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Heating water from PV system


Tony Swash

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6 minutes ago, SilverNodashi said:

I currently have a 2KW PTC element (works more efficient than a normal element) in my geyser, with a Geyserwise timer running from 14:00 to 18:00. The water is generally 58 degrees by roughly 16:30 and then it switches off.

I would move the geyser feed to the other phase so it can run off excess solar which is fed from the Goodwe during the day, presuming your DB board is already split in two. Or does the Goodwe run your whole house?

To change the element, get in the roof, switch off your geyser, drain the geyser and remove the element, and replace with a new one. I would caution though, that you might need a plumber if your house has a geyser COC, or if you really feel uncertain about this. 

My DB is spilt in 2, essential and non essential like geyser, pool pump, aircon and oven. I thought that only essentials would fall on back up for night use. But now I see the geyser is on the battery back up. 

As you suggested, move the geyser feed to the other phase so I can use excess solar....can this be done without using the battery? I am told this can't be done without rewiring and putting another DB etc.

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6 minutes ago, Fuenkli said:

I guess the best you can do is to put the geyser on a timer and program the Goodwe not to use the batteries during the time the geyser is on. The best time for the geyser to heat would be early afternoon when the batteries are fully charged. I would also change the element to a 1 or 2 kW type.  

Can this be programmed? Not to use use batteries? 😣 I was told can't be.

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1 minute ago, xinath said:

My DB is spilt in 2, essential and non essential like geyser, pool pump, aircon and oven. I thought that only essentials would fall on back up for night use. But now I see the geyser is on the battery back up. 

As you suggested, move the geyser feed to the other phase so I can use excess solar....can this be done without using the battery? I am told this can't be done without rewiring and putting another DB etc.

without being overtly suspicious here...

1st off you have 2 dbs and were told that one is for essential loads like the geyser. now it turns out your geyser is wired to the other db...MAJOR PROBLEM!

the people who are behind this MAJOR PROBLEM also told you

5 minutes ago, xinath said:

I am told this can't be done without rewiring and putting another DB etc.

what???

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17 minutes ago, Gabriël said:

it seems your geyser is wired to your pv system - no comments as to the genius who did it - 1st will be to get it back to grid OR get a 1kw element in there and setting the timer for good sunlight hours [or manual if you have a cloudy day] if it still is on the pv with a 1kw element. now that this load is taken care of i am sure your batteries will carry you through a patch of load shedding if you don't stress them out.

Please help me understand...in order to use the excess solar, must my geyser be put on grid and not PV?

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4 minutes ago, Gabriël said:

without being overtly suspicious here...

1st off you have 2 dbs and were told that one is for essential loads like the geyser. now it turns out your geyser is wired to the other db...MAJOR PROBLEM!

the people who are behind this MAJOR PROBLEM also told you

what???

I suspect the wiring is incorrect. They geyser is not wired into the non essential load.... correct?

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2 minutes ago, xinath said:

Please help me understand...in order to use the excess solar, must my geyser be put on grid and not PV?

Both.

The Goodwe inverter is `n grid-tie, so it feeds PV power (and battery power if needed) back into the grid. Your house, in simple terms, is "the grid".

Now, the Goodwe has two feeds, one for essentials (which uses the batteries for backup) and the other for non-essentials. Both feeds are, or can be, fed from PV power. When Eskom trips, only the essential loads get power, again from either PV or batteries, or both.

 

The geyser should be moved to the non essential loads side, then it will be fed from PV, and / or Eskom.

You shouldn't NEED another DB just for this, chances are it's a matter of moving the live and neutrals. BUT, it sounds like you're not an electrician so I would highly recommend getting a qualified electrician to do it. Get someone else's opinion if you want. It sounds like your current sparky's see a gap to make extra money unnecessarily.

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5 minutes ago, xinath said:

Please help me understand...in order to use the excess solar, must my geyser be put on grid and not PV?

as i have it the geyser would be a good place to use excess solar especially as you have a conventional geyser but with a 4kw element the pvs will not be able to carry a moderate household load [we don't really know what is on the essentials side of the db, there could be other things wrongly wired!]  plus the geyser. so 1st of get a lower wattage element into the geyser [plus the correct timer settings] in which case i would say it can stay on pv.

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@xinath I think there is some confusion here regarding how your inverter works.  You have to know this in order to fully utilize its potential. The Goodwe manual has some good information and there is lots of excellent stuff on the web regarding the difference between inverters and how they work.

