Solar PV to a subpanel

cros13

So... I'm building a new DIY solar PV install for a family member. I'm planning out and doing the ground mounts and solar install, with a RECI doing inspection and final connection.

Starting him off with a 4.2kWp array and using microinverters on the back of every panel for the first time (I've previously used string inverters). But the plan is to expand the system over time to 12.6-15kWp.

For those who don't know much about solar, I'm going from DC to AC with a small 240W DC-AC inverter on the back of every panel. The AC cabling at the back of the panel connects to the last and next panels, with 15-16 panels per string, these wiring harnesses are 6sqmm with IP67 connectors.

The microinverters are EN50438 certified and there are two layers of automatic disconnection when AC is not present, at the end of run terminal and at each microinverter. Power output from the array will be dynamically de-rated to the power consumption measured by a clamp meter between the the ESB meter and the CU .

I'm running power back through a 35 meter buried duct to a subpanel in a shed which is already fed from the main consumer unit by a 16sqmm SWA with 63A breakers. The subpanel is already used to feed two EV chargepoints (230V/48A total) and I'll be replacing both with smart chargepoints which can load share automatically (I can set them for whatever total load I want from 4A single phase up to 44kW 63A 3-phase).

I've specced 16sqmm 5-core SWA, so that in the event the government introduces a feed-in tariff I can dump the micro inverters and go to a three phase string inverter located at the arrays (the microgenerator MEC is 5kW single phase and 11kW for 3-phase). Manual disconnect switches both ends of the run (array-side and subpanel-side). Needless to say, 45 meters of that spec of cable is pricey.

So I've got 2 questions:
The future three phase requirement will max out at 25A per phase and the intervening single phase installs (4.2/8.4/12.6 kW) will throughput 18A, 36A or 55A peak respectively, can I lay 10sqmm 5 core and run live and neutral parallelled over pairs of the 5-core, or split the individual micro inverter strings among the cores?
Will there be any electrical regs issues bringing the solar in at the subpanel rather than the main CU?
My reading so far is that a dual supply notice must be placed at the meter, consumer unit and subpanel.

rolion

You lost me here... it looks like you know everything !
Whats the question !??

2011

cros13 wrote: »

So... I'm building a new DIY solar PV install for a family member. I'm planning out and doing the ground mounts and solar install, with a RECI doing inspection and final connection.

Is this a domestic installation? If so RECI can't certify your work. Anything other than "minor electrical works" (see forum charter for more details) in a domestic installation must be carried out by a registered electrical contractor.

Starting him off with a 4.2kWp array and using microinverters on the back of every panel for the first time (I've previously used string inverters). But the plan is to expand the system over time to 12.6-15kWp.

Cool.

For those who don't know much about solar, I'm going from DC to AC with a small 240W DC-AC inverter on the back of every panel. The AC cabling at the back of the panel connects to the last and next panels, with 15-16 panels per string, these wiring harnesses are 6sqmm with IP67 connectors.

So 15 or 16 microinverters? How do they sync with each other and the ESB supply?

The microinverters are EN50438 certified and there are two layers of automatic disconnection when AC is not present, at the end of run terminal and at each microinverter.

Out of interest, why disconnect when AC is not present? Is this output AC from the inverter?

Power output from the array will be dynamically de-rated to the power consumption measured by a clamp meter between the the ESB meter and the CU .

Not sure what you mean here. Are you modulating the load according to the power available from the solar array?

I'm running power back through a 35 meter buried duct to a subpanel in a shed which is already fed from the main consumer unit by a 16sqmm SWA with 63A breakers.

Impossible to know if these cables are correctly sized. Under nominal load conditions what percentage volt drop is there at the furthest point on final circuits?

The subpanel is already used to feed two EV chargepoints (230V/48A total) and I'll be replacing both with smart chargepoints which can load share automatically (I can set them for whatever total load I want from 4A single phase up to 44kW 63A 3-phase).

Load share from both the solar and ESB supply?

I've specced 16sqmm 5-core SWA, so that in the event the government introduces a feed-in tariff I can dump the micro inverters and go to a three phase string inverter located at the arrays (the microgenerator MEC is 5kW single phase and 11kW for 3-phase). Manual disconnect switches both ends of the run (array-side and subpanel-side). Needless to say, 45 meters of that spec of cable is pricey.

What is the max input voltage to the inverter units? (I assume the output is 230V, 50Hz 1 phase).

The future three phase requirement will max out at 25A per phase

With a 400V line voltage 25A per phase is 17.32 kVA. Above you state that this is 11 kW. Is the power factor that bad ??

and the intervening single phase installs (4.2/8.4/12.6 kW) will throughput 18A, 36A or 55A peak respectively, can I lay 10sqmm 5 core and run live and neutral parallelled over pairs of the 5-core, or split the individual micro inverter strings among the cores?

Not too sure what you mean. Can you draw it out?
Paralleling conductors is permitted.
The essentials are that cables are correctly sized and adequately protected.
Remember when generating small amounts of power at low voltage smaller sized cables will result in higher losses due to volt drop.
Moving the inverter(s) as close as possible to the panels may help reduce the cable losses.

Will there be any electrical regs issues bringing the solar in at the subpanel rather than the main CU?

I can't see an issue with that.

My reading so far is that a dual supply notice must be placed at the meter, consumer unit and subpanel.

I'm not familiar with that to be honest, but what you are suggesting makes sense to me.
I am working in renewables at present but we connect in to the grid on a much larger scale.

Dardania

2011 wrote: »

and the intervening single phase installs (4.2/8.4/12.6 kW) will throughput 18A, 36A or 55A peak respectively, can I lay 10sqmm 5 core and run live and neutral parallelled over pairs of the 5-core, or split the individual micro inverter strings among the cores?

