Proportional controlers to manage Geyer loads

[NoordSolar]

Has anyone tried any proportional power controllers to accurately dump available solar power into a geyser. Devices usually chop up the mains 50 hz waveform. What you can achieve is a fine tuned load matched to available power . Problem is geyser is usually 2 or 3 kw element and if you want to maximize self consumption with only 1 kw of excess PV power you have to import 1 -2 KW of power , - it would be better to run at 1 kw at 100% solar ( duration to get to desired temperature will be higher ) . An example http://www.solarcontrols.cz/en/wattrouter.html  also http://www.directindustry.com/prod/celduc-relais/product-12114-525556.html ( available from ElectroMechanica )

 

[cvzyl]

NS, I have a Solar Immersion unit installed. It works great, dumps any excess to the geyser. Only problem now is that by around 15:00 geyser is on temp and thermostat switches it off. Have to look at increasing the thermostat.


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[SilverNodashi]

15 hours ago, NoordSolar said:

Has anyone tried any proportional power controllers to accurately dump available solar power into a geyser. Devices usually chop up the mains 50 hz waveform. What you can achieve is a fine tuned load matched to available power . Problem is geyser is usually 2 or 3 kw element and if you want to maximize self consumption with only 1 kw of excess PV power you have to import 1 -2 KW of power , - it would be better to run at 1 kw at 100% solar ( duration to get to desired temperature will be higher ) . An example http://www.solarcontrols.cz/en/wattrouter.html  also http://www.directindustry.com/prod/celduc-relais/product-12114-525556.html ( available from ElectroMechanica )

 

That's definitely something to try. I see the ElectroMechanica unit is about R450. 

CBI has something similar, which I'm contemplating using: https://www.cbionline.co.za/products/energy-control-unit-electronic

[NoordSolar]

21 minutes ago, SilverNodashi said:

That's definitely something to try. I see the ElectroMechanica unit is about R450. 

CBI has something similar, which I'm contemplating using: https://www.cbionline.co.za/products/energy-control-unit-electronic

CBI Either on  or off , not proportional control 

[SilverNodashi]

29 minutes ago, NoordSolar said:

CBI Either on  or off , not proportional control 

Fair enough, your approach is a bit different from mine, I have excess PV power to use and the CBI unit will help to activate the geyser element when the PV power is not being used by other appliances. 

I quickly scanned through the ElectroMechanica manual, and couldn't see the exact unit you referred to, please share the link or part number?

[NoordSolar]

11 minutes ago, SilverNodashi said:

Fair enough, your approach is a bit different from mine, I have excess PV power to use and the CBI unit will help to activate the geyser element when the PV power is not being used by other appliances. 

I quickly scanned through the ElectroMechanica manual, and couldn't see the exact unit you referred to, please share the link or part number?

http://www.em.co.za/downloads/J-Timers-and-control-relays.pdf   , Page J15 Item S04 or others around that page in catalog

[SilverNodashi]

17 minutes ago, NoordSolar said:

http://www.em.co.za/downloads/J-Timers-and-control-relays.pdf   , Page J15 Item S04 or others around that page in catalog

That's a different unit than what I looked at. Do you have documentation on this? The catalog doesn't quite explain how it would work. 

 

Using something like this would greatly depend on which inverter you have. If it's straight from PV, then it would probably work. But if you're using a Hybrid inverter, you would probably sit with the issue that the inverter would want to switch over to eskom / batteries if the load is more than the available PV power. Unless you could limit the output on this SSR to only 1KW, which I can't see if it's possible.

[NoordSolar]

HAve not searched for specific documentation for this but I see the usage as such that when you have an excess of solar say 1 kw from 11am to 2 pm you can run your geyser effectively as a 1 kw unit for 3 hrs as apposed to a 3 kw unit for 1 hr .  In a typically household you will seldom get 3 kw of surplus solar power but often will get 1 kw (or what ever number you choose )  You could permanently set the device to a fixed number or varying it trough a controller of a rheostat - easier than retro fitting a 3 phase element to a single phase geyser and selectively switching elements in and out to match available power . This is all to avoid using battery power as battery  usually costs more than Escom per Kw ( excluding "availability fees ".

 

[SilverNodashi]

4 hours ago, NoordSolar said:

HAve not searched for specific documentation for this but I see the usage as such that when you have an excess of solar say 1 kw from 11am to 2 pm you can run your geyser effectively as a 1 kw unit for 3 hrs as apposed to a 3 kw unit for 1 hr .  In a typically household you will seldom get 3 kw of surplus solar power but often will get 1 kw (or what ever number you choose )  You could permanently set the device to a fixed number or varying it trough a controller of a rheostat - easier than retro fitting a 3 phase element to a single phase geyser and selectively switching elements in and out to match available power . This is all to avoid using battery power as battery  usually costs more than Escom per Kw ( excluding "availability fees ".

 

I am not sure it will work as you think it might. The geyser element will want to use it's rated current, i.e. 13.6A @ 220V. So, as you say, with a restat you could probably "tune" the geyser element down and then use this device. But then, if you did tune it down to 1Kw (or just replace it with 1Kw) then you could use the cheaper CBI unit as well. 

 

The way I see it, this device will switch whatever your load is, upto 10A (too little for 3Kw geyser in anycase) on and off, controlled by the source. I don't see any mention about it controlling the current as well. So, you would have to add a 20A rheostat, and soon this whole excercise is just too expensive. 500w PV will set you back say R4K. How much will this cost?