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Okay understood....thank you to all....I have gained so much more than I thought😣

Correct me if I am wrong:

In order for the system to be correctly wired:

  1. Essential and non essential loads both need to connected to PV and grid.
  • this is so that excess power can be diverted to the non essential loads like geyser, aircon, oven etc
  • If there is not enough power for say aircon, then it should start pulling from the grid and not the battery 
  • My geyser needs to move onto the non-essential load on the DB, this will then eliminate the geyser pulling power from the battery?
  1. The PV will run the house needs and simultaneously charge the battery  in order to minimize grid use
  • Example on a cloudy day, there is enough power to supply the house, but barely to charge the battery - would this affect the performance of the battery in the long run. What I mean is, does the battery need to be charged to 100% everyday? It is currently set up for night use at 70% DOD, I have a 20% back up for load shedding.
  • what takes preference battery charge or running currents needs first?
  1. I will look at getting a plumber to change to a 2kw PTC element for the geyser, sounds like a cheaper solution rather than adding a solar geyser, then set timer
  2. My panels are north facing, Its mid day and the sun is also shining on the south side, would it be wise to add additional panels here? I added PV panels and solar pool panels and now have no more space on the north facing side.
  3. If my inverter is 5KW and I already have 3.96 array, does this mean that I can only add a max of an additional 4 panels (using a 330w)?
  4. Lastly and apologies for so many questions.......what is the average persons night use when everyone is asleep? I have the usual, fridge, chest freezer, outside lights x2  (all led), electric fence, alarm. I see it fluctuates but on average 400-500w, does this sound correct?
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@xinath i think it would be best if you call your installer over and have him explain to you in detail how your system works. It goes beyond the scope of what i can do here. Maybe @plonkster can? I can answer some of your questions though.

29 minutes ago, xinath said:

does the battery need to be charged to 100% everyday

no. you have lithium batteries. there is no partial state of charge problem to worry about.

 

33 minutes ago, xinath said:

I see it fluctuates but on average 400-500w

mine is around 350W. Your night consumption is rather high. Try to find the reason and see if you can reduce it.

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On 2019/03/10 at 3:59 PM, Tony Swash said:

Hi All,

I was always keen on heating the water in my 150l geyser so I installed a 2kw element 220 vac and had it switch on via a Geyserwise controller from 6am - 8am.

Result- Disaster. The current drain on the batteries was so high that after running the house all night, once the geyser came on the inverter tripped due to low voltage. I spoke to the guys at Geyserwise and they sent me a 400 watt PTC based 48 vdc  element. This gets turned on at 9 am and merrily runs until 5 pm using the excess power from my panels. 

At the end of the day the geyser (inside and lagged) reaches a temperature of 56 degrees C. I find that this is sitting at 50 C in the morning and easily provides a bath and a shower. I have forgotten it on a few occasions and the temp was 72 the next day. The PTC can run dry if the geyser has no water. I use the geyserwise set to 52 degrees so if the weather is cold it kicks in the 2000 watt PTC element (220 VAC ) and runs for about 15 mins.

Morning 

 

Do the guys from Geyserwise install this?

I want to change over, any recommendations for someone in Jhb North?

Is the kick over to the 2kw on cold days is automatic or do you have to set it somewhere?

 

Thanks

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  • 5 months later...

Sorry guys, new to this so don't want to show too much ignorance here, but why not fit a DC element that feeds directly from the charge controller which dumps when the batteries are fully charged? That way all the excess electricity is used to heat your water, without having to go through batteries and an inverter?

Or do I have this completely wrong?

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  • 1 month later...

I've added a 100litre geyser in series to my 150litre eskom geyser. Replaced the 2kw element with a 4kw element. I'm running straight to the element,  no inverter or any controller.  I have 4 280/300watt panels connected in series (thermostat is disconnected,  waiting for my SSR and heatsink to replace thermostat function) .  That way I match the element ohms quite closely to the panels resistance. It push +-810watts into the 100litre geyser.  My average water temperature is between 60 and 75 degrees.  When we shower/bath,  water flow from the 100litre geyser into the 150litre Eskom geyser.  So I end up with a hot 150litre geyser,  and the next day the 100litre have time to heat up before the water get used in the afternoon.  This week my Eskom geyser never switched on.  I burn 6 units a day,  compared to 12 units when I didn't preheat the water. The PV panels are mounted on my bakkie's carport acting as the roofsheets.  Double win: Shade for my bakkie + hot water. 

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  • 2 weeks later...
On 2019/09/07 at 6:35 PM, phil.g00 said:

It's not impossible, but what must be addressed is the in-line thermostat is not rated to break DC and or that high a current and obviously the element has to changed to suit.

Having investigated the Geyserwise PV system I notice they use PTC heating elements. The reason (I reckon) is because they don't want to have to switch DC which is what they use to heat the element. The PTC current drops off substantially when it gets to temperature.

So if you use a PTC elements you don't need a thermostat.?? 

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35 minutes ago, Richard Mackay said:

So if you use a PTC elements you don't need a thermostat.?

I am not familiar with these, it would seem like it would work though.

My thoughts:

I have considered something like this to limit voltage spikes to the batteries during switching, that will also delay the throttling of my PV inverters, so as to make use of the excess power.

It goes like this for a DC geyser element:

My MPPT's (outbacks) have a 200Hz PWM output that can be configured to a voltage relative to the battery charging voltage (amongst other things).

I would use this PWM output to switch an SSR so as to get a smooth, but very fast, variable load. I'd then put the thermostat in series to supervise the pulse stream.

Incidentally, this is how I'd make a dump load for wind generation. ( Which I don't have)

Victon MPPT's have a similar contact I believe but it is straight ON/OFF,  they have a PWM output but it seems to be solely linked to a nightlight function.

 

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