PV - payback period

a148pro

Is there any established view on approximate payback times for solar PV?

This was touched on in this thread http://www.boards.ie/vbulletin/showthread.php?t=2057783191

and also in Conor's plan for energy freedom thread
http://www.boards.ie/vbulletin/showthread.php?t=2057550775&page=3

I'm just trying to justify it myself

Lets say 5k to install a 3kw system with the diverter to heat your water with excess

In my case I would anticipate energy usage of about 7kw per day, with an extra 2kw at night

Guestimate method:

Lets assume I could actually meet the energy usage per day with PV for half of the year. This is clearly not possible - the weather wouldn't allow it and I'd have to be super efficient with my energy usage to ensure I didn't need to top up from the mains. But lets just assume it for the purpose of argument.

Current energia switcher rate, .13 cent per Kwh
.13 x 7= .91c per day. x 365 / 2 = €166 saved per year

That would be a 30 year payback, even on the above assumptions which are unattainable

I appreciate you will also meet some electricity needs the rest of the year but I'm not sure how much that will work given I've overestimated its capability for the 6 months for the purposes of example.

So the scope to catch up is in the heating of water. Conor's thread recorded 221 kwhs going into the hot water in a given April.

Again, for utlility, lets suggest this goes in 6 months of the year. Some months it will obviously be significantly higher. Some months it will be zero.

Another thread estimates water heated by gas costs 4.5c per kwh (I'll have newly installed GFCH with water on separate circuit)

So 221 x 4.5c = 9.95 per month
Assume it achieves this over 6 months, 59.67 per year

So on those numbers amount saved per year is
166 + 60 = €226

= 22 year pay back

Pv watts estimation tool method:

Alternative and probably more accurate way of estimating cost is that pv watts allows you to estimate what your system will generate. http://pvwatts.nrel.gov/pvwatts.php

In my case, without changing any of the parameters for the system beyond putting it as roof mounted (I don't know the angle), at a .13 day rate it gives me €335 per year, giving me a 15 year payback, less if rate was higher and if inflation was a factor. BUT that assumes I use all the energy created which I assume is impossible. I have to think that some of the energy would go back to the grid when the tank was warm enough?

Also I can't break down how much of the electricity I can offset against gas that would otherwise be used to heat the water, for the purposes of calculating repayment period.

Incidentally that tool suggests I would generate 2581kwh of usable electricity per day which would give me an average of 7kwh per day, suggesting my guesstimate above is only 50% of the capacity


Comments?

Am I missing / miscalculating something?

Apologies if this is well covered ground on here but I couldn't find an answer

Does anyone have any real world figures for the amount of kwh they used as opposed to generate? And for the amount they still export where they are using a diverter?

If I get an electric car which will actually be home a fair amount as we don't drive enough, will that have a significant improvement on payback?






Some riders:-

- I assume energia will only offer that rate for a year and it will then revert to maybe 17c - if it did the total amount in first calculation would increase to 277 per year and amount would reduce to 18 years

- as against that you could schedule appliances to avail of night rate

- I appreciate Conor's thread was a 2.2Kwh install, I'm costing 3kw above

- there will also, presumably, be energy inflation. I see a paper here estimating 4% per year. It also covers repayment period but I can't quite understand the graphs.
http://tippenergy.ie/wp-content/uploads/An-Economic-Analysis-of-Solar-Photovoltaic-Installations-in-Ireland.pdf

- feed in tarriff may arise in future

unkel

a148pro wrote: »

- feed in tarriff may arise in future

That's it. If you hope or expect a FIT or if you just want to do your thing for the environment, by all means go PV. There is just no economical reason to do so at the moment. Having an EV plugged in during they day barely helps. You can charge it at night at night rates, and public charging is still completely free in this country.

a148pro

unkel wrote: »

There is just no economical reason to do so at the moment.

Well what is the actual payback period has anyone calculated? And at what payback period do you say it is worth it. Personally, I don't mind about 15 years, combined with the feel good factor of actually trying to live off clean energy for a bit.

Much beyond 15 years and it just becomes hopeless.

Capt'n Midnight

Also factor in that PV is getting cheaper all the time.

