Meter to measure self consumption

[Pressure]

Hello all - I would appreciate some advice please.

I have a 5.6kw PV system, professionally installed, and in operation for 5 years. However I have never been able to really tell how much generation I am self consuming. The aim is to contribute to the high energy consumption of an ASHP.

Is there an inexpensive meter I (or an electrician) can fit which will show how much I am self consuming?

I can see generation from the Solar Edge portal and from the FITS meter (I am paid on generation and deemed export, not actual export). I can see my import from Octopus (not much different to before PV).

But I can’t specifically measure self consumption. Hence I can’t calculate return on investment, or build a business case for battery storage.

I can’t help feeling I have missed something basic . Surely it’s possible to track how much of the system’s output I am actually using?

All advice is gratefully received!

 

[ProDave]

Directly measuring self consumption is not easy. But it is easy to get an electrician to install an export meter. Or if you have a smart meter, that will already be measuring export. So the amount you generate, less what you export, is how much you self use.

Do you have batteries, and are you signed up for export payments?

 

[Pressure]

Thank you ProDave.
I am on the old FITS scheme which pays for all generation plus deemed export, which is tracked via an Elite M17 meter, which I report manually to my FITS provider, Good Energy. So it just records generation, rather than export.

The import meter is a bit smarter - fitted by Octopus, so their portal can report import in great detail. Looks like an EDMI ES10-B which can do wireless data collection. Octopus also doesn't give me any figures for export.

So I don't think my meters are smart enough to show export - but I could be wrong!

I don't have batteries. It looks to me like people who have batteries as well as PV seem to be able to track self consumption although I don't know what they have that I don't!

What sort of export meters are available - are they expensive?

Many thanks again!

 

[Pressure]

Right: some progress, I think.
This page from Bulb: https://help.bulb.co.uk/hc/en-us/articles/115001232832#h_823d3aac-d839-4df1-956b-58f948cc820a
... describes how to access smart meter data on the EDMI SMETS2 meter, which I appear to have. I followed the instructions and lo and behold, not gave me a number for export!



So at minimum this gives me a baseline to check my export at the end of each month. (Not as good as it flowing straight into a UI, but good enough for an amateur.)

However, this page: https://www.smartme.co.uk/export.html
... indicates that "The SMETS 2 specification requires the following data to be recorded and stored.

Half-hourly electricity data:
3 months of active energy exported
3 months of reactive energy exported."

So does that mean I've exported 1,198kwh since early October? If so, that leaves me with a quandary: I think I've only generated 265KWH from PV since the end of September! Might this be the total export since it was installed?

 

[johnb2713]

I don't have batteries. It looks to me like people who have batteries as well as PV seem to be able to track self consumption although I don't know what they have that I don't!

Have you looked inside the inverter software (if any), my Growatt and Victron inverters both have that information.

In my case theyre not accurate because each inverter sees the other one as import from the grid which it isnt. With single inverter though it was spot on.

 

[Pressure]

Sadly, my Solar Edge portal only gives me generation numbers - you only get import by buying a £400-500 add on device.

I don't have batteries - one reason I want this data is to build a business case for batteries - and it often seems like battery owners have this data at their finger tips.

Thank you for your suggestion though

 

[binky]

Have you looked inside the inverter software (if any), my Growatt and Victron inverters both have that information.
View attachment 14718
In my case theyre not accurate because each inverter sees the other one as import from the grid which it isnt. With single inverter though it was spot on.

that sort of info tends to be linked to hybrid battery inverters, it's only since fitting batteries that fitting a CT clamp has become normal. I don't think most older standard PV inverters have the function to measure export, unless they can be used with export limitation, and I'm not sure they even measue the export total quantity, just limit the rate of export.

 

[binky]

Sadly, my Solar Edge portal only gives me generation numbers - you only get import by buying a £400-500 add on device.

I don't have batteries - one reason I want this data is to build a business case for batteries - and it often seems like battery owners have this data at their finger tips.

