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domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 11:26pm 22 Sep 2019

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Sorry, lost the link to this topic, may be in the electrical section?

The suburb we intend to build in is residential with one hospital, which may draw a lot of power, so I am ignorant if my proposed inverter will ever drop out at >256VAC.

This forum had a simple solution, perhaps too simple to work properly:

Voltage sensing relay Geya GRV8-02 set to 255VAC to trip with a 5 sec. delay to stop repeatedly tripping and on tripping connecting a contactor to drive the 2.4 kW heating element from my 6.6kW PV. Q 1.: Does that sound OK to you?

WA does not allow feeding in more than 5kW if I wish to get the generous feed-in tariff of seven (7!) cents/kWh and I have chosen to be on three-phase power. The builder is offering a 13 kW reverse-cycle aircon. in my contract. 24 panels are needed for 6.6 kW, which legally can be 1.33 times larger than the 5kW limit.

Q2.: Unrelated to hot water, sorry, what is your opinion what I should do here and that question is definitely a tall order!

Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.

Winston Churchill

Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 1578

Posted: 12:40pm 23 Sep 2019

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The relays are not expensive but perhaps you might be better to wait and see how you go with the over voltage. If it's a new suburb they may tap the transformer correctly and you'll be a long way off overvolting. You Might also be able to have a chat to the installer and get him to raise the over volt to 260.
And before anyone arcs up with dire warnings of gloom and doom, I regularly see those voltages over the 2 years I have been here and yet to have a problem. Not unsual for power here at Midnight or 3am to be 250.

I have a voltage sensing relay on my hot water system.
Don't know how many times in different places it won't work. Lucky the relay and the HWS don't look on forums to know because so far it's worked perfectly.

There are a number of ways to set these up, I took my HWS completely off the off peak and run it off the relay alone. In over 18 Months only had to trip it in manually 4 Times but that would depend on the weather where you are and how many days hot water the tank stores. I think anything over 3 days is an ask from heat loss alone.

A timer could also be added so if the relay hasn't fired in 48 Hours, it will automatically kick in for say 6 hours and then reset.

As far as your solar limit goes, being a new home you are in a perfect position to set this up from the start. If you have the roof space, nothing at all stopping you from putting up a second array to feed the HWS direct. With a twin element tank, one element could be solar fed and the other from the mains. You could also use second hand panels to get the cost down.

You don't need the second array to do all the work, It probably won't do a lot in winter other than maybe if you are lucky negate the difference between the Cold Sub 10o incoming water and the 25-30 water temp coming in in summer. Couple of KW array would probably take care of all your summer and beyond water heating.

You have to set it up right for DC heating but certainly not impossible or expensive.
Another way to go would be have a second tank that the water went into before going to the main take that was hooked to an array. this would then be totally separate and pre heat the water before it went to the main tank. Wouldn't have to be as big as the main tank either. You could also set the temp on that higher than the main tank to allow for some dilution and extra heat capacity.

Y0U have to weigh up YOUR individual circumstances though. How much hot water you use, how many days are cloudy where you will be, what's your power going to cost on and off peak etc.

Are you sure you are limited to 5 Kw export? On the other side of the country here it's generally limited to 5 KW SINGLE phase and pretty much whatever you like 3 phase. Usually the FIT and other sweeteners cut off at 10KW so would pay to stay under that.

Another thing is Putting up more panels but getting an inverter where you set an export Limit. This means you could have 20 KW of panels but the most that will ever go back to the grid is 5 KW. If you have a house with a pool or that is all electric this can be a great thing because you run the house off your own power and send the full 5 KW back to the grid for a credit which then offsets your Night time useage.
Generally, and there is a wide range to put it mildly in power rates, You need to feed back about 3x what you use to negate the bill.

I have a large system because it gives me more power in winter when I really need it, Comes on earlier in the morning and later into the afternoon evening, gives me some power on wet and overcast days and I can run my AC etc and still be exporting.

2.4 is on the small side for most HWS these days but it is the one I'd go for. Much better with solar to go with more time than more power IMHO. Just check that is the element you are getting rather than a 3.6 or 4.8.

I also have an array that only comes on song when the AC is working. I do it with mechanical relays but a modern inverter would handle it just the same.
If you went to say 12 Kw of panels if you could fit them ( I have 9kw+ just on the shed) you could be running the AC and the pool pump for instance as well as everything else and still be feeding in the full 5 KW.

Ask the Builder what AC he is putting in? There are a lot of no name Chinese/ Cheapo brands now, Personally with a bit of insight, I wouldn't have anything other than Daikin or Fujitsu. If you have never heard of what he wants to install before, chances are the Fridgy that comes out in 5 years time when it stops working won't have either.

