11 minutes ago, The Terrible Triplett said:

Ag tog!

Trek jou been.
You have been against this way forever that's why

1 hour ago, plonkster said:

It's only the three coldest months when one might say "it does not work at all"

does that not greatly depend on the fact that, although some pvs track the sun, not the same can be said about the collector of a solar geyser?

Just now, viper_za said:

You have been against this way for ever that's why

Depends on the situation. 

I do agree I have over time with more factual experiences shared by others, done a 180 on some of it.

Today a EV system makes no sense if you have a solar PV system also. Even a heat pump becomes a question if you run the geyser element off the Axpert.

BUT, always a BUT. If you are Cpt based with lots and lots of cloudy days (with no freaking rain) in winter with even less sunlight, and shorter daylight, EV tubes have a chance for they do preform better than solar panels on cloudy days - all year round.

Does it justify the cost of a EV system? Tough one to answer..

5 minutes ago, gabriel said:

does that not greatly depend on the fact that, although some pvs track the sun, not the same can be said about the collector of a solar geyser?

EV system still preform under clouds. They need the UV rays, like when you still get sunburnt on a cloudy day.

Clouds must be really thick before EV tubes stop completely. And the outside temp makes no difference, they are evacuated tubes.

As long as there are UV rays, they will do their best.

But, it is a tough one to justify if you have spare solar panels and a inverter.

53 minutes ago, The Terrible Triplett said:

Ag tog!

I said use a Axpert (obviously with panels and not Eskom) to heat the geyser.

For to spend R20k on a solar geyser, if the above is done, is a waste?

What is not true Viper? 

EDIT: Obviously the Axpert is used for more than just the geyser, like dishwashers et al, just to be precise before I get "bitten" again. 

EDIT2: I fixed the sentence above also @viper_za

This will be too expensive. The axpert requires batteries to start up. 

There are other solutions for this very need, one being from Geyserwise. They have a specially designed MPPT for geyser elements. Combined with their geyser controller and dual AC/DC element,  you could use Eskom as a backup. 

Or use a geyserrobot. http://www.geyserrobot.co.za/Technical_Details/technical_details.html

43 minutes ago, SilverNodashi said:

This will be too expensive.

Yes true, if you don't have a solar system already. If you have it, use it more.

I like that Geyser Robot!!! 

1 minute ago, The Terrible Triplett said:

Yes true, if you don't have a solar system already. If you have it, use it more.

I like that Geyser Robot!!! 

I paid about R70,000 to run my geyser off solar. But now I can also run the pool pump, microwave, kettel, TV, computers, compressor, welding machine, etc off solar 

The guy who build that geyserobot is a real uber geek! As part of his display he had like 40x 10W panels connected to it just to show how it works. If memory serves right you could have as much panels as the rating of you element, i.e. 3KW PV for a 3KW element. 

Well for my money the low pressure systems really works very well. My 200l Geyser is now a year old and we had to use the grid only about 5 time to heat up the water. With me the wife and the 3 kids everybody has a warm bath / shower. Just because I have about 1.5kw of power extra during most days I decided to install a 1kw element in my geyser and boy did that make a difference now in winter. We would get about 60 - 65 deg per day after most of the hot water was used overnight. Now with the help of the little element I have managed to get 97 deg on Sunday but on average I would say I get 80 to 85 deg.

Ps. You could actually hear the geaser boil :0 

 

 

31 minutes ago, PaulF007 said:

I have managed to get 97 deg on Sunday

hi paul, you have ev tubes i presume.

Low pressure systems are really cheap to get and install. You get flat panel and EV tubes types. Flat panel being cheaper. 

My brother did a DIY one from scratch. Then he bought a EV tube one for R1500 2nd hand.

And the tend to boil in good conditions, which is not an issue.

1 hour ago, gabriel said:

hi paul, you have ev tubes i presume.

Yes or rather think so ,,, 

Got one from these okes 

http://www.thesunpays.co.za/low_pressure_systems.htm

There has been a fair amount of discussion of cost. I have heard of a Freestater (no not @Chris-R) who has connected 3x 250W panels in series directly to his geyser element No MPPT no inverter just DC straight into the element. On most days the geyser is hot enough. He has recently got a extra panel to increase his heating capacity slightly.

 

3 hours ago, Chris Hobson said:

There has been a fair amount of discussion of cost. I have heard of a Freestater (no not @Chris-R) who has connected 3x 250W panels in series directly to his geyser element No MPPT no inverter just DC straight into the element. On most days the geyser is hot enough. He has recently got a extra panel to increase his heating capacity slightly.

 

I can't see why it won't work. It's a big resistor after all. But I suspect an MPPT charge controller problem just draws more "juice" out of the PV array and help quite a bit. The element itself won't be able to regulate volts or ampere so it would probably just run flat at maximum volts and use whatever ampere it can get?

8 minutes ago, SilverNodashi said:

I can't see why it won't work. It's a big resistor after all. But I suspect an MPPT charge controller problem just draws more "juice" out of the PV array and help quite a bit. The element itself won't be able to regulate volts or ampere so it would probably just run flat at maximum volts and use whatever ampere it can get?

WEeeellll... no. Depending on the resistance of the element, it will pull the panels down to some voltage that may or may not be close to Vmp. If it pulls it down too low, then you lose all the power above that. You need to either use an MPPT, or carefully match the panels with the element so they run close to Vmp.

That guy adding a 4th panel? He may well find that it does nothing... it all depends of course :-)

5 minutes ago, plonkster said:

WEeeellll... no. Depending on the resistance of the element, it will pull the panels down to some voltage that may or may not be close to Vmp. If it pulls it down too low, then you lose all the power above that. You need to either use an MPPT, or carefully match the panels with the element so they run close to Vmp.

