Battery bank size & solar

[temptress]

520 ah domestic
90 ah engine
140w solar on mppt controler
160 amp balmar alternaetor
Ampair wind genny
1000w generator - rarely used

Biggest use is the fridge, upgraded the insulation which improved the efficiency


Charging is fine in the Caribbean not so good in Scotland. I will add another 100w of solar.

 

[truscott]

420 ah domestic
75 ah engine
240w solar via mppt controller
80 ah Hitachi alternator through VSR and Alphapro Smart Charge regulator

Planning on acquiring Honda EU20i
Searching for windgen currently

Cheers, PT

 

[silver-fox]

Best advice I ever read on the subject was by Nigel Calder in his Boat Owner's book

Key points are

- don't discharge below 50% on a regular basis otherwise you have a short battery life
- most systems (which are based on automotive components) charge batteries to just 80% (as per previous posts)
- in hot climates the fridge is the remorseless consumer of amps!

Given the above you only have around 33% of the batteries AH available for use.

So calculating your storage requirements becomes quite easy

If you want to consume 100AH per day, and are happy with one day's duration, then you would need roughly 300AH service battery capacity to stay above 50% charge after 1 day.

Most people find themselves in an escalating "arms race" between consumption and generation as we pile more gadgets on board, with many opting for generators as a solution. I hate the idea of polluting some quiet anchorage with the noise of a generator and won't have one on board. So I have taken steps to reduce consumption by switching over to LED lights and massively increasing the insulation around the fridge and opting for a keel cooled compressor.

My current arrangement which is just adequate in the Med is as follows
Service Batteries 600AH
Solar 160W
Rutland 913 wind Genny
4 stage Sterling Regulator on my standard 60A alternator

Future plans are to upgrade the 913 to a later, more efficient, model and to double the solar. This is more in anticipation of increased consumption, as we all seem to be addicted to our computers and smart phones, rather than meeting today's consumption needs.

 

[geem]

400 AHr and 330w.

It should be remembered that batteries are just storage devices that will average out a load they do not generate any power.

In summer we have loads of power. In winter I would prefer more power, but a larger battery bank just averages out the good and bad days. It does not give you more power.

if you are using using a generator a large battery bank is important to ensure a suitable acceptance rate during the (hopefully) short generator run time. If using solar the output is a over a much longer duration a smaller battery bank sizes are sensible. Wind is a bit in between.

The most cost effective battery bank size (in terms of cost per year) is to aim for about a 40-50% discharge rate. Some people have a battery bank size where 10% discharge is a normal cycle. Batteries will die of old age no matter what you do.

A bank of half the size (with a 20% average discharge) would be half the cost, half the weight (and lugging batteries is not my favourite boat task) and last about 85-90% of the larger bank.

The aim is not for the longest lasting battery bank, rather a combination of the least inconvenience (buying new batteries is difficult in out of the way places and they are bloody heavy), together with lowest cost per year. The size of the battery bank is strongly influenced by the day to day variations in output and consumption.

If your average discharge is in the 20-40% level, and greater than 50% is rare, you are close to sweet spot of battery size for solar.

In the Ionian over summer solar output is very consistent, but with 150w of solar you will need to be reasonably frugal. 150w over summer will generate perhaps 80Ahrs a day.

Enlarging the battery bank from 400 AHrs to 600 AHrs, only gives any extra 100Ahrs @ 50% discharge. If it is 4-5 days between plugging into shore power this is only an extra 20-25 AHrs per day. (In my case I only plug into shore power every couple of years so the battery bank will only average the solar panel output) You could get the same useful AHrs with an extra 40-50w of solar. Solar panels have a much longer life than batteries so if you can do this it is better alternative.

In short, I would try an add more solar if this is possible rather than worry about small differences in battery bank size.

I wouldn't disagree with anything you have said but I would add this. A large battery bank gives some resilience. We run our 4.5kva gen set to make water only. The battery charging function is only 30amp output. Not great for an 800 amphr bank. We also have a 120amp alternator on the engine. We also have a 3kw inverter. When the genset failed due to faulty injector whilst crossing the Atlantic this winter we still made all the water we wanted by running the engine whilst using the watermaker through the inverter. The output from the engine alternator can't keep up with our 1.5kw watermaker motor but the large battery bank acted as a buffer with no ill effects. We ran the engine for a couple of hours after we finished making water when we had no wind and with the towed generator and lots of solar we got the batteries back up to a good state of charge.
My view if you are going off to sail far and wide would be to fit lots of different charging systems, as much solar as you can and a big battery bank. Run everything through the main bank (800 amp hr in our case) except engine starting (dedicated 220 amp hr in our case) forget VSRs and just use 1,2,both switch for alternator output always connected to charge domestic bank. Dual output solar regulator and towed generator regulators prioritise engine bank charging first so never need to switch alternator to engine battery. Very simple and resilient. We have never needed to turn the switch to charge the engine battery from the alternator but it's there if we need it. Hope I haven't upset anybody

 

[noelex]

- most systems (which are based on automotive components) charge batteries to just 80% (as per previous posts)
If you want to consume 100AH per day, and are happy with one day's duration, then you would need roughly 300AH service battery capacity to stay above 50% charge after 1 day.

