Explain these comments on a Gary Does Solar video?

[Alan Ambrose]

In this recent video, there's a couple of comments that I'm not sure I quite get. Here's a link to the video:

 

 

Why Are The DNOs Limiting Your EXPORT And Even Your INVERTER SIZE?

 

https://youtu.be/Bvpl9pvg8zk?si=4rLhJ-me57Pcwabu

 

 

Here are the two comments (I've highlighted the relevant bits that were raising questions for me in bold):

 

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One detail - only grid tie need approval. If your system isn't capable of pushing power into the grid (that's not capable as opposed to "set to 0") then you sidestep it at the cost of no export revenue. Setting up a big non grid tie inverter and putting the house on that with the grid as an input (generator basically) lets you side step all the mess in the difficult cases. It's not usually the best option but if you are getting 3.6kW and especially if you are also refused G100 with a bigger inverter it's definitely worth doing the maths on houses where you want bigger batteries and inverters, and remember it also lets you avoid the MCS costs too. I am guessing plug in solar is going to make it even more of a circus especially if they got 250,000 G98s submitted the month it goes legal 😎 Our setup actually has some grid tie with grid tie batteries and solar, and some non grid tie with other batteries/solar that runs the heatpumps and some other bits. It was the only way to make this big old building work within the allowed G99.

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The inverter size limitation is to do with failure cases with export limitation. If they calculate that the export limit fails, and the resultant voltage would exceed legal upper limits at your house, and your inverter voltage shutdown protections also fails, then they impose a choice: 1. Stipulate Inverter size limits, 2. Provide a quote to the solar installer for reinforce the DNO’s network so that it can accept the higher inverter size (often many thousands of pounds). At my house, I have an 8kw inverter with a 5kw export limit. When exporting 5kw, the voltage is about 247V. So there is some headroom between the export limit and the upper legal voltage. There are two a get out clauses though: 1. Install a 3.6kW inverter, but with 7kW Maximum Power Point Trackers. That enables you to hookup 7kw of solar, and at maximum power: 3.4kw can be fed to a dc coupled battery, even though the AC output is limited to 3.6kW. Sunsynk offers such an inverter. 2. Don’t connect your inverter to the grid. DNO’s only have jurisdiction over connections to their network. They have no jurisdiction over off grid systems. You could have an 8kw+ inverter supplying your house off grid. Then you can choose whether your house is connected to the grid, or your inverter, using a changeover switch. There’s no opportunity for export, or charge up with cheap overnight electricity though.

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The reason I'm asking is that I'm planning on having a lot of panels and inverter power and self consuming as much as possible. I'm planning on over capacity so that I can make the shoulder seasons (i.e. spring & autumn) mostly self-consumption too. I don't really care about the export - I'm guessing the rates will continue to fall until it's a waste of time.

 

 

 

 

[JohnMo]

Lots of panels on a G98 inverter, massive overclock is the way to go. Easy no permission needed, just a G98 notification.

 

Self consumption is fine in theory, in practice difficult especially in the summer, you just end with loads of hot water you can't use. Just go with Octopus and pay £250 and get the export (wish I did it 3 years ago), East Suffolk you will generate tonnes of energy even with a 3.68kW export limits.

 

My advise, self install as many panels as you can to stay within the max voltage limits of your inverter, it's cheap, spend £250 to get with octopus. Export everything you don't normally consume.

[Dillsue]

10 hours ago, Alan Ambrose said:

 Setting up a big non grid tie inverter and putting the house on that with the grid as an input (generator basically) lets you side step all the mess in the difficult cases.

This is basically an off grid setup with the inverter taking one or more energy sources to power the house. Intended to use batteries and PV with a generator as a backup. In terms of the inverter generating anything, and being regulated by the DNO, it only generates power to supply the house as so far there's no grid connected. Now swap the generator input for a grid connection and as far as the grid is concerned the inverter is only a load but no generation capacity on the point where the grid is connected.

 

10 hours ago, Alan Ambrose said:

it  also lets you avoid the MCS costs too

MCS isnt required for any installation works. If the video is suggesting otherwise then take it with a pinch of salt

 

10 hours ago, Alan Ambrose said:

 DNO’s only have jurisdiction over connections to their network. They have no jurisdiction over off grid systems. You could have an 8kw+ inverter supplying your house off grid. Then you can choose whether your house is connected to the grid, or your inverter, using a changeover switch. 

As stated use a changeover switch to choose if your house is supplied from the grid OR from an off grid system that the DNO doesn't regulate.

 

What's your concern about what is said above??

[Beelbeebub]

I get limiting the export for the reasons laid out in the video, but the idea of limiting the inverter seems to rest on the theory that the export limit might fail and the inverter pump out whatever it's maximum at that moment is. 

 

But that seems to assume that the export limit system (a current meter and some software) would fail. Irrc my system just shuts down if the current clamp isn't working. Surely the whole point of g100 export limit certification is to make system the design and implementation is as foolproof as possible. 

 

Moreover, if the DNO is worried that you 8kw inverter could lead to severe problems if it were to pump the full 32a or whatever instead of the 16a limit into the local grid, that implies the local grid is running very very close to it's margin, less than 16a in fact, which could easily be gobbled up tomorrow by a neighbour notifying a g98 install. 

 

What I'm getting at is: has anyone actually heard of a dno limiting the inverter size for a regular hybrid inverter install with g100 limit certification? 

[Dillsue]

1 hour ago, Beelbeebub said:

What I'm getting at is: has anyone actually heard of a dno limiting the inverter size for a regular hybrid inverter install with g100 limit certification? 

If a DNO does limit the inverter size then effectively they're saying they dont trust the ENA standards and/or the G100 certification/self certification process

[Beelbeebub]

1 hour ago, Dillsue said:

If a DNO does limit the inverter size then effectively they're saying they dont trust the ENA standards and/or the G100 certification/self certification process

Exactly, which makes a mockery of the whole idea of g100 certification. 

 

Maybe someone could bring out some sort of 2way breaker - 80/100a incoming (as per normal) but 16a outgoing (or whatever the dno says the limit is) that would provide an extra layer of protection. 

[Dillsue]

The other rationale for a DNO limiting inverter size could be customer tampering with G100 settings?? AFAIK G100 settings are supposed to be password protected with an installer/manufacturer password that the customer doesn't know. There's been several posts on here where people have said they'll lift the export limit above the DNOs approved limit as they have the installer password.

 

The battery inverter I've just installed has a single password that protects G100 settings and all "advanced" settings including TOU charge scheduling. Technically I shouldn't have access to the G100 settings but legitimately have access to the TOU settings so this inverter is poorly designed from a G100 compliance perspective.