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Forum Index : Microcontroller and PC projects : H/W system with 6,6 kW solar PV in WA, do I need a solar H/W panel?
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| domwild Guru  Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Hi, In WA we do not have an off-peak tariff and for a new build I am wondering if with a 2.4kW heating element in a 200 l tank (two pensioners) I can save myself the plumbing, one solar H/W panel, pump and temp. sensors necessary for a split system by going directly from inverter to element via electrickery? For single phase 5kW is max. to be exported (WA), but panels are allowed to be 130% larger, so in WA they are all selling 6.6kW panel systems. Bad news as an aside: Just read in one state (VIC?) they are thinking of dynamic export limits, so your inverter will have to listen to the web and adjust - get a new inverter?? So called "hot water energy diverters" cost about $1,000, they become active if export is greater than 100W and use smarts like PWM or phase shift to feed the H/W element. Q.: If I ask my electrician to install a voltage sensor after the inverter and a contactor to switch in the element, will 1. that work, and 2. can I save myself putting a solar H/W panel, etc. on the roof? Also, in the suburb (Bentley) I am not too sure if inverters switch off habitually during lunch time as the voltage goes above 256VAC and that would be another trigger to switch the element in. Have lost the link to a forum member, who had success without a $1,000 diverter, so I am asking for help again. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Myself personally, I would not even think about going to a Direct water heating panel for exactly the reasons you state. Running wire is easy, Plumbing is not so much so and is more expensive as well as invasive in the home and I believe more complicated to replace when needed... although that may be not a concern for you as replacement of things for me isn't a big issue when they are likely to be around longer than I will be. The BIG problem with direct heating for me is in winter they often do nothing and in summer, your water may be boiling by 10 am and then the heater sits there doing.... nothing. With PV, once the water is hot the power is offsetting your other household consumption and/ or giving you some feed in credit to offset your night time costs. PV is working for you all the time basically, direct is a one trick pony and from what I see, is more exy than PV anyway. 6.6 panels on 5 Kw inverters are pretty standard setups now. Haven't heard of Dynamic export limits but not surprised. They will wheel out all sorts of cock an bull excuses but really what it amounts to is trying maintain as much revenue as possible for the power companies and Tax $$ for the gubbermints. Be aware that -some- power co's allow you to have say 10 Kw of PANELS but an EXPORT limit of 5KW. The panel array is arbitrary, the inverter doesn't care. I have inverters hooked to double and more their rating and they are perfectly fine. The advantage is panels are cheaper than inverters and when you over clock them, it just means you make more power in the morning and afternoon periods where in my experience the REAL benefits are. Peak power is fleeting, keeping the average up is where the money is saved. You may like to check retailers in YOUR area to see what the deals are. May well be 6.6/5KW is all you can have but do your home work and CHECK. Diverters are IMHO a complete and utter ripoff and tantamount to a scam. Let me pull some rubbery guesses out the air and crunch the maths for your situation. Lets call the diverters $500 because they are available for that and that is enough to prove my point anyway. For the $500 cost, not counting insulation you could buy @ say an average price of .30C KWH, 1666 KWH of electricity. Going by a guess of 2 people who don't shower for 30 min at a time, I'm thinking the cost of heating your water is going to be about $50 per quarter, 200 Yr. maybe. so $500 is going to buy you 2.5 years of power. BUT>>> you need to SAVE that $500 between what it would cost you without the inverter. No way in heck the MARGIN which is what you need to look at because they don't make the HW completely free is going to save you that in even 5 Years because it's the DIFFERENCE of with and without you have to look at, not the cost of the water heating normally. If we take those figures as somewhat realistic, and I have made them conservative in omitting install cost for a start, You can see that at bare minimum it's going to take you 7.5 years just to recoup a $500 cost, Plus install on the things. I have seen some websites do breakdowns on the things and they came up with 10 years and like me think the klunker is the things are not going to last near that long so like batteries, they will never recoup their cost in savings of their purchase price so are a dead LOSS not a saving at all. Something else to keep in mind... In winter when your incoming water temp is colder and requires more power just to offset that to summer incoming temps, You will have very Little excess solar to divert to the tank anyway so the diverter will do very little to nothing. In summer the thing may only need to kick in for an hour or 2 and