If you have to borrow money you might save more by buying it in a year or two when it costs less.

rolion

a148pro wrote: »

Well what is the actual payback period has anyone calculated? And at what payback period do you say it is worth it. Personally, I don't mind about 15 years, combined with the feel good factor of actually trying to live off clean energy for a bit.

Much beyond 15 years and it just becomes hopeless.

i spent almost 12 months doing the maths for the PV panels. In meantime,i end-up geting solar tubes,with many thanks to SEAI grant.

Not been smartie here...but if can you tell me how many hours of sunshine are tomorrow and/or the first day after PV instalaltion and i can forecast the R o I. I got lost through your numbers or other any types of forecasting... rubbish and not based on the real world . You can generate in sunny day 20 KWh but by not been able to use a mere 5Kwh is damaging your results.

As i said before,check this link HERE and select Ireland.
See what other PVs intalled across the country can do in a pecific period of time.

I compare my system wih a chap from Lucan,dont know the PV owner.
But,sometimes,despite of only 15Km distance,the difference is very visible.
My system generated 4MWh in 12 months, thats 4,000 x .15c = €600 . Worth it !? By the numbers yes BUT how much actually went in to my own cunsumption !? I can do the maths from the meter readings,from the inverter reports ,from the immersion reports and so on.I can give you all the info,can you do it ??

As per below graph,May was the best one... with almost 200 more than August.
Now,the reason that diff is there it could be related to the position of the panels,the angle of the fittings and the shadow of the roof/trees and so on.
If i can have the space i will have had a tracker installed.




Today,i had 9KWh generated,most of it between hours of 11:30am and 2pm.
Yes,it did covered the electricity appliances in my house (my home takes almost 500Wh if ... empty of people) and then diverted to the immersion (actually doubled the solar tubes heating the water in cylinder). The day before,barely reached 600Wh curve.




Immersion today did a great job,having almost 5Kw saved from going free on to the grid :

unkel

rolion wrote: »

My system generated 4MWh in 12 months, thats 4,000 x .15c = €600

But here's the thing. It's not really worth €600. Lowest day time rate is with Energia 12.67c/kWh incl VAT.

So the maximum value if you use 100% of your production for stuff that you can not run cheaper with gas or with night rate electricity, then it is worth a maximum of €500 in theory.

In practice you could charge your car, run your dishwasher and dryer at night. At 6.65c/kWh. So then the saving is just what based on what you need to run during sunlight hours anyway, like your fridge. So then you get maybe 20% at 12.67c and 80% at 6.65c, so total worth only €300

But that is using your production 100% which is not going to happen unless you divert to immersion, saving just 4c/kWh compared to gas (minus the extra cost of installing the diverter which is about half that again), so say you use 20% at full rate, 30% at low rate, and 50% to hot water, then the total value of the 4000kWh produced per year is a shocking €220 per year

And a system in perfect conditions in Ireland generating 4000kWh per year must be what, about 5kW panels, so maybe €6k to install?

If so, payback time about 30 years, without even taking into account maintenance on the hardware or the opportunity costs of money...

rolion

:@unkel

We have been here already ... we may need to meet and chat around a cup of fairtrade organic coffee ... more than happy ! I'll bring my hungry powerfull diesel jeep and you can bring your lovely EV.

I do always calculate 4,000 KWh at .15c per electricity, i dont mix the gas and boiler and so on, as my PVs are generating electricity for my immersion and for my greenhouse heating ceramic elements (once the tank is full due to solar tubes). Immersion costs me €380 from an electrical shop in Monaghan.According to my logging system,after one year,is almost paid in more than 75%.

I got all the equipment from UK as trade-to-trade, as a start-up for being a PV distie or an installer. Went for the top of the tops,premium LG panels and ABB inverter. Saved thousands in installation fees,at least 3 grands in local rip offs ! I did all the numbers crunching fun first year then, just let the God Sun to take over and do it's best job...

Do you have a PV system ?

I anyone wants to buy one,just shop around.Definitevely check local first then nationwide.
Try a bit of DIY on your side,is not so highly skilled job !
Buy the panels from a well known supplier (i can recommend one in Finglas that can help you with "know-how" too) , get a local roofer to install the raillings and then a local spark to connect the cables !
Is not a big deal,trust me,been there. ALL of my systems are DIY,with little support on the end side of things.

