Low wind speed energy harvesting using supercapacitor (URGENT)

Hi all,

I am going to build a low wind harvesting system using supercapacitors. The 3-phase AC output from the turbine is then converted into DC using rectifier.

After that, I have to construct a electronic circuit (consists of supercapacitors, MOSFET, Arduino, current sensor and etc) and I have to determine when to charge the supercapacitors and when to discharge to a battery.

Anyone has any idea for the construction of the electronic circuit? Which model of Arduino should be used?

Thank you.

Don't need a battery just charge a supper cap

Any model Arduino will be fine.

"low wind speed" and "energy" are almost contradictory.

...R

Low wind speed only if you have multiple gears to convert that low speed into faster rotation on your motor/s.

What type of turbine ? Whats its cogging resistance ?

To be able to give practical advise, we need to know more about the turbine and the voltages you want to use.

Common supercaps are low voltage although there are some for car audio systems for 12v.

The basic concept is to charge the capacitor up to a certain voltage above the battery voltage. Then use a comparator to switch it across the battery until the voltage drops to a lower level and repeat.

Weedpharma

Hi, The OP is trying to make a windcharger version of a PV MPPT. You store charge from the windcharger in the supercap until it is enough to [u]efficiently[/u] transfer it to the storage batteries.

I have had to replace the caps on such a system, many years ago, but have not actually seen it working.

You will also have to provide for dumping energy or feathering the windcharger if the energy throughput is too high, such as when the batteries are at full charge.

Tom.... :)

As TomGeorge has said, you need more than a simple charger. When the battery is full, there is no load on the turbine so it can freewheel to destruction. To prevent this you need to use a shunt regulator to short the extra output to ground.

Weedpharma

Domino60: Low wind speed only if you have multiple gears to convert that low speed into faster rotation on your motor/s.

Alas, while it may be necessary to run the generator at a higher speed, gears waste energy and at low wind speeds there is very little to start with. That's why wind farms are located in windy areas.

...R

Hi,

I think we need to know more.

What power is the wind turbine? What voltage is its output rated at? What size super-cap are you thinking of? How big are the storage batteries?

What is your electronics, programming, arduino, hardware experience? Is this a school/college/university project?

Tom.... :)

Normally when the super capacitor voltage is smaller than the load (battery voltage) no charge occurs, so its impossible to harvast low wind energy that would otherwise be available, until the alternator output > battery voltage. Once this condition is met normal charge occurs trough rectification.

To use the low voltage stored on a capacitor one needs a boost converter whose output directly supplies the battery. So its possible to have 15 or 20V stored on the capacitor charging a 48V battery at reduced power, for example. When the capacitor voltage reaches 12V the DC-DC is stopped until the capacitor is once again charged. This is because efficiency drops and we dont want to go all the way down to zero to let the alternator gain speed (Otherwise it would stall).

I use a similar aproach to charge my EV altough the reason is to both to have PFC correction and step mains voltage to 440VDC, however I have thought about using a similar method to use the exixting hardware to charge from a 48V-72V solar array.

To do this basically one needs a DC-DC boost converter operating in constant current mode. This is better handled by an external circuit, such as an UC3842 based boost converter. Here's an example available on eBay which I have personally used for LVDC (up to 60V).

150W DC-DC Boost converter

The exact requirements will depend on the alternator/load voltages and power levels (altough 150W is plenty for "low wind operation")

The arduino keeps log of the super capacitor voltage and once the set point is reached enables the boost converter. The voltage will drop and the circuit will be switched off. The exact time the circuit remains on depends essentially on the alternator output. Programming wise this makes things simple, so any arduino could be used. If you wish to perform the duty cycle generation for the boost converter directly on the arduino things get more complex. Again I recomend using a dedicated analog IC for such purpose.

A top thereshold voltage disables the DC-DC if the capacitor voltage goes up rather than down. This is to ensure charge occurs normally trough rectification if the wind suddently starts blowing.

An interesting point: One doesnt necessarily need super capacitors for this purpose. Any normal capacitor will work will this aproach. One can have a 20ms on 10S off duty cycle for example, without loss of efficiency. As the alternator power increases, the duty cycle also increases.

It should be without saying that this is a not a beginner project. There's not a lot of programming but there's a lot of hardware mods required.

so, as I understand, the OP has a slow speed wind turbine. a super cap that will charge up until it reaches a point the stored energy can be moved to the battery pack. being low speed, the battery pack will be over sized, so will rarely ever get fully charged.

on a high wind event, the charging might be sufficient to fully charge the battery and once charged, there is a problem of over charging.

the choices are to either add a load or prevent generation.

looks like all he is asking for is help with the circuit to use the power stored in the cap to charge the batteries.

does that sound about right ?

dave-in-nj: so, as I understand, the OP has a slow speed wind turbine.

As we have not heard any more from the OP you may well be correct.

But my reading of the Original Post (and the title) is that the OP wishes to generate power when the wind-speed is low. I assumed that to mean that he is in a location that does not normally have high wind speeds and I don't think his concern is about protecting the system from overload. Rather the opposite.

I have no idea whether the use of supercapacitors (or any capacitors) would make the overall system more efficient or less efficient. In general I expect that every gizmo between the generator and the battery will reduce efficiency a little bit. And batteries are, themselves, very inefficient.

...R

An (URGENT) problem and no further response? Maybe he worked it out already and no longer needs our help.

Weedpharma

weedpharma: An (URGENT) problem and no further response? Maybe he worked it out already and no longer needs our help.

Weedpharma

maybe he was close to having his power shut off.... lost the net, now can't figure out how to charge the batteries ?

dave-in-nj: the choices are to either add a load or prevent generation.

Generally preventing generation would speed up the alternator to the point things would get damaged.

As to loading it, I've done it on the past with a transistor in the linear region shorting the output to 13.8-14.4V. I Think some bikes also use this approach. It does need a fairly large transistor, compared with PWM, but the output is cleaner (no inductive spikes, load supplied by the source rather than battery during float charge).

One could also use PWM or on/off to a load with an analogue comparator with hysteresis.

Any of the approaches would be best taken care by discrete components rather than a uC.

weedpharma: An (URGENT) problem and no further response? Maybe he worked it out already and no longer needs our help.

Weedpharma

Maybe the wind was so slow he run out of power? ;)

casemod: Generally preventing generation would speed up the alternator to the point things would get damaged.

just turn the fan to the side. no rpm, no charge.

or just add a load such as a heater or lamp. very common and very easy to do.

Sorry guys, I had a very busy week and didn't manage to reply.. Thanks for the feedback anyway.

Currently, I am facing a problem in the low current. As all of you aware, the wind speed in Malaysia is approximately 10-12 m/s.. In order to charge up the capacitor, I need at least 20m/s of wind speed. Hence, I am thinking of building a differential amplifier that can sense the low current.

Fyi, I charged the battery for 10++ hours and it drains out within half minute on just a very small load. (small fan)

Any suggestion for that? Or there is any other solution that u guys can think of?

Thanks again for all the replies. I appreciate it.

Regards, Jay See

Power of the wind turbine = 1.5kW

Storage battery = 12V