Thank you for your suggestion though

sounds about right for Solaredge .

You can fit a simple single phase inveter into the meter tails between the distribution board(s) and smart meter, and reverse wire it so it measures leccy going out rather than in. That way what goes out is surplus from the PV

 

[Pressure]

Many thanks @binky !

 

[ProDave]

Start by taking a weekly reading of generation and export, then you will get a good idea.

What steps are you taking to maximise self use? As a minimum you should be using the big appliances like washing machine etc near the middle of the day, and be using a solar PV diverter to send excess to your immersion heater.

 

[Pressure]

Yes, I now have a reasonable model of where I am with self-use. My installer was able to confirm that the 1138 figure is cumulative export since install on 28/9/21. Pro rata, that gives me a self-use percentage in 2022 of 67% - much better than I expected / feared.

Obviously with lockdown a lot of self use came from all the family working from home, so lots of daytime / insolation computer usage, washing etc.

I believe our biggest cost is the ASHP - although I would really like to get some actual data on that versus the electric oven. The mechanical heat recovery and ventilation system is also I suspect a big cost - I think switching it off in the summer made a noticeable difference. (Had to switch it on a bit in December due to condensation building up, we built an incredibly air-tight house!).

Unfortunately the diverter has not worked out. Our POV installer put in a 4Knox diverter, which drove the immersion via the Daikin ASHP internal unit, and Daikin were not happy at all about the 4Knox cabling going into their unit, and the potential risk arising from both the Daikin unit and the diverter triggering the immersion simultaneously. They threatened to pull out of the ASHP maintenance agreement (which is essential IMO). So we disconnected it. Shame.

Other negatives are:

• the house is zero carbon / all electric - so the cooker and hob are electric, and most meals are outside of insolation periods
• the ASHP itself is efficient, because it runs little and often, but that also means some running at night
• still too much washing in early mornings - due to work schedules

As a result the import is still huge - 11,227 KWH in 2022, which is our most efficient year yet. So I want to understand the usage from the ASHP and the cooker, but it's hard because they're "wired in" rather than being on plugs (not that I know what good plug-meters exist!).
And I also want to start looking at the business case for batteries - that could make a big difference to self-use, especially if I can get on a time-of-use tariff without the daytime rate being crippling...

Thanks once again all!

 

[johnb2713]

They threatened to pull out of the ASHP maintenance agreement (which is essential IMO).

Just out of interest, why do you feel it's essential? It's a big fridge with a heat exchanger to the water.

 

[Pressure]

Therein lies a tale, John.

We built the house in 2008-9, moving in November 2009. We specced the systems and identified suppliers in 2006-7. Back then, ASHPs and renewable energy generally were not well understood and suppliers were few, and by definition inexperienced. Solar panels were scarce and expensive, and ASHPs were pretty much bleeding edge.

Our main contractor was awesome and we're still in touch with them. The ASHP supplier did the unit, the underfloor heating, and all plumbing - which saved us lots.

They also had no idea what they were doing, grossly over-specified the system with every conceivable boondoggle, just in case it was needed, were a nightmare to communicate with, and though they got the install done... by the time we moved in, they had gone bust.

We never did get any renewable heat incentive for the ASHP - the supplier didn't know they existed. Nor did they suggest or arrange a maintenance contract with Daikin.

Fast forward a few years, and the then current, but early model, Daikin ASHP external unit failed.

It was both heart breaking and terrifying.

Also by then the house had won a couple of RIBA housing awards, and Daikin, to their immense credit, offered to replace the whole external unit for free - on the proviso that we sign up with them for a maintenance contract, which we gladly did, and would have done before, had we known they existed.

A boiler maintenance contract at the upper end of the market is around £250 a year (I just checked!) and the Daikin maintenance isn't a lot more.

And for the peace of mind, for me, and given my experience, I gladly pay for it!

