# Thread: Eskom or the wind ?

1. ## Eskom or the wind ?

Hi all.

There are enough electrical gurus floating around this ( my favorite ) forum so thought I would ask for some guidance here.

After the latest (expected) shock from Eskom, I have started to think about alternate energy for some basic things around the house.

Now not being an expert electrical person, can anyone tell me if I have the right logic here .... ?

Am looking at wind powered generators but not too sure about the maths.

A wind turbine ( yes, I am on a very 'breezy' hill ) generates ( it's specs say ) 1 kW. ( I assume this is per hour, and at optimum speed ? )

So that 1000w at 12 volts = 83 amps.

So I connect this to a deep cell battery ( 105 Ah ) and it will take 1.27 hours to charge.

The system requires a charge controller, so when the battery is fully charged and registers 14 volts, it switches the input from the turbine to a heating element, say, feeding my pool ( I know : minute amount of heating, but protecting the battery ).

On the other side of the battery, I have a 1000W inverter. So this takes the 105 Ah 12 volt from the battery and converts to 220 volt ( 105Ah x 12v ) to 1260 Watts, and assuming there must be some loss in the process, say 15%, I get out 1071 Watts. ( and 1071 W / 220 V = 4.86 Amps )

Now I have 10 energy saving bulbs ( 11 w each ) = 110 watts total per hour, and the battery and inverter should run these for 1071 / 110 = 9.7 hours.

I have used ( Eskom-less power ) of just over 1Kw. I have saved a grand total of just R 1 ?? Well, today at least. for the month R30, for the year R365, and for as long as my system doesn't require any costly maintenance.

Is my logic here correct ?

2. Originally Posted by daveob
The system requires a charge controller, so when the battery is fully charged and registers 14 volts, it switches the input from the turbine to a heating element, say, feeding my pool ( I know : minute amount of heating, but protecting the battery ).

What your maths shows is done right, you can save about R1 per hour of wind power.

3. ## Thanks given for this post:

daveob (09-Mar-10)

4. Thanks for the reply Dave_A. Wasn't sure if my logic was correct.

Now that brings me to the next bit ...

1. with a 1000W inverter, there's no way I will be able to run my kettle ( 2000 W ) as it would draw too much power too fast ? This means I would have to increase the inverter capacity, or would the kettle element just heat water using as much power as the 1000W inverter gives it, thus taking longer to boil ?

2. on the subject of the charge controller and dumping the excess power that the battery can't take into a heating element, would I be able to simply dump the excess 12v power straight into the (isolated) geyser element ? This would be done by the charge controller that detects the battery at full charge, and the power being 'dumped' would vary depending on the speed of the wind turbine. Does a heating element like that accept varying voltages ( 12v or 220v and different Amps ), or would I have to convert the dumped power to smoothed 220 V ?

3. with the varying speed and output of the turbine, would there be a limit that one can use to charge a deep cell battery ? For example, can I hook up a 83A charging system onto a battery without damaging it, or would it be wiser to use, say, 20A for charging, and dump the rest to the geyser element ?

As I see it, if the average saving is going to be about R1 per hour of wind per charged battery ( I could run more batteries if the turbine outputs enough power to charge them ), and assuming it runs 5 hours per 24 hour cycle, I could save R5 / day = R150 / month ( that's for this year before increases of 25% pa ). So if the capital outlay is in the region of R15k, cost recovery is a little over 5,5 years. Thereafter, the power, at that point costing R370 pm ( 25% incr. pa ) is all free.

At the same time, I would have to become considerably more energy efficient to reduce the overall energy consumption so that the wind power becomes a larger portion of my total usage - aiming for about 50 / 50 split between wind and eskom.

An interesting article I read points out that a lot of devices, although plugged into the 220V socket, simply reduce the voltage back down to 12V. This includes the PCs, home entertainment, etc. In these cases, the devices could be modified to run directly off the battery bank without using the inverter and the associated conversion loss. Investing in 12v lighting ( eg LED downlights which are extremely energy efficient ) can help save considerable energy. Apparently, the worst things to run from this type of system, are things like fridges / freezers. I think it is a combination of the amount of power they use, and the fact that they do not run well from inverters ( except for the expensive pure sine wave versions ).

