dnoble Posted June 25, 2018 Share Posted June 25, 2018 Hello all. Planning to have 4-6KW solar PV on my new build. Not going to go for the FIT since it's now so paltry. Thinking about DIY fitting the solar panels to the roof of my new build while the scaffolding's up, Can get 4kw worth for <2K it seems. The house has not yet had first fix, and in early stages so I was thinking about getting inverter and sorting connection later (probably next year) I'm not an electrician and would like to know if it's feasible/safe to do this and leave them on the roof, presumably connected together in series with a cable into the house to connect at a later date? Link to comment Share on other sites More sharing options...
ProDave Posted June 25, 2018 Share Posted June 25, 2018 Run the DC cable into the house and into the DC isolator switch. Then it is safe for connection later when you are ready. Remember high voltage DC is a lot more dangerous than AC Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 25, 2018 Share Posted June 25, 2018 16 minutes ago, ProDave said: Run the DC cable into the house and into the DC isolator switch. Then it is safe for connection later when you are ready. Remember high voltage DC is a lot more dangerous than AC That's what our in-roof installer did, except the DC isolator switches (one for each string) were fitted outside, to a plinth that I fitted to the house frame that projected slightly outside where the cladding was going to go. 25mm flexible conduit ran up the wall (behind the cladding) and over the roof (under the battens) with the four runs of single core DC cable. The order of installation was fit the roofing battens, then fit the in-roof panel mounts (very easy to do as a DIY job) then install all the slates, fascias, gutters etc, then fit the solar panels to the mounts and connect them up to the cables, in two strings. Doing it this way minimised the risk, as the four cables coming from the two (turned off) isolators were not connected to anything, so could have plugs/sockets crimped on whilst they were dead. The panels all had flying leads with pre-terminated plugs and sockets, so it was just a matter of plugging everything together. The connectors are designed to minimise the potential to touch any live connection, so the plugs and sockets are safe to connect with the panels generating. If the order of work is planned out like this before hand then there should never be a need to have to terminate any potentially live cable. If the house is reasonably well insulated, then it's well-worth looking at fitting the inverter outside, as they do generate a fair bit of heat when running flat out. We have ours mounted at the back of the house, fairly high up on the North wall, so it never sees direct sunlight and is able to run cooler than it would if it were inside the house. Apart from potentially extending the life of the inverter by keeping it cooler, it also reduces the heat flowing into the house on hot sunny days, which is a definite advantage. Most inverters are IP rated, or have an IP rated version, making outside installation pretty easy. Link to comment Share on other sites More sharing options...
PeterW Posted June 25, 2018 Share Posted June 25, 2018 6 minutes ago, JSHarris said: Apart from potentially extending the life of the inverter by keeping it cooler, it also reduces the heat flowing into the house on hot sunny days, which is a definite advantage. Most inverters are IP rated, or have an IP rated version, making outside installation pretty easy. I’ve been looking at micro inverters as the whole installation ends up outside which seems to be of benefit as there is nothing other than an AC isolator and connection indoors. This would be a pure DIY install and no FiT so RoI is more important than anything else. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 25, 2018 Share Posted June 25, 2018 My only concerns with microinverters are that they most probably run pretty hot, as they are under the panels, so must get a fair bit of heat from the sun, and the need to erect scaffolding to replace any faulty inverters. Inverters are bound to have a shorter life than panels, so although microinverters seem to be a really good idea, it's the practicalities that bother me. A failed microinverter could easily cost a couple of thousand pounds to replace if a full scaffold has to be erected in order to gain access. Replacing a wall-mounted inverter would be a lot cheaper, just isolate it, unplug the cables, unhook it from the wall, hook on the new one and plug it in and switch it on. 1 Link to comment Share on other sites More sharing options...
jack Posted June 25, 2018 Share Posted June 25, 2018 9 minutes ago, JSHarris said: ... and the need to erect scaffolding to replace any faulty inverters. You've identified about the only advantage I can find for having a flat(ish) roof with parapet wall - no scaffolding needed to replace a microinverter! 1 Link to comment Share on other sites More sharing options...
dpmiller Posted June 25, 2018 Share Posted June 25, 2018 why not bring the DC cables through the felt and have the microinverters in the attic? 1 Link to comment Share on other sites More sharing options...