Building an eco house has, as they say, been a learning experience

 

[binky]

I believe our biggest cost is the ASHP - although I would really like to get some actual data on that versus the electric oven. The mechanical heat recovery and ventilation system is also I suspect a big cost - I think switching it off in the summer made a noticeable difference. (Had to switch it on a bit in December due to condensation building up, we built an incredibly air-tight house!).

ASHP use a lot of electric. MHRV system isn't much more than just a fan running, but, you probably don't need it in warmer months. A friend of mine has a Passive Haus, and switches it off. He also only has a 1kw electric heater for the worst of the winter months.

Unfortunately the diverter has not worked out. Our POV installer put in a 4Knox diverter, which drove the immersion via the Daikin ASHP internal unit, and Daikin were not happy at all about the 4Knox cabling going into their unit, and the potential risk arising from both the Daikin unit and the diverter triggering the immersion simultaneously. They threatened to pull out of the ASHP maintenance agreement (which is essential IMO). So we disconnected it. Shame.

I would disconnect the immersion from the Daikin and use the diverter. I'm assuming you can programme the ASHP not to operate during daylight hours to allow the solar to heat water? I assume you also have a hot water tank, so a modern tank keep water hot for quite aa long time, like days, so I would be looking to use the ASHP only of an evening.

Other negatives are:

• the house is zero carbon / all electric - so the cooker and hob are electric, and most meals are outside of insolation periods
• the ASHP itself is efficient, because it runs little and often, but that also means some running at night
• still too much washing in early mornings - due to work schedules

cooking doesn't use huge amounts of leccy, unless you cook an awful lot, tumble driers are the worst appliance.

As a result the import is still huge - 11,227 KWH in 2022, which is our most efficient year yet. So I want to understand the usage from the ASHP and the cooker, but it's hard because they're "wired in" rather than being on plugs (not that I know what good plug-meters exist!).
And I also want to start looking at the business case for batteries - that could make a big difference to self-use, especially if I can get on a time-of-use tariff without the daytime rate being crippling...

Thanks once again all!

11,227 does seem a lot!

 

[ProDave]

Unfortunately the diverter has not worked out. Our POV installer put in a 4Knox diverter, which drove the immersion via the Daikin ASHP internal unit, and Daikin were not happy at all about the 4Knox cabling going into their unit, and the potential risk arising from both the Daikin unit and the diverter triggering the immersion simultaneously. They threatened to pull out of the ASHP maintenance agreement (which is essential IMO). So we disconnected it. Shame.

With my own ASHP I have disabled any use of the immersion heater by the ASHP. Why would I ever want to use a resistance heater when I can use the actual heat pump? If the heat pump fails I can manually use the immersion and light my stove for heat.

So no conflict.

I also installed yet another electricity meter just to measure what the ASHP uses. On a Friday I go round and take 5 meter readings to enter into my spreadsheet.

Another load that is easy to time shift, is when does the ASHP heat the hot water? I have mine set to only start heating DHW at 11AM on the basis most days by then it will be near peak solar PV generation, so best time to heat the DHW.

 

[johnb2713]

With my own ASHP I have disabled any use of the immersion heater by the ASHP. Why would I ever want to use a resistance heater when I can use the actual heat pump? .

To increase the temperature of the DHW tank about 65 degC once per week to avoid Legionella.

From the .gov website:

The primary method used to control the risk from Legionella is water temperature control.
Water services should be operated at temperatures that prevent Legionella growth:

• Hot water storage cylinders (calorifiers) should store water at 60°C or higher
• Hot water should be distributed at 50°C or higher (thermostatic mixer valves need to be fitted as close as possible to outlets, where a scald risk is identified).
• Cold water should be stored and distributed below 20°C.

A competent person should routinely check, inspect and clean the system, in accordance with the risk assessment.

You must identify 'sentinel' outlets (furthest and closest to each tank or cylinder) for monthly checking of the distribution temperatures. You should also check the hot water storage cylinder temperatures every month and cold water tank temperatures at least every six months.