General consensus seems to be that wind is a lot more energy productive than solar panels. Also, that any power source ( wind / solar, etc ) is NOT likely to be a total replacement for the eskom grid feed, but rather a suplimentery source.

5. Originally Posted by daveob
Am looking at wind powered generators but not too sure about the maths.

A wind turbine ( yes, I am on a very 'breezy' hill ) generates ( it's specs say ) 1 kW. ( I assume this is per hour, and at optimum speed ? )

So that 1000w at 12 volts = 83 amps.

So I connect this to a deep cell battery ( 105 Ah ) and it will take 1.27 hours to charge.
If it's a lead acid battery then it will require much less than 83 Amps (more like 4-10 Amps) for a longer period of time (4-5 hours, maybe longer depending on the power in the battery when charging commences) the voltage will need to be around 13.5 volts, not 12v to effectively charge.

Originally Posted by daveob
The system requires a charge controller, so when the battery is fully charged and registers 14 volts, it switches the input from the turbine to a heating element, say, feeding my pool ( I know : minute amount of heating, but protecting the battery ).
Most systems like this would be better with an intelligent charger. This prevents the battery being charged too quickly or overcharged. The intelligent unit monitors battery temperature amongst many other things to determine the charging rate that won't overheat the battery or damage the plates. Even when the battery is fully charged there is usually a trickle charge applied to keep the battery charged.

Originally Posted by daveob
On the other side of the battery, I have a 1000W inverter. So this takes the 105 Ah 12 volt from the battery and converts to 220 volt ( 105Ah x 12v ) to 1260 Watts, and assuming there must be some loss in the process, say 15%, I get out 1071 Watts. ( and 1071 W / 220 V = 4.86 Amps )
I would pay particular attention to the device ratings. A 105Ah battery is often only rated to deliver the kind of power you're talking about for a very limited period of time. Batteries are rated in Ah but this can be misleading, it doesn't mean they will deliver the power for hours at a time, most batteries are designed for engine starting applications where they are under high load for a few seconds. Likewise the ratings on inverters are often maximum output ratings not continuous ratings. For a continuous rating you can often deduct 20-25% from the max rating.

Originally Posted by daveob
Now I have 10 energy saving bulbs ( 11 w each ) = 110 watts total per hour, and the battery and inverter should run these for 1071 / 110 = 9.7 hours.
A cheap camping type inverter could have losses of 50%. A state of the art inverter could have losses of 10%. CFL lamps don't like 'modified sine wave' (a misleading description if ever there was one) inverters, it buggers up the internal electronics and leads to poor starting, overheating, flashing and premature lamp failures.

Originally Posted by daveob
I have used ( Eskom-less power ) of just over 1Kw. I have saved a grand total of just R 1 ?? Well, today at least. for the month R30, for the year R365, and for as long as my system doesn't require any costly maintenance.

Is my logic here correct ?
At the risk of sounding like the harbinger of doom the problem with the system will be the initial outlay costs and replacement battery/batteries every 3 years or so.

Wind turbines aren't cheap to buy or install and they can be noisy when running as well. You'll almost certainly also need accepted council plans which further bumps up the costs. Even the electrical installation is fairly expensive. Cabling is rated by current so it will be thick wiring even though it's only low voltage (the cabling for the wind turbine of 1 kW @ 12 Volts will need to be thicker than a normal residential supply cable from the street) . An intelligent battery charger is also a couple of thousand Rands.

In my humble opinion this is the kind of thing you would do as a labour of love, not as an exercise to reduce your electric bill by a Rand a day.

Directly solar heating your geyser water will be far more cost effective.

6. ## Thank given for this post:

Dave A (10-Mar-10), daveob (09-Mar-10)

7. Originally Posted by daveob
1. with a 1000W inverter, there's no way I will be able to run my kettle ( 2000 W ) as it would draw too much power too fast ? This means I would have to increase the inverter capacity, or would the kettle element just heat water using as much power as the 1000W inverter gives it, thus taking longer to boil ?
A 1kW inverter running a 2kW kettle will either damage the inverter or cause it to trip.

