Best Ratio of solar panels to batteries in 'bank'

[barroca grande]

Hi, my boat build has jumped forward 5 months so I really need to decide on some nitty gritty stuff.

 

Having played with the idea of electric drives etc I have decided that my main requirement is to have solar panels to 'top up' the batteries on days that I do not move the boat. Bog standard diesel engine (I will be asking another question on this one later) will then fully charge the batteries when I am moving. I anticipate only not moving on one maybe two days at a time when I am on board the boat. I will have the following equipment on board but will not necessarily run them on non moving days so although they might be expensive wattage wise I don't want any answers to be too concerned with whether the panels can run them. I do not expect them too.

 

Laptop computer and little canon IP90 printer. (I might get extra batteries for the laptop and re charge when engine is running)

induction hob

tv (evenings only)

lights etc as normal (led's and low wattage etc) will also have back up solar powered lights etc

fridge

12v washing machine (potentially one of those diddy twin tubs)

combi/microwave oven. (Now I will also have a Cobb, a single gas camping stove and a chilli penguin stove etc)

hot water immersion heater (emergency use only and on a timer so can only be on max 1hr) I will probably be insulating the hot water cylinder to within an inch of its life.

diesel central heating

Envirolet loo with 12 volt thingy to be switched on when it is struggling to cope normally.

 

 

 

The question is this:

 

Is there a best ratio of solar panels:size of battery bank:engine size. I have allocated between 6 and 7 foot of roof length for the solar panels and if I can still get them they will be the flexible ones rather than the kyocera glass ones. Ideally I don't want it to be immediately obvious that I have solar panels for scroats to pinch. I realise that they wont be optimum as they will not point to the sun.

 

If I have a largish bank of batteries say 6 x 200Ah for 'domestic' use will that be too large for the solar panels to top up. Will it also cause problems for the engine and propulsion when charging batteries from flatish?

 

Simple answer please in words of one syllable or less as I tend to get a bit glazed with talk of amps/watts/etc

 

I know batteries must not go below 50% or bad things happen so will have a smart guage fitted to keep an eye on things and will run engine if necessary.

 

Thanks in anticipation.

 

Kath

[Ex- Member]

Being a fan of solar and proposing to fit them myself, from what I gather any solar panel will put charge into your batteries whatever the size of the bank. If you're proposing 6x200 amp batteries, then you'll need a lot of solar to charge them up solely from solar.

 

We have 9 x 110 amp batteries so 990amps We're planning on 500watts of solar Through the summer we'll probably produce too much energy almost certainly if cruising as well. But in the winter solar production will drop massively so we'll under produce most probably.

 

If you're looking to use solar as the main power supply so not depending on engine running then you'll need a lot which you can calculate by trying to work out your daily usage of amps, then obtaining enough panels to service that usage. The size of the battery bank really isn't an issue, other than more batteries will hold more power. I don't think there's a ratio that could be fixed for this, it all depends on what energy you use.

 

A long thread on this was posted some time ago.

 

 

http://www.canalworld.net/forums/index.php...hl=solar+panels

[smileypete]

Simple answer please in words of one syllable or less as I tend to get a bit glazed with talk of amps/watts/etc

 

I know batteries must not go below 50% or bad things happen so will have a smart guage fitted to keep an eye on things and will run engine if necessary.

 

Thanks in anticipation.

 

I'd expect it's best to match the amount of solar power to the normal daily energy use rather than the battery bank size.

 

The Smartguage will tell what % of your battery bank you're using in a day, so provided the batteries are fairly new, the % can be multiplied by the battery bank size to get your daily energy use in amp hours.

 

 

Once the normal daily energy use in amp Hours from a 12v battery bank is known.

 

Multiply this number 2 to find out how many watts of solar panel is reasonable upper limit.

 

This will help ensure all the available solar power is used even on the sunniest day.

 

 

So if you use 50 amp hours from your 12v battery bank in a day, a reasonable amount of solar power is around 100 watts.

 

(If you have a 24 volt battery bank then multiply the amp hours by 4 and not by 2)

 

 

All in my humble opinion,

 

cheers,

Pete.

[MikeV]

Hi Kath,

 

I assume the diesel central heating will be able heat the hot water as well, so you will only normally use the immersion heater when on shore power. The big power hogs would seems to be the combination microwave/grill and the induction hob. I can't see any solar system keeping up with those!!

 

I assume, perhaps incorrectly, that you are aiming to be "gas-free"? Not sure why, as IMHO gas is the easiest way to provide energy for cooking.