then the water will be hot and it will sit there doing nothing. Again. You would be FAR better off get putting a $50 Timer on your HWS so it only came on between say 10 and 2. Sure there will be cloudy days when you will pull from the grid but the diverter wouldn't have worked in that case anyway so you would be no worse off.... and you have at least $450 up your sleeve in the price difference which will probably offset the timer inefficiency difference for 10 years anyway. Q.: If I ask my electrician to install a voltage sensor after the inverter and a contactor to switch in the element, will 1. that work, and 2. can I save myself putting a solar H/W panel, etc. on the roof? Yes. Both times. I put a voltage monitor on My HWS with a relay to carry the load of the element. Mine is 3.6 KW but I would recommend a 2.4. This will pull less current but take longer to heat the water which shouldn't be an issue. If you pull more current than is coming from the solar, You'll be pulling the rest from the grid and paying for it. I'd even suggest going to an 1800 or 1200W element if you can get them. Some days my relay doesn't kick in at all but we have 3 days before the water goes too cold with no input at all. Even if you don't get the water up to full temp and only offset what you have used for the day, still perfectly fine. I turn my heater right down in winter to save even more power. The greater the difference between the water temp and the ambient temp, the greater the heat loss. I'll turn it right up again now when I remember so I can bank some extra heat if he get some bad weather. Also, in the suburb (Bentley) I am not too sure if inverters switch off habitually during lunch time as the voltage goes above 256VAC and that would be another trigger to switch the element in. The way my setup works is the Voltage relay (about $40) is set to look at the voltage in the circuit. The solar pushes it up when it's generating and when it hits the trigger limit which indicates there is plenty of power, it kicks in. Clouds come over, output drops, so does the relay and sits there waiting for the next good output. Some days, does not heat at all and we don't even notice. In the last 22 Months since I put it on, I have had to kick it in manually 4 times. Your weather may be different but that's been my experience. I took the HWS from the off peak to a standard power feed to which the solar is attached to so I get NO hot water bill at all. Given I'm in excess of my solar power over what I use about 8-9 months of the year, I'm getting free hot water at least that long. Again I would say even a timer on your HWS would put you far ahead of one of those stupid Diverters. -MAYBE- and it's a HUGE maybe, if you had a house full of kids and a 10KW HWS they -MAY- return their investment but I still highly doubt it. For a house of 2 mature people, not a hope in hell even if they did last 20 Years. Your hot water is a big thing in making your solar pay for itself. Naw all this said, be aware that a lot of new inverters have diverters built in. Fronious, SMA and others have the feature in the inverter that they will send power to your HWS before they send it back to the grid. Again this is another homework exercise for you. See what they cost above a standard inverter. You may be able to buy 10 after market voltage relays for the price difference of the inverter with built in diversion. Also look at the cost of the power for the heater as against what you get as a FIT You said there is no offpeak so I would be certain you are better off using your own power before sending it to the grid. Just to add to my Novel ( I have to write one of my white paper guides on this as well) there is another alternative still and potentially a very good one.... The limits on panels are for GRID TIE. You can basically do what you want with off grid if you are concerned about the rules and regulations ( which I am not) and as such you can set up your water heating to be independent of your grid tie system. Used panels are very cheap now, I pay at most, $100 Kw. IF you had the roof ( or yard space) You could set up an array and dedicate that solely to the water heating. I would expect 2KW would be all you needed to cover the great majority of your needs. The best way to do this would be invest a bit more in a dual element heater. Put the bottom one on the solar and the top one on the normal power or voltage relay etc. Doing it this way it would not take anything most of the time from your grid relay and you would get more FIT to offset your night useage. Yes, this IS more work and expense and it may not suit your situation but I'm just throwing it out there as maybe it does. You can run DC power BUT, you have to have special relays to handle it. Not difficult, just have to get the right gear and set up the tank a bit different. nI am using such a system for greenhouse heating and it works well. Some of the resident geniuses here have put up some circuits for controllers to make this type of setup give peak efficency so maybe they would do one for you if your expertise lies in other places as does mine. Even direct connected, you'd probably get all the heating you wanted the majority of the time if you did the numbers on the resistance V's panels. The final suggestion would be look at how