MikeSharp01 Posted June 25, 2018 Share Posted June 25, 2018 1 minute ago, dpmiller said: why not bring the DC cables through the felt and have the microinverters in the attic? Probably cos they would be in the insulated part of the building, If cold roof then its a better idea I guess, you can get to them but the standard connectors / cables probably won't run that far. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 25, 2018 Share Posted June 25, 2018 1 hour ago, jack said: You've identified about the only advantage I can find for having a flat(ish) roof with parapet wall - no scaffolding needed to replace a microinverter! I think it's a really big advantage, given the relatively high cost of scaffolding. 1 hour ago, dpmiller said: why not bring the DC cables through the felt and have the microinverters in the attic? It wouldn't be easy to get the cables through a modern breathable roof membrane, and would be a lot of faffing around to try and get the cable entries watertight, or at least arranged so they ran up under an overlap joint and were taped down, as well as the potential problems of having them in a warm (perhaps very hot) roof space, which may not be a lot better than having them under the panels. There's always the option of running a pair of cables from every single panel to an easy to access area., though. Cable losses are pretty small, as the current wouldn't be that high from a typical 250 to 280 W panel. Whether or not it's worth it is another matter. Link to comment Share on other sites More sharing options...
dnoble Posted June 25, 2018 Author Share Posted June 25, 2018 Many thanks for this Jeremy and Dave. I had an idea there was a risk but useful to have practical advice. The roof gets a bit of dappled shade in a portion from a nearby Ash tree, especially away from midsummer when the sun's lower. I see people have pre-empted my next question which was; What are peoples thoughts on micro inverter fitted panels. Is it worth the extra cost (or should I just coppice the tree!) Points about having to replace micro-inverters are worth thinking about (how would you know one had stopped working anyway; is there a way of monitoring the output of individual panels?) Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 25, 2018 Share Posted June 25, 2018 Microinverters often have a monitoring system built in that reports back to a data collection unit, so you can check performance and health. For the sort of shaded conditions you describe then microinverters are a good choice, but equally good, and perhaps more reliable (the jury's out on that) might be to fit panel optimisers, like the Solar Edge system. Optimisers don't have the high voltage switched mode inverters built in, so are a lot simpler internally. All they do is optimise the output from each individual panel using a maximum power point tracker (MPPT). This deals with partial shade every bit as well as a microinverter system, but means that you still run DC down to a conventional inverter. The advantage is really that the primary cause for concern in the microinverters (and big inverters), the high voltage commutation capacitors, aren't up on the roof, but remain in the main inverter. Commutation capacitor life is the primary life-limiting factor in an inverter, and is proportional to temperature - the cooler you can keep the capacitors the longer they will last. 2 Link to comment Share on other sites More sharing options...
SteamyTea Posted June 25, 2018 Share Posted June 25, 2018 7 hours ago, dpmiller said: why not bring the DC cables through the felt and have the microinverters in the attic? You are not allowed to have the inverters in the loft anymore, unless there is dedicated cooling for them. Link to comment Share on other sites More sharing options...
dpmiller Posted June 25, 2018 Share Posted June 25, 2018 2 hours ago, SteamyTea said: You are not allowed to have the inverters in the loft anymore, unless there is dedicated cooling for them. according to...? Link to comment Share on other sites More sharing options...
