Solar PV quote Good or bad?

[volcane]

hi,

 

grinding slowly through build completion and only now able to consider a PV system.

 

larger house, fully electric consumption 12000 kWh annually

8 kW split Daikin heatpump

500 litre DHW tank (2 immersion)

2 W machine, 2 Dishwasher, Tumble dryer(heatpump)

2 MVHR

always at least one working from home

high care requirements, laundry washing.

Large South. slightly east facing roof.

 

all opinions welcome.

 

have quote as below 10.5k

 

- 18x4 30W jinko 430W n- type solar panels

- 1x go energy 3.6kW hybrid inverter

- 1x give energy 9.5kwh battery

- 1x myenergi Eddi

- Installion commissioning and certification

[AppleDown]

1 minute ago, volcane said:

hi,

 

grinding slowly through build completion and only now able to consider a PV system.

 

larger house, fully electric consumption 12000 kWh annually

8 kW split Daikin heatpump

500 litre DHW tank (2 immersion)

2 W machine, 2 Dishwasher, Tumble dryer(heatpump)

2 MVHR

always at least one working from home

high care requirements, laundry washing.

Large South. slightly east facing roof.

 

all opinions welcome.

 

have quote as below 10.5k

 

- 18x4 30W jinko 430W n- type solar panels

- 1x go energy 3.6kW hybrid inverter

- 1x give energy 9.5kwh battery

- 1x myenergi Eddi

- Installion commissioning and certification

From my recent research that seems fair enough - getting similar supply and install quotes in SE. Have you asked DNO if you can have that capacity yet?

[volcane]

limited to 3.6, seem not to be as excited about extra panels as they used to be. Opensolar seems to indicate that we could use most of the 6000 kWh generated, not fully convinced.

G99 fast track could allow another battery and second inverter plus a few more panels but installer advised to go with quoted system initially.

in NI

[sharpener]

Quote seems reasonable for what they are proposing to fit.

 

If you cook by electricity I think you will need a bigger battery and bigger inverter to cope with winter evenings. Depends if your aim is to rely on charge overnight on a ToU tarifff, or can top up as well during the day e.g. on Octopus Cosy (can you get it in NI?).

 

Probably the 7kW PV will be too much for you to use it all in summer, but not enough in winter. HP will drain the battery if you are trying to have it run off that on dull, short winter days.

 

All based on our exp of 6.9kW PV, 5kVA Victron Multiplus II, 10.65 kWh Pylontech over the last 18 months, so quite similar, HP yet to be installed.

[Conor]

Don't see the point in the Eddi if you have batteries and an ASHP. The microgen export tariff is the same as the economy 7 night rate, so never makes sense to heat water with the immersion, no matter where the electric comes from. 

 

Why not a 7kW inverter commissioned at 3.78kW if a G99 application is unsuccessful? You'll miss out a huge amount of generation (therefore money) during the summer.

[JohnMo]

19 hours ago, volcane said:

3.6kW hybrid inverter

give energy 9.5kwh battery

 

8 hours ago, sharpener said:

If you cook by electricity I think you will need a bigger battery and bigger inverter to cope with winter evenings

Couldn't agree more. We have a 6kW inverter and 13.5kWh battery. Inverter is about the right size so you don't keep pulling in grid electric while you make the tea for example, an oven and couple of hobs all asking for power at same time will exceed 3.6kW very easily.

 

Mid winter we only go to about 7pm on the battery, so 5.5hrs short of the whole day.

 

PV diverter, if you have a smart meter and MCS certificate as said by @Conor no point just export, if no smart meter you will get 4.5p kWh, so diverter to hot water. No MCS use diverter.

[sharpener]

20 hours ago, volcane said:

G99 fast track could allow another battery and second inverter plus a few more panels but installer advised to go with quoted system initially

 

G99 application won't cost much if anything. If you can afford it I would install the biggest system you can bc

• DNO might take a more conservative view later about adding generation so get your bid in first
• Other ppl agree the proposed system is probably not big enough for yr needs
• Yr current installer may go out of business or not want to do it later
• My experience is that getting other installers to add to a previous system is sthg they don't want to do
• Battery mfrs continually change their product ranges so being able to add capacity later is not a given
• It will be cheaper overall bc of economies of scale, and some costs e.g. repeat scaffolding will be avoided

My intention in 2011 was to expand later with a 3rd 2kW inverter, but once batteries became affordable that was not a sensible route to go down.

