Table:
|  |  | Years Ended |  |  | Change |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
| (Dollars in thousands) | 2019 | 2018 | 2017 | 2019 over 2018 |  | 2018 over 2017 |  |
| Production start-up | $45,915 | $90,735 | $42,643 | $(44,820) | (49)% | $48,092 | 113% |
| % of net sales | 1.5% | 4.0% | 1.4% |  |  |  |  |
Paragraphs:
Production start-up
Production start-up expense consists primarily of employee compensation and other costs associated with operating a production line before it is qualified for full production, including the cost of raw materials for solar modules run through the production line during the qualification phase and applicable facility related costs. Costs related to equipment upgrades and implementation of manufacturing process improvements are also included in production start-up expense as well as costs related to the selection of a new site, related legal and regulatory costs, and costs to maintain our plant replication program to the extent we cannot capitalize these expenditures. In general, we expect production start-up expense per production line to be higher when we build an entirely new manufacturing facility compared with the addition or replacement of production lines at an existing manufacturing facility, primarily due to the additional infrastructure investment required when building an entirely new facility.
The following table shows production start-up expense for the years ended December 31, 2019, 2018, and 2017:
During 2019, we incurred production start-up expense at our new facility in Lake Township, Ohio. We also incurred production start-up expense at our second facility in Ho Chi Minh City, Vietnam in early 2019. During 2018, we incurred production start-up expense for the transition to Series 6 module manufacturing at our facilities in Kulim, Malaysia and Ho Chi Minh City, Vietnam. We also incurred production start-up expense for the transition to Series 6 module manufacturing at our facility in Perrysburg, Ohio in early 2018.
Question:
When will production start-up expense be higher?
Answer: In general, we expect production start-up expense per production line to be higher when we build an entirely new manufacturing facility compared with the addition or replacement of production lines at an existing manufacturing facility, primarily due to the additional infrastructure investment required when building an entirely new facility.