Specification for a Solar System

[Deleted User]

Grumpy_chap said:

Thanks @QrizB
Do you have any advice on how to select a solar company?
I only know one person with a system, but the company they used is no longer trading.
Doing online searches, there seems to be very little process to split the best from the worst - a slick website means little.

I assumed the "Grid independence 95%" meant really big batteries charged all summer and powering me through the whole winter except, maybe, a few days by late February when the battery is depleted

Where do you live? I used YouGen as a starter for both my installations and eventually I chose a local company that had a proven portfolio of commercial and private installations.  I would have gone for a supplier that was £500 cheaper but he failed to quote for an in roof mounting system, and his preferred solution was to drill through slates ( which in fairness is MCS approved). We had a couple of slate issues that I picked up after the installation was completed and as the installers were only 15 miles away they were quick to return to site before the scaffolding came down.

Grumpy_chap

Thanks for the additional information @QrizB and @[Deleted User].

Home is West London, so I have sent some enquiries to the people QrizB used (they drive past me from Kent to get to QrizB in Berkshire), Tesla (probably going to be expensive), two companies from YouGen plus one from an internet search.  With a 50% response rate, that will mean 2 or 3 budget proposals to compare with the Council "scheme".

Hopefully the proposals will give enough extra information to allow some kind of assessment to be done before the next steps.  Certainly more than the Council "scheme" offering to do "something for some money".

Fingers-crossed.

Martyn1981

Dolor said:

Grumpy_chap said:

OK - so, the Council ran a "scheme" where they get an amazing rate for "group buying" solar.  I did my enquiry and have now received my proposal, which is rather sparse on details:

Personal recommendation for solar system:  £9,889
Generate 6,287 kWh per year
Grid independence 95%
To accept this offer, please simply click "accept", pay the £150 deposit to allow us to carry out your survey.

How on earth is anyone meant to assess an offer of such great level of detail?

A system that generates 6287kWhs a year would suggest a 7/7.5kWp array. However, until the installer has consulted with your DNO he will not know whether there is likely to be an export limit. The DNO’s advice doesn’t come free. I assume that a battery is included in the quote? A battery of any size is deemed to be a generator and it requires DNO approval irrespective of the size of the PV array. Unless the installer knows how much energy you will be using each year, I doubt the the 95% Grid independence claim is valid. For example, I have a 7kWp array (export limited to 5kWs) and a PW2. We consume about 4500kWhs/year of which 800kWhs is imported during the Winter months. There is no way that I will get close to 95% Grid independence.

I am happy to be told that I am wrong but I have yet to see batteries other than a PW2 that will ‘island’ the home from the Grid if the power fails. The PW2 Gateway isn’t cheap. A battery set up with a dedicated 13 amp socket is not the same as an uninterrupted supply to the whole house. A set up such as the PW2 has the additional advantage that there is no need to shut down the solar output if there is somewhere for it to go within the home or battery. Standard arrays with batteries have to shut down when there is a Grid failure to ensure that there is no export to the Grid.

Hi Dolor, may I ask you a (possibly stupid) question regarding the PW2 and Gateway? I applied to be part of a V2G trial, but was blocked by the DNO as my export limit (of 5.9kW) was maxed out, and the kit that was to be installed hadn't received G100 (or was it G99) compliance meaning that it absolutely couldn't export if something went wrong. I was told that the same would obviously apply to battery storage, unless it too was guaranteed not to export leccy that would bring the total above the export limit.

Now, I know that the PW2 Gateway kit is very clever, and as you mention, can island the house, so am I right to assume that it does meet the DNO requirements, and is accordingly certified?

I'm not sure if I want to go down the battery route, especially this expensive route yet, but I love the idea of being more self sustaining, and I've also noticed that there is a great 'Tesla' leccy deal available, I think 8p/kWh (import and export), which is interesting!


Edit - One more question, sorry, but Elon recently said that the PW2 was performing better than expected, regarding battery longevity, and suggested that output could be increased 50-100% when temps aren't too high or low, which I assume applies to most of the UK, most of the time.

