Solar PV and Heat pumps - the economics

[MYLOUBYLOU]

Reading up whether solar PV is a good investment, seems there is a payback period of at least 15 years. What I am unsure of is do those calculations take into account running a heat pump? I guess the time they are generating most output is when you are using least electricity.  If it could heat the water in summer you could use more of the produced energy, have read about diverters. Has anyone got experience of retrofitting to existing system? We have ecodan packaged cylinder running 14kw ecodan ho with ufh throughout 

Edited November 21, 2021 by MYLOUBYLOU

[ProDave]

I am of the opinion that without subsidies now, solar PV is only worth it if you can self fit very cheap.

 

My own system is 4kWp ground mounted that cost me £1500 to buy the kit and self install it.  My original prediction was it would take 6 years to pay back the cost from self used electricity saving.  With the recent rise in electricity prices i suspect that will now be nearer to 5 years payback time.

 

I self use nearly all that we generate and that is achieved by using the big appliances (washihing machine etc) in the middle of the day, timing the ASHP to heat the DHW from 11AM onwards (when PV generation should be good) and dumping excess to hot water (about 1/3 of what we generate goes into the immersion heater)

[Marvin]

35 minutes ago, ProDave said:

I self use nearly all that we generate and that is achieved by using the big appliances (washihing machine etc) in the middle of the day, timing the ASHP to heat the DHW from 11AM onwards (when PV generation should be good) and dumping excess to hot water (about 1/3 of what we generate goes into the immersion heater)

This is what I am installing but a 5.12kWp roof mounted self installed system which will cost about 3k. 1kW immersion with adjustable CT clamp on PV 240v output cable and the same for EV charging set at 2kW after.

Also the higher PV power produced in the summer will be used for cooling via the ASHP air to water coils in MVHR system.

 

We will see what happens.

 

M

[Dave Jones]

maybe a batter solution is battery storage and time shift usage to pay very cheap all the time.

[ProDave]

42 minutes ago, Dave Jones said:

maybe a batter solution is battery storage and time shift usage to pay very cheap all the time.

It will become viable one day, but every time I have looked, the cost of the "free" time shifted electricity is no cheaper than just importing it, when you properly cost the system cost and battery replacement cost at end of life.

 

It will become viable one day as battery prices fall and electricity prices rise but i am not convinced we are there yet.

 

It is a real shame the DNO's are not more flexible.  They are stuck in the mindset that if you have 4kW of PV then you are likely to export 4kW and so their network has to be capable of supporting that and in a lot of cases they just say no to more than 3.68kW.  It should be possible to install a second PV system that only charges the batteries when the sun is out and that properly monitors export and ensures it never discharges the batteries at a rate great enough to cause any export.  A system like that ought the be possible even when you are limited to 3.68kW.

 

Of course one could DIY build such a system and just not tell anyone.........

[SteamyTea]

For every £1000 spent, and assuming that a PV system will last 20 years, that is £50 a year you have lost.

£50 buys between 200 and 350 kWh.

If you say kW of installed solar cost £1000 and yields 1MWh/year, that is potentially a saving of £140 to £240 a year.

So take away the £50, that is potentially £90 to £190 a year saving.

So maybe the trick is to only install a small amount of PV, say enough to heat your DHW demands for half the year, rather than over install and feel you are loosing money because you cannot utilise it all.

 

(I used 14p and 24p a kWh as my import figures).

Edited November 21, 2021 by SteamyTea

[ProDave]

I have said before, a typical 4kW system with a G98 inverter limited to 3.68kW is easy to self use most of it, as long as you have a HW tank and a diverter to send surplus to the immersion heater.

 

It is when you go above 4kW that it becomes harder to self use, so the returns on a larger system are diminishing, and that is probably the point batteries start to make sense.

 

If I can self use so much of what I generate without batteries then at my level the argument for batteries becomes:  Will batteries enable me to make more productive use of the surplus vs just dumping it in the immersion heater.

[SteamyTea]

6 minutes ago, ProDave said:

Will batteries enable me to make more productive use of the surplus vs just dumping it in the immersion heater.

You can always use more hot water, that makes the numbers look better.

