Navitron Renewable Energy and Sustainability Forum

SOLAR PHOTOVOLTAIC => Solar Photovoltaic Systems => Topic started by: charlesd on November 19, 2018, 02:24:38 PM



Title: Ground Based Solar PV advice
Post by: charlesd on November 19, 2018, 02:24:38 PM
Hi all.
I am looking into the possibility of having some solar PV. I have no real idea of what I'm looking for other than the ultimate goal is to help mitigate my current electricity costs. Having done a bit of research I have come to the conclusion (maybe incorrectly) that my roof is unlikely to be suitable (too steep,dormer and velux's and faces east/west) but I own the field behind my house and would like to explore the feasibility of putting pv panels there.
I have an idea in my mind of about 15 panels in a single row. There is not an ideal cabling route from the field to the incoming electric supply (which is where I assume I would need to get cables too) but I've done some basic measurements  and with some digging and then routing through the garage and the house to the current meter location is about 80m. I would like to do as much of the basic work myself providing that is within the rules so I would want to do digging for cabling build the frame to mount the panels on. If I'm able I'd be happy laying the cables and mounting panels etc and ideally just have an installer connect the bits together to make it all work. So the as a first few questions, Is my idea practical? How much of the work is OK to do yourself? would installers be happy to work with someone who wants to do a lot of the work themselves?
Thanks
Charles


Title: Re: Ground Based Solar PV advice
Post by: rogeriko on November 19, 2018, 09:12:25 PM
If you only want to lower your electric usage during the day you dont need an installer. You just need a competent electrician to sign off the new circuit you will have for the inverter and cabling and to inform the DNO. You will need planning for anything over 9 sq meters of panels.


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 20, 2018, 11:47:55 AM
Hi,
Thanks for the advice about planning, I've chatted with my local planning officer this morning and know what I need to do there but before I pay (460) for the planning application I need to get an idea of the feasibility/costs/scope of the work.
I'm based in the PE 12 area near Holbeach if anyone can recommend a friendly installer who could advise /quote ?

Thanks
Charles


Title: Re: Ground Based Solar PV advice
Post by: billi on November 20, 2018, 02:31:59 PM
Hi ,  i would go for Rogers idea and   try to source the gear myself , and a ground mount frame is easy to built safe and cheap

I would say one can find a 4 kW PV Panels and Inverter for 2000-2500 GBP  today

Billi


Title: Re: Ground Based Solar PV advice
Post by: nowty on November 20, 2018, 03:12:14 PM
Charlesd - if I had a field around the back I would not limit myself to a 4kw install, especially if your going to the trouble of laying 80m of cable.

Whats your annual electricity consumption ?

Do you have single or three phase supply ?

How is your house heated ?

I was round someones house picking up some gear I bought on fleebay the other week and we were chatting about PV.
I assumed they had a standard 4kW install, then they told me to look out of their back window.
They had a field at the back, had put a 3 phase supply in and installed 50kW of panels !  :hysteria


Title: Re: Ground Based Solar PV advice
Post by: biff on November 20, 2018, 04:44:52 PM
Hello Charlesd and welcome to the forum,
                                     Thank you for opening the query on PV . We don,t get near enough queries on PV as of late. You are in good hands and the lads are very experienced and of course helpful.
Roger is actually a busy installer whose help here on the forum has been invaluable. Billi, whose experience is in electronics and off Grid applications, is one of our original moderators. Nowtry is a star in his own right , in fact I think the guy is borderline genius if not a genius.   And we have many many more famous members whose expertise is legendary.
   These guys have done their best to keep me right and I know they will do their best for you,
                               Good luck,   Biff


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 21, 2018, 09:32:08 AM
Thanks for the welcome and continuing replies.
To add a little more detail my current energy use if I'm reading it correctly is around 7000kwr per year costing me between 2.50 and 3 on the average day. Both my wife and I work from home and our usage is quite high during the day because of that. We heat or primarily with a wood stove and oil central heating and have no mains gas. I want to be able to claim fit if possible hence my thoughts that I need an installer? I'm happy to source parts and build frame etc digging the cablec trench is not a concern i have some other jobs the need a digger including replacing some water pipes in the field so would do that at the same time. Budget would probably restrict me to somewhere between 10 and 20 panels also the conversation I had with the planning officer suggested that something considered domestic will be easier to get through planning.
If I go with sourcing the equipment myself what are the basics required? Also will I need any sort of building near the panels or can all the other bits be at the house end of the cable?
Cheers Charles


Title: Re: Ground Based Solar PV advice
Post by: nowty on November 21, 2018, 10:23:50 AM
At 7,000 kWh per year, your electricity usage is about the same as mine 7 years ago before all this renewable business. I brought that down to under 1000 kWhs, although you wont get it that low without a lot of PV and battery storage. But its just an illustration as to what can be done.

