Choice of intelligent switches ?

Cardew

Hobbo2006 wrote: »

We had chalked up 101kWh's on the Immersun from 13/09/12 to 31/10/12 but only 19kWh's since.

This is where a realistic appraisal of benefit v cost is needed if you have gas
CH.

So with a 4kWp system in Southern England someone with gas CH(I know Hobbo hasn't got gas) the 120kWh would have saved less than £5 in over 3 months.

It would be reasonable to assume that in the next 3+ months the same <£5 savings might be obtained.

Compare that with the manufacturer's claims!

Dave_Fowler

Cardew wrote: »

So with a 4kWp system in Southern England someone with gas CH(I know Hobbo hasn't got gas) the 120kWh would have saved less than £5 in over 3 months.

It would be reasonable to assume that in the next 3+ months the same <£5 savings might be obtained.

Compare that with the manufacturer's claims!

Some of the claims by the manufacturer are far too optimistic. I've just had a quote for a solar thermal system (didn't ask for it, it just arrived) saying I could save £113 a year on hot water heating for a system costing £5000. I think that is also very optimistic.

Since fitting my 'Immersun' look-alike on 24th October I've had 4 days when I have not needed to use the gas water heating, plus quite a few other days when it just needed a top-up. I have probably fed 62kWh into the immersion in just under 2 months. I'm pleased to say my home-built system cost around £130 fitted.

Dave F

sly_dog_jonah

Our ImmerSUN has diverted 242kWh in the same period (well 89 days) from a 3.7kWp system. I'll reserve judgement on the rate if return until I've got a full-year of figures, both for kWh's diverted and Gas consumption saved (which of course is hard to measure due to the variable and seasonal requirements of central heating). Naturally the return at this time of year will be much less, as the ImmerSUN diverts *excess* generation to the immersion. It will really come into it's own around March time for us I reckon, after which I doubt our boiler will be needed at all.

Cardew is being a bit selective with his 'estimates' by ignoring the losses in a gas boiler, whereas an Immersion is a much more efficient converter of kWh to heat. But of course the returns are greater depending on what fuel you use to heat your water otherwise.

Martyn1981

sly_dog_jonah wrote: »

Our ImmerSUN has diverted 242kWh in the same period (well 89 days) from a 3.7kWp system. I'll reserve judgement on the rate if return until I've got a full-year of figures, ...

Been pondering those numbers and your earlier posts, and Hobbo's numbers. I don't think 120kWh's in the last 3 months of the year is actually a criticism. On the contrary, it seems to support yours and others estimates of 1,000kWh+ potential leccy diversion pa.

Looking at Hobbo's numbers, 120 in last 3 months,
+ first 3 months of year, where generation should be approx 10% to 40% higher (depending on orientation and roof pitch)
+ 6 middle months, where Hobbo was diverting more than 3.5kWh/day at the very tail end (mid Sept).
+ losses in the gas system (as you say).

Onto another thought - unit price. I would suggest anyone considering an 'intelligent switch' approach, to do some careful number crunching over their tariff, and cost comparative alternatives:-

If 2 deals cost the same - but one has a single price, plus standing charge, whilst the other is twin tariff - then presumably the twin tariff will give greater savings, as the Apr to Sept gas savings could (should?) impact tier 1 units at perhaps 7p to 8p.

A similar approach works with leccy bills, where if pre PV costs are similar, it would seem logical to go with a twin tariff that has a narrower band, so a 16p and 14p tariff would probably save more than 20p and 10p, by 'knocking off' 14p's rather than 10p's, assuming off course the pre PV totals are similar.

Some quarterly number crunching is essential as generation is uneven. And consideration needs to be given to the 'width' of the quarterly gas tier 1 bands too.

Mart.

Cardew

sly_dog_jonah wrote: »

Cardew is being a bit selective with his 'estimates' by ignoring the losses in a gas boiler, whereas an Immersion is a much more efficient converter of kWh to heat. But of course the returns are greater depending on what fuel you use to heat your water otherwise.

A 'bit selective' - I concede!

The average (tier 2)price of gas on the better tariffs is approx 3.5p to 4p/kWh. including VAT and excluding any discounts.