I can take the risk to say get a 30 tubes solar system and a 3KW PV system. Costwise,is the best deal out there if you can mix the SEAI grant and the DIY job.Do not go crazy on the PVs only ,due tosome legal requirements .. be smarter,apply for a SEAI grantget the soalr tubes and the auxiliary items and as well,the PV system filling-up the roof.The solar tubes,partially paid by Mr. Grant will assure you 100% / 24/7/365 a nice bath water and the PV panels trough the immersion,will minimise the DeltaT so that you have the most efficient system out there,that the fcuking money can buy today and give you satisfaction in the every and any short,medium or long term R o I !

Personal,i love & enjoy my eyes every day when i have to leave or arrive at my home:

unkel

Good point, let's not underestimate the feel good factor

But unfortunately, it does not make economic sense. Buying cheap (second hand) parts and doing all the fitting yourself could of course bring down the pay back period substantially. I'd love a PV system myself, but the sums don't work. The day we get a net FIT (or any reasonable FIT really), is the day I'm on the phone to organise getting a PV system installed.

Gumbo

Sometimes it’s not only about payback.
I done my PV as I had the roof off for construction. There was no better time.
I’m in the construction busnisestso I pulled in all my favoirs. Got my 3kw system installed with immersion divertor for €2900.

Same as thermal, if all I get is hot water and base load then I’m
Doing something to help the environment. Again today, I came home to fill tank of hot water. 2
Showers and the 2 kids washed from Solar heated water. It’s november so I’m
Pleasantly surprised although it was quite sunny today. I sent 4kwh to the immersion throughout the day.

unkel

And if you're going to stay in your new house for who knows, 30 or 40 years, maybe even more, it will eventually pay for itself. In your case a lot quicker than that.

And it could very well happen that sometime in the near future we will get FIT. How can we not? As soon as that happens, there will be inflationary pressure on parts and install costs

a148pro

Rolion are the figures in your first graph pv generated or pv used?

If used then it looks to be worth it

Not to be picky but has no one done the numbers on the basis of pv used and kwh put into the immersion so actual payback can be worked out?

I still think I'm going to go with - a bit frustrating to have to spend 5 k to find out how well it'll work though. Where the fcuk are the government, trying so hard to reduce our carbon output, in all of this? Really disappointing

quentingargan

There is another angle to all this. Electricity is a premium source of energy. It is (in theory) ecologically better to export your electricity and heat your water with gas. This is because somewhere else, it is taking 2.5 kwhrs of gas energy to produce 1kwhr of electricity.

For this reason, the better approach is an EXPORT tariff (or better still, nett metering). Everyone is campaigning for a PRODUCTION tariff, planning to use immersion divert devices, but that is not the right approach as you end up funding PV systems that are simply used to heat water. An as has been pointed out, gas is so cheap that the payback is huge.

But if you are going to heat water with your surplus (and the current government policy gives you little choice) then like many, I live in an area where gas isn't available, and using an oil to heat a boiler, flue, pipes etc., just to get 120L of hot water in a cylinder is going to cost more than 4.5c. So I prefer to consider water heating at my night rate of 8.5c

unkel

a148pro wrote: »

Not to be picky but has no one done the numbers on the basis of pv used and kwh put into the immersion so actual payback can be worked out?

Problem is you can't. PV used is skewed by the fact that some / a lot of it could have been run at night rates. And kWh put into the immersion has to be offset by the far cheaper use of gas to heat your water vs the extra cost of the immersion diverter

I'd say my above figures are as realistic an estimation you will get. A typical 2.5kW PV panel system in Ireland generates about €100 real worth of electricity per year.

a148pro

I think thats a little jaundiced in fairness Unkel. We could all go down the pub, drink water and charge our phones or use a laptop or watch tv there. We could ask our friends to wash our clothes.

The calculation is on the basis of how much energy that you ordinarily use can be replaced by solar. In my case, I will use 7kw hours per day, whether I have solar or not. I will therefore save .13c for each kwh solar replaces. I think there is a good argument that that rate will rise strongly over the coming years. I assume energia will charge non switcher higher rates in due course? if the insurance scam is anything to go by these companies all take turns in offering the best rates

thereafter its a q of how much of 7kw I can get from solar and how much gas kwh I can save by heating with the excess.

