Solar Panels

[Deleted User]

scarletjim said:

As a newbie to all of this, the iBoost seems to quite tricky to assess. I've seen one person say that it saved them only £7 in a whole year (!) whereas for you it must be several hundred pounds (I don't know how much fuel it is 'substituting', but that's quite a lot of generated kwh that the iBoost is using, so it must be considerable).

We have what I believe to be a 'heat only boiler' (i.e. not combi or system), a Worcester model fitted only a couple of years ago, and an Ariston hot water cylinder upstairs in the airing cupboard. It's about 15 years old, but seems to be fine. I'm currently monitoring how much gas we used to heat it. Would you or anyone here know if that made us likely candidates to significantly benefit from having iBoost, or is it not as simple as that?

I have a solar diverter (EDDI) which uses excess solar to heat my water. On an average day, this is saving me about 6kWh of gas OR about 3.5kWh of Grid electricity from March through until October. Break even - I doubt it.

I have a 6.35kWp array and a 13.5kWh battery on two roofs (south and east) generating about 6000kWh/year of which we consume about 3800kWh (we have an EV).

The ‘problem’ with a large array is that it generates far too much energy on a day in August (36.7kWh so far) to make use of, and too little in December (110 kWh with daily output ranging from 10.3kWh to 350Wh).

Was it worth the cost for a large array and battery? Yes, my break even point moves closer each time the cost of electricity rises. 

Evan3020

How did they only get a £7 annual saving?
My annual 1309 kwh diverted is £366 at todays prices or £650 at Octobers, you could argue that it replaced gas so should be priced as such.
I suspect the person you mentioned who only saved £7 was heating the water with gas and not giving the iboost anything to do.
You should also have a fully functioning immersion with the thermostat set at max (75 degrees)

QrizB

Evan3020 said:

How did they only get a £7 annual saving?
My annual 1309 kwh diverted is £366 at todays prices or £650 at Octobers, you could argue that it replaced gas so should be priced as such.

Your calculations are onlky correct if your diverter is replacing standard-rate electricity.

If you are substituting solar electricity for mains gas, and your gas tariff is around 7.4p/kWh, 1309kWh is worth £97 not £366.

At October's tariff of around 14p/kWh, it will be worth £183 not £650.

Alnat1

Think gas to heat the tank is still better for me, 11p Tracker gas or 35p Agile electric.

Daily use at the moment under 4kWh, will go up a bit in winter, water will be colder and boiler will need turning up from 50C to 55C for the central heating side of things (only one control)

[Deleted User]

Alnat1 said:

Think gas to heat the tank is still better for me, 11p Tracker gas or 35p Agile electric.

Daily use at the moment under 4kWh, will go up a bit in winter, water will be colder and boiler will need turning up from 50C to 55C for the central heating side of things (only one control)

It is not a simple 3:1 relationship. As suggested above, we use considerably less electricity to re-heat our cylinder than we do gas. 

Gas boilers are less efficient than an immersion heater. Moreover, gas boilers re-heating a HW cylinder are operating outside of the condensing band at Max TSet temperature. Heat is also lost in the piping between the boiler and the cylinder (yes, this contributes to heat in the home). Finally, on start up, if the say, the boiler temperature is 25C and the HW cylinder is at a higher temperature, the heating coil will remove heat from the cylinder until the temperature of the boiler flow water exceeds the cylinder temperature.

The differences can be quite stark in terms of kWh used. It is worth running your own trial: use gas for a week and then run the immersion heater for a week.

Alnat1

Our tank is in a cupboard on the landing, almost directly above the boiler (fitted on back wall of integral garage) so very little distance to lose heat in the pipes. The HW tank is not already at a high temperature when it is heated because we only heat for 40 minutes each morning and after 2 showers (bathroom next to tank cupboard) most of the heated water has been used.

We have a solar/battery system and have not installed equipment to use excess solar to heat the tank (wild guess, would cost £500 to get it fitted?)  The previous owner of the house was a plumber who refitted the combi boiler with a heat only boiler/duel coil tank (in anticipation of solar maybe?) but did not install any wiring or a switch to use electricity to heat the tank. So we'd still need to pay an electrician to sort that.

We're on Agile Outgoing so prefer excess generated to go back to the grid, especially late afternoon, when we get paid around 25-40p for it.

My maths and physics aren't great but in my simple head I'm doing it the best way for us now. Paying 40-50p a day for hot water doesn't seem too bad.

Evan3020

Whatever works best for you, I get FIT payments from 2015 so its in my interest to use as much as i can and export as little as i can.

Alnat1

@Evan3020 Yes, those that get FIT (or have EV tariffs?) have a different way of using their system to those of us who don't get a guaranteed income from our panels. It's not a one size fits all.

I admit that in the month after install, before my export payments were set up, I was trying to use as much free electric as I could. I ran out of things to wash and had quite a lot of baking in the freezer!!

Evan3020

Yes, begrudge seeing that export symbol on my iboost buddy, i have to think of some way of using that power.
This year has been great, April was exceptional so i have had 500kwh plus in April, May, June and July so far and August is off to a flyer with 71 kwh just 3 and half days in.

scarletjim

I'm back again! Two questions this time - firstly for @[Deleted User] - you say above:

"I have a solar diverter (EDDI) which uses excess solar to heat my water. On an average day, this is saving me about 6kWh of gas OR about 3.5kWh of Grid electricity from March through until October. Break even - I doubt it."

Is EDDI basically the same thing as iBoost that others here have spoken of? And are you saying that it saves you about £107 a year? (6kwh of gas per day, say 30 days pm for 8 months at 7.4p per unit = £107)

If so then at a cost of just a few hundred pounds, it would break even in about 4 years? Am I missing something?