This is one of those projects that I've
taken years to actually get around to doing. As someone who objects to
paying huge profit making organisations for services, as well as wanting
a degree of self sufficiency, this article describes some steps towards
Three 40W panels at the left and two 60W panels on the right provide virtually all the 12V power to the house and garage. The 5W panel in the centre is for maintaining unused SLA batteries and an emergency light. At the rear are the evacuated tubes for water heating. The 22W panel for the garden shed can be seen in the distance. Another 80W of panels has been added since this photo was taken.
For years I've been accumulating and building
things that run on 12V, and my garden shed has had a simple 12V solar power
installation since 1999, so 12V was the natural choice for the house system.
I have noticed over many years the poor installation of 12V systems resulting in the impression that they're a very poor compromise and not really practical. The reason for this is voltage drop in the wiring. Unfortunately, because the voltage is low and not dangerous, all sorts of scraps of wire get used. Alternatively, ordinary 2.5mm 240V building cable is used. The problem is that for a given power, an appliance operating on 12V draws 20 times the current than if it worked on 240V. So, the voltage drop along the connecting cable is far more significant. The fact that there aren't as many volts to start with really shows up. End result is dim lights in many installations. Another thing that taints so many solar installations is the use of cheap and low powered lights. Those 8W fluorescent lamps so often seen in boats and caravans are a good example. The light output of these is considerably less than the 240V equivalent. And the use of light bulbs meant for automotive use gives one the impression of living in a dark cave.
My system was to have none of this. By careful planning it is quite possible to wire up a house for 12V and not feel the system is a compromise.
The Solar Panels
The heart of the system is of course the solar panels. I have acquired 240W worth of solar panels. The first set are three 40W panels which I attached to a steel frame I welded up, using only lead acid batteries to provide the welding current. Being ordinary mild steel, I then painted the frame with cold gal. Not as good as the real thing, but better than anything else I could paint it with. The whole assembly was hauled up onto the roof and pointed north. Two 60W panels were later added and connected in parallel to the existing ones, providing in theory, up to 20A charge current. In reality, charge current is about 10A. The solar panels are around 15 years and it is a known fact that output decreases with age.
The 40W panels face north. I set up the 60W panels to face a more westerly direction to make more use of the afternoon sun.
This was the key to the whole thing being useable. Insufficient wire gauge and dim lights would surely result. Working out the length of the longest run and allowing a one volt drop at 10A, I calculated that 16mm cable would be acceptable. To further improve the situation, I decided on a ring main. For those unfamiliar with this, a ring main is essentially a loop which starts and finishes at the source, with loads tapped off along the way. What this means is that at the most distant load you have halved the voltage drop as there's two sets of conductors in parallel feeding it.
The red and blue conductors are 16mm single insulated building wire running around in a loop under the house. You can see a tap off where two sets of 2.5mm TPS cables feed nearby sockets. Beneath is the existing 240V wiring.
I spent a weekend attaching the 16mm conductors
to the floor joists under the house. The tap offs to the wall sockets inside
the house were done with short lengths of 2.5mm TPS cable. The 16mm wires
were stripped, the 2.5mm wires wrapped and soldered around them, and covered
in tape. The joints were staggered to prevent shorts should the tape come
off (as it always does). I deliberately avoided any form of screw connector,
knowing of the higher resistance connection these provide.
To the left is an example of the 12V sockets fed from the tap beneath the house. I used period repro mounting blocks and bakelite sockets to keep in with the style of the house. To the right is the original 240V power point installed in the house when first connected to the public electricity supply. At that time it was generated at the Carrington Hotel in Katoomba.
Australia is fortunate being the only country in the world that has a standard Extra Low Voltage (32V or less) plug and socket configuration. It's known as a "T socket" or by the Clipsal part number 482/32. Current rating is 15A and rugged construction means these fittings are far superior to any form of cigarette lighter type of connector. The fact they are constructed and installed like other domestic electrical fittings means they are unobtrusive inside the house. Surface, flush mount, and cord extension sockets are available in this configuration. Despite this, there are many horrifying examples of ordinary 240V power points being used for 12V. It seems to be common practice overseas, particularly, to use mains type sockets for alternative energy installations. Pity the poor appliance when it gets plugged into the mains! Not only does the appliance suffer damage, but most 12V appliances have exposed parts connected to the supply exposing the user to an electrick shock when plugged into 240V. The "T" fittings are available from all electrical wholesalers, and from some alternative energy, caravan, and boat accessory suppliers, so there is no excuse not to use them. These fittings had their origins back in the days when many Australian rural homes had their own 6-32V lighting plant.
Australian standards stipulate that the top pin is positive when used with DC. The bottom pin is negative or the earthed side of the supply.
To fit in with the existing 1930's style electrical fittings in my house, I mounted a pair of brown 482/32 sockets on reproduction wooden mounting blocks, and installed them adjacent to the existing 240V power points in each room.