Not too sure what you mean. Can you draw it out?
Paralleling conductors is permitted.
The essentials are that cables are correctly sized and adequately protected.
Remember when generating small amounts of power at low voltage smaller sized cables will result in higher losses due to volt drop.
Moving the inverter(s) as close as possible to the panels may help reduce the cable losses.

Will there be any electrical regs issues bringing the solar in at the subpanel rather than the main CU?

I can't see an issue with that.

My reading so far is that a dual supply notice must be placed at the meter, consumer unit and subpanel.

I'm not familiar with that to be honest, but what you are suggesting makes sense to me.
I am working in renewables at present but we connect in to the grid on a much larger scale.

As 2011 says, definitely need to see that schematic drawn out to address the query about paralleling etc.... for reasons regarding your second query

On the issue of dual supplies etc... you more need to provide a G59 relay to disconnect the PV if there is no mains from ESB Networks.
See description here: http://www.connectingindustry.com/ElectricalEngineering/what-is-g59.aspx
I would guess your inverter panels have this circuitry already? You mention this:

The microinverters are EN50438 certified and there are two layers of automatic disconnection when AC is not present, at the end of run terminal and at each microinverter. Power output from the array will be dynamically de-rated to the power consumption measured by a clamp meter between the the ESB meter and the CU .

I would be a little concerned that if there are multiple automatic disconnections ongoing, one PV could indicate to others that there is mains, so there may in fact not be any mains disconnection... There is only a single "end of run terminal"?

2011

Dardania wrote: »

On the issue of dual supplies etc... you more need to provide a G59 relay to disconnect the PV if there is no mains from ESB

That makes sense, I misread that part of the post.

cros13

2011 wrote: »

Is this a domestic installation? If so RECI can't certify your work. Anything other than "minor electrical works" (see forum charter for more details) in a domestic installation must be carried out by a registered electrical contractor.

It's severable, there is a separate commercial supply which I can connect all this stuff to and move loads. The shed subpanel from the domestic supply is beside the commercial panel. So I could do it as commercial, although this will prevent him using the power for the domestic loads.

I have an existing agreement with a RECI, I do the ductwork, grounding rods, pull the cables. He terminates cables (including grounding my mounting frames etc.) and connects it all up. The Solar PV side is just low voltage DC and plugging in pre-terminated cable harnesses, they only fit together one way...

2011 wrote: »

So 15 or 16 microinverters? How do they sync with each other and the ESB supply?

The first stage will be 16 microinverters, when I get to 12.6kWp there will be 48-50. There's a central controller that talks to the micro-inverters over bluetooth low energy. It's physically connected to the end of run block to sync to the supply. This controller also talks to the clamp meter over the network (I'm also bringing a 48V supply over CAT6 out to the array to provide network and power to the controller). The micro-inverters power up (for comms purposes) when power is present on either the AC or DC side.

2011 wrote: »

Out of interest, why disconnect when AC is not present? Is this output AC from the inverter?

Yes output AC from the inverter. So if grid power is not present the inverter isn't pumping out power (it's also has no grid frequency to sync to). The two layers of disconnects is an EN50438 requirement.

2011 wrote: »

Not sure what you mean here. Are you modulating the load according to the power available from the solar array?

I'm load following. Consistently allowing import of a small amount of power and modulating the output of the microinverters in response to load. So I'm not exporting at any time.

2011 wrote: »

Load share from both the solar and ESB supply?

Load sharing between the car chargepoints. Seperate supply from the subpanel to each chargepoint, but an RS485 comms cable between the two chargepoints. They coordinate, so for example as car A's battery gets close to full and the on-board charger dials back from drawing say 230V/30A to 230V/6A, chargepoint B tells car B's on-board charger it can draw more power.

2011 wrote: »

What is the max input voltage to the inverter units? (I assume the output is 230V, 50Hz 1 phase).

On the DC side on the microinverter it's up to 45V/9A, the panels I'm using top out at 38V. It's one of the advantages of the microinverter setup that you can keep the DC side low voltage.

2011 wrote: »

With a 400V line voltage 25A per phase is 17.32 kVA. Above you state that this is 11 kW. Is the power factor that bad ??

No, It's a combination of not having settled on the exact layout/mounting solution yet and wanting some additional headroom. Also the possibility a small wind turbine might be added later.

2011 wrote: »

Not too sure what you mean. Can you draw it out?
Paralleling conductors is permitted.
The essentials are that cables are correctly sized and adequately protected.
Remember when generating small amounts of power at low voltage smaller sized cables will result in higher losses due to volt drop.
Moving the inverter(s) as close as possible to the panels may help reduce the cable losses.

I'm just looking at putting in the 5-core SWA for future flexibility. I specced out 16sqmm so that I could feasibly do the single phase install up to ~50A using just one of the conductors for live and neutral respectively. But paying €550 for 45 meters of cable is a big chunk out of the budget, paralleling conductors on 10sqmm cable would save a few shekels for other parts of the project. The shed subpanel is also connected to the main panel through a 5-core 16sqmm...

cros13

Dardania wrote: »

On the issue of dual supplies etc... you more need to provide a G59 relay to disconnect the PV if there is no mains from ESB Networks.
See description here: http://www.connectingindustry.com/ElectricalEngineering/what-is-g59.aspx
I would guess your inverter panels have this circuitry already? You mention this:

I would be a little concerned that if there are multiple automatic disconnections ongoing, one PV could indicate to others that there is mains, so there may in fact not be any mains disconnection... There is only a single "end of run terminal"?

There is an end of run terminal for each string of up to 16 panels. This terminal is not just a dumb terminal block, it also contains a G59 relay, so in the event on of the inverters malfunctions and does not stop outputting AC there is a fallback. So it's two layers of G59 relay (or functional equivalent), one at each inverter, and one at each end of run terminal.

2011

cros13 wrote: »

He terminates cables (including grounding my mounting frames etc.) and connects it all up.

I see.
What size area do the panels cover and how far are they from the sub-board?

(I'm also bringing a 48V supply over CAT6 out to the array to provide network and power to the controller).

