Solar PV vs Grid

[binky]

those Renusol brackets are great, quick and easy to install. doesn't leave much option for cable tying, but you will find the panels have a few small holes in to cable tie the DC strings and stop them flapping in the breeze. Main thing is to try and keep the panel connectors out of the troughs of the roof. Although they theoretically can be immersed 1m deep in a puddle, in reality that doesn't work well and if continually exposed to water around them, creates earth leakage faults that prevent the inverter starting up. To make maintenance easier you could install a rail across the bottom of the roof to walk along - could be done with unistrut which is cheaper than solar rail. Use a bit of black conduit between the panels, and you can get a thing called Dektite for the cable entries

https://static.prod.cmostores.com/u...ext.-cable-7119.jpg?auto=compress&w=800&h=800

Given your rural location, have you considerd a wind turbine for those cold dark draughty winter nights?

 

[coulter]

Thanks Binky, some great tips! Haven’t heard of Dektite before but looks like a great solution for going through the roof.

Like the idea of the walkway rail! I’ve plenty of 41mm unistruct lying here, do you mean just a simple run screwed down to the roof a wee bit below the panels or something more elaborate?

Haven’t considered wind turbines as I know nothing about them but I do get plenty of wind up here! Can you elaborate a wee bit more on that option please?

Many Thanks.

 

[binky]

Thanks Binky, some great tips! Haven’t heard of Dektite before but looks like a great solution for going through the roof.

Like the idea of the walkway rail! I’ve plenty of 41mm unistruct lying here, do you mean just a simple run screwed down to the roof a wee bit below the panels or something more elaborate?

Haven’t considered wind turbines as I know nothing about them but I do get plenty of wind up here! Can you elaborate a wee bit more on that option please?

Many Thanks.

I would put the walk way a few feet below the panels, simply screw it to the roof. You could just walk along the ridgeline along the top of the panels, but as you have spare unistrut, it's a nice thing to install to aid putting the panels on, and should you need any access for any reason in the future. I was thinking of that because you havn't got ladder access along a large part of that roof, and being a reasonable steep pitch, you may well find the roof a 'bit slippy'.

Wind turbines I dont know much about, but work on the basis that say 2kW will work at more like 500w except in strong winds. I've looked into them a few times, but I have very close neigbours as I live in a terrace, so can't have anything of a decent size, or too noisy. Typical sort of output curve below for a 200w unit.

From what I have seen they are no more difficult to install than PV, you can buy them in kit form, only difficult bit is getting the tower up with a lumpy turbine on the end . The big advantage is 24/7 generation, especially on those cold wintery nights when it's blowing a gale and you really need the heating and PV is crap because the days are short and dark. Turbine will also charge the battery of course.

 

[johnb2713]

I installed a 1kW turbine at a model fly club field to power the weather station and the burglar alarm batteries of our shipping container used as a clubhouse. It worked very well except for one thing, noise. It would spin up to speed and then the controller would add load to charge the batteries, it would then slow down until the controller reduced the load, speed up, slow down and cycle went on and on. It was so bad we added a timer to switch it off when members were there flying and back on overnight.

 

[coulter]

Thank you gentlemen, yes I am thinking that maybe a wind turbine is a whole different story and would need a lot more careful analysis before going down that route. I think for now I will crack on the PV panels and see where that leads.

Binky, would you bolt the unistruct right through the roof cladding into a purlin below or just simply use stitcher screws directly into the cladding sheet the same way as the renusol brackets?

Many Thanks.

 

[binky]

Thank you gentlemen, yes I am thinking that maybe a wind turbine is a whole different story and would need a lot more careful analysis before going down that route. I think for now I will crack on the PV panels and see where that leads.

Binky, would you bolt the unistruct right through the roof cladding into a purlin below or just simply use stitcher screws directly into the cladding sheet the same way as the renusol brackets?

Many Thanks.

sticher screws should suffice, as long as you use enough of them , it's all that will be holding the panels on. You could use longer roofing screws if you have wooden beams underneath the roof - I like to insert screws on the 'peaks' and not in the valleys of metal roofs, even if that's how they tell you to do it in roofing instructions. My thinking is that relying on a rubber washer to keep the roof from leaking for more than 10 years is 'optimistic' so why make holes in the valleys where the water runs.

 

[Geoff1946]

My thinking is that relying on a rubber washer to keep the roof from leaking for more than 10 years is 'optimistic' so why make holes in the valleys where the water runs.

I thought that when I re-roofed my garage, but on reflexion the valleys are supported so don't flex under load, particularly being walked on. Conversely the peaks can flex, and will release the pressure on the sealing washer if the screw is into timber below. That's why the joining peaks should just be attached together with stitching screws.

 

[binky]

I thought that when I re-roofed my garage, but on reflexion the valleys are supported so don't flex under load, particularly being walked on. Conversely the peaks can flex, and will release the pressure on the sealing washer if the screw is into timber below. That's why the joining peaks should just be attached together with stitching screws.

I replaced my garage roof, and put all screws through the 'tops' it does tend to flatten the roof profile slightly so it 'spreads' a little, but I still prefer not having water running directly over the washers. I regularly walk over my roof to clean my solar panels, and not had any leaks so far.

