Power Diverter - Is it worth the cost?

amcalester

I’m buying a house that comes with PV panels and I’ve been quoted €800 to add in a Power Diverter.

I have 2 questions.

What does a power diverter do and is €800 (including VAT) installation a fair charge?

quentingargan

Depends on how many panels you have. And €800 seems steep. If you have 6 panels, and use very little power during the day, a diverter is probably worthwhile. There are cheap ones that use a triac. These can cause distortion of the grid. The better ones have very high frequency switching and are better. But these usually are about €350 plus VAT. Should only take a couple of hours to fit.

rolion

@amcalester
How many panels do you have installed on the roof ?
However that quoted price is typical of ripoff times these days.

The diverter makes sense only over a specific amount of panels.
I have one and I love it... read more HERE

Enjoy it

amcalester

Thanks for the posts.

To be honest I’m not sure how many panels or what the surface area is. It’s a new build so these haven’t been installed yet.

I don’t know much about it and up to now there’s been 101 other things to deal with so I’ve done no research.

I’ll find out how many panels there are.

What else should I ask the builder in order to see if it’s worth getting?

I’ll be working from home a few days a week so will be drawing power during the day.

quentingargan

I wonder can you ask the builder to give you more panels? A lot of silly systems are installed with 3 or 4 250 watt panels to tick the boxes on Part L. Without planning, you could ask if the builder would bump that to 7 x 290 watt panels.

The extra cost of a few panels and a larger inverter are negligible.

Above about 1.5kw (6x250w) it is probably worth having a diverter. If you use 1/3rd of the power yourself, a 1.5kw system would push about 900 kwhrs into your immersion. Displacing oil, that would be about €80 a year. Displacing gas is a bit cheaper.

unkel

quentingargan wrote: »

If you use 1/3rd of the power yourself, a 1.5kw system would push about 900 kwhrs into your immersion. Displacing oil, that would be about €80 a year. Displacing gas is a bit cheaper.

Displacing gas that would be a saving of about €40 per year (gas costs about 4c per kWh times 900kWh saved). That is less than the depreciation / maintenance cost of a solar PV diverter.

In other words - it is cheaper to just give away your excess solar PV to the grid for free than to install a solar PV diverter.

Morally better and financially better. A rare combo...

amcalester

unkel wrote: »

Displacing gas that would be a saving of about €40 per year (gas costs about 4c per kWh times 900kWh saved). That is less than the depreciation / maintenance cost of a solar PV diverter.

In other words - it is cheaper to just give away your excess solar PV to the grid for free than to install a solar PV diverter.

Morally better and financially better. A rare combo...

That's the conclusion I've come to.

In my case I'd be displacing gas so it would take 20 years to see a return and I could do a lot more with the €800 now than spread over 20 years.

unkel

amcalester wrote: »

That's the conclusion I've come to.

In my case I'd be displacing gas so it would take 20 years to see a return and I could do a lot more with the €800 now than spread over 20 years.

And in the 20 years you are likely to have needed to replace the inverter twice (expected lifespan of about 10 years). So go figure!

Gumbo

amcalester wrote: »

Thanks for the posts.

To be honest I’m not sure how many panels or what the surface area is. It’s a new build so these haven’t been installed yet.

I don’t know much about it and up to now there’s been 101 other things to deal with so I’ve done no research.

I’ll find out how many panels there are.

What else should I ask the builder in order to see if it’s worth getting?

I’ll be working from home a few days a week so will be drawing power during the day.

Brand new build, my guess is a 1kw system.

amcalester

kceire wrote: »

Brand new build, my guess is a 1kw system.

Yeah, that’s what a neighbor told me he has.

Haven’t bothered to check up with the builder, I just told him not to bother with the installation.

niallers1

Diverter should cost about 400 euro + VAT fitted.

amcalester

niallers1 wrote: »

Diverter should cost about 400 euro + VAT fitted.

Even at that it doesn't seem to be worth it.

I got a few other quotes off the builder for other bits of work (attic flooring, outside taps/plugs etc) and some of the quotes were twice what I was expecting so I think he's pricing certain things to discourage people from getting the work done.

