Solar panel or additional battery capacity - best value for money?

[mcframe]

you can never have enough charging power

Well, yeah, but you've got to have somewhere to put it ;-)

200W of solar on a weekend boat is wasted; on a transat it might power a watermaker for a couple of hours; on a 3 month-long med cruise it might be just the ticket.

 

[William_H]

Charging batteries

Well everything is relative but our OP is interested in value. A smart alternator controller will get more charge more quickly into the battery. However if you add batteries in parallel they will by nature take more charge current. So by adding batteries you get more charge for a given engine run on standard regulator. Note we talking total charge (AH) here not % of charge which will still remain lowish on a short engine run.
Batteries will eventually die so buying more especially if the old ones are old +4 years then new batteries will not necessarily be a waste of money.
As said solar is very big expensive and inconvenient when you have a diesel engine to do the charging. (or shore power)
So I suggest one or more new batteries (if you can fit them in easily) and extra switching so you can isolate them or charge them from engine. You do not need diode isolation or even VSR if you are careful and know what you are doing re charging and discharging. Enjoy the trip olewill

 

[Babylon]

Increase capacity, reduce consumption, engine to recharge

In response to the OP...

Think in terms of three things:
1. How to increase your capacity
2. How to put energy back in, and how fast
3. How to limit your consumption

One 102Ah domestic battery will only give you about 50aH maximum usable, so I'd add a second battery of the same type and capacity (or if the original is getting long in the tooth, I'd buy two new identical batteries at the same time), giving you up to 100Ah before you irreperably damage the bank.

A reasonable 240v shorepower charger will easily put all 100A back into your bank overnight every few nights; engine running (under load) will do the intermediate recharging.

You can 'plan' on 1-2 hours motoring per day if you like, but the weather might have other ideas.

As I understand it, a bigger alternator OR an alternator booster will put charge back into you batteries more quickly than neither. (On my new Beta I specified a 70amp alternator and removed the very old Sterling booster.)

Fit a manual fresh-water footpump for £50 - saves volts and gives you access to your water if your electrics fail altogether. Also replace saloon festoon bulbs with LED versions for about £6 each - brighter light for less than 10% of the power consumption.

Ween the kid off the TV immediately, cold-turkey, now! TV is extremely bad. Kids will very quickly find something else to play with, like pointy dividers or a fire-extinguisher, so give them Duplo to lose in the bilges, pencils to colour in your charts, toy trains to mash into your varnished surfaces, etc. Provide picture-books to give them mischevious ideas. If you're feeling brave you can provide some old fishing line to turn your saloon into a spider's web. All good stuff!