Solar Water Heating and savings???

Bob-Dubery

Let me nail my colours to the mast before I go any further. I think SWH is a very good idea and I want it to work - for reduction of CO2 emissions and for reduction of pain inflicted upon my wallet.

OK.... anybody else running such a system? And do you see benefits? I've got SWH installed, from an SABS and Eskom approved supplier. I'm not sure it's doing that much for me in practical terms.

Some notes/points for consideration

1: I am finally emerging from a 2 year plus foul up with City Power. For most of that time I have either not been metered for electricity consumption or was metered for somebody else's consumption (when the new sub-stations were put into our suburb the sub-contractor cross-wired meters and houses). So I don't have much in the way of reliable historical data to compare the current situation against. However the new meter is digital and thus very easy to read. This is such a novelty that I read it most days so that I can monitor consumption.

2: Now that we have a meter proven to be correctly connected to our house I know for sure that currently we are consuming about 690 Kw/h a month. This is for a house with 2 adults, both working (IE out of the home during office hours)

3: The SWH DOES work. It can produce very hot water. But it tends to do this when we're not home to use it. On clear weekend days I have monitored the system by the simple method of feeling what comes out of the hot tap. By about 15:00 it's really hot. But by 20:00 it's cooling off with the sun down and the water naturally cooling off again.

4: So if we were home in the early to mid afternoon we'd probably get enough hot water to take a shower and wash the dishes. But we're not home then.

5: Contrary to what "experts" have told me, the system doesn't get very hot on overcast days ("yes sir, but there's still lots of UV even when it's cloudy, so the system will work").

6: We have electrical back up so that if there's no solar heating on any given day a conventional element will kick in. I control this with a timer switch. Because we are out of the house for about a 1/3 of the day, and because we really don't need hot water betwen 10pm and 5am I can afford to have the element turned off for long periods of time. I suspect this is where any real saving is actually occuring. Recently, when there was going to be lots of cooking and washing of dishes going on, I overrode the timer for a day - big increase in consumption for that day (but the stove was working hard too).

7: Some time ago, before the aforementioned sub-contractors screwed up everybody's billing, I fitted energy saver globes throughout the house - no exceptions. This actually did bring about a worthwhile saving (in two ways: lower cost of lighting the house, longer service cycle so you don't have to change globes that often - I have some that are over 5 years old now and still working fine).

8: I think savings may be possible with SWH if you can tailor your lifestyle to fit in with SWH. If you could shower and do the dishes at 3pm you'd get a lot of use out of the system. In fact generally I see this as the big challenge with reducing electricity consumption - lifestyle has to change.

Any comments?

IceCreamMan

i did an exercise of this nature to weigh up the pro's an cons...

the main pro was get off the grid (as much as possible). This could be priceless in the years to come ...

cons are the initial outlay of dinero which in reality may never actually be recouped in monetary terms (savings) however some of the benefits are not tangible like reduction in harmful gases an the like.

currently still erming an ahming ... i believe load shedding is to make a comeback this year, that may push me over the edge an have a system installed.

StephenG

as much as I also wanted it to work - solar water heating is pretty much a con and total waste of money.

Bob, as u point out - it does not get very hot at all on cloudy days.

people will achieve far greater savings by putting their water heaters on a timer to come on about an hour before you wake up in the morning and then an hour before u get home - and also wrap your geyser in a thermal geyser blanket - that helps cut power usage as well.

the cheap solar heating installations uses the suns energy to heat your water, but only as long as the sun is shinning on it - ie: during the day.. it does not keep your water hot, therefore no sun = no heat.

so solar will not get you off the grid.

the only way to get off the grid is to use solar charged battery packs.. then u use the power from the batteries instead of eskom power....... however, now we into the realm of mega mega bucks.. about R150,000 in batteries should be able to power your geyser and get you off the grid, however (and heres the nut kicker) the batteries have a 10 year life span.... they also, coincidently, also have a 10 year pay back period in an average sized house.. so just when you finally getting the solar batteries to start paying for themelves,you gotta replace them...

as with all things in life, there are no easy cheap solutions..

