Marvin Posted June 1, 2021 Share Posted June 1, 2021 Hi Can you buy equipment that will monitor the 240v ac output amperage/wattage from a PV system, and depending on the power, turn relays on/off to swap the power supply to and from a PV or mains supply to different circuits. This assumes the PV is not connected to the mains My brother always says its not if, but how much, so I suppose my real question is would this be expensive to do. I am working on a 5120W PV home system. There is still lots to decide including splitting the system to connect to the mains in part as I can use the rest for several low wattage continual use items in the house with battery storage including the MVHR. Thanks Marvin Link to comment Share on other sites More sharing options...
ProDave Posted June 1, 2021 Share Posted June 1, 2021 If you have mains electricity then why do you not want the PV grid tied? I am not aware of anything that can do what you want but I am sure you could design and build something, but all the loads you want to individually switch would have to be linked to a bank of changeover relays. And then it relies on the selected equipment presenting a constant load and not minding a brief interruption to the power as it switches over. If the PV is gried tied, as is normal, then the usual thing to use up surplus is dump excess to the immersion heaters, or battery charging for use later. 1 Link to comment Share on other sites More sharing options...
Marvin Posted June 1, 2021 Author Share Posted June 1, 2021 Thanks Pro Dave. 1 minute ago, ProDave said: If you have mains electricity then why do you not want the PV grid tied? Didn't know I could put 5160w system into grid? 2 minutes ago, ProDave said: all the loads you want to individually switch would have to be linked to a bank of changeover relays. And then it relies on the selected equipment presenting a constant load and not minding a brief interruption to the power as it switches over. Yes. I expected a bank of relays and the brief interruption to the power, so am avoiding the internet/wifi . 5 minutes ago, ProDave said: If the PV is grid tied, as is normal, then the usual thing to use up surplus is dump excess to the immersion heaters, or battery charging for use later. Ah! so does this mean you can have inverters that limit the supply to the grid? We have an Electric Vehicle with a slow charger so would use that dump first and or the batteries ( as the batteries will be used during the night will probably be the priority). Link to comment Share on other sites More sharing options...
ProDave Posted June 1, 2021 Share Posted June 1, 2021 You can connect a 3.68Kw inverter to the grid without prior permission under G98. Over 3.68Kw requires DNO approval under G99 BEFORE you connect it. So the first thing is to ask your DNO. You may find, like here, they will want to charge you to upgrade your local grid before giving permission. If that is the case you might want to look at a 3.68Kw grid tie system and a 2Kw off grid / battery system as separate items, and load switch big appliances to the off grid system, or just have big appliances like washing machine always powered from the off grid system and only switching back to the grid when the batteries get too low? 1 Link to comment Share on other sites More sharing options...
TonyT Posted June 1, 2021 Share Posted June 1, 2021 Or get an inverter that limits the output to 3.68 kW and connect up the 5kW 1 Link to comment Share on other sites More sharing options...
Marvin Posted June 1, 2021 Author Share Posted June 1, 2021 Thank you ProDave and TonyT I prefer the inverter with the limiting 3.68kW as, when available, I can use more to charge the car. Also it sounds a bit geeky to start messing around with relays etc and no matter how brilliant it will not impress the boss! 27 minutes ago, ProDave said: load switch big appliances to the off grid system, or just have big appliances like washing machine always powered from the off grid system and only switching back to the grid when the batteries get too low? Yes we have to avoid the big power items using batteries. We are going to wait for technology to catch up on the battery front... Link to comment Share on other sites More sharing options...
SteamyTea Posted June 1, 2021 Share Posted June 1, 2021 Did we ever get a real solution to the difference between system size and inverter size? 1 Link to comment Share on other sites More sharing options...
Wil Posted June 2, 2021 Share Posted June 2, 2021 (edited) 19 hours ago, TonyT said: Or get an inverter that limits the output to 3.68 kW and connect up the 5kW This also requires prior approval from the DNO as it's a G100 connection and doesn't come under G98 for 3.68kWp systems. Assuming you mean a 5kWp inverter with 5kWp of panels that limits it's output to the grid to 3.68kW rather than as I describe below... I had to go down the route of connecting 5kWp of panels to a 3.68kWp inverter to avoid the DNO charges mentioned above. There'll be some clipping on high sun days, but the array in total should output for longer and put out more power than 3.68kWp of panels on the 3.68kWp inverter. Currently trying to invent new dump loads to keep my voltage rise in check... Edited June 2, 2021 by Wil clarity on inverter size 1 Link to comment Share on other sites More sharing options...