 

What size inverter are you specifying for driving the microwave and hob?. Or are you going to have a mains generator, in which case you can charge the batteries when you are running the generator for these appliances.

 

If you are going to run the microwave and induction hob off the batteries (no mains generator) then adding any solar panels does not make any financial sense. You're only going to recharge them successfully from the engine.

 

If your motives are purely eco-based, then go for the biggest panels you can accommodate/afford as you will never keep up with the power demands of the microwave and hob. Unless of course you eat alot of salads!! //Mike

[barroca grande]

Thanks for all replies so far.

 

So the simple answer is - biggest solar panels can afford.

 

Size of battery bank - ditto - apart from consideration of power taken from engine to recharge whilst moving.

 

Biggest suitable inverter etc (this is where I start to get hazy and confused will leave this to the experts when fitting out boat)

 

Keep an eye on consumption with the smart guage and use engine when needed.

 

Gas scares me and are heavy to lug around. Will be having separate diesel tank so wont have to do complicated math when filling up.

 

Yes hotwater will primarily be provided by engine then diesel c/h then as back up from the batteries.

 

Cooking will not solely be done by microwave or induction hob as have other sources. (baked beans from cans!!) etc I eat to live not live to eat.

 

Thanks again

 

Kath

[alan_fincher]

Gas scares me and are heavy to lug around.

I often wonder if properly installed gas represents any greater danger to life aboard a narrowboat than 240 volt "mains" electricity.

 

Will you only be having diesel heating, or will this be backing up the fairly ubiquitous multi-fuel stove ?

 

If you do have a wood/coal burner, these have probably proved about as hazardous on boats as gas installations.

[Chris Pink]

Thanks for all replies so far.

 

So the simple answer is - biggest solar panels can afford.

 

Size of battery bank - ditto - apart from consideration of power taken from engine to recharge whilst moving.

 

Biggest suitable inverter etc (this is where I start to get hazy and confused will leave this to the experts when fitting out boat)

 

Keep an eye on consumption with the smart guage and use engine when needed.

 

Gas scares me and are heavy to lug around. Will be having separate diesel tank so wont have to do complicated math when filling up.

 

Yes hotwater will primarily be provided by engine then diesel c/h then as back up from the batteries.

 

Cooking will not solely be done by microwave or induction hob as have other sources. (baked beans from cans!!) etc I eat to live not live to eat.

 

All these things are subjective but my twopenneth;

 

It's actually irrelevant how much solar you have you will almost certainly have too much in the summer and not enough in the winter. Possibly a sensibly medium is an estimate of how much would provide your needs at equinox. My take is that anything helps and generation is a case of bits from different sources.

 

the smallest possible inverter will be a. the most efficient in use and b. cheaper.

 

diesel is not an efficient method of heating both in fuel cost and maintenance cost and gas is pretty safe if used sensibly (like knives!). If you are depending on your engine for hot water then you will by default have a generating source to factor in.

 

microwaves and induction hobs are so not boat friendly in power use. You will have to change aspects of your lifestyle to live on a boat so why not look at how you approach fast food - it doesn't always need shed loads of power to bring to table.

[Lesd]

I think Smiley Pete's approach above is very sensible. I dont see the point in huge batery banks personlly and there is no realcorrolation between panelsand bank size,only usage. Your equipment doesnt seem particulary excessive to me either, normalmodern liveaboard stuff. As an example we have most things on your list, I work from home about 50% of the time and use a lp top lots when orking. Our buggest amp eaters are the lap top and our fridge. On bad days we use 100-150 amp hours at a guess, lesser days maybe 75ah's. We have 2 x 130w Kyocera panels and move most weekends, during this summer (not a great one this year) wevery rarely start the engine mid week !

Oh and we have 550ah of domestic batteries that never go belo 50%. The panels have been great, we can tilt they t the sun though that seems tomake a difference, I willmeasure the difference toflat one of these days.

Hope that helps

Les

[barroca grande]

Will you only be having diesel heating, or will this be backing up the fairly ubiquitous multi-fuel stove ?

 

 

Chilli Penguin Multi fuel stove (see original post) Will have CO detectors etc

 

As an example we have most things on your list, I work from home about 50% of the time and use a lp top lots when orking. Our buggest amp eaters are the lap top and our fridge. On bad days we use 100-150 amp hours at a guess, lesser days maybe 75ah's. We have 2 x 130w Kyocera panels and move most weekends, during this summer (not a great one this year) wevery rarely start the engine mid week !

Oh and we have 550ah of domestic batteries that never go belo 50%. The panels have been great, we can tilt they t the sun though that seems tomake a difference, I willmeasure the difference toflat one of these days.

