load diverter

[noah]

If all goes to plan I shall have a few kw to use on site so I am looking to buy/cobble together a load diverter which will ensure that the minimum goes out to the grid. As I see it I need a combination of a reverse power sensor and a dimmer.
If reverse power is detected, dimmer ramps up until power is in equilibrium and vice versa.
As this is not a LOAD controller (for stabilising voltage and frequency) it can be a bit sloppy, i.e. if 1/4 amp is going either way it can be ignored.
Does something like this exist (maybe its  standard with inverter based systems?). If not does any one have any ideas and would one of you electronically more literate types like to collaborate on design and build?

BTW I am looking at a 6kw capactity

[Justme]

My understanding is that such a device is not needed at all.

The power is produced & if there is a demand for it it gets used locally first. It only gets exported if no local demand exists.

Justme

[noah]

If you are continually producing power and do not use it on site then power will be sent into grid. If you are not being paid for export then this is a free gift to the outside world. A diverter would automatically send any unused power into something (eg heating) . Don`t want to waste any of my precious power on the hoi polloi.
B

[stephend]

Could you provide some more details about your power generation system?  Is this solar with a charge controller, batteries and then grid export?  or grid connected inverter only?  Which make of inverter, etc?

[Justme]

If you are continually producing power and do not use it on site then power will be sent into grid. If you are not being paid for export then this is a free gift to the outside world. A diverter would automatically send any unused power into something (eg heating) . Don`t want to waste any of my precious power on the hoi polloi.
B

Then either get paid or dont grid connect, simples.

You could set up a secondary system that powers specific items & then charges the bat once no power is needed. Then use the bat to supply power when the
I assume wind turbine (as its 6kw) is not producing. 6 kw is a lot to use on site if its producing often.

Justme

[noah]

This is a hydro scheme so power produced is pretty continuous. During winter it would be more advantageous to use any surplus on site for heating. Whether it is worthwhile signing up to export during summer depends on what schemes are around next year. A load diverter would mop up any surplus and push it into resistance heating. Primary load would still take precedence and only the minimum needed would be imported from the grid.
This is an induction generator system. No inverters present. Full output is 5.5kw.Actual output? I`ve had 3kw on a cobbled together test rig. I think 5.5 is achievable with the proper gear. Rarely any shortage of water.
B

[stephend]

I would cobble together a control system from Phidgets (www.phidgets.com).  1 current sensor on the output of the turbine, another on the input to your home.  If A > B, then turn on relay 1, etc.  The nice thing about using a computer controlled system is that you can do fancy decision making with it.  E.g., you can have more than one load, ranked in order of priority and you can turn on different loads based on the available power and the weather.
You could then also expand the system to perform even more automation tasks, such as only turning the washing machine on when there's spare power (but once it's turned on, leave it on, no matter what the power fluctuations). 

If you're a bit handy with a soldering iron you could do the same thing with Arduino or PIC or other microcontroller. 

[Justme]

With 132kwh available every day I would either get paid for the excess or ditch the grid. Even with an all elec house for cooking & heating you should not use that much in a day.

Also with so much available 24 7 when will you use up whats been stored / diverted?

Dont know if you could fool a grid tie type one using a UPS or just go for a bat system with big inverter/s but a small battery bank as you dont ever actually need it to supply power just to hold the system voltage.

[guydewdney]

I have looked for such a device - and no - it doesnt exist.

The solution I thought of is a crude version of stephend's - usign reverse power relays in series - eg from these guys http://www.pentagoninstruments.com/acatalog/shop.html

the first relay set at 500w reverse, the next set at 1kw reverse etc etc and connect to export cable.

Sometimes however - KISS and just have two watt meters - and if you see loads going out, switch on the immersion

[Justme]

My inverter & solar charge controller both have a virtual switch that could be used to trigger a load & you can set various conditions to trigger it.

