Induction cooktop wants to draw power from grid when solar fully available

Hi all,

I have a 3 kWp grid-tied system with Huawei SUN2000-3KTL-L1 inverter and Huawei LUNA2000 5 kW/5 kWh battery.

A few days ago we changed our regular electric cooktop with an induction cooktop and when it's running it wants to draw a certain amount of power from the grid, even though the panels are at full output midday and the battery is full as well. So it does it at night, too. Battery full but it wants to rely on the grid instead. It's usually 200 W to 500 W from the grid and only the rest it will take from solar (or battery, or both). Say if the load is 1500 W, it will only draw 1000 W from the inverter. Regular electric cooker used to draw all 1500 W from the inverter.

I know regular electric cooktop was a fully resistive load and I have read that induction cooktops can show this kind of behavior with solar inverters since their load profile is quick ON/OFFs, much different from electric cooktop. So I guess every time it does its quick ON/OFFs, inverter inertia is not sufficient for the 1000-2000 W load and instead it simply gets power from the high inertia grid.

Do you think this is what's happening here? And if it is, which parameters of the inverter I might experiment with, if any? Like active/reactive power change gradients, or some other power parameter? Or should I just leave it alone as this is normal behavior with certain solar inverters and induction cooktops?

Thanks

Will the inverter do off-grid backup? Try turning the grid off and see if it works. What’s the breaker rating on the cooktop supposed to be?

Now you’ve made me nervous!

wpns said:

Now you’ve made me nervous

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Me too..An induction cooktop was going to be my next project. I hope I don't have to wait for a heat pump version. /s

wpns said:

Will the inverter do off-grid backup? Try turning the grid off and see if it works. What’s the breaker rating on the cooktop supposed to be?

Now you’ve made me nervous!

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SUN2000 is by default an anti-islanding inverter, if you turn the grid off, it will shutdown. But it has an offgrid mode which you could enable but that's not what I want as I do need the grid sometimes. I did try it once though a few months back, it provided offgrid power from panels and battery. I suppose if I enabled it again, cooktop would have no option but to draw everything from the inverter. But again not my preferred setup, I'm not ready to go completely offgrid.

Cooktop is supposed to be on a 16A breaker, and it is. Why is that relevant?

bt77 said:

SUN2000 is by default an anti-islanding inverter, if you turn the grid off, it will shutdown. But it has an offgrid mode which you could enable but that's not what I want as I do need the grid sometimes. I did try it once though a few months back, it provided offgrid power from panels and battery. I suppose if I enabled it again, cooktop would have no option but to draw everything from the inverter. But again not my preferred setup, I'm not ready to go completely offgrid.

Cooktop is supposed to be on a 16A breaker, and it is. Why is that relevant?

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Don't think the intent was to go off grid, only to try it to trouble shoot.

I had this issue in general with my Sol-Ark inverter. At high draws, some grid was being used. Turned out I had my CTs attached to the opposite pins. But, as you had your other range working properly, I doubt that's the issue.

That's really strange. I suspect it has to do with the cooktop switching on and off quickly.
I have 0 issues with mine but I'm not selling back to the grid only using it for backup (0 export).

Have you tried running it on the highest setting? This should stop the frequent switching on and off, I know it's not a solution but would prove the theory it's the fast switching causing the problem.

42OhmsPA said:

That's really strange. I suspect it has to do with the cooktop switching on and off quickly.
I have 0 issues with mine but I'm not selling back to the grid only using it for backup (0 export).

Have you tried running it on the highest setting? This should stop the frequent switching on and off, I know it's not a solution but would prove the theory it's the fast switching causing the problem.

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If it's constant draw, it's not the hit that's doing it. I get spikes with my heat pump starting, but it goes back to normal.

I read elsewhere of this problem. Supposedly turning on a light (oven?) Solves the problem. Sounds wierd to me, but electical gadgets are filled with gremlins to me.

42OhmsPA said:

That's really strange. I suspect it has to do with the cooktop switching on and off quickly.
I have 0 issues with mine but I'm not selling back to the grid only using it for backup (0 export).

Have you tried running it on the highest setting? This should stop the frequent switching on and off, I know it's not a solution but would prove the theory it's the fast switching causing the problem.

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I just did Boiled some water at full power.

2500 W load, 1000 W from panels and 1500 W from battery, no grid.

So yeah, I think the ON/OFF theory stands. It could be an inertia problem when it switches on so draws from grid. Probably after a few seconds it draws all from inverter but then the cooker does another OFF-ON, some hundreds of watts from grid again, and so on.

If you are on grid, it does not have to do a super precise job of matching demand to allow your equipment to function. Different story off grid, if it can’t ramp fast enough stuff stops working

Is the average energy zero from grid or is it not able to correct that over time? How is your net energy consumption billed by the power company? Often there is some averaging interval where the net energy is computed over and then translates to credits and charges.

Cooking is not that much energy FWIW. On my $.45/kwh I don’t think it’s worth my time to worry about other than for electrical engineering education reasons. What is the worst case cost concern on your bill? EDIT: Did you confirm your mental model of how bill calculation is done is correct? And my other question above of whether it achieves net zero energy despite lagging feeds into this more. It is just a matter of software programming to achieve this even with slower responding hardware

bt77 said:

I just did Boiled some water at full power.

2500 W load, 1000 W from panels and 1500 W from battery, no grid.

So yeah, I think the ON/OFF theory stands. It could be an inertia problem when it switches on so draws from grid. Probably after a few seconds it draws all from inverter but then the cooker does another OFF-ON, some hundreds of watts from grid again, and so on.

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Yeah, software control loop to balance with the grid is probably too slow, probably not much you can do about it other than live with it. I kniw EG4 18Kpv has a ‘fast zero export’ function, but that doesn’t help you.

bt77 said:

Cooktop is supposed to be on a 16A breaker, and it is. Why is that relevant?

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Just wondering how the peak draw of the appliance might match the inverter rating. Looks like you are OK plus or minus imbalance, but it looks like software control loop as above.

zanydroid said:

If you are on grid, it does not have to do a super precise job of matching demand to allow your equipment to function. Different story off grid, if it can’t ramp fast enough stuff stops working

Is the average energy zero from grid or is it not able to correct that over time? How is your net energy consumption billed by the power company? Often there is some averaging interval where the net energy is computed over and then translates to credits and charges.

Cooking is not that much energy FWIW. On my $.45/kwh I don’t think it’s worth my time to worry about other than for electrical engineering education reasons. What is the worst case cost concern on your bill? EDIT: Did you confirm your mental model of how bill calculation is done is correct? And my other question above of whether it achieves net zero energy despite lagging feeds into this more. It is just a matter of software programming to achieve this even with slower responding hardware

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I agree. At the end of the day power of 400 W for 10-15 seconds means pretty much nothing in terms of energy, which is used for the bill calculation. I mean 400 W for 15 seconds is about 1.666 Wh Even if you had 1000 of these intervals in a month, then the total energy would be 1.666 kWh. Energy costs like €0.40/kWh for me. So yeah, I guess I will ignore it.

Thanks for all the replies.