Gearhead

Y'all are confusing lotsa things.
Firstly, the thing about hot water on cloudy days IS true for evacuated tube solar collection and not for cheap flow-through-black-bucket setups.
Secondly, the electrical heating should be to maintain the hot water temperature (series setup) and not be switched on when needed (parallel). We were very happy with the serial setup and savings in our previous house.
Thirdly, with proper insulation a tank should not loose more than a few degrees overnight, rather than tens of degrees. Go have a look there.
Fourthly, the real energy consuption is in heating in winter rather than the bloody hot running water. If you want to save quickly on hot running water, install a gas burning geyser. These things are small, simple and only heat the water when you open the tap. Massive money saver. Heating in winter (I'm not even talking insulating house here) can be done very well with vacuum solar collectors - they do it in Sweden even. It just costs a fortune in collectors and you do need water underfloor tubing. We have had the tubing installed and will have them put a heatpump before winter - with added bonus of warm running water for 1/5 of the energy consumption.
Lastly, using batteries for heating purposes is downright silly. The efficiency of collecting - storing - transforming - heating is less than 3% so by the time your wallet's empty, you will have about 2 mins of running water. For the day. Using batteries for guitar amplification or recording purposes makes more sense, but that is not what OP asked about...

Bob-Dubery

Gearhead wrote: Y'all are confusing lotsa things.
Firstly, the thing about hot water on cloudy days IS true for evacuated tube solar collection and not for cheap flow-through-black-bucket setups.

IOW the salesman lied to me or, more likely based on other exchanges I have had with him post install, doesn't have the foggiest idea how the gear he is selling works.

Secondly, the electrical heating should be to maintain the hot water temperature (series setup) and not be switched on when needed (parallel). We were very happy with the serial setup and savings in our previous house.

OK... you'll have to spell that out to me in nice simple words that I can get my tiny little mind around.

Thirdly, with proper insulation a tank should not loose more than a few degrees overnight, rather than tens of degrees. Go have a look there.

Thanks

vic

StephenG wrote: as much as I also wanted it to work - solar water heating is pretty much a con and total waste of money.

Bob, as u point out - it does not get very hot at all on cloudy days.

people will achieve far greater savings by putting their water heaters on a timer to come on about an hour before you wake up in the morning and then an hour before u get home - and also wrap your geyser in a thermal geyser blanket - that helps cut power usage as well.the cheap solar heating installations uses the suns energy to heat your water, but only as long as the sun is shinning on it - ie: during the day.. it does not keep your water hot, therefore no sun = no heat.

so solar will not get you off the grid.

the only way to get off the grid is to use solar charged battery packs.. then u use the power from the batteries instead of eskom power....... however, now we into the realm of mega mega bucks.. about R150,000 in batteries should be able to power your geyser and get you off the grid, however (and heres the nut kicker) the batteries have a 10 year life span.... they also, coincidently, also have a 10 year pay back period in an average sized house.. so just when you finally getting the solar batteries to start paying for themelves,you gotta replace them...

as with all things in life, there are no easy cheap solutions..

+1 to that. The geyser blankets is a must and easy to do.

singemonkey

I had totally different advice re timers - also from an engineer ? (and a German one, so he must know what he's talking about ?). He reckoned that maintaining temperature is more efficient than reheating, cooling, reheating. Admittedly, I couldn't see the physics in this, since heating is constant energy expenditure, whether maintaining or heating from ambient until you need the extra energy to convert the water's state to boiling, right? (which obviously you don't need to do for tap water)

But I also agree with gearhead. Bob, it does sound like there's something wrong with your system if it's losing heat so quickly. Also, the saving should still be huge just by raising the temperature of the water such that the element only needs to raise it a couple of degrees. I also agree with gearhead that, first point being true, that the system should still work fairly well in overcast.

