SolarImmersion

travellerboy

theboylard wrote: »

Cheaper than that

Please share, after all that's what this forum is all about - moneysaving !

zeupater

willemm1 wrote: »

... My immersion use for showers plus washing-up wouldn't exceed 100 kWh pa so a pv immersion diverter device could at most save me £16 pa ...

Hi

I think that for most 100kWh/year for showers and washing up would be a little pessimistic .... that's an average of 274W/day(100/365), the equivalent of heating a kettle for just 5.5minutes/day((274/3000)*60) for the washing-up .... alternatively, using the 1kW raising 1tonne by 1C in 1Hr 'rule of thumb', a small 140l DHW cylinder raised from 10C to 60C just once a week would consume going-on 400kWh/year (0.14*50*52) ... roughly speaking, boiling a kettle daily for the washing-up and heating the DHW for one shower/week uses around 500kWh/year ..

HTH
Z

Ectophile

100kWh/year does seem remarkably low. 273Wh/day wouldn't even replace the heat lost by the tank if you didn't actually use any hot water.

I reckon I use about 4-5kWh/day keeping my water hot using a gas boiler. That figure is very approximate, as the amount of gas used is so low that it barely registers on the meter (it's somewhere between 10 and 20 cubic feet/day).

Martyn1981

Glad I'm not the only one struggling with these posts.

I read em several times yesterday but couldn't make head nor tails of em.

willemm1 claims to only add 100kWh to DHW, which hardly seems possible? And,

lisyloo keeps talking about showers when the sun isn't shining so the boiler has to come on(?) but refers to a Solar iboost so presumably must have a hot water tank, which should be heated during the boiler cycle or the diverted excess solar during the day, not (necessarily) whilst the shower is running ...... surely?

Having read many 'reports' on MSE and elsewhere, it seems that lots of people are diverting around 800 to 1,000kWh's of leccy pa (equivalent to about 1,200 to 1,400kWhs of gas), so I'd guess a saving of about £50 to £60 pa. So the decision to purchase should be based on the cost of purchase/install and personal projected savings - which will be different for each household. But also depends on current source of heating - if leccy or oil (rather than gas) then savings will be significantly higher, and less marginal.

Mart.

lisyloo

so presumably must have a hot water tank, which should be heated during the boiler cycle or the diverted excess solar during the day, not (necessarily) whilst the shower is running ...... surely?

Correct. Apologies I didn't realise there were so many different setups.
Yes I have a hot water tank that gets heated by gas on a timer.
I have reduced it significantly since we have had solar PV installed, but still need it running in the morning because can't risk not having hot water before work.
This means the water is relatively hot so the use of Solar PV is limited.

I reckon we save about 15p per day on average e.g. 3KW at 5p for gas.
That's about £55 per year.
If unit is say £230 then that's over 4 years just to pay for the unit.
Not sure how long they last but I don't think there is a warranty/guarantee for that long on solar Iboost so there's a risk it'll pack up before the 4 years pacy back time and even then you haven't actually saved any money.

We didn't pay for ours as it was chucked in for free during the negotiation phase, however with hindsight I don't think I'd pay for one with the setup that we have i.e. needing hot water for work before the sun comes up.

I am not of course saying it wouldn't work for a different setup.
If you have an electric shower or can take showers when it's sunny then clearly it's a different ball game.

Martyn1981

lisyloo wrote: »

Correct. Apologies I didn't realise there were so many different setups.
Yes I have a hot water tank that gets heated by gas on a timer.
I have reduced it significantly since we have had solar PV installed, but still need it running in the morning because can't risk not having hot water before work.
This means the water is relatively hot so the use of Solar PV is limited.

Right, I'm with you now, but this sounds like you might not be making the most of the set up. I don't have a diversionary switch (no hot water tank) but having read loads of comments, it all seems to be down to the set-up.

For you, presumably, the best situation would be a water tank temp that just makes it through the morning. This would allow for more 'sunlight' diversion. If the tank has been heated too high by the gas (after showers are finished) then there's less 'room' for the 'sunlight'.