Marvin Posted June 2, 2021 Author Share Posted June 2, 2021 (The thing I like about Buildhub is the wealth of knowledge shared and differing opinions which usually results in a solution! And the people who have the patience to explain - thank you.) I am now contacting DNO.... Link to comment Share on other sites More sharing options...
severnside Posted June 2, 2021 Share Posted June 2, 2021 16 hours ago, SteamyTea said: Did we ever get a real solution to the difference between system size and inverter size? We were quoted for 8.76kWp panels with Solar Edge inverter SE 6000H. The installer said these inverters can be configured to limit export to 3.68kWp. If I have load I can use all the capacity but if there is not sufficient load it will cap output to DNO limit Link to comment Share on other sites More sharing options...
SteamyTea Posted June 2, 2021 Share Posted June 2, 2021 6 minutes ago, severnside said: The installer said these inverters can be configured to limit export to 3.68kWp. If I have load I can use all the capacity but if there is not sufficient load it will cap output to DNO limit Yes. I am not really on about what is possible, rather if it is allowed. I just seem to remember that it is the system size i.e. the modules combined output that set the limit. Not sure where one would get this information from, maybe a called to the DNOs. Link to comment Share on other sites More sharing options...
Marvin Posted June 2, 2021 Author Share Posted June 2, 2021 No clear response over the phone from DNO. Email sent requesting clarity on the following: Under the Energy Network association (ENA) EREC G98 regulations, I understand there is a limit of 3.68kW which can be fed into the network. There are inverters that can be limited to 3.68kW feed into the network whilst handling a home generated PV array above this. Obviously these are G98 compliant inverters. Please confirm these inverters set at less than 3.68kW comply with your requirements under a G98 connection. Kind regards I'm sure I will go blue if I hold my breath... As I have just received the automated response! M Link to comment Share on other sites More sharing options...
TonyT Posted June 2, 2021 Share Posted June 2, 2021 https://www.sma-uk.com/solar-systems/export-limitation.html try this 1 Link to comment Share on other sites More sharing options...
Marvin Posted June 3, 2021 Author Share Posted June 3, 2021 Further delving seems to suggest that ProDave is on the money. I have seen G99 applications when an inverter has a feed-in limiter. Sometimes they are inspected by the DNO to see they are working properly and sometimes locked by the electrician and signed off to the DNO. I wait to SSE's response. M Link to comment Share on other sites More sharing options...
SteamyTea Posted June 3, 2021 Share Posted June 3, 2021 I the 'olden days' when FiTs started, there where several thousand '4kW' systems installed with larger that 4kW module arrays. Even though the output was limited to 16A per phase, the overall yield was significantly greater, maybe up to a MWh/year. This was not too much of a problem electrically, especially if the local grid was robust, but it pissed off the people paying the FiTs as they had to pay out a lot more, maybe over £500/year, for 25 years, tax free. So the MCS/FiT/RHI people put a limit on the module array size, so a normal 4kW system could not have more than 4kW of modules on the DC side. What I have been unable to establish is if this is monitored/enforced by MCS only, or it is a DNO 'thing'. I do know that if a single MCS installation company fitted too much PV in an area, they were liable for the local grid/transformer upgrade, and in some instances, just a couple of rural installations could trigger an upgrade. The company I worked for got caught out on this one, a 6 kW install with full permission, then a week later a 4kW installation on the other house under usual installation rule, i.e. no prior approval. They were fighting with WP about the 20 installation in one street of about 50 houses when they went bankrupt. It would be nice to get a definitive answer to this. Link to comment Share on other sites More sharing options...
Marvin Posted June 8, 2021 Author Share Posted June 8, 2021 On 03/06/2021 at 22:48, SteamyTea said: It would be nice to get a definitive answer to this. Ok here we go. This is how it's going for me: SSE phoned to ask if anyone had replied to my email. I said no. Gentleman asked what inverter I purchased. I said I would have a look at the invoice. Gentleman asked where I purchased the inverter. I said Midsummer Gentleman asked if I had the order number. I gave the order number Gentleman then told me the inverter I had and he would raise an order for a CT clamp! He seemed to accept that an inverter with a limiter is ok. Time will tell. I will update when there is progress. Marvin Link to comment Share on other sites More sharing options...