This does not apply with large solar arrays that have become practical as solar power has got cheaper.
With solar power the longer charging time and adjustable settings on regulators mean you can achieve a SOC around about the 95% level. At the moment by battery bank is accepting 0.5A @ 13.9v. It is only 2pm. By the end of the day the house bank will be close to 100%.

You are also forgetting that for a boat with a reasonable solar array (where this is the main source of power ) the solar array will directly provide a lot of the consumption.

To use your example a boat that consumes 100Ahr might use 70% of that while the solar output was greater than consumption. The battery will only be discharged 30 AHrs overnight. This if we assume the 300AHr bank was charged to 95% the minimum SOC would be about 85%, not 50%.

 

[noelex]

I wouldn't disagree with anything you have said but I would add this.

It is a forum, disagreement is fine that is how we all learn.

For a crusing yacht it better in my view to set up systems that do not rely on a generator. This removes a major source of hassle.

With cheap and efficient solar panels as well advancements in energy saving such as led lighting and tablets this is feasible. Although it may involve some compromises particularly if done year round like we do.

If you want to do this an important part of the equation is choosing energy efficient appliances. Our watermaker for example is one of the energy recovery models drawing just 9A @12v. Thus there is no problem running it off a small battery bank in fact it normally runs entirely on solar output.

The approach with and without a generator is very different. In the former case you need a very large battery bank, high capacity watermaker ( to make water while the generator is running) energy efficiency is not so important. In the latter case you need as much solar and/or wind as you can squeeze on board. A small battery bank is fine, a low capacity energy recovery watermaker is best approach (if you want one) other appliances need to be chosen for their energy efficiency.

I think people mix up advice from these two different approaches.

 

[geem]

It is a forum, disagreement is fine that is how we all learn.

For a crusing yacht it better in my view to set up systems that do not rely on a generator. This removes a major source of hassle.

With cheap and efficient solar panels as well advancements in energy saving such as led lighting and tablets this is feasible. Although it may involve some compromises particularly if done year round like we do.

If you want to do this an important part of the equation is choosing energy efficient appliances. Our watermaker for example is one of the energy recovery models drawing just 9A @12v. Thus there is no problem running it off a small battery bank in fact it normally runs entirely on solar output.

The approach with and without a generator is very different. In the former case you need a very large battery bank, high capacity watermaker ( to make water while the generator is running) energy efficiency is not so important. In the latter case you need as much solar and/or wind as you can squeeze on board. A small battery bank is fine, a low capacity energy recovery watermaker is best approach (if you want one) other appliances need to be chosen for their energy efficiency.

I think people mix up advice from these two different approaches.

I agree. Where we depart is choice of watermaker. I favour the simple and robust cat pump approach with a large motor. These need a generator but since we have one that's fine. The rest of our our boat is superb efficient with all LEDs and an efficient fridge freezer.
Our boat used to be all electric when we bought it. A silly arrangement as you had to turn the generator on to make a cup of tea. Due to this approach we have space for 1000amp hr of batteries plus two 110 amp hour starter batteries.
My long term plan is to build the generator Diesel engine into a slow revving direct drive watermaker with a pulley running a spare 160 amp alternator with smart charger. We would have no 240 volts other than via the 3kw inverter and the smaller 200w inverter for laptop charging etc. this way the generator engine would run at 1500 rpm instead of 3000 rpm. The engine would be quieter, use less fuel and should last a lot longer. The generator engine is a twin cylinder Perkins 10hp industrial unit with fresh water cooling. At 1500 rpm it makes 4 hp which will be more than enough to run my 2hp watermaker load. We currently make 130 litres per hr from our watermaker set up so only run it about every 4 to 5 days. We also carry a spare motor and cat pump. If we get a membrane pressure vessel failure we can bypass it and run on one membrane. I like belt and braces. I built my watermaker from EBay parts for £1500. I have enough spares to build another one!

 

[Petronella]

Lower Tech Option

450AH house batteries (4 Trojan 6v 105s)
200W solar panels mostly tilting on guard rails, one usually shaded
Towed generator for long passages (2-3 amps 24 hours per day)
Ancient Four Winds rigging wind generator (3-5 amps - should be more - in steady 20k trade winds)
Diesel generator: Thrown away

We don't generate much electricity because we don't use much. A small well insulted, top opening fridge, a couple of computers and LED lights plus some basic navigation instruments. We live aboard almost all the time and never need to run the engine to generate electricity. Usually the solar panels are sufficient for our needs. Occasionally if it is cloudy for a couple of days we might put up the wind generator to top things up (twice this year in the BVIs). Trojan batteries are supposed to Absorb for an hour a day at 14.8v. Rarely they do, usually they get up to about 13.8v but I don't think they have ever been below 12.3v first thing any morning this year. That's good enough for me.

