Another solar question - is it worth using spare capacity to charge house batteries?

[wonkywinch]

I bought a Renology 200W folding panel to charge my ePropulsion Spirit tender motor (via the optional solar charger from ePropulsion). Is it worth spending extra money on an MPPT controller and feed into the (lead acid) house system when not being used for the outboard?

A 2016 Beneteau with Cristec charge controller for alternator/shore power into lead acid engine, thruster and two parallel 80AHr (12v) house batteries. It's wired via a NASA battery monitor so, as Paul suggests, I could wire the correct side of the shunt but I wondered if it's worth buying an MPPT controller and using the 200 watt panel to top up the domestics?

We do anchor a fair bit but get into the habit of an hour running the engine in the morning to charge batteries and heat the water.

Question only prompted by looking out the window for the second week running and seeing decent sunshine here on the south coast of the UK.

 

[rogerthebodger]

IMHO any way of topping up the chare of any battery is worth while

I have a 50-watt solar Charing y engine star battery 800 watt charging my domestic battery an a 30-watt charging my dingy electric outboard trolling motor with regulators to prevent over charging

 

[Sandy]

Personally, yes as you have the panel.

 

[PaulRainbow]

Definitely. 200w should power the fridge, lights (LED), water pump, toilet pump, chargers etc during the Summer.

 

[B27]

Running the engine just to charge batteries and heat water is a bad move.

I was rafted against some stinking long term cruiser whose engine smoked horribly because he was in the habit of doing this.

 

[Neeves]

Anything that allows you to reduce engine running time is good for both you, your neighbours and the frequency of engines servicing. You will generate decent charge from a 200 watt panel - it seems a complete waste not to use it. You will still need to run the engine to heat the water.

Take advice on water heating.

I might suggest that if you are going to integrate the existing panel into the yacht charging system that you consider, or plan for, a bigger MPPT controller and another panel(s). Panels are cheap.

Your lead acid battery bank is now at least 8 years old. It might be nearing end of life though if well cared for could last another 8 years. If it is nearing end of life - you have other options just over the horizon. Now might be a good time to consider them.

Jonathan

 

[William_H]

IMHO it is the problem of finding a place for solar panels on a boat. So presumably OP has mounted this 200w panel successfully. Probably no room for any more panels. So Yes panel should be wired to feed the boats electrical system as well not just for the O/b charge. A change over sweitch at the panel output would do the job and yes worth buying an MPPT controller. It does sound however like OP has to run the engine for water heating. Which of course means plenty of alternator power as a by product. Pity to run the engine like that. Some other sort of water heating? diesel or gas? ol'will

 

[noelex]

It is always a shame to waste electrical energy on a boat. A google search indicates your panel has a Vmp (under STC conditions ) of 20.4 V and this will benefit from a MPPT controller (assuming a 12v house system). Making use of any surplus energy is always sensible.

If you install more panels in the future a dedicated controller per panel is a better solution. There is no need to purchase a larger controller to allow for future expansion. The popular Victron 75/15 would be a good match for your 200w panel.

Feeding the 200w solar panel directly into the house bank (via a MPPT controller) and then charging the ePropulsion battery from the house bank may be the more efficient system.

 

[wonkywinch]

The house batteries were allegedly replaced just before we bought the boat last year but in another post, I mentioned the CO alarm issue when the boat is left with the charger on so plan to go to the boat today to investigate.

My panel isn't mounted, it's a neat fold up thing so the issue is how to arrange the wiring for easy connecting/disconnecting.

The panel > house batts > epropulsion charger would work as I currently have a 700W inverter built in and the outboard charger is rated at 200W.

 

[B27]

Looks like quite a big boat to only have 160Ah of house batteries?
But what are the real daily needs in Ah?
I assume the e-outboard will push that up a bit?

If you can live for say two days on 80Ah, then any solar you harvest simply extends the time you can stay without running the engine to charge., assuming your alternator will put back most of the Ah in a typical passage.