I assume this relates to the 5kW steady output, not the 7kW short output, but that would still lift the 5kW to ~7.5kW, which hits a magic figure - the 7kW car charger. So with adequate battery charge it could run for an hour, and add a 'fast' 30ish miles of range on its own.

Does this mean anything to you, have you heard anything on this?

Thanks.

[Deleted User]

Martyn1981 said:

Dolor said:

Grumpy_chap said:

OK - so, the Council ran a "scheme" where they get an amazing rate for "group buying" solar.  I did my enquiry and have now received my proposal, which is rather sparse on details:

Personal recommendation for solar system:  £9,889
Generate 6,287 kWh per year
Grid independence 95%
To accept this offer, please simply click "accept", pay the £150 deposit to allow us to carry out your survey.

How on earth is anyone meant to assess an offer of such great level of detail?

A system that generates 6287kWhs a year would suggest a 7/7.5kWp array. However, until the installer has consulted with your DNO he will not know whether there is likely to be an export limit. The DNO’s advice doesn’t come free. I assume that a battery is included in the quote? A battery of any size is deemed to be a generator and it requires DNO approval irrespective of the size of the PV array. Unless the installer knows how much energy you will be using each year, I doubt the the 95% Grid independence claim is valid. For example, I have a 7kWp array (export limited to 5kWs) and a PW2. We consume about 4500kWhs/year of which 800kWhs is imported during the Winter months. There is no way that I will get close to 95% Grid independence.

I am happy to be told that I am wrong but I have yet to see batteries other than a PW2 that will ‘island’ the home from the Grid if the power fails. The PW2 Gateway isn’t cheap. A battery set up with a dedicated 13 amp socket is not the same as an uninterrupted supply to the whole house. A set up such as the PW2 has the additional advantage that there is no need to shut down the solar output if there is somewhere for it to go within the home or battery. Standard arrays with batteries have to shut down when there is a Grid failure to ensure that there is no export to the Grid.

Hi Dolor, may I ask you a (possibly stupid) question regarding the PW2 and Gateway? I applied to be part of a V2G trial, but was blocked by the DNO as my export limit (of 5.9kW) was maxed out, and the kit that was to be installed hadn't received G100 (or was it G99) compliance meaning that it absolutely couldn't export if something went wrong. I was told that the same would obviously apply to battery storage, unless it too was guaranteed not to export leccy that would bring the total above the export limit.

Now, I know that the PW2 Gateway kit is very clever, and as you mention, can island the house, so am I right to assume that it does meet the DNO requirements, and is accordingly certified?

I'm not sure if I want to go down the battery route, especially this expensive route yet, but I love the idea of being more self sustaining, and I've also noticed that there is a great 'Tesla' leccy deal available, I think 8p/kWh (import and export), which is interesting!


Edit - One more question, sorry, but Elon recently said that the PW2 was performing better than expected, regarding battery longevity, and suggested that output could be increased 50-100% when temps aren't too high or low, which I assume applies to most of the UK, most of the time.

I assume this relates to the 5kW steady output, not the 7kW short output, but that would still lift the 5kW to ~7.5kW, which hits a magic figure - the 7kW car charger. So with adequate battery charge it could run for an hour, and add a 'fast' 30ish miles of range on its own.

Does this mean anything to you, have you heard anything on this?

Thanks.

Under domestic control, the PW2 cannot be forced to export. However, if PW2 owners subscribe to the Tesla Energy Plan, Tesla will manage all Grid exports. Those that have signed up to this have found that where there is a DNO-imposed export limit, that this limit is set in the Gateway as a ‘site limit’. In my case, I live in a rural area and I have an export limit of 5kWs. It follows that if the Tesla Plan was enabled, my export could be solar; a mix of solar and the PW2, or the PW2 up to the 5kW limit. The 8p/8p plan is for Tesla EV owners only: lesser mortals only get 11p/11p. I haven’t signed up for the plan because I am concerned about the increased battery churn. At the moment, I only import about 700kWhs a year but the Plan suggests that this would increase to over 4000kWhs which is a full cycle a day compared to about 2 or 3 cycles a week off plan. Leaked documents have also suggested that the Plan is changing and they will move to a 22p/day standing charge.

