PLC to manage renewable power sources

jaraujo1

Member
Join Date
Sep 2009
Location
Lincoln, California
Posts
2
I have unsuccessfully tried to find Automatic Transfer Switch (ATS) to handle multiple renewable power sources

- Multiple source of power: wind, solar, generator based on methane gas (human and animal waste) and others.

I was wandering if anyone have used PLC to handle the following tasks:

- Mix feeding one, two and other power sources altogether (parallel feeding to an UPS which in turn will feed the final loads.

I envision the following challenges:

- Low voltage signal generation from the high power source to
drive the PLC to provide the needed information

- The PLC program will handle the following tasks:
(a) Be able to simultaneously harness the power of the wind and the sun if both are available to feed the UPS.
(b) Be able to discriminate and harness the power of either if we have wind but not sun or viceversa.
(c) Be able to tell the methane generator to turn on if either of the wind or sun sources are not available.
(d) Be able to transfer power to the utility grid if the generated power exceed the load demand.
(e) Be able to use power from the grid if none of the renewable sources are available.
(f)If utilitlity power is available, grid hook up to sell power to the utility or to take power from the utility in the low probability event all the renewable sources are down.



Thanks,
 
OK see you have some terminology problems here. In essance you want to
1. Have multiple sources of power
2. Determine which source(s) has power and switch (parallel) them to what I assume is a DC bus.
3. DC bus will feed a battery and an inverter to convert to AC
4 Battery and inverter combination can be called a UPS depending on how you configure the inverter.
5. You want to parallel the inverter output to the AC utility.
6. You want the PLC to be the brain for all this.

Let us do teh hard part first.
1 Paralleling any generation source to a utility takes their permission and they have right of inspection and accptance of your equipment.
2. You do not need a transfer switch all you need is a breaker (or maybe contactor) with all sorts of protection on it - overcurrent, reverse power, and others determined by utility, etc etc.
3. You may be able to get all this control stuff in the inverter package. Recommend you look at Solectria website.

I would need to know what kind of generator you intend to use to comment and how you want to do that. IF DC it just ties with an output relay or breaker to DC bus. If AC you can tie to the house or to the utility if you want - going to take more controls.

One very important point depending on your state - your utility may be required to let you generate to them. HOWEVER those laws do NOT force them to let you do it unsafely. You really need to talk with the utility. Do not trust word of mouth, neighborhood solar gurus, vendors - I repeat talk with the utility. They have the legal capability and WILL disconnect you IMMEDIATELY - no court order required - if caught cheating a meter or unsafe non approved by them equipment.

The DC is a little easier.
1. Battery - will be your last resort so you can have PLC keep track of remaining KW Hr (volt x Amp hour) in it - basically amps in - amps out type calculation. Gets a little more complicated than this but in a nutshell. I would stay with wet lead acid yes you have to water yes you need to run gravities BUT it is the one that is best understood and least cost and most reliable. As a former submarine electrician who has spent a little time on em that is what I would do. battery will ahve to an output breaker / disconnect and overcurrent protection. PLC can also control charge rate whether from DC sources or from AC bus charger.
2. Other DC sources. I think it fairly easy to detect if you have enough energy. Wind could be done with a draft switch and solar could be done with solar radiometer ie temp detector in block of aluminum or a fancy sensor.
3. Both of these would have their own output breaker and overcurrent protection and some means of controlling DC bus voltage especially to prevent battery overcharge / overheat.

As mentioned I am a former nuc submarine electrician did all that generation, battery management stuff - we called it Barb Power and Light - that is what we were. I am a good electrician but would be challenged not so much by connecting all this stuff up and making it work but more so by the controls and sensor selection and the control algorythms in the PLC. This is NOT a good do it yourself project much less with stuff from Radio Shack or local sunshine company. I recommend
1. Talking with utility and see what they will require
AND see if they can recommend a couple engineering outfits. Ask them for a couple good "my own utility 101" books that you may be able to get from library.
2. Unless you are a very competent controls electrician or EE get a qualified engineering outfit to at least draw you up a block diagram of how all this works, a preliminary parts list and estimate of total cost.
3. Check out the Solectria web page - they make a couple home size units and commercial stuff (including 3 phase starting at 15 Kw?) and I believe they have some info on solar cells.
4. Talk with a couple of industrial battery outfits - the ones that sell forklift and UPS batteries and UPS systems. It is best to tell them you know nothing about electricity except flashlight batteries (even if you are a PHD EE and designed the BPA and TVA grids) get their brochures and recommendations for the 101 book.

Hmmm thinking on it a little more you forgot geothermal and heat pump. After all the money you are putting in whats another 20 K for a well and heat pump system. Course you could save on the well and make the swimming pool an ice rink in the winter I guess. You also forgot hydropower - you need to buy a house with a HIGH water fall.

I know of 2 or 3 solar etc etc outfits but they are here in Seatle.

Dan Bentler
 
Great information, thank you!

Dan,

Your feedback was great.....Your background is a great fit for a potential project and a new company direction I am trying to develop. Would you please contact me as follows:
[email protected]

Juan A. Araujo, MSEE,PE
Licensed Electrical Engineer
California, Nevada, Arizona and Texas
Principal, Dream Engineering
Consultant, Electrical Design Consultants
Math Adjunct Instructor, Sacramento City College
 
Hi Juan,

I think you'd have bigger fish to fry than just the ATS configuration.

Wherever you have multiple generators operating in parallel you need to be able to control
a) reactive power generation/consumption
b) frequency of operation

If you've got high end inverters on this stuff then it's not a problem. But if you've just got a cheap AC generator (as with the methane fueled generator) then you'll be hard pressed to sync this up with the main distribution network. Failure to have this generator synched to the distibution network when you bridge them together will result in very large currents, which will undoubtably short out your main breakers, as well as likely supply fuses to your neighbours (all depending on the rating of the generator, it may well die before the fuses / breakers).

It's most definately not just a case of shorting your 'generators' onto the incoming supply..
This is even true inside your own little supply network. If the wind turbine is an AC generator it will be tough to tie that into the PV system which would be an inverter.. you will again have synchronisation issues.
 
Juan,

We have done various mixed signal applications whereby the controller is configured for various voltages.

From your description, you will require analog signals as well as digital.

If you are interested in discussing your application further, you can contact me through the link at the bottom of this post.
 

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