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Design & Install PV Systems with Batteries
- 3 day practical course & online content
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Grid-Connected PV Systems Design & Install Eighth Edition
$176/ inc GST
- Comprehensive handbook over 500 pages
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Hi there, I’ve been reading your technical paper on Power Factor and Grid-Connected Photovoltaics, and it’s been an excellent resource for clearing up some confusion I had around the topic. I’m just wondering if you can also provide an insight into what happens with the relationship between kVA, kVAR and PF when the inverter is exporting power to the grid? (i.e. the output is greater than the demand of the building)
Hi Gareth, Thanks for your question in regards to the power factor technical paper. We appreciate your comments for the same.
For answering your question on the relationship of kVA, kVAr and pf I will use the metering convention for energy meters. Click here for graphic.
In the export mode, the active power would be negative and the reactive power could be either positive , negative or unity (depending on the inductive, capacitive or resistive nature of the generation). Injecting energy into the grid with a non-unity power factor needs to be checked with the local supply authority. Most local supply authorities required the exports to be at unity power factor and hence the utility side power factor gets affected. So that’s why a lot of supply authorities are keen on getting zero exports and having people install zero export devices for certain size systems. The power factor (pf = kW/KVA) can be considered negative for the export mode as the active power is negative for the export mode. Note that kVA or the apparent power is just the vector sum of active and reactive power and hence doesn’t have a sign associated with it.
Why do we have to spend time learning how to match modules and inverters etc? Surely there is computer software that does all that for you!
Yes, there is computer software available to assist the designer in his task, however without access to the base code you have no idea how the software programmer has performed the various calculations and if they have taken into account all the various Australian Standards, Clean Energy Council and local supply authority requirements. Also, most of this software is put out by inverter manufacturers and only allows you to design systems around their particular offerings. Far better to know how to do the calculations your self, if speed is desired, setup a spreadsheet with all the necessary calculations so you can see and manually check the results as necessary or update to changing requirements.