 

If I had my time again I would - DNO permitting - have covered the entire roof with 28 not 16 panels from the start and benefited from 75% more FIT income. This would have more than paid for an 8kVA Victron inverter in place of the 5kVA. This is only just big enough now and will not be able to supply the HP from battery on top of everything else. Fortunately it has 50 amp grid pass-through capability.

[G and J]

6 hours ago, Conor said:

Don't see the point in the Eddi if you have batteries and an ASHP. The microgen export tariff is the same as the economy 7 night rate, so never makes sense to heat water with the immersion, no matter where the electric comes from. 

 

Why not a 7kW inverter commissioned at 3.78kW if a G99 application is unsuccessful? You'll miss out a huge amount of generation (therefore money) during the summer.

I’m just starting to get my head round how the Solar PV systems can work.  Am I correct in thinking that in this instance if the batteries are full and there is excess solar power compared to ambient demand, then the Eddi will dump the spare power to, say, an immersion heater rather than just dump it back to the grid?

[sharpener]

Yes that's right.

 

There are some complex arguments though.

 

If you have an HP then it is theoretically better to use that for HW at all times bc it has a CoP of maybe 3 when producing HW rather than the Eddi/immersion which is by definition 1.00. From the planet's pov this is the best answer.

 

Many ppl program the HP to produce HW in the early afternoon when

• air temp is higher so HP is slightly more efficient
• the sun is most likely to be out
• demand for space heating is less
• Octopus Cosy e.g. has a cheap window 1300 - 1600

 

or as I plan to do, in the small hours when I can buy electricity for less than Octopus will pay me for exports during the day.

 

When the sun goes behind a cloud the PV generation may however fall below what the HP needs. If it draws on the battery well and good, you have only the round-trip losses to consider. If it draws from the grid you will have to pay for that (but is still good for the planet bc total demand is still lower). So in these circs the Eddi may reduce your personal bill. Whether this is worthwhile depends on balance of import and export tariff you are on.

 

Also it is a useful backup and in summer you may want to switch the HP off completely to save wear or bc you sit outside near it.

 

 

Edited May 19 by sharpener

[JohnMo]

1 hour ago, G and J said:

just starting to get my head round how the Solar PV systems can work

A snapshot of our battery app. Showing an hour today, doing DHW heating and the spike is kettle going on at the same time. It's cloudy today and only generating around 1kW

 

 

Yellow is PV output 

Green is electric demand from house 

Blue is what the batteries doing, below red line is being charged, above red line is giving electricity to house 

Red is what the grid is doing.

 

So today, when we do hot water heating, the PV isn't sufficient, so we borrow from the battery, as soon as the heating is finished, excess PV flows in to the battery until fully charged.

[G and J]

2 hours ago, sharpener said:

 

 

Also it is a useful backup and in summer you may want to switch the HP off completely to save wear or bc you sit outside near it.

 

 

Are ASHPs ok if they are turned off for a few months?  I like the notion that the ASHP isn’t running when I’m quietly snoring in my hammock a few yards from it, plus I wear out a cheap immersion element rather than expensive fans.

[JohnMo]

1 hour ago, G and J said:

Are ASHPs ok if they are turned off for a few months?  I like the notion that the ASHP isn’t running when I’m quietly snoring in my hammock a few yards from it, plus I wear out a cheap immersion element rather than expensive fans.

Would assume so, they will probably start the circulation pump so it doesn't stick themselves via the controller. So would switch off completely.

 

[G and J]

2 hours ago, JohnMo said:

A snapshot of our battery app. Showing an hour today, doing DHW heating and the spike is kettle going on at the same time. It's cloudy today and only generating around 1kW

 

 

Yellow is PV output 

Green is electric demand from house 

Blue is what the batteries doing, below red line is being charged, above red line is giving electricity to house 

Red is what the grid is doing.