I have not seen this at such a high voltage before over CAT6 before.
We generally use 24VDC for control / comms.

Yes output AC from the inverter. So if grid power is not present the inverter isn't pumping out power (it's also has no grid frequency to sync to). The two layers of disconnects is an EN50438 requirement.

Yes, makes sense.

I'm load following. Consistently allowing import of a small amount of power and modulating the output of the microinverters in response to load. So I'm not exporting at any time.

OK, stupid question: If you never plan to export why bother syncing at all?

Load sharing between the car chargepoints. Seperate supply from the subpanel to each chargepoint, but an RS485 comms cable between the two chargepoints. They coordinate, so for example as car A's battery gets close to full and the on-board charger dials back from drawing say 230V/30A to 230V/6A, chargepoint B tells car B's on-board charger it can draw more power.

Interesting.

On the DC side on the microinverter it's up to 45V/9A, the panels I'm using top out at 38V. It's one of the advantages of the microinverter setup that you can keep the DC side low voltage.

So on the output side of the inverter it is around 1.7A
My earlier point was that if the cabling on the DC side was the same size as the AC side the DC losses would be much higher (per m) as the current is far larger.

No, It's a combination of not having settled on the exact layout/mounting solution yet and wanting some additional headroom. Also the possibility a small wind turbine might be added later.

So possibly >11kW 3 phase inverter? Not really a domestic installation anymore!

I'm just looking at putting in the 5-core SWA for future flexibility. I specced out 16sqmm so that I could feasibly do the single phase install up to ~50A using just one of the conductors for live and neutral respectively.

If I installed this cable I would have 2 cores connected in parallel for the phase, 2 connected in parallel for the neutral and the 5th core would be the earth. In the event of going 3 phase I would have a conductor per phase. I assume that is what you are proposing for the 5 x 10 sq. SWA ??

But paying €550 for 45 meters of cable is a big chunk out of the budget, paralleling conductors on 10sqmm cable would save a few shekels for other parts of the project. The shed subpanel is also connected to the main panel through a 5-core 16sqmm...

I doubt that there is a large price differential between 5 x 10 sq. SWA and 5 x 16 sq. SWA. I would always go for the larger cable, projects have a habit of growing legs!

cros13

2011 wrote: »

I see.
What size area do the panels cover and how far are they from the sub-board?

It's about 60-80sqm of panels spread over 160sqm, they will be ~27 meters from the sub-board. 35 meters through the duct. They are actually located closer to the CU, but I'm avoiding cutting into tarmac and mass concrete.

2011 wrote: »

I have not seen this at such a high voltage before over CAT6 before.
We generally use 24VDC for control / comms.

It's standard IEEE802.3at PoE+. Provides up to ~30W which I can split out with a PoE-powered switch and power multiple downstream devices. Unlike 24V passive PoE on the off-pairs of 100BaseT CAT5 this involves active negotiation by the powered device with the PSE on the far end.

2011 wrote: »

OK, stupid question: If you never plan to export why bother syncing at all?

It's not that there's a plan to never export, it's just there's currently a financial disincentive to do so with no export tariffs available and a low usage surcharge. In this setup I can login to the cloud management for the controller remotely the day net metering is announced and allow export.

2011 wrote: »

So on the output side of the inverter it is around 1.7A
My earlier point was that if the cabling on the DC side was the same size as the AC side the DC losses would be much higher (per m) as the current is far larger.

In my particular install each inverter won't exceed 1.05A peak even in theory at midday in July.

2011 wrote: »

So possibly >11kW 3 phase inverter? Not really a domestic installation anymore!

I think with the advent of multiple EV households, what's considered typical domestic loads may need some reconsideration. It's reasonable to have two or three cars drawing 230V/32A each for up to 8 hours. In australia, they allow domestic single phase to export up to 50kW. Part of the solution is going to be home batteries, and a 13.2kWh/7.0kW output battery is something I'm considering for phase 2 of this particular install.

2011 wrote: »

If I installed this cable I would have 2 cores connected in parallel for the phase, 2 connected in parallel for the neutral and the 5th core would be the earth. In the event of going 3 phase I would have a conductor per phase. I assume that is what you are proposing for the 5 x 10 sq. SWA ??

exactly.

2011 wrote: »

I doubt that there is a large price differential between 5 x 10 sq. SWA and 5 x 16 sq. SWA. I would always go for the larger cable, projects have a habit of growing legs!

Yeah, it's not a whole lot, maybe €150... and partially it's naval gazing on my part, I tend to over-engineer things (in case you haven't noticed).

2011

cros13 wrote: »

It's about 60-80sqm of panels spread over 160sqm, they will be ~27 meters from the sub-board.

In that case are you considering both equipotential bonding and local earth rods?

It's standard IEEE802.3at PoE+. Provides up to ~30W which I can split out with a PoE-powered switch and power multiple downstream devices. Unlike 24V passive PoE on the off-pairs of 100BaseT CAT5 this involves active negotiation by the powered device with the PSE on the far end.

Not something I have been involved with before.

It's not that there's a plan to never export, it's just there's currently a financial disincentive to do so with no export tariffs available and a low usage surcharge. In this setup I can login to the cloud management for the controller remotely the day net metering is announced and allow export.

Fair enough, but until that day arrives why bother syncing? Life becomes simpler when you don't have to sync. You can design it so that it can be synced at a future date. You won't need it certified until it is synced.

In my particular install each inverter won't exceed 1.05A peak even in theory at midday in July.

How is that? You said that "on the DC side on the microinverter it's up to 45V/9A"? I would expect the inverter to be > 95% efficient.

I think with the advent of multiple EV households, what's considered typical domestic loads may need some reconsideration. It's reasonable to have two or three cars drawing 230V/32A each for up to 8 hours. In australia, they allow domestic single phase to export up to 50kW.

My point is that if you have a system that can export 50 kW I would expect that ESB will not consider your installation to be a domestic installation.