much of your power cost goes to hot water in the first place. If you are as I suggested spending around $50 a quarter for hot water, then the extra cost of an inverter with built in how water circuit may not be worth it for you and a timer or relay would repay itself far more quickly. I really love my relay and it gives me great satisfaction. Yeah, we are careful in winter as there isn't any power to spare but it was only the other day I announced to the family, " Solars Up, you can shower till you look like a prune and wash your clothes hot enough so they only fit a doll when they come out, I don't care for now." It's a very satisfying thing not having to worry about the cost of something know you are getting it for free. :0) All our water is recycled into tanks I water the garden with so we get double use out of our water as well. As there isn't ever enough water for the garden and as I have to use the hose, may as well enjoy what we do use. Anyway, I would straight out say a person was mad to entertain the use of one of those Diverter things but a voltage relay or even a simple timer are good, smart, small investments that will pay themselves back quickly. |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Thanks, Davo for that long explanation. I believe you have helped me before on this forum and topic, but I managed to lose all the info, but this time I am going to print it out. It has even been suggested to set the thermostat a bit higher to store the energy that way, but may need to have extra plumbing to stop young children from being scalded. The idea of using two elements is a good one. I would say tanks fail due to the owners (me!) forgetting to replace the sacrificial anode every six (?) or so years, so elements can probably be had from scrap yards, but possibly not so many low kW ones. My builder is putting a 13 kW reverse-cycle aircon. in and as this thing is an absolute monster, it will pay me to place more panels on the roof anyway. The builder is quoting about $400 extra for three-phase connection and one firm is quoting $300 extra for a three-phase inverter. If the web is correct, I could even export 3 x 5kW, but one sales woman said, in WA you lose your generous feed-in tariff of 7c/kWh if you export more than 5 kWh in total? As you have a "black belt" in electrickery, may I ask if it is worthwhile to go three-phase in our house hold? Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| BrianP Senior Member  Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Please allow me to chime in here(sorry Davo)... Yes set the thermostat higher, BUT... There will be a trade-off between extra energy stored & that lost. I don't know how you would arrive at the median without months (years?) of trial & error. Also, the extra cost of mixer valves to limit the supply temp may well tip the iceberg in favour of NOT going this way. Here in Vic. the max delivery temp for showers etc. is strictly mandated. And, the life of the element will reduce with higher temps. You've reminded me to check my sacrificial anode...  Re the aircon - the 13kw only applies when & if it's working flat chat. You may never reach this level. When you add the cost of a 3phase connection (I'm surprised you only been quoted $400 extra - but if this is a new install it might be right). If you were upgrading an existing installation you would need new mains & switchboard. By the time you add this and the inverter cost, plus the potential loss of the "generous" (I think not) FIT I'm not sure it's worth the 3phase option. You would need permission from the supply company anyway, & I'm not sure it's possible for a domestic installation. It will take a long while to recover the cost. We only have a 3phase connection because of the 24kw of floor heating, apparently we were lucky to get that at the time, & it is now absolutely no value to us. It's actually a disadvantage because we would need a 3phase inverter to grid connect the solar. Apologies if I've hijacked the discussion, but your circumstances WILL change down the track & seldom in your favour...  B |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Happy my rantings can help someone. People here have helped me which I greatly appreciate so glad I can pass it on. I used to crank the HWS up to the max in my last house because it only had a small system and by cranking it hotter you effectively get a bigger tank because you use less hot water and more cold. As I and Brian alluded to, the hotter the water, the greater the losses as well. The greater the difference between hot ( the water) and cold ( the ambient Temp) the more readily the heat wants to get to the cold. -I- would only turn the temp up if you run out of hot water and if you think that may be a possibility ( unlikely with 2 people) get a bigger one from the start. Of course bigger tank, more surface area, greater losses still. I think the 200 set to min temp, (65-70?) would be ample. Also remember, if you heat this thing through the day and you shower at night normally, then the thing will have only heater up hours before and the losses will be minimal. If you normally shower in the morning, different story. Not a benefit you'll have but either way, if the water heating is substantially free, then not so much a concern for losses. As for the mixer