CHOOSING THE RIGHT SIZED SYSTEM FOR YOUR NEEDS
Choosing a system is generally based on a number of criteria
How economical are the consumers on the boat?
This is probably the most important driver. See Preparing for Solar . A well configured boat for off grid living will be largely 12v based and certainly have a 12v fridge, probably 12v sockets for charging devices up and likely a 12v Tv and LED lighting. This is kind of a "perfect" configuration making no use of an inverter to generate mains which requires a lot more power.
Most boats however will require some use of an inverter perhaps just for a TV which is not too bad (all mains electronic devices these days are fairly low power draw and although not as efficient as running 12v units they do not place massive loads on an inverter) but often for a main powered fridge which is much more "amp hour" hungry and sometimes a mains powered freezer too. Part of the process is calling for a chat so I can find out what you are running and make a recommendation on system size. Basically the more power you draw (and inverter based mains kit draws a lot more) then the more solar you will need. Sometimes it might be better to rethink your power draw and change things for lower voltage equipment then have less solar!
Battery bank size
The battery bank size also dictates the amount of solar required to ensure its topped up on a daily basis – again the bigger the bank the more solar is required. One very common issue I come across on a regular basis is banks that are way too small. The customer is anxious to get solar as they struggle on a daily basis with power. On chatting through I find they only have two 100 ah batteries and are trying to keep a fridge going and run a TV lights etc. So you may need to have a look at your battery bank size as well.
What type of user are you?
Are you just an occasional holiday boater non live aboard? Are you continuously cruising? Are you living on a linear mooring with no power? These are the kind of questions that will again drive you towards the right system. A holiday boater only wants the batteries to be topped up when they get to the boat and is unlikely to stay somewhere on their travels for long so probably only needs small scale solar. A continuous cruiser needs power on a daily basis but mixes crushing with stopping for a few days. So a good solid mid range system is often best. The boater living on a linear mooring with no power needs the larger system as they are not wanting to run and engine every day just to generate power.
As always budget comes into it. In all truth you can never have too much solar as the controller backs off once it's done its job. The more you have the quicker the batteries top up and the more you can draw. So if you want to be totally safe and secure that you have enough power then over specifying the system is the way to go.
So in choosing a system it is a little bit like the "how long is a piece of string" argument as we have to weigh up the 4 factors above. Part of our service is doing just that. You call up and I will run through a whole series of questions and arrive at a recommendation – often two different systems where budget will be the deciding factor. If you are limited on budget I can accurately advise whether a smaller system that you really need will offer any advantage – it usually will but at the lower budget where a larger system would be better it may not give you the full autonomy that the larger system would but will almost certainly help. I am very much a believer in setting your expectation levels before you commit to buy.
However, from experience of installing systems on close on 1000 boats, generally these are the systems chosen.
Holiday boater using the boat every now and then and assuming it's fairly 12v orientated. Then the 165w is a good option.
Live aboard continuous cruisers tend to go for 330w or 495w depending on their load – if 240v refrigeration then probably the 495 if 12v then probably the 330. These are our two most popular systems (well the old 300 and 400 were that have now been replaced by these new higher power systems!)
Live aboards on moorings with no power such as linear moorings have the greatest challenge in that they are not naturally needing to move often and so really want to minimise or eliminate engine run time so often a larger system is the way to go. The other category for larger systems tend to be large barges with heavy 240v usage and/or very large battery banks. In these instances a 660w or 990w system is the way to go. The 990w system will generate up to 60a continuous charge rate and really does give you the kind of power you would get from a plugged In charger system.
So in summary really the first phase is call for a detailed chat and we can weigh up the options based on how your boat is setup, how much you want to sit without running the engine and how much do you want to spend.