With PV in your location in optimal conditions (south facing and no shading), you will generate circa 1,000 kWh per each kW of panels you install, so if you install 5kW of panels (20 standard panels) you would expect to generate 5,000 kWh per year.

Without batteries you will typically use half and export half, so expect a third off your leccy bill. With batteries over half off your bill is possible, but the economics of doing so are questionable.

If you have a hot water tank heated via an immersion heater, a simple Immersun type diverter will give you free hot water (Mar to Sep) from the other half which would have been exported.

If you want FITs you need an installer but cabling and ground mount frames can be done by yourself. Its possible to buy all the equipment yourself too but you are unlikely to find an installer willing to use the equipment so you need to decide whether to go the FIT route or DIY (non FIT) route. It used to be a no brainer with the historic high FIT payments but its now not so clear cut.

If you dont get the system commissioned by next March you wont get any FITs at all (might even be earlier if there is a rush).

All equipment (apart from panels) can be back at the house, as long as the DC voltage from the panels is at the high end you wont lose much efficiency.


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 21, 2018, 01:40:02 PM
Ok so it sounds like I have a diy option which might mean cheaper install and equipment costs but no fit. Or an installer and higher costs but would get fit if it's all in and done march (end of?). The march date looks tight given the planning permission requirement from memory it's 12weeks.
Is there an ballpark figure for what the fit element of say a 4kwh set up of panels might be and difference in cost between an installer and diy? Basically if there's not much in it I think I'd rather spend the upfront on more panels and go diy but if the fit element is significant then it may be worth getting on with the planning application asap.
Cheers Charles


Title: Re: Ground Based Solar PV advice
Post by: nowty on November 21, 2018, 02:13:29 PM
FIT Rates
https://www.ofgem.gov.uk/system/files/docs/2018/07/fit_generation_and_export_payment_rate_table_01_july_-_31_march_2019.pdf

Basically assuming you can get an EPC (Energy Performance Certificate) for "D" or better you get roughly 6p per kWh you generate. This includes the export element which is simply deemed export, i.e its not metered so you get it anyway on half your generation even if you export nothing. You get this for 20 years, is tax free and indexed linked with RPI.

If your property cannot make a "D" rating then you get less than 3p per kWh you generate which comprises almost all of the export element. As you have got oil heating, you may have difficulty making a "D" rating. Others will have more info on the likeliness of this.

So if you did a 5kW system that would give you 300 per year on top of your energy bill savings. Or 140 if your property cannot meet the EPC "D" rating.



Title: Re: Ground Based Solar PV advice
Post by: rogeriko on November 21, 2018, 06:59:49 PM
Personally I would DIY the install and use the money saved to buy a battery system. As Billi said you can easily find 4 or 5 Kw of panels and an inverter for 2500. I have a 5kw grid tie inverter on Ebay at the moment for 250 and nobody is buying it, there are tons of panels for under 100 pounds each.


Title: Re: Ground Based Solar PV advice
Post by: offthegridandy on November 21, 2018, 08:29:56 PM
Agreed, Roger.


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 21, 2018, 08:58:45 PM
So if I'm understanding correctly the consensus seems to be that the best bet would be to just buy panels and an inverter and to get my friendly sparky to connect it all up.
I understand this way I don't get the fit but I assume I still get something for electricity I generate but don't use? How does this work do I have another meter or does the smart meter I have know the electric is going out instead of coming in?
Battery storage I'm really not sure about yet but am I correct in assuming that if I leave them out initially I can retro fit reasonably easily at a later date?
And finally for now it looks like most panels ive googled are about 1mx1.6m approx is this fairly standard? I have to show the area I'm I tending to use for the planning app but obviously won't decide or buy any panels until I actually have it.
Once again thanks for your being patient with what are probably stupid questions but the more I look into this the less I seem to understand.
Cheers Charles


Title: Re: Ground Based Solar PV advice
Post by: rogeriko on November 21, 2018, 09:13:47 PM
The fit is now so small its not worth bothering about. You will have free electric and hot water during the day time for about 6/7 months of the year. And later when you install batteries they will cover your electric needs at night as well. Put as many panels as you can, its okay to connect 6kw of panels to a 3.8kw inverter.


Title: Re: Ground Based Solar PV advice
Post by: sam_cat on November 22, 2018, 08:03:23 AM
So if I'm understanding correctly the consensus seems to be that the best bet would be to just buy panels and an inverter and to get my friendly sparky to connect it all up.

Yes, the FIT is so small now its hardly worth bothering with. DIY install + sparky will allow use of second hand kit and should save you a pretty penny. Plus you are MUCH more familiar with how it was installed and setup.


