New smart timer from CBI

[ians]

My geyser is an old gravity geyser ... avg consuption using the timer which included cold showers and baths ... 6 kwhr
with the ASC unit on bypass ... avg consumption ... 8 kwhr per day hot showers and hot baths ... no geyser blanket installed.

I have a 1 kw element in my geyser ...set to 55 degrees.

For R125 extra per month ... for hot shower and a happy wife ... worth every cent.

[Justloadit]

Hi Dave
At the coast PV panels ability to absorb energy sits at around 30% max whereas solar water type system ability is around 70% .

Can you show any documentation attesting to this?

Whilst the coast gets less sun radiance than inland according to the studies, except when you are lying on the beach , the scientific study shows that Durban gets approximately 2/3 less than Johannesburg per annum.
I have been reading when there is no cloud cover at midday approximately 2.6kW out of my 2.6kW array, which translates to over 1000w per square meter of sun radiance. The 1000w/m square is the reference that PV manufacturers use as a reference that their panels can produce electricity at 25°C, so my panels are producing the 2.6kW at a temperature around 50°C indicating a higher watts per square meter.

Solar Radiance Maps

[GCE]

With regards to the PV dedicate to a geyser in my mind makes no sense at the coast. I understand the logic in near freezing temperatures where the convention solar water type systems burst seals etc.
At the coast PV panels ability to absorb energy sits at around 30% max whereas solar water type system ability is around 70% .

.

My statement was a bit jumbled and confusing even to myself now having read in again.

At the coast the temperatures are moderate and we don't get close to freezing vs further inland.

At the coast using a solar water heater , the chance of the pipes freezing during winter are almost zero vs some inland areas where the temperatures will drop below freezing at night and could cause the water to freeze in the pipes exposed .Once the water freezes it tends to expand and burst seals , joints etc.
The maintenance on a solar water heater system in colder areas would increase the costs of the system over the longer term and so in my mind would be more cost effective in the long run to use PV panels to produce energy through an element to heat the water.
At the coast the scenario is different.

The efficiency of PV vs water solar heater - The efficiency of PV extracting energy from the sun is at around 30% per square meter vs Solar water heating at around 70% per square meter .
I cannot find the notes from a course I did with Solar Edge inverters which showed the tests and graphs of both technologies to back up the statement.
I did find the following piece in-between notes that I have pasted below.

Matuska, Tomas & Sourek, Borivoj. (2017). Performance Analysis of Photovoltaic Water Heating System. International Journal of Photoenergy. 2017. 1-10. 10.1155/2017/7540250. Performance of solar photovoltaic water heating systems with direct coupling of PV array to DC resistive heating elements has been studied and compared with solar photothermal systems. An analysis of optimum fixed load resistance for different climate conditions has been performed for simple PV heating systems. The optimum value of the fixed load resistance depends on the climate, especially on annual solar irradiation level. Use of maximum power point tracking compared to fixed optimized load resistance increases the annual yield by 20 to 35%. While total annual efficiency of the PV water heating systems in Europe ranges from 10% for PV systems without MPP tracking up to 15% for system with advanced MPP trackers, the efficiency of solar photothermal system for identical hot water load and climate conditions is more than 3 times higher.

[Justloadit]

Hi GCE

The reference from Matsuka is in relation to the type of conversion process one uses when using PV. There is the MPPT tracking which gives the most efficient conversion for PV panels. I do not want to go further than this in explanations, as there are many good quality videos on Google explaining the type of conversion process available.

The crux of the mater is the word "Efficiency", in relation to the discussion at hand, efficiency does not play into the process of heating water, but the efficiency related here is the amount of energy one can extract from one square meter of surface area. If you have an empty roof, and you need 3 square meters or one square meter to get the water heated, does it really even matter?

Right now lets look at evacuated tubes versus PV panels.

Evacuated tubes work, but the efficiencies thrown about by installers are very optimistic. Bear in mind that I have had an evacuated 12 tube system on my roof for 10 years, so I am very in tune to what it can and can not do.
Some points that come up with measurements that I did as follows : -

Evacuated tubes
Summer
Starting temperature most mornings at 6AM was approximately 45 degrees, because my geyser timer would switch the geyser on from 5 to 6 so that I could have a decent shower in the morning.
End of the day at 17H00 maximum temperature of my geyser 52°C - no one at home to use the hot water. After the wife had a shower, temperature dropped to 42°C, there was sufficient water for my shower. Being summer, water does not have to be very warm. Temperature loss over night approximately 5°C so at 05H00 the geyser temperature was usually between 35 and 37°C.

Winter
Starting temperature most mornings at 6AM was approximately 43 degrees, because my geyser timer would switch the geyser on from 5 to 6 so that I could have a decent shower in the morning.
End of the day at 17H00 maximum temperature of my geyser 47°C - no one at home to use the hot water. After the wife had a shower, temperature dropped to between 32 and 37°C depending on how long the shower took. There was insufficient water for my shower, so switch the geyser onto mains. Usually took 45 minutes to bring the temperature above 45°C for my shower.