Originally Posted by daveob
2. on the subject of the charge controller and dumping the excess power that the battery can't take into a heating element, would I be able to simply dump the excess 12v power straight into the (isolated) geyser element ? This would be done by the charge controller that detects the battery at full charge, and the power being 'dumped' would vary depending on the speed of the wind turbine. Does a heating element like that accept varying voltages ( 12v or 220v and different Amps ), or would I have to convert the dumped power to smoothed 220 V ?
A 220V element will produce almost no heat if supplied with 12 v. Approx only 1 Amp will flow@ 12v.

Originally Posted by daveob
3. with the varying speed and output of the turbine, would there be a limit that one can use to charge a deep cell battery ? For example, can I hook up a 83A charging system onto a battery without damaging it, or would it be wiser to use, say, 20A for charging, and dump the rest to the geyser element ?
You can't charge a standard lead acid battery at 83Amps without it boiling. A battery charger will limit the current to the battery, 'dumping' power shouldn't be necessary. You can't directly hook up the turbine to the battery.

Originally Posted by daveob
As I see it, if the average saving is going to be about R1 per hour of wind per charged battery ( I could run more batteries if the turbine outputs enough power to charge them ),
A 1kW turbine should be able to charge several batteries.

Originally Posted by daveob
At the same time, I would have to become considerably more energy efficient to reduce the overall energy consumption so that the wind power becomes a larger portion of my total usage - aiming for about 50 / 50 split between wind and eskom.
I think realistically you'll be able to run a few lightweight appliances or light on the wind system. If you take the hot water cylinder out of the equation and you cook with gas then you might make a 50 / 50 split.

Originally Posted by daveob
An interesting article I read points out that a lot of devices, although plugged into the 220V socket, simply reduce the voltage back down to 12V. This includes the PCs, home entertainment, etc. In these cases, the devices could be modified to run directly off the battery bank without using the inverter and the associated conversion loss.
It's possible but will vary from appliance to appliance. Many appliances use a switch mode power supply which has two or thre different voltage rails on the output so 12v might be only one of the voltages required for it to run.

Originally Posted by daveob
Investing in 12v lighting ( eg LED downlights which are extremely energy efficient ) can help save considerable energy. Apparently, the worst things to run from this type of system, are things like fridges / freezers. I think it is a combination of the amount of power they use, and the fact that they do not run well from inverters ( except for the expensive pure sine wave versions ).
12 volt LED's are prone to damage from voltage surges which over-drives them and causes failure.
Fridges and freezers with 12v induction motor compressors are available, Danfoss do a good range but they're heavy on power requirements. Absorption fridges are better suited (NH3), they will often run on a 300watt heater (maybe less) for a decent sized fridge. They're also not too fussy about sine wave quality and they can also use gas (LPG) as a power source.

Originally Posted by daveob
General consensus seems to be that wind is a lot more energy productive than solar panels. Also, that any power source ( wind / solar, etc ) is NOT likely to be a total replacement for the eskom grid feed, but rather a suplimentery source.
[/QUOTE]
Solar panels are far more productive if they're heating water rather than photovoltaic.

8. ## Thanks given for this post:

daveob (10-Mar-10)

9. ## Wind Power RMS

When you want to calculate the output power of a device, such as the wind-power generator you need to consider a few other facts.

The output power of the unit is, say, 1000W (this is probably max output), use the RMS value (70%) to determine the constant power out, 1000/70% = 700W.

Understanding electrical principles is difficult if you don't have the manual but here's an example of a computation I had to do for a Golf Car charging facility.

10. daveob, you need to approach this from a different angle.

PC's can be converted to 12V, but the PSU's are much more intelligent and distribute the load on various factors, to the different components. In short, don't try and convert your PC to 12V, you could easily end up blowing your CPU & HDD. BUT, if you have electronics experience, then you'll need to modify the PSU and cut out the transformer part to get it to work with 12V. PSU's don't have a traditional coil transformer, but rather some fancy circuitry. BUT, you would need clean power, so it's safer to use a pure sine wave inverter (the more expensive ones) for this.