 

That's what I wanted to hear thank you.

 

microwaves and induction hobs are so not boat friendly in power use. You will have to change aspects of your lifestyle to live on a boat so why not look at how you approach fast food - it doesn't always need shed loads of power to bring to table.

 

It is a combi/microwave so dispensing with an oven per se. The chilli penguin can bake potatoes and probably do casseroles etc and boil kettle in winter etc. In original post I did point out that I would have a Cobb and a small gas camping stove to supplement the cooking arrangements. I decided on the induction hob because that is what an all electric boater uses as it is so quick therefore uses less electricity and only when pan is on.

 

 

the smallest possible inverter will be a. the most efficient in use and b. cheaper.

 

Now that is useful to know. Thanks

[Marc Harris]

Just a very quick point on inverters.... there are 2 types (if you aren't already aware).

 

1. Quasi-sine wave: Doesn't quite provide a "smooth" ac current like mains, and will make some equipment produce a buzzing sound, or not work properly.

 

2. Pure-sine wave: Mostly better than mains ac, and will work with anything. These can cost 10x the price of a quasi-sine inverter for the same output.

 

http://www.partsonsale.com/learninverters.htm - provides more info if you need.

 

hth

 

Marc

[barroca grande]

Expensive or not pure is what I want on account of running laptop.

 

Thanks

 

Kath

[Ernie]

Expensive or not pure is what I want on account of running laptop.

 

Thanks

 

Kath

I think you will find that the laptop will be quite happy on almost any inverter.

 

It’s equipment with phase controlled motors etc. that are fussy e.g. washing machines, electric power tools etc.

[Ernie]

Hi Kath,

The item that would concern me the most is the induction hob (also the combi oven if you think it will be on for any length of time in a day) as it is going to consume serious amounts of power. Are you going to have a generator to run it? I would not want to try and run it via an inverter due to the load on the batteries and the problems associated with getting the batteries re-charged again (it’s much easier to discharge the batteries than it is to re-charge them).

 

As you know, we live aboard and our single (well, my single) biggest headache is batteries and keeping them in a good state of charge.

 

We have a 660Ah battery bank (6x110Ah) and our only real loads are the 12V fridge, 12V freezer and the computer. Even with these fairly light loads (compared to an induction hob or combi microwave) we have the hassle of having to run the engine or the generator for 2/3 hours a day when we are not cruising to get the batteries back up.

 

I must admit to being a bit over protective of our batteries (they are expensive items these days and will only continue to go up in price due to their lead content and the world price of lead), I try to keep them above 65% at all times so that I have a bit of a safety net so to speak.

 

We almost always run the generator in the evenings (up till 20:00) if we are watching the TV or running the washing machine or using the PC for any length of time. I also fire up the generator every time SWMBO needs to run the hair dryer, hoover or microwave (only ever used for defrosting).

 

As for gas, most boat yards will change the cylinder over for you if you flutter your eyelashes at the guys (I guess this statement will get me in trouble with someone out there ). If I were you, I would definitely got for gas for cooking and possibly hot water and heating as well.

 

Best of luck with your new boat.

[Chris Pink]

Expensive or not pure is what I want on account of running laptop.

 

Thanks

 

Kath

 

A laptop only needs a small quasi-sine inverter, sub £100 probably, 2-300 watts.

[Lesd]

Kath,

Sorry Imay have mislead you on my earlier post, I just re-read your original post and specifically you kit list. We are live aboard but dont have an induction hob, microave or use an immersion heater. They sound very much like amp eaters tome, so if you use them you will use a lot more than the 100-150ah I mentioned and need significantly more solar panels to replenish things. BTW We use a large 5 burner gas hob which is fab and heat water from engine if cruising or from Webasto when stationary (30 mins running is enough for 2 showers and washing up).

Les

[Ernie]

Kath,

I missed the Immersion heater same as Les, I would not want to run an immersion heater from batteries (not even a 1kW version) due to the high load on the batteries.

If you are seriously wanting to have all the electrical loads that you list above, look into a good quality, built in diesel generator - another can of worms....

[smileypete]

Gas scares me and are heavy to lug around. Will be having separate diesel tank so wont have to do complicated math when filling up.

 

Why not get a locker and pipework put in, if you change your mind later it will be easier to fit a gas cooker without loads of disruption.

 

If you use gas for cooking only a bottle will last ages, and FFDs on cookers stops problems with unlit gas burners being left on.

 

cheers,

Pete.

