Solar power controller

I’m installing a 75W solar panel. It will charge a 100Ah car battery which will drive LED lighting around the house, maybe more. Rather than buy a charge controller, I have decided to build one. It’s function is fairly straight forward. Their will be two relays. One connecting the panel to the battery, the other connecting the battery to the load.

The panel relay will be on while the battery voltage is below 14v, then turn off to avoid overcharging, then turn on again when the battery voltage falls to 13.8.

The load relay will turn off if the battery voltage drops below 10v to avoid over discharging, then turn on again when the battery voltage reaches 11v.

These figures are estimates based upon various things I have read on the net and will probably need some tweaking, but you get the idea.

There is a more efficient charge control system called Maximum Power Point Tracking (MPPT) which is beyond my design capabilities at ATM, but I may have a go at some stage. A good MPPT can apparently add as much as 30% power under certain circumstances by ‘matching’ the source voltage/current with the battery charging voltage/current using high frequency switching techniques, allowing the panel to always be operating at it’s highest efficiency. (Perhaps someone knows where I can get a kit?)

The simple solar controller I’m designing will of course use a PICAXE to manage the monitoring and switching. To improve accuracy, I’m thinking of using a zener to drop the battery voltage into the <5v range, rather than using a simple divider. I’m also thinking of having the relays wired so that they conduct when no power is applied and turn off when powered. It seems to me that this could save a little power.

I foresee no problems at this time and have begun to order parts, but I would like the benefit of any advice/experience here at the forum. TIA.

You may want to have the battery cut back in between 12-13 volts. If the drain is enough you may end up with short spurts of activity during the day and no lights at night.

This is actually a great project.

It was one of my first projects with microcontrollers and like you, I started out with a simple design and grew it from there. I currently have an 80 watt panel charging 3 car battery size deep cycle batteries.

Here is a design tip that I did not take myself and regretted it: keep the wires between your battery and PICAXE as short as possible and use wire rated for more than what is needed. In this case larger is better. Actually the rule of thumb is less resistance is better. Generally, larger the diameter of wire the less resistance it has. Even if your wire has only 0.1 ohm of resistance, at 4 amps you will measure 0.4 volts difference from where you measure the battery voltage and the actual battery voltage.

I would suggest that the first mod you do is to replace the relays with mosfets. Several reasons: a mosfet uses essentially no current at all while the relays may use a couple of hundred milliamps each. Mosfets costing a few dollars each are a lot cheaper than the relays. Your 75 watt panel will put out between 3-4 amps into your battery and a single mosfet will handle that with no problem.

Have fun!

Dave E

MPPT Controller

Although not capable of handling your 75W/100Ahr setup, this MPPT controller has been around for years, and although no longer available as a kit, it is nevertheless a very versatile product. The assembled product (MTC4.3) can be found here or you can purchase the CTC4.3 PIC chip and design your own controller to handle your setup.

A very informative writeup is available here, which includes the complete schematic and detailed operation. I have NO association with this company.

Richard

I'd question your proposed lower voltages but that's always a mute point so I'll leave it at that.
MPPT is simple in theory. Monitor the power put into the battery, adjust the load on the panel, if the power goes down, adjust the other way, if it goes up, carry on adjusting. In practice, you only need to monitor charge current. The tricky part is the switching regulator design which needs to be adjusted.
The way I've done it is to produce a constant current switcher and use the PICAXE to provide the demand signal via PWMout.

The other approach which I've yet to try in ernest, is to make your switcher control the panel voltage. This method requires a second panel of the same type with a constant load as a reference. Monitor the voltage and use a lookup table to determine the optimum panel voltage to run at.

Re "I foresee no problems at this time"

Famous last words of many an enthusiast ordering parts, myself included!

Simplest charger is a constant voltage. But have a look at the UC3906 specs though to see how complex it really is. For a start, the volts do not indicate the charge state. And the volts change under load. And an 80% charge will be reflected to some extent by the volts, but you will have a different value depending on whether you are charging, discharging or even if you have left it for 1 hour vs 2 hours. And then there is the change in volts due to temperature.

Plus you need to occasionally do an overcharge to stir up the electrolyte. And if you really want to do things properly, you need to mechanically move the cell a bit from time to time to prevent layering of the electrolyte (that stirring comes for free when you put a battery in your car and drive around).