I understand this way I don't get the fit but I assume I still get something for electricity I generate but don't use? How does this work do I have another meter or does the smart meter I have know the electric is going out instead of coming in?

Nope, any excess that goes back to the grid is provided gratis. Look into a solarimmersion controller.. Any excess is dumped into your hot water tank


Battery storage I'm really not sure about yet but am I correct in assuming that if I leave them out initially I can retro fit reasonably easily at a later date?

I have been doing the sums every 6-12 months and it still doesnt make financial sense, but yes, it can be retrofitted.

And finally for now it looks like most panels ive googled are about 1mx1.6m approx is this fairly standard? I have to show the area I'm I tending to use for the planning app but obviously won't decide or buy any panels until I actually have it.

Yup, pretty standard size (give or take a few mm)


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 22, 2018, 10:34:24 AM
With the above advice (thanks) and some googling a decision has been made.
I'm going to submit a planning app for 20 panels in the field. With a bit of luck I should be able to complete that this weekend and get it submitted based on the council's expected timescales I should know somewhere from end of Jan to mid Feb.
Whilst that is going on I can research the equipment (for research read more questions  :) ) that I'm going to need.
One immediate question the electrical set up in my property is slightly odd in that the meter and supply arrive at one side of the house and the consumer unit is the other. I have an isolater near the meter and then effectively really long "meter tails" to the consumer unit which run through the loft diagonally from the meter to the consumer unit. Does the PV stuff (inverter etc) need to be nearer the meter or consumer unit as in my case the separation in probably 20-25m in terms of cabling?
Cheers  Charles


Title: Re: Ground Based Solar PV advice
Post by: TT on November 22, 2018, 12:12:14 PM
It needs to be at the consumer unit end.
The end closest to the main fuse is just local isolation-fusing required due to the tails longer than2.5 m or 3 metres in length.



Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 22, 2018, 02:28:47 PM
It needs to be at the consumer unit end.
The end closest to the main fuse is just local isolation-fusing required due to the tails longer than 2.5 m or 3 metres in length.

Thanks that's what I was hoping and should make the cabling a bit easier.

Routing the cable as intend it will go through the garage before entering the house so my next question is the garage wall a good location for the Inverter and whatever goes with it or should it be outside like in some sort of meter type cupboard? Or does it not matter where they go?




Title: Re: Ground Based Solar PV advice
Post by: JohnS on November 22, 2018, 02:47:28 PM

It needs to be at the consumer unit end.
The end closest to the main fuse is just local isolation-fusing required due to the tails longer than 2.5 m or 3 metres in length.


Is there a reason for that?

If it is more convenient, I would have thought that you could put a Henley block next to the isolator and feed the inverter into it via a mini consumer unit, eg a 'garage' unit.  Using Henley blocks is a well recognised way to install solar PV and it has many advantages over feeding into the consumer unit.  My install is doe via a Henley block as there was no spare mcb in the consumer unit.

Warning: I am not a qualified electrician.


Title: Re: Ground Based Solar PV advice
Post by: Pat_ on November 22, 2018, 07:21:16 PM

It needs to be at the consumer unit end.
The end closest to the main fuse is just local isolation-fusing required due to the tails longer than 2.5 m or 3 metres in length.


Is there a reason for that?

If it is more convenient, I would have thought that you could put a Henley block next to the isolator and feed the inverter into it via a mini consumer unit, eg a 'garage' unit.  Using Henley blocks is a well recognised way to install solar PV and it has many advantages over feeding into the consumer unit.  My install is doe via a Henley block as there was no spare mcb in the consumer unit.

Warning: I am not a qualified electrician.

Plus one. I fitted a Henley block. It solves many issues related to RCDs, and it allows proper import/export monitoring.


Title: Re: Ground Based Solar PV advice
Post by: rogeriko on November 22, 2018, 11:17:32 PM
If you want to use all your generated power on site and not export any then the inverter has to be in the garage and connected to the consumer unit where your Immersun will go, for hot water, and your Zappi, to charge your electric car and many other things that havnt even been invented yet.


Title: Re: Ground Based Solar PV advice
Post by: linesrg on November 23, 2018, 05:32:39 AM
Charles,

As rogeriko says if you are planning on using diversion devices then go with sticking the inverter near your consumer unit. My incoming mains is 45mtrs away from the consumer unit in my kitchen.

I had to run 40mtrs of Cat5 cable to connect the Immersun 1070 wireless monitor to a point where the Immersun unit in the Utility Room could 'see' it.

Installing the likes of a Powerwall or Powervault at my property would be 'difficult' to say the least and I'm not sure the technology yet exists to facilitate a smart meter being fully functional.

I have considered having the electric meter moved from the far side of the steading to the near side and this may yet be required to get a functional smart meter and I'm not at all sure who would have to pay for that.

