Solar panels of the same size may produce variable amounts of electricity - this discrepancy arises from variations in the functioning age of the solar cells, the quality of the solar cells, and with what technology they were produced. Early solar cells, for example, are not quite as efficient as modern solar cells, so you'll find that with a trusted solar panel manufacturer, quality increases as the technology involved becomes more advanced and precise.
As another example, two identical solar cells are purchased. One is left in storage and the other has been in use for three years. Solar panels have an effective lifespan of about 20 to 25 years, and their value and wattage output decrease steadily over time. The solar cell that has been in storage will be more valuable than one that has been actively converting sunlight to electricity for a long time.
In summary, although two solar panels may seem identical, there are a number of other factors you need to take into consideration. Just because a given solar cell is more expensive per square centimeter than another solar cell, it does not mean that the second one is a bargain. Quality, age, and technology all play a role in the cost of the solar cell.