Powerwall Installation - UK - Site Import Limits (100A DNO fuse)?

[hooky]

A question about Gateway 2 Site Import Limits - what should this be (have been) set to by the installer? (UK based, so US answers probably don't apply)

We've just had 2 PWs installed at our home a couple of days ago. We're on a 100A DNO fuse, but have quite a few high-demand units, a couple of Model S's (sharing a 50A connection), a few heat pumps, induction heater etc etc.

Even though we've got 8kW solar, with Octopus Intelligent we're currently paying less to import electricity overnight than we get from Scottish Electric via SEG for export during the day, so I've got charge from grid enabled (which we will definitely utilise in the winter anyway to heat the house during).

First night of charging the PWs yesterday, and checking this morning I can see that even though there was a 6 hour window for them to charge up, they went full pelt at 5kW each for an hour - and during that time we hit a max demand of 24kW (~109A at the 220V we were then receiving). Thankfully the DNO fuse and none of the consumer fuses blew, but I thought that during installation the Gateway should have been set such that it would not draw more Amps than the supply is suited for via "Site Import Limits"?

I've given the installers a call, but their technician is currently off sick so nothing they will look at until next week.

I'll be able to manage this in the meantime by bringing down the charge rate on the EVs, and managing other loads, but just wondering if this was an oversight by the installers? Also, as they've had a quite a few minor snags/issues along the solar/PW installation road, I've lost a bit of trust in them, so I was wondering if anyone knows what import limit they should be putting on the Gateway when they do log in next week? I don't want them to hamstring us with too low a limit, or go too high forgetting about voltage drop.

Thanks for any guidance!

 

[BGbreeder]

There are ways for your tech to set the import limits on the Powerwalls, but I'm not sure that is the way that I would go. In the interests of flexibility, I would be inclined to alter the charge rate on your vehicles on the thought that a) that preserves a rapid charge up of the batteries for use later in the day, and b) you have control over which vehicle charges first/more. I'm just thinking with winter and variable weather, it probably makes fiscal sense to have the powerwalls at full charge first. Here in the US, they are rolling out charge on solar for Tesla vehicles, but there are third party solutions that might help you.

A largely electric home with two electric vehicles would be a squeeze on a 100A on this side of the pond without some active management. I suspect that practice will make perfect as they say, and I would be inclined to buy some extra fuses for the learning phase. (Do you have fuse wire fuses?)

All the best,

BG

 

[hooky]

Hi BG,

Thanks for your thoughts - the 100A sort of is equivalent to 200A for the US as our voltage is nominally 230 so can provide 23kW draw (more like 21kW with voltage drop). We've been managing ok with all the demand to date, but effectively with the PWs I'm now trying to squeeze all the grid draw into a 6 hour window to get the best rates (the overnight right is 1/4 of the day rate) and use solar/PWs for the other 18 hours.

I'm not an electrician, but effectively we have two 100A fuses - one that the electricity company (DNO) have control of which is before the meter (their responsibility), and then one between the meter and our consumer unit (our responsibility). If my fuse goes, we can deal with that ourselves, but if the DNO's blows we have to call them up and wait for them to show - it's this that I'm really hoping to avoid during the learning curve; I'm currently drawing up a spreadsheet to plan my load balancing accordingly!

Cheers

H

 

[BGbreeder]

Good luck.

Blowing a DNO fuse would be annoying, though since you have Powerwalls, potentially not that bad as by the sound of it you aren't three phase, which is another degree of complexity. I'm not an electrician either, but I have dealt with British wiring and electrical setups.

Just FWIW: Your feed is a little less half of what is typical here. While we are 120VAC, we are fed from the grid at 240VAC, which is 120V to ground. Confusing, I know. So, a modern house here is 200A @240, aka 48kW. Here large homes in hot areas are fed with multiples of that.

All the best,

BG

 

[Vines]

It sounds like your installer should set a site import limit of around 18-20 kW. Usually the site import limit is set to 80% of the breaker or fuse rating around here. It may be that your fuse is actually 100% rated but I do not know those specific details about your grid.

 

[hooky]

Good luck.

Blowing a DNO fuse would be annoying, though since you have Powerwalls, potentially not that bad as by the sound of it you aren't three phase, which is another degree of complexity. I'm not an electrician either, but I have dealt with British wiring and electrical setups.

