So now I have a solar PV system how do I make the most of it???

Exiled_Tyke

warrenb wrote: »

I already have Hive heating so they have just released a smart plug which I use.

How are you finding it? I was thinking of getting one.

ely_ellis

EricMears wrote: »

Difficult to be sure your DHW tank is really full of hot water. Unless immersion element is right at bottom of tank or you have a destratification pump, there's usually some cold water at bottom of tank.

The immersion element is right at the bottom of the tank.
I understand that it won't be 100% hot, but that would be the same as if I used the central heating boiler to heat the water. The internal coil that heats the water from the central heating starts around 6 inches above the immersion heater element, so in theory it would give less hot water, although I know in practice, it will heat to a higher temperature and so the bottom of the tank would generally be hotter than with the immersion heater.
Our system is a closed system, so as soon as the hot water tap is turned on, the tank fills with 'icey' cold water from the main.
But for the sake of things, it's a full tank of hot water.;)

EricMears

ely_ellis wrote: »

The immersion element is right at the bottom of the tank.

That's quite unusual - but ideal in this situation.

ely_ellis wrote: »

I know in practice, it will heat to a higher temperature and so the bottom of the tank would generally be hotter than with the immersion heater.

That doesn't have to be the case. The thermocouple in the immersion heater can be changed for a new one of almost any value for around £15
(I was going to add a specific link but that occupied 10 lines of text ! Just look at www.plumbcenter.co.uk and enter immersion thermostat into search box )

You could have target value right up to 95 deg C (I have) but if you go very much above the normal 60 deg C you'd really need to fit a blending valve to the DHW outlet.

shavy65

ely_ellis wrote: »

it will heat to a higher temperature and so the bottom of the tank would generally be hotter than with the immersion heater.

Hey, echoing what Eric was saying, I have turned the stat on the immersion right up (to 5 I think it is) and the tank stat which I`m presuming starts/stops the DHW from boiler is at around 4.


My thinking was that if it`s a good solar day and I only use some hot water, say a basin full, then the water will be topped up from the immersion diverter rather than the boiler.


I may be way off though, any advice welcome

orrery

warrenb wrote: »

I have forgone the expense of an IBoost for the heater in the conservatory
I have a Smart plug which when I see the production is up I just switch on via wifi.
£20 against £350.

I've tried this with all sorts of bits of technology, including a 110V site transformer to reduce the immersion power to 750W. Even then, this sort of manual turn on and off is a double edged sword - if the sun goes in you end up heating with power that costs 14p instead of 4p per unit. I gave up in the end and installed a solarImmersion box.

zeupater

shavy65 wrote: »

Hey, echoing what Eric was saying, I have turned the stat on the immersion right up (to 5 I think it is) and the tank stat which I`m presuming starts/stops the DHW from boiler is at around 4.

My thinking was that if it`s a good solar day and I only use some hot water, say a basin full, then the water will be topped up from the immersion diverter rather than the boiler.

I may be way off though, any advice welcome

Hi

Safety point from from a previous discussion to be aware of .....

HTH
Z

zeupater wrote: »

JimLad wrote: »

Found some on my phone from a few weeks ago before the iboost was installed. Looks like the tank is 150L and the immersion goes 1-5.

I did some googling of the model and it appears the numbers mean the following...

1 = 10°C, 2 = 25°C, 3 = 40°C, 4 = 55°C & 5 = 70°C

Would should I have it set at to optimise my free hot water but minimise danger?

Hi Jim

Realistically, 70C is starting to get on the dangerous side unless you have TMV protection on your taps ... effectively the time to severe burns from hot water isn't linear - at 50C it's around 1minute, 60C ~2seconds and 70C it's instantaneous ...not even enough time to swear and pull your hand away ... we operate our solar thermal above 70C, but that's with a whole house TMV in place - without one I'd be far more cautious ...

If the thermostat maximum setting is 70C you shouldn't really be getting that much additional water expansion that the pressure relief or temperature safety valve would open. My worry in the earlier posts is along the same lines as Hengus & piinks related to the accuracy of the thermostat. Do you have a (cooking ?) thermometer which can measure temperatures up to 100C ? - if so try to test the water temperature against the thermostat setting .... as it stands, it certainly sounds like a temperature/pressure related issue which, considering that there's a requirement to safety check a pressure cylinder annually, must either be related to turning the temperature up, or a component failing since the last service ...

HTH
Z

cannonballdaze

cannonballdaze wrote: »

Here's something you can do that's practical and cheap;

Buy a Caravan Kettle - normal size and functionality but it uses 1000 watts to boil water rather than the 2000+ watts of a normal kettle.

This means more of the power will come from your panels when they are generating.