I took the diesel generator out because it didn't work when we bought Petronella and we never used it. That meant I could close up two through hulls.

I haven't needed a watermaker yet. We can carry 380 litres of water in tanks and loads more in 20l and 5l containers which we have filled up without a problem throughout the Med and the Caribbean. We filled up in Lanzarote this year and had plenty of water for four of us on our (very slow) 29 day Atlantic crossing. Now every couple of days we take a few containers to shore and fill them, usually for free, whilst doing the shopping. You can get thousands of gallons of this water for £1,500 or whatever a watermaker will cost.

I guess what I'm saying is that you can have a very enjoyable time with a much lower tech set up than many other posters have in all but the remotest parts of the world. No electric pumps to go wrong, no watermaker to go wrong, no generator to go wrong, no shower pumps to go wrong, no macerator or electric toilet to go wrong - all things that can keep you in expensive marinas waiting for parts instead of enjoying friends in a quiet anchorage. As other posters have said remember there are two sides to this equation - supply and demand. Think carefully about what your really need/want and then size your capacity appropriately.

It does help of course to live in sunny and/or windy places! We couldn't do this in the UK I don't think but it's certainly do-able in the Med, except maybe for a few winter months, and definitely throughout the tropics.

 

[sailaboutvic]

Reading these posting with interest and it just hit me , we got no where near the equipment we need to be full time Liveaboard , how have we managed the last six years ? so tomorrow I am planning to order a water maker, and gen set , up my solar panels from 190w to 500w throw away my heave duty battery which cost me 100 euros each and been working now for three years 365 days a year , still going strong for AGM at @ 800 euros a battery , up the battery bank from 400 to 700AH and then at last I will be a real Liveaboard , or maybe not , do any one here still remember when we sails with just a set of charts , compass , pencils and a rule one house battery and one engine battery or in some cases just one battery and still had enough power to leave the anchor light on all night . The problem isn't we have got enough power to supply our battery bank BUT too much equipment putting a big demand on our battery bank .

 

[Thedreamoneday]

Thanks everyone, there's been some really interesting posts which have put my mind at rest.

We will have 400ah domestic and 150w tilting solar, we only have a low consumption of fridge, led lights, plotter (if needed) and the usual ipad/ kindle, so from the previous posts I feel will be ample, especially in Greece till sept/ oct time when maybe an extra 80w solar and marina will keep us to where we need to be during the rest of the year. I'll add a dedicated starter battery so the 400ah is purely domestic and see how we get on, I just didn't want to be that p.i.t.a who starts up their engine in a lovely cove somewhere.
Thanks again.

 

[sailaboutvic]

Thanks everyone, there's been some really interesting posts which have put my mind at rest.

We will have 400ah domestic and 150w tilting solar, we only have a low consumption of fridge, led lights, plotter (if needed) and the usual ipad/ kindle, so from the previous posts I feel will be ample, especially in Greece till sept/ oct time when maybe an extra 80w solar and marina will keep us to where we need to be during the rest of the year. I'll add a dedicated starter battery so the 400ah is purely domestic and see how we get on, I just didn't want to be that p.i.t.a who starts up their engine in a lovely cove somewhere.
Thanks again.

For what you have just discribe you will have plenty in the summer months

 

[Slow_boat]

We have 330ah of leisure batteries and no solar yet. New batteries and 200w solar to be fitted this yeas. We have a sterling management system, so not sure what sort of regulator we'll need.

If it weren't for the fridge I wouldn't bother, but swmbo does like her cold musçudet. We found that normal engine running out of and in to harbour/anchorage was enough to keep the batteries topped up, but bing somewhere more than24 hrs meant running the engine to chargeup.

 

[ip485]

800ah house, 1,000w solar with outback controller, 8.8kw genset as backup.

Biggest problem is heating the water without resorting to genset or engine. A 1.5kw immersion heater would be perfect.

 

[macd]

800ah house, 1,000w solar with outback controller, 8.8kw genset as backup.

Look, this is a boating forum. Power stations should chat somewhere else.

Re: water heating: you can get a 500W (c40A at 12V) element with standard immersion heater fittings. I imagine your panels could run that, used judiciously.

 

[sailaboutvic]

800ah house, 1,000w solar with outback controller, 8.8kw genset as backup.

Biggest problem is heating the water without resorting to genset or engine. A 1.5kw immersion heater would be perfect.

Do you find you get other people power cable pass on to you ?

 

[TQA]

8 kw generators seemed to be fairly common on boats on the East coast of the USA and down into the Carib. on boats that anchored out overnight.

It allows you to run the usual RV based AC unit a fridge and a microwave.

I got quite close to buying a nice Hunter Passage with one and factored into the deal was the expectation that I could sell it. To that end I floated a trial balloon on Craigslist and was inundated with inquiries.

1000 w solar? The only boat I have seen with that much is the Flying Buzzard. [ A 1951 Clyde built steam tug recently seen in Antigua doing sterling service as the committee boat for Classic race week. ]