GreenSophie Posted April 23 Share Posted April 23 I’m so sorry if this has been asked before. We have a large shed with a south facing roof around 100m from the house and would like to install 8-10 solar panels on it to provide electricity for the house and export any surplus to the grid. Digging a new cable run between the house and the shed would be a nightmare so we wondered if we could put an inverter in the shed and then use the existing mains cable which runs from the house to transfer the AC power produced by the solar set up to the house. It is a 3 core, 25mm armoured cable, each core has 6 strands of copper wire. It’s around 100m long and the shed has its own consumer unit. We’d want to be able to continue to use the cable to supply power to the shed. Sorry if this sounds a bit vague, we just want to know if the project is viable before contacting an electrician. Link to comment Share on other sites More sharing options...
JohnMo Posted April 23 Share Posted April 23 You may have issues, really depends on the voltages at the moment. I would check your current voltage in the shed first and report back. Link to comment Share on other sites More sharing options...
ProDave Posted April 23 Share Posted April 23 If it really is 25mm armoured cable, then you are okay, but only 6 strands per core it is far more likely to be a lot smaller. Can you post any kind of picture of the ends of the cable, e.g. where it terminates at either end? Or get an electrician to measure Zs at the shed and post the reading he gets here, from that we can work out the likely volt drop (will be volt rise with PV generation) Link to comment Share on other sites More sharing options...
GreenSophie Posted April 23 Author Share Posted April 23 Thanks so much for your quick replies. it’s definitely 25mm diameter armoured cable. Here’s a pic of the inside of the shed consumer unit and you can see the earth core has quite thick copper wire strands. No idea if that helps! Link to comment Share on other sites More sharing options...
ProDave Posted April 23 Share Posted April 23 Yes that looks like 25mm. At 16A (typical 4kW PV array) you are likely to get about 3 volt drop over that cable, which should be fine. Remember that will be voltage rise when it is generating. So as long as your mains voltage is no higher than 250V (it should not be) you will be fine. Most inverters trip or start limiting when they reach 253 volts. Link to comment Share on other sites More sharing options...
GreenSophie Posted April 23 Author Share Posted April 23 Voltage in shed is 242, in house is 245. So you’re spot on, ProDave 😊 really silly question, but can the same cable be used for both mains supply to shed and solar generated supply to house? Link to comment Share on other sites More sharing options...
ProDave Posted April 23 Share Posted April 23 1 minute ago, GreenSophie said: Voltage in shed is 242, in house is 245. So you’re spot on, ProDave 😊 really silly question, but can the same cable be used for both mains supply to shed and solar generated supply to house? Yes it can. With those voltage readings you will be fine. Lucky the original person properly sized the cable for the length. It is surprising how many sheds you find wired with a bit of wet string. I was asked to check a DIY garage conversion complete with electric panel heating, electric water heating and an electric shower. The whole thing was fed with 2.5mm cable. Link to comment Share on other sites More sharing options...
GreenSophie Posted April 23 Author Share Posted April 23 Thanks so much! Is this something that we can specify ourselves and get a competent electrician to install? The solar companies seem so expensive and it’s quite a simple set up. Link to comment Share on other sites More sharing options...
Bramco Posted April 23 Share Posted April 23 Yes you can, it's not rocket science - there are plenty of web sites around with packages of PV with inverter, some with roof fastenings. Try ITS technologies - we've found them to pretty competitive - but there's also Trade Sparky and many more. On the electrician front, I'd make sure that your electrician is happy with you doing the work and them signing it off. A lot of electricians won't sign off someone else's work and then you'll be forced down the MCS surcharge route (the solar installation companies). There's a break point in terms of whether you need to inform the DNO about the installation. Below about 3.6kW you don't need to but above that you need to go through their process - all of the DNOs have information on their websites about what forms you need to fill in etc. You don't need an MCS certificate to complete this step. Also you need to check whether there are any planning restrictions, like for example you being in a conservation area. There's loads of info on-line about how to do this and a lot on this forum on how people have gone about things. I'm sure you should be able to manage to do it yourself. Simon Link to comment Share on other sites More sharing options...
GreenSophie Posted April 23 Author Share Posted April 23 Thanks Simon, that’s so helpful! Link to comment Share on other sites More sharing options...
Conor Posted April 23 Share Posted April 23 I did 90% of our install myself, spark did the connection from inverter to the consumer unit and provided the safety check paperwork. Fitting the panels and stringing them together is pretty simple stuff. 1 Link to comment Share on other sites More sharing options...
ProDave Posted April 23 Share Posted April 23 3 minutes ago, Conor said: Fitting the panels and stringing them together is pretty simple stuff. Don't be too casual about it. A DC string can be a lethal thing to get wrong. Link to comment Share on other sites More sharing options...
Conor Posted April 23 Share Posted April 23 10 minutes ago, ProDave said: Don't be too casual about it. A DC string can be a lethal thing to get wrong. AHH. I used optimisers that made everything safe (1v per panel) until commissioned. Good point tho. 1 Link to comment Share on other sites More sharing options...
Dillsue Posted April 24 Share Posted April 24 On 23/04/2024 at 13:09, Bramco said: There's a break point in terms of whether you need to inform the DNO about the installation. Below about 3.6kW you don't need to but above that you need to go through their process - all of the DNOs have information on their websites about what forms you need to fill in etc. You don't need an MCS certificate to complete this step. Your DNO always needs to know about generating equipment connected to the grid, no matter the system size For PV, if its under 3.68kw max export to the grid and you're using a type approved inverter, notify them after installation using a G98 notification. If its over 3.68kw max export, you need to get your DNOs permission before you connect using a G99 application. Link to comment Share on other sites More sharing options...
GreenSophie Posted April 24 Author Share Posted April 24 Thanks so much everyone. Any ideas on how to go about finding an electrician who could do the work? Every time I search, I just get the solar companies. I’m in the north Essex / south Cambs area. It’s not a big install - 6 panels and an inverter and we’d fit the panels ourselves. Link to comment Share on other sites More sharing options...
GreenSophie Posted April 24 Author Share Posted April 24 Just seen that ITS who Bramco recommended do a 50 quid design offer and as part of that provide a list of installers. So that might be our best option. Link to comment Share on other sites More sharing options...
SteamyTea Posted April 24 Share Posted April 24 25 minutes ago, GreenSophie said: Any ideas on how to go about finding an electrician who could do the work Any properly qualified and insured electrician can do it. The electrical and testing side of it is very straightforward. Link to comment Share on other sites More sharing options...
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