Saturday, Oct 23, 2004 at 11:01
Thank you to the people kind enough to mention me and my books in connection with solar.
Magnus is of course absolutely right when he says that there's any number of sources of information - but sadly only too many can be unintentionally misleading.
The main problem is that, unlike most things electrical, what should work just fine by following a few basic electrical principles, does not necessarily work with solar. This is actually a field where no prior knowledge can actually be preferable.
I'll attempt to answer any queries on this
Forum - but meanwhile here's a few things to consider:
1. Solar module produce a lot less that you may think.
Working into a typical 12/24 volt system, (unless a very sophisticated device called a 'multiple power point tracker' is included solar modules do not and cannot produce their apparanetly claimed output. Reality is about 65-70% of what is says on the box.
2. A typical deep-cycle battery is (typically) good for less than 50% of its apparant amp/hour capacity.
Charged via a standard vehicle alternator/regulator, a conventional lead-acid battery rarely if ever exceeds 70% full charge. A 100 amp/hour battery is thus rarely charged beyond 70 amp/hours.
It cannot be discharged much below 40% remaining charge without incurring damage. Most battery makers quote 50% maximum.
3. Almost everyone who does their own wiring uses cable that's at least 50% too small.
Why? Because appliance makers specify the cable to be used in square mm; but the auto cable invariably used is specified as the overall diameter in millimetres - insulation as
well. In other words Engel tells you the conductor size to use - the auto parts store sells you cable rated by the size hole it will pass through.
Example. 4 mm auto cable (which is what is you'll get if you ask for 4 mm cable) is usually 1.8 - 2.0 sq mm.
That's why most of your 12 volt fridges disappoint.
I do go along with Magnus view re gas fridges. It makes sense (unless you are driving most days) as any electrical fridge is responsible for about 60%-70% of total draw.
Finally - solar can be made to work extraordinarily
well if implemented properly. It is not hard to do, but one has to very wary of campfire mythology and most magazine articles on the subject.
The problem is not so much what people don't know. It's what they think they know that simply isn't true.
My home north of
Broome is all-solar (2.2 kW of solar modules for the main system) a further dedicated 480 watts (at 48 volts and driving a three-phase brushless motor) for our 3000 litre/hour swimming pool pump.
Our OKA has used solar since 1996 for its 70-litre autofridge, umptgeen halogen globes and, until recently, a big Westinghouse sat phone - and has not run out of power once.
Collyn Rivers
FollowupID:
340563