valves.... That may well be a requirement anyway regardless of your temp setting. Over here the max from bathroom taps is 50oC. I -think- kitchen sinks are different. Your Plumber/ builder will know. Personally, I'm a bit Meh about that. My kids grew up without mixers and I don't ever remember them burning themselves. Spose if they came from a home that had them and they were not properly supervised in someone elses house... I'm just old school and was very big on teaching my kids personal responsibility but that's another outdated story. I have been through the local Friendly scrap yard a few times and all I could find was 3.6 and 4.8 elements so that may be true. OTOH, you can get loads of different elements from Fleabay for $30 delivered... even 12, 24 and 48V ones. Just check it's an inverter type. I think they nearly all are now but it would pay to check and work out a deal to upgrade if it's not. I would also Highly recommend a Daikin or a Fujitsu Unit. Good mate of mine is in AC and that's the only 2 brands he will touch even though there is more money for him in a lot of others. I think it ALWAYS pays to have as many panels as you can but I'm obsessed so ... :0) I believe it varies from provider to provider but most times over here it's 10 Kw so regardless of the number, there's definitely a cut off limit. As I said before though, that's EXPORT which is different to GENERATION. As it is, you could have 20KW of panels ojn the roof but if you only EXPORT 5kw or whatever the number in your area is, you are fine. Why would you want 20 Kw of panels but limit export to 5? Because you could still be exporting 5kw and getting your 7C fit when the water is heating, the mrs has the oven on baking and the clothes dryer or pool pump ( say) is running. That would all be free and you'd be earning .35C hr rather than paying $1.20 hr to run it all. Hard to say. I imagine you will actually have fairly low useage. If your not having a pool or something else high demand other than the AC which will probably only pull 4-5 Kw anyway (13Kw will be the Cooling power not the demand) you don't need 3 phase. They tend to dictate it if you need it because they will limit you to how much you can pull per phase and work it out on I think it's 80% of your total POTENTIAL draw. They will say if you have for instance the water heater, stove/ oven, pool pump, loaded power circuits, AC on etc your draw will be this much and they have a formula as to what that "equates " to in probability and come up with a number. If that number is higher than the per phase allowance, then they will dictate you have to have 3 phase and spread the load. The rating per phase also differs. Some places and older homes could have 60 or 80A. Now it tends to be 40A but again, different with every provider so you have to check what the deal is in YOUR area. If you didn't have to get 3 phase, I probably wouldn't. The only real benefit is you have the potential for BIG power. If you are going to have a big garage/ workshop that the next owner could potentially put machinery in like lathes, mills, Big welders, plasma cutters etc, then that would likely add resale value if you ran it there as well. If it's a more average home with an attached garage primarily for vehicles, then I'd say there is no advantage. Also, it -may- cost more for a 3 phase AC and your builder may want to pass that on. I have a 3 phase AC now but when it dies, I'll be going single phase on that for my own reasons and the recommendation of my mate in AC. I remember when looking at this place I went to the meter box and a couple of other blokes arrived very quickly then we all headed to the shed to see if it was on there. It wasn't but it's only going to cost me $1300 to get it put up there so not bad I reckon. I know it killed off 1 other buyer who was keen on the place who literally walked away when there was no 3 phase up the back so the $1300 may have been saved 10X over taking him out the bidding! I only want it so I can pump back the full power potential from the 9 Kw of panels I have on the shed and I want to put a 3 phase diesel Generator up there I can run the whole house from in case of power outages which I'm certain we will be getting this summer when the grid overloads from lack of base load power. I could just up the single phase there now to 6mm and run everything bar the air but by the time I do that, probably going to cost couple of hundred more if that to go the whole hog and run 6MM 3 phase. Definitely be an advantage at resale time here. Thing is even only having single phase up there now, with the solar I CAN pull bigger power. I have wired a Hi current outlet(s) up there which is handy when I want to run the compressor and the plasma at the same time which is overloading a standard circuit. On a clear day, I can run them both and more and still have power to spare as I have 15A from the mains and another potentially 20A from the solar. 