Thread: Solar electricity production

Originally Posted by JDNSW

kitchen wood fired stove, which also provides hot water for the floor heating system.

Any more info on this John? I am thinking of building an underfloor heating system myself - to capture some more heat from the (open) fire.

Originally Posted by Tank

Is it possible to stick an alternator (car 65/85amps) on top of a pole with fan blades and run wiring to a battery and harness the wind to charge said battery

Unfortunately it’s not so straightforward.

Because the fan blades will never rotate anywhere near the speed of a motor, the alternator needs to be rewired and even then they are never very effective.

The only real way to get an alternator set up to work is to use the same principals that the large windmills use and that is to have a very large diameter blade set up connected to a step-up gear box and then connect this to your alternator.

I think cost would start to become a problem when trying this sort of a set up.

Originally Posted by Tank

Is it possible to stick an alternator (car 65/85amps) on top of a pole with fan blades and run wiring to a battery and harness the wind to charge said battery, if so, hows about a blueprint on how to wire it up, and of course would it work, Regards Frank.

It is possible, but as Drivesafe comments, it is not that simple. A car alternator is not a good point to start from, although there have been moderately successful attempts. The first problem is speed - the minimum useful speed for an automotive alternator is around 1000rpm, and for various reasons it is not feasible to run a windmill this fast with sufficient blade area to provide the kilowatt or more of power needed. So gearing is needed = complication, cost and loss of efficiency. Secondly, the automotive alternator uses battery excitation = loss of efficiency plus complication to switch it off when the wind drops and back on when the wind restarts. All modern small wind generators use permanent magnets. This has the advantage of efficiency plus simpler control - for example, overspeeding can be controlled by shunting the output into a dummy load.

A major design problem is the need to start generating at winds as low as perhaps ten kilometres per hour, but escape damage at wind speeds in excess of 100km/h. This means you need a large blade area, start generating at low rpm, and have foolproof mechanisms to prevent overspeeding and to feather the blades out of wind as speed increases.

John

Great forum addition lads.

I've just subscribed to the whole forum

Originally Posted by JDNSW

When we started building the house in 1994 we investigated the relative costs of getting the power on and getting a stand alone power system. In the end, the costs came out around the same, so we went with the stand alone system.

While living in a caravan and building the house, we used a 12v 300VA Sine Wave inverter, with a pair of 12 v batteries and three 60w panels. This was supplemented by a 2.5kva petrol generator. This system was also used in the house as an additional supply, with the batteries replaced by a set of 400AH cells, and an extra panel added.

The house power system is in fact two identical systems, for redundancy - either can run the house at a pinch, but generally the load is shared, with the two major loads, refrigerator and freezer, being one on each.

Each system is based on a 24v bank of 760 AH cells, charged by a tracker with eight 75w panels via a BP controller or a 40A charger. Each system has a Selectronics 2kva (6kva for 30 seconds) sine wave inverter.

The battery chargers were originally powered by the 2.5kva petrol generator, later replaced by a 6.5kva petrol generator, and now usually by a 5kva Lister diesel generator.

A fairly recent addition has been a 200w nominal wind generator on one system. I intend to get another of these.

Problems:- Two of the 60w panels have failed (out of warranty), one apparently due to lightning, the other apparently a manufacturing fault. One 75 w panel was replaced under warranty.

One Selectronics inverter failed spectacularly shortly after installation ( I suspect a loose nut or something in it initiated a short) and was repaired/replaced under warranty.

Both tracker electronics modules have failed - and the manufacturer is defunct, and parts are unavailable; and they removed all the ID information from the ICs, and no circuits are available.

Two of the big cells were replaced under warranty, and another eleven have failed in recent years - fortunately, I managed to get hold of a part life set of twelve. But with the batteries fourteen years old, and an expected life of about ten years, I am looking at having to get at least twelve new cells in the reasonably near future!

Apart from the problems mentioned, the electronics have given no trouble. Routine problems are frequently due to bad intercell connections, or more recently, failing cells.

Apart from the power system, hot water is provided by a pair of solar collectors on the verandah roof. These have a frost valve to prevent freezing rather than operating a closed loop. They feed into a gravity tank in the roof, which is boosted by the kitchen wood fired stove, which also provides hot water for the floor heating system. This has proved to be totally successful, just that you have to light up the fire to get hot water during overcast, even if the weather is warm.

This what you were looking for?

John

Thanks John, a top report.

If you could get your hands on it, what would you like to get that is either not available or is too expensive at this time?

Originally Posted by isuzurover

Any more info on this John? I am thinking of building an underfloor heating system myself - to capture some more heat from the (open) fire.

The kitchen stove has a purpose designed water boiler which surrounds all sides of the firebox (except for the firedoor opening, about half the front, and the top and bottom). This is plumbed via a small circulating pump and a branch to the hot water system to a double manifold about two feet above the floor in the middle of the house. From this manifold there are six double spirals of pipe (a special low density poly pipe sold for the purpose) within the slab. The pipes were laid out on top of the reinforcing and wired to the mesh about every metre. The slab had to be thicker than normal by the diameter of the pipe (20mm), and the system was filled with water to stop it lifting when the slab was poured.

There is a small header tank with a ball valve to provide pressure relief and ensure the system is kept filled. (This is essential to prevent the possibility of explosion.) Each separate circuit is provided with a control valve which allows regulation of heat to different areas of the house. The circulating pump is controlled by two thermostats plus a switch - one thermostat keeps the pump off until the water returning from the hot water system reaches the set temperature, and the other switches the pump on regardless when the water rising from the stove approaches boiling point.

I would doubt that you would get enough heat from an open fire, although I suppose it depends on how big the fire is.

Hope that helps,

John

Hi, I am also very interested to where this thread will lead. Thanks Drivesafe for initiating it and to John for the great report.

Re the wind generators and alternators, I have heard of the inverter drive out of a Fisher and Paykel washing machine being used in conjunction with wind generators - one of those future projects.

I am also surprised at the high falure rate of the solar cells and controllers.

Erich.

A friend in Coonbarrabran had a HW system that worked solely from water heated from their stove. They had a header tank above the stove and used natural circulation to heat the water.

Obviously no cooking no hot water, but it did seem to suit them.