I'm sure picaxe can do all this. But the people who sell solar panels have been working on this problem for a long time, and they do have some economies of scale which brings the price down. And that price often includes MPPT, which involves inductors and switching regs, and at 75W a switching reg is not a trivial problem.

Thanks peeps.

Good link rWave.

I figured a car battery would be more forgiving during the early experimental stages of development. Also, I just happen to have one

Once I get the basic system installed and running, I’ll start looking at improving efficiency. Here in the north of England, overcast being the usual condition, I don’t expect to get nearly as much a 75W. Probably half that, averaged over a year, maybe less.

I have posted this same request on the EPE forum and between the two, I’m learning some good stuff. Thanks all.

What overall LED lighting load? Even 1-10W of LEDs can go a really long way. What sort of 70W PV? Some types (especially the new & cheaper CIS/CIGS) do very well under overcast & hazy conditions. You really need to specify your seasonal solar resource & demand better.

Even assuming 4 hours of bright sun equiv. daily you'll really only be gathering say 4 hours x ~4-6 A = ~ 20Ah daily. This is only 20% of the battery capacity, & of course your load may become quite demanding, meaning the battery will rarely be threatened with overcharge. Naturally a run of bright summer days (nice dream..) may "cook" things, especially since you may have less lighting load then as well as well. If this is a prospect you may well want to get further battery storage rather than have the regulator dump the excess.

I've been involved with a similar (but larger) off grid project here in sunny NZ, & after near endless commercial regulator tinkering the "more battery storage" pathway became the best prospect. This setup initially had too much summer sun (& easy load), but insufficient winter sun to match the then heavier load. Stan

Hi,

I have 3 tunechargers from JMC (older version), I've modified 2 of them, one for 24v (60v) output (couple of resistor changes) and one that's running at 12-13w instead of the standard 7-8 by unwinding the inductor a bit. When asked I if my ideas to make it more powerful would work, he said, give me 10,000 euro and I'll work on it for you, so I guess I wasn't a million miles off, nice try JM

How they work is quite simple and could be replicated with a picaxe for sure. Not studied the 4.3 docs in detail but I guess it's similar to the old one with a few add-on features like EOC and CLEAN, neither of which are very difficult the way it's been done. The input is fed into an inductor by 40-50% duty PWM by the PIC, the high voltage kick back is fed into storage capacitors, when they reach the set voltage a mosfet switches and dumps the charge to the battery, that's it. MPPT is in my mind almost a given as you are "sucking" all the input regardless of voltage.

Have thought many times about building a picaxe version, just never got round to it, would be cool though, especially if the input's and outputs are paralleled you should be able to build any size device a la JM's parallel charging theory and timing is not critical.

With regard to turn off voltage, on a car battery you could go to 14.4 no problem. Essentially overcharging for an hour or two is common place on PWM charge controllers. I'm sure someone on here could give a AH/current to time estimate. As mentioned above the other "possibly better" way is by temperature rise.

The 30% extra is essentially just converting the bit you normally lose. IE

If your 75w panel is rated at (lets guess) 19v at 3.94A, but your battery is (lets say) 12.6v at rest (reasonably charged), you'll get something like 3.94A in bright sunshine but alas at 12.6v you'll only be getting around 49.6W from your panel (34% less than you paid for) which is why MPPT controllers have such big claims. I bought a Blue Sky 30 amp job for my 4x125w kyoceras, and although haven't measured like for like as my Xantrex C40 died, I "feel" it's doing a better job. Next thing is a tracker, that could release another 20-30% or so I read. Another job the picaxe can do without too much trouble, if only I had the time

Miles
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volcano classic vaporizer

I'm quite a fan of switched-mode techniques for charging. Control and power conversion is excellent (if you can write good code).

I'm confused by: "To improve accuracy, I’m thinking of using a zener to drop the battery voltage into the <5v range, rather than using a simple divider."
- eh?
How you going to work that one? Zener V varies with current and temperature. So will it really "improve accuracy"? I assume you are thinking of a series zener/resistor where the zener 'subtracts' say 8 volts? I think a nice pot div with 10 bit ADC is plenty good enough. And the tempcos of the resistors will at least cancel partially.

You’re right Dippy. (Of course)

@ciseco

That SEPIC charge pump looks very cool. Good data is given in the PDF regarding upsizing too. Can’t help being sceptical about the efficiency claims though. I have some questions about this circuit.

If I built a little experimental model, how would I measure the efficiency? V*I in against V*I out with a resistor load I presume, but the PWM makes measuring the V*I input problematic doesn’t it?

