Indeed. I’ve made some people (on social media… so not people I know too well ) quite angry by telling them heating water with LPG does not save money. And nobody wants to hear they just threw their money away.
In the end, as I always say, nature tends to lend itself very well towards being approximated by mathematics, or in other words, a little bit of math tells you. You google the calorific content of LPG, convert that to kwh, and multiply it by the efficiency of your “gas geyser”, which is typically not very brilliant. LPG is more expensive just about every time. The trouble is that people replace an electricity bill with a gas bill… and only focus on the electricity savings afterwards.
The same actually happens in the perenial EV vs ICE debate. “Oh, you just wait until you have to replace a battery!”, they say, but nobody realises that in the time the battery lasts, you will spend about the same amount of money on petrol.
Thought about this … as I’ve read that exact sentence many times over many posts on a few forums.
Yes, for some it does for NOW … BUT … WHEN the replacements start, as it is a “voice in the dark”, a theory, not my problem “today”, I would bet my left whatever that people will have a very changed view.
Time will tell, but not today.
EDIT: Cause over time, needs change, perspectives change, budgets change … everything changes just like nothing lasts forever.
Let me add another point about heatpumps. When you have a week-long outage, as is now common in many parts of the country, you really appreciate the low consumption of a heat pump. The 3kW element that you didn’t worry about, is suddenly a huge thing when it has to be juggled with other things.
Similar to @Swartkat, I also have gas water heating as a backup. When we moved into this house, everything was gas. I soon discovered that we run though 48kg of LPG in about 5 weeks (not just ourselves, I also had a tenant at the time). I discovered however that they kept the old electrical geyser as a backup… so during covid I simply switched back to this, and then when that started hurting too much, I installed a heat pump. So now the gas is the backup, and this works really well for us. During an extended outage the inverter can run the heat pump, and if that also fails due to low sunshine, we can switch to LPG.
Whew! These discussions stray far and wide…
WWP posted a challenge about heating water with solar PV.
I hear his call because panels aren’t hard to come by and are cheaper than they have ever been so why isn’t there a simple ‘plug and play’ PV hot water system on the market?
I read the thread but I don’t comment on any thread on that forum anymore for many years now.
I feel people make it overly complicated and those types of installations sound messy to me and potentially more maintenance is required. Dangerous even if not done correct.
I see that he also has a 150L geyser but supposedly no inverter or panels yet. If it is merely heating water that he is interested in, then he should look at those geyserwise thingys with dc elements etc and all else that was suggested but have it done properly.
But why would you want to go through the whole shebang in getting panels etc only to use it for water heating? That solar could be applied elsewhere as well.
Then rater get a small 3Kva inverter, heat your water the normal way and have some savings elsewhere when the geyser is charged.
WWP has posted good results:
Just a quick update from his secret project:
the lowest temp we had was 38 degrees.
it was during the recent cut off low, which caused cloudy conditions.
since then, hot as hell.
for those claiming, that one can use the extra power…and dump it else where.
it would be foolish to think of it.
you might need all the power you can get in a day, so if you did want to dump extra power, to where will you dump it?
we do accept that we might have a day or two with cooler water.
but its not a concern, a quick boil of the kettle and pot, sorted us out.
both temp sensors are still working great.
stay safe.
This is available from a respectable RE company from Rayton (gold prospectors town)
I’ve never been there but have heard of RE shows they have had in the past.
They fit into the lexicon of ‘underground’ music which I followed fanatically back then. (Rodreguiz was in this category until SA rediscovered him)
So I’m following dedicated PV water heating in much the same spirit and I’m sure I’ll find undiscovered gems one day…
It is 6x 550 watt Canadian solar panels in series connected via a contactor to a 3kW geyser element. The contactor is switched via a separate 12V powered W1209 Thermostat module.
That is unusually well matched! Assuming those are Hiku6 panels, their Imp is 13.2A, which is bang on what a 3kW element would want at 230VAC RMS. That means the voltage will draw down to about 230V all on its own, and all he had to do is make sure that his total panel voltage is a little higher than this. Panels have a Vmp of around 41V, so 6 in series puts you around 246V. Not bad at all!
When you match it this well, you actually don’t need an MPPT at all. MPPTs are about matching the impedance.
In full sunlight, you are well matched. But, without a MPPT, if solar input drops to 50%, then power output will drop to 25%. Efficiency goes off a cliff very quickly in sub-optimal conditions.
This is a fair amount of power to heat the standard geyser and your controller will need to switch it off often to prevent the geyser from boiling.
The switching of the DC is the challenging bit.
that part is a secret. Going through that thread he was asked about it (DC rated contactor) but basically just went with “well, the contacts will fail at some stage - it is worth it for warm water and giving the finger to Eskom”.
Yeah, the thing is with switching DC with a contactor not rated for it, it’s not only the contacts that fail, its often also your roof trusses and then the fire spreads from there…
Naaah, that’s an admission. He used whatever he had. It’s an AC contactor. Maybe it is rated for 600V and he can get away with it for a while. In the thread he speaks of a “very high rated contactor”, ie something bulky.
Other thoughts I had, first I thought, at those current levels, maybe something solid state (like a MOSFET) can be used, then I realised voltages are a bit high for that. So you’d look at an IGBT then, but those seem a bit pricey in turn.
One would hope he put it somewhere easy to inspect and far away from the roof.
Edit: What if you used a 600VAC rated three phase contactor and wired all three contacts in series. That theoretically gives you a 1800VAC rating, which could (maybe) get you up to 240VDC-ish. I would probably still not trust my handwaving-math here, but if you had to work with what you had, that would help.
Perhaps if you also add an adequate snubber, otherwise you could still produce a sustained plasma flame. All-in, I would not recommend it. It’s also a more expensive solution than using an IGBT.
The honourable Fluffy posted this on the Alternative Energy site:
“You do know that the geyserwise unit is an inverter. It’s just a DC-DC inverter because they burnt their fingers (excuse the pun) with their older units that tried to switch DC”
He’s referring to the MPPT that Geyserwise use which has a low voltage switch input that enables the device.
Just to double up on the safety they also install a MPPT element that goes high resistance at 75°C
I was looking at “solid state relay” type packaging units, which seems to start at R800 at least. Granted, that is in all likelihood cheaper than an actual DC contactor, but probably not cheaper than the one he had on the shelf already
) quite angry by telling them heating water with LPG does not save money. And nobody wants to hear they just threw their money away.
