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Geyser load control on RE system


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For those who have solar PV an excess of energy will typically be available in the day when the sun is shining.

Obviously it's a good idea to utilize this excess power to power a large load (e.g. your geyser) so as to maximise the efficiency of your system.

For those who are powering their geyser with AC power from their inverter/s how do you control the geyser load on the system so it doesn't exceed the power that's available?

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19 hours ago, Richard Mackay said:

For those who are powering their geyser with AC power from their inverter/s how do you control the geyser load on the system so it doesn't exceed the power that's available?

The main goal is to use as much of the excess power as possible to reduce your electricity bill, in only a few installations, you will be able to mach the loads to the available power right through the day, but it most cases in trying to do so you will exceed the available power (Still better than drawing the full demand from Grid)

20 hours ago, Richard Mackay said:

how do you control the geyser load on the system so it doesn't exceed the power that's available?

Normally with a timer. (And in my case that will change to Sonoff soon) 

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Only a Sonoff POW would deal with that kinda power, and even that is a bit sketchy. 

If you could get a twin element geyser it would be easy with some basic home automation to activate the second element to overheat the geyser every time you have excess power available. 

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58 minutes ago, calypso said:

Only a Sonoff POW would deal with that kinda power, and even that is a bit sketchy. 

Why, if I might ask. 

13 minutes ago, Richard Mackay said:

How would you install the Sonoff POW

Just in series with the geyser. 

1 hour ago, Richard Mackay said:

Which Sonoff product are you referring to?

In my case it will be a Sonoff basic. 

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I have a Geyserwise that's configured to start about an hour after the batteries normally reach their 100% SoC on condition that the water temp is less than a preset °C.  It's crude because it falls over on overcast days, so I'd also like to build some logic into it that takes actual SoC & spare PV power into account.  But that would require some form of home automation to be put into place, and my setup is not at that stage yet 😞

PS: I use a Sonoff Basic to activate a "proper" relay to turn my pool pump on and off.  No way I'd run 750 W through the iffy little relay inside the Sonoff.  I agree with calypso - I'd hesitate to do it any other way, even with a Sonoff POW.  There's another post on the forum that shows a Sonoff POW that tried to run a pool motor.  Not a pretty sight...

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5 minutes ago, ChristoSnake said:

No way I'd run 750 W through the iffy little relay inside the Sonoff.

I hope the member on this forum that runs his 800 watt water pump on a basic will jump in. His been doing it for over a year now and that motor peaks at 20 amps startup. 

My geyser has a 1kw (resistive load) element, no inrush current, 4 amps max on a 10 amp relay??

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There's another post I saw where someone did the logic.

It boils down to a loop that checks whether the batteries are discharging over a certain period of time.  If so, it turns the geyser element off for a set period, after which it retries the whole thing again...

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Just now, ChristoSnake said:

It boils down to

what is really boils down to, is that you need some special sensors to measure light intensity and from that you can calculate how much power you should expect on that  specific moment -minus your current load will tell what exess power you have. 

We are so quick to say that if we have excess power we will use it to heat the water, but very few of the guys know how to see if you really have access power,  its just not that easy. 

Start your geyser when the batteries are full, even if you only have 500watt excess power, that is 500watt you dont have to pay for. 

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Yep, it is indeed not that simple to know when you have excess power!

You may turn on the big element/pump, and then change your situation from "excess energy" into "running at a loss" and "draining batteries to keep up" (depending of course on your inverter's config).  And there may be load-shedding scheduled for that evening, and that may be a Bad Thing ® when you're married and your wife expects a steady supply of electrickery that evening.

I normally check in on the system in the afternoons and turn off the pool pump if required (via the Sonoff) so that I do not have nasty surprises.  But I really do want to automate the process...

 

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47 minutes ago, Jaco de Jongh said:

I hope the member on this forum that runs his 800 watt water pump on a basic will jump in. His been doing it for over a year now and that motor peaks at 20 amps startup.

Here in attendance!

I have a Sonoff basic on my pressure pump and its been there for over a year now like Jaco says, I also have the POW on my geyser, its not been in there for as long as the basic has been on my pressure pump, but so far so good.

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46 minutes ago, Jaco de Jongh said:

I hope the member on this forum that runs his 800 watt water pump on a basic will jump in. His been doing it for over a year now and that motor peaks at 20 amps startup. 

My geyser has a 1kw (resistive load) element, no inrush current, 4 amps max on a 10 amp relay??

Using a 10amp Sonoff on a 750 w swimming pool pump with startup current off 8 amp for more than a year and so far no problems .

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I have a heat pump. It draws a lot less than a geyser element. It DOES need some regular maintenance. I run it twice a day *. Once early in the morning (this usually leave us enough battery to get us through until PV starts charging) and once in the middle of the day. I also have extra insulation on the geyser itself and all the hot water pipes clad. 

On a cloudy day we may run into a situation where we have to draw some mains, but it's still less than a regular geyser, the battery never discharges past 40% when we have grid, and most days it's not a problem.


* I only really need it on early days when our househelp is here, but it has only 3 programmes and they are by time only, not day of week. I thought of putting the more usual sort of timer switch in, but I recall being told that it's not good for the system to just turn the compressor off, that the "brains" of the system must control everything and be allowed to shut the compressor down. I can't get hold of anybody at Kwikot to tell me if this is so or not. 