Replacement PV panels, I only have summer measurements for now, but one can extrapolate to winter because of studies done on existing installations that we have done
Set both geysers thermostat to maximum point which is approximately 65°C

Summer - I have 2 geysers running on 10 panels of 260W HV PVs -
Starting temperature most mornings at 6AM above 50°C on my Kitchen geyser, and above 42°C in the bathroom geyser as referred to above. Depending on the day, a clear day, by 12H00 both geysers at 65°C, an overcast day, between 13H00 and 14H00 both geysers over 65°C
After the wife had a shower, temperature dropped to 52°C, there was sufficient water for my shower. Being summer, water does not have to be very warm. Temperature loss over night approximately 5°C so at 05H00 the geyser temperature was usually between 45 and 47°C. Still hot for the morning shower, and the kitchen geyser around 50°C, depends on the number of pots get washed the night before.
Since installing it, I have not switched mains on yet. I read between 6.5 to 7.5kWH per day for both geysers running of PV

Winter, extrapolating from studies on other geysers installed, in the highveld we do not usually get overcast days in winter, so I reckon that by 14H00 hours, both geysers will be at 65°C.
Not sure of the exact losses over night, and the water replenished during hot water usage. Will have to wait for winter to get exact numbers. Experience from other installations done, the performance was good.

The issue with evacuated tubes is that there is a major issue between the balancing of the number of tubes for summer and winter. Winter is the time that the hot water is the issue not summer. In winter we want a higher water temperature, both to deal with the cool air in the bath room which appears to be colder when bathing, and also to deal with the heat loss differential in the ambient environment due to the winter cold.

Most evacuated tube systems are designed for summer, so that the water temperature does not go too high, as there is no way of controlling this save for reducing the amount of heat capturing, if there are too many tubes, then the water boils which can be an issue for geyser cylinders which must not only handle the temperature, but also the higher pressure.

Now with the 40% reduction in sun radiance in winter, the number of tubes that is selected for summer, just does not heat the water sufficiently in winter with out a mains back up. So the system does not quite cut it.

Placing more tubes for the winter usage then requires more controls which increases the over all cost of the evacuated tubes. This is usually not explained to customers, and customers think they are helpig the planet with out realizing that they are subsidizing the extra water heating with mains.

[GCE]

Hi
He ,Matsuka, also makes a statement with regards to solar water heating

While total annual efficiency of the PV water heating systems in Europe ranges from 10% for PV systems without MPP tracking up to 15% for system with advanced MPP trackers, the efficiency of solar photothermal system for identical hot water load and climate conditions is more than 3 times higher

There are numerous articles on advantages and disadvantages of each system .

A lot depends on what is being sold as to which articles are high lighted.

I am selling neither

[Justloadit]

I did a search using Matsuka, and found this article - Performance Analysis of Photovoltaic Water Heating System
Not sure if you were referring to this.

The difference that their report and my system, is that they used 2kWatts of D.C. a as a base point with out any temperature controller, with a number of different immersion heater elements, and then switched between them according to the sun radiance, to maintain MPPT (Maxim Power Point Tracking).
My system boosts a 1.3kW array to 300v D.C. and then with the MPPT, it varies the voltage to the existing mains element, where the existing geyser elelent can be used to control the geyser temperature. Efficiency of the thermostat is irrelevant, as the cost of energy is negligible if one does not take the initial cost as part of running costs.

I have had the evacuated tube for 10 years, and compared it to the PV, there is no comparison, PV beats it hands down. Granted I require more roof space for the PV panels, so efficiency of the systems in comparison can only be done with respect to the amount of energy you can extract for the amount of surface area you have available.

If you have plenty of roof space, use PV, the installation costs are low as compared to the evacuated or plate heaters, in which plumbing and circulating pumps have to be installed. PV requires the frame bolted to the roof rafters, and then an electrical connection to the controller to the geyser.
With some observations done, I would rate the flat plate solar heaters better than the evacuated tube heaters, but again, to maintain the balance of summer over heating of the water due to higher sun radiance and lower hot water usage, require mains back up in winter to maintain the necessary hot water requirements. Actual temperature measurements of flat plate as recommended by installers for hot water usage, only yields a maximum of 48°C in winter at the end of the day if no hot water is used during the day.

So as I have stated before, when efficiency is touted about, please request the exact reference of the reference to the efficiency, and then make an informed decision.

I remember showing the Usedasun System to an ESKOM representative, and the first question he asked "So what is the efficiency of the system?" to which I answered "100%"
He said "Impossible!", to which i replied "What do you mean by efficiency?"
He replied "PV panels are only 15% efficient!"
To which I replied, "Yes, the efficiency refers to the amount of surface area that the sunlight strikes to produce the amount of equivalent electrical energy. Since I am not paying for the sunlight, so who cares, I simply add a few more panels for my application , after all I have plenty of unused surface area which the sunlight covers, and by using the PV panels I reduce the incident heating in the roof where the PV panels are. So efficiency is irrelevant"

To add to the mix, what the ROI of any system is not purely based on the installation and hardware cost, but also the cost of the back up mains to maintain the supply of heated water over the lifespan of the system. Therefor calculating the cost of a PV based system must include the reduction of the cost of the system if a flat plate heater was used, and then also subtract the cost of mains to maintain the heated water in the flat plate application against the minimal cost of mains in the PV system.

What is interesting is figure 13 of the paper mentioned above. Look at the performance of the MPPT output versus the flat plat performance. It seems that the values contradict the conclusion, if surface area is not an issue.
PV panels are getting more efficient and cheaper. There are now offers for 400W PV panels, so effectively 3 of these panels could meet your PV heating needs.