Part of the solution is going to be home batteries, and a 13.2kWh/7.0kW output battery is something I'm considering for phase 2 of this particular install.

I think the future is ultracapacitors. They are too pricey at the moment, but hopefully this will change in time. I have used small supercaps for small UPS (in place of batteries) in the past and it worked very well. However there are ultracapacitors available that bring capacitors to another level. They can store quite a few MJ for energy in a relatively small space. Compared to batteries, vastly superior power density, performance does not drop off like it does with batteries, ambient temperature does not impact them as much either. Not cheap though....

Yeah, it's not a whole lot, maybe €150

Spend it! Nothing else makes sense.

... and partially it's naval gazing on my part, I tend to over-engineer things (in case you haven't noticed).

cros13

2011 wrote: »

In that case are you considering both equipotential bonding and local earth rods?

Yeah, I'm hammering in a 2.5 meter grounding rod at each physical array, with both the metalwork and the SWA armor grounded there, shed side has a good ground. Still deciding between a commercial 16 panel mounting solution (8x2) and a DIY design (multiple 5x1s). So in the case of going the DIY route the final install could be ten 5x1 arrays with ten grounding rods!

2011 wrote: »

Fair enough, but until that day arrives why bother syncing? Life becomes simpler when you don't have to sync. You can design it so that it can be synced at a future date. You won't need it certified until it is synced.

Controller, microinverter etc. were designed with the assumption that you would be exporting.... so the standard install syncs to grid frequency.

2011 wrote: »

How is that? You said that "on the DC side on the microinverter it's up to 45V/9A"? I would expect the inverter to be > 95% efficient.

My panels will be 20-38V at a lower amperage. Those are the micro-inverters limits.

2011 wrote: »

My point is that if you have a system that can export 50 kW I would expect that ESB will not consider your installation to be a domestic installation.

Sure.

2011 wrote: »

I think the future is ultracapacitors. They are too pricey at the moment, but hopefully this will change in time. I have used small supercaps for small UPS (in place of batteries) in the past and it worked very well. However there are ultracapacitors available that bring capacitors to another level. They can store quite a few MJ for energy in a relatively small space. Compared to batteries, vastly superior power density, performance does not drop off like it does with batteries, ambient temperature does not impact them as much either. Not cheap though....

Maybe... a lot of work to be done to get to that point. Lithium-Ion is already at the point where I can pick up an off the shelf 13.2kWh AC battery solution from Tesla with built-in inverters for ~€6k incl. VAT. I'd say the next step is DC charging the cars from the batteries (both are ~400V DC these days) with DC expanding out into the home from there. Why are we running LEDs, phone chargers and LCD TVs off AC?

Dardania

cros13 wrote: »

2011 wrote: »

Load share from both the solar and ESB supply?

Load sharing between the car chargepoints. Seperate supply from the subpanel to each chargepoint, but an RS485 comms cable between the two chargepoints. They coordinate, so for example as car A's battery gets close to full and the on-board charger dials back from drawing say 230V/30A to 230V/6A, chargepoint B tells car B's on-board charger it can draw more power.

Is this using the type 3 EV charger load shedding comms? If so, very cool.

cros13 wrote: »

Dardania wrote: »

On the issue of dual supplies etc... you more need to provide a G59 relay to disconnect the PV if there is no mains from ESB Networks.
See description here: http://www.connectingindustry.com/ElectricalEngineering/what-is-g59.aspx
I would guess your inverter panels have this circuitry already? You mention this:

I would be a little concerned that if there are multiple automatic disconnections ongoing, one PV could indicate to others that there is mains, so there may in fact not be any mains disconnection... There is only a single "end of run terminal"?

There is an end of run terminal for each string of up to 16 panels. This terminal is not just a dumb terminal block, it also contains a G59 relay, so in the event on of the inverters malfunctions and does not stop outputting AC there is a fallback. So it's two layers of G59 relay (or functional equivalent), one at each inverter, and one at each end of run terminal.

How does each end of run terminal's G59 coordinate, such that one G59 doesn't convince the others that it is the mains?

cros13

Dardania wrote: »

Is this using the type 3 EV charger load shedding comms? If so, very cool.

Type 2 Mode 3. I've been looking at a DIY solution but the cheapest way is to just use Tesla Wall Connectors in slave mode.

Dardania wrote: »

How does each end of run terminal's G59 coordinate, such that one G59 doesn't convince the others that it is the mains?

Haven't investigated that yet. TBH for phase 1, it's not important as there will only be a single string with a single end-run terminal.

Dardania

cros13 wrote: »

Dardania wrote: »

Is this using the type 3 EV charger load shedding comms? If so, very cool.

Type 2 Mode 3. I've been looking at a DIY solution but the cheapest way is to just use Tesla Wall Connectors in slave mode.

Dardania wrote: »

How does each end of run terminal's G59 coordinate, such that one G59 doesn't convince the others that it is the mains?

Haven't investigated that yet. TBH for phase 1, it's not important as there will only be a single string with a single end-run terminal.

Have a look at this thread: https://www.boards.ie/b/thread/2057711250?fuid=102757964 with this unit - seems interesting?:
https://www.indiegogo.com/projects/zappi-charge-your-ev-with-your-pv-solar/x/16155030#/
might work out a bit cheaper?

and with the G59 - singular you're fine I'd say, but with three...maybe there's a way to trip the breaker if any one of the three G59s sense a loss of mains on the utility side? And they can somehow filter the other 2 out in future....

Also, forgot to mention - a problem I only read about in the last few years with UPS' (possibly even here on boards?): sometimes it can be difficult with local power generators to get enough short circuit current to trip a breaker in the event of a short. just to bear in mind if you ever want to use the PV in a mains outage situation

cros13

Just to illustrate matters... I had a few bits and pieces in the back of the car, and I was sitting here at junction 14 charging, so I thought I'd take some photos.

click for full size.