If you want hot water when anchored for extended times, you can't beat either a generator or a wet eberbasto. Particularly for an extended season in the UK.

 

[Sandy]

I've never heard of a relationship between size of vessel and battery bank amp hours. Can you explain?

 

[Neeves]

Instead of running the engine for hot water you could spend, approx stg100, for an instant on gas hot water heater (I assume you have gas) and you could feed the hot water for a shower through the shower location hatch. Look at camping/caravan retail outlets. We had a plumbed in Bosch hot water heater for our shower and washing up (but its was a bit big for a Mono - the camping options are much neater). With the heater (boiler) 'outside' you would not need worry about the gas installation. You would need to tap into the existing cold, freshwate (easy if its Guest), pipework and it would be fed by your existing fresh water pump.

Hanging your solar panel off the stanchions/life lines with braces to the toe rail when at anchor offers you lots of space for a really decent solar display (and others use such systems when passage making). If you invest in the same panels (as they are easier to store when not on the yacht) as you already have and one MPPT controller it might be cheaper and need less cable than a series of MPPT controllers as you grow the bank (or you could end up with, say, 4 MPPT controllers with 4 sets of cabling one each from each panel to each controller).

Jonathan

 

[Neeves]

I've never heard of a relationship between size of vessel and battery bank amp hours. Can you explain?

Small yachts have less room for big battery banks and the accompanying weight ruins sailing performance. Bigger yachts have more room for electrical toys (radar, for example) or bigger fridges and need bigger battery banks. The relationship is vague - except bigger yachts tend to have bigger battery banks.

However whatever the size of the battery bank its always just too small as the well used law comes into play.

'Your electrical needs always grow to slightly more than the electricity available (no matter the size of the yacht)'

Solar panels suffer from similar laws

Derived, after much research, from Parkinson's Law

The Law is also based on the idea that after much strategic thinking you decide, say, on an investment on new and larger accomodation - soon afterwards your strategic thinking is found to have been too small - so you want a bigger office, larger battery bank or more solar panels + all the support costs, the desks and computers for the office, a bigger charge controller etc etc.

How many people buy a smaller yacht than the one they are moving from?



Jonathan

 

[B27]

I've never heard of a relationship between size of vessel and battery bank amp hours. Can you explain?

It seems the OP can't store enough electricity for his stays away from shore power.
So there's a choice of either more capacity, or generate your own.
Bigger boat, more people, more lights on, more expectation of 'home comforts' = longer periods off grid.
More toys, radar maybe?, more power required by the autopilot.
There's a fair correlation between bigger boat and bigger batteries.
But most over 30ft seem to have more than 160Ah?
Two 110Ah's is pretty common for a mid-sized boat, which is more what I meant.
Just the other day, someone was telling me I should put two 110's in my 28ft boat.

 

[Sandy]

Small yachts have less room for big battery banks and the accompanying weight ruins sailing performance. Bigger yachts have more room for electrical toys (radar, for example) or bigger fridges and need bigger battery banks. The relationship is vague - except bigger yachts tend to have bigger battery banks.

An interesting argument.

My 10 meter boat uses the exactly same kit as a 15 meter boat: nav lights; VHF; AIS; Chart plotter; Radar; autohelm and house lights. Perhaps there are some differences around the edges, crew desperate to charge their mobile devices or a larger fridge (for those who use or need them).

It all comes round to the way you want to sail, e.g. day sails from marina to marina with the ability to plug into shore power or multi-day passages where you need to generate your own power by whatever means you choose, and the way you sail them, e.g. have the radar on as soon as you are underway or as it is needed (with AIS I am using the radar less and less; usually when in fog when I am more likely to be motoring due to lack of wind).

Right I must go and do some chart corrections, print out September's pages of the Nautical Almanac and check my sextant.

 

[Sandy]

View attachment 180953View attachment 180954

Those look a pretty well designed bit of kit. URL saved in my 'would be nice to have folder'.