| First some background, sorry for the long comment but I can see you need a bit of a primer before we get to your question: Transmission lines and generators such as solar panels and wind turbines work at very different voltages. Once you need to convert the extra step to convert from AC to DC or VV isn't a really big challenge. Solar panels output anywhere from 20 to 100V, these are ganged into strings and strings are then coupled to inverters to create relatively low voltage AC, or each panel has its own inverter (not very common in solar farms). Those inverters feed into a local parallel grid which is then stepped up to join the national grid using a feed line (typically 10 to 50 KV, depending on the size of the farm and the local grid). Very large solar farms can have their own local understation where the voltage is stepped up to long haul voltage. Sometimes there is co-generation with another source (such as solar/wind, solar/natural gas or some other combination). https://group.vattenfall.com/press-and-media/newsroom/2019/v... Wind Turbines usually have generators that output anywhere from 10KV to 50KV depending on the capacity and the manufacturer. This can be variable frequency current or, in a tightly grid coupled turbine it can be at the grid frequency (you can tell the difference from a distance because all of the turbines in a wind farm like that will move in lockstep with each other, this is a good indication that they are AC synchronized). At the base of every turbine you will find a an inverter and/or a step up transformer like with the solar farms. A typical turbine will do anything from 1 MW (which really is small these days, but which used to be state of the art not all that long ago) all the way up to 14 MW behemoths. https://www.ge.com/renewableenergy/wind-energy/offshore-wind... These are most impressive up close, to put it very mildly, think of an Eiffeltower but it rotates... HVDC transmisison lines themselves are super high technology and you're definitely not going to find these running from every Wind Turbine to the grid, what you will most likely find is a local, intermediate AC network from a bunch of wind turbines and/or a number of solar farms to a concentration point and then a much higher voltage line from there to the national grid. 'intermediate' for shorter connections is anywhere from 10 KV to 50 KV, and for longer interconnects up to several 100 KV, all the way up to 800 KV for the longest and most power carrying lines. The engineering behind all this stuff is super impressive. https://en.wikipedia.org/wiki/High-voltage_direct_current Then, to answer your question: AC suffers from something called the skin effect, it essentially means that only a small part of the cross section of a powerline carries current, effectively limiting the carrying capacity of the line to a fraction of its theoretical DC limit. So by using DC rather than AC for very long connections line losses can be minimized and much more power can be transferred through a line because those losses translate into heat generated in the line. So HVDC makes very good sense for the long haul links coupling remote areas. They might even make sense intercontinentally (though I'm a bit more skeptical about this after the pipeline attack on the NS pipelines, HVDC lines would be quite fragile and very difficult to repair after an attack). Note that you always have these losses, but the overhead of the AC->DC->AC conversion is such that it only makes sense for longer lines or lines carrying a very large amount of power. But even the shortest AC line suffers from that skin effect. I hope this answers your question. |