So, minimum* temp set for gas heating, and maximum* temp set for immersion. Hopefully that way 'sunlight' heating at end of day will supply hot water in the morning (stored overnight). If the tank temp is high enough the thermostat won't let the boiler even switch on. If the tank temp isn't warm enough, then it'll switch on as per settings but only add enough heat to get by, leaving room for more 'sunlight'.

However, TBH, if you're saving around £55 pa, then you're probably doing it right already. You just don't want that tank too warm/hot in the morning after showers are complete, especially during BST months.

* within reason.

Mart.

willemm1

Hi again

My original post did make clear that hot water usage (other than for drinking/cooking) is very subjective as we all live very different lives and circumstances. Low power use comments made me recheck my figures, based on true consumption measured with plug-in monitor.
As said, I live alone, retired (25 years ago). I only shower once a week (I'm the dry-skin non-sweaty kind, so non-smelly either in case you're wondering).

For the record my total usage is 1,275 kWh pa or 3.5 kWh average day. Oil CH could heat my HW cylinder but I simply don't need a tank full. A 3 kW top-mounted immersion meets my needs, enough for a good hot shower.

Washing up – only use hot water after cooked meal once a day. Cereal breakfast and sandwich lunch plates rinse clean in cold/lukewarm water.

I did miss one calculation so here's my revised breakdown p.a.
showers immersion 52 x 1.5 kWh = 78 kWh
washing up 365 x .09 kWh (2 mins @ 2700 watts kettle) = 33 kWh
wash/shave 365 x .09 kWh (2 mins @ 2700 watts kettle) = 33 kWh
Total 144 kWh pa @ 16p = £23 pa.
A £475 install would give a ROI of 21 years.

As travellerboy took the trouble to mention, this forum is about money saving, and don't get me wrong – I'm not a penny pincher, but if I'm prepared to switch on appliances as suits my purposes I can't justify diverter costs. Being retired does give advantage of making the most of pv surplus by delaying use of washing machine/tumble drier/iron/kettle etc until a useful amount is generated, and my Sunnybeam bluetooth remote monitor provides this info. Needs a watchful eye on cloudy days but I get far more savings from export this way than I would with a diverter. A 500 watt electric fire is a handy boost in winter when pv output allows.

My savings would actually still be less than £23 pa as I'm already getting benefit from panels even without decisive switching.

Finally can I push home my real reason for posting in the first place. I don't like being conned and I feel the public are being conned or at best misled by extravagant savings claims being made by pv diverter makers. Is there anyone out there saving £300 pa? £200? £100? How much did your electrician charge to install? £180 seems an awful lot for an hour's work. How about some input from users with realistic (measured) savings, make of diverter and install cost? Also are you happy to fork out the cost of a new installation if yours packs up after warranty of no more than 3 years? This device is growing rapidly in popularity I suspect due to savings claims but it lacks substantial evidence of what it really saves, and the uninitiated deserve to know the facts before spending their hard earned cash.
I was about to buy one - until I did my homework.

Let me put my opinions another way. I like diverters in principle as useful, money saving devices but feel they are over-priced, especially for those unqualified to install them (that's for most). Warranties should be at least 5 years (imho). Maker savings claims need to be qualified. I hope I've given enough background for others to make buying decisions based on hard facts, not unjustified savings claims.

lisyloo

Thanks Martyn.
No we don't heat water with gas after a shower, but it's heated beforehand to make sure it's acceptable for a shower.
That means that the full tank minus one shower doesn't leave that much for sunlight to do.

My point essentially is that requiring hot water in the morning (NOT negotiable) is at odds with the perfect set up to save maximum amount of money.

