Grid code rules

Been down a bit of a rabbit hole lately thinking about this, ever since I started planning to tie my boat's Victron Multiplus setup into a shore power arrangement that might eventually involve some grid export.

The European grid code situation is genuinely fascinating — and a little alarming. Germany's been setting the pace for years, but Spain's recent requirements have caught my eye. It made me realise how patchwork this all feels across the continent, and how easily UK installers and DIYers can get caught out, especially post-Brexit when we've drifted away from some of the EU frameworks but haven't always replaced them with anything cleaner.

For those of us with hybrid setups — I'm thinking boat, cabin, EV charging all potentially talking to each other — the G98/G99 engineering recommendations from Energy Networks Association are the UK's answer to this. But honestly, how many people here have actually read them cover to cover? I'll admit I've skimmed them at best.

What I'm specifically curious about is:

• Frequency response settings — are you manually configuring these on your Victron kit, or leaving defaults?
• Anti-islanding protection — how many DIY installs actually have this properly sorted?
• DNO notification — have you gone through the formal process, or is it all sitting in a grey area?

I suspect a lot of off-grid setups that could export occasionally are operating in a regulatory no-man's-land. Not necessarily dangerously, but not formally compliant either.

Would love to hear from anyone who's navigated the G98/G99 process properly, or who's looked at what Spain and Germany are doing and drawn lessons for UK installs.

@DaiHenderson the grid code stuff is genuinely a rabbit hole — G98 vs G99 depending on export capacity is where most people get tripped up first. For shore power arrangements it's worth checking whether you're actually exporting at all, because if the Multiplus is set to PowerAssist mode only and never pushes back to the grid, you might sidestep a lot of the compliance headache entirely.

My static caravan setup is pure off-grid so I've never had to deal with it directly, but I looked into it when I briefly considered a grid-tie element. DNO notification requirements caught me off guard — some people think it's optional until they try to sell the property or boat.

What's your export limit looking like? That'll determine which route you're actually down.

@DaiHenderson my shepherd's hut taught me that the moment you start saying "might eventually involve the grid," HMRC, DNO, and three different regulatory bodies materialise out of thin air specifically to ruin your weekend.

For the boat side specifically though — worth checking whether your marina DNO even has a consistent stance on G98/G99 for floating dwellings, because I've seen it vary wildly depending on which engineer picks up the phone.

Victron's ESS assistant does handle the anti-islanding requirements automatically which is one less headache — but getting your G99 application past the DNO without an approved installer sign-off is a different beast entirely.

@BatteryPaula that HMRC point genuinely hadn't crossed my mind and now I'm spiralling slightly 😅

@DaiHenderson I'm in a similar boat (literally — narrowboat with a Multiplus-II). What I found confusing early on was whether the DNO cares at all if you're purely consuming from shore power with no export whatsoever. From what I've gathered, if the Multiplus is set to only charge and never push back onto the shore supply, you might sidestep a lot of the G98/G99 headache entirely.

Has your setup actually got any generation source that could theoretically export, or is it batteries-only? That seems to be the crux of where the grid code obligations actually kick in for most of us. My solar panels are what complicated things on my end — without them I think it'd be far simpler.

@DaiHenderson one thing worth flagging that nobody's mentioned yet: the Multiplus II has G98/G99 compliance built in via firmware, but you need to explicitly enable the relevant grid code through VEConfigure or VictronConnect — it doesn't just activate automatically. Caught me out when I first set up my garden office feed arrangement.

Also worth checking whether your DNO classifies the boat as a "generating unit" the moment you have any export capability configured, even if you're not actively exporting. That distinction affects which notification pathway you're on before you even start the G98/G99 conversation.

The MCS and DNO registration paperwork is fairly straightforward once you know which forms apply, but the sequencing matters — DNO notification before commissioning, not after.