My parents have had these systems twice, and they've been very happy with the results and savings. My hunch is that you need to figure out what's going on with your system and maybe go and compare yours with what other people are running.

Gearhead

@OP: a serial setup is where the cold water gets into the solar collector reservoir first. It gets heated throughout the day. The water from the solar collector reservoir outlet goes into the electrical geyser (standard type) and the outlet of the electrical geyser is your hot running water. If you use your warm water for a shower in the morning, the electrical geyser starts getting hot water in from the solar one. This might not be exactly the right temperature, but 90% of the work will have been done. This works even better if you set the temperature of the electrical system substantially lower than the solar one will max out on.
For example, you start with water at 20 degrees and the solar thing beefs this up to 90. It cools down overnight to 70 degrees and by morning flows into the electrical system that only starts re-heating it at 60. The latter might sound like a low temperature, but I'm sure you shower at a much lower temperature and even for doing the dishes it is quite hot.
In general, people jack up their hot water temperature to have more warm water from the same tank - fooling yourself that is. The serial setup already has twice the volume in hot water available so it does not need to be run at more than 60. Thia also cuts down on themal leakage.

@Vic: the german was wrong (they get that from time to time, even Dutch people do ? ) since the heat loss is linear to the temperature difference between reservoir and ambient. Maintaining temperature only makes up for heat losses so that's also linear with the average difference.

Bob-Dubery

singemonkey wrote: I had totally different advice re timers - also from an engineer ? (and a German one, so he must know what he's talking about ?). He reckoned that maintaining temperature is more efficient than reheating, cooling, reheating. Admittedly, I couldn't see the physics in this, since heating is constant energy expenditure, whether maintaining or heating from ambient until you need the extra energy to convert the water's state to boiling, right? (which obviously you don't need to do for tap water)

I think you have to factor time in. We effectively leave our geyser without power for 19 hours a day. I'd agree that it probably takes a lot more energy to heat the water in the first place, but if you can afford to not heat at all for long periods of time then that saving outweighs the cost of having to reheat from cold (and on a clear day the water in the geyser isn't cold when the element kicks in in the afternoons).

But I also agree with gearhead. Bob, it does sound like there's something wrong with your system if it's losing heat so quickly.

Ja. We still have the old "non-solar" geyser in situ and I recall that had very good insulation. The sales guy assured me that the solar geyser had super-duper insulation blah blah but it's become clear that he is really clueless about the kit he is providing.

So a geyser blanket seems the way to go, but the geyser is up on the roof, exposed to the elements so I don't know how long the blanket will last.

Either that or I just strip all the solar stuff out again, reconnect the old geyser and see what I can get for the solar panels.

deefstes

I can't really add any valuable comments. I've recently moved into a house with solar geysers (augmented by an electrical system) but I have yet to receive a utilities bill from council so that I can establish the typical consumption of our household.

Here are one or two comments though:

X-rated Bob wrote:5: Contrary to what "experts" have told me, the system doesn't get very hot on overcast days ("yes sir, but there's still lots of UV even when it's cloudy, so the system will work").

It is not the UV component of sunlight that heat things up, it is the Infra Red component (other side of the spectrum). Sure, when it's overcast you do get sunburn (thanks to the dangerous UV rays) but you don't feel it until it's too late (thanks to the absence of IR rays) which is why overcast weather is so deceptive. But no, I fail to understand how UV rays would heat up your SWH.

X-rated Bob wrote:6: We have electrical back up so that if there's no solar heating on any given day a conventional element will kick in. I control this with a timer switch. Because we are out of the house for about a 1/3 of the day, and because we really don't need hot water betwen 10pm and 5am I can afford to have the element turned off for long periods of time. I suspect this is where any real saving is actually occuring. Recently, when there was going to be lots of cooking and washing of dishes going on, I overrode the timer for a day - big increase in consumption for that day (but the stove was working hard too).