Inverter installation instructions would advise that the inverters should be installed in an open location so you wouldn't want to be boxing them in, my SMA's can generate quite a bit of heat when working.

Regards

Richard


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 23, 2018, 07:50:00 AM

I have considered having the electric meter moved from the far side of the steading to the near side and this may yet be required to get a functional smart meter and I'm not at all sure who would have to pay for that.
Hi Richard.
My current meter and consumer unit locations came about as a result of some major house renovations in 2016 and involved quite a bit of discussion and a number of site visits from western power. The result of which was there was no way I could have the meter located any where other than where the supply cable terminated. In addition I was not permitted to have the supply cable running through my house or around the outside.
The guy from western power was actually really helpful and said that the set up in most houses wouldn't be approved by them now if asked but as most people don't bother to ask they stay as they are.
In my circumstance as I was removing the roof and the pole the supply came ln to I had to follow there rules and pay the bill. So I suspect you may have the same issues if you wanted to relocate and the costs can be really high. Although I eventually negotiated a sensible amount I started of with a quote of around 10k to move a pole 10 yards and relocate the meter and this was because they condemned the old pole and meter location!!
Cheers Charles


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 24, 2018, 12:54:29 PM
Quick question while I'm filling out planning app.
Assuming I'm making my frame fixed what's the best angle for the panels to sit at and am I correct the due south facing is best?
Cheers Charles


Title: Re: Ground Based Solar PV advice
Post by: rogeriko on November 24, 2018, 01:02:41 PM
Due south is best but try to devise a way to tilt the panels up and down its not difficult to hinge the bottom and then make the tops adjustable. Otherwise 30 degrees is the standard. Go to PVGIS to work out the best angles for the different seasons.    http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php#


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 24, 2018, 02:43:47 PM
Due south is best but try to devise a way to tilt the panels up and down its not difficult to hinge the bottom and then make the tops adjustable. Otherwise 30 degrees is the standard. Go to PVGIS to work out the best angles for the different seasons.    http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php#
Thanks Roger.
I'm looking at making the frame adjustable if i can but for the planning app 30 degrees should suffice. I doubt there going to come out and measure the angle after there up after all.


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 26, 2018, 05:28:59 PM
OK planning app is in now I need to build a shopping list.
I'm intending to make mounting frames myself I'm an OK welder so its just getting a rough drawing together and ordering steel.
Panels and inverters I'm not sure about at all. There seems too much choice for a novice so is there any general advice. What separates a 100 panel from a 400 one and are any differences worth it? Are there any good suppliers/brands that can be recommended? What I've seen regarding inverters so far seems to suggest you get what you pay for and research has led me to a few brands (SMA/Fronius/solar edge), should I be looking at others ?
Cheers Charles


Title: Re: Ground Based Solar PV advice
Post by: nowty on November 26, 2018, 06:59:38 PM
Panels - Usually the 400 ones are high efficiency, like the LG or Panasonic but that is only of use if you have a finite small roof area and need as much wattage as possible for a fixed area.

As you have a field, as long as you have got permission for a reasonable amount of area, then cheap standard 250w panels will do. It then comes down to how attractive you want the panels, i.e. all black ones cost a little more than the cheapest blueish polycrystalline ones. As long as they are MCS approved, there is not much between them in terms of quality.

Examples,

Cheap standard - 95 for 260w

Mid price all black - 150 for 300w (all black)

Expensive high efficiency - 346 for 340w

As you can see the cost per kW can vary considerably but if you have 5kW of cheap panels installed you still generate the same as 5kW of expensive panels.


Inverters - Traditionally it has been better to stick to the better brands like SMA, ABB, etc, but the cheaper Chinese stuff has improved so you could consider some of the stuff from Growatt or Sofar. I would consider a second hand inverter and buy two so you have a spare. In fact my SMA inverters are all second hand with a spare one in the shed for good measure and significantly cheaper than buying new and paying extra for the extended warranty.


Title: Re: Ground Based Solar PV advice
Post by: stannn on November 26, 2018, 07:15:48 PM
Nowty, although you are a star I have removed your links to PV on eBay. You cannot expect Navitron to approve of advertising rivals. Right, play on.
Stan


Title: Re: Ground Based Solar PV advice
Post by: offthegridandy on November 26, 2018, 08:42:25 PM
Charlesd. To avoid rust and interaction between steel and the panels frames aluminium, why not use aluminium profile  for the mounting frames as well. I have 4.5Kw of panels, all ground mounted on treated timber frame work, metposted into  the ground with aluminium sub frames for the panels to drop into.  Been up for years now and still  going well.

There is a thread here somewhere if your interested.

Andy


Title: Re: Ground Based Solar PV advice
Post by: nowty on November 26, 2018, 09:57:23 PM
Second that, my garden ground mounts (ahem ladder stores of course :onpatrol) are made of tantalised fence posts screwed together with galvanised coach screws and anchored to the ground with galvanised metaposts.