The light circuit was also run using the ring main technique, with a loop of 4mm cable in the roof. This was fed by a 4mm run from under the house. As I am a firm believer in the beauty and light quality of incandescent lamps, I elected to install them in each room. No politically correct compact fluoros here! To be practical, small incandescent bulbs as used in caravans or the like just aren't acceptable. The lights had to be as bright as the 240V counterparts. For years, GLS (household style) incandescent lamps have been available in 12V among other low voltages. They are available in ordinary B22 bayonet cap or E27 Edison screw. Not only is their light output the same as the mains equivalent, but it means you can use ordinary domestic light fittings in an extra low voltage system.
These 50W 12V lamps work as well as their mains powered counterpart.
To save disfiguring the walls with extra switches, and reducing the amount of wiring (i.e.. voltage drop), I used pull chain lamp sockets. As these have never been a standard fitting in Australia, I bought them from the U.S. Of course it meant that Edison Screw bulbs have to be used. It just so happened I have a lifetime supply of these in 36W and 50W rating. Incidentally, the U.S version of Edison Screw base is shorter than the European/Australian one. This means that U.S bulbs don't always make contact when screwed into European/Aussie sockets.
Naturally, with 100's of amps available from the batteries, some sort of overload protection has to be provided. I simply used 240V MCB's as I had them and the rating suited. While they might be rated "AC only", the fact is that at 12V an arc cannot be maintained across the contacts, so it is acceptable to use them this way. 240VDC would be another story.
Separate light and power circuit breakers are installed where the battery feed comes in under the house.
Light and power circuit breakers under the house. The paralleled 16mm conductors coming from below is the battery feed from the garage. The start and finish of the power ring main is visible connected to the links at the top. The right circuit breaker feeds the light circuit by 4mm wire. At the left is the 240V feed from an inverter located with the batteries.
There is about 8m between the batteries and this point. To reduce voltage drop, two paralleled lengths of 16mm wire were used.
I started off with four Yuasa 6V 90Ah batteries giving 12V at 180Ah. Originally, these came from 2WS where they were part of a UPS. I don't know how old they were, but they looked well used when I got them in early 1999. Initially they were used in the garden shed, charged by a 22W panel and did good service. However, the increased demands from the house showed up their deterioration so they were replaced with four 6V 232Ah batteries made by U.S. Battery.
With the present charge current available it would be pointless increasing the capacity as they would never be fully charged. The batteries are located in the garage, and also feed light and power circuits there.
The original 6V 90Ah batteries which have since been replaced with four 232Ah units. The AVO7 meter is temporary for testing the wind generator.
Regulating the charge
Solar panels provide a constant current charge. This means that a controller is needed to disconnect the panels when the batteries have reached full charge. This is around 13.8-14V. I used the comparators in a 555 to sense this, with the voltage reference determined by a LED. When the batteries reach 14V, a relay opens disconnecting the solar panels, thus preventing over charge. An ammeter shows charge current. Of course, a diode is in series with the solar panel input to prevent reverse current flowing at night.
The grey box is the charge controller. Meter shows charge current, while the two LED's show status; that the battery is connected and if the battery is fully charged. To the right can be seen the circuit breakers for the garage light and power circuits. To the lower left is a 240V 300W inverter based on the Electronics Australia design from June 1982. This provides a 240V supply to the house during power failures. My version of this inverter incorporates an auto start circuit.
Air X wind generator
Well before I'd started setting up this system, I'd bought an Air X Marine wind generator. These are made by Southwest Windpower and seem to have a good reputation. Although they are obtainable in Australia, I bought mine from Florida. It cost me about $860 Aussie. Here, I'd be paying about $1400. I actually ended up with the Marine version by mistake, even though I paid for the Land version. So it worked doubly well for me.
The Air generators are said to provide 400W at 12V, but I think you need a pretty fierce wind to get that.
It's mounted on a 5.5m high 48mm diameter length of galvanised pipe. I have temporarily mounted it at the back of the house. I say temporarily because I have yet to work out the best position for it. Even though it picks up the south westerly winds, the trees and house do cause turbulence.
Air X facing south.
How does it all perform?
First thing evident that my choice of wiring
gauge paid off. Voltage drop is not a problem. In retrospect, I should
have used a thicker feed for the light circuit as there is a slight dimming
when more than one light is turned on. However, very rarely is a light
on in more than one room, and it's the change in brightness that makes
it obvious, not that the light is actually dim and unusable.
The solar panels work well. One hot day I had a fan pulling 7A all day and still had plenty of charge left that night. In fact one can be slack about leaving lights on.
And the wind generator? Well, to be honest, it's useless where it is. Being so close to the house results in it turning out of the wind when it picks up speed. It will have to be moved further away. Even so, the solar panels provide sufficient current and the wind generator isn't really needed.
The Yuasa batteries failed after one summer. This was not surprising given their age and indeterminate history. I replaced them with four US Battery 232Ah 6V batteries. This gives me 464Ah at 12V; a huge increase in capacity. These batteries have not gone flat since installation during August of 2007.
I think the key things in an alternative energy system are 1)suitable wiring thickness, 2)more charge capacity than needed, 3) more battery capacity than needed, and 4)lights and appliances as good as their mains counterparts.
As for the typical solar panel and car battery bodge with speaker flex and car bulbs, forget it.
cablehack at yahoo dot com