40A is only about 10 Kw so if that is their limit and you have electric stove, electric HW and AC, you'll have to go 3 phase for sure. If their allowance is 60A or above, you should be right with single phase. If the stove is gas, you may scrape in on a 40A. It's another variable you will have to ask about as to what applies to where you are building as it's all different in various places according to the provider. There is also the option to bring 3 phase to your meter box but only be connected to one phase. That may be the best option to go for if allowed in your area. Means you can expand in the future without the high cost of bringing the 3 phase from the pole and may be an advantage at resale. If somone later wants to put in a pool or spa or whatever, then all they do is hook up from the board and get another meter if needed. Again, If you don't NEED it, I personally wouldn't bother. As your export will be limited to 5Kw it seems ( check were the FIT cut off is, 5 or 10 KW?) regardless, then no advantage there. If the cutoff is 10 KW, then see if you have the space to put that many panels up in a WORTHWHILE direction and what the roof tilt will be. Also check for potential shading issues from trees and double story Neighbours etc. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Mate, more inputs and POV the better I say! Big difference between Hijacking and valuable input and presenting additional aspects of consideration. One thing I was going to say in regards to the Voltage relays was I had the perfect day for it today. Morning was gloomy and looked like more rain. by 10:30, the sun was out bright and hot BUT, with the haze the inverters were maxxed out that early. By 12:30 it was pretty gray again and by 1:30 the sun was back out. Another 30 Min and sun died for about another hour then after that it was a beautiful afternoon till the sun went down. I was working outside so watching things and the relay tripping in and out. Perfect day for the relay to really earn it's keep. These 4 seasons in one day are not rare if not frequent round here. At first I thought I'm only going to get a partial heat today and I wasn't worried. By the second sunny period I thought probably be about breaking even but when I checked the last time, there was still plenty of sun and the thermo on the heater had tripped meaning the tank was up to full steam again. I have the voltage relay and a 20A relay in a weatherproof box on the side of the heater. Relay senses the line voltage and when it gets to the voltage I have set which from memory is 249, it kicks in. I know at this level there is enough solar to run the heater with some clearance. it's set to a minute delay when the voltage falls below that before it kicks out and 15 sec when the voltage is met before it kicks in. The control box is simply wired between the supply and the heater itself to make power available or not. heater thermostat functions as usual and isn't touched. Probably less than $80 tied up in it all up and money REAL well spent in my opinion. Made that back the first quarter I set it up. Just these sunny/dark/sunny/ dark days we get here allow it to pay for itself as does the often cloudy mornings that burn off into scorching sun in the afternoon where a timer would not be as efficient. I read about one controller that checks the weather forecast and works off the predictions as to when to turn on etc. Yeah, good luck with that! Mate of mine lives a short distance away and he can be getting drowned and we don't get a drop and vice versa. Happened just a fortnight ago. He was here and went home in the pouring rain and 3KM up the road and back to his place, bright sun. He lives on tank water so wasn't real pleased about that! :0) I think rather than have a controller tapped into the weather forecast, one would do better with a Light sensor pointing up and calibrated to light levels to switch the HWS in and out. Could easy do that with a small solar panel on a resistor that drove an SS relay for the heater. Sure be loads cheaper as well! |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Davo99 said: "Just check it's an inverter type. I think they nearly all are now but it would pay to check and work out a deal to upgrade if it's not. I would also Highly recommend a Daikin or a Fujitsu Unit. Good mate of mine is in AC and that's the only 2 brands he will touch even though there is more money for him in a lot of others." Please add to this list a Mitsubishi Heavy Industry unit. I've had 7kw unit in the lounge (my main work room) for years & it's about the quietest & most efficient unit available. If you run it in economy mode (more than enough) you can't tell that it's on - so quiet. (In economy mode the priority is on the heat pumping side rather than power usage). It must be a MHI one (Mitsubishi Heavy Industries unit as distinct from the consumer variety.) Heating in winter only adds 2-3 kwh to the power bill even when it's on all day. We also have 2 smaller units - kitchen & study - which are only used occasionally on demand. The 7kw unit is by far the most efficient. You can tell I'm a fan (no pun)...  Be careful about getting sucked in to buying what you might think is a good Aussie brand. i.e. Kelvinator, Electrolux, etc. They are nothing like what you would expect - just cheap Asian rubbish. You would be in for a life of pain. These units are being flogged by the big retailers because they can make a quick fortune, & when they fail prematurely (a lot do) they may well be replaced but you will most likely have to foot the re-installation bill. B |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