There is a lot to the HWS and solar setup and you have to look at what applies to YOU in every aspect and crunch the numbers. No good spending more than you will ever get back like on something completely unviable like a battery for instance or too many panels. Our hot water worked out to be about a dollar a day and one needs to keep that in mind when doing things to see how long the ROI is going to be. No use spending $5000 to save $300 a year. If you are spending $600 a year, then the returns may be far more rapid and pay off much better.

There are many things that the cheapest option is just to pay the bill ( and minimise rather than eliminate it) because trying to reduce it too far, say with batteries, is going to cost you more over all than you can ever get back. OTOH, I like as much independence as possible and am setting up to go off grid if that becomes the most viable option. It isn't right now but in the not too distant Future....?
We had very high bills as does everyone in the electricity dependent area, so the solar and other investments I made paid off in moths rather than years. I knew exactly how long each one was going to take to repay before I jumped though.

There are a lot of aspects to things that only you can know so no one other than you can make the final decision.

Myself, I would advise people to put up the biggest systems they can.
It's not about having 10KW of power or whatever the maximum is, it's about having 3 KW+ at 8 am and 5pm in summer ( I have 4 KW at 7Pm in the warm months) and still making a few KWH a day when the weather is crap.

Its the ramp up and ramp down that's where the real benefits are, not the peak power at 12Pm and that's where the largest systems pay off even over smaller, more efficient ones.

domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 07:50am 04 Nov 2019

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Thanks for all the info again, Davo.

A question:

There are two Geya Monitoring voltage relays with Numbers 01 and 02 at the end of GRV8.
GRV8-01 has a Hysteresis setting and a time delay setting, 02 only has a time delay setting.

I have always (wrongly) believed they are both the same as a time delay is necessary to stop the relay "machine gunning" if the voltage flickers. What is the difference between the two?

Thanks.

Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.

Winston Churchill

Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406

Posted: 11:00pm 04 Nov 2019

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Should work.

Use the excess available power to heat water.

When the water reaches max temperature, then start disconnecting strings of panels.

Cheers, �Tony.

Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 1578

Posted: 12:05am 05 Nov 2019

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The hysteresis as I use it is to stop the relay chattering when it turns itself on and the voltage drops.

Say you have the thing set to turn on at 255V. It switches in the 3.6 Kw? load and immediately the voltage drops to say 252V. Instead of the thing dropping out then kicking in and so on, You set the turn off voltage to say 250V. This will allow for The voltage drop the load itself causes and another appliance to be turned on without the relay falling out. It's a little trial and error to set up but very easy. You can see the voltage readout right on the screen so you can see what the load causes and set accordingly.

The time delay is also a stabilisation.
I am still quite surprised at how much the Light levels and solar output can fluctuate.
Clouds are one thing but you can also get Birds and I occasionally even get planes casting shadows enough to make an output drop seeing they can be pretty low on approach or departure from the local airport.

The time setting means the Voltage has to be at or below the presets for a certain time before the relay unlatches. This means if you get a bird or a brief cloud passing over, the thing does not immediately disconnect. It also means that if the voltage is high enough to connect, it waits a little to make sure. You might have some appliance that switches out briefly that causes the voltage to go up and rather than the relay latch then fall out, it waits to make sure there is enough power.

Conversely, with the hysteresis, If something switches in like a fridge or a pump with a high start up load, the initial inrush current even if it drops the voltage to below the cut-out, doesn't trip the relay because it waits to see if the drop remains. I have a Number of pumps and things like Compressors, welders etc that really hit the voltage hard on start up but cause much less droop running. Having the time delay does not make the relay drop out because the voltage goes below threshold for a couple of seconds.

From memory I have mine set to 15 sec for the delay.

I have a few of these things now and built a couple into cases with leads for various portable jobs I found.
One I used for diverting power to heat a drum of water in my little greenhouse.
Another one went on the clothes dryer so it turns on when there is excess power.
I'm able to " Stage" them by setting the voltage a little different so as to give them priority. water heater is first then other things are set a volt above. have one on my septic pump too so it only pumps when there is excess voltage. This way when the water is hot and the thermo cuts it out, the power can be put to other uses without the inverter dropping out.

I have cured that problem now but I still like using these things. At very least, it stops the inverters throttling and I get the max output from them as much as I can use it.

For hot water diversion, they simply sh*t on everything else.
Sure, they may not do weather prediction or other things I find Highly suspect on actual practicality some other products have, but the relays don't cost $700-1200 either like these other things which means they pay themselves back in months rather than years or if ever.

For use with swimming pool pumps or anything else, I haven't seen a cheaper or more practical devise to match them either. You could use a timer but they aren't much cheaper and will still run when you are pulling from the grid like on a cloudy day. Anything that is specific to any use is always stupid expensive and is highly questionable if it would repay it's own cost let alone anything beyond that.

I have had the first one on the HW Coming up to 2 years now and never had a problem with it. One of those things I look at and think what an absolute winner and am thankful I found the things because they have been so damn useful, cost effective and reliable.

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