I can hope for the answer to the first q to be at least 166 euro a year. The second q unfortunately I have no idea of as I don't know at this stage how much gas it'll cost to heat my tank, quite apart from anything else.

I have to hope that batteries or FIT intervene. If batteries become affordable or FIT comes in it'll be a lot more viable.

In any event I intend to do it and find out.

I find quentin's comments very interesting. Hadn't thought about it from the perspective of the environment generally. Really very fcuking frustrating.

unkel

a148pro wrote: »

The calculation is on the basis of how much energy that you ordinarily use can be replaced by solar. In my case, I will use 7kw hours per day, whether I have solar or not. I will therefore save .13c for each kwh solar replaces.

Yes, that's fair enough. With your usage of just over 2500kWh, you would not have a night meter. What gets me is people saying they save 15c / kWh for excess electricity going into the immersion diverter. Eh no, that's worth more like 2c / kWh

a148pro wrote: »

I think there is a good argument that that rate will rise strongly over the coming years.

That remains to be seen. With smart metering and the increase of solar PV, we will most likely see rates far lower than now during peak sun and peak wind (making home solar PV worth even less than it is now)

We will also most likely see rates far higher than now during peak demand when there is no sun / wind

a148pro

Jaysus. If my installing PV without FIT leading to a reduction in the price of electricity generally, leading to an even longer payback time BECAUSE PEOPLE LIKE ME TAKE THE HIT AND GET PV then I'll get a second tank and diverter just to spite them.

What do you reckon the payback is for thermal so unkel?

That old 4c per gas kwh not intrude on that? Trying to work out cost of heating tank with gas and google suggesting 9.2kwh for 120 litre tank. Given I'll have at least 240 litre tank, we're looking at 70c to fill a full tank each day, E262 a year.

From speaking to people with thermal, I'm giving to understand it'll only really work for about 6 months. I found some people even more pessimistic than that. But that would only be 130 per year savings no? Which would be an appalling payback time also?

I mean of the two electricity is a lot more expensive, another reason why on paper at least you'd think electricity was what to target

rolion

unkel wrote: »

Yes, that's fair enough. With your usage of just over 2500kWh, you would not have a night meter. What gets me is people saying they save 15c / kWh for excess electricity going into the immersion diverter. Eh no, that's worth more like 2c / kWh

You are really taking the piss with your maths...

If my PV panels already installed and making their photons happy harvesting are generating NOW 5,000Wh and i'm using 3,000Wh for some appliances THEN,magic happens and the extra ADDITIONAL free electricity of 2,000Wh is been diverted to immersion for a full 60 minutes so that today i had 5,000Wh used by immersion via diversion AND saved from going free to the grid AND / OR avoid using the gas boiler ... how do you make the maths so that it will worth only 2c !?? (please change the figure to match any of the owners systems,it just for the purpose of the demonstration )

Just dont get it...if it were exported,it costs me around minus 9c (ex FIT) and if i had to use the gas,dunno how much it will take my 18KW Viessman to get the 2KW electricity converted in gas language metering,taking in consideration that ALL of the radiators in the house has to be switched off to get maximum return from the gas heating coil in the cylinder. Same,if i had to use the electric immersion it will have been more.

Please justify the figures ,as they are massively correct OR wrong !
Thanks.


PS
My figures are a bit on the "unknown" side as i have the PVs and the solar tubes.

unkel

Do I seriously have to explain it again? 1kW from PV panels diverted to immersion competes with heating hot water from a gas boiler. Which costs about 4c/kWh in gas. So that is your benefit

But since an immersion costs about €500 to buy and install, you have to take this cost into account also, which can be converted into a cost per kWh of something like this (again I'm trying to keep the maths as simple as possible). Say you divert 1250kWh to your immersion per year and your immersion diverter lasts for 20 years (optimistic), that means that every kWh diverted costs 50000/(1250*20) = 2c/kWh

So your net benefit of every kWh of your PV going into your immersion is 4c - 2c = 2c

Gumbo

Most people have an Immersion as standard though and don’t need to buy one?
The argument PV V Thermal is ongoing and both are only minimal nett gain but they do take some strain from the environment and both contribute very slightly to a greener environment.

PV competes with cheap gas water heating just the same as thermal competes with cheap gas water heating.