That guy adding a 4th panel? He may well find that it does nothing... it all depends of course :-)

As I said, an MPPT would work better. 

Quickly checked, a 2KW element has a resistance of 35.6 ohm. 

2 minutes ago, SilverNodashi said:

As I said, an MPPT would work better. 

Yeah sorry, missed that. But I know some people match the panels to the element so they can get away without that. In the end it will work, it's a big resistor as you say :-) How well it will work, that depends.

Have to be up again in about 4 hours, catch a train to Amsterdam and fly back to SA. International travel is cool and all... but it sucks :-)

I have the 150 and 300l suntank and buyer beware, only in mid summer can I maybe get 60 degrees,   the 300 just doesn't perform at my house . the 150 l does better but cant write home about it either . they are both flat plate . big one 3 panels small2 panels and thermo siphon , I even tried placing a circ pump on the 300 but only a slight improvement . and yes I have had them here to check it  and they got something rightish but then its back to its old self . and yes I have  toped up the antifreeze and water . 

right now I don't have anything good to say about flatplate solar geysers. on the other hand my brother in laws low pressure 150 with evac tubes works wonderfully .

also the geyserwise and heating element are at  halfway so cant really get accurate readings

cheers

I also have a 300l flat plate s untank. They are indirect solar heaters, hence the poorer performance when compared to direct heaters.

@DeepBass9 I'm sure you would like to use an equation, so here it is:

Q = m x Cp x dT   ------- (1)

where:

Q = Energy required to heat your 'substance' 

m = Mass that you are looking to heat

dT = Final temp minus Initial Temp ( T2 - T1)

then

P = Q / t    ------- (2)

P = Power required to deliver or that you have in place to transfer the above calculated energy in a required or resulting time 't'

t = time required for a given power base to deliver the required energy, or time required to reach a final temperature from an initial

So:

(2) ---> (1)

P = [m x Cp x dT] / t

And finally:

t =  [m x Cp x dT] / P

Given:

m = you have not defined a mass so I will use 100kg (100l) then you can simply multiply the calculated time by 2 for 200l, or 3 for 300l etc.

Cp = water is 4.183kJ/kg.K (at 55C)

dT = 30C as you have stipulated, so you could be starting at 25C and want to get to 55C but you have not stated your starting point which is irrelevant since you asked how long to raise the tempt by 30C (I.e. dT)

P = 2kW heating element

thus:

t =  [100 x 4183 x 30] / 2000

t = 6275s (1h44m) for every 100l -->

Now that you have the final equation you can play around with different scenarios for size of geyser, heating element installed, temperature rise and amount of water!

Edited July 14, 20178 yr by Trev
Unit carry problem in formula! Worried me the whole day. Check my math. I should try art instead ;-)

thanks @Trev, pretty impressive, especially for me who dropped maths in st 8 for art - [way back in the sixties; i believe the art teacher was a sexy creature so a couple of us did the same ] so forgive me for reverting to http://processheatingservices.com/water-heating-time-calculator/  at the 'university' of google

7 hours ago, maxomill said:

also the geyserwise and heating element are at  halfway so cant really get accurate readings

hi @maxomill , i don't really understand what you say here but i find that the geyserwise does not always give accurate readings - sometimes it will report 27c when i open a tap and the water is definitely in the 40's. maybe the measuring unit is placed in the wrong position.

re your remarks on the flat plate, i agree. it is far less effective than ev tubes and if i had to go for it again it would be a no-brainer which one to buy - i blame my decision to go for flat plate squarely on the lack of expertise an or knowledge of the solar 'expert' - and of course my own lack of knowledge.

On 4/11/2016 at 9:45 AM, DeepBass9 said:

Can someone please explain how to calculate how much energy it takes for heating water?

@gabriel the original query by DeepBass9 starts with the above quoted question...

Calculators do not explain much, just like 'join the dots' or 'paint by numbers' for artists 

40 minutes ago, Trev said:

Calculators do not explain much, just like 'join the dots' or 'paint by numbers' for artists

i appreciate, it is at times the 'way' to get there which is important in order to understand the end result, other times the bottom line, i.e. what the calculator gives, is sufficient.

interesting to note, way back in the 80s an acquaintance of mine [a general practitioner] had a  calculator [i believe a texas, not quite sure] and he got suspicious of a result, he worked out the formula by hand [lang deling etc] and found the calculator to be in error. needless to say they just replaced the unit without any real excuse, which stresses the point made in  psalm 146:3 'Put not your trust in princes, nor in the son of man, in whom there is no help.'

 

2 hours ago, gabriel said:

hi @maxomill , i don't really understand what you say here but i find that the geyserwise does not always give accurate readings - sometimes it will report 27c when i open a tap and the water is definitely in the 40's. maybe the measuring unit is placed in the wrong position.

re your remarks on the flat plate, i agree. it is far less effective than ev tubes and if i had to go for it again it would be a no-brainer which one to buy - i blame my decision to go for flat plate squarely on the lack of expertise an or knowledge of the solar 'expert' - and of course my own lack of knowledge.

It sounds like the temperature probe might have pulled out of the pocket a bit. Or there's a lot of scale buildup on the pock. That, or it gets electrical interference from a 220V source. That probe wire shouldn't be close to 220V

13 minutes ago, SilverNodashi said:

It sounds like the temperature probe might have pulled out of the pocket a bit

thanks silver, i'll have to fix it - wrong thermostat readings could cost dearly! [no scale build-up yet, about 4 months old]