mixing multiple power sources

Question

I have 500 watt wind turbine which gives watt around 100-500 depending upon weather condition.

I use it for led lighting. total led wattage is around 500 watt.

so most of the time not all of the led are turned on. how do i add external power source which can complement wind power ? ( i.e. circuit should prefer to use wind power whenever available, else use grid power. )

thanks.

edit:

http://electronics.stackexchange.com/a/51756/1312 explain it further. also read comment. can capacitor help in combining multiple power source ?

Answer 1

There are various ways to do this. One way is to connect the wind turbine to a grid power inverter. Power from the turbine will be dumped back onto the grid when it exceeds what you are using (when the LEDs are off). Otherwise, it will offset the power drawn from the grid. For example, if the turbine is putting out 300W and your are using 500W, 200W of that will come from the grid and 300W from the turbine, minus losses in the system of course.

Depending on how important efficiency is and whether grid power going down is a issue, you could run the LEDs from DC with a battery. Both the turbine and the grid charge the battery as needed, but less will be automatically drawn from the grid when power comes from the tubine.

Answer 2

Summary:

A very simple system is possible.

• If WT output is AC rectify to DC.
  WT output must inclde a "blocking diode" to stop "backfeed" from mains power supply.
  This diode is usually part of the rectifier.

• Smooth WT DC enough that it will operate LEDs OK by itself without flicker etc when there is enough energy available.

• Wind turbine makes power at some nominal DC voltage = V_WT_Out.
  Assume this is ~= 12V below but any other voltage is OK.
  Idfeally this voltage is the maximum power point voltage for the WT - but this will seldom match VLED_load. A MPPT controller can be used to maximise energy provision but that is a subsequent step.

  This voltage V_WT_Out is in the allowable LED operating voltage range.
  WT actual Vout will rise above this voltage if load is very light and will fall below this voltage when WT is too heavily loaded.

• Independent of this solution a "controller" stops WT Voltage to LEDs from rising above max allowed value when load is light. This controller can be as simple as a voltage controlled switch that sends excess power to eg a light bulb or water heater.

• Mains power supply is provided which outputs a steady DC voltage via a "blocking voltage". The power supply voltage on the output side of the blocking voltage is named Vpsu.
  Crucial requirement: Vpsu is stable so that it varies very little between no load and full load. This is easily achieved electronically.

  Vpsu is inside the LED allowable operating range.

  Vpsu < V_WT_out by a small amount.

System "just works".

• When WT can supply load OK then WT Vout will be above V_WT_Out and diode from mains supply will "block".

• When WT can supply only part load WT Vout will be pulled down by excess load untiL voltage reaches Vpsu, when Vpsu will supply any excess.

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DETAIL:

This is an update answer based on the folowing now known parameters as at December 2nd 2011:

Object

• Save money by using wind turbine to power LED lighting as much as possible.

Known:

• 500 Watt, 12 VDC LED lighting load.

• Wind turbine with output typically in 100 - 500 Watt range.

• Grid electricity always available.

• No battery.

Assume:

• Nominal 12VDC wind turbine output.

• Higher under no load.
  Drops below 12V if loaded excessively.

• The WT output may be used relatively "raw" - eg providing 3 phase rectified DC output in a 12V DC system, OR may have use advanced controllers such as MPPT (Maximum Power Point Tracking) equipment. Regardless, the term eg 'WT output' will be used for simplicity and any extra assumptions and equipment wll be discussed when relevant.

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WT = Wind Turbine.

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(1) The easiest and cheapest system is to use diodes to combine power from the two sources.

The grid power system is a psu (power supply unit) which contains a "blocking diode" so that a voltage higher than it can be applied to its output without causing it damage and without causing current to flow back into the supply.

The output of the grid power psu is set to V_LED_min (ie a bit less than 12 V in this example).

The WT output is fed to the LEDs via a "blocking diode". This prevents grid power psu curent flowing backi into the WT system.

At any stage that there is energy available from the WT (wind turbine) it will cause the 12V "rail" to rise above V_LED_min and automatically supply whatever energy it is able to. When wind energy is adequate this will automatically provide all power from the wind.

As there is no battery this is almost a complete answer.

This is also, perhaps surprisingly, also an essentially complete answer for systems in which WT energy never exceeds the current LED load. Only when WT_energy > Current_LED_load do you need a battery or fancier control systems.

While the above method of using diode feed from WT and grid supply would also work with a battery, better controllers can produce better rsults

Answer 3

I believe what the underling question is; is it possible to have a two input inverter with a single output? The inverter would have a primary channel which it would derive its output power from “first” (being the turbine) and supplement the remaining power needed from a more reliable source such as the grid. This would be used for a hungry continuous load such as a heavy freezer. The idea, I believe, would be to offset the power needed to power a load with a generator that even at its best, would not be able to power a “hungry” load. A switching device would not be suitable because the power would need to be “mixed” from two different sources. I don’t believe that is possible.