So Hobbo's 120kWh would cost £4.20 to £4.80. If we take the average efficiency of a gas boiler as, say, 75%, then we have a figure of between £5.60 and £6.40.

Any attempt to value them at Tier 1 prices smacks of desperation - in any case for all future tariffs most companies are dropping the tier structure and re-introducing a daily standing charge.

Anyway my point was to challenge the manufacturer's claims of £100 pa savings for gas and £220 for oil.

zeupater

Cardew wrote: »

.... Any attempt to value them at Tier 1 prices smacks of desperation - in any case for all future tariffs most companies are dropping the tier structure and re-introducing a daily standing charge.

Anyway my point was to challenge the manufacturer's claims of £100 pa savings for gas and £220 for oil.

Hi

We use gas as our backup heat source for solar thermal and have a tiered supply tariff. I cost savings as being the displaced fuel at tier1 for the two warmer quarters and at tier2 for the winter quarters .... our thermal system meters energy transferred to the cylinder therefore it's pretty easy to do this.

Considering that our total gas consumption over the two warm periods this year was around 15kWh, this is the correct approach for us and is totally logical ... others would simply need to gauge what their own tier1/tier2 balance would be and apply the appropriate apportioned cost/unit.

HTH
Z

Martyn1981

Cardew wrote: »

A 'bit selective' - I concede!

Any attempt to value them at Tier 1 prices smacks of desperation - in any case for all future tariffs most companies are dropping the tier structure and re-introducing a daily standing charge.

Anyway my point was to challenge the manufacturer's claims of £100 pa savings for gas and £220 for oil.

What an oddly selective comment (my bold)!

Just checked my last two sunny quarters (2008, nah, I'm jesting) Apr-June and July-Sept.

We used approx 1200kWh, and 450kWh respectively (heating, water and gas oven (not hob)). Apr to June was exceptional this year, as we used intermittent heating through to mid May, whereas normally heating goes off late Mch/early Apr.

Checking price deals on-line the two cheapest companies were NPower with a tier 1 qtr of 1143kWh, and Scottish Power with a tier 1 qtr of 670. (Npower cheaper due to discounts) So in a normal year all savings would be at tier 1 prices.

Given that probably 75% or more 'diversion' will take place during those months, and using some actual, and some guessed diversion, I get:

Winter months 250 / 75% efficiency * 3.948p = £13.16
Summer months 750 / 75% * 7.642p = £76.42
Total = £89.58

Clearly each households circumstances will differ.

Mart.

Martyn1981

Just asked for advice from Energetic on his thread:

Martyn1981 wrote: »

Hiya Energetic, looking for some thoughts, following a chat with the neighbour yesterday.

He borrowed my barrow to take in a ton of coal stuff (didn't see exactly what it was) and some logs I'd put aside. We started chatting about PV and ST.

Thanks for thoughts, suggestions.

Mart.

and was wondering if any of the Immersun owners, or perhaps Zeup regarding ST, had some thoughts on this thread?

Cheers.

Mart.

Hobbo2006

Hi All,

I mentioned early in this thread that there was a mark 3 version of the solar immersion switch coming out. Well finally I had an email about the release and details of the product. It looks to match the Immersun but at a lower cost of £199 + £9 P&P. I guess you'd need someone to install it for you too.

www.solarimmersion.co.uk

[Deleted User]

Hobbo2006 wrote: »

Hi All,

I mentioned early in this thread that there was a mark 3 version of the solar immersion switch coming out. Well finally I had an email about the release and details of the product. It looks to match the Immersun but at a lower cost of £199 + £9 P&P. I guess you'd need someone to install it for you too.

www.solarimmersion.co.uk

Looks good :-)

I originally went down the immersun route installed professionally but was aborted at ther last min for various reasons. Then looked at installing it myself as it is a very simple install. But, back of a fag packet calculations... at £360 plus incidentals to install it is simply not worth the effort as too expensive. Does not payback until well out of warranty!!!

Also, when I was away on my hols for three weeks last Oct I turned off the water heating function of the ecodan ASHP but left the heating on as usual. As I keep a spreadsheet of regular meter readings there was almost no difference in leccy consumption despite having the DHW turned off. In a nutshell when the sun is out DHW is heated for free already.

I'm still interested in installing such a device but not at £360 so this other device is a step in the right direction