SteamyTea Posted June 25, 2018 Share Posted June 25, 2018 I think the IEEE brought it in when they updated the regs. Might have been MCS, but they do not set the electrical rules, just the FiT/RHI ones. I had left the industry by then, but when chatting at my old electrician, he mentioned it. I always thought it strange that the inverter was tucked away up in the loft. Seemed harder work to fit them as well. Clarification on this point would be useful. Anyone got a set of the lasted Edition. Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 26, 2018 Share Posted June 26, 2018 Im on a steep ( vertical ) learning curve with PV so this and another thread running here are extremely informative, keep it going ! After the electricity gets out of the panels not a problem, its getting the juice out of them, optimised and inverted that seems to be the minefield. For a mixed orientation, fragmented arrangement of say 5-6kW, it seems that optimisers and a single external or garage / outbuilding mounted inverter seems to best way to go in terms of reliability, yield and ease of maintenance. Running cables from each panel into the ( accessible ) loft space seems the sensible approach, as then only a failed panel will require access to / roof work. That leaves the problem of making a reliable means of penetrating and subsequent repairing of the multiple transits ( penetrations ) through the airtight layer. What have others done here to get the cables from roof to airtight envelope? Plenty of detail please ! Link to comment Share on other sites More sharing options...
jack Posted June 26, 2018 Share Posted June 26, 2018 2 hours ago, JSHarris said: Microinverters often have a monitoring system built in that reports back to a data collection unit, so you can check performance and health. The Enphase microinverters that we have used to allow per panel reporting (I think) but that function's been cut back. I believe installers and Enphase can still see it. You can still see which panels are producing more power than other panels in real time, based on their colour. This was last night at 8:45 - very little power being produced per panel: You'll also get an email if there appears to be a fault. We had that when it snowed earlier this year - the system was expecting the panels to produce power, and when they didn't do so, itsent me an alert. I watched over the next day or so as they individually woke back up as the snow cleared from them. Our microinverters have a 20 or 25 year warranty. Of course, this is only as good as the company that backs them, but Enphase seems to be pretty solid. There's also the issue of longevity of the system itself: what happens if in 10 or 15 years one of them stops working - will they be in a position to provide a drop-in replacement? Having a flat roof means that we can access them pretty easily, as long as the company's still around and replacements are available. As for why we went with this rather than a regular two string inverter, we have various trees shading parts of the roof at different times of the year. The company we used spent quite a bit of time standing on our roof mapping out the surrounding trees, and then modelled the output of the course of a year. The microinverters were a clear winner over the standard inverter approach. I think another thing they do is produce a bit more at the start and end of the day - from memory, it's something to do with the minimum string voltage required for the inverter to turn on in a regular system. Link to comment Share on other sites More sharing options...
Alexphd1 Posted June 26, 2018 Share Posted June 26, 2018 (edited) 5 hours ago, Nickfromwales said: Im on a steep ( vertical ) learning curve with PV so this and another thread running here are extremely informative, keep it going ! After the electricity gets out of the panels not a problem, its getting the juice out of them, optimised and inverted that seems to be the minefield. For a mixed orientation, fragmented arrangement of say 5-6kW, it seems that optimisers and a single external or garage / outbuilding mounted inverter seems to best way to go in terms of reliability, yield and ease of maintenance. Running cables from each panel into the ( accessible ) loft space seems the sensible approach, as then only a failed panel will require access to / roof work. That leaves the problem of making a reliable means of penetrating and subsequent repairing of the multiple transits ( penetrations ) through the airtight layer. What have others done here to get the cables from roof to airtight envelope? Plenty of detail please ! This is our plan.... We would be using micro inverters if we didn't have already a inverter. The panels will be in roof and are having each join between the panels in the attic so we can check individual panels, bypass a failed panel or add in micro inverters in the future without going on the roof. We will be using ufh pipe (12mm) as a sleeve, making up 6mm mc4 male/female cable extensions so not removing the connectors on the panel (this would invalidate the warranty), thread the extensions through the 12mm mlcp, spraying approx 400mm open cell insulation to seal one side of the pipe and using air barrier tape to seal the cable to the mlcp pipe. Edited June 26, 2018 by Alexphd1 1 Link to comment Share on other sites More sharing options...
Ian Posted June 26, 2018 Share Posted June 26, 2018 (edited) 20 hours ago, JSHarris said: It wouldn't be easy to get the cables through a modern breathable roof membrane, and would be a lot of faffing around to try and get the cable entries watertight, or at least arranged so they ran up under an overlap joint and were taped down, as well as the potential problems of having them in a warm (perhaps very hot) roof space, which may not be a lot better than having them under the panels. There's quite a few standard fittings available for getting cables through flat roofs - generally they are of the 'standpipe' type design such as this one: https://www.roofingsuperstore.co.uk/product/roof-nek-flat-roof-small-pipe-cable-entry-point.html or this one: http://klober.co.uk/shop/product/flavent-cable-outlet Edited June 26, 2018 by Ian Link to comment Share on other sites More sharing options...
