Computing stuff tied to the physical world

Solar PV production

In Hardware on Jun 2, 2013 at 00:01

This is the sort of graph I’ve been waiting for – now that there is more sun, at last:

Screen Shot 2013-05-29 at 00.28.30

(the steep increases and decreases are probably due to shadows from the other roofs)

All values were obtained from the SB5000TL inverter as 5-minute readouts over Bluetooth:

  • total delivered power on AC mains – 29 kWh for the entire day
  • total incoming power on the east-facing roof (12 panels)
  • total incoming power on the west-facing roof (10 panels)

The east-facing panels are actually slight to the north, and the west-facing ones slightly to the south. Which might explain the similar peak production levels despite the different number of panels, i.e. different “insolation” angles.

The peak values are not the highest I’ve seen so far. A cold day with light clouds recently pushed the maximum to over 4700 watts. But that was a rare event. These values are fine with me – I find such levels of solar PV output in a location well up north on this planet (52°N, to be precise) pretty amazing, in fact.

  1. WOW! Beautiful, tale telling graphs!In PV-world speak, production is often expressed as kW/kWp to factor in different numbers of panels, see user graphs at e.g. at sonnenertrag. kWp is the peak production in Watt (watt?) of the set under perfect circumstances. Cumulative kWh/kWp then shows if the west panels can catch up with the east panels for total day production. A challenge in your graphing app, I assume, as it not ony needs two series, but also two y-axes (kWh/kWp, kW/kWp). Looking forward to a sunny week!

    • Two axes is supported by Dygraphs – just haven’t coded it in yet.

  2. Cold sunny days are the best, solar cells are very temperature dependant (which is why solar cells in the desert are not a great idea). Nice graphs!

    • I suppose one could use some of the energy for a bit of forced air cooling, in such climates?

  3. These are “spot” watt values for the different inputs of your SMA transformer .. right? And not the agregrated kWh generate in the 5 minutes since the last readout converted back to watts.. correct? (because I do not see those figures via SMA Explorer)

    And the Watt from the AC side? is that kWh generate in the last 5 minutes, converted back to Watt or also Watt Spot values? And taken from the SMA transformer of from your kWh counter downstairs in the meter cabinet?


    • Yep – spot values, hence approximate. But the total figure is the aggregated value from the SMA inverter, hence should be accurate. See also this recent post.

  4. “well up north on this planet” Heh – coming from 63N I still think you are pretty far south.

  5. @jcw Forced air cooling doesn’t work out, you need the surrounding air to be cooler, which is part of the problem. In the end it’s far more effective to use other simpler technologies, like heating liquids with mirrors, where the ambients heat works for you rather than against you. And as a nice side-effect you get distilled water as a by-product, which can be quite valuable in a desert area.

    The long and short of it is that solar cells are only part of the solution.

    FWIW, I picked this up from the online course Solar Cells, Fuel Cells & Batteries from Standford University.

  6. I notice a 10% drop in output with temperature (which, funnily enough, ties up with my panel’s spec) and I wish there was some way of keeping the panels cool in the summer….a combined PV and water panel I wonder?

  7. You can of course cool the panel with water and use the heat byproduct

    These are hybrid panels that produce hot water and more electricity.

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