SolarImmersion

willemm1

Hi zeupater
You are I'm afraid confusing the issue. My figures are not estimates but actual, measured with a mains plug in monitor into which the appliance is plugged.
A quick calculator cross-check (meter indicates appliance power consumption) is that 30 minutes at 2850 watts = 1,425 watts so my 1.5 kW per shower is correct. The water is hot (unmeasured, thermostat set 55c) but any hotter needs a cold mix and I get a good shower. The immersion top mounting does ensure max use of what's heated.
Your suggestion that I'm underestimating shower power by a factor of 3 just doesn't hold water (sorry!)

Martyn1981

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.

Can you play with any of the settings?

Think of the hot water tank as a battery, it doesn't really care when it's charged or discharged. So if the PV can heat the water a little higher than the temp that activates the boiler then the boiler shouldn't switch on (possibly from Apr to Aug?).

Remember that whether the water is used in the afternoon, ten minutes after sunset, or in the early morning, they're all technically the same, a battery discharge after the last PV charge, and before the next PV charge.

Obviously there will be some losses overnight, but if well insulated, with factory foam, and a couple of jackets on top, then it should still be too hot in the morning. So the boiler reaches its heat cycle time, checks the temp and says 'nope not needed'.

You take some hot water out, then it heats back up during the PV cycle. If there's not enough to heat it past the boiler thermostat setting, then the boiler will top up during its cycle.

[Edit: Zeup beat me too it ...... and he understands it better than me! M.]

Mart.

zeupater

Martyn1981 wrote: »

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.

Hi

We average somewhere around 4 to 5kWh.t/day delivered from our solar thermal system and that's more limited by usage than capacity, so the above diversion figures seem reasonable, maybe even a little on the low side for a larger pv system ...

HTH
Z

lloyd2

I had an immersion smart controller put in with my 4kw solar panel system.
It heats up the tank once during the day and that's it. If it gets used up, it gets cold by the evening, so l dont know if it was worth the £300 l paid to include it. So l put my gas boiler on for 2hrs in the morning and 1 in the evening. I had it all installed early in March, on a very hot day maximum l had 21kw generated, averaging 15kw on dull days may be 4kw. I haven't submitted my first meter read yet, so far its reads 501 kw. Previously l would spend £3 per day on electric so wondering what l have saved. Plus the pre-pay meter seems to stop when its sunny so l am eager to see what the return will be....

lloyd2

I had an immersion smart controller put in with my 4kw solar panel system.
It heats up the tank once during the day and that's it. If it gets used up, it gets cold by the evening, so l dont know if it was worth the £300 l paid to include it. So l put my gas boiler on for 2hrs in the morning and 1 in the evening. I had it all installed early in March, on a very hot day maximum l had 21kw generated, averaging 15kw on dull days may be 4kw. I haven't submitted my first meter read yet, so far its reads 501 kw. Previously l would spend £3 per day on electric so wondering what l have saved. Plus the pre-pay meter seems to stop when its sunny so l am eager to see what the return will be....

willemm1

Hi lloyd2
You don't say what type/make of smart controller you have. There are "smart controllers" and "intelligent diverters". Some, older types, are just a switch for a pre-set time, or only switch if export is over a set amount - say 1 kW.
Intelligent diverters continually top up an immersion, with some switching anything over 30 watts, others over 200 watts, after any other temporary domestic demands are met such as kettles, irons, vacuums etc.
My generation for March was 280 kW, and for this month up to yesterday 249 kW so 529 kW in all. You should have the advantage over me if your panels are south facing as mine are west facing. My average annual generation over 30 months is 3,100 kWh. If your panels are south facing you might better that by 20% or more, depending on other factors like angle and shade.
I reckon my total export at around 80% pa so if you had an intelligent diverter it should "drip feed" the immersion throughout the generation period subject to the threshold at which the device kicks in.
I think you need to check just what your installer provided you with, and you should have been given some guidance/user manual about the switch you have. With a 4 kW pv system it should be doing better than you seem to be getting

lisyloo

Thanks guys, I understand now and it makes sense.

I know the guys that did our install worked late (we had dual aspect with solar edge) but it's a shame they don't optimise this for you or if they have to leave at least tell you about it.
I'm not a DIY person and it'll take me far longer to find the right screwdriver and work it out.

mickyduck

As described above by a couple of people.
Immersion heater is at the top of the tank and the thermostat set 15 C above the Tank thermostat which is halfway down the tank.
When the sun shines the tank is heated by Solar PV...IF the tank temperature drops below 50 C at the bottom of the tank and the boiler was on it would be topped up to 50 C. Water heating by the boiler is turned off for most of the year.

