A manager at the GreenTech Energy Corporation claimed that the research costs for new solar panels should be funded by the government, arguing that the sales of solar panels are expected to be less profitable than those of other energy products. The manager supported this claim by stating that each solar panel is sold to a customer only once, while energy products like batteries are sold repeatedly to the same customers. Which one of the following, if true, most weakens the support offered by the manager for the claim concerning the sales of solar panels?