I believe there are a few different makes around that use Mitsubishi compressors which are a quality unit. Trouble is it takes a bit of digging to find out if you can and then there are the other factors... Control boards, general construction quality, quality of other parts such as valves and condensers. Better off sticking with the MHI units in the first place and knowing that the things are built to a complete standard rather than a quality component surrounded by thrown together crap. Looks like another on again, off again day today. Bit of cloud haze so the inverters will be maxxing out. The rain has meant the weeds in the garden have taken off so I'll go pull out the old urn and boil some water with solar power and do some Cheap....errrr, Organic! Weeding. :0) |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Haha! My gutters go to MY tanks! I have town water but I have put in quite a few IBC's for capturing water for the garden. The downpipes that don't have tanks I have disconnected so they run on the ground and into the gardens. Hasn't rained properly in the 2 years we have been here and having problems with things cracking due to being so dry. Not letting any water go to waste, just running it on the ground here is an asset. Rained last week and I was looking at all the water going down the storm water open drain out the front. Next time we get some fleeting rain, I'm going to take my petrol Pump out the front, put the pickup hose in the drain with a large strainer and pump the water back up onto my lawn. I'll block the pipe under the driveway to dam the water as there is quite a lot of water that pools there and I should get a decent amount to pool up. I have a HUGE gum tree out the front that must suck hundreds of litres a day at the expense of the grass and the lawn has cracks in the soil that literally nearly throw me off the mower when I go over it. It would take a Biblical amount of water to saturate that front area again. I have 2x 38M 3/4" fire hoses so I'll hook them up and set the pump going. Next time we get some rain, I'll be prepared. :0) |
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| Rudge Newbie  Joined: 11/09/2019 Location: AustraliaPosts: 9 |
Re: New Build. I had exactly these questions just three years ago. Luckily I chose the solar PV option and my electrician added a simple $25.00 timer switch in the distribution box. Now the H/W can only come on during my chosen hours of sunlight and for just two of us, mainly, it works a treat. When we go travelling I just trip the breaker off and when we return I go to over-ride and have hot water within the hour. I should have chosen a lower wattage element because sometimes the power used exceeds the solar at that point in time if a bit cloudy. As was suggested above, heating for longer at a lower rate would be a bit better but quite honestly I can wait until the current element breaks. This option far outweighs the cost of solar h/w plumbing. I did not understand that the new sub-division we built in has three-phase at every distribution board, and nobody pointed it out. My single phase inverter only shows the loads on the one phase, including the H/W, so I can't see the impact of the A/C and the hot-tub because they are on the other phases. I am assured that my solar generated power is correctly accounted for even if it only feeds the one phase - perhaps someone can re-assure me. Either way it would be nice to see the impact of the Aircon. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Do you mean your INVERTER only shows the single phase loads or your METER only shows the loads? I can't see how any inverter could show loads, it would have to have all the current for that circuit running through it.... like a meter. If you meant a meter, if you only have one, that covers all phases and the solar. If you have 3 Meters and another for the solar, that's Different..... and wrong. Your solar should cover all phases.... Unless you have a bootleg system like mine which has and inverter ( or more) on each phase for that reason. I would have thought for a new Build 3 years ago you would have had a smart/ electronic meter and that would cover all phases and the off peak if you have it. If you want to see individual consumption, You could have a small meter fitted on the hot water and the spa which I imagine would have a dedicated HD circuit as well. The meters are only about $50 for a single phase and shouldn't be exy for a sparky to fit or if you are handy you can easy DIY it. You could also fit the meters at the Hot water system or spa in a weatherproof enclosure if they are outside. You can get them off ebay that have an Inductive coil you put ropund the active cable. The unit just plugs into the power but carries no load at all. I have a couple of them and have found them to be surprisingly accurate and very handy. had one on my own HWS for a while which was very informative.... and scary as to how much power the thing could use! You can get the meters off fleabay for around $25. This is the Type I have with the CT clamp which allows you to measure the high Current. CT meter |
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| Rudge Newbie Joined: 11/09/2019 Location: AustraliaPosts: 9 |