Site overview:


Path of the duct:


The Micro-inverter, cable harness, end-run terminal and controller:

freddyuk

If the only advantage of using Micro Inverters is future expansion then I cannot see the benefit as running DC from the Arrays back to a standard cheaper and more reliable GT inverter will avoid cable losses and the problem of individual inverter failures/replacement cost. There will be a lot of connections with Micro inverters. You can run 4mm over a considerable distance within inverter spec or just up it to 6mm if you want to. Your 35metres is not a problem with 4mm runs in dedicated conduit.
Do you have lightning protection?
Are the Micro Inverters certified under EN50438 with specific Irish settings?
I am not an EV expert but as I understand it you need DC charging supply so is there no way to have DC - DC system within regs? Converting DC to AC and then back to DC is introducing losses and complication. Run DC supply into DC board and then convert what you need into AC for load supply while EV charging off the DC supply?

freddyuk

I'm not a fan of micro inverters either. Too much to go wrong in hard to get to places (for roof mounts). I think the place for an inverter is conversion on demand not at source. Less losses and more versatile just string DC to where it needs to be.

freddyuk wrote: »

..as I understand it you need DC charging supply ... Run DC supply into DC board and then convert what you need into AC for load supply while EV charging off the DC supply?

Couldn't agree more.

cros13

freddyuk wrote: »

If the only advantage of using Micro Inverters is future expansion then I cannot see the benefit as running DC from the Arrays back to a standard cheaper and more reliable GT inverter will avoid cable losses and the problem of individual inverter failures/replacement cost.

There are other advantages to using the microinverters:
MPPT tracking per panel reduces the impact of shading or panel mismatch.
No high voltage DC, which particularly in a ground mount system means less safety hardware needed

The main thing for me was gaining a bit of design flexibility. I could literally set up a single inverter and panel in the workshop to be able to work out the load/supply management side of things.

My previous installs have used DC optimisers and string inverters. With the additional cost of DC optimisers the cost was almost identical to microinverters.

freddyuk wrote: »

There will be a lot of connections with Micro inverters.

There's one T cable with a 4 core 6sqmm trunk and the microinverters wired in parallel. I can do a 16 panel install including mounting the panels in under an hour.

freddyuk wrote: »

You can run 4mm over a considerable distance within inverter spec or just up it to 6mm if you want to. Your 35metres is not a problem with 4mm runs in dedicated conduit.
Do you have lightning protection?

It's going to be very extensively grounded.

freddyuk wrote: »

I am not an EV expert but as I understand it you need DC charging supply so is there no way to have DC - DC system within regs? Converting DC to AC and then back to DC is introducing losses and complication. Run DC supply into DC board and then convert what you need into AC for load supply while EV charging off the DC supply?

No, at home the cars charge from AC 3.3 - 22kW depending on the supply and onboard charger (that's in the car, the chargepoint is just a a local RCBO and a fancy socket that signals available amperage using a control pilot wire).

I can charge the cars via DC but that involves building comms hardware to talk to the cars charging computer (LIM) and BMS (and that's different for each car, one uses the japanese CHAdemo system which extends the CAN bus out of the vehicle, the other uses the european CCS which uses IPv6 over GreenPHY PLC). That's a lot of work and complexity to avoid a little efficiency loss at the inverter and onboard charger. It makes sense for pulling 50-350kW DC 400V/800V/1200V at up to 400A but not for home charging. There are rumors Tesla will launch a home DC charging solution which will allow you to pull power from the 400V powerwall home batteries, but they use yet another incompatible PLC system (although I suspect they will support CCS from the Model 3 forward).

At the moment I'm not looking at the car's consumption. The cars mainly charge overnight, use up to 50kWh per night and on nightsaver buy power for ~6c/kWh.
The main advantage of the PV system is it offsets load during the day when the rate is ~15c/kWh. I have per-minute consumption data for the premises for the past three years and I used PVWatts & weather data for the past 30 years from Birr (closest weather station) to calculate average hourly production for each of the 8760 hours in the year.

Overlaying one on to the other I estimated that:
Phase 1 (4.18kW PV) will offset 33% of the consumption cost (not overall consumption)
Phase 2 (13.2kWh AC battery) will offset 42% of the consumption cost
Phase 3 (+4.18kW PV) will offset 54% of consumption cost
Phase 4 (+4.18kW PV) will offset 78% of consumption cost

With the addition of the battery in Phase 2 I can start to cover evening consumption up to the off-peak hours.

cros13

cros13 wrote: »

There are other advantages to using the microinverters:
MPPT tracking per panel reduces the impact of shading or panel mismatch.

It's usually only a very expensive 10% output gain compared to "direct drive".
It also increases the low load consumption / panel inefficiency. Same for DC optimisers.
Personally I'd string the panels at load voltage + expected system losses. Not put them where they are going to be shaded and make sure they are matched.

Alternating current is certainly convenient, and definitely there is a sensible point where it's much cheaper add panels to offset the losses in the system. It just wears on me to see embedded losses in generation systems.

cros13

cros13 wrote: »

Why are we running LEDs, phone chargers and LCD TVs off AC?

Cable cost and switchgear issues.
I use half and half.

2011

cros13 wrote: »

No high voltage DC, which particularly in a ground mount system means less safety hardware needed

What do you mean by "high voltage"? We normally describe < 50V as ELV and >50V and <1kV as low voltage. The threshold for HV varies depending on what country you are in and who you talk to. I assume that what you are describing is LV, as such the protection required is limited to reasonable mechanical protection and fuses or MCB.

Out of interest has the D.C. Output from the solar panels any reference to earth? If so where does it get it from, the inverter or is the negitive grounded ?

cros13

Sir Liamalot wrote: »

Alternating current is certainly convenient, and definitely there is a sensible point where it's much cheaper add panels to offset the losses in the system. It just wears on me to see embedded losses in generation systems.