Would I be correct in assuming that the fatter the inductor wire (Lower resistance), the shorter the PWM duty should be? How do I decide what is the best frequency and duty? It seems these would have a large impact on efficiency.

Nice non micro based switching controller design http://www.solorb.com/elect/solarcirc/scc3/ may give you some ideas.

OK, however I'm not seeing any inductors in this design and am therefore suspicious of its overall efficiency - which I usually look for in PV units as the price per PV watt is so darn high!

Yes, Boriz, that's how you measure efficiency and yes those can be the problems.
However, with fast switched-mode design and properly chosen components you can get a very good result with simple VI-in vs VI-out measurements.
Most of us can get about 90-95% efficiency on the switched mode section for power transfer.
Obv a little is lost if you have diodes in the circuit.

The post by LizzieB is a nice simple circuit but is not true switching. The circuit design could not produce true switching (as in switched-mode). All it can do is on-off.
And the lack of regulation is implied in the text. Whilst it claims 20Amp rating... read the text.
And I don't think the diode heatsinking is good enough either if the unit were enclosed. My switcher design (in a box) requires fan cooling for the diode (2 in // btw) and it uses a bigger heatsink than shown in that project, and mine is flat out at 10 Amps.


I'm not going to rattle on about s/mode but the inductor plays an important part.
And with a properly regulated controller you could have a 10MegaWatt panel safely connected to a car battery.
An exaggeration yes, but in the non-Australian parts of the world it makes sense (technically) to overspecify the panel to compensate for the dull times of the year.
Your wallet may disagree.

Solar tracking is interesting. Obviously can make a huge difference but, mechanicals/reliability/cost aside, is a little impractical if the panels are on the roof of a normal house.

I've said this before, but ... For small systems (say < 1kW) with custom mechanicals, solar tracking,although entertaining!, is just not worth it. It's far more cost effective & RELIABLE to just slap on another PV or 2, perhaps angled for morning/aft conditions. Furthermore the CIS/CIGS PVs just arriving perform very well in overcast & off angle conditions anyway.

It's often hardly worth seasonal tilt adjustment, & many setups deliberately fix their PVs at a pitch that maximises the (more valuable) winter sun at the expense of decreased summer uptake.

Me too on the efficiency front, I suspect difficult to calculate and even more so what actually ends up in the battery. I like in the docs, "High efficiency, 100% automatic", mmmm cleverly worded two statements, 100% automatic, but what's high efficiency mean???? hehehehe
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Cummins B Series engine

manuka in your opinion what's the downside, you didn't clarify and I'd really like to understand, you've I guess looked into it before?

My reasoning was just cost. If we take as you suggest adding another 2 panels thats ?800-?1000. A powerful linear actuator, bit of box steel and some bearings would cost a lot less. Wasn't thinking of two axis, makes it much more of a mechanical nightmare than I could ever manage.

I manually adjust mine once a year for vertical, does make a huge difference, but then I guess Nottingham isn't too close to the equator
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magic flight launch box

Stan, I hear your wise words and CIS/CIGS looks reaalllly good. I read efficiency approaching 20% for a particular CIS and CIGS installation.

I've just spent 20 minutes searching for CIS/CIGS panels available in UK. Not much luck.
But I keep reading "(Other solar technologies such as CIS, CIGS, and CdTe contain cadmium which is considered an extremely toxic metal by the Department of Labor.)"

This phrase has been used on numerous webites - it is obvious that it is cut'n'paste from a central source. EG:
http://www.solarequip.co.uk/acatalog/PV_Solar_Panels.html
(halfway down page under "Roll-Up Solar Panels")

Any comments? I can't see where the Cadmium comes into CIS/CIGS , but obv CdTe, however I'm no chemist. Is this scaremongering? Or just salestalk to encourage purchase of silicon stuff?

And I still can't find decent sized CIS/CIGS panels in UK. (I'm not asking you to Google, I'm just saying it ain't easy).

"High efficiency, 100% automatic"

- yes, clever juxtaposition of words so that the skim-reader gets the wrong idea. Though this is the 'right idea' intended by the author. And "100%" and "automatic" is almost tautology.

Well, I wouldn't have tracking on the roof of my house. Late afternoon on a windy day and my roof would blow off (pardon me vicar). Just another mechanism that requires expensive servicing in 5 years time. I can, however, see the benefits in some apps.