Use a cheap mitre saw to get easy 30, 45 and 60 degree cuts to give the required angles.

Then simply screw on the aluminium mounting rails for the panels.

And make a fancy border around the panels with deckboards if required.


Title: Re: Ground Based Solar PV advice
Post by: eabadger on November 27, 2018, 07:16:40 AM
made ours out of scaff poles and joints, the whole thing tilts for winter/summer sun height

steve.


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 27, 2018, 08:41:49 AM
Thanks for the ideas guys. I have looked through some older threads and the scaffold poles frame looked like a great idea. Unfortunately I don't have any spare poles so whatever I get would have to be bought. 50mm box is not really any dearer than scaffold poles if your buying and square is easier to weld. I'm not keen on wood I'm having enough issues with tanalised fenceposts needing replacing in under 5 years in some cases and I'm worried about it warping over time.
I might do a combination a steel subframe with wooden rails to attach the panels too would stop the interaction between the steel and aluminium. I'm going to mock up a model before I start so I can finalise the design. I'll post a picture when I've done it if I can work out how.
Cheers Charles


Title: Re: Ground Based Solar PV advice
Post by: eabadger on November 27, 2018, 11:07:00 AM
hi,
i could have, but didnt weld, see attached joint system, used unistrut for rails, made attachment a doddle.

steve


Title: Re: Ground Based Solar PV advice
Post by: todthedog on November 27, 2018, 03:45:09 PM
Made mine with box, bolted not welded. Living in France at the time scaffold poles not an option.
 I would have used them if available. I made sure the bottom was clear of the ground to allow easy strimming.

A copy of this design
https://www.builditsolar.com/Projects/PV/DougEnphase/DougEnphase.htm

With perfect hindsite maybe I would have allowed for changing between summer and winter settings.

Despite the brilliant engineering of Clockmans trackers I am unconvinced that the increased production is worth the effort, complication and expense. I think that if the money is available I would stick to simplicity and more panels.


Title: Re: Ground Based Solar PV advice
Post by: eabadger on November 27, 2018, 04:40:03 PM
my thoughts exactly TD.
but i had poles to hand so.....
the tilting sure makes a big difference, the original fixed array is outputting far less currently.

steve


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 27, 2018, 04:46:32 PM

A copy of this design
https://www.builditsolar.com/Projects/PV/DougEnphase/DougEnphase.htm

This was the design I saw first and thought looked simplest I was just going to swap the poles for 50mm box. Then I thought it should be simple enough to hinge the front support and make the rear support in 2 sections that slide past each other then just bolt them together at certain points to allow adjustment of the angle. Nothing complicated just simply loosen the  bolts slide it up or down to adjust and re tighten. The plan is to make the array in 3 sections each with 6 panels on each so I don't have to move the whole lot in one go. The additional steel parts and time to make it adjustable will probably be negligible in the scheme of things, and if I don't think it makes a difference I'll just leave it set in one place.

On a completely different note I'm trying to work out roughly the size of cable I would need. Most of the cable calculators I've tried online seem more suited to 240v ac stuff and I'm trying to estimate what I will need for approx 5kwh of panels running around 100m to the inverter. I'll ultimately check it all with my sparky but I'm just getting ballpark shopping list ready.

Cheers Charles


Title: Re: Ground Based Solar PV advice
Post by: smegal on November 27, 2018, 05:11:40 PM

A copy of this design
https://www.builditsolar.com/Projects/PV/DougEnphase/DougEnphase.htm

This was the design I saw first and thought looked simplest I was just going to swap the poles for 50mm box. Then I thought it should be simple enough to hinge the front support and make the rear support in 2 sections that slide past each other then just bolt them together at certain points to allow adjustment of the angle. Nothing complicated just simply loosen the  bolts slide it up or down to adjust and re tighten. The plan is to make the array in 3 sections each with 6 panels on each so I don't have to move the whole lot in one go. The additional steel parts and time to make it adjustable will probably be negligible in the scheme of things, and if I don't think it makes a difference I'll just leave it set in one place.

On a completely different note I'm trying to work out roughly the size of cable I would need. Most of the cable calculators I've tried online seem more suited to 240v ac stuff and I'm trying to estimate what I will need for approx 5kwh of panels running around 100m to the inverter. I'll ultimately check it all with my sparky but I'm just getting ballpark shopping list ready.