Sure, and simple string inverters and poly panels would be the cheapest price/watthour option. Limited shading is sometimes unavoidable, particularly with the sun low in the sky during winter, which when a battery system is introduced can have an outsized impact on both the perceived and actual self-consumption. At one point I was looking at splitting this array south-west to the and south-east, which would have hurt the overall production numbers but evened out production a bit through the day. Anyways... moot point in this case especially considering I've already bought the microinverters.

Sir Liamalot wrote: »

Cable cost and switchgear issues.
I use half and half.

Sure but in the future we could have much more standardised 12/24V DC power in homes with a lot more limited penetration of AC on the customer side. So more of a mainstreaming of household DC power from the socket on the wall and in lighting.

2011 wrote: »

What do you mean by "high voltage"? We normally describe < 50V as ELV and >50V and <1kV as low voltage. The threshold for HV varies depending on what country you are in and who you talk to. I assume that what you are describing is LV, as such the protection required is limited to reasonable mechanical protection and fuses or MCB.

350V to as much as 600V per string. Enough that in a ground mount situation I'd have to maybe put up some wire mesh to block access by children or pets. in the microinverter scenario cabling is tied up at the top of the panel and all connectors are tamperproof.

2011 wrote: »

Out of interest has the D.C. Output from the solar panels any reference to earth? If so where does it get it from, the inverter or is the negitive grounded ?

The frame of every panel gets grounded with 2.5sqmm copper and the inverter casing does too. In the event I do DIY mounts it will be not far off this:

2011

cros13 wrote: »

350V to as much as 600V per string. Enough that in a ground mount situation I'd have to maybe put up some wire mesh to block access by children or pets. in the microinverter scenario cabling is tied up at the top of the panel and all connectors are tamperproof.

Ok, that's low voltage.
No reason to have anymore protection than any other LV cables used in that type situation.
Armored cables and / or suitable cable containment, fuses etc...

So in this scinerio you would connect all of the panels in series?

The frame of every panel gets grounded with 2.5sqmm copper and the inverter casing does too. In the event I do DIY mounts it will be not far off this:

That tells me that the frames are connected to each other and then connected to earth electrodes. My question is does the DC output from the solar panels have a reference to earth?
When you say that the voltage output from a string is up to 600V is that with reference to earth?
Is the input side of the inverter module galvanically isolated from the output?

cros13

If you ignore the americanness of this diagram you get a pretty good idea of how I see this working, the difference in my case is a grounding bus in a panel at each array, ground in the SWA back to the shed connecting those busses to the existing grounding bus in the shed (though that's up to the RECI). Within the microinverter is ground fault detection and isolation:



okay so it's quite a bit different 'cause of the local busses et al.... I really need to do some actual diagrams myself, I'm finding it difficult to explain how I see this stuff in my head... my vocabulary is failing me... as is google image search for representative diagrams

Don't get hung up on the up to 600V DC string inverter stuff... that's a different type of install to what i'm doing with the microinverters. The DC portion here is 0-38V preterminated positive and negative from the panel directly connected to the microinverter (also on the back of the panel mounted to the frame). The microinverter uses MPPT (maximum power point tracking) so Vref for that purpose is variable. Internally inside the panel I'm......trusting the frame is isolated properly from the cells?

2011

2011 wrote: »

What do you mean by "high voltage"? We normally describe < 50V as ELV

< 120V for DC.

Stoopid question...are ground arrays not inherently easy to earth without electrodes.

cros13 wrote: »

which when a battery system is introduced can have an outsized impact on both the perceived and actual self-consumption.

Please elaborate, I don't understand.

cros13 wrote: »

Sure but in the future we could have much more standardised 12/24V DC power in homes with a lot more limited penetration of AC on the customer side. So more of a mainstreaming of household DC power from the socket on the wall and in lighting.

I've looked at this a few times already having 12VDC & 48VDC at my disposal and it's never been worth my while running separate radials to glean a few % efficiency from already minuscule loads. Instead it's better cascade inverters so that the large ones aren't running idle at minimum efficiency.
It's very expensive in cable to run ELV around a house, for little gain and the cost of all the high current DC switchgear will make your eyes water.
Sheds, boats, campervans, cabins are another matter though...for those I'd argue you don't need 230VAC it comes down to scale and if induction or frequency are necessities of the installation.

I use native DC in my power plant room and 230VAC everywhere else. Easier plug my phone in in a room with a battery than chasing walls for a 150W ELV supply.

Plus standardising appliance voltage will be a long time coming.

cros13 wrote: »

...so that in the event the government introduces a feed-in tariff ...

Don't hold your breath, I believe our government are in negotiations to sell the sub-station capacity to private enterprise. Power companies are becoming very defensive about who can use the sun.

2011 wrote: »

I would expect the inverter to be > 95% efficient.

It's nearly always a massaged figure under ideal conditions.
If an inverter listed having a 30W quiescent has a 30Wp panel attached to it how efficient is it on a cloudy day?

There's good reason they only publish the top 20% of the load graphs, and for all the praise of MPPT you'll find inverters are most efficient when gen. voltage = load voltage.

cros13

cros13 wrote: »

Limited shading is sometimes unavoidable, particularly with the sun low in the sky during winter, which when a battery system is introduced can have an outsized impact on both the perceived and actual self-consumption.

Sir Liamalot wrote: »

Please elaborate, I don't understand.

I've got four really lean months in terms of production from November to February where every available watt gets either stored or consumed. If say the grass is too long or the hedge at the far end of the field is a bit too high it can have a drastic effect on production at the end and start of the day.

During the summer I'm also kind of relying on some of the long tailing of production at the end of the day because daily production will exceed the battery capacity and instantaneous self-consumption... so the avg. ~259W AC (from ~337W DC) produced during the last hour of the 28th of July is more valuable for delaying / offsetting power from the battery.

Ah gotcha, power on demand I call it.