Who knows though, it's my first house and money/value has lost all meaning.

niallers1

Builders catch you on variations. Variations to original quote is very profitable for them.

denismc

How is your water going to be heated in the summer? I assume you have some sort of immersion tank?
Thing is your diverter will heat water until it reaches maximum temperature and then it will just export the surplus, so if your immersion is small then 2-3kwh will give you a tank of hot water pretty quick but you would really need to be using it throughout the day to get maximum value.

Costwise these things really don't make sense, but if the thought of your all your surplus going to grid for free upsets you then maybe get one.

unkel

denismc wrote: »

Costwise these things really don't make sense, but if the thought of your all your surplus going to grid for free upsets you then maybe get one.

Sums it up nicely

Personally, I'd rather give my surplus away for free to the grid. Or you could say to other people or to the environment.

quentingargan

unkel wrote: »

Sums it up nicely

Personally, I'd rather give my surplus away for free to the grid. Or you could say to other people or to the environment.

Exactly! While you are using a diverter to heat your water, somewhere else, a gas fired station is burning 2.5kw of gas to produce 1kw of electricity. It is a shame to use electricity to heat water in this way.

In the UK, where you get paid for PRODUCING electricity (even if you use it yourself) a small fortune is being spent subsidising hot tubs, unnecessary storage heaters etc.

It would have been far better if Elec Ireland had kept up its payments for exports

rolion

My inverter takes 4 years to pay off the initial €400ish delivered and DIY installed.
I dont know where you guys take these many years figures and so on...

As i said,even if you have smaller panels outage(and not making a quick recovery of the RoI),it will pre-heat your cylindder' bottom and then take the water up by the main device and top-it up to 60ish degrees...thats the secret, not bringing to higher temps,but pre-heating...

I hate,completely hate ... giving away for free,solar electricity.


Below,my PV Diverter today.
The figures are lower because the solar tubes are heating the cylinder very quickly and the diverter just goes in "tank warm" mode then sits idle, giving away the xtra electricity for free.

amcalester

Thanks all for the replies, I’ve gone from knowing absolutely nothing to knowing extremely little. That’s progress.

Even at 4 years I could better use that money for other things now, perhaps in a year or 2 I’ll re-visit.

rolion

amcalester wrote: »

Thanks all for the replies, I’ve gone from knowing absolutely nothing to knowing extremely little. That’s progress.

Even at 4 years I could better use that money for other things now, perhaps in a year or 2 I’ll re-visit.

Been like you years ago...took my time and even read/logged Sun's angles for my location on a daily / weekly basis.

We are here to share our experience and "money" and not to tell you what to do today or in year 2 with your budget...that game going to be fun for you only.

Wish you good luck...

unkel

rolion wrote: »

My inverter takes 4 years to pay off the initial €400ish delivered and DIY installed.
I dont know where you guys take these many years figures and so on...

I've done the sums on this forum a few times. How about your calculations to show your pay back time is only 4 years?

And fair comparisons please. 1kWh overproduction towards heating your hot water is not worth €0.14. It is worth about €0.04 (the cost of using the equivalent of 1kWh in gas or oil with an efficient boiler) And do take into account the €400 diverter has a lifespan of about 10 years

rolion

unkel wrote: »

I've done the sums on this forum a few times. How about your calculations to show your pay back time is only 4 years?

And fair comparisons please. 1kWh overproduction towards heating your hot water is not worth €0.14. It is worth about €0.04 (the cost of using the equivalent of 1kWh in gas or oil with an efficient boiler) And do take into account the €400 diverter has a lifespan of about 10 years

Lets not get started … again.
We will reduce the "extremely little" that the OP knows to completely nothing.
Not lastly, for me to spend an additional €500 (diverter) along with €4,000 (PV kit) is way much easier to do "now" … rather than €500 alone in 2 years...

My immersion diverter dashboard figures are above and in posts posted few times already...they do not lie and are true real numbers.
If today I have "exported" to my cylinder 5Kwh,thats … gas, oil or electricity ?
Why do compare with gas ? I haven't switched on my gas boiler since end of April.