[noah]

If the system fulfils full potential then being paid for excess may be worthwhile.(dont count chickens) Don`t believe that I cant use 5.5kw: during the day my workshop soaks up far more than that all the time and 5kw doesnt actually go all that far when heating a cold stone 5 bedroom house.
I`m not comfy with computer controlled stuff (in this instance): simple problems require simple solutions. If I had a hierarchy of loads which required switching then an intelligent setup would be the solution. But here there are only two options: current going out? ramp up the ballast, current coming in? ramp down the ballast.
I have looked at a couple of reverse power relays but theyre not cheap (Broyce I`ve usually found quite reasonable and they are over £120 each)
With the amount of power possibly available the load dump needs to be  something which will soak up the power for indefinate periods: in this case a tank with 6kw of heating elements plumbed in to the central heating will do nicely. I`ll do exporting in summer.

[Justme]

Don`t believe that I cant use 5.5kw: during the day my workshop soaks up far more than that all the time and 5kw doesnt actually go all that far when heating a cold stone 5 bedroom house.

Perhaps during the day for a few peak moments but not 24 hours per day. Oh & the house will never be cold if you have that much elec going spare.


How much do you use (from actual meter readings not guesses) per day?

With a bat system you could save up the excess at night to use in your workshop during the day.

[noah]

Workshop (really factory) uses 6kw+ for lights. (+ about 300kwh/day 3 ph supplied by diesel generator).
Our house has a Rayburn and a Villager both fed by offcuts from factory. In winter Rayburn is on most of the time and Villager on for usually a few hours. Not sure what the heat output of these is but I guess at least in the 8/10 kw range. This adds up to approx 24 hours at 8kw and this house is not warm by most peoples standards (judging by our visitor reactions). Insulation could be improved I`m sure. We are facing a wood shortfall this winter hence the desire to use all excess power for heating.

[Alan]

What is this 6 K.W. device. ?

6 K.W. at what voltage. ?

What grid connect inverter are you using. ?

If you use the Aurora grid connect inverter and dump load it will supply up to 7.2 K.W. into what ever type of heater you connect to it.

The dump load can be modified to operate at a reduced voltage.

If you switch off the inverter A.C. supply all power will be diverted to your heater.

(  Remove all thermostats in the heater load. The load is there to protect the inverter. )

More high tech but still  keep it simple approach.

Presuming your 6 K.W. device is three phase. ? Use a three phase bridge rectifier to give you a D.C. voltage for the control system.

http://uk.farnell.com/vishay-formerly-international-rectifier/26mt100pbf/bridge-rectifier-25a-3ph/dp/9098550


connect as many  voltage sensing relays as you require.

http://uk.farnell.com/jsp/search/browse.jsp;jsessionid=14YDEUT2UW3EYCQLCIQZKBQ?N=0&Ntk=gensearch_001&Ntt=sm+125+230&Ntx=&suggestions=false&searchTerm=sm+125+230&_requestid=265680


RELAY, VOLTAGE SENSE, 50-500V  D.C.

Use the relay out put to switch either one relay for each phase if you are switching A.C.

Relay

http://uk.farnell.com/releco/c3-a30x230a/relay-11-pin-3pco-230vac/dp/1086849

Base

http://uk.farnell.com/releco/s3-s-s3-bc-s3-c/socket-din-11-pin-relay/dp/1086859?in_merch=true&



( Meaning one voltage sense relay will operate three larger relays, one connected to each phase of your generator. Use the loads of the same wattage and connect in star. ( more advice could be offered if required. ))

Or use three phase solid state relays.

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=2181921

Either connect a three phase star or delta connected load direct to this.

Or use a three phase bridge rectifier.

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=2278839

And use one heater load connected to this.

( thermo stats can be used to switch the three phase solid state relays or the mechanical relays. )

Lots of voltage sensing relays can be used if required.

Not so keep it simple. Use PIC micro and voltage sense driving pulse width modulated I.G.B.T.  It works very well but bit of rocket science required.

Can explain in more detail if required.

Edit. Assuming that your device is connected using  a G59 / 83 relay current in any cable will be export. Use current transformer and voltage relay or relays to switch various loads in steps.

With PIC and current transformers quite doo able.



With current transformer on export connection feeding a voltage relay / loads is doo able.

Regards

Alan

[Justme]

Workshop (really factory) uses 6kw+ for lights.

We are facing a wood shortfall this winter hence the desire to use all excess power for heating.

So wire it direct to the lights for when they are on & when switched off direct the power to heating in the house. A simple set of timers (put all lights on a timer for on & off & then a second one to turn on the heating) should do that.

Job done.