For large loads, at $0.32 to $0.50/kWh in Hawaii it is now much more economical to disconnect from the grid entirely, unless you have some limiting factor that would prohibit large scale low cost mounting of a huge number of 1.65 x 1.0 (60-cell) or 1.99 x 1.0 meter (72-cell) size high efficiency PV panels. The ROI can be well under 6 years.
In this context I am not referring to lower-cost, but lower efficiency thin films, nor triple junction or concentrator type cells...
High efficiency = 5W STC rating per 156mm cell or better. More W per square meter. For example you can get cheap 72-cell panels that are rated at 320W, the best ones which are exactly the same dimension will be rated at 370, 375 or 380W. That is for typical modules which measure exactly 1.99 x 0.99 meters.
In large-scale solar, but not large enough to use a huge land area and low-cost thin films, there are two standard sizes of panels. 60-cell 1.65 x 0.99m and 72 cell 1.99 x 0.99 meter. These are standardized to work with a wide variety of different mounting systems.
There are many different grades and quality levels of polycrystalline and mono crystalline silicon solar panels.
The very best monocrystalline Si panels are made by Sunpower, but they have a significant price premium as compared to a pallet load that I could buy right now with my Visa card of qty 20, 370W panels. The commodity 370W are 65% of the price but only a few % less efficient.
Those are best in class research cell efficiency for each technology type. The silicon cell based panels you can buy now are 17.5-22% unless you are spending a lot of money.
Special thin films cells in a lab may be 23%, what you can buy economically for a grid scale utility power plant is more like 14-15%.
This is at the very top end of the thin film market for what is now commercially available, and is 17%. See datasheet.