Cheers Charles

Try this:

http://www.solar-wind.co.uk/cable-sizing-DC-cables.html


Title: Re: Ground Based Solar PV advice
Post by: TT on November 27, 2018, 06:48:46 PM
Why not put the inverter in a small kiosk at the end of the panels and then run 230vac back to the house.
Keeps the dc cables and losses low.
Then a swa back to the house, along with a cat 5 or 2


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 27, 2018, 07:44:20 PM
Quote

Try this:

http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

Thanks

I'm assuming 40v per panel so 18x40 is 720v
A 5kw system so 5000/720 about 7amps
That gives me 4mm cable over 100m with 1% loss that seems ok to me assuming I'm putting ok numbers in.
I would probably use 6mm to allow for a bit of future expansion.


Title: Re: Ground Based Solar PV advice
Post by: marshman on November 27, 2018, 08:07:47 PM
Quote

Try this:

http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

Thanks

I'm assuming 40v per panel so 18x40 is 720v
A 5kw system so 5000/720 about 7amps
That gives me 4mm cable over 100m with 1% loss that seems ok to me assuming I'm putting ok numbers in.
I would probably use 6mm to allow for a bit of future expansion.

You might want to consider splitting into 2 strings of 9 panels. The reason is that 720V is quite high and may well be above the maximum input voltage of an inverter. 360V is better and should give you more choice of inverter. So you need to redo that calculations based on 14 amps.

Personally I would prefer TT's suggestion of a small cabinet next to or underneath the PV panel mount and running an SWA AC cable back to the consumer unit. A lot of inverters have a decent IP rating.

Roger


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 28, 2018, 07:46:58 AM
If I mount the inverter near to the panels. Does it need any a.c. power of its own as well or will it just work from the power from the panels? Also most inverters seem to need access to Wi-Fi and there's no Wi-Fi in the panels location would I also need to resolve this somehow?


Title: Re: Ground Based Solar PV advice
Post by: JohnS on November 28, 2018, 08:03:48 AM
The inverter will have AC power.  It comes from the same cables that it feeds the power out to the consumer unit/henley block and thence the house and the grid.   ;)  ;D

You don't need a separate cable.

As regards wifi, it depends on how obsessive about measurement you are.  I get by with a cheap energy monitor clamped on a cable into the henley block.  It displays real time output and daily output.  Plus weekly meter readings.


Title: Re: Ground Based Solar PV advice
Post by: TT on November 28, 2018, 08:04:50 AM
The inverter doesn't need a separate supply to work.
Cable from solar panel to inverter
Inverter to consumer unit.

A cat 5 cable may resolve the Wi-fi issue if the inverter has a Ethernet connection.

I have no Wi-fi connection or cat 5 cable  just simply read the meter every 3 months, I'm not interested in data, spreadsheets etc that's just me.


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 28, 2018, 08:11:52 AM
The inverter will have AC power.  It comes from the same cables that it feeds the power out to the consumer unit/henley block and thence the house and the grid.   ;)  ;D

You don't need a separate cable.

As regards wifi, it depends on how obsessive about measurement you are.  I get by with a cheap energy monitor clamped on a cable into the henley block.  It displays real time output and daily output.  Plus weekly meter readings.
Thanks John & TT
Seems each time I think I understand something it gets a little more complicated :)
But I think it now seems the most sensible idea is locate the inverter near the panels. Them as 2 strings of 9 rather than one of 18 to lower input voltage and probably include a data cable alongside the a.c. cable for monitoring the inverter should I wish too.


Title: Re: Ground Based Solar PV advice
Post by: eabadger on November 28, 2018, 02:58:34 PM
we get our data back by Ethernet over power units about 120m, the house end connects wirelessly to router to remove risk of static damage due to storms.

steve



Title: Re: Ground Based Solar PV advice
Post by: nowty on November 28, 2018, 05:01:25 PM

But I think it now seems the most sensible idea is locate the inverter near the panels. Them as 2 strings of 9 rather than one of 18 to lower input voltage and probably include a data cable alongside the a.c. cable for monitoring the inverter should I wish too.


We have had this DC verses AC over long cable runs debate before. I believe the consensuses was to run the DC over the long runs.

I think the main reasons were,

1) You can run DC at a much higher voltage than your mains AC voltage so you can achieve higher efficiency and / or use smaller cables. You could get away with 4mm or 6mm two core cable.

2) You can live with high DC voltage drops as the inverter has a large operating input voltage range and will just adjust its MPPT and still give out a stable 230v mains output. But if you run long AC cables you either need enormous cables to keep the voltage drop down or you risk the inverter tripping out by its AC output going over voltage whenever you get high solar outputs. Your going to need at least 10mm and need a 3 core cable.




Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 28, 2018, 05:11:16 PM

But I think it now seems the most sensible idea is locate the inverter near the panels. Them as 2 strings of 9 rather than one of 18 to lower input voltage and probably include a data cable alongside the a.c. cable for monitoring the inverter should I wish too.


We have had this DC verses AC over long cable runs debate before. I believe the consensuses was to run the DC over the long runs.