I know that, with my university physics, I'm supposed to be able to calculate this but I'd be curious to know which works out cheaper;
a. keeping hot water hot all day
b. heating cold water n times per day
It' snot a simple calculation, which is why I won't bother, but stuff like how well your system is isolated from external temperature drops, how often you heat it up etc. will affect the outcome.

X-rated Bob wrote:8: I think savings may be possible with SWH if you can tailor your lifestyle to fit in with SWH. If you could shower and do the dishes at 3pm you'd get a lot of use out of the system. In fact generally I see this as the big challenge with reducing electricity consumption - lifestyle has to change.

Amen. I definitely think that the only way to really save (and now I'm referring to the bigger picture with respect to environment as well), you'd need to change your lifestyle. I for one certainly could benefit (as would the environment) by showering at different times of the day, recycling more, irrigating the garden more intelligently, buying more wisely etc. etc. etc.

Bob-Dubery

Gearhead wrote: @OP: a serial setup is where the cold water gets into the solar collector reservoir first. It gets heated throughout the day. The water from the solar collector reservoir outlet goes into the electrical geyser (standard type) and the outlet of the electrical geyser is your hot running water. If you use your warm water for a shower in the morning, the electrical geyser starts getting hot water in from the solar one. This might not be exactly the right temperature, but 90% of the work will have been done. This works even better if you set the temperature of the electrical system substantially lower than the solar one will max out on.

Which is what we initially had, but it didn't seem to work that well. However see my OP.... the solar geyser loses a lot of heat for some reason.

Bob-Dubery

deefstes wrote: Amen. I definitely think that the only way to really save (and now I'm referring to the bigger picture with respect to environment as well), you'd need to change your lifestyle. I for one certainly could benefit (as would the environment) by showering at different times of the day, recycling more, irrigating the garden more intelligently, buying more wisely etc. etc. etc.

We've been recycling for some time now. Our local rubbish tip takes paper, cardboard, tins, glass and plastic (including plastic bags) and old motor oil for recycling, so we started separating our trash and I'd take a run down to the tip on weekends. Now Pikitup (who handle domestic refuse removal for the Jo'burg municipality) are piloting a recycling scheme in our suburb and provide bags for various types of recyclable refuse that you fill and then put out alongside the wheely bin.

Bob-Dubery

Gearhead wrote: For example, you start with water at 20 degrees and the solar thing beefs this up to 90. It cools down overnight to 70 degrees and by morning flows into the electrical system that only starts re-heating it at 60.

OK... but how does that flow happen overnight? Surely you have to empty water out of the electrical geyser to let in the water from the solar geyser? My challenge was how to make that happen.

aja

singemonkey wrote: I had totally different advice re timers - also from an engineer ? (and a German one, so he must know what he's talking about ?). He reckoned that maintaining temperature is more efficient than reheating, cooling, reheating. Admittedly, I couldn't see the physics in this, since heating is constant energy expenditure, whether maintaining or heating from ambient until you need the extra energy to convert the water's state to boiling, right? (which obviously you don't need to do for tap water)

Visualize two systems: 1. geyser that is very well insulated against heat loss by means of blanket etc. 2. geyser that is not insulated well against heat loss at all.

Now think about two methods: A. constant heating is done by the element and thermostat in order to maintain the water temp throughout the day. B. a timer is used to heat the water up from its current low temp to the required high temp just before the hot water is required.

So we have the following scenarios and explanations:

(system)/(method)

1/A - This is the best method - since the system is well insulated, little heat loss occurs and little energy is required to maintain temperature. When water is used, the cold water that flows in is raised to a higher temperature. i.e. if the hot temp is 65'C and the coldwater is 12'C, the overall geyser temp after some cold water is added may be around 40'C. So the element must heat the water from 40'C to 65'C.

