Still more reading material Maxim AN484 on solar chargers. Buried in the appnote is a paragraph that claims:

Applications in which the solar-panel voltage is higher than the fully charged battery voltage demand a step-down converter. As an example of applications demanding a step-down converter, configuring the MAX797 controller as a current source and its internal 5V linear regulator can power the external comparators. The device is well suited for charging a car battery from two 12V solar panels.

So there might be your analog SMPS solution for a smallish < 10A solar array.

Thinking out loud, it would look like a Pic 16HV616 would do the same job as the Maxim797 part. The pic has an internal 5V regulator, a-d, a couple of comparators, and a hardware PWM. Wouldn't a half bridge PWM configuration operate the external mosfet's in the same way the Maxim part does?

P.S. Forgot Max797 pdf

but it works with 5 V outout how does that get adapted for 12 volts ? (well 13.5)

hm well I'll give the datasheet a good read.

I've just highered the stakes by deciding to go 24 volts straight off. I bought 1 12 volt 44 Ah battery to get me started and then decided to go and try and retreive my old car battery from a mate which was supposed to give it back to me ages ago. so now i have 2 X 12 volt batteries and I expect its quite appropriate to run on a 24 volt system with all the advantages it brings (less amps flying around when things get bigger) and now I'm pretty safe from overcharging the battery as its 1 A/hr max instead of 2 A. I'll still need a charging controller though

If you're putting batteries in series it's absolutely essential that they are exactly the same make and model of battery, and both in the same condition. Putting random batteries in series is asking for trouble.

Ideally they should have sequential serial numbers as well. This may seem silly but it's the best way to make sure they have nearly identical chemistry.

oh dear no their not the same one being new and one being out of my deceased car. just how much trouble can it cause ? I would guess they are both of the same type as they're both cheap ones, what about in paralel ?

Umm how about sulfuric acid all over the place when your batteries boil over because a couple cells invert or fail, or worse fire. Don't do it. Parallel is almost as bad.

ok so why will these things occur ? they are both normal car batteries and will be fed current, what is the greatest danger in charging or discharging ?, I could charge them idividually (1 per panel) but when it comes to using them errrr maybe a switchover circuit if its worth bothering

Because over time the plates in a car battery disolve and become uneven, slight boil overs and gassing from normal charging and the byproducts of the charging process also build up causing each cell to charge and discharge at slightly different rates than a new battery. When this imbalance occurs stronger cells will start discharging through weaker cells even if the battery is just sitting there which just further worsens the problem, remember each 12 volt battery is itself 6 smaller cells. You add two packs into the picture and you compound the problem even more especially if they're two batteries from two different cars as they may have different plate structures which will cause there charge and discharge characteristics to be different. Best case scenario is you end up with two dead batteries sooner than you want, worst case scenario is those imbalances are bad enough to cause a cell to boil over and you end up with Sulfuric acid all over the place, and worse it shorts out the other cells and they all boil over too, and start a fire from the large discharge when the whole pack shorts out. Just keep them completely separate.
A good solar charging system isn't gonna do you any good with crap batteries.

so its the charging that going to be an issue ? I can charge them seperately one panel per battery.

Basically your saying that by putting them in series I will be forcing one cell to pass more current than it would want because another one wants it so ?? so I take it its not a case of the cell that wants more power will have to make do with what the ones passing less will want.

Do I correctly assume that discharging them in series will not be an issue provising I don't try to take huge currents out and make one work harder than it can ? I could use voltage sensing cicuitry to cut the supply when anyone of the two batteries is getting discharged.

if I put the panels in series and the batteries in series but also had a centre "tap" from the battery junction to the panel junction then they would be each individually charged but i would still be able to get 24 volts back for the inverter

hm well maybe I'll just return the new battery and use my old one and then invest next in some real batteries (4 X Trojan 6V 220 A) rather than getting more panels next, won't feel the pinch so much if I get my tax rebate (another long story)