@BjoernK, responding to your question on this thread 
Your usecase would be perfectly covered with this node as well. I’d like to add some “best practice” on additional configuration on that:
Prioirities:
You should arrange the 3 shelly devices in a order so that the 2 kW has the highest priority, followed by 1kW, followed by 0.5 kW. This would make Opportunity Loads try to enable the “most expensive consumer” first, skipping to the lower priority rods, if it does not yet fit into the budget.
This would give you the best possible resolution to maximize self-consumption there, as you could heat with 0.5, 1, 1.5, 2, 2.5, 3 and 3.5 kW in a staggered way.
Minimum durations:
You generally can set them up as you prefer and feel comfortable, heating rods are not very sensitive to frequent on/off behaviour, but if arranging the consumers as suggested, you should not pick the same values for every device.
Reasoning: When a solar shortage occurs, consumers will be turned off in reverse-priority order. If all have the same rest-duration, that would lead to the consumer with the lowest priority finishing its rest-duration, first. If solar then is already restored, it may be turned on again, just to have a higher priority consumer becoming available 5 seconds later - and causing a switch of these 2 again.
Rather than that, I would - along with above priorities - go with something like: 30s for the 2kW, 45s for the 1 kW and 60s for the 0.5kW element. This would ensure, that if all 3 are turned off at the same time, the highest priority one is also available again, first.
(But that is just my experience, you may find other settings to work better based on your system / expectation)