1/B - this method will not benefit much from the extra insulation since heat loss during the day is irrelevant as all heating occurs an hour or two before the water is needed. In this method, the element mst raise the water temperature from somewhere around ambient (25'C or so) to 65'C, requiring lots of energy.

2/A - this method is not very good since a portion of the heat added by the element is lost continuously at a fast rate.

2/B - similar to 1/B, the element needs to raise the water temperature by a large amount.

So you can see that method 1/A has the advantage that the element only slightly needs to raise the water temperature, saving energy requirements.

All numbers are made up and it really does depend on how well the insulation works etc...

As gearhead said, the heat flow depends on the delta T, so a larger geyser at lower temp may be a more efficient option.

aja

p.s. a concrete water storage tank in the basement is the way to go ?

X-rated Bob wrote:
Gearhead wrote: For example, you start with water at 20 degrees and the solar thing beefs this up to 90. It cools down overnight to 70 degrees and by morning flows into the electrical system that only starts re-heating it at 60.
OK... but how does that flow happen overnight? Surely you have to empty water out of the electrical geyser to let in the water from the solar geyser? My challenge was how to make that happen.

can't you use the electrical geyser as the storage tank for the solar heating system?

Gearhead

Electrically maintained solar tanks are only available in 'split' systems and Bob has a sitop tank. Plus, most people already have an electrical system before they buy solar.

Wizard

Wizard is coming to the conclusion that a lot of engineers play guitar ...

singemonkey

Aja, I'm confused. If, in 1/B, heat loss is irrelevant, how is 1/A actually better? 1/A takes advantage of the insulation, but 1/B doesn't need it. 1/A must surely use as much energy over the day as 1/B uses to heat from ambient twice a day? After all, the same amount of heat loss is being compensated for?

Of course the other factor is the availability of hot water all day - which is useful if, like me, you keep wildly erratic ablution times (I've just run my bath right now, at 13:00 or thereabouts, as it happens ?)

@Deeftes: UV couldn't be converted to heat by, say, using a material that absorbs UV? In the same way that microwaves are converted into heat in your microgolf? Or am I way off base here?

Seems to me though that the bottom line is that whichever method you use, the solar panels are adding heat into the system. The more added, the less electric city is required to pop up to a lovely simmer = lighter load on your wallet. Of course it all depends on how effective the solar system is. Bob's doesn't sound too hot ☹

Gearhead

A system that looses heat but is not kept at the same temperature will gradually go to a lower temperature. This lowers the average temperature and therefore the average heat loss. Thus it is more efficient in terms of energy. Less so if you want to run yer bath long after it has been reheated.
Singe is right about the UV. The sun emits lotsa wavelengths and the trick of designing a proper solar collector involves using coatings to transfer a broad band of these wavelengths.

vic

singemonkey wrote: Aja, I'm confused. If, in 1/B, heat loss is irrelevant, how is 1/A actually better? 1/A takes advantage of the insulation, but 1/B doesn't need it. 1/A must surely use as much energy over the day as 1/B uses to heat from ambient twice a day? After all, the same amount of heat loss is being compensated for?

Of course the other factor is the availability of hot water all day - which is useful if, like me, you keep wildly erratic ablution times (I've just run my bath right now, at 13:00 or thereabouts, as it happens ?)

@Deeftes: UV couldn't be converted to heat by, say, using a material that absorbs UV? In the same way that microwaves are converted into heat in your microgolf? Or am I way off base here?Seems to me though that the bottom line is that whichever method you use, the solar panels are adding heat into the system. The more added, the less electric city is required to pop up to a lovely simmer = lighter load on your wallet. Of course it all depends on how effective the solar system is. Bob's doesn't sound too hot ☹

the IR (infrared) portion of the sun's spectrum heats things up (with a bit of UV-Vis contribution)....in the case of microwaves...what happens here is that the frequency of the MV's excite water mols (in the foodstuffs) to vibrate and rotate which is then converted to heat energy....I think... :?