You can easily convert your 220V lights to 12V, but you need to clearly mark everything, otherwise the standard bulbs won't work
get a solar heater if possible and try to switch to gas for cooking, even on the kettle.

You're TV will probably run very happily on 600 - 1000W inverter.
Now, with this behind us, change your perspective a bit: Calculate how many watts you'll need to run everything you need, and get an inverter that's at least 30% bigger than that. i.e. if you need to run 3000W, get a 3900W inverter. This is cause most of the times the printed label is for peak rating, and the running watts is less. And in general you don't want to run anything at full rating the whole time, it will get hotter than it's intended to.

Now you need to calculate how many 105AH batteries you need to run that inverter @ the intended wattage.

Once done, you need to calculate how much power you'll need to recharge the batteries within reasonable amount of time, normally about 6 - 10 hours. Remember, the recharge time is really only applicable when there's been no wind for a while, otherwise the excess power that you wanted to dump will actually be used by some of the appliances, like the PC, TV on standby, etc.

Try and build a 24V, or even 48V system if possible. 24V will need less half the Amps as 12V to deliver the same Watts. i.e. 12V x 200A = 2400W, OR 24V x 100A = 2000W. This also means you can use smaller (thus lighter & cheaper) cables throughout the system

And, as a handy tip: use a DB for everything. You could probably use your existing DB for this, since all the wiring already terminates in one box and it has circuit breakers already. BUT, keep a standard. i.e. if you go 12v with the downlights, then you need to make sure all lights circuit breakers & circuits are 12V. On the plug points, make sure they're all on 220V and connected to the inverter.

If possible,rather use 2 or 3 smaller inverters than one big one - it gives a bit redundancy, and load balancing to the system i.e. if the the lights are all one one inverter with 4 batteries, and plugs on another inverter with 4 batteries, then you can effectively disable the plugs while having lights (i.e. for maintenance on batteries / plugs, OR the lights could still work while your other appliances have depleted the batteries and there's no wind)

11. ## Thanks given for this post:

daveob (15-Mar-10)

12. Originally Posted by SoftDux
If possible,rather use 2 or 3 smaller inverters than one big one - it gives a bit redundancy, and load balancing to the system i.e. if the the lights are all one one inverter with 4 batteries, and plugs on another inverter with 4 batteries, then you can effectively disable the plugs while having lights (i.e. for maintenance on batteries / plugs, OR the lights could still work while your other appliances have depleted the batteries and there's no wind)
There are 'scalable' inverters available where you can take 2 separate 5kw inverters and series connect them to make a single 10kw inverter. Later if you need more power you can purchase a third one and add it to the other two and make 15kw output. Also if you have 3 of these inverters you can wire then in parallel to give you a three phase output. They can also handle multiple power inputs from batteries, solar panels, wind turbines, hydro etc as well as grid (eskom) power and have a built in battery charger. The output is always flawless sine wave, they're not cheap but you get what you pay for. The last one I purchased was around 12 grand a couple of years ago.

13. Originally Posted by AndyD
There are 'scalable' inverters available where you can take 2 separate 5kw inverters and series connect them to make a single 10kw inverter. Later if you need more power you can purchase a third one and add it to the other two and make 15kw output. Also if you have 3 of these inverters you can wire then in parallel to give you a three phase output. They can also handle multiple power inputs from batteries, solar panels, wind turbines, hydro etc as well as grid (eskom) power and have a built in battery charger. The output is always flawless sine wave, they're not cheap but you get what you pay for. The last one I purchased was around 12 grand a couple of years ago.
Yea, those are the ones I'm referring to

14. This is the system I mentioned. They also have lots of info on connecting wind and solar systems etc on this site in the 'support and downloads section. There's also a pricelist in Euros but it's not for the faint of heart. 3000 Euros for a 5kw multiplus inverter/charger.

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