Truth e told, PV and thermal are not worth the money of financial gain is the main desire from the system.

unkel

kceire wrote: »

Most people have an Immersion as standard though and don’t need to buy one?

It's the extra cost (€500) of the immersion diverter that has to be deducted from the value of the kWh sent to the immersion

kceire wrote: »

PV competes with cheap gas water heating just the same as thermal competes with cheap gas water heating.

Yep. Exactly the same. The only gain is what it would otherwise have cost to heat the water with the cheap gas.

And yes, for most people thermal PV would have a poor pay back time. We were a bit exceptional ourselves as we needed part of the work carried out anyway (a bit like yourself as you were building a new house fitting PV is cheaper than retrofit) and we need a lot of hot water (5 people household, 4 women, girls soon all teenagers that seem to spend their lives in the bath / shower )

And yes, you do it for the environment too and for the feel good factor associated with it. Like donating to charity or doing volunteer work

a148pro

Unkel what do you estimate your payback on thermal?

Anywhere we can lobby for a FIT or does it not actually make sense in a bigger picture?

quentingargan

a148pro wrote: »

Anywhere we can lobby for a FIT or does it not actually make sense in a bigger picture?

You have until next Friday 10th to make a submission on the consultation process. See HERE.

TomOnBoard

Here's a paper I came across that was done in 2015 by someone studying for for a M.Eng. It might prove helpful to see how someone else approached the payback perspectives around PV in a public service installation in Tipperary.

http://tippenergy.ie/wp-content/uploads/An-Economic-Analysis-of-Solar-Photovoltaic-Installations-in-Ireland.pdf

rolion

unkel wrote: »

Do I seriously have to explain it again? 1kW from PV panels diverted to immersion competes with heating hot water from a gas boiler. Which costs about 4c/kWh in gas. So that is your benefit

But since an immersion costs about €500 to buy and install, you have to take this cost into account also, which can be converted into a cost per kWh of something like this (again I'm trying to keep the maths as simple as possible). Say you divert 1250kWh to your immersion per year and your immersion diverter lasts for 20 years (optimistic), that means that every kWh diverted costs 50000/(1250*20) = 2c/kWh

So your net benefit of every kWh of your PV going into your immersion is 4c - 2c = 2c

Thanks for reply.

I promise is the last topic on this matter.
I agree to disagree with you... as personal don't know the KWh of the gas boiler equivalent in thermic energy transferred in to the cylinder coil dedicated only for water.
Keep in your mind that the 1KWh of gas goes to warm / heat / over_heat the whole house radiators and unless you have a smart way to switch off the heating VS water or alternate between them,i see it as a waste of that so small, but important KWh @4c per some unit.
I remember somehow that a gas boiler iniially goes to maximum power pre_set in the firmware to heat the water to the preset temperature then "slows" down the gas flow and keep the water at the constant set temperature with a variable 4c unit cost. So, a 22KWh gas boiler takes initially more than 1Kwh @ 4c to start-up and bring the temperature in the cylinder and in the house... of course, all reported over to time curve variable.

Also, and not lastly,the most important factor,i don't have to switch,power on or go near the gas boiler from March until September-ish to heat the house by warm the water .

All above being true... that's why i am in doubt about the gas boiler versus PV immersion.
I repeat myself,best solution is a mixt of both systems.

Have fun...

a148pro

This time I can actually see the payback bit. They're suggesting 10 year payback?
Some economy of scale issue or much higher day demand of public buildings?

They also suggest that this would not be economically viable as half the systems wouldn't be functioning after ten years?

But at least, reassuringly, they suggest 4.75% predicted annual rise in cost of electricity which should take my payback time down a year or two.

a148pro

rolion wrote: »

Thanks for reply.

I promise is the last topic on this matter.
I agree to disagree with you... as personal don't know the KWh of the gas boiler equivalent in thermic energy transferred in to the cylinder coil dedicated only for water.
Keep in your mind that the 1KWh of gas goes to warm / heat / over_heat the whole house radiators and unless you have a smart way to switch off the heating VS water or alternate between them,i see it as a waste of that so small, but important KWh @4c per some unit.
I remember somehow that a gas boiler iniially goes to maximum power pre_set in the firmware to heat the water to the preset temperature then "slows" down the gas flow and keep the water at the constant set temperature with a variable 4c unit cost. So, a 22KWh gas boiler takes initially more than 1Kwh @ 4c to start-up and bring the temperature in the cylinder and in the house... of course, all reported over to time curve variable.

