Horace42 said:

In my opinion, I say the batteries matter - they are an essential part of the energy supply/demand system - and cannot be ignored in the energy balance equation - if as you say the size is irrelevant - then leave them out - see how you get on.

I have 6x 230Ah batteries.

I have 1x 170w solar panel.

I run my engines between 4 and 13 hours most days.

My daily 'consumption' is around 100-120Ah

 

My other boat has 2x 130Ah batteries and 3x 100w solar.

 

Does that give any understanding of batteries vs solar ?

Edited by Alan de Enfield
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7 minutes ago, Horace42 said:

In my opinion, I say the batteries matter - they are an essential part of the energy supply/demand system - and cannot be ignored in the energy balance equation - if as you say the size is irrelevant - then leave them out - see how you get on.

Sigh... you’re still not getting it. 

 

1. Do an energy audit

2. Calculate how you will replace 1 on a daily basis. 

 

If 2 is less than 1 then work out how to either increase 2 or decrease 1. 

 

When you have reconciled 1 & 2 and only when you have done so then select a battery bank size of at least three times 1. This is true for any boater who doesn’t wish to replace his batteries annually. 

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58 minutes ago, WotEver said:

1. Do an energy audit

2. Calculate how you will replace 1 on a daily basis. 

 

If 2 is less than 1 then work out how to either increase 2 or decrease 1. 

 

And bear in mind 2 will not involve solar, as solar output is negligible in the three winter months.

 

As solar comes on stream in spring it simply replaces some of the engine/generator running time. 

 

This is is only true for all-year-round power consumers obviously. If the boat is laid up in winter then solar just about counters self-discharge of the batteries in my experience. 

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4 hours ago, WotEver said:

 

Sigh... you’re still not getting it. 

 

1. Do an energy audit

2. Calculate how you will replace 1 on a daily basis. 

 

If 2 is less than 1 then work out how to either increase 2 or decrease 1. 

 

When you have reconciled 1 & 2 and only when you have done so then select a battery bank size of at least three times 1. This is true for any boater who doesn’t wish to replace his batteries annually. 

^^^^^^^^^^

Wot he said.

3 hours ago, Mike the Boilerman said:

 

And bear in mind 2 will not involve solar, as solar output is negligible in the three winter months.

 

As solar comes on stream in spring it simply replaces some of the engine/generator running time. 

 

This is is only true for all-year-round power consumers obviously. If the boat is laid up in winter then solar just about counters self-discharge of the batteries in my experience. 

^^^^^^^^^^^

And wot he said too.

Both of the above are top quality advice.

 

The bit about not having to replace batteries annually is to do with the fact that under charging batteries leads to their early demise.  By undercharging I mean not charging them to 100% twice a week and never running them below 50% at any time, though the later is an economic decision to balance the initial cost of a sufficiently large battery bank compared with the replacement interval.

 

N

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8 hours ago, WotEver said:

 

Sigh... you’re still not getting it. 

 

1. Do an energy audit

2. Calculate how you will replace 1 on a daily basis. 

 

If 2 is less than 1 then work out how to either increase 2 or decrease 1. 

 

When you have reconciled 1 & 2 and only when you have done so then select a battery bank size of at least three times 1. This is true for any boater who doesn’t wish to replace his batteries annually. 

Sorry, but I don't need to get it!  It is not me asking for advice.

 

What is helpful is your simplified process of steps 1 and 2,  but a breakdown of each stage is need to ascertain what is to be taken into account and how it is to be measured or estimated.

On the face of it, it sounds more like a rule of thumb for estimating battery size - a factor of 'three times'?  - I guess comes from 8 hrs use per day.

 

Anyway I am sure the OP, not versed in the finer points of these things, would like to know how the results of stage 2 can be used to get the size of the solar panel.

 

But on the basis of you statement that 'this is true for any boater' it suggests boats without solar panels are included. Therefore any boat designed to your rules - and without land lines or running the engine, or using anti-social generators - or windmills - has anybody invented a wave-generator (operated by passing boats that don't slow down) - then if to rely on solar panels will need power equal to 1/3rd of the battery bank.  Which could amount to a large panel area to cope with bad weather and could bring the roof size into the equation.

 

Both are easy things to find out - but as I said - for starters.  The experts can do their own exact sums when they have got all the necessary additional facts to do the energy audit.

 

 

 

8 hours ago, Alan de Enfield said:

I have 6x 230Ah batteries.

I have 1x 170w solar panel.

I run my engines between 4 and 13 hours most days.

My daily 'consumption' is around 100-120Ah

 

My other boat has 2x 130Ah batteries and 3x 100w solar.

 

Does that give any understanding of batteries vs solar ?

Yes, To me it does. Because my engineering knowledge enables me the appreciate the whole technical process to my own satisfaction.

170W at 12V is about 14A so in an 8 hr day will give 120Ah. Seems about right.

3x100W at 12V is 25A so will charge your other boat batteries in about 10 hours - so again seems OK.

The point is - does a single 170w panel on the first boat, and 3x100w on the second boat, work for you.

That is the bit that really matters.

 

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3 minutes ago, Horace42 said:

Anyway I am sure the OP, not versed in the finer points of these things, would like to know how the results of stage 2 can be used to get the size of the solar panel.

 

The missing link is the OP stating how many months of the year he wants his solar to supply all his power needs for. 

 

This information along with his power audit would allow a possibly suitable panel size to be suggested. 

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7 minutes ago, Mike the Boilerman said:

 

The missing link is the OP stating how many months of the year he wants his solar to supply all his power needs for. 

 

This information along with his power audit would allow a possibly suitable panel size to be suggested. 

Good, we are getting somewhere.

 

9 minutes ago, Alan de Enfield said:

I would be in a hell of a mess if I was charging my batteries at 12v.

14 amps ? Do you have any real-life experience of solar panels ?

None whatsoever of any use today, stemming from a total waste of money when they first came out 30 years ago, when in my case they failed to work properly. From that experience I would not touch them with a barge pole (sorry, accidental pun) - until the technology has evolved to iron out all the problems. 

But here I am not asking you to charge your batteries at 12V - 14A or whatever. I assume you are expert enough to know what you are doing, and where you and other experts in these things who can comment.

But I know enough about engineering theory to handle all the electro-mechanical technical matters, and these are the things that need reliable facts - of which there is a shortage - leading to guesswork - that causes the hassle.

 

 

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Ok for simplicity, lets assume the OP uses a steady 100AH at 12v per day, every day of the year. 

 

Let us also assume my own solar behaves typically. I use 30AH per day at 24v, equivalent to 60AH at 12v.

 

My 560W of MPPT solar supplies ALL my electricity from about the beginning of May to the end of September. That's five months of the year. In addition at each end of the season I get about a further month where I get 50% of my electrical consumption and a further month each end where I get perhaps 20% of my electrical consumption. The remaining three months I get nothing. 

 

So assuming the OP wants to replicate my solar performance in his own boat, he will have to scale up 560W of panels by 100/60. He will need 930W of panels and an MPPT controller.

 

Does that shed any light?

 

(Notice battery size didn't come into the calculation?! ;) ) 

 

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