The Gateway 2 is fully certified under G100 for islanding. I recall that there were 4 commissioning tests all of which had a less than 3 seconds compliance target: Remove Power to Gateway ( loss of 12 volt and 240 volt power supplies detected); Remove Power to Meter; Loss of Comms between AC PW2 and Meter, and Loss of Meter Data Detected. I know that many people are not aware of these requirements when it comes to V2G.  On the 4 occasions that I have had an actual outage, the Gateway response has been instantaneous.

Press reports about PW2 improvements are at best vague. PW2s manufactured after Nov 2020 appear to have the relevant software/hardware but they have to be set up at installation. I am not sure where this leaves me. There has also been a lot of discussion within The Tesla Motors Club forums about the difference between battery capacity and power output 

My experience of the PW2 has been good. Like many, I get frustrated by the Tesla algorithm which uses the last 2 days solar to decide how much energy to take from the Grid when it is cost saving mode. If there are two days with little solar, this can leave me with a battery with a very low SoC. That said, the battery does have the facility to set a minimum SoC to cater for outages, so it is possible to force the PW2 to charge during an off peak period.

Grumpy_chap

Thanks for the advice, but can I check what some of the terms mean here please?

[Deleted User] said:

I am happy to be told that I am wrong but I have yet to see batteries other than a PW2 that will ‘island’ the home from the Grid if the power fails. The PW2 Gateway isn’t cheap. A battery set up with a dedicated 13 amp socket is not the same as an uninterrupted supply to the whole house. A set up such as the PW2 has the additional advantage that there is no need to shut down the solar output if there is somewhere for it to go within the home or battery. Standard arrays with batteries have to shut down when there is a Grid failure to ensure that there is no export to the Grid.

FWiW, I paid just over £16k for my array with SolarEdge and in roof fitting on two separate buildings; PW2 with Gateway and a Zappi and EDDI. We have not required any Grid energy since late February. Putting to one side payback, it was the right thing for us to do and it is a great feeling knowing that the home is being powered by the sun.

PS Your original 20kWhs battery storage sounds great but with a PVGIS solar output target of 160kWhs in January, you might struggle to keep them charged with solar power, and struggle to charge them when Grid energy is cheap.

PW2 = TESLA Power Wall 2?

Solar Edge.  I have seen that term and understand it to be desirable, but no idea what it is or what it means or does.

PVGIS = ??

QrizB

Grumpy_chap said:

Thanks for the advice, but can I check what some of the terms mean here please?

PW2 = TESLA Power Wall 2?

Solar Edge.  I have seen that term and understand it to be desirable, but no idea what it is or what it means or does.

PVGIS = ??

PW2 - yes, Tesla PowerWall 2

Solar Edge - a deluxe inverter company (I'm sure they're more than that!)

PVGIS - the EU's photovoltaic geographical information system, a good source for map-based output predictions, freely available at https://ec.europa.eu/jrc/en/pvgis

Martyn1981

Dolor said:

Martyn1981 said:

Dolor said:

Grumpy_chap said:

OK - so, the Council ran a "scheme" where they get an amazing rate for "group buying" solar.  I did my enquiry and have now received my proposal, which is rather sparse on details:

Personal recommendation for solar system:  £9,889
Generate 6,287 kWh per year
Grid independence 95%
To accept this offer, please simply click "accept", pay the £150 deposit to allow us to carry out your survey.

How on earth is anyone meant to assess an offer of such great level of detail?

