Arduino folks, is this sort of idea achievable?

[Gareth J]

Was reading whoever it was' thread that was making a PC tower rotary converter and got me thinking about a project I'd like to think through.

Background;
-OK understanding of most standard electrical components, happy fathoming my way round general 240v and 12v stuff
- basic conceptual understanding of microprocessors but no real world experience getting them to do things I want them to.

We have a small wind turbine that feeds the national grid when we over produce.

I'd like to design and maybe build something that would let me use some of the extra electric produced when it's really windy.

You can buy (and I have one; "solar iboost") gadgets that check electric flow to the grid via clamp meter and load up a basic heating element to store some energy "for free". This works fine but is limited to things that can handle varying voltages. Heater/heating elements/immersion heaters.

I want to design something that will check for oversupply and fire a relay when that oversupply reaches a preset amount. With a timer relay I can then run anything on 240v for a set period. I'm thinking of anything that will do a bit of energy storage, compressor, water pump, fridge, that sort of thing.

I can use the output from the solar iboost to tell me when there is oversupply.

I had briefly attempted to think of a way I could do this analog but quickly gave up. Maybe there is something simple though? Best I could come up with was to stick a relay onto the output of the iboost along with the heater I currently use. If the voltage got high enough to fire it, it would go. But this varying voltage would arc and quickly kill a relay I think.

How much learning would be required to do this with little raspberry pi type things? And where would be the best place to start?

Cheers!

 

[AndyStobbs]

Contactor is the relay, and maybe the timer from a star / delta starter, if it can be adjusted for the delay you want..

 

[Wedg1e]

We've been experimenting with some LCD displays that replicate analogue meters used to display Volts and Amps on old machines; they can be scaled, programmed and whatnot and IIRC they have a couple of outputs/alarms that can be set at whatever voltage/current you want, so one of those could, I imagine, read the mains directly and have its output configured to switch over at some suitable point. I think we got them from RS but I can find out...

Edit: this sort of thing...

http://uk.rs-online.com/web/p/digital-panel-multi-function-meters/8494624/

 

[carbon]

Not sure if this is what your after Monitoring relay it would need an additional contactor to switch the load

 

[Gareth J]

Not sure if this is what your after Monitoring relay it would need an additional contactor to switch the load

Yes, using that to fire a similar timed relay looks like it'd do just what I want! I know crouzet do a suitable one for the timer as I've used one before.

Those "clever" relays ain't cheap but pretty damn useful.

Thanks for the other replies too, useful also

 

[Robotstar5]

Broyce Controls do a nice selection of monitoring relays.

 

[carbon]

This site may have what you're looking for OpenEnergyMonitor but i haven't looked through the forum

 

[HughF]

So instead of selling your extra wind turbine kWhrs, you want to run them into a dump load???

I'd check the programming guide for the wind inverter, it might already have a facility for a dump load connection.

If the dump loads are on the downstream side of the inverter (the output) then they'll be running on inverter power, so it will be clean.

 

[GW8IZR]

Are the loads *only* going to be supplied during periods of excess generation?

In other words are they going to be on their own circuits?

Getting a signal and conditioning a contactor is straight forward enough, deciding what can be fed from time to time and still remain useful seems a bit more complex.

 

[garethp]

Hmm, I'm no expert but I don't think it'll work very well. What happens if you get a short gust? The relay would switch your load on and start to draw power but in the mean time the wind has dropped and you end up importing electric. I think most dump loads are resistive and PWM controlled for a reason.

I suppose you could program the arduino to switch a relay if excess power has been available for more that say 1 or 2 mins, then stay switched on for a preset time period unless the excess power drops to a preset low level?

A couple of links I've come across which may help are;

https://openenergymonitor.org/emon/
http://www.navitron.org.uk/forum/index.php/topic,16451.0.html

 

[Gareth J]

So instead of selling your extra wind turbine kWhrs, you want to run them into a dump load???

I'd check the programming guide for the wind inverter, it might already have a facility for a dump load connection.

If the dump loads are on the downstream side of the inverter (the output) then they'll be running on inverter power, so it will be clean.

Yes. However, the turbine is only a few kW so exported juice is estimated, not measured. Anything I can make useful use of is a bonus, 1kwh saved is 1kwh earned.

The inverter is an older transformer type and has no clever bits that I'm aware of.

Are the loads *only* going to be supplied during periods of excess generation?

In other words are they going to be on their own circuits?

Getting a signal and conditioning a contactor is straight forward enough, deciding what can be fed from time to time and still remain useful seems a bit more complex.

Yes, I'd run a socket I could plug stuff into that could be used as a dump load.

This is indeed part of the thought process. The best I've come up with so far is a workshop beer fridge - how decadant! Or a baby compressor to keep tanks topped up -actually useful. Or a dehumidifier - quite sensible as high wind often brings high humidity.