[NoordSolar]

Its a phase controled device - I so instead of giving the element a full 180 deg cosine waveform  per  50 hz cycle it will for instance switch on at say 90 deg so providing zero current first the first 90 deg and full current the next 90 deg . and so one every 180deg . So in this example effective power if 50% of the nominal full power for a complete waveform 

[NoordSolar]

Here is a spec sheet , see fig 3 for transfer characteristic http://uk.rs-online.com/webdocs/0d13/0900766b80d1305c.pdf

[SilverNodashi]

21 minutes ago, NoordSolar said:

Its a phase controled device - I so instead of giving the element a full 180 deg cosine waveform  per  50 hz cycle it will for instance switch on at say 90 deg so providing zero current first the first 90 deg and full current the next 90 deg . and so one every 180deg . So in this example effective power if 50% of the nominal full power for a complete waveform 

I hear you, with the half sinewave, but I still don't think it will work as you hope it would. By the looks of it, you would need something in-between to monitor your load, available PV energy and usage and then activate as needed. If it's cloudy or rainy, say at 11am, the geyser should be switched off. If you suddenly switch on the kettle, this should switch off. A Raspberry Pi with either SolWeb or AICC ^might^ work, but will probably need some custom coding to accommodate this particular device and setup.

The Wattrouter which you linked in the OP, and cost aprox R4800 (before import + VAT + import duties) might work in this case, but will only work with a grid-tied inverter (#1), and may, or may not work with your inverter (I don't know what you have). 

#1: http://www.solarcontrols.cz/en/wattrouter_faq.html

 

Perhaps @plonkster or @Chris Hobson could chime in on this?

[___]

Dimmer switch. Creates radio noise. Harmonic distortion. Bad power factor. The inverter cares about VA not W. I've thought of it before but I still think a dual element setup is better. On phone now.. Might expand later.

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[Chris Hobson]

I use a simple relay that is closed by high battery bank voltage and with the fact that the Karoo is sunny most days it works well. Tried to keep it simple. Geyser element changed to 1500W which is more in tune with the excess generated by my PV array.

http://www.ebay.com/itm/Multi-function-Voltage-control-Relay-Timer-Delay-Switch-Voltage-Protection-12V-/271832274268?hash=item3f4a77555c:g:PsQAAOSwbYZXcIJf

 

[___]

Ok, full keyboard in hand again. So when you chop the waveform, say at 90° and 270° (it's so weird to use degrees when training wants me to use pi/2 and 3*pi/2 :-) ), you halve the rms effective value, but the peak voltage and current stays exactly the same. In practice you will therefore find that you have a 3000VA apparent power with 1500W real power, and a power factor of 0.5... not because the load is inductive and capacitive but because of the distortion introduced by the chopper.

It should get slightly better if you chop at angles greater than 90 or 270, so that your peaks come down, but it remains a noisy business.

I asked this question on stackoverflow once and the answer was to use a step-down transformer. A standard 220V->110V transformer will turn your 3000W element into a 750W element (power goes up with the square of the voltage for resistive elements). So that's not proportional control, but it could be a tool for creating a couple of discrete steps.

The only other thing I can think of: Autotransformer/Variac with a stepper motor! :-) Would have to be a beefy stepper motor with large driving circuitry... sounds like too much trouble already.

Or turn your AC into DC and PWM it with an inductor/capacitor to smooth it. A buck converter in other words. Also sounds rather complicated for the task...

:-)

[SilverNodashi]

Just now, plonkster said:

Ok, full keyboard in hand again. So when you chop the waveform, say at 90° and 270° (it's so weird to use degrees when training wants me to use pi/2 and 3*pi/2 :-) ), you halve the rms effective value, but the peak voltage and current stays exactly the same. In practice you will therefore find that you have a 3000VA apparent power with 1500W real power, and a power factor of 0.5... not because the load is inductive and capacitive but because of the distortion introduced by the chopper.

It should get slightly better if you chop at angles greater than 90 or 270, so that your peaks come down, but it remains a noisy business.

I asked this question on stackoverflow once and the answer was to use a step-down transformer. A standard 220V->110V transformer will turn your 3000W element into a 750W element (power goes up with the square of the voltage for resistive elements). So that's not proportional control, but it could be a tool for creating a couple of discrete steps.

The only other thing I can think of: Autotransformer/Variac with a stepper motor! :-) Would have to be a beefy stepper motor with large driving circuitry... sounds like too much trouble already.

Or turn your AC into DC and PWM it with an inductor/capacitor to smooth it. A buck converter in other words. Also sounds rather complicated for the task...

:-)

Nice explanation, thanx

 

In my case, I just need to get a 1KW geyser element and use that CBI unit + timer to use the excessive PV energy during the day. 

[SOLARWIND]

It would be beneficial to use a directly solar heated geyser with electrical back-up and a lower wattage element to suit the available solar power. Added insulation to the geyser will also extend the time the water will remain useful.

Using a load-shedding controller with a relay and a contactor, you can reverse the logic, meaning that when current increases, you could switch ON something instead of switching it off. These controllers come in various sensitivity from 5A to 60A which is useful if you want it to react sooner. Then you use one with a low Amp rating on the sensing side.(This is only the indication of the minimum value of current that will cause the device to shed the load on its other terminals and is not its max current rating).

Surplus solar generation usually occurs on bright summer days.......days when you'd rather want to use that power to cool your home or to filter your swimming pool. Run your aircon(s) or swimming pool pump when you have surplus power.