SteamyTea Posted June 8, 2021 Share Posted June 8, 2021 1 hour ago, Marvin said: SSE phoned to ask if anyone had replied to my email SSE are not a DNO as far as I know. They are only interested in the billing side really. You should be able to find out who your DNO is with a bit of googling. Ah, seems SSE are the DNO in Scotland, Link to comment Share on other sites More sharing options...
Marvin Posted June 9, 2021 Author Share Posted June 9, 2021 11 hours ago, SteamyTea said: Ah, seems SSE are the DNO in Scotland, And on the isle of wight which is where I am... Link to comment Share on other sites More sharing options...
SteamyTea Posted June 9, 2021 Share Posted June 9, 2021 5 hours ago, Marvin said: And on the isle of wight which is where I am... which will be the second S Link to comment Share on other sites More sharing options...
Marvin Posted June 9, 2021 Author Share Posted June 9, 2021 On 08/06/2021 at 21:05, Marvin said: Ok here we go. This is how it's going for me: SSE phoned to ask if anyone had replied to my email. I said no. Gentleman asked what inverter I purchased. I said I would have a look at the invoice. Gentleman asked where I purchased the inverter. I said Midsummer Gentleman asked if I had the order number. I gave the order number Gentleman then told me the inverter I had and he would raise an order for a CT clamp! He seemed to accept that an inverter with a limiter is ok. Time will tell. I will update when there is progress. Marvin Oh my! Never take a call on your mobile when your trying to drill holes in a roof. Well it embarrassingly turns out that the call was from Midsummer and not SSE. I had sent an email to both on the same day about roughly the same subject. So I still wait for a response from SSE. I'm sure I will never live this down.... Link to comment Share on other sites More sharing options...
Marvin Posted June 12, 2021 Author Share Posted June 12, 2021 Latest: Thank you for your email. Unfortunately I am unable to assist with your enquiry as Distribution General Enquiries at Scottish & Southern Electricity Networks (SSEN) are responsible for raising non-emergency electricity network jobs for central southern England and northern Scotland. However, our G59 Protection Settings department will be able to help resolve this matter as they primarily deal with all enquiries of this nature. I have taken the liberty of copying in our DEPARTMENT NAME team into this reply, and I am sure a member of their team will be in contact with you shortly. Kind regards Link to comment Share on other sites More sharing options...
Marvin Posted June 17, 2021 Author Share Posted June 17, 2021 Latest: Email received from DNO raising questions. My responses in red: Does your enquiry relate to a new generation connection or existing connection? New generation feed-in to existing supply Site Address for Generator: My home. Type of Generator Photovoltaics Capacity of Generator: Panels capable of generating 5.120kW but limited by inverter to 3.68kW with ct Clamp. Make and model of inverter: Sofar Solar Grid-tied Inverter Product model: SOFAR 6KTLM-G2 with ct clamp. Import and export MPANS xxxxxxxxxxxx This system has NOT been installed yet. Link to comment Share on other sites More sharing options...
Marvin Posted June 17, 2021 Author Share Posted June 17, 2021 (edited) For those of you who are not in the know, I am trying to obtain permission to connect my proposed 5.12kW photovoltaic system to the mains electricity using an inverter which would limit the feed-in to the mains to a maximum of 3.68kW thus avoiding having to obtain prior permission (and possible costs) from the distribution network operator (DNO) under G98 rules. The question I am trying to find the answer to is whether this design of a system; able to produce more than 3.68kW, but with an inverter set up, which limits the amount that can be fed into the mains grid to a maximum of 3.68kW, is OK under G98 rules. Latest DNO reply: Thank you for confirming the information below. I have forwarded your email to our MCC Generation Team, if they are not able to assist I have requested that they let me know and I will locate the correct team that can answer your query. Regards Edited June 17, 2021 by Marvin Clarification 1 Link to comment Share on other sites More sharing options...
TonyT Posted June 17, 2021 Share Posted June 17, 2021 You have an import MPAN You have a home address, so that’s 2 bits of info you could have given them Link to comment Share on other sites More sharing options...
Marvin Posted June 17, 2021 Author Share Posted June 17, 2021 The result is that under the rules I have to apply under a G99 application for anything capable of feeding in more than 3.68kW even if the inverter can be limited to 3.68kW I will upload info later on. Link to comment Share on other sites More sharing options...
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