SteamyTea Posted June 26, 2018 Share Posted June 26, 2018 (edited) 1 hour ago, Nickfromwales said: Im on a steep ( vertical ) learning curve with PV Just Ohm's Law really. Change the amps or the volts and you get different power. The amps or voltage are changed when the internal resistance of the module varies with different light levels and temperatures. Some people may notice that they are getting less power this week that they were in April (did we have any sunny days this year back then). This is to do with sun angles and panel temperature. It is the sun angles that people tend to get hung up on, but usually that is set by the design of where you want to place them, so you have little choice. I did suggest that if you have lots of area and choice, you could have as much PV as you like by switching the arrays as the sun moves across the sky, while still staying within the DNO imposed limits. Surprised no one has picked up on that. You do need a big DC switch though. Or power down the inverter, switch array, power the inverter back up. Edited June 26, 2018 by SteamyTea Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 26, 2018 Share Posted June 26, 2018 51 minutes ago, SteamyTea said: I did suggest that if you have lots of area and choice, you could have as much PV as you like by switching the arrays as the sun moves across the sky, while still staying within the DNO imposed limits. Surprised no one has picked up on that. You do need a big DC switch though. Or power down the inverter, switch array, power the inverter back up. Much as I like the sound of that, its just impractical. If a tracker system could be devised that automated the process, thats another thing, but cost and complexity soon adds up. My thoughts are either a 2 x 50% fragmentation, or 3 x 33% fragmentation across the roof wherever possible for longer, lower, but much more consistent generation. That should, where practicable, be installed with a view to not 'maxing out' at midday and therefore the inverter not shutting down at 253v. Just wondered if dumping into a resistive load would help drop the local voltage if 253v ever gets attained or exceeded? Such fun Link to comment Share on other sites More sharing options...
SteamyTea Posted June 26, 2018 Share Posted June 26, 2018 (edited) Not many location suffer the voltage problem, a few rural ones maybe. Trackers are just a waste if time really. If they were so great, all the solar farms would have them. If you go for a multi-split system, then you need to make sure the inverter can handle the number of strings, or have multiple inverts. You have to remember that an inverter needs a minimum voltage to start working. And it is best to undersize inverters, so you are limited on choice. My idea uses a single inverter and a box of switches. You could dump to a load, but take the day before yesterday, that load would be on for a fair slice of the day, much easier to just disconnect excess generation surely. Edited June 26, 2018 by SteamyTea Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 26, 2018 Share Posted June 26, 2018 (edited) 1 hour ago, SteamyTea said: Not many location suffer the voltage problem, a few rural ones maybe. Trackers are just a waste if time really. If they were so great, all the solar farms would have them. If you go for a multi-split system, then you need to make sure the inverter can handle the number of strings, or have multiple inverts. You have to remember that an inverter needs a minimum voltage to start working. And it is best to undersize inverters, so you are limited on choice. My idea uses a single inverter and a box of switches. You could dump to a load, but take the day before yesterday, that load would be on for a fair slice of the day, much easier to just disconnect excess generation surely. All depends whether or not your excess is exporting free but rotating your meter anticlockwise to boot Edited June 26, 2018 by Nickfromwales exporting not importing "D'oh!" Link to comment Share on other sites More sharing options...
richi Posted June 26, 2018 Share Posted June 26, 2018 58 minutes ago, Nickfromwales said: All depends whether or not your excess is exporting free but rotating your meter anticlockwise to boot ...assuming your meter doesn't have a fraud flag that trips when it runs backwards Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 26, 2018 Share Posted June 26, 2018 1 hour ago, richi said: ...assuming your meter doesn't have a fraud flag that trips when it runs backwards Prisons dont seem that bad these days 1 Link to comment Share on other sites More sharing options...
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