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 doing that.
From left to right, panels are: 2x 40W, 3x 40W, 2x60W, 2x60W. The evacuated tubes for the water heater are behind the 3x 40W panels.
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 440W 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 old and it is a known fact that output decreases with age.
Later, two more 40W panels were added, and another two 60W panels. All the 40W panels face north east, and the 60W panels face north. This gives useful output for most of the day. Because of trees, there is no point having panels facing west. The positioning was set up at the time of year when the days are shortest, since the roof shadow from the main part of the house blocks out sun for a lot of the morning, if the panels are too far forward. The two right panels also have to be positioned so as not to block the sun to the evacuated tube collectors for the water heater.
While the possible output from all the panels is 440W, this never happens in practice. Firstly, the positioning of the panels is such that they do not all receive full sunlight at the same time. Also, the power rating for solar panels is at their open circuit voltage; about 20V for 12V panels. The power output is reduced when connected directly to the batteries since the maximum voltage is around 14.5V. Modern microprocessor controlled charge regulators contain a switchmode converter to allow the panels to develop more power by allowing them to work at their most efficient voltage.
This was the key to the whole thing being usable. Insufficient wire gauge would be a recipe for dim lights. 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. 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.
Australia fortunately has a standard Extra Low Voltage (32V or less) plug and socket configuration. Like our 240V socket, the ELV socket is also of U.S. origin. It is further described here. 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 electric 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 have been 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. 12V incandescent bulbs in GLS style with a B22 base are no longer sold in Australia, but I have a life time supply of them. They're still available in the U.S. with an E26 base, but probably won't be forever. These days, there has been a marked switch to LED bulbs for low voltage systems. At least they are available with E26/E27/B22 bases so "mains style" fittings can be used with them.
These 50W 12V lamps work as well as their mains powered counterpart.
To save disfiguring the walls with extra switches, and to reduce 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 (E26) is shorter than the European/Australian one (E27). This means that U.S bulbs don't always make contact when screwed into European/Aussie sockets.
Vintage radial wave streelight is fitted with a 12V 40W B22 based bulb. It is switched by a PIR sensor modified for 12V.
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 radio station 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 gave 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.
When these failed in 2017, they were replaced by three Narada 12NDF100 AGM batteries. These are 100Ah each. The batteries are located in the garage, and also feed light and power circuits there. I am aware that paralleling batteries is not the best way to increase current capacity, but the batteries were obtained at a good price. The reason is that if a cell shorts out in one battery, a high current will flow into that battery from the other good one(s). The correct way is to use larger 2V cells in series. If one shorts, the others are not affected.
When deciding how much battery capacity to have, the charge input current has to be taken into account. The batteries will never full charge if their capacity is too great, relative to charge current. A good rule of thumb is that battery capacity is such that full charge is achieved by the middle of the day.
Three 100Ah batteries store the solar charge.
Because lead acid batteries are damaged if they are fully discharged, a mains powered back-up charger switches on when the battery voltage gets to 10.8V. This only happens after several cloudy days if high demands have been made on the batteries.
Regulating the charge
Solar panels provide a constant current charge. This means that a controller is needed to ensure the batteries do not overcharge once they are fully charged. I used the comparators in a 555 to sense this, with the voltage reference determined by a LED. An ammeter shows charge current. Of course, a diode is in series with the solar panel input to prevent reverse current flowing at night. A more detailed description of the charger is described here.
Garage switchboard contains the charge controller, regulator, and mains charger. The two 200W light bulbs at the top control charge current for the mains charger.
An auto-start 300W inverter feeds 240V AC to a power point inside the house. This is useful for operating low power mains appliances during a power failure.
This inverter is based on a design from Electronics Australia, June 1981. It provides 240V to a power point in the house.
Because during charge, the batteries can reach 14.4V, the supply to the house and garage is regulated. While some loads tolerate 14.4V, some are stressed by the higher voltage. Hence, this regulator was installed.
Voltage is regulated to 13V which allows for some voltage drop in the wiring.
Air X facing north. Unfortunately, the location provided poor output.
First thing evident is 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 a little careless about leaving lights on.
And the wind generator? Well, to be honest, it was useless where it was. Being so close to the house resulted in it turning out of the wind when it picked up speed. It would have to be moved further away and raised higher. 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. In 2017 they falied and were replaced with sealed AGM batteries, which have been a lot better.
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.