Solar inverter shading scanning algorithm power consumption? - Page 1
Forum section: electronics / general

author: cj0
author_rank: Newbie
timestamp: August 19, 2021, 07:35:32 am
content: Solar inverters contain a maximum power point tracking (MPPT) algorithm, mostly some form of Perturb and Observe.Solar inverter manufacturers sometimes add enhancements for partial shaded situations. That is for cases where there are multiple local maximum power points (an I-V curve with more then one peak and a valley). SMA calls it ShadeFix (formerly known as Optitrac Global Peak), Fimer names the algo PowerGain.All these solar inverter partial shading algorithms do some for of I-V curve scanning. Thus at such a scanning moment, there is less energy produces.Who knows more about the "power consumption" of such algos in terms of lost production for situations when there is no partial shading?

author: Siwastaja
author_rank: Super Contributor
timestamp: August 19, 2021, 11:35:42 am
content: Well, shadows move slowly (minutes), and it's not a disaster if the system spends on local maximum for some dozen seconds. Panels itself do not store much charge, meaning you can change the current/voltage setpoint often to observe the change, like for example once for every mains cycle. For example, if you scan 10 different voltage setpoints, each scan lasting for 20ms, you are spending 200ms producing less than optimal power (say 50%). If this happens once a minute, the efficiency loss is 0.17%.Such quick napkin calculation is to show that if the manufacturer does not screw this up, it should be trivial to optimize the loss to negligible values. But obviously you can always mess things up, even in fairly simple cases.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 19, 2021, 01:04:14 pm
content: Isn't ShadeFix a PV optimizer, the difference from most PV optimizers is that only the panels affected by shading need one installed?

author: cj0
author_rank: Newbie
timestamp: August 25, 2021, 04:52:46 pm
content: Aside: shadows by clouds can move quickly (when the wind is strong). Though this mostly matters for large surface PV generators.I think that Power One (formerly owned by ABB, now Fimer) messes up their PowerGain. Power Gain does periodically scan the full MPPT range to find the absolute optimum power point and is enabled by default. According to marketing this scan happens within milliseconds.Having "Multiple Max Scan Period - Value" set at 30 seconds, I was astonished that "within milliseconds scanning" is clearly visible when measuring power generation even at 1 second intervals (1Hz):Note: around 16:35:30 "Multiple Max Scan" a.k.a. PowerGuard was disabled.To calculate the power loss, the graph of one 5 second dip was used:Power before scan: 21,65 kW Power after scan: 21,45 kW Average power estimate without scan: 21,55 kWActual measured power:second 1: 18,55 kWsecond 2: 19,17 kWsecond 3: 18,88 kWsecond 4: 16,45 kWsecond 5: 19,81 kWaverage: 92,87 ÷ 5 = 18,574 kWAverage loss during 5 seconds: 2,976 kW.Total loss: 14,88 kWs = 4,1333 Wh every 40 seconds = 372 Wh per hour.A guesstimate: 4,5 kWh per day for a day with a production of 12 hours (equivalent to about 260 kWh). Thus 1.7% power lost having PowerGuard enabled when there is no partial module shading. Thus 10 times more production/efficiency losses then you would have guessed.