Also, and not lastly,the most important factor,i don't have to switch,power on or go near the gas boiler from March until September-ish to heat the house by warm the water .

All above being true... that's why i am in doubt about the gas boiler versus PV immersion.
I repeat myself,best solution is a mixt of both systems.

Have fun...

Most systems should have hot water on a separate cylinder which can be heated independently without heating all the rads. Mine was plumbed badly and still heats the rads but I am hopeful that my new system in new house will be able to heat the water without heating the rads.

In fairness, there may be a cost benefit to not running your boiler during the Summer, which might reduce my payback by another few months.

unkel

rolion wrote: »

Keep in your mind that the 1KWh of gas goes to warm / heat / over_heat the whole house radiators

:eek:

You either have multiple zoning and / or you have a radiator switch off valve in your hot press that you use for the summer

No wonder you reckon that heating the water with gas is not such a good idea

rolion

unkel wrote: »

:eek:

You either have multiple zoning and / or you have a radiator switch off valve in your hot press that you use for the summer

No wonder you reckon that heating the water with gas is not such a good idea

Thanks.
Lets try to be constructive and with facts.

TBH, I "wasn't aware" of the zoning, as my home is built by those fcuking greedy developers one house cash a week and cheap paddys labour wih no conscience... i had 2 pipes from the boiler running all the house,back and forth.
I had to spend my hard earned cash and DIY a proper zoning with Honeywell EvoHome solution...
So,if i a house does not have zoning,as most of them, will need to get one,which i guess is more than the e500 of an inverter.

I am not disputing the fact that gas boiler are more efficient versus my inverter but,i friendly advise to read about gas boilers,their operating mode such as the modulation maximum output versus minimum output per cycle(which can be as "high" as 5KWh ), flame demand control and start-up / shut-down cycles loses (nicer features present only in recently manufactured models) before jumping to conclusion of exact cost of heating a hot water cylinder by that amount.
Heating the house at 40ish is not the same as heating the water at 60ish,cost and time wise.

I can't say that i know al the details behind the cost of a gas boiler heating a 300L cylinder versus an immerision,there were some numbers crunched by someone,on a previous thread, sorry. Mainly, because the boilers doesnt have a meter or a counter like the electrical appliances,to indicate the inside out of the operating parameters. I wonder why gas boilers does not have this feature !??

unkel

So if you have zoning why don't you use them separately?

And for people without zoning, I'm pretty sure a radiator switch off valve is mandatory. Turn it off in summer, when you just want to heat the water, not the rads. Madness to heat your rads when you only want hot water...

dathi

unkel wrote: »

Do I seriously have to explain it again? 1kW from PV panels diverted to immersion competes with heating hot water from a gas boiler. Which costs about 4c/kWh in gas. So that is your benefit

But since an immersion costs about €500 to buy and install, you have to take this cost into account also, which can be converted into a cost per kWh of something like this (again I'm trying to keep the maths as simple as possible). Say you divert 1250kWh to your immersion per year and your immersion diverter lasts for 20 years (optimistic), that means that every kWh diverted costs 50000/(1250*20) = 2c/kWh

So your net benefit of every kWh of your PV going into your immersion is 4c - 2c = 2c

love the fact you include cost of diverter but seem to have a magic gas boiler that will never need replacing over 20 years or servicing or standing charges /carbon tax

unkel

You need a gas boiler anyway. It is not an optional extra investment like an immersion diverter.

Look lads, I would love the sums to work. I'd have PV on my roof tomorrow. Problem is, as things stand they are a bad investment with a very long pay back period

rolion

unkel wrote: »

Look lads, I would love the sums to work. I'd have PV on my roof tomorrow. Problem is, as things stand they are a bad investment with a very long pay back period

This is your opinion and i respect it.
I forgive you about the lesson on zoning!

For those like me that have PVs,is too late as we enjoy them already (4,000KWh past 12 months).
For those that thinks to get them,go for the higher numbers you can afford or mix PVs with Solar Tubes. Higher numbers,bigger investment but faster return and bigger satisfaction.