[Thorfun]

we've all had this conversation many times before and for some, me included, it's not about economics at all. it's about a warm fuzzy feeling that I will be generating my own electricity and I won't be as reliant on the grid.

 

but everyone's situation is different.

[joe90]

Well despite having planning for solar with my build I missed the FIT date and decided against it at the time but with recent price rises and as @ProDave has done for himself a self install is beginning to appeal again, I just need to make sure I live long enough to get my investment back ?.

[Marvin]

16 minutes ago, joe90 said:

I just need to make sure I live long enough to get my investment back ?.

Well this calculation is getting worse by the minute!  ???

[TonyT]

I hope I can live long enough to recoup the investment of my kitchen…...  oh wait that’s not what life is all about

[Nickfromwales]

Most of the systems we install exceed our estimates, and the breakeven point is typically year 13.5, so probably year 14.5 when you include the second inverter being fitted when the original one snuffs it.

A robust panel ( we're either LG or Solarwatt ) will still be producing a useful amount of output in year 30, so worst case is 10-15 years of "free" electricity after breaking even. The maths do work out for sure, and the real question should be; "how long will you be at the property" for to see this return  If you're moving out in 10-15 years don't bother, or just fit a token array ( circa 2kWp ) to offset vampire / base loads and give a bit of kerb-appeal when marketing.

Edited November 21, 2021 by Nickfromwales

[SteamyTea]

5 minutes ago, Nickfromwales said:

and give a bit of kerb-appeal when marketing

I heard, like swimming pools, it is one of the worse things you can have when it comes to selling.

[Nickfromwales]

Just now, SteamyTea said:

I heard, like swimming pools, it is one of the worse things you can have when it comes to selling.

Not if you hand the crowds a series of print-out's of the PV production, with a brief of the savings in not importing all of the electricity needs  Then it's irrefutable marketing power.

 

[SteamyTea]

1 minute ago, Nickfromwales said:

Not if you hand the crowds a series of print-out's of the PV production

As long as you show the monthly output in Kw/h.

[Nickfromwales]

1 minute ago, SteamyTea said:

As long as you show the monthly output in Kw/h.

 

3 minutes ago, Nickfromwales said:

a series of print-out's of the PV production

[Russdl]

12 minutes ago, Nickfromwales said:

Most of the systems we install

Didn’t realise you were MCS certified Nick, is that a new thing for you?

[patp]

No one has mentioned the planet yet

 

On the subject of kerb appeal I have to say I hate the look of most installations and resisted retrofitting them to our old cottage. If installed inset into roof tiles they look much better. We have even had compliments on our array that cover the whole of our South facing roof.

[PeterW]

Seeing loads installed round here with batteries now - seems to be the next “fad” as they don’t need an MCS certificate to flog it back to the grid as it’s all deemed “self use”. 

[JohnMo]

I used energysavingtrust.org.uk - PV calculations for the below.

 

3kw array.

My postcode, roof angle and direction etc

 

Yield forecast 2331kWh/y.

We pay 17.02p per kWh

If we use full yield savings are £396/y

System cost £2300, including immersion diverter, additional electrical installation costs around £500.  Rest is self installed.

 

Plan to self consume and will not get paid for any export.

 

If I only manage to consume 90%, yield would be equal to £356

£2800/£356 = 7.8 years

 

 

 

 

[Nickfromwales]

Yup, a load of members have installed away from the MCS register eg self-install. You only need to be MCS to register the installation for the export guarantee scheme.......but;

1 minute ago, JohnMo said:

Plan to self consume and will not get paid for any export.

Same as @ProDave, who uses his diversion and strategic consumption to avoid export / promote self-consumption......

 

which means no mandatory need to register.

[ProDave]

You do have to notify the DNO under G98 that you have installed a system, but you don't need to be a member of any organisation to do that.

[JohnMo]

Good point

2 minutes ago, ProDave said:

You do have to notify the DNO under G98 that you have installed a system, but you don't need to be a member of any organisation to do that.

 

[ProDave]

To put it into perspective, I have so far only exported 290kWh.  If I was eligible to be paid the smart export at 5p per kWh, I would have received the grand total of £14.50 so far.  But to be allowed to claim that small payment, I would have had to pay an MCS installer to have fitted and certified it.  That low level of payment would never repay the MCS cost.