Why not split the solar array in half ? take care of the max power input in your inverter but it would have less losses than shunts.
Splitting the array is not an option because of how it is wired. The other limitation is the charger/inverter only has 2 mppt tracking inputs and both are in use.
The power loss in a shunt that clamps voltage to 550V in this array would be minimal since the voltage could only exceed this in very vary circumstances. The main likely scenario is during a sudden sunny episode after a storm in cold weather. In that situation, the mppt tracker would likely have reduced the load and allowed the voltage to rise to a relatively high level with low solar generation. A sudden large increase in sun could cause the array voltage to exceed 550V and approaching the 640V open circuit voltage before the mppt tracker increases loading. This is about the only circumstance in which the shunt would dissipate energy. I'm uncertain exactly how much energy the shunt would have to dissipate in that situation to clamp the voltage to under 550V, but I'm guessing it should be well under 20% of the array wattage rating so 1 kw at worst.
So, I'm considering a couple strings of 50 watt zeners in parallel. I would use at least 2 strings for redundancy. Another possibility to reduce dissipation in the zeners is to include a light bulb/heating element in the string. One concern is voltage accuracy of the zeners since typical high power zeners only have 5% tolerance.
Posted on: May 14, 2025, 03:04:49 15:04 - Automerged
It is curious that some particular zener models of similar wattage are much less expensive than others. For example, this 1N3336B Zener, 68 V, 50 W, DO-5 is $5 from a distribution.
https://www.newark.com/solid-state/1n3336b/zener-diode-50w-68v-do-5/dp/10P4952The zener's in series don't have to all be the same voltage. I imagine having one that is the rated voltage for a DC fan to cool the heatsink they would be mounted on. Another problem is I don't have a power supply that operates up to 600V to test this. Any idea to produce a relatively high wattage 600-700V power supply may be with a variable transformer feeding a step up transformer and bridge rectifier/capacitor. Since the 600V is well below the breakdown voltage of typical small transformers, it should be possible to use an ordinary 120VAC to 24VAC step-down transformer in reverse. To get 650VDC, I would need 460VAC so a ratio of about 4 operating from 120VAC utility voltage.