However,i cannot say it loud and clear, G I G O -=>Garbage In - Garbage Out in relation to formulas,numbers and ... the famous now 2c !
I dont think we have a proper setup to determine the generation versus returns (unless Conor wants to do his magic with spreadsheets again,over 12 months ,generation vs consumption) .

Happy harvesting...

a148pro

rolion wrote: »

This is your opinion and i respect it.
I forgive you about the lesson on zoning!

For those like me that have PVs,is too late as we enjoy them already (4,000KWh past 12 months).
For those that thinks to get them,go for the higher numbers you can afford or mix PVs with Solar Tubes. Higher numbers,bigger investment but faster return and bigger satisfaction.

However,i cannot say it loud and clear, G I G O -=>Garbage In - Garbage Out in relation to formulas,numbers and ... the famous now 2c !
I dont think we have a proper setup to determine the generation versus returns (unless Conor wants to do his magic with spreadsheets again,over 12 months ,generation vs consumption) .

Happy harvesting...

You have the set up rolion? You can say how many kwh you used as opposed to generated? That's the bulk of the payback. The immersion is probably only about 50 euro a year. I would have thought it was quite calculateable too, just work out how many kwh it takes to heat a given tank to a given level, then look at your figures for diversion to immersion to work out the saving.

I suspect its 20 year pay back, falling steadily with energy inflation and the reducing price of panels. With a grant, FIT or affordable batteries it'll reduce again.

Either way it seems to me it still makes more sense than solar thermal, for which I have yet to see any payback figures whatsoever, and for which the excess is unusable.

a148pro

unkel wrote: »

You need a gas boiler anyway. It is not an optional extra investment like an immersion diverter.

Look lads, I would love the sums to work. I'd have PV on my roof tomorrow. Problem is, as things stand they are a bad investment with a very long pay back period

Yes but there is a saving by not running the boiler for most of the summer also. I assume. Maybe its actually bad for boilers to be left idle. I presume the saving is very hard to quantify also.

a148pro

a148pro wrote: »

Yes but there is a saving by not running the boiler for most of the summer also. I assume. Maybe its actually bad for boilers to be left idle. I presume the saving is very hard to quantify also.

Also I think daithi's point is also that we should really be factoring in the cost of the boiler, plus servicing, into the kwh cost of the heat

unkel

Not if you have a boiler already, or if you have to install one anway. But yes, if you decide on a new build house what heating / solar / etc systems you are getting in, everything should be included.

And no, it doesn't cost anything to run the boiler for the summer. Apart from the use of gas. And I don't think it's bad to leave it switched off either.

And yes, it's fairly easy to calculate the value of PV excess going to the immersion. It is worth what it would otherwise have cost you with gas. Minus the extra investment to get the PV excess going to the immersion. Or in other words roughly 4c/kWh minus 2c/kWh for the purchase of the inverter. So it's worth about 2c/kWh

a148pro

No I think if you're going to do it correctly you should work out the total purchase and installation cost of the boiler, including all servicing over the years, and then divide it by the total amount of kwh it will produce over the lifetime. That's whether you install it now or not as that is the actual cost of the gas per kwh, particularly if you're going to compare it to the cost of the solar per kwh factoring in the cost of the immersion.

It'll probably only add a cent per kwh. But its important also because each kwh you generate with solar extends the lifespan of the boiler also. I can't work out in my head whether that value would be included in the averaged cost per kwh of the gas.

a148pro

Also there is a carbon tax on the gas rate too I see on my bill?

unkel

If you need a boiler anyway, or have one already, the depreciation / maintenance or any other fixed costs is not part of the variable cost of a unit. Basic economics

rolion

a148pro wrote: »

Either way it seems to me it still makes more sense than solar thermal, for which I have yet to see any payback figures whatsoever, and for which the excess is unusable.

Let me just say that solar tubes makes more financial sense taking in consideration a very healthy €1,500 grant from SEAI ! That's almost 50% paid already.
Of course,between PVs and solar tubes,even if is no Sun up there... solar tubes will heat the cylinder while the PVs will warm the inverter and associated cable.
I have both.

unkel

rolion wrote: »

Let me just say that solar tubes makes more financial sense taking in consideration a very healthy €1,500 grant from SEAI ! That's almost 50% paid already.

The subsidy was helpful alright!