Hmm, I'm no expert but I don't think it'll work very well. What happens if you get a short gust? The relay would switch your load on and start to draw power but in the mean time the wind has dropped and you end up importing electric. I think most dump loads are resistive and PWM controlled for a reason.

I've thought about this, if I use the output of my iboost as the input signal, set high enough, it'll only kick in when the wind is really going for it and background loads are low. There will inevitably be times when the wind drops or another load elsewhere clicks on and I'm using electricity from the grid. I accept that this will happen. I think that it should average out in my favour though.

Thanks for the link too.


Thanks for all the replies, I'm still scoping this idea out for the time being so all drawbacks/ideas appreciated

 

[HughF]

I'd go battery/midnite classic mppt controller/outback gvfx inverter, personally and ditch the current setup - that way you get some standby power for when the mains goes off

 

[GW8IZR]

GW8IZR said: ↑
Are the loads *only* going to be supplied during periods of excess generation?



Johnser replied:

Yes, I'd run a socket I could plug stuff into that could be used as a dump load.

This is indeed part of the thought process. The best I've come up with so far is a workshop beer fridge - how decadant! Or a baby compressor to keep tanks topped up -actually useful. Or a dehumidifier - quite sensible as high wind often brings high humidity.

The output from your iboost thing could simply switch a timer relay which if sized appropriately would be fine.

I'd be tempted to charge a battery and invert back to mains - the added conversion loss would be better than something thats going on/off almost randomly.

I'm just going through a similar process with solar harvesting but I'm distributing the DC and not bothering with 240V, the target is 'always on' stuff like the CCTV, trickle charge maint of vehicles and alarms that all run nicely from 12V

 

[wookie]

We have a small wind turbine that feeds the national grid when we over produce.

I'd like to design and maybe build something that would let me use some of the extra electric produced when it's really windy.

Okay, just to check I've understood your setup correctly...

Your wind turbine is a grid-tied setup, i.e. it has a control panel that is connected to the mains in your house and it produces 240V. You don't need do anything else with that setup it's fine.

If your wind turbine makes 1Kw and you are using 3Kw then you are importing 2Kw from the national grid, if however your turbine is making 1Kw and you are only using 400W then you are exporting 600W to the national grid and not getting paid for it.

There are some combined import/export electric meters that will actually go backwards if your exporting, so you then use the national grid effectively for energy storage, but these are rare and good luck getting your supplier to agree to fit one.

Since you can't control how much power you make the only thing you can do is have a diversion controller send the excess you produce to an immersion heater (for example) rather than let it go to the back to the grid, electric heaters are excellent for this job as you can switch them on and off as fast or slow as required without them complaining, something your compressor/fridge/water pump won't like.

So your best bet is a diversion controller, I suggest you look here https://openenergymonitor.org/emon/mk2/diversion in order to ideally balance your supply versus load you might be switching your heater on/off multiple times a second.

 

[HughF]

Why aren't you net metered???

 

[Gareth J]

Why aren't you net metered???

It's the way they did it when it was installed. An estimate 50% of total generation is exported. We get paid a pitiful 3p or something like for the estimated export.

I have a diversion controller attached to this inverter but it's on my workshop's phase and there is only so much heat I want. Hot water isn't particularly needed. Especially in summer.

There is a similar setup attached to another phase but there's a house on that so not enough over generation to bother worrying about.

I don't have masses to play with, the iboost says it averages just over 10kwh diverted power per day for the last month.

 

[Gareth J]

I'd go battery/midnite classic mppt controller/outback gvfx inverter, personally and ditch the current setup - that way you get some standby power for when the mains goes off

Would be nice but I'm not about to go out and buy a massive stack of batteries and new inverters - just don't have the funds. Besides, I think this might upset the electric company, the "total generation" tarrif is the only thing that pays the interest on the machine. If they stopped that, it'd be pointless.

 

[Gareth J]

The output from your iboost thing could simply switch a timer relay which if sized appropriately would be fine.

Yea, I think that's more or less what I want to try, but need something a bit "clever" too as the varying voltage could quickly kill a standard relay.

 

[WorkshopChris]

I am watching this with interest, i need to upgrade a 3 phase supply to a new small workshop.
Problem is all the units on the farm share the same 100a incoming supply.
I want to add a contactor to the 63a 3 phase socket for the old miller tig so that if the total demand from the other workshops nears the limit it will sound an alarm for maybe 5 or 10 seconds then kill the welder power therefore saving the main fuses.

I have been looking at the open source stuff, but that unit from rs looks very good.

I will see if i can find you the data sheet for a under and over voltage relay i saw fitted to a friends compressor control panel the other day.