I think the main reasons were,

1) You can run DC at a much higher voltage than your mains AC voltage so you can achieve higher efficiency and / or use smaller cables. You could get away with 4mm or 6mm two core cable.

2) You can live with high DC voltage drops as the inverter has a large operating input voltage range and will just adjust its MPPT and still give out a stable 230v mains output. But if you run long AC cables you either need enormous cables to keep the voltage drop down or you risk the inverter tripping out by its AC output going over voltage whenever you get high solar outputs. Your going to need at least 10mm and need a 3 core cable.



I have to confess now to being a bit confused.
I understand that a high dc voltage will mean smaller cables and less loss but it was suggested that a typical inverter would not work with those high voltages.
I guess in simple terms can I string 18 average panels together and link those to an average with about 100m of cable or am I looking at something more complicated?


Title: Re: Ground Based Solar PV advice
Post by: nowty on November 28, 2018, 05:33:19 PM

I have to confess now to being a bit confused.
I understand that a high dc voltage will mean smaller cables and less loss but it was suggested that a typical inverter would not work with those high voltages.
I guess in simple terms can I string 18 average panels together and link those to an average with about 100m of cable or am I looking at something more complicated?



Most inverters will only go up to around 600v although an SMA 4000TL (version 21) will go up to 750v so you could just about get away with a single string.

You can still have two strings of 9 @ 360v and connect them together in parallel so you only need a single two core cable back to the house with the inverter. You can get a pair of (MC4 parallel branch connectors) to do this.

The main problem with a long AC cable run is not inefficiency, its the AC voltage drop where the inverter will have to increase its voltage output to compensate for the long cable run and risk going over voltage.

Example, my house has an incoming mains voltage of typically 250v. For every 1kW I export, that voltage as measured at the meter tails increases by circa 1V, so at max 3.6kW export the voltage is typically 254v. But if I also had 100m of 6mm cable between the meter tails and the inverter, I would have another 8v at the inverter output so that would be 262v which would make it trip out.




Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 28, 2018, 08:15:03 PM
Thanks nowty
I think I'm slowly getting there. It does look like I would need a bigger cable for my 14amp 360v set up or accept a slightly higher loss a 16mm2 cable for a 1% loss or  6mm cable for a 3% loss.
The bit I'm not sure about is what is an acceptable percentage loss because 100m of 6mm swa is a lot cheaper than the 16mm2.
But I would feel much better with the inverter in the garage than in the field. In my experience most things break when it's cold dark and raining  :)


Title: Re: Ground Based Solar PV advice
Post by: marshman on November 28, 2018, 08:28:45 PM
In my experience most things break when it's cold dark and raining  :)

Ah, but that is the great thing about PV, it doesn't work when it is dark, so if it is dark you won't know if it is broken or not  ;D

Nowty does have a very good point about the inverter tripping out because the voltage gets too high. Something I had forgotten about, but it is a problem I was plagued with for several years until UK Power Networks eventually changed the voltage tap on the local transformer. But our grid supply never fell below 240V when fully loaded with no PV feeding. On a sunny day with no load, and anything more than about 2.4kW pf PV, it would  regularly exceed 260V in the house and higher at the inverter 25m away - result inverter disconnects! So maybe D.C. to the house would be a better option.

Roger


Title: Re: Ground Based Solar PV advice
Post by: biff on November 28, 2018, 09:59:23 PM
 Keen observation Nowty, :crossed
                                   Biff


Title: Re: Ground Based Solar PV advice
Post by: snyggapa on November 29, 2018, 07:29:37 AM
If I were installing in a field and assuming no obstructions to cause shade, I would be tempted to go either 2 or 3 strings, and not orient them all the same direction - so have some on one string facing WSW, some facing ESE and some due south - in order to maximise the duration during the day of usable generation rather than the total amount. Or a SW/SE split on 2 strings

Once battery storage comes in, you may favour want max generation if you can store the excess, but a big south facing setup will generate a lot during the middle of the day which you may not be able to use - so splitting to orient some towards the morning sun and some towards the evening sun may increase the amount of usable (to you) power generated whilst both will still provide a good solid rump during the day.


Title: Re: Ground Based Solar PV advice
Post by: charlesd on November 29, 2018, 08:54:57 AM
If I were installing in a field and assuming no obstructions to cause shade, I would be tempted to go either 2 or 3 strings, and not orient them all the same direction - so have some on one string facing WSW, some facing ESE and some due south - in order to maximise the duration during the day of usable generation rather than the total amount. Or a SW/SE split on 2 strings

Once battery storage comes in, you may favour want max generation if you can store the excess, but a big south facing setup will generate a lot during the middle of the day which you may not be able to use - so splitting to orient some towards the morning sun and some towards the evening sun may increase the amount of usable (to you) power generated whilst both will still provide a good solid rump during the day.
Planning application is in now so I don't think I'll be changing it.  :)
Both my wife and I work at home so I think we'll make more use of daytime generation than the average person. Also during the summer we use oil to heat the hot water so some sort if solar immersion controller (really like the idea of these) should allow us to cut our oil bill as well so it all.  I would like to think about batteries later too but I think they still have a good way to drop before I'll be buying them.