Here's one for sale in Aldi @ £9.99 beginning March 17th. Can also be ordered online with free delivery.

https://www.aldi.co.uk/caravan-kettle/p/069429019168000

Cheers - Joe

In view of some scepticism at the savings to be had, I did an experiment and calculation on the savings to be had from using a 1000w kettle and came up with the following;

Time to boil one litre of water in hours (187 secs / 3600); 0.051944444 of an hour.

Current Kettle Power in KW; 2.2500

Power used in KWh; 0.116875

My KWh Unit Cost; £0.10660

Cost of Kettle Boil; £0.01246

Estimate cost of new kettle using .40 less power; £0.00748

Difference per boil; £0.00498

Difference for 6 boils a day; £0.03

Savings in one year; £10.91 + 5% VAT

So, something like a one year payback :-)

Joe

Exiled_Tyke

cannonballdaze wrote: »

In view of some scepticism at the savings to be had, I did an experiment and calculation on the savings to be had from using a 1000w kettle and came up with the following;

Time to boil one litre of water in hours (187 secs / 3600); 0.051944444 of an hour.

Current Kettle Power in KW; 2.2500

Power used in KWh; 0.116875

My KWh Unit Cost; £0.10660

Cost of Kettle Boil; £0.01246

Estimate cost of new kettle using .40 less power; £0.00748

Difference per boil; £0.00498

Difference for 6 boils a day; £0.03

Savings in one year; £10.91 + 5% VAT

So, something like a one year payback :-)

Joe

The maths on the power useage is pretty much identical to what I came out with. Of course it all depends on when and how much you use the kettle.

For us I reckon we average about 2 litres a day and most of that it early morning and evening when we aren't getting 1Kw out of the system. I can honestly say I don't know anyone who averages 6 litres of boiled water a day. Then of course there are the gloomy days when we don't get enough to cover the kettle and the base load (then I use gas which I calculated came out slightly cheaper and warms the kitchen where I tend to work). Then of course there will be those occasions where the full-power kettle can be used so no potential savings there. So all in all, even with the cheapest of the travel kettles I reckon it would take most people considerably longer than a year to achieve pay-back. I think in many cases a travel kettle will not anywhere near to covering its cost.

ajbell

You boil water when you have the power not the other way round.
I will boil water just to stop exporting.

zeupater

cannonballdaze wrote: »

In view of some scepticism at the savings to be had, I did an experiment and calculation on the savings to be had from using a 1000w kettle and came up with the following;

Time to boil one litre of water in hours (187 secs / 3600); 0.051944444 of an hour.

Current Kettle Power in KW; 2.2500

Power used in KWh; 0.116875

My KWh Unit Cost; £0.10660

Cost of Kettle Boil; £0.01246

Estimate cost of new kettle using .40 less power; £0.00748

Difference per boil; £0.00498

Difference for 6 boils a day; £0.03

Savings in one year; £10.91 + 5% VAT

So, something like a one year payback :-)

Joe

Hi

Looks like you've fallen into a logic trap here ....

Basically, leaving solar aside, it's not power you need to consider - it's energy, so if you heat a given volume of water from a given start temperature to boiling point with either a 3kW or 1kW kettle then (within reason - kettle mass, in cycle heatloss etc) the same amount of energy will be needed, it's just the timescale which varies ..... now, upon bringing the effect of solar into the picture it's an assessment of the average ratio of self generation vs imported power which becomes important. Realistically, the proportion of annual generation hours above 3kW is pretty low, much lower than that where above 1kW is available and significantly nowhere near the hours those where only 500W is spare, which is probably where the majority of generating hours are over a year, therefore represents what is likely available when you want a cuppa (morning/evening/winter/dull/raining etc).

Of course, everyone will be different, but as a pure sanity exercise - if we leave high generation and low generation aside and assume that there is a constant ~500W of generation available, then a 3kW kettle would be importing 83%((3-0.5)/3) of it's power with a 1kW kettle importing 50% - of course with time being a relative variable, the percentages also apply to the total energy .... a saving of 33% (83-50) of the energy therefore exists in this scenario .... so that leaves the payback, which is pretty simple a £10 kettle costs the equivalent of 83kWh of electricity at 12p/kWh(10/0.12), which would be the equivalent of boiling around 800lites of water (rule of thumb ~1kW for 1Hr raises 1Tonne by 1C), which would be (say) 1600 kettles part filled with 500cc of water ... what's that ? ... just over 4 boils per day for a year (1600/365) to justify the kettle ? ..... coincidentally a figure in the same ballpark, but the logic is on more of a sound basis ....

So, a basic sanity check works out at ~4x500cc boils/day to breakeven over 12months, that gets me to around lunchtime most days, but remember, this is just a basic exercise ... all I know is that our 1kW kettle gets used quite a lot and, using our own variables, definitely paid for itself years ago .....

HTH
Z