GetOffYourGas wrote: SageBrush wrote:
This is why I dislike "solar farms". There are many better uses for that land (including keeping it as wild habitat!) then large arrays of solar panels. Instead, solar should be focused on rooftop installations - that way the land has true dual-use. We are a long way from saturating the usable roof space.
Now a real impact of solar is the energy-intensive production process. I was told that the EROEI for my panels was almost 10 years. It may have gotten better since, but it will always be greater than zero for any energy generation.
EROI is about 2 years.
I've seen photos of ground mounts in Europe where they continue to use the land for agriculture.
Both good news. I'm impressed if we've really improved EROEI by a factor of 5 in only 7 years.
I've never seen a ground mount system in the US, where the land is used for anything else. I'm not saying it doesn't exist, but it is the exception in both the Northeast and the Southwest where I have seen large solar farms. I still think rooftop is our best option, since the buildings (and roofs) already exist.
Rooftop gives the best power density and lowest environmental impact, but the amount of it is strictly limited. Smil's book on power density includes the results of a study of rooftop solar potential in the Tokyo Metro area, which is currently the world''s largest megacity and representative of forecasts for where most of the world's urban population growth will be concentrated between now and 2050, and looking at all available roofspace in that area, it's orientation etc., IIRR the conclusion was that no more than about 10% of the metro area's demand could be generated using rooftop PV only. Germany has the highest % of rooftop solar in the world (and 44.3 GW total PV, both roof and ground mount, as of July), owing to extensive subsidies (which have been and are being gradually reduced). Per Smil the size of the rooftop systems have been increasing, with more and more going on MUDs and commercial buildings rather than detached homes.
Unfortunately I had to return the book to the library (interlibrary loan), so I don't have the exact figures handy and am working from memory. Just to remind everyone who's interested in what the actual power densities of deployed renewables are, I highly recommend it (like I do all of Smil's books I've read, especially those on energy transitions and technological change):
Power Density: A Key to Understanding Energy Sources and Uses
Re ground mounts, parking lots show how PV can allow concurrent usage, although whether the typical monopole supports count as ground mounting is arguable:
The Design Basics for Solar Parking Lots You Need to Know
Still, if there's enough room to park cars under the panels there's enough room for grazing/horticulture/silviculture (xmas tree farms etc.) if the amount of light getting through and around the panels is adequate for photosynthesis, assuming the concrete pads for the pole bases are kept small. The tradeoff for allowing concurrent use for such mounts is that the tilt angle is normally kept quite low, reducing the capacity factor. Providing water to clean panels in desert areas may be a bigger issue.
Re EROEI, ten years seems far too long, as even a decade or two back the number was around 3-4 years IIRC. However, even if it were 10 years, as the panels will be useful for 40 or more (with decreased output, to be sure) you're still well ahead.