Title: Re: Ground Based Solar PV advice
Post by: kristen on November 30, 2018, 10:52:29 AM
Without batteries you will typically use half and export half, so expect a third off your leccy bill. With batteries over half off your bill is possible, but the economics of doing so are questionable.

Both my wife and I work at home so I think we'll make more use of daytime generation than the average person.

Yes, that was my thought too (only just read the whole thread). Working from home, and assuming not an excessive-PV-capacity installation, I think likely that exports might be trivial ... but if the export is on an assumed 50% basis, rather than actually metered, that might help the Man Maths!

Maybe read your meter during the day - several times a day? - for a few days to forma  view of the run-rate when you are both working from home?


Title: Re: Ground Based Solar PV advice
Post by: charlesd on May 13, 2019, 02:30:15 PM
Hi All,
Just thought I'd post an update as I finally got everything finished and final connections made today and sparky left about an hour ago.
Thank you all who gave me advice I did follow some of it  :)
For the rest of today I'm just going to sit and watch the generation meter go up :)

Charles


Title: Re: Ground Based Solar PV advice
Post by: nowty on May 13, 2019, 02:40:40 PM
Charles, how big a system did you go for in the end ?

A pic would be nice.


Title: Re: Ground Based Solar PV advice
Post by: charlesd on May 13, 2019, 02:53:55 PM
Hi
I went for 5.5kw of panels in the end.
I'll try to post a few pics later today if I get the chance.

Charles


Title: Re: Ground Based Solar PV advice
Post by: nowty on May 13, 2019, 03:29:18 PM
By the looks on the forecast for your postcode, your going to be generating 30+kWh's per day for the next 2 days.

Enjoy. :crossed

(https://i.postimg.cc/Bb05QLdP/PE12.jpg) (https://postimages.org/)


Title: Re: Ground Based Solar PV advice
Post by: charlesd on May 14, 2019, 10:15:43 AM
Panels

(https://i.postimg.cc/SnJpPtwr/panels.jpg) (https://postimg.cc/SnJpPtwr)

And the inverter and switches

(https://i.postimg.cc/crzzv1bR/inverter.jpg) (https://postimg.cc/crzzv1bR)

I also had a solar immersion controller fitted so hopefully I can turn the oil boiler off for the summer.

Managed 20kwh yesterday and it didnt get switched on till after lunch  :)

Just over 5kwh today so far.

Cheer
Charles


Title: Re: Ground Based Solar PV advice
Post by: rogeriko on May 14, 2019, 08:18:47 PM
Those 2 panels down at ground level are going to get covered by weeds in a week and block production. You had better put some plastic membrane there to stop anything growing there.


Title: Re: Ground Based Solar PV advice
Post by: charlesd on May 15, 2019, 07:00:58 AM
Those 2 panels down at ground level are going to get covered by weeds in a week and block production. You had better put some plastic membrane there to stop anything growing there.
It's on the plan for this weekend.


Title: Re: Ground Based Solar PV advice
Post by: billi on May 15, 2019, 10:24:01 AM
well thats an intresting one , or i remember my thoughts now when installed my ground mount PV  (but PV was  about 3.5 $ per watt)   to have a mirror at the bottom  or water in form of a pond   to reflect  light

i ended up doing nuthing like that  , what was  a mistake , cause strimming weeds and grass  near the panels was not too easy and   seeing little stones  and cuttings  flying around,  them was not too pleasant

external Mirror foil is about 2 Euro  per m2


Billi


Title: Re: Ground Based Solar PV advice
Post by: charlesd on May 15, 2019, 08:38:24 PM
The 2 additional panels were not part of the original plan but I went with it instead of moving the fencing too much to keep all 18 panels together. I'm intending to put some membrane and old slabs down so the weeds shouldnt be an issue.
Cheers
Charles


Title: Re: Ground Based Solar PV advice
Post by: sam_cat on May 15, 2019, 08:48:32 PM
Water in form of a pond   to reflect  light

Dont do the foil, would look bad... But a pond would be awesome, as the evaporation cooling effect as well will keep ambient temps down, further improving the output!


Title: Re: Ground Based Solar PV advice
Post by: steve on August 30, 2019, 08:38:47 PM
hi there , just wondering what cable you went with for you runs back to the invertor ? did you run cabling for 2 strings or can you combine the strings for the run back?
many thanks Steve