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2 hours ago, Jaco de Jongh said:

How would you know you have excess power available?

Good point, without pushing back to grid its not as easy to determine. 

I guess one could use the logic that if conditions are right (time and weather) and loads are low (batteries charged), then start second element. If starting the second element results in draw from the at any time, then shut it off. 

Loop the automation and you should be good. 

 

Sonoff's are cheap chinese, you really dont want to try and push them limits on them. Plenty of stories online with them blowing up. I have never had issues (have about 25), but then all push small loads.

For a geyser, sonoff pushing a contactor is safe. 

Edited by calypso
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At the moment I'm building a solar system from scratch and I have been thinking about this. There are 2 advantages in my situation, first we can push back in Holland and 2nd There will be 10,8 kWp on the roof and 30 kWh DIY batteries. So what I will do is measure SoC with Victron BMV702 and use the relay to tell my home automation computer (Hubitat) the SoC is let's say 90%. At 80% it should turn the geyser off again. This will feed the geyser with 3 kWh when no other discharging or charging is involved.  After this the process will repeat when SoC is 90% again. I will be using an IKEA outlet (zigbee) to switch the geyser element. Hope this will work out well.

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Not being as familiar as I would like regarding this subject I asked this question wanting to know what other users do. I have a Sunny Boy SB 4000TL-20 and if a multi function relay is fitted you can configure it to detect the PV power available. (This is an optional addition that can be fitted as I understand it)

This is an extract from the manual when one configures it for this function: 

The multifunction relay switches the loads on or off depending on
the amount of power available from the PV array. If a battery is
integrated in the system, the multifunction relay will still switch the
loads on or off depending on the amount of power available from
the PV array, not from the battery.

I would expect any inverter to have this capability since it's critical to do dynamic load control rather than a timed schedule that presumes power is available..

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2 hours ago, ChristoSnake said:

Some folks had less luck running heavy duty loads directly off a Sonoff and shared their stories here.

One was a 200l geyser. they come standard with a 4kw element, no way a sonoff can handle  that. The 2kw element that lasted for 6 months only, I am pretty sure that was a loose connection, I have seen that way too many times in the last 30 years.. 

I dont think any of those to were caused by a substandard product.. but thats just my ipinion.. 

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5 minutes ago, Jaco de Jongh said:

"4kw element, no way a sonoff can handle  that" and "I am pretty sure that was a loose connection"

Agreed on both - those burn marks do suggest a loose connection!  Pity the connectors on the Sonoff Basics are so small that you can't get a proper cable in there and fasten it properly.  I even battle to get a normal screwdriver in there 😞

2 hours ago, Richard Mackay said:

The multifunction relay switches the loads on or off depending on the amount of power available from the PV array. If a battery is integrated in the system, the multifunction relay will still switch the loads on or off depending on the amount of power available from the PV array, not from the battery.

Richard, my guess is that the relay will cut the relay (& the load connected to it) when the available PV supply is less than the current load.  That's very easy to measure by the inverter, even though this will vary continuously if you have scattered clouds.

The opposite is more difficult to measure.  If your load is only 1 kW, the PV supply will also be 1 kW (plus a bit to cater losses in the inverter, cabling, etc.) unless you feed back into the grid at that time.  The only way (in my experience) to know if there's additional PV available is by switching on an additional load and then seeing whether the PV power increases to handle it fully.

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4 minutes ago, ChristoSnake said:

Agreed on both - those burn marks do suggest a loose connection!  Pity the connectors on the Sonoff Basics are so small that you can't get a proper cable in there and fasten it properly.  I even battle to get a normal screwdriver in there 

Yes that is true . The connecters of the Sonoff basic and POW 2 can be improved . Very easy to make a bad connection . I still like them but triple check the connections .

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So I've been thinking about this for a while, as I have a 1kw geyser element on a Sonoff TH16 with temperature control. I think the best plan I've come up with for determining if there is extra PV available is to use PV voltage. It definitely seems like there is a relationship between PV voltage when the load is low, and how much "extra" I could be getting out of the system. I have 4 x 340W panels with a V(operating) of 37.74V, or around 151V total (panels are in series.) If I look at my history, I can see on sunny days with no load, the PV voltage is about 155V, whereas on rainy days, it never really goes above 130V.

Under load is a different story, as the panels seem to operate at max power around 130V. I use Home Assistant on a Raspberry Pi to manage all of this so have setup a small routine to check the PV voltage during peak sun hours and low load. If above 150V, turn geyser on. I can then check how much I actually get and if it's terrible, turn the geyser off. If I get to 4pm and then geyser temp is still too low, I run it anyway to get to a minimum temp (55°C for us) to make sure I can have a warm shower at bedtime.

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10 minutes ago, JaseZA said:

So I've been thinking about this for a while, as I have a 1kw geyser element on a Sonoff TH16 with temperature control. I think the best plan I've come up with for determining if there is extra PV available is to use PV voltage. It definitely seems like there is a relationship between PV voltage when the load is low, and how much "extra" I could be getting out of the system. I have 4 x 340W panels with a V(operating) of 37.74V, or around 151V total (panels are in series.) If I look at my history, I can see on sunny days with no load, the PV voltage is about 155V, whereas on rainy days, it never really goes above 130V.

What inverter do you have? Doesn't it have the facility to indicate what power is available?

 

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