A system that generates 6287kWhs a year would suggest a 7/7.5kWp array. However, until the installer has consulted with your DNO he will not know whether there is likely to be an export limit. The DNO’s advice doesn’t come free. I assume that a battery is included in the quote? A battery of any size is deemed to be a generator and it requires DNO approval irrespective of the size of the PV array. Unless the installer knows how much energy you will be using each year, I doubt the the 95% Grid independence claim is valid. For example, I have a 7kWp array (export limited to 5kWs) and a PW2. We consume about 4500kWhs/year of which 800kWhs is imported during the Winter months. There is no way that I will get close to 95% Grid independence.

I am happy to be told that I am wrong but I have yet to see batteries other than a PW2 that will ‘island’ the home from the Grid if the power fails. The PW2 Gateway isn’t cheap. A battery set up with a dedicated 13 amp socket is not the same as an uninterrupted supply to the whole house. A set up such as the PW2 has the additional advantage that there is no need to shut down the solar output if there is somewhere for it to go within the home or battery. Standard arrays with batteries have to shut down when there is a Grid failure to ensure that there is no export to the Grid.

Hi Dolor, may I ask you a (possibly stupid) question regarding the PW2 and Gateway? I applied to be part of a V2G trial, but was blocked by the DNO as my export limit (of 5.9kW) was maxed out, and the kit that was to be installed hadn't received G100 (or was it G99) compliance meaning that it absolutely couldn't export if something went wrong. I was told that the same would obviously apply to battery storage, unless it too was guaranteed not to export leccy that would bring the total above the export limit.

Now, I know that the PW2 Gateway kit is very clever, and as you mention, can island the house, so am I right to assume that it does meet the DNO requirements, and is accordingly certified?

I'm not sure if I want to go down the battery route, especially this expensive route yet, but I love the idea of being more self sustaining, and I've also noticed that there is a great 'Tesla' leccy deal available, I think 8p/kWh (import and export), which is interesting!


Edit - One more question, sorry, but Elon recently said that the PW2 was performing better than expected, regarding battery longevity, and suggested that output could be increased 50-100% when temps aren't too high or low, which I assume applies to most of the UK, most of the time.

I assume this relates to the 5kW steady output, not the 7kW short output, but that would still lift the 5kW to ~7.5kW, which hits a magic figure - the 7kW car charger. So with adequate battery charge it could run for an hour, and add a 'fast' 30ish miles of range on its own.

Does this mean anything to you, have you heard anything on this?

Thanks.

Under domestic control, the PW2 cannot be forced to export. However, if PW2 owners subscribe to the Tesla Energy Plan, Tesla will manage all Grid exports. Those that have signed up to this have found that where there is a DNO-imposed export limit, that this limit is set in the Gateway as a ‘site limit’. In my case, I live in a rural area and I have an export limit of 5kWs. It follows that if the Tesla Plan was enabled, my export could be solar; a mix of solar and the PW2, or the PW2 up to the 5kW limit. The 8p/8p plan is for Tesla EV owners only: lesser mortals only get 11p/11p. I haven’t signed up for the plan because I am concerned about the increased battery churn. At the moment, I only import about 700kWhs a year but the Plan suggests that this would increase to over 4000kWhs which is a full cycle a day compared to about 2 or 3 cycles a week off plan. Leaked documents have also suggested that the Plan is changing and they will move to a 22p/day standing charge.

The Gateway 2 is fully certified under G100 for islanding. I recall that there were 4 commissioning tests all of which had a less than 3 seconds compliance target: Remove Power to Gateway ( loss of 12 volt and 240 volt power supplies detected); Remove Power to Meter; Loss of Comms between AC PW2 and Meter, and Loss of Meter Data Detected. I know that many people are not aware of these requirements when it comes to V2G.  On the 4 occasions that I have had an actual outage, the Gateway response has been instantaneous.