 

[coulter]

sticher screws should suffice, as long as you use enough of them , it's all that will be holding the panels on. You could use longer roofing screws if you have wooden beams underneath the roof - I like to insert screws on the 'peaks' and not in the valleys of metal roofs, even if that's how they tell you to do it in roofing instructions. My thinking is that relying on a rubber washer to keep the roof from leaking for more than 10 years is 'optimistic' so why make holes in the valleys where the water runs.

Thanks Binky, yes I think I’d prefer to fix on top of the ridges too. I think I would need to put a rubber washer between the unistruct and roof cladding though just to be sure! I have steel purlins under the cladding.

 

[coulter]

Hi again folks, Just about to place my order for 24 x Canadian Solar 360 watt panels and a 6.0kw Solis inverter. As previously discussed, I have no plans to install batteries in the foreseeable future but I'm having some second thoughts on this and wondering if I should install a hybrid invertor just in case!

The 6kw hybrid inverter is £430 more expensive than standard inverter, what would you guys advise? Are there any drawbacks in installing a hybrid inverter without fitting a battery pack?

Many Thanks.

 

[coulter]

Also, if I were to install a 12kw output heat pump in the future would there be any merit in having some battery storage then?
My own thoughts are that the heat pump would probably use up to 50kwh per day in winter while the PV would only generate maybe 3kwh, so the befit of having say a 5kwh battery would be negligible.
Has anyone else got any practical experience with this type of setup?
Thank you.

 

[devore]

Hi coulter - I'm in a similar situation to you with considering a battery but will probably not get one to start off with. I think I will go with a hybrid inverter just so I have the option later on, or if I come across a good offer on a battery. I reckon the Spring to late Summer part of the year a battery would come into it's own as there could be alot of excess there to store for evening use.

Do you mind me asking what your plan is for placement of equipment? Are you using exisiting ducting from the shed to the house, and are you planning on housing the inverter in the shed? I am planning a similar enough setup myself and thats how I stumbled on this thread.

Edit: Are you using Midsummer or a supplier like that for the panels? Am shopping around at the moment for prices so am very confused at the moment!

 

[coulter]

Hi Devore,
Thank you for your post. I now have my system on order and waiting on delivery. I finally opted for the hybrid inverter just to give me the flexibility in the future. I am not planning on fitting a battery initially until I see how the performance works out and also what I may receive in the form of a feed in tariff from my supplier.

My garage is over thirty meters away from the house and has a 6sq mm swa supply cable. I am planning (rightly or wrongly) on fitting everything at the garage, the panels on the east/west roof and the inverter beside the distribution board in the garage. My thoughts are that the existing 6sq mm supply is adequate to carry the maximum 25amps that the system can generate back to the house and grid.

I am in the electrical trade and have ordered the complete system through a local electrical wholesaler. If you have an electrical wholesaler in your locality it might be worth talking to them too, most are usually interested in additional business!

 

[Chrisbee]

What surprised me but is very obvious once you see it, is that having batteries fills in all the dips in power as clouds move across the panels. The dip is significant.


Without batteries, if your household load is being supplied from the panels and the sun goes in a bit, supply often dips below demand and the rest has to be supplied from the grid.

With batteries, they top up while supply exceeds demand and are there to fill in the gaps. Mine go up and down all day, but with a general upward trend until they're full. Then they often supply our evening demand, including cooking, before usually being flat by around bedtime.

 

[johnb2713]

What surprised me but is very obvious once you see it, is that having batteries fills in all the dips in power as clouds move across the panels. The dip is significant.


Without batteries, if your household load is being supplied from the panels and the sun goes in a bit, supply often dips below demand and the rest has to be supplied from the grid.

With batteries, they top up while supply exceeds demand and are there to fill in the gaps. Mine go up and down all day, but with a general upward trend until they're full. Then they often supply our evening demand, including cooking, before usually being flat by around bedtime.

We run pretty much the same except we charge the batteries during off peak 00:30 to 04:30 and then of course we run 100% on battery until the solar PV wakes up, normally the batteries are down to 50% by the time they start to charge from solar. Most days we hit fully charged by late afternoon, in the height the summer by mid morning on many days. From then on we run on the battery once solar PV stops and recharge again at night.
Our battery is 7kWh I'm going to add a 14kWh AC coupled battery a) to increase capacity and b) to add another 5kW of inverter to the system.

 

[coulter]

Thanks as ever folks for your valuable contributions. I have now taken delivery of the PV system and hope to start the installation on Monday.

Just a couple of quick questions if I may:
I will be using two strings of 12 panels each, should I use two separate DC isolators or run both strings through the one 4 pole isolator that has been supplied with the system?
Should I run the DC cabling inside galvanised steel conduit on the inside of the garage roof or is PVC conduit acceptable or advisable?

Thank you.

 

[binky]

Thanks as ever folks for your valuable contributions. I have now taken delivery of the PV system and hope to start the installation on Monday.

Just a couple of quick questions if I may:
I will be using two strings of 12 panels each, should I use two separate DC isolators or run both strings through the one 4 pole isolator that has been supplied with the system?
Should I run the DC cabling inside galvanised steel conduit on the inside of the garage roof or is PVC conduit acceptable or advisable?

Thank you.

check rating of the 4 pole isolator, bit that should be fine of supplied with the gear.

PVC conduit is perfectly acceptable, and far easier to work with.

 

[coulter]

Thank you Binky.