In my case I needed to replace the original 120l poorly insulated hot water cylinder which came with the house (built in 2000) with a very large high quality highly insulated cylinder. Which was expensive and took a lot of work as we got the biggest that physically fitted into our hot press and a lot of piping, the pump, and other stuff had to be re-routed / re-installed

Reason for the upgrade was that I replaced the broken 1.5bar pump with a 2 bar pump myself which meant the cylinder was empty after one shower of about 15 minutes. And we all do like our showers / baths in this house

I had to do this anyway, so the cost of this is not calculated as part of the pay back period of the solar system. The rest of the system pay back time is about 7-10 years. But only because we have a large system (40 tubes) and the 5 of us use a lot of water

For a typical household the payback is way longer than that

Gumbo

unkel wrote: »

If you need a boiler anyway, or have one already, the depreciation / maintenance or any other fixed costs is not part of the variable cost of a unit. Basic economics

It’s only a €1200 grant for thermal. And the costs are at least 5k before the grant.

The cheapest 30 tube kingspan thermomax system I could get my hands on was 3700 with a 300L cylinder. That’s was pulling in favours from the area I work in. That was after the grant payment.

unkel

Indeed. Sounds like a decent price. I paid a bit more than 3700 after the grant, but I've a 40 tube Kingspan Thermomax system with a high quality 360l cylinder. The hot press is no longer "hot"

Not quite sure what I would have had to pay anyway (if I hadn't gone solar) for just the cylinder and related work, but it might be in the order of €1500

The difference between the two is relevant for the solar pay back time...

rolion

Guys,not sure where you get those prices,really sorry!
If you paid them,enjoy it.

I've been asked for €1,700 by a well known solar company to install 7 PV panels on my roof with ALL of my parts sitting in the front garden. Told them good luck somewhere else and i did it myself.
Solar tubes, due to the grant and installer signature,not too much play there.
Got €1,500 with €300 bonus for the 4th grant aplication.
40 tubes from Joules, as supplier.
Even now,despite the cold,i still have 20 degrees warm liquid flowing trough the roof circuits ( i know,pump is off).

a148pro

I was told I was ineligible for the grant, 200 square meter house, 5 occupants

Loads of people didn't even ask our particulars but said they'd look after the grant, which I assume means there is no grant, but we'll tell you there is in case you go elsewhere because they tell you there is

TomOnBoard

a148pro wrote: »

I was told I was ineligible for the grant, 200 square meter house, 5 occupants

Loads of people didn't even ask our particulars but said they'd look after the grant, which I assume means there is no grant, but we'll tell you there is in case you go elsewhere because they tell you there is

This thread is about PV payback. There is no domestic grant for PV. Any financial support for PV will fall under the HRI scheme.

a148pro

TomOnBoard wrote: »

This thread is about PV payback. There is no domestic grant for PV. Any financial support for PV will fall under the HRI scheme.

Yes I know, I started the thread! I'm just responding to the comments about the grant for thermal vis a vis their respective cost effectiveness.

Gumbo

rolion wrote: »

Guys,not sure where you get those prices,really sorry!
If you paid them,enjoy it.

Nope, I have Solar PV. Those are the prices I got for the thermal. They are very good, and I don’t think they can be beaten even now, unless you care to show us where they can be got supplied and fitted with a joule 300L stainless steel cylinder cheaper?

rolion wrote: »

Guys,not sure where you get those prices,really sorry!
If you paid them,enjoy it.

I've been asked for €1,700 by a well known solar company to install 7 PV panels on my roof with ALL of my parts sitting in the front garden. Told them good luck somewhere else and i did it myself.

What panels have you got?
What kw size system?
Did that include the divertor?

I paid €2900 for my 3kw system, supplied and fitted including an eddi immersion divertor.

You could in theory get a sparks to fit everything as it’s relatively straight forward to a sparks from what I seen during its installation.

rolion wrote: »

Solar tubes, due to the grant and installer signature,not too much play there.
Got €1,500 with €300 bonus for the 4th grant aplication.
40 tubes from Joules, as supplier.
Even now,despite the cold,i still have 20 degrees warm liquid flowing trough the roof circuits ( i know,pump is off).

You may have got them fitted a year or 2 ago?
The SEAI downgraded the grant from 1500 to 1200 recently as I applied for and was granted but I never went through with it due to going PV.