While land isn't free, solar doesn't need land, it needs sun. By which I mean there's an awful lot of free rooftop space available, and a lot of space which would benefit from a roof (like car parks at the mall).
So it's not competing for land against say buildings or agriculture.
Now sure, the owner of the roof may want some rent etc, but that really doesn't alter the cost of the energy, it just spreads the benefit.
Commercial rooftop is somewhere between but still more expensive than a solar farm. Rooftop has the advantages that it delivers where the load is, and there are often subsidies available, plus some marketing kudos. But if just considering land cost by installing rooftop instead of solar farms is usually not an economic tradeoff.
Utility-scale solar PV comes in anywhere from $24/MWh to $96/MWh
Unsubsidized residential rooftop PV has an LCOE between $117/MWh and $282/MWh,
the LCOE of community and commercial and industrial (C&I) solar ranges between $49/MWh and $185/MWh.
When factoring in federal tax subsidies under the US Inflation Reduction Act, including domestic contest provisions, rooftop PV comes in at $74/MWh to $229/MWh, and community/C&I rooftop PV at $32/MWh to $155/MWh.
It is hard to find good comparative figures with similar assumptions (e.g. incentives, location, year), but the above give a ballpark.
Why are we choosing rooftops instead of a central location for solar, like we do for all other types of electricity generation?
At first sight, it seems economies of scale would make it easier to have one company handle a solar power station, rather than now having to pay expensive home solar panel loans and maintain them.
>> Why are we choosing rooftops instead of a central location for solar, like we do for all other types of electricity generation?
solar is different to say coal, because the economics of home-generation, and grid generation are not miles apart. In other words it's not like I can have a coal-fired power station at home, but I can have solar panels. Up to now electricity generation has been constrained to large-scale (hydro, coal, nuclear etc). The advent of solar, and to a lesser extend small-scale wind and hydro, makes local generation more accessible.
>> rather than now having to pay expensive home solar panel loans and maintain them.
Solar maintenance is minimal. (Again, not like a turbine generator.) Loans are a function of capital. It takes capital to populate a home roof, and capital to build a power plant. If you have no capital then the point is moot. As an individual I have enough capital to fund my solar system without loans. (I get about a 14% return on that capital.) I don't have enough capital to fund a power station.
Other benefits of home generation include more resilience should the grid fail. So for example, after a storm, power lines may be down, but I get electricity during the day. That's a bonus though, not the main driver.
So to answer your question - it's not either or, it's both. There's a lot of roof-top solar in my city (measured in gigawatts), there's also solar farms generating power.
Lastly' I'll point out that distribution _from_ my house is cheaper than from a plant, because I generate a few spare kw, and the wire already coming into my hose is sufficient for that. So no new (grid) hardware is required.
> In other words it's not like I can have a coal-fired power station at home, but I can have solar panels.
Not that it matters to your point, but you can, they're just awful — there many reasons why everyone moved away from heating homes with open fireplaces.
(My current apartment in Berlin is old enough to have a chimney, but there's no unit attached to it; likewise the house I grew up in back in the UK has a chimney, but it was bricked off since before I could remember, possibly before I was born).
There's relatively little economy of scale in placing solar panels (compared to other energy sources). A lot of the scale advantage has already been achieved by mass producing identical panels.
The only people pushing rooftop solar are the ones who haven't thought about it very hard. Roofs are expensive. We build them to A) hold up the most likely loads and B) keep our water. Putting a bunch of solar panels on them makes them worse at both, especially when we have a lot of unused land. I mean monumental amounts.
I guess the viability of roofs depend on the construction techniques in your area. In my experience roof's here have plenty of extra load availability, and I'm not sure what effect the panels would have on water.
In my area something like 5GW of solar has been installed on rooftops, and that has moved the needle.
And of course land availability varies a lot by country.
Geez yes I meant keep out water but I'm on mobile and not very careful! Yes, if we're talking about Hong Kong or somewhere with extremely high urbanization maybe the calculus is different, but that's a political issue more than a technical one. Every city on earth has land not utilized for living or heavy ag within a very reasonable distance.
So it's not competing for land against say buildings or agriculture.
Now sure, the owner of the roof may want some rent etc, but that really doesn't alter the cost of the energy, it just spreads the benefit.