Sorry. I should have said my 'Inverter Monitoring Software' which displays the Solar Power and Exported Power. Here is a screenshot. The H/W cut-in can be clearly seen, usually for an hour or so each morning and a couple of blips later in the day. Cheers  Edited 2019-10-07 21:53 by Rudge |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
I can see what you mean. A smaller element definitely would work better here to stop the draw going below the generation and costing you almost 2 Kw of power from the grid. Then again, if that's for an hour probably costing about .60C. I know you can get 3 phase meters that have 3 CT's to go on every phase and will record and show the numbers for each phase like above and have wi fi or networked monitoring. Last time I looked they were about $120 from memory. You would certainly be pulling some power when you put on any 2 larger loads like AC and pool or AC and water heater. Even an electric stove if you had one would put you behind with anything else like the spa running. Still, better to have the power you do than nothing. What is your average power cost per quarter? |
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| Rudge Newbie Joined: 11/09/2019 Location: AustraliaPosts: 9 |
Yes no doubt about the element but as you say it might be 0.60 a day. I am interested in the metering/monitoring that you mention. Any pointers as to source? Average over last 11 quarters our current bills show units billed 1073; units credited 1608 per qtr. This cuts out the variations in charges rebates etc. and gives a bottom line figure. We also travel quite a bit. In dollar terms about $150 per qtr and we are sensible but not frugal so I reckon that's pretty good. |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 840 |
Hi all, I've been out of range for a few days - a very interesting discussion. MY new build will have 3-phase mains connection and say 20+ PV panels. I've been thinking Heat Pump for the HWS rather than a direct heating element. (There are likely to be a separate Heat Pump for the in-slab hydronic heating and a small gas heater for the 2.5 x 6 x 1.8 pool - the only gas usage in the house??) Any comments? Cheers, Andrew Edit: I should add that I'm in suburban Melbourne Edited 2019-10-08 16:38 by Andrew_G |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
I have no experience with hot water heat pumps but they do seem to be the flavour of the month amongst the green/ energy concerned. Just because they are popular and touted as the way to go does not mean they are good or live up to expectation. I was only just discussing them with my mate who does AC and a lot of pool heating work. The upshot was he wouldn't have one himself and does everything he can to deter his customers from them. He says they are not nearly as reliable or long lived as traditional electric or gas heaters despite being 2-3 times the price. He says the main failure points are the compressors or the control board and cited a case of an aquatic centre that had them installed that he was endlessly repairing under warranty till they were no longer covered where he replaced them with gas had no more problems and the centre owners blood pressure went back to health levels. He said they virtually all have problems and short lives. I said have they not got better over time? He said yes, they were not nearly as bad as they used to be but they were still be hind in reliability. He thought the savings in running were negated by the purchase price and inevitable repairs and down time. Goes against what a lot of people say but he's dealing with many of them every day. Anything he has is good enough for me and I have learnt anything he won't touch is best avoided on my part as well. I think the price alone would need looking at closely. What would be the DIFFERENCE ( savings ) on a heat pump to a conventional resistance heater given the house will have solar and the water could be heated for free anyway? Looking at the other way, the heat pump will use a lot less of that solar so what are you going to do with it/ get for it if it's exported seeing your other heavy usage in the spa will be on gas? The other thing my mate mentioned and I would look into is the efficiency curve of the things. Once they get to a certain temp the efficiency falls off fast till they use a resistance heater to work as well. I have heard some people say some units will work to Minus temps but again, are they operating at 10% peak efficiency or 90%. In winter your solar output will be minimal anyway and a conventional heater may be pulling a lot of it's power from the grid but at least you have significant money up your sleeve over the cost of the power over the heat pump. I would be looking at the warranty on the heat pump and asking if I would save the extra in purchase price over a resistance heater in the savings between the 2 in the warranty period. If the heat pump savings won't cover the extra cost in the warranty, then I wouldn't have a heat pump myself. If you had the HWS on solar with an off peak rate boost, the extra $1500-2K of the heat pump is going to take a LOOOONG time to repay itself over a resistance heater. I'd look at your usage ATM and work out the time frame for the heat pump to repay itself. If it's 5+ years or out of warranty, then it's a definite risk. Sure you might get much longer out of one as would be expected than just the