 

[ProDave]

To increase the temperature of the DHW tank about 65 degC once per week to avoid Legionella.

From the .gov website:

The primary method used to control the risk from Legionella is water temperature control.
Water services should be operated at temperatures that prevent Legionella growth:

• Hot water storage cylinders (calorifiers) should store water at 60°C or higher
• Hot water should be distributed at 50°C or higher (thermostatic mixer valves need to be fitted as close as possible to outlets, where a scald risk is identified).
• Cold water should be stored and distributed below 20°C.

A competent person should routinely check, inspect and clean the system, in accordance with the risk assessment.

You must identify 'sentinel' outlets (furthest and closest to each tank or cylinder) for monthly checking of the distribution temperatures. You should also check the hot water storage cylinder temperatures every month and cold water tank temperatures at least every six months.

I had this debate on another forum.

The consensus (from a number of educated people) was if you have treated mains water, and it is stored in an unvented hot water cylinder then there is no need for this. There will be no bugs in the water as delivered and no means for them to enter. I have been running my DHW tank at 48 degrees for several years, it will heat hotter in summer with surplus solar PV but not in the winter.

It you have a private water supply or an old vented cylinder with a header tank then keeping it hot is important.

Care to tell me how many cases of legionairs there are in the UK? All the reported ones I have heard about seem to be related to air conditioning cooling systems, not domestic hot water tanks.

 

[johnb2713]

I had this debate on another forum.

The consensus (from a number of educated people) was if you have treated mains water, and it is stored in an unvented hot water cylinder then there is no need for this. There will be no bugs in the water as delivered and no means for them to enter. I have been running my DHW tank at 48 degrees for several years, it will heat hotter in summer with surplus solar PV but not in the winter.

It you have a private water supply or an old vented cylinder with a header tank then keeping it hot is important.

Care to tell me how many cases of legionairs there are in the UK? All the reported ones I have heard about seem to be related to air conditioning cooling systems, not domestic hot water tanks.

I have no beef either way, it's something i'd been told about during heat pump installation planning. I was answering your question "why would you use a resistance heater when you have an ASHP"

I have no idea what the spread of the infection is, the way I feel today, I may have got it

 

[Geoff1946]

I've been taught that there CAN be small amounts of legionella bacteria present in mains water, and that given certain temperature conditions and the water static for some time these bacteria can multiply.
It is also doubtful if just occasionally raising the temperature of a storage tank would eliminate existing bacteria, unless a destratification pump is also fitted to ensure that ALL the tank is heated, right down to the bottom.
A further risk exists with, "dead legs", where water stands for long periods in disused or seldom used lengths of pipe. For this reason a place where I worked had a procedure to ensure that every tap in the building was run for a while every week, even if the area was not in use.

I agree that problems actually seem few, now that water cooled air conditioners have been eliminated.
I also note that when visiting warmer countries, such as Cyprus, water systems and storage tanks are located on roofs, supply pipes are on or close to the surface of the ground and all the plumbing rules followed in the UK seem completely forgotten.

 

[Pressure]

Legionella is - I am told - a big deal for hotels, hospitals and other sites with long pipe runs ("dead legs" as mentioned by @Geoff1946 . It's less of a big deal domestically. Our house is just barely big enough for it to be more than an academic question although not a huge deal. Daikin on their maintenance visits always check there's a weekly boost. And I do look forward to extra hot showers on a Saturday!

@binky and @ProDave you raise important questions which I am working through. I'd really like to see if its possible for us to "start heating DHW at 11AM". In fact, we may be - I'll need to check.

However underfloor heating is operating under the principle of "ASHPs + UFH want to work little and often", so may run overnight. I think that's correct? (Although a good argument for a battery...)

I would also really like to know the actual consumption of the ASHP - is fitting a dedicated meter the only way to do this? And is it hard / expensive to do? I need to ask Daikin how they would do it too!

Many thanks once again for the advice - it really is incredibly helpful to get feedback from experts!