More Solar PV Immersion Questions...

Hobbo2006

grahamc2003 wrote: »

Before answering, I'd like to ask if there are any compelling reasons for everyone having a bath everyday?

While I wouldn't advocate going back to my childhood and a weekly bath, perhaps cutting the baths by 50% is perfectly feasible (and even socially desirable with our current water and energy situation).

The water in your tank when hot has a varying temperature - hottest at the top and coolest at the bottom, and the thermostat set temperature at the thermostat. As you draw off hot water, the hottest is drawn off first, and gradually the water drawn becomes cooler, even ignoring the effects of cold water entering the bottom of the tank (incidentally, the design is such that little mixing occurs when the water enters, precisely to minimise the new cold water cooling the warm water in the bottom of the tank).

To get more heat stored in your water, you could turn your thermostat up - but be careful that it's not so hot to be a danger of bad scolding to you or your kids. Usually, for cost reasons, it's better to turn the thermostat temp down.

It should cost about 1.5kWh for a hot bath, making reasonable assumptions. Do you turn the immersion off before taking the last bath?

We like the routine of bath bottle and bed for the little ones. Gets them ready for bed and the mrs likes to relax when the kids are done for the day. I've added a timer now so that the water doesn't reheat until the next day, which should bring the cost down. Just might need a bit of trial and error before we get the right balance of hot water without heating water in the evening.

zeupater

Hobbo2006 wrote: »

yes that's our only way of heating water, we have warm air heating. Yes our elec costs 12.67p with southern electric.

Hi

Then it's likely that you should be concentrating on looking at utilising a nighttime electricity tariff (E7 etc) in order to reduce your energy costs .... have you considered this ?

For info : is the warm-air heating also electric or is it gas ??

HTH
Z

EricMears

Even an E7 supply wouldn't - on its own - help Hobbo ! It would give a full tank of hot water at 8am but any water drawn off in the afternoons/evenings would need replenishing at daytime rates.

A larger DHW cylinder has got to be best solution - heating that with E7 in wintertime & PV in summer would give best savings.

zeupater

EricMears wrote: »

Even an E7 supply wouldn't - on its own - help Hobbo ! It would give a full tank of hot water at 8am but any water drawn off in the afternoons/evenings would need replenishing at daytime rates.

A larger DHW cylinder has got to be best solution - heating that with E7 in wintertime & PV in summer would give best savings.

Hi

I was working on the previous post re:"I've added a timer now so that the water doesn't reheat until the next day, which should bring the cost down" so if the timer works surely it would be advisable to use E7 overnight as opposed to daytime rates ....

Regarding the water running cooler at the end of each day's cycle - I'd simply look at the thermostat setting and see if there's any possibility of storing more energy (heat) in the same volume. It was mentioned earlier that a larger cylinder could be the answer, however it could also be possible to fit a 'whole house' thermostatic mixing valve to the existing setup and simply squeeze more energy into the same stored volume and still protect from scalding - this could be the cheapest solution if the pipe routes allow .... it's what we have in place to maximise heat energy storage ...

HTH
Z

EricMears

zeupater wrote: »

Hi

I was working on the previous post re:"I've added a timer now so that the water doesn't reheat until the next day, which should bring the cost down" so if the timer works it would then surely it would be advisable to use E7 overnight as opposed to daytime rates ....

HTH
Z

But in #1

There are plenty of posts about how to use the excess PV and re-route it to the immersion. Currently I have just timed the immersion for mid-day rather than after bathtime at 7pm-8pm.

which seems to suggest he's hoping to get enough free energy to heat the water from PV. Have to agree with you that it seems a tad optimistic - may well work May to Aug but no chance in Dec !

zeupater

EricMears wrote: »

But in #1

which seems to suggest he's hoping to get enough free energy to heat the water from PV. Have to agree with you that it seems a tad optimistic - may well work May to Aug but no chance in Dec !

Hi

If it's a standard 3kW heater it's a hiding to nothing, a complete waste of both the pv generation and money spent on imported electricity ... E7 has to be the answer if gas isn't available as there aren't many days when a 3kW immersion heater using timed daytime electricity with the support of pv would work out anywhere near to being as cheap as gas or E7, even between May & August .... I certainly wouldn't try it if I didn't already have ample water heating.

HTH
Z

Cardew

Hobbo2006 wrote: »

yes that's our only way of heating water, we have warm air heating. Yes our elec costs 12.67p with southern electric.

If 7.6kWh's out of your total daily consumption of 11-12kWh is for water heating surely Economy 7 would be a sensible option?

You are using around 60% of your daily consumption on water heating; you could easily increase this to > 70% off-peak consumption.

Hobbo2006

Thanks for all your replies.

The warm air heating is gas.
Elec is our only option for heating water.

Only reason for timing the immersion for 11am is that we usually have at least 1kW spare at the moment so at least some of the leccy would be free, rather than using the immersion at 8pm when it's all being imported. The timer was only meant to bridge a gap to better solutions.

zeupater

Hobbo2006 wrote: »

Thanks for all your replies.

The warm air heating is gas.
Elec is our only option for heating water.

Only reason for timing the immersion for 11am is that we usually have at least 1kW spare at the moment so at least some of the leccy would be free, rather than using the immersion at 8pm when it's all being imported. The timer was only meant to bridge a gap to better solutions.

Hi

Have you looked into changing the gas heating system ? .... If you don't want the disruption of changing to a wet heating system I believe that there could be a solution based on a combined gas warm air unit which has the ability to also provide pumped heat to a vented hot water cylinder so you'd have far less disruption from the piperuns .... depending on the age of your current system this could provide a potential saving in your heating costs (pilot light / efficiency) as well as seriously cutting your water heating costs so it's well worth researching ...

HTH
Z

EricMears

Hobbo2006 wrote: »

Thanks for all your replies.

The warm air heating is gas.
Elec is our only option for heating water.

Only reason for timing the immersion for 11am is that we usually have at least 1kW spare at the moment so at least some of the leccy would be free, rather than using the immersion at 8pm when it's all being imported. The timer was only meant to bridge a gap to better solutions.

I'd been working on the assumption that your house must be on an 'all-electric' estate or too far away from a main road to connect to gas main.

Electricity really isn't an economical way of getting DHW in the normal run of things and even 'helping it along' with a 'free' PV supply is only going to work on a minority of days.

The price you've quoted for electricity seemed very high to me ! My daytime rate on E7 is less than that and I'd have thought a non-E7 supply ought to offer a cheaper rate (although to some extent best electricity deals vary by region and you may not be in the most competitive area). Well worth you looking into changing suppliers - either via the MSE website or the 'Quidco' website usually has even better deals.

The best you could hope for from Solar is that around half of your electricity is free on a good day in the summer or around 10% of it on an average winter day. E7 would give you a permanent 50% discount on overnight heating and you could still get a daytime boost from Solar when available.

Certainly not worth changing central heating system from warm air to radiators just to get cheaper DHW. Warm air heating is said to be more efficient than radiators.

In the 'good old days' you'd have had an 'Ascot' in the bathroom. Whilst that's not really a good idea these days, there is a modern replacement such as :-
http://www.bhl.co.uk/product/MAIN_MULTIPOINT_BF_HEATER_EXC_FLUE_KIT

but that's only one quick example - you could very likely find a better deal with a more thorough search.