Press reports about PW2 improvements are at best vague. PW2s manufactured after Nov 2020 appear to have the relevant software/hardware but they have to be set up at installation. I am not sure where this leaves me. There has also been a lot of discussion within The Tesla Motors Club forums about the difference between battery capacity and power output 

My experience of the PW2 has been good. Like many, I get frustrated by the Tesla algorithm which uses the last 2 days solar to decide how much energy to take from the Grid when it is cost saving mode. If there are two days with little solar, this can leave me with a battery with a very low SoC. That said, the battery does have the facility to set a minimum SoC to cater for outages, so it is possible to force the PW2 to charge during an off peak period.

So, so many thanks, much appreciated.

So, can I test your patience, and just check I'm understanding all of this correctly then:

Para 1. The PW2 won't export, even by mistake, hence it's G100, so therefore I might be able to do this then, despite being at max DNO allowance, since it can't 'add' to PV export in error?
Your explanation of your 5kW limit, is exactly what I needed to know regarding battery export, so again, the battery would never allow the total of battery and PV export to exceed an agreed DNO limit? I appreciate you've already confirmed this, but I'm triple checking, that that's what the G100 compliance means, and hence why it's so important.
Thanks for the concerns about the Tesla leccy plan, I'm very interested in an 8p tariff, who wouldn't be, but also share your concerns about battery life.

Para 2. Brill, thanks.

Para 3. Yep, I figured it would be vague given the comments from Elon were so recent, and the launch/announcement today(?) about the PW+, which in the US seems to combine technology, taking the solar inverter on board, and meaning the PV doesn't talk to the grid, as it now all flows through the PW+.
My thoughts about car charging at 7kW, where more just ponderings, and I suppose wouldn't actually require 7kW from the PW as some would be coming from solar, but my experiences lately, with a granny charger, are that almost all charging can be from PV, but a battery buffer would be nice, to eliminate all import, as generation fluctuates. Taking this up a gear to 7kW, would be fun, to say the least.

Para 4. Nice to know, thanks again.


PS - Regarding your having SolarEdge, if you have any shading, then you will probably be very pleased with this. Both of my systems are SolarEdge, and despite having more than a little shading, primarily a large central chimney (semi-detached) to the south, which panels butt up against, have consistently met or exceeded PVGIS estimates for my rooves, based on zero shading.

[Deleted User]

TEP is a frequent and active discussion on the Octopus Smart Energy Forum. I raised the question of export limits and a guy on the forum kindly posted a screenshot of the settings in his Gateway 2 which showed a Site Limit of 7KWs: his export limit. This isn’t a setting that a PW2 owner can change but I guess that installers must have some way of changing it if the DNO agrees a higher export limit. He confirmed that he has never seen an export to the Grid in excess of the site/export limit. I will have another look through the PW2 specification to see how the site limit is covered.

In the latest iteration of the PW2 App, Tesla has markedly reduced the ability for access/customisation. For example, a third-party had developed a programme to change the peak/off tariff settings (in cost saving mode) each day in line with Agile tariff changes. The programme has now been withdrawn. 

SolarEdge works brilliantly with my set up as I have 2 roofs which are separated by 90% with one (a garage) partly shaded until about midday. Even though I have a 7kWp array, my roof set up means that on a really good day the 5kW peak is only capped for about 2 hours with the array running for about 13 hours even in early April. I am running at about 15% above PVGIS for the year so far.

Reed_Richards

I have my battery on the DC side of the inverter.  I don't know if that helps with "islanding" but my inverter, made by Goodwe, will do this.  I have the lights, fridge freezer and router wired to the "island"; no point in trying to run the whole house as that would drain the battery too quickly. It works if I turn off the power at the mains; I am still waiting for the power cut that will really put it to the test.

[Deleted User]

Reed_Richards said:

I have my battery on the DC side of the inverter.  I don't know if that helps with "islanding" but my inverter, made by Goodwe, will do this.  I have the lights, fridge freezer and router wired to the "island"; no point in trying to run the whole house as that would drain the battery too quickly. It works if I turn off the power at the mains; I am still waiting for the power cut that will really put it to the test.

I assume that you have the relevant G100 certification?