warranty period ( and any consumer law remedy you could get beyond that) but the feedback I have got from my mate who deals with them all the time as well as what I have read would not encourage me to take a chance. If the savings breaks even or better, which I would think is a slim chance, then a heat pump may be very well looking at especially if you can get an extended warranty on the thing to further hedge your bets. I WOULD look at getting an inverter with a hot water diverter built in compare the costings on that because the savings over all just from the solar on a conventional heater would mean your water was virtually free 8 months of the year or more. There are a LOT of considerations and you have to apply them to YOUR situation in your power cost, solar generation, off peak and regular power rates, return on Investments times etc. When you have calculated all aspects with great precision and detail, Take a roll of the dice and see how you go in reality! :o) |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Davo99 said: "He says they are not nearly as reliable or long lived as traditional electric or gas heaters despite being 2-3 times the price. He says the main failure points are the compressors or the control board and cited a case of an aquatic centre that had them installed that he was endlessly repairing under warranty till they were no longer covered where he replaced them with gas had no more problems and the centre owners blood pressure went back to health levels." I've also heard on the grapevine that HWS heat pump units have an abysmal reliability track record. You would wonder why. If the aircon manufacturers can make an ultra reliable system why would it be too hard for the HWS heat pump lot? Seems like there's an opening for a "good" manufacturer here - we all need hot water (assuming you do shower occasionally) B |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
That's pretty much the question I asked, they are the same process, what's the difference. I do remember him telling me there was one, can't remember what it was but I think it had something to do with the hotter temps of the water with the compressors anyway. All I need to know is that I trust his judgement and that of another friend. If I want something I know they have or have looked into, I just ask what they recommend and go get it. I said to the other friend about a month ago I got something. He said what made you buy that one? I said you told me they were good, I know you do you home work thoroughly, I don't need to waste my time to come to the same conclusion, I just go get it! I also looked at heat pump clothes dryers a while back for my father. Good Lord! Standard Dryer, $300. Heat pump energy saver, $2500+ Are they serious? $2000 PLUS buys a LOT of hours worth of power on a clothes dryer to start. Like the HWS, the heat pumps still use some power so if one uses 500W and the other uses 2000W, the difference is 1500W not the full 2000w The conventional model would use. The way I figure it, that is about 4.5 Months, 24/7 you could run a conventional dryer or 3300 hours before you even broke even on the heat pump dryer. As Dad said, I'd have to use the thing every time I wash and live till I'm 150 to get my money back on the thing. Given he -might- use it 4-6 times a year.... we bought the $300 machine... with out all the programming and setting and other built in failure points! I think the same numbers would need to be crunched on a HWS. Another aspect would be repair if something does go wrong hence my warranty concerns. Only 2 things on a resistance HWS, The element and the Thermostat. That's it. Both very simple to do as a DIY job, done them many times for different people. 5 min each one. Heat pump... very different kettle of fish. If it's the board it's pretty much remove and replace and the boards, if available, are not cheap. Compressor, same thing. several hours of labour involved at very least. Gas is NOT cheap now either so more expense there. I seem to recall mate saying heat exchangers were a common failure point on those too. He's on anything are never cheap. I think there is a BIG difference between being the cheapest to run and the lowest cost of ownership over the products life. |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 840 |
Davo, Interesting comments - they certainly cut across "learned" and "current" "wisdom". I'm not saying you are wrong - and I'm perfectly happy to question the newest bright idea, particularly before I pay hard earned $$ for it. Can you possibly check with your "mate" whether he is not convinced about heat pumps: a) For pools only, or b) for HWS too? Most of the "good news stories" I see are about heat pumps for HWSs and hydronic heating (not pools). I pressed my "pool man" about why he was suggesting gas heating rather than a heat pump for the pool. He argues that design and innovation resources for heat pumps have gone into HWS and the like, and that pool heating innovation has lagged behind. He also pointed out that heat pumps are less effective in cold weather. (all this presents me with a slight dilemma as I am keen to be off the gas grid and go all electric. You are saying go electric heating element off PV . . .) Cheers, Andrew |
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