Explain these comments on a Gary Does Solar video?

[JohnMo]

13 minutes ago, Dave Jones said:

the problem with self install is no MCS paperwork. Octopus wouldnt accept any export from me (for payment) without it.

I just paid the £250 will break even in a year and still way cheaper than a mcs install.

[Dave Jones]

Just now, JohnMo said:

I just paid the £250 will break even in a year and still way cheaper than a mcs install.

 

i tried also, octopus refused without MCS cert. How did you manage it ?

[JohnMo]

The operators don't seem to understand the process. You have to go through a dedicated part of the website

https://octopus.energy/help-and-faqs/articles/export-without-mcs/

[-rick-]

50 minutes ago, joth said:

Fair point 🤣

What I was trying to say was it would be unnecessarily complex to try and design something elaborate into the standards requiring "intelligent" collaboration across a system of inverts communicating with each other, when you can achieve it within the existing pretty dumb standard.

 

100% though knowing this country the 'smart' solution requiring 24/7 internet connectivity is what will get proposed at some point.

[Beelbeebub]

1 hour ago, -rick- said:

 

This is exactly what's being proposed by the grid (see the link I posted earlier). Reducing the minimum acceptable voltage to 207V.

 

Modern equipment shouldn't really care about the voltage being that low (the minimum voltage in Europe is 207V and almost all electronics we have bought in the last 30 years have been designed to work in that market). Link suggests a 4% reduction in resistance heating output, slightly dimmer lights. Most tricky issues being non-inverter driven motors and UPSes with to high a brown-out setting (likely can be adjusted).

Yes, if the can widen the window by lowering the bottom it will help. 

 

Current UK is 240 +10/-6 ie 216 to 253

Europe is 230 +/-10 which is 207 to 253

 

I think our asymetric limit was fudge when we standardised with Europe and everyone actually stayed the same. 

 

Bu as you say - all modern equipment will function absolutely fine at lower voltage. 

 

There might be an issue with higher currents for constant power devices at the lower voltage. 

 

I noticed my inverter (solax) has a power based export limit. Eg 3.6kw whilst my DNO specified a current limit (16a).

 

The lower minimum voltage could mean those of us with power based limits will have to assume 207v ie 3.3kw rather than being able to set 3.6 or even 3.9kw.

[-rick-]

5 minutes ago, Beelbeebub said:

The lower minimum voltage could mean those of us with power based limits will have to assume 207v ie 3.3kw rather than being able to set 3.6 or even 3.9kw.

 

Would expect you to use the nominal voltage for these calculations. ie, 240V. Up to the network to be designed for the variance.

[-rick-]

Also, just thinking about the situation you'd be in if the voltage was 207V. It would mean that the local substation is under very heavy load from a local consumer and near tripping off. Therefore, the extra current produced by your inverter at that voltage might be the thing that prevents the grid from tripping.

 

An argument may be that the current limit protects the cables, but I would guess that it's the substation transformer that is the limiting factor in almost all locations. In fact the areas where you may see voltage dipping to near 207 are likely all rural with pole transformers and long lines. Likely meaning that a generator closer to the consumer may reduce the voltage drop in the lines and be even more beneficial.

[joth]

3 hours ago, -rick- said:

Likely meaning that a generator closer to the consumer may reduce the voltage drop in the lines and be even more beneficial

Yes! We talk a lot about renewables requiring grid reinforcement, but in many cases renewables *are* the grid reinforcement. Especially if a battery is also installed at the far end of that long bit of wet string. 

[Beelbeebub]

4 hours ago, -rick- said:

Also, just thinking about the situation you'd be in if the voltage was 207V. It <snip> in the lines and be even more beneficial.

Yes, although the problem might be that to achive 207 during a winters night with all the electric heaters on at the hypothetical remote farm, the output at the substation might need to be cranked up 249v

 

Obviously the farmer's near neighbour's solar isn't going to help then. 

 

It would help the farmer if he had low voltage when the sun was shining (say a big air con load) but the transformers are not automatic. They are mainly set and forget. An engineer needs to visit and physically move some contacts to change the voltage 

 

If the houses near the substation are all cranking out loads of power on a sunny day that is what will push the voltage over. 

 

All that said, some batteries at the farm would help as they would be able to reduce the load on the wires, thus reducing the current and voltage drop.  So whilst a 90a draw from the grid onky might drag the voltage down to 207, the 45a from grid and 45a from batteries wouldn't, so the transformer voltage could be set lower. 

 

As an aside, this "solar reduces load on wires" principle is why I think some of the panic over plug in solar is overblown.  I did some basic calculations and I think, for any correctly functioning socket circuit the 4a/800w plug in solar can produce isn't able to overload the cables and might even allow higher loads than the circuit breaker is set to without overloading the cables. 

 

Of course if there is a faulty or out of spec socket circuit, plug in solar might cause a problem, but at that point normal use would also cause the problem. 

 

[SteamyTea]

1 minute ago, Beelbeebub said:

All that said, some batteries at the farm would help as they would be able to reduce the load on the wires, thus reducing the current and voltage drop

Short term it may be cheaper to install some batteries, rather than change transformers.

I am sure someone at the DNOs has looked at that.

[Alan Ambrose]

@billt >>> My system is off grid and AC coupled using SMA inverters.

 

Is that totally off grid? You have generator back-up or something similar?

[SteamyTea]

On 28/04/2026 at 15:22, -rick- said:

Changing grid frequency is how the overall grid responds to load as frequency directly affects power generated due to the spinning generators that make up most of the grid.

While that is correct in a simple system i.e. one large generator and multiple variable loads, in a dynamic system, where there is intervention, the formula is not simple.

If I remember my electrical engineering correctly, rotational speed is proportional to voltage and as voltage lags current (current is infinite at zero voltage), a certain amount of variability makes a tiny difference.  It is only when generation equipment goes out of bounds that it become a problem i.e. a generator becomes a motor (though I am sure they have systems to stop this) or a generator slows too much and overheats.

We like to think that the grid has a very stable 50 Hz, sine wave, but in reality it is very messy with a mixture of frequencies and even some DC in it.

 

A quick look at Gridwatch shows that for the vast majority of the time (99.98%) the frequency is pretty stable between 99.99 Hz and 50.07 Hz).

Interestingly (to me anyway) is the extremes of low and high generation.  When demand is low, the frequency drops down for the mean, and when demand is high, it increases.

This is where intervention is happening most.

 

If we take the samples between 20000 MW and 40 MW (94.42% of demand), the mean frequency is 50 Hz, bang on the money (well to 2 decimal places).

 

The National Grid really is an engineering marvel and it costs us less than a quid a day.

[markc]

Grid frequency is rarely 0.2% above or below (+/- 0.5% is the statuary limit) so makes very little difference.

[SteamyTea]

41 minutes ago, markc said:

Grid frequency is rarely 0.2% above or below (+/- 0.5% is the statuary limit) so makes very little difference.

Yes, which is part of my arguement about using it to detect load, and then use it for local management.

I prefer to let they big boys, who knows what they are doing, manage that side of it.