What if "owner" has no gas but only electricity available to heat the cylinder !?
Would that make a difference in those numbers ? What if I decide to get a short quick burst of hot water using the immersion rather than heating up the whole house from the gas boiler ? IS the same efficiency if I heat the whole house radiators rather than the only immersion ? Can anyone think to switch on the gas boiler to heat water in the cylinder when in the house is 25 degrees ?

The diverter has a lifespan of unknown,10 years ago were no diverters therefore we don't have past data...I could say my diverter will keep me 10 years longer than the panels , because is … mine and is white.

And not lastly...I hate giving away free electricity...when I'm going to get something back for free from supplier(s) then I will happily do it too... in writing.

Enjoy it...whatever fit plan you have, with or without diverter...

unkel

You're avoiding the real and simple sums again, rolion. Like you have before. You really should not make claims about pay back periods of 4 years to people like the OP who deserve honest answers.

rolion wrote: »

If today I have "exported" to my cylinder 5Kwh,thats … gas, oil or electricity ?
Why do compare with gas ? I haven't switched on my gas boiler since end of April.

How is when you last switched on your gas boiler relevant? You exported 5kWh to your cylinder today. That is worth €0.20 because you do have a gas boiler.

I admire your thrust towards renewable energies, we should all be at it. But please be honest and don't misrepresent the figures here. You are not helping anyone by doing that

dathi

unkel wrote: »

?

And fair comparisons please. 1kWh overproduction towards heating your hot water is not worth €0.14. It is worth about €0.04 (the cost of using the equivalent of 1kWh in gas or oil with an efficient boiler) s

and the cost of oil per kwh is not 0.04 it is 0.075 and even that price does not allow for losses due to inefficiencies in the boiler

Gumbo

unkel wrote: »

How is when you last switched on your gas boiler relevant? You exported 5kWh to your cylinder today. That is worth €0.20 because you do have a gas boiler.

I suppose the reason why the last gas boiler use is relevant is to show that if the diverter wasn't in place, then the OP would be using gas to heat hi water.


Are you sure it only costs 20c to heat the hot water cylinder?
Ive a 200L hot water cylinder.

I have a 3kw Solar System.
I haven't turned my gas boiler on since end of April, so i've gotten all my hot water needs from the solar array. Ignoring heating the house as i'm sure nobody is heating the house over the last month or 2.

Also, the invertor has a 10 year lifespan, I haven't heard of any diverters only having a 10 year lifespan.

unkel

kceire wrote: »

Are you sure it only costs 20c to heat the hot water cylinder?

Ah no. What I am saying is that if you use a diverter to heat your hot water, the savings are what it would have cost you with a gas boiler. A gas boiler costs 4c per kWh, so that is the saving (so 20c for 5kWh produced and diverted in the above example). The saving is not the 14c per kWh you pay for electricity at peak rate.

dathi wrote: »

and the cost of oil per kwh is not 0.04 it is 0.075 and even that price does not allow for losses due to inefficiencies in the boiler

I don't really know anything about oil for home heating. But a good quality condensing gas boiler is 98% efficient and gas costs about 4c per kWh

Gumbo

unkel wrote: »

Ah no. What I am saying is that if you use a diverter to heat your hot water, the savings are what it would have cost you with a gas boiler. A gas boiler costs 4c per kWh, so that is the saving (so 20c for 5kWh produced and diverted in the above example). The saving is not the 14c per kWh you pay for electricity at peak rate.



I don't really know anything about oil for home heating. But a good quality condensing gas boiler is 98% efficient and gas costs about 4c per kWh

Ok I’ll have to check that out. I’m due to swap my gas soon so I’ll check what the rate is. Does the 20c include the cost of the gas also or just the electrical power to burn the gas or am I totally lost here

On the other hand, brand new condensing has boilers would not be 98% efficient. More like 92ish%.
And allowing for losses they are only 80ish% efficient.

