Solar Farms vs Roof Tops


I am wondering why people choose to start a large farm rather than attempt to set up a series of roof top farms?

Does this purely have to do with scale, or are there particular efficiencies related to one or the other that makes it better for harnessing the sun's power?




  • System2
    System2 Posts: 6,290 admin
    Difference Between Consumer and Industrial?


    Is there a big difference between consumer solar panels and industrial farm ones?

    I've read somewhere that "...1 square inch (6.5 cm2) of solar cells can generate about 70 milliwatts of electricity,..."

    Is this universal, or are industrial ones more/less efficient?


  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Solar Farms vs Roof Tops

    Solar Roofs, up the efficency factor maybe 20% or more, over a Farm. The Roof does not have the transmission line losses that exist for long distance power transfer. As fossil fuel becomes more expensive, more solar and wind is likely to "fill the gaps", at least in the daytime. This will be more advantageous in the sunnier/winder areas, where a cloud passing overhead won't black out a city. There may be a need for more local storage (to allow for transient clouds).
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
    Re: Solar Farms vs Roof Tops

    I merged your two discussions into one thread since they are both related and the answers/topic overlap.

    Your first question regarding Commercial vs Residential panels and if they are the same... Yes and No...

    The basic panels are the same. Glass with some sort of solar PV material behind the glass.

    There are different classes of materials... The more efficient (watts/sq.) tend to be mono or poly-crystalline silicon cells wired together. Good Efficiencies (~12-18%) of solar energy is converted to electricity.

    Another type is the Amorphous Cell panel... Similar to crystalline silicon panels but tend to be less efficient (~8-10% or so).

    The silicon panels tend to be around $3 per watt in larger quantities and the amorphous panels tend to be around $1-$2 per watt.

    If you have lots of open space, a large installation may choose to use the "less expensive per watt" panels--but there are drawbacks--you need more mounting, wiring, cleaning because you need ~2x the surface area for the same rating.

    Then there is the whole solar thermal way of generating electricity... Using thermal panels/arrays to (usually) run a steam boiler/generator. These are more complex (in-terms of mechanics) but are probably in the 20-30+% efficiency range and can be cheaper to install. However there are other issues (need water to run cooling towers, typically have mechanical tracking of some sort, etc.).

    Solar at Home vs Commercial Farm? To be honest, much of the economics is driven by tax credits, rebates, and subsidies (US GOV website).

    To a degree, residential solar PV installations will be encouraged/tolerated until they become a significant share of the market (in California, solar PV is probably 0.5-1.0% of the total grid supply.

    Once they hit some magic number (10%+?)--they will become both an economic force (i.e., whole in which tax monies and rate payers' monies are dumped into subsidizing others) and an engineering issue (hundreds of thousands small, uncontrolled, generators feeding/overloading/destabilizing the overall grid).

    By the way, typically we talk about Watts per Sq Foot/Meter as a descriptoin of solar energy--Typically, the maximum solar energy is around 1,000 watts per sq. meter...

    And Power=Voltage*Current -- So, voltage, by itself, is not the best way to discuss solar power.


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset