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

John_Pierpoint

For what it is worth and anecdotal evidence is not scientific, without factoring in 3 weeks holiday last year balanced against several absences by my wife trying to sort out her parents' estate 3 hours drive away (ie staying away overnight) not to mention babysitting the grandchildren (1 hr & 1.5 hrs away). No prizes for working out who uses the most power.
This household's usage of full price electricity is down from 1.85 KWh000's to 1.15 and Economy-7 from 2.7 to 2.4 though to the "improvement" should be added another 0.3 making 0.6 and 0.6 for both economy-7 and full price. [the Economy-7 was 0.3 ahead of the the comparable figure in early March at the end of the heating season, at the start of the PV season].

I am at home most days and can turn on the immersion when there is a sunny lunch time. Dish washer and clothes washing/drying is done in sequence when the panels are above 2.5 kW. The old but well insulated for its age chest freezer gets a time clocked rest for the first "half" of the night and again from (say) 07:30 (breakfast time) until (say) 09:00.

So some water heating has been transferred from the 01:00 - 08:00 period into probably the 10:00 - 14:00 BST zone. Daily decision is made at 06:30:D

old_grouser

Hello Druids!
I've not been here for a while, but am interested in how part of the discussion has moved towards intelligent switching to feed the immersion heater, and whether it's good value. I've only skimmed the last few pages of posts so far, but my impression is that the discussion of the cost of conventional water heating assumes that gas is 100% efficient.
Well, not with my boiler and pipe runs it isn't! Earlier this summer I measured gas consumption against Economy 7 electricity consumption to heat water, and found that gas was roughly twice as expensive per unit-of heat-at-the-tank as cheap rate electricity (though we do get a lot of warm towels as a by-product of using gas). So at Schloss Grouser the price to beat is roughly the cost of seven units of Economy 7 from the grid - say 40p per day. That makes the Immersun etc payback period a long one. On the other hand, I'm generating 2000kw/h a year that I'm not using, and I'd like to do something with it!
Apologies if I've missed something!
OG
3.29kwP facing south

Cardew

It is pertinent to point out that this whole debate on immersion heaters is academic for many people as more and more have combi-boilers - i.ee not HW tank.

Hobbo2006

Cardew wrote: »

Even though you are using 'full' daytime electricity prices of around 12p/kWh, I concur with zeupater that your assumptions are wildly optimistic.

Of course those heating water with gas or electricity will have to cost their savings per kWh at much lower rates - 4p/kWh and 6pkWh with a modern boiler.

Indeed I am surprised that you don't have an Economy 7 tariff and heat your water at around 5p/kWh. On some tariffs the 'break even' percentage for using E7 is below 20% on cheap rate. That 20% can be achieved without any water heating.

Doesn't look like Economy 7 tariffs are going to work in my case.... The daytime costs are higher which doesn't fit in with having a family at home during the day. I'd also need to pay for a new meter. Are you sure you're on the cheapest tariff? Uswitch are saying the following.

"As a general rule of thumb you would need to use more than 40% of your electricity at night to make Economy 7 cost effective. Some Economy 7 plans charge almost twice the standard night rate for any electricity used in the day, which can cancel out the benefits of the cheap electricity you get at night.
The more electricity you use at night and the less you use in the day, the more money you will save with Economy 7."

KevinG

Hobbo2006 wrote: »

As a general rule of thumb you would need to use more than 40% of your electricity at night to make Economy 7 cost effective.

In the case of Scottish Power's tariffs I know it works out at rather less than 40%.

Hobbo2006 wrote: »

Some Economy 7 plans charge almost twice the standard night rate for any electricity used in the day, which can cancel out the benefits of the cheap electricity you get at night.

No idea what they are on about there - a normal day rate would be around twice the night rate anyway.

Cardew

Hobbo2006 wrote: »

Doesn't look like Economy 7 tariffs are going to work in my case.... The daytime costs are higher which doesn't fit in with having a family at home during the day. I'd also need to pay for a new meter. Are you sure you're on the cheapest tariff? Uswitch are saying the following.

"As a general rule of thumb you would need to use more than 40% of your electricity at night to make Economy 7 cost effective. Some Economy 7 plans charge almost twice the standard night rate for any electricity used in the day, which can cancel out the benefits of the cheap electricity you get at night.
The more electricity you use at night and the less you use in the day, the more money you will save with Economy 7."

Ignore Uswitch! their 40% is only for some tariffs. Simply work out how much electricity you presently use, and then how much you would use heating water on economy 7.

I live in the Midlands. Let us take the UK average annual consumption of 16,500kWh gas and 3,300kWh electricity.

Using Energyhelpline, the cheapest tariff is First utility at £1035 and then two Scottish Power tariffs at £1039 and £1046.

Using the same figures but 20% electricity on Economy 7(night usage) and the cheapest tariff is £1022 with Scottish Power.

So on only 20% night usage economy seven is £13 cheaper.

Use most 'real world' combinations of consumption and the break even point for the cheapest tariff is still around 20%.

As said above it is easy to achieve around 20% night usage without heating water - don't forget night rate lasts well after most people are up and about in the morning.

Use your own consumption figures - with your own assumption of night rate consumption - and then add in say 6kWh a day( 2,190kWh) for water heating on economy 7.

Even in your unusual case(gas heating but not gas HW), to justify spending £xhundred by using daytime electricity rates at around 12p/kWh is questionable.

P.S.
Some companies do not charge to fit an Economy 7 meter.

nobby1963

Hi All,

Anyone taken the plunge with the Immersun yet ? if so hows it going ?

sly_dog_jonah

nobby1963 wrote: »

Hi All,

Anyone taken the plunge with the Immersun yet ? if so hows it going ?

Awaiting delivery of the Immersun to our installers.

nobby1963

Keep us `posted` please !

kabads

We're due to have installed PV panels this week (4kw system) and I'm wondering what the best way (both for environment and for cost) is of heating our water.

Currently, we have a condenser gas boiler feeding a megaflo 210i tank (not sure what this really is categorised as, but it runs on electricity). Both are boiler and tank are approximately 2 years old. The way I understand it, the gas boiler feeds the tank (set at maximum) with hot water, which the tank then keeps hot.

Is there anyone here who could give an opinion on timings - currently, we set our megaflo/boiler to heat water at 4am ready for morning showers. However, with pv panels, I guess we are better heating the water during the day and then showering in the evening/afternoon (the megaflo claims to have a heat loss of 1.57 kw.h/day@65 degrees C). However, what should the boiler be set to? Should we let the megaflo heat most of the water (under the power of solar pv), or would that put it under too much strain?

Any tips appreciated? TIA
Adam