2011

Sir Liamalot wrote: »

Stoopid question...are ground arrays not inherently easy to earth without electrodes.

They need a local earth as they are large, conductive and quite some distance away from the earth electrode of the existing installation.
The MET could be at a different potential.

2011

cros13 wrote: »

If you ignore the americanness of this diagram you get a pretty good idea of how I see this working

Yes, it shows that the DC negative output from the solar panel is grounded.
Therefore the DC bus has a reference to earth.

the difference in my case is a grounding bus in a panel at each array, ground in the SWA back to the shed connecting those busses to the existing grounding bus in the shed (though that's up to the RECI).

The REC should be directed by the designer unless the REC is the designated designer (needless to say regulations must be complied with).
How is the cable between the solar panel and the inverter protected??

freddyuk

1. If we are talking grass and hedge shading then arrange the Array in landscape rows thus the top row will be full chat until dark while the bottom row will be maximised by the inverters as far as they can. Shading the bottom of a module in portrait will kill 100% of the output.

2. My point about lightning is that a direct hit will wipe out the installation whether grounded or not? Having a nearby strike can put transient spikes into the system which can blow sensitive electronics so how does the system handle this? In a string inverter the inverter can be "isolated" between the DC incomers and the inverters to help prevent damage but this would not happen with micro inverters? Enphase seem to recognise the problem and recommend suppression in addition to the inbuilt protection which suggests the inbuilt protection is not really going to help being attached to the module.
As you have already committed to micro inverters you may need to invest in better protection as they are fragile compared to string inverters with robust protections inbuilt. Having a spare string inverter which can be replaced in a few minutes is a good plan. Changing all the micro inverters and attached comms would be a headache.
3. It would indeed be wise to protect a ground mount from public/innocent access by at least a fence and warning signs.

2011

A direct hit by lighting can fry electronics no matter what you do. Don't think that lighting protection systems can provide any guarantees. All you can hope to do is minimize the damage.

2011

2011 wrote: »

They need a local earth as they are large, conductive and quite some distance away from the earth electrode of the existing installation.

Yes but if it's a metal frame buried in the terra firma does it still require an electrode. Is the support not exactly that or is it concrete we are trying to avoid.

What lightning arresters do you recommend Freddy?

2011

Sir Liamalot wrote: »

Yes but if it's a metal frame buried in the terra firma does it still require an electrode. Is the support not exactly that or is it concrete we are trying to avoid.

Concrete is not a great conductor so a metal frame stuck into a lump of concrete is going to have a high resistance to earth compared to an earth electrode that goes 1.5m into the ground. You want to avoid a person that is touching the frame having a potential difference across them. Remember the MET that the frames are connected to could be at a very different potential than the ground local to the frames.

Perhaps this does not require earth electrodes, but this should be assessed, demonstrated and documented before a call is made. This can be tested by measuring the resistance between the frames and earth when disconnected from the MET. Not that hard to do ( see Wenner test).

Regarding lighting protection:
Normally a specialist company would be called in. They would carry out a risk assessment and a design would be based on this.
Copper tape (for example 3 x 25mm) is normally used for the down conductors for a lighting protection system. These would be secured every foot or two. Air termination points would also be normal. Small cross bonding cables are not comparable.

I'd try to avoid pouring concrete tbh.

I see these things a lot advertised as lightning arresters for PV.



Just wondering if they're mustard cutters?

freddyuk

Sir Liamalot wrote: »

Yes but if it's a metal frame buried in the terra firma does it still require an electrode. Is the support not exactly that or is it concrete we are trying to avoid.

What lightning arresters do you recommend Freddy?

You can use ground anchor posts thus doing away with concrete entirely and having a good earthing of the frame. Takes seconds to install each post with jack hammer/generator and correct kit.

I am not recommending any safety devices as this should come from the supplier. As I have said a direct hit is not going to leave much standing. An arrestor on the din rail at the combiner box is the way I would do it. However I cannot recommend something that I cannot test! It is possible it will save the electronics but not certain and I have never had to find out! As it is a gamble you are simply increasing your odds by having something in the circuit.
Here is one supplier http://www.surgedevices.co.uk/ (I have no connection with them)

freddyuk

freddyuk wrote: »

However I cannot recommend something that I cannot test!

Yet another reason I need a Tesla coil. :pac:

2011

It is important to note that surge protection and lighting protection are two very different things.

2011

freddyuk wrote: »

You can use ground anchor posts thus doing away with concrete entirely and having a good earthing of the frame.

This may be possible, but how the only way to know that is to test it and determine that the connection to earth is satisfactory.

cros13

2011 wrote: »

How is the cable between the solar panel and the inverter protected??

Both are about only a few tens of cm long. it's just the fixed pre-terminated cable at the back of the panel.

freddyuk wrote: »

1. If we are talking grass and hedge shading then arrange the Array in landscape rows thus the top row will be full chat until dark while the bottom row will be maximised by the inverters as far as they can. Shading the bottom of a module in portrait will kill 100% of the output.

True, just giving that as an example. I'll be mounting portrait, because it'll be a bit tidier for mounting and cabling. The array is positioned a best as I can manage but there's all sorts of shading issues with ground mounted arrays in the real world.

freddyuk wrote: »

2. My point about lightning is that a direct hit will wipe out the installation whether grounded or not? Having a nearby strike can put transient spikes into the system which can blow sensitive electronics so how does the system handle this? In a string inverter the inverter can be "isolated" between the DC incomers and the inverters to help prevent damage but this would not happen with micro inverters? Enphase seem to recognise the problem and recommend suppression in addition to the inbuilt protection which suggests the inbuilt protection is not really going to help being attached to the module.