I was told by one company it would save 50p per day and I reckon it's closer to 15p and for me it wouldn't be worth paying for the device.

zeupater

willemm1 wrote: »

Hi again

My original post did make clear that hot water usage (other than for drinking/cooking) is very subjective as we all live very different lives and circumstances. Low power use comments made me recheck my figures, based on true consumption measured with plug-in monitor.
As said, I live alone, retired (25 years ago). I only shower once a week (I'm the dry-skin non-sweaty kind, so non-smelly either in case you're wondering).

For the record my total usage is 1,275 kWh pa or 3.5 kWh average day. Oil CH could heat my HW cylinder but I simply don't need a tank full. A 3 kW top-mounted immersion meets my needs, enough for a good hot shower ...

... I did miss one calculation so here's my revised breakdown p.a.
showers immersion 52 x 1.5 kWh = 78 kWh .....

Hi

Like you, we're pretty low users of electricity (we actually use a little less, but close) and have solar thermal DHW with gas backup for extended inclement conditions. However, I'm pretty sure that you're still underestimating the proportion of your total annual energy which the DHW cylinder is consuming - here are some basic estimated figures ....

On a 140l copper DHW cylinder with a top mounted immersion, the cylinder will be around 40" high with a 27" element, so most of the cylinder will be directly heated. Working on an average cold water entry temperature from the header tank to the cylinder of 10C and raising the cylinder to a 'cool' shower temperature of 45C results in just under 5kWh((45-10)x.14), and of course, with there being a full week between heating cycles and allowing for standard cylinder heat-loss there would be little residual heat to effect the calculation.

... It's therefore likely that you're underestimating the DHW for a weekly shower by a factor of at least 3, whilst remembering that 45C is pretty cool for a shower, whereas periodic heating to ~60C is recommended/required for thermal disinfection of DHW storage systems, something which is particularly important considering that the main (/only ?) use of the DHW is for showering .... At a safe weekly 60C the usage would be 7kWh((60-10)x.14), giving a realistic annual range of 250 to 400 kWh against the estimated 78.

Considering the above, I'm really struggling to follow how a dedicated heating of the DHW cylinder for a weekly shower would consume so little energy ....

HTH
Z

zeupater

lisyloo wrote: »

Thanks Martyn.
No we don't heat water with gas after a shower, but it's heated beforehand to make sure it's acceptable for a shower.
That means that the full tank minus one shower doesn't leave that much for sunlight to do.

My point essentially is that requiring hot water in the morning (NOT negotiable) is at odds with the perfect set up to save maximum amount of money.

I was told by one company it would save 50p per day and I reckon it's closer to 15p and for me it wouldn't be worth paying for the device.

Hi

I think what Mart is trying to convey is that you may be unnecessarily heating the DHW on a daily basis and this could be addressed by looking at your thermostat settings.

For example, let's say that both the gas boiler and solar-immersion thermostats are set to 60C and at sundown the cylinder was at 60C. Overnight the cylinder will cool, let's say ~5C, so the boiler will cut in the next morning to top-up to 60C again ... that's probably the most inefficient use of a gas boiler there is - heating the boiler, pipes & contents to 60C in a almost certainly non-condensing mode, just for a 5C uplift of water. What you're effectively doing is heating the water from a temperature which would burn the skin in ~15seconds to one which would do so in 5seconds. Adding insult to injury (forgive the pun) after the shower, the tank top temperature will be at 60C and the contents will be partially stratified (~60C top to ~10C bottom), so if the immersion thermostat is at the top, it will not call for any further 'free' energy to be delivered from the solar panels until it's cooled sufficiently, resulting in a possible unnecessary solar heating shortfall which the boiler would need to make-up for the next day ....

The suggestion is to ensure that the gas boiler is used on a 'top-up' basis and not as the primary heat source, which may be the case if the thermostats are not set correctly. Have a look at both the CH DHW thermostat attached to the cylinder (not the one on the boiler!) and the immersion settings and check that there is a difference of around 5C, with the immersion being higher, to see if that helps change the balance ... (if you don't know how to check/change the immersion, just knock the CH DHW thermostat down by 5C).

HTH
Z