Roof, mmm, neither would I , if I built one it would be firmly on the ground, my garden slopes nearly due south.

You just made me think, I've got a couple of 5 watters, so with a little motor and a piece of dowl I could mock up the two side by side and compare
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Sichuan FAW Toyota Motor

boriz said:

If I built a little experimental model, how would I measure the efficiency? V*I in against V*I out with a resistor load I presume, but the PWM makes measuring the V*I input problematic doesn’t it?

Click to expand...

Indeed that is exactly how you would do it.
If the input/output is properly decoupled, then the PWM should not be an issue. However, using an averaging method (which most DVMs do anyway) then it will be very close to the truth. For accurate measurements of ANY waveform you need to use a true RMS measuring technique. Some of the more expensive DVMs offer this but a homebrew method is to measure the amount of heat produced.

Before setting off on a new SM design. It pays to do the sums on the components which will effect efficiency first. The main areas of loss (in no particular order) are as follows.

Input/output caps. Use low ESR caps. Loss=ripple I*R
Inductor resistance. Loss=R*switch current*duty.
Inductor magnetic losses. (see inductor data sheet)
Switch losses. Loss=Ron*Switch current*duty.
Rectification losses. ie, the diode volt drop*output current.
Snubber & quiescent losses. (power needed to run the circuit & keep it safe)
Copper losses. IR losses down cable and PCB tracks.

On low power low voltage designs (<20W) , more often than not the diode drop and quiescent current is the major factor. The output diode alone on a 5v/1A supply will cost about 10%.

The "best" PWM frequency depends largely on your magnetics. A poor design for example where the frequency is too low would allow the inductor to go into saturation. This would result in HUGE magnetic losses often in the order of 70% loss. To high a frequency can result in large switch losses. This where the FET (or whatever) spends a long time (relative to switch time) in linear mode dissipating IR in the switch. In active rectifier (to avoid diode losses) designs, getting the timing wrong can lead to losses which exceed those of the diode loss.

Bottom line, the theory is VERY simple, the practice is EXTREMELY complex.
Saying that, it is quite simple to produce respectable switchers that offer 80% or more without getting too complex. It's getting better than 95% that sorts the men from the boys.
Even at 80%, a MPPT controller is likely to give better all round results than just slapping a PV onto a battery. Particularly in lower light levels.

I just wonder about the calcs here. With a small-ish panel and big-ish battery like that isn't the battery going to spend more time fractionally charged?

We've covered PV Panel spec elsewhere so don't want to go over old ground.
And this is regardless of charging techniques.

Battery maintenance issues are a bit complex - you want long battery life but that implies NOT discharging it very far [even 'deep cycle' types] very often and also expending 'wasted' energy charging somewhat past full to keep lead plates in good condition... the bottom line seems to be about 70% net return on energy stored into the battery though at various points in the battery life cycle power return efficiency is better than 90%.... There is a good paper at the www.nrel.gov site about batteries and solar PV... and a lot of wishful thinking that things are better than they are... at least _I_ hope so...

And there are the up and coming lithium technologies which are currently still expensive - making our own power and storing it is fun but not cheap unless the alternative is very expensive... Reducing power use is still the best cost effective way [negawatts] - unless
you have alot of wind or a nice stream going by... ZBBenergy.com seems to be developing an interesting zinc/bromine storage but I don't know how efficient it is... soon the ideal battery will appear... I hope...

If you're feeling brave, then for a few £k, you can now get hold of an early model Toyota Prius. You will then have a 300v 7Ahr NiMh battery complete with 44KW switcher/charge controller. You also get thrown in a 1.5L petrol powered generator for use on rainy days.

CIS/CIGS = Copper Indium Gallium (di) Selinide & no Cadium! It seems the reporter is confused with CdTe types, which of course do have a tad. Even this is very small & encapsulated however- it's more benign that mercury in flouro. lamps.

CdTe PVs are in fact better performers at higher temps- all other types (Si, CIS etc) show a fall off in output as the panel temp increases. This is yet another reason why angling to face the (hot) sun may not be worth it.

I love mechanicals, but know only too well (from wind energy work) that MEGA over-engineering is needed for outdoor reliability. Aside from storm damage/visual eyesores-will the system keep performing without frequent attention? In contrast, PVs just firmly attached to a suitable wall/roof are near invisible & almost hurricane proof (to use a current climatic woe).