Sure, but I'd consider this to be more of a problem if it was a roof mount without the local earth of the ground mount arrays. The whole lightning protection for solar arrays is a bit... overstressed. There are plenty of arrays out there with all sorts of more serious issues. With lighting protection the only thing I'm worried about would be the shed and house. Common bonding should help avoid a lot of issues.

freddyuk wrote: »

As you have already committed to micro inverters you may need to invest in better protection as they are fragile compared to string inverters with robust protections inbuilt. Having a spare string inverter which can be replaced in a few minutes is a good plan. Changing all the micro inverters and attached comms would be a headache.

I think the opposite, comms for the microinverters is wireless. So to switch out a microinverter I can just cover the panel, pop the MC4s and connection from the AC trunk (with a disconnect tool), take off two bolts and the grounding bolt, swap in the new one and re-pair when I get back inside. A string inverter is at least a two man job even lifting it.

A spare string inverter is ~€1500 sitting there. A spare microinverter is less urgent because in most situations the 49 other microinverters will be working fine. Even if I want to buy a spare they are only €85 a pop.

2011

cros13 wrote: »

Both are about only a few tens of cm long. it's just the fixed pre-terminated cable at the back of the panel.

Fair enough. I guess a short is unlikely but it would be bad news for the solar panel.

Sure, but I'd consider this to be more of a problem if it was a roof mount without the local earth of the ground mount arrays. The whole lightning protection for solar arrays is a bit... overstressed.

I agree and I think a risk assessment would come to the same conclusion.

The only time I had lightning protection installed on a metal structure that was at a comparably low level was a tank farm which stored flammable solvents.

freddyuk

2011 wrote: »

It is important to note that surge protection and lighting protection are two very different things.

Aren't we concerned with surges caused by lighting? If there is lightning about it does not have to touch the installation to cause potential damage via voltage spike. That is my understanding.

2011

freddyuk wrote: »

Aren't we concerned with surges caused by lighting? If there is lightning about it does not have to touch the installation to cause potential damage via voltage spike. That is my understanding.

I agree with all of the above, but my point still stands.

air

2011 wrote: »

My question is does the DC output from the solar panels have a reference to earth?
When you say that the voltage output from a string is up to 600V is that with reference to earth?

The DC output of the panels is totally isolated from the panel frames and earth normally. String inverters continuously monitor resistance to earth and shut down if it reduces below an arbitrary figure - usually a few M ohms.
So someone would have to expose and grab both conductors in order to receive a shock from the wiring if the system was in operational condition.

air

2011 wrote: »

Fair enough, but until that day arrives why bother syncing? Life becomes simpler when you don't have to sync. You can design it so that it can be synced at a future date. You won't need it certified until it is synced.

You can't do anything useful with solar panels unless you either sync them to the grid to offset import or install a battery system. The micro inverters that the OP is installing won't do anything at all without a grid connection.

2011

air wrote: »

The DC output of the panels is totally isolated from the panel frames and earth normally. String inverters continuously monitor resistance to earth and shut down if it reduces below an arbitrary figure - usually a few M ohms.
So someone would have to expose and grab both conductors in order to receive a shock from the wiring if the system was in operational condition.

Well I suspected that this may be the case until the OP posted this schematic in post #24 where it describes the negative wire on the DC output as "grounded conductor white":



The reason I asked the question is because I am working on the design of a DC system coupled to an inverter at present as part of a project at work.

You can't do anything useful with solar panels unless you either sync them to the grid to offset import or install a battery system. The micro inverters that the OP is installing won't do anything at all without a grid connection.

Yeah, I see what you mean. I have no experience with PV arrays.
I was just thinking aloud.

air

No worries, my comment was with reference to string inverters, not micro inverters.
There are actually string inverters that can operate with either side earthed, I think it's a requirement for some thin film amorphous solar panels.
You may as well just ground the negative on the system at work, it's the common convention.
Just beware if you ground the positive for some reason that the wiring colours reverse!

2011

air wrote: »

No worries, my comment was with reference to string inverters, not micro inverters.

Fair enough.

You may as well just ground the negative on the system at work, it's the common convention.

Well as it happens I decided not to, it is an isolated system

Just beware if you ground the positive for some reason that the wiring colours reverse!

Interesting, I never heard that.

air

Isolated battery systems are well and good at extra low voltage but I wouldn't be a fan of them without monitoring above that, especially if the battery system is reasonably accessible / open. Too much risk of the system becoming inadvertently earthed somewhere leading to unexpected results for those maintaining it.

2011

air wrote: »

Too much risk of the system becoming inadvertently earthed somewhere leading to unexpected results for those maintaining it.

What do you mean by "unexpected results" ?

This is common practice in certain applications such as marine and regenerative braking systems on vehicles. For me the advantage is that the system can sustain a single fault, making it more robust.

air

Without monitoring you're relying on that isolation being maintained for the single fault tolerance to be preserved. Submarines etc used lamps to indicate isolation faults for this reason.
If the battery system or any DC load becomes inadvertently grounded at any point due to a fault or miswiring you'll have no way of knowing. Then you could have someone touch an exposed battery terminal for example and get a shock where they previously got none. Not such a big issue for low voltage batteries obviously but at higher voltages it's very significant.

On the wiring colours, it makes sense. Blue is 0V regardless of whether the system if positively or negatively earthed. Gives people half a chance if they start mixing up AC and DC supplies I guess.

2011

air wrote: »

Without monitoring you're relying on that isolation being maintained for the single fault tolerance to be preserved. Submarines etc used lamps to indicate isolation faults for this reason.

Agreed.

My understanding is that isolated systems are used on lots of other marine craft (such as ferries and trawlers) for critical systems (such as navigation equipment) due to its single fault tolerance.

If the battery system or any DC load becomes inadvertently grounded at any point due to a fault or miswiring you'll have no way of knowing.

In our case we would check this during commissioning.

On the wiring colours, it makes sense. Blue is 0V regardless of whether the system if positively or negatively earthed. Gives people half a chance if they start mixing up AC and DC supplies I guess.

Yes, it makes sense. I just hadn't seen this in any standard, can you point me to the document that states this?

I have been looking at IEC60445