unkel

In case anyone wonders why it might look like I'm playing devil's advocate - I'm all for renewables. I already have a large solar thermal system for hot water, I have an EV as the main family car (doing 95% of our mileage) and I also have solar PV, which I am expanding at the moment. But we have to admit it to ourselves, solar PV (without a feed in tariff) makes not an awful lot of financial sense unless you can either install it cheaply, have the system in place for a very long time, or actually use much of the electricity yourself that you would have had to buy from the grid otherwise. Or a combo of the above

kceire wrote: »

Ok I’ll have to check that out. I’m due to swap my gas soon so I’ll check what the rate is. Does the 20c include the cost of the gas also or just the electrical power to burn the gas or am I totally lost here

I think you're a bit lost there

It is just the cost of the gas. It is confusing as the unit for gas use is m3. But if you look at your gas bill, you can see that your are billed for the kWh equivalent of gas use. Call it the "energy value" of gas or something like that

And that equivalent costs about 4c per one unit of electricity

dathi

unkel wrote: »

gas costs about 4c per kWh

no it doesn't because you don't include the standing charge in the price to get an accurate price you would need your total yearly usage add the standing charge vat and carbon taxes and divide by the number of kwh used .

unkel

Nope. If you have a gas boiler and a live gas subscription anyway, the fixed costs (like maintenance, depreciation, standing charge) are there already. Same for your electricity supply

The revenue of a kWh from your solar PV diverted to your immersion competes directly with the cost of a kWh of gas used to heat your water. The latter is 4c. From which you have to deduct the fixed costs of the diverter to get your net benefits. At that stage there is just about nothing left. Or worse, it actually loses you money to install a diverter...

dathi

unkel wrote: »

Nope. If you have a gas boiler and a live gas subscription anyway, the fixed costs (like maintenance, depreciation, standing charge) are there already. Same for your electricity supply

The revenue of a kWh from your solar PV diverted to your immersion competes directly with the cost of a kWh of gas used to heat your water. The latter is 4c. From which you have to deduct the fixed costs of the diverter to get your net benefits. At that stage there is just about nothing left. Or worse, it actually loses you money to install a diverter...

thats like saying it cheaper to get my wife to drive me in my car as she only has to pay for the petrol

quentingargan

There are a few other questions here. Gas is 4c and the boiler is 91% efficient when heating the house and running for a few hours at a time. How efficient is it when it has to heat up its flu, intermediate piping and water etc., just to heat 200l of water in the hotpress? It would be useful to know. One of the arguments of the solar thermal brigade is that hot water in the summer is more expensive because the boiler is less efficient when only heating a cylinder.

AND

Is it better for the boiler to run it occasionally during the summer, rather than leave it cobwebbed for 6 months at a time?

rolion

@OP,sorry for completely throw offtopic your question

I have PVs and diverter.Based on past years usage,is well worth having it only if the amount of panels are over 2.5KW installed power,otherwise it will not be efficient.It will cycle on / off for small amounts of energy and disapoint you.Not lastly,no one gets free electricity off the grid so why you be the one doing it !??

More important is the usage and time slots for PVs,as someone said above...PVs combined with correct usage gives you maximum return / benefits. I generated 30KWh with PVs whole sun_day time and in the evening,i took 6KWh for cooking... whats the point you may ask ?

I'm waiting for PV storage...that will be the killer of the big boys that are holding the mass public development and deployment of the solar panels.
Compared PVs with tubes,i can have the Sun heating today my cylinder at 80 degrees and use that water over the 2 days period,thats storage and thats why sometime (mostly in summer time),solar tubes are better than PVs !!

A gas boiler does not take 4c to warm up the water.I don't have "the photons" now, but do a home work and read about "gas boiler modulation" and you will see that is more than the 4c per kw per litre...there is a maximum start-up and a minimum running configuration of the modulator,based on the return water temperature and controller.Not laslty,without a proper zoning,gas boiler / heating is not so efficient even if sometimes is a secondary result if you want warm radiators.And then talk about other invisible charges...

Have fun.

denismc

rolion wrote: »

I have PVs and diverter.Based on past years usage,is well worth having it only if the amount of panels are over 2.5KW installed power,otherwise it will not be efficient.It will cycle on / off for small amounts of energy and disapoint you.Not lastly,no one gets free electricity off the grid so why you be the one doing it !??








Have fun.