Expect to pay ~US$5-10/Watt for larger PVs, but 2008's fossil fuel price hike has predictably firmed global prices. Given both this & rapidly changing solar technologies, I'd be inclined to go for a more modest initial testing setup. Hence -come in Dippy- UK outlets such as Conrad-Anderson offer the 40W CIS Shell/Siemens PowerMaxTM Eclipse ST40,as do assorted camper firms at £180 incl. VAT => http://www.power4motorhomes.co.uk/eclipse_st40.htm. You'll be pleased to note their 5 year warranty.

These UK prices are nearer US$10/W, & almost double those of similar Siemens(Shell) CIS in the US (=> http://www.jatsgreenpower.com/siemens.html ), so some arm twisting/wholesaler chasing may be in order. Down here in the sunny south seas it's typical for boating/camper firms to charge twice the going rate on almost anything off grid,& my Blighty experiences indicate retailer greed is even more prevalent in the UK. Tell them you're from NZ, & they may feel obliged to sharpen their pencil on account of the mutton we sent Britain during the war.

Thanks Stan. Message received.
Thats a good price per watt. Appreciated very much.

I'm a little confused as usual re the performance of these modern marvels.

That Shell ST40 40Watt @ '12V' nom panel.
Size (in frame): 1.293 x 0.328m = 0.42 sq m.
7Kg
10 year limited warranty ffrom Conrad Anderson.


A Solarex (BP Solar) old fashioned 40W @ 12V nominal
Size (in Frame): 0.77m x 0.5m = 0.385 sq m.
5.5 Kg
25 year limited warranty from Solarex

mmm... granted the frame size can vary, though a manuf will get away with the least material possible.
I thought these fancy CIS were meant to be a lot more efficient?
Per total sq m the Solarex gives the same power (at Std levels) with 10% less overall area and weight.
Doesn't that go against the theory?
The ST40 price is far better I agree.


Having said that I've just searched further and found:
http://www.shell.com/static/ar-es/downloads/shell_for_businesses/Shell Powermax Ultra 40.pdf

Size:
0.635 x 0.550 m = 0.35 sq.m.
That's more like it!! Price unknown.

But, By God, they don't make it easy to contact them or Avancis to ask a simple question like "How much and where can I buy one?" .
No email contact but they are kind enough to give me a phone number in Germany and directions from the airport. Pah!!
By car coming from direction Nürnberg:

leave the motorway at exit “München Nord” and take the A99 to Salzburg
leave at exit “Putzbrunn/Hohenbrunn”, go ahead to Putzbrunn
turn left at Karl-Marx-Ring, then turn right to Otto-Hahn-Ring
-Jeez!!
(Hippy has gone quiet, he must be stuck on the Karl-Marx-Ring)

CIS typically are still just ~10%, as it's CIGS that's superior (~19% claimed). Compare this with amorphous (~5%) , polyX (~10%) & monoX(~12%). Some Si types, especially the deeply etched, have exceeded 20% however.

As stated earlier, this is a MASSIVELY developing field, probably equiv. to changes in PC CPUs, & I hence suggest your own trials be modest for fear of being caught out. IMHO the best is yet to come (maybe 2009?), as spin off effects of the nasty mid 2008 fuel hikes are only just being geared up for.

So maintainence is the problem, I'd intended putting them in front of our hedgerow, so that would help a bit as a wind break. I know what you mean about wind, my turbine has to be lashed down really well and still stretches the cables somewhat. I'd thought the least expensive frame could be based on scaffold tubes turning on mini wheel hubs (it's just that I have some kicking around, btw got a whole 1000cc front end if any one wants anything from it, just come and collect). As it would be at ground level the weight isnt really an issue. Manuka, what's your thoughts, should I try it, or not bother?

Miles
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vaporizers

I have an almost south facing sloped roof. Simple enough to measure the suns position at noon and fix the panel at the appropriate angle. It cost £300 (75W) so £4/W. Not too bad. I’ll prolly pay £100 or so more for fittings/wiring/control/LEDs.

Monocrystaline panels are supposed to be good with off-angle and subdued light conditions. I’ll install a basic setup then start working on improving efficiency.

Are those inductor figures correct for upscaling the MTC4.3? Should they be mH, not uH? I can wind my own transformer, but on a uH scale I won’t get many turns.

BMC mini? "10" wheels? Still way too large for trials - 10W range is more feasible IMHO! Keep in mind you'll need 2 axis tracking too (daily & seasonal!).

