a597, the electrochemistry hasn't changed much in the last 15 years or so. Your sealed cells will either be gel, or more likely some form of matrix-supported wet cell, which contain a regeneration chamber to capture the hydrogen released at the anode by the discharging process and direct it to the cathode for reuse . This only works if the discharge rate is sufficiently low, so if you run a high load, you'll lose some electrolyte to the atmosphere as the pressure within the enclosure becomes too great and is vented. You'll also lose some if you overcharge. Either way, they're probably NOT true deep cycle cells, even if they're advertised that way. Tha fact that you only discharge to 11.9V means that you're not "deep" cycling your batteries at all, taking them to around 50% of charge. A true deep cycle flooded cell should be able to recover from much deeper discharge than that with no problems, although sealed and gell cells suffer if that happens.

A good set of flooded cells with minimal maintenance (checking electrolyte levels and SG, properly set float and discharge levels, proper control of loads) will last 7-10 years with little loss of performance. For mobile homes it makes sense to use sealed cells because acid is corrosive and it saves hassles on the move. Demands are typically low as well. for fixed installation deep cycle storage or traction batteries are the only solution.

RAPS doesn't cost 4-10 times the cost of GC for no good reason, you know.

There's a good reason for only discharging to 11.9 volts, this is for battery life, a fully charged battery lasts longer. These batteries are deep cycle marine batteries at a fraction of the cost the ones you are talking about, with the same lifespan. The 11.9 discharge rate is controlled by the inverter to protect the battery's from over discharge.
You don,t need a diesel generator to charge 12v batteries.
An excellent system and cost affective.

Whatever works for you, I guess. It's not the sort of thing that would suit most people, however, except when they're on holidays in their caravan perhaps.

Bazz- I don't remember the statistics, though I could dig out my last electricity bill- but on average, with the reabate at 60% I'm now only paying a loss of only 1/3 of my original electricity bill (with the rebate covering the remaining 66%.
Note that I only have a quarter of my roof covered (with another quarter taken up by my Solar Hot Water system- actually making it a third of my available roofing space), and I have a large family with about three computers running for several hours a day with a few others that get some daily usage on top, and like a571, many of my appliances have a terrible power-conservation rating (and I plan to replace them as we have found these to be the main reason our bills are so high). Cutting these (or adding additional panels, or both) would put me into a position of profit, even when the rebate slumps.

Why rebate- my wife talked me into it, if I'm honest- as apparently generating our own power is illegal- but either way we decided the rebate would be a good opportunity to get our money back faster (and it definitely is), before redirecting the power internally (if it is legal of course).

Antisceptic- coming from an engineer who works with PV systems that is definitely good to know. Could you tell me the kind of maintenance procedures that would need to be physically required to keep the storage unit in check?
Cost-wise it is actually not a problem- your figures are similar to what I paid, and it sadly isn't much different to what I would have been paying in power bills over just a few years at the rate they had been going recently (I had been paying a huge increase despite halving my power usage on the first bill I recieved when the prices spiked- which motivated me to quickly transfer as I was being ripped off despite improving my practices- ditto on water).

KH, it's not that hard to maintain your batteries, but it takes a bit of organisation, especially at first, when you're working out how much you use and how much you need to supplement, if any, with some form of generation.

Basically you need to maintain your electrolye levels and concentration within certain bounds. The concentration is measured using a hydrometer to measure Specific Gravity, since sulfuric acid solution is quite a bit denser than water and gets denser with increasing concentration.

http://www.chembuddy.com/?left=CASC&right=density_tables

It might only need to be done once a week once you're properly used to running the sytem, but in the early days you'll have lots of ups and downs in power as you try to balance loads and supplies.

The system that a597 has is very simple, but it won't give you the reliability or the capacity that you seem to want. Have a talk to a good, properly qualified RAPS designer. There's bound to be someone close by. If what you really want is to be self-sufficient, but without the hassle of a generator, you can use a stand-alone system with the grid on the other side of a changeover switch instead of a generator.

There are lots of options, but you do need someone to have a look at your particular needs and design accordingly.

Thankyou antisceptic, that is good to know.

Out of curiosity, if a597's batteries can only safely cover a lower capacity- would it be possible to counter this by purchasing additional batteries and dividing what I generate between them? (not necessarily what I'm planning when cost factors in, but considering all options).