Do you mind me asking how many KWhs per year are you diverting and what size is your pv system?
Thanks

rolion

Ok,i dont want to play around the panels or tubes...
The secret is to maximise the consumption when the generation is at its peak time.

As below,i managed to stay under the dangerous red line but in the evening i maxed out due to cooking... i reckon no battery / storage will have taken care of the process...but day time,diverter worked excellent !

Just now,while doing the reports...wife cooking in the oven...PVs doing a nice constant 3.7Kwh enough for the whole house ... THEN ... she turned the kettle on and consumption spiked to over 5ish !!! I had to tell her to turn off the oven,turn on the kettle,wait till kettle finished THEN resumed on the oven !!
In this sequence i will have powered the kitchen of the panels completely ! But no...human factor and habits.




@Denis
My 5KW DIY system is live H E R E ... please feel free to play with the reports.
Cant give you access to reports on diverter as is a closed system,as you can see above is doing pretty ok if i dont have to report it to gas...
Is doing "badly" in the summer,as i have solar tubes as well and it reaches "idel time" pretty quick... but overall is warming up the cylinder's bottom nicely. The higher the numbers,the better returns.

Merrion

rolion wrote: »

I'm waiting for PV storage...that will be the killer of the big boys that are holding the mass public development and deployment of the solar panels.
.

Storing the PV excess in a phase change material heat battery (rather than an electrochemical one) is probably cheaper and they should not degrade over time.

rodoconnor

@ Rolion
Have you come across any load management system which might work well for solar pv in a domestic setting?

a148pro

Energia used to be the cheapest and are currently at 5.5c including carbon tax

I suspect the energy companies, like the insurers, probably take turns to be the cheapest so you won't get that rate indefinitely

We also need to factor in energy inflation. Price will only go up particularly with trump and the russians in that mix

If we knew the answers to Quentins questions would also help - efficiency loss in general and in summer when just heating water, whether it is better or worse for a boiler to be idle for half a year it would also help. If use of boiler in and of itself caused depreciation we would have to factor that in.

But I think its quite clear that its not a clearly good investment. If it was a break even proposition over ten years, and it reduced your reliance on fossil fuels, I would be willing to do it.

Incidentally, why is it so expensive? If you had a wifi switch on your immersion, a wifi enabled monitor on your meter and solar stuff and an app would it not do the job? (I say that without having solar)

quentingargan

a148pro wrote: »

Incidentally, why is it so expensive? If you had a wifi switch on your immersion, a wifi enabled monitor on your meter and solar stuff and an app would it not do the job? (I say that without having solar)

Not quite. Your immersion is 3kw and you may have 1kw of surplus power, so you run a sort-of dimmer switch on the immersion controlled by a clamp on the grid to the house.

Some cheap units literally are a dimmer switch, using a triac to switch the immersion on and off 100 times a second. That really screws with the shape of the sine wave, not just in your house, but in all your neighbours as well. Properly designed units use high frequency switching.

a148pro

quentingargan wrote: »

Not quite. Your immersion is 3kw and you may have 1kw of surplus power, so you run a sort-of dimmer switch on the immersion controlled by a clamp on the grid to the house.

Some cheap units literally are a dimmer switch, using a triac to switch the immersion on and off 100 times a second. That really screws with the shape of the sine wave, not just in your house, but in all your neighbours as well. Properly designed units use high frequency switching.

Ok thanks - I just thought it was a q of turning your normal immersion on

unkel

a148pro wrote: »

Ok thanks - I just thought it was a q of turning your normal immersion on

You can if you have a big enough array like Rolion. Just switch on the immersion when the sun comes out in full any time between 11AM and 2PM in summer

Human immersion diverter

Humans are the least reliable part of any system.

quentingargan

unkel wrote: »

You can if you have a big enough array like Rolion. Just switch on the immersion when the sun comes out in full any time between 11AM and 2PM in summer

Human immersion diverter

Good luck with that. Here is a graph of a typical day for my 1.5kw system. . Even trebling that, getting to switch on and off the immersion just right will be fun. And don't forget to knock it off when you use the kettle, or the toaster, hair drier etc.