As a guide to commercial solar tracking systems check the 100W caravan offering =>http://www.campervanstuff.com/shop_stuff/index.php?mod=product&id_prd=1052 retailing at ~£1850 (over US$3500 hence ~US$35 a Watt!)! Caravans don't have the roof space for slapping on more PVs of course, whereas the average home & backyard does. Do the maths - as a 100W PV may cost US$600,for US$3500 you could buy another 5 of them & angle to grab those errant sunbeams!

As also often mentioned, you really need to factor in local daily & seasonal conditions, as dawn fogs etc may give a poor solar potential at sunup, but great late afternoon sun. Your tracker may zoom in on a piddling morning resource & not be able to cope with the afternoon abundance. In the tropics it's often just the opposite- clear dawns but downpours & serious haze mid-late aft etc.

If you have the funds it's better to put in larger battery banks, which will help get thru' those rainy days. No tracker works in the rain of course, & previous sunny days solar resources may have been excessive for your tiny battery & wastefully dumped...

Clock drive. Convert an old grandfather clock mechanism. Tracks the sun perfectly even in overcast conditions, ready to take best advantage of breaks in the cloud. A small geared motor can return the panel to it’s morning position and wind up the clock at the same time.

Nah, how about a nice RTC, tap in your lattitude, nice AL Gore rythm (Global warming algorithm) and it does the calcs for panel-pointing. Piece of Cake. Forget sensing.

Ok. (You started it)

A GPS, PICAXE and two axis drive. Just place it anywhere and it automatically does it all.

True. I made one last year. And at least I managed to get a gag in - albeit poor..

Back of the envelope scribble tells me that the sun’s apparent path through the sky will be about 45 degrees higher in mid summer than in mid winter. Is that right? So a full solar tracker would need two axis, one of 180 deg freedom (east to west) the other of 45 deg freedom (north to south). Correct?

There are many sites giving elevation and azimuth data during the year - take a look...
it's not totally simple but basically aligning the axis of your array [that it rotates around] north south and tilting the array so the sun is perpendicular at noon will give you pretty good tracking for a few days... [flat plate NOT concentrator]. So you don't have to adject the tilt very often but do have to rotate the array daily... to keep the sun perpendicular to the flat array... it varies with you your latitude and time of year.

Do-not-sweat-tracking-the summer-sun,-as it's-the-WINTER-resource-that'll-be-most-valuable!

I've been thru' this endlessly with modest off grid PV setups, & these environmental, seasonal & human factors usually reveal themselves as far more important than electronic issues. For starters, & assuming installations in European/mid US/Aust-NZ latitudes, you naturally use MORE energy in winter (if only for lights). In summer you'll probably be away & never get to use much of what you gather, meaning significant wasteful dumping...

Such seasonal variations are usually best handled by greatly increasing your storage. I know of skinflint off grid setups here in NZ with only a few hundred Watts of PVs, & the most trivial of controllers,feeding sheds full of ex forklift/phone exchange batteries that provide ~1000s of Ah reserve. These take weeks of summer sun to reach full charge, but they've then months of modest winter use on tap. Right up to this year, when scrap metal prices zoomed, such lead acid batteries could often be picked up (tease- they're VERY heavy) at "mates rates"* if you were prepared to collect them yourself. (*In NZ mates rates usually means a dozen amber ale)

Sophisticated control electronics & sexy PV tracking etc will be quite incidental if only ~100Ah is on tap, as just a few cloudy/rainy days may drain such modest batteries to shut down.
Stan

Possibly this PICAXE project could be tweaked for solar??? It's not mine, just something I surfed around and found.

http://www.thebackshed.com/windmill/charger1.asp

boriz said:

Ok. (You started it)

A GPS, PICAXE and two axis drive. Just place it anywhere and it automatically does it all.

Click to expand...

Mono use this type of system commercially - alebit single axis only - still rely on customer pointing the panel north (for us aussies!) initially

I've done it with a cheapy PLC with RTC - easy peasy!

Well, great minds think alike eh? But the greater minds think of it first... always the way.

Hammy, that is just a 'posh' version of Boriz's idea and similar ones posted over the previous aeons. I'm sure it's fine and 'well done' to the author.
But it doesn't take advantage of switcher methods which can provide great efficiency and good regulation.
Maybe Boriz should look at that design.
In my own design I current sense on the charge side and the load side.