 

So today, when we do hot water heating, the PV isn't sufficient, so we borrow from the battery, as soon as the heating is finished, excess PV flows in to the battery until fully charged.

Interesting.  I’ll re read that a few times and try and get my head round it.

 

Our current thinking is that batteries have a payback period of circa 10 years, just based on some fairly broad brush calcs.  At that payback we will wait until after we know exactly how much our build will cost overall before finally decide to add batteries or not.  I appreciate that it’s a ‘how long is a bit of string’ question, but what sort of payback period do you feel you are looking at for your batteries?

[JohnMo]

Its a difficult calculation really, if you can export and get paid for it, not sure the maths will ever make much sense. If you have PV and don't get paid for export but only have a G98 sizes array and home during the day, again not much sense as you can self consume reasonably easily. Once you get more PV or areaway all day self utilisation gets more difficult, so the battery allows you self utilise almost every you produce. They also allow you to use TOU tariffs. In even in Dec I was able to utilise 75% of off-peak priced electric.

[JamesPa]

2 hours ago, JohnMo said:

Would assume so, they will probably start the circulation pump so it doesn't stick themselves via the controller. So would switch off completely.

 

Since I installed pv in 2011 I have turned off my gas boiler completely from May to September.  So far the circulation pump hasn't seized!

[sharpener]

2 hours ago, JohnMo said:

Would assume so, they will probably start the circulation pump so it doesn't stick themselves via the controller. So would switch off completely.

 

Assume you mean not switch off completely i.e. leave energised but turn off on its controls so the pump anti-jam cycle can run.

 

2 hours ago, G and J said:

what sort of payback period do you feel you are looking at for your batteries?

 

Last time I looked it was ~6 years IIRC. Octopus Cosy has two 3-hr cheap periods every 24 hours so you can get two full cycles a day which is twice as good as E7.

 

It also gives us a second bite at charging the Thermal Store. If you are looking for payback then a TS (basically the biggest tank of hot water you have got room for) is better per delivered kWh of space heating than a battery, not least bc of its 20+ yr projected life.

 

Not mentioned yet is adding provision for an EV. That soaks up quite a bit of our surplus generation. Intelligent Octopus Go is in some ways a better deal that Cosy but only cheap at night.

 

Edited May 19 by sharpener

[JohnMo]

4 minutes ago, sharpener said:

Assume you mean not switch off completely i.e. leave energised but turn off on its controls so the pump anti-jam cycle can run.

Good spot

 

4 minutes ago, sharpener said:

Octopus Cosy

Can't get that, as smart will not talk to outside world.

[sharpener]

47 minutes ago, JohnMo said:

 

54 minutes ago, sharpener said:

Octopus Cosy

Can't get that, as smart will not talk to outside world.

 

OP might - or might not, he is in NI.

[G and J]

5 hours ago, JohnMo said:

Its a difficult calculation really, if you can export and get paid for it, not sure the maths will ever make much sense. If you have PV and don't get paid for export but only have a G98 sizes array and home during the day, again not much sense as you can self consume reasonably easily. Once you get more PV or areaway all day self utilisation gets more difficult, so the battery allows you self utilise almost every you produce. They also allow you to use TOU tariffs. In even in Dec I was able to utilise 75% of off-peak priced electric.

The area of our south facing roof limits us to circa 5kW of panels, and as we are both retired we are often around during the day, so maybe batteries won’t be on my list.  
 

But another research topic now added to my ever expanding list - TOU tariffs. 

[G and J]

5 hours ago, sharpener said:

 

Assume you mean not switch off completely i.e. leave energised but turn off on its controls so the pump anti-jam cycle can run.

 

 

Last time I looked it was ~6 years IIRC. Octopus Cosy has two 3-hr cheap periods every 24 hours so you can get two full cycles a day which is twice as good as E7.

 

It also gives us a second bite at charging the Thermal Store. If you are looking for payback then a TS (basically the biggest tank of hot water you have got room for) is better per delivered kWh of space heating than a battery, not least bc of its 20+ yr projected life.