[MikeV]

A laptop only needs a small quasi-sine inverter, sub £100 probably, 2-300 watts.

DC-DC converters are much cheaper. Maplin (www.maplin.co.uk) do the iGo Juice AC/DC computer power supply for about £40. From their homepage click the "Power Supply Finder" link and you can enter your laptop model.

 

I don't use an inverter for TV or laptop. Both are supplied through DC-DC converters. The TV is theoretically 12V anyway, but I use an Amperor (www.amperordirect.co.uk) "voltage stabiliser" designed to handle the 11-15V voltage variation as well as suppress power spikes. These will be more efficient than inverting up to 240V and then converting back to 12VDC.

 

Regarding gas - you don't have to have the 13Kg cylinders that most boats have. I remember a show boat at Crick where the owner had opted for the 7Kg cylinders located in the semi-trad lockers because he had a bad back.

[Chris Pink]

DC-DC converters are much cheaper. Maplin (www.maplin.co.uk) do the iGo Juice AC/DC computer power supply for about £40. From their homepage click the "Power Supply Finder" link and you can enter your laptop model.

 

True, unfortunately i use an Apple Mac and Apple won't allow the use of 'their' power connector by any 3rd party and guess what - their 12V adaptor doesn't charge. But your advice is sound for anything that will.

[killarney]

There is no relationship between panels / batteries / engine. There is a relationship between the size of the panels and how quickly they can charge the batteries, given the size of the batteries. And of course, the speed at which the batteries are charged is based not only on the size of the panel, but the time of year (worse in winter than summer), and the angle from the sun of the panels.

 

Large installations will rotate the panels to track the sun, and this will improve efficiency by 20 to 25%, however this is not practical on a boat and therefore there is an assumption that this efficiency is lost. The best you can hope for in a moored NB is to have the panels pointed directly at the sun at noon (which is also unlikely on a NB).

 

And finally, the amount of power produced will be significantly affected by the amount of sun (so recently, not very much). Rain does have a much bigger impact than clouds, but modern high efficiency panels will still produce power when it is raining (maybe only 10 to 20% though).

[Smelly]

Fair to say that we got our panel recently and it gives between 12.8 and 13V in light rain so there's something being produced. Once I've got an ammeter hooked up I'll know how much as well.

[alan_fincher]

A laptop only needs a small quasi-sine inverter, sub £100 probably, 2-300 watts.

The inverter we run a laptop from, (the only 240 volts we have) is the cheapest of the chap 150 watt jobs, at about £25.

 

You can often get basic ones of 300W to 500W for prices in the £30-£40 range. (Maplins regularly have deals).

 

A massively expensive pure sine inverter is totally pointless for running things like laptops.

 

A DC to DC convertor, as already mentioned, is another option, and doubtless slightly more efficient.

 

The following is my view only, but I'll put it fairly bluntly.

 

If you are considering induction hobs, electric ovens, etc, then I'd say solar panels are largely academic. You will need to run engine or generator so much to keep up with your power hungry appliances, that the relatively small amounts of power you can get from solar mean you might as well just run the engine or genny a bit longer.

 

And heating water with an immersion heater, other than from a land-line, really makes no sense at all, (IMO).

 

Alan

Edited July 22, 2008 by alan_fincher

[Ernie]

Why not get a locker and pipework put in, if you change your mind later it will be easier to fit a gas cooker without loads of disruption.

 

If you use gas for cooking only a bottle will last ages, and FFDs on cookers stops problems with unlit gas burners being left on.

 

cheers,

Pete.

Excellent advise. Personally, I wouldn’t consider buying a second hand boat that didn’t have a gas hob and oven – or, was enabled so that they could be easily added without too much hassle and expense.

[Lesd]

Just a thought, if your worried about gas and designing a boat from scratch. We minimised the amount of pipework in our boat by having the gas locker against the rear bulk head on our cruiser stern (it doubles as a seat). We have a reverse layout with the kitchen at the stern. The gas pipework goes through the bulkhead from the locker via shut off valvale straight to the hob and oven. I doubt there's 5' of pipe in the whole installation. We also mounted a gas detector just underneith to be double safe. Electric cooking eats amps !

[barroca grande]

If I did decide to use gas solely for the hob and used those smaller 7kg cylinders (as per MikeV would it be possible to keep them under the work surface? Or is that a real no no?

 

Access to the galley is easy as I have a side door with proper grown up steps down. (The galley is right in the middle of the boat).

 

 

 

 

I did have a really long post here before but I lost internet access just as I 'posted' so lost it all and can't be bothered to redo it.