Just FWIW: Your feed is a little less half of what is typical here. While we are 120VAC, we are fed from the grid at 240VAC, which is 120V to ground. Confusing, I know. So, a modern house here is 200A @240, aka 48kW. Here large homes in hot areas are fed with multiples of that.

All the best,

BG

Thanks for the correction - so there's still a 240V PD, it's just split between a positive 120V and a negative 120V rather, than 240V to 0, interesting. I guess if you touch a live wire at least it's "only" a 120V shock. Every day is a learning day!

 

[BGbreeder]

Thanks for the correction - so there's still a 240V PD, it's just split between a positive 120V and a negative 120V rather, than 240V to 0, interesting. I guess if you touch a live wire at least it's "only" a 120V shock. Every day is a learning day!

Yes, that is the original logic. Of course fatal levels are now known to start at 48V or so, so not perfect, but better than some other parts of the world. Generally, we phrase the two 120V AC sources as being different phases (set 180 degrees apart), though confusingly referred to as single phase by many (in contrast to three phase, commonly occurring in a 208V phase to phase and 120VAC to ground, and very uncommon in residential settings). There are lots of other variants. Here is just the list Tesla Powerwalls support.

All the best,

BG

 

[LampyDave]

A question about Gateway 2 Site Import Limits - what should this be (have been) set to by the installer? (UK based, so US answers probably don't apply)

We've just had 2 PWs installed at our home a couple of days ago. We're on a 100A DNO fuse, but have quite a few high-demand units, a couple of Model S's (sharing a 50A connection), a few heat pumps, induction heater etc etc.

Even though we've got 8kW solar, with Octopus Intelligent we're currently paying less to import electricity overnight than we get from Scottish Electric via SEG for export during the day, so I've got charge from grid enabled (which we will definitely utilise in the winter anyway to heat the house during).

First night of charging the PWs yesterday, and checking this morning I can see that even though there was a 6 hour window for them to charge up, they went full pelt at 5kW each for an hour - and during that time we hit a max demand of 24kW (~109A at the 220V we were then receiving). Thankfully the DNO fuse and none of the consumer fuses blew, but I thought that during installation the Gateway should have been set such that it would not draw more Amps than the supply is suited for via "Site Import Limits"?

I've given the installers a call, but their technician is currently off sick so nothing they will look at until next week.

I'll be able to manage this in the meantime by bringing down the charge rate on the EVs, and managing other loads, but just wondering if this was an oversight by the installers? Also, as they've had a quite a few minor snags/issues along the solar/PW installation road, I've lost a bit of trust in them, so I was wondering if anyone knows what import limit they should be putting on the Gateway when they do log in next week? I don't want them to hamstring us with too low a limit, or go too high forgetting about voltage drop.

Thanks for any guidance!

I have been doing some research about this recently. Our system is Intelligent Octopus, 80A DNO cartridge fuse, 2 x PW2, 1 x MyEnergi Zappi charger & Eddi immersion heater. Our DNO won't go above 80A fuse, and to be honest, the voltage drop when we're at full load is significant enough (drops from 237V at no load to 220V at 75A) that it would be unwise to fuse any higher without running a new feed and that's going to be Pricey...

The Myenergi system (Zappi charger) has a wired grid coil and will limit to a set current - and that is how we've been running for the last 12 months. However, because it's the charger that's limiting it has meant the car doesn't get a 'full' charge overnight. For instance, if the PWs are charging at 10kW, the dishwasher at (say) 2kW and the rest of the house at 1kW then there's only about 4-5kW left (depending on voltage) left for the car out of the 80A.

After some to and fro with Tech Support, I am now aware that the Powerwall Gateway can have a 'Site Import Limit' set (as you mention in your post). That is set in kw instead of amps (which is a pity, but ho hum), but it has now been set at 17kW for our system. Tonight is the first evening that I've tested it with everything on, and sure enough the Powerwalls are charging at a reduced rate (about 8kW / 4kW each) to keep the import down to 17kW - but the car is charging at 'full' speed. The Powerwalls will still be fully charged well within the off-peak period, and the car isn't being 'throttled'. Result happiness

If your voltage goes to a minimum of 220V when under max load then 95 amps x 220 volts = 20.9kW. If it dips lower than that then re-calc with the lowest voltage and you should be all good. Obviously (especially as it's a newly installed system) it's a conversation to be had with your installer once they're back with you.

I don't know whether it's 'normal' to set the Site Import Limit during installation - there wasn't one set on our system until a few days ago.