 

Not mentioned yet is adding provision for an EV. That soaks up quite a bit of our surplus generation. Intelligent Octopus Go is in some ways a better deal that Cosy but only cheap at night.

 

Hmmmm, interesting notion, the heat store, will ponder, but suspect that finding space for a sensible sized store and the extra plumbing complexity may make it less attractive. 
 

I've just looked up the Octopus Cosy tariff and a heretical idea has popped into my head.  Suppose I arrange things so our system does all its heating and DHW, washing machine and dishwasher usage, etc. within the low periods.  
 

Does that mean my payback for solar pv becomes 30 years or so?  Not having solar will mean I miss out in free hot water but if that’s in reality the only thing on that side of the balance sheet then is the investment justifiable?

[RobLe]

22 hours ago, JohnMo said:

 

Couldn't agree more. We have a 6kW inverter and 13.5kWh battery. Inverter is about the right size so you don't keep pulling in grid electric while you make the tea for example, an oven and couple of hobs all asking for power at same time will exceed 3.6kW very easily.

We have a 4 bed all elec house, induction hob, tiny gshp, kettle, toaster, all usual mod cons.  We make no attempt to desynchronise things when cooking etc - often turning on stuff together, and so I guess our 3.6kW 15kWh hybrid inverter must max out and a bit of peak mains sneaks in sometimes.  Even so, in the last 30 days the app ‘Octo-Aid’ says our IOG low rate use is 99.7%, peak rate 0.3% - somehow it can’t end up that significant.  What did make a noticeable difference was tweaking the offset power, to ensure we weren’t trickling in 10W all the time.

 

[JohnMo]

11 hours ago, G and J said:

The area of our south facing roof limits us to circa 5kW of panels, and as we are both retired we are often around during the day, so maybe batteries won’t be on my list.  
 

But another research topic now added to my ever expanding list - TOU tariffs. 

Just spent 30 mins calculating saving of PV (6.5kW), battery(13.5kWh) and E7 tariff and no PV or battery and standard tariff.

 

Below is based on actual ASHP kWh used (metered) and long term monitoring on energy taken by the house (cooking, washing, borehole pump, sewage system, MVHR, lights, averages out at 17kWh/day)

 

So during the heating season we are saving about £725, by allowing us to take a big proportion of the energy on a low tariff and some generated PV.

During non heating season including running ASHP in cooling mode as required looking at a saving of £635, by making a better utilisation factor for PV and if required only taking in low tariff electric.

 

So a total saving of £1360 per year. Equivalent to a 58% reduction in annual energy costs.

 

For us and our spending on Battery and PV (self installed) its about 6 years pay back.

[SteamyTea]

18 hours ago, G and J said:

Suppose I arrange things so our system does all its heating and DHW, washing machine and dishwasher usage, etc. within the low periods

What I have been doing for 20 years with E7.

No capital expenditure either or complicated controls.

[G and J]

7 hours ago, JohnMo said:

Just spent 30 mins calculating saving of PV (6.5kW), battery(13.5kWh) and E7 tariff and no PV or battery and standard tariff.

 

Below is based on actual ASHP kWh used (metered) and long term monitoring on energy taken by the house (cooking, washing, borehole pump, sewage system, MVHR, lights, averages out at 17kWh/day)

 

So during the heating season we are saving about £725, by allowing us to take a big proportion of the energy on a low tariff and some generated PV.

During non heating season including running ASHP in cooling mode as required looking at a saving of £635, by making a better utilisation factor for PV and if required only taking in low tariff electric.

 

So a total saving of £1360 per year. Equivalent to a 58% reduction in annual energy costs.

 

For us and our spending on Battery and PV (self installed) its about 6 years pay back.

May I ask what the electricity unit rate you are using in that calculation ? (And PS I’m sorry if I’ve given you a headache lol)

 

At 6 years payback I’d be tempted.  
 

Also, am I correct in thinking that one has to have an MCS approved installer to get a FIT?

[G and J]

1 hour ago, SteamyTea said:

What I have been doing for 20 years with E7.

No capital expenditure either or complicated controls.

And that I think is my base case against which other scenarios are compared.