Electricity usage average daily from 1 Dec to 31 March is 4.8 Kw. These are actual meter readings so MOST days I have some surplus from my array. As stated previously my personal circumstances mean that as long as I get a "good generation" day every few days all is fine. If there is a prolonged dull period which is forecast I can either turn on the gas boiler or use the electric shower.

ChopperST

Been watching this thread with interest.

We had the Immersun 2 put in as part of our 4kW install in January. Since the start of last month we have used the gas boiler infrequently with the Immersun providing the vast majority of our hot water. There is two of us having showers in the morning and the Mrs has a bath most nights. On good days the Immersun will dump 10-11 kWh to the tank.

Our house is a new build with a modern unvented cylinder which holds the heat really well. I have taken to simply topping the tank up in the morning if the shower temperature is too cold with a manual boost of the tank with the boiler.

The Immersun has a calculator in it to work out how much you have saved v heating by gas and from January to April its just ticked over £20 (this doesn't take into account standing charges). Will be interested to see how we go through the summer but for me the investment was definitely worth it. I don't think it will give the same returns as the panels themselves but I like the notion that we are not reliant on fossil fuels exclusively for our hot water heating needs.

zeupater

willemm1 wrote: »

Hi zeupater
You are I'm afraid confusing the issue. My figuresare not estimates but actual, measured with a mains plug in monitorinto which the appliance is plugged.
A quick calculator cross-check (meter indicatesappliance power consumption) is that 30 minutes at 2850 watts = 1,425watts so my 1.5 kW per shower is correct. The water is hot(unmeasured, thermostat set 55c) but any hotter needs a cold mix andI get a good shower. The immersion top mounting does ensure max useof what's heated.
Your suggestion that I'm underestimating showerpower by a factor of 3 just doesn't hold water (sorry!)

Hi

The issue isn't 'how many kWh can a 3kW appliance consume in 30 minutes', if it was then I'd agree it would be 1.5kWh.

There are a number of issues at play here... the amount of energy it takes to heat water (approx.1kWh to heat 1000l by 1C), the initial temperature in the cylinder, cylinder capacity, the immersion size & rating and the length of time (&control) of the heating cycle.

If you've measured it, then that's what you've done, however, to have an immersion which can be plugged into a monitor is unusual (but not unknown) as most are hardwired to a dedicated fused spur on a dedicated circuit ...

Okay, another logical approach ... let's completely forget about everything except 10C water feed in and 55C out ... how much water does 1.425kWh heat ? .... 32l(1.425/(55-10)) using a quick rule of thumb ... Supposedly, the average domestic non-power shower head passes around 8 litres of water /minute, and the average shower takes 8 minutes, that's 64litres mixed on say a 3hot/1cold basis to a shade under 44C, which would require 48litres of 55C DHW to 16litres of 10C cold supply .... this seems to suggest that the 1.425kWh could theoretically heat enough water for a 5minute 20second((32/48)*8) shower, but there would need to be a relatively well designed mechanism to ensure that the water temperature delivered at the end of the shower is the same as the beginning by avoiding blending and doing this in a really small cylinder designed specifically for this length shower, and no more ... the smallest I am aware of is around three times larger at over 90litres ... and, of course, there would be absolutely no leeway for any warm water to be left after the shower ....

What is apparent is that anywhere near 30minutes would not be enough time to heat a even a small cylinder to 55C using a 3kW immersion heater. The only realistic conclusion to draw would be that the current cylinder has been retrofitted with a very short immersion, or the cylinder was originally a twin element E7 unit with a night-time immersion for E7 heating all of the water and a short 'top-up' element to provide a little extra heated water during the day, but whichever is the case, providing enough DHW to have a decent shower would be dubious and whatever water is heated would need to be used pretty quickly.

My own opinion regarding solar DHW heating (as I've mentioned a number of times before) is that anyone considering it really needs to address the storage capacity in order to bridge a number of dull days without needing to resort to a fall-back heating source …. this is something which solar diversion unit salesmen/installers and literature fails to address. If willemm1 had one installed it's very likely that the (possible) current 3kW immersion (probably~10” ish) would have been connected without even checking the length, which would have limited the amount of DHW to a level which would be bordering on completely useless.

Anyway, back to solar diversion - I agree, installers are expensive and the units are overpriced for what they are, but if you're willing to accept a long-term return it is possible as others on this forum could testify ... we don't have one, but if we didn't already have a solar thermal system it would certainly be on the shopping list, as, of course, would a cylinder sized to cope with a period of consecutive dull days in order to maximise savings ....

HTH
Z