Expenses
Research and development expense. Research and development (“R&D”) expense includes: materials to build development and prototype units, cash and non-cash stock-based compensation and benefits for the engineering and related staff, expenses for contract engineers, fees paid to consultants for services provided, materials and supplies consumed, facility related costs such as computer and network services, and other general overhead costs associated with our research and development activities.
Research and development expense for the three months ended September 30, 2022 increased $11.5 million, or 69.0%, to $28.1 million, from $16.6 million for the three months ended September 30, 2021. The overall growth in R&D investment is commensurate with the Company’s future expansion into new markets, new product lines, acquisitions and varied vertical integrations.
Research and development expense for the nine months ended September 30, 2022 increased $34.5 million, or 91.7%, to $72.1 million, from $37.6 million for the nine months ended September 30, 2021. The overall growth in R&D investment is commensurate with the Company’s future expansion into new markets, new product lines, acquisitions and varied vertical integrations.
Selling, general and administrative expenses. Selling, general and administrative expenses includes cash and non-cash stock-based compensation, benefits, amortization of intangible assets and related costs in support of our general corporate functions, including general management, finance and accounting, human resources, selling and marketing, information technology and legal services.
Selling, general and administrative expenses for the three months ended September 30, 2022, increased $43.2 million, or 101.7%, to $85.6 million from $42.4 million for the three months ended September 30, 2021. This increase was primarily related to increased headcount, which resulted in increased salaries and stock-based compensation, as well as rebranding expenses.
Selling, general and administrative expenses for the nine months ended September 30, 2022, increased $155.8 million, or 146.1%, to $262.4 million from $106.7 million for the nine months ended September 30, 2021. This increase was primarily related to increased headcount, which resulted in increased salaries and stock-based compensation, as well as branding expenses.
Contingent consideration. The fair value of the contingent consideration is related to earnouts for the Giner ELX, Inc., United Hydrogen Group Inc, Frames, Applied Cryo and Joule acquisitions. The change in fair value for the three and nine months ended was $0 and $(2.6) million, respectively, primarily due to fair value remeasurements.
Interest income. Interest income primarily consists of income generated by our investment holdings, restricted cash escrow accounts, and money market accounts. Interest income for the three and nine months ended September 30, 2022 increased $9.3 million and $13.7 million, respectively, as compared to the three and nine months ended September 30, 2021. The increase is primarily related to the increase in interest rates during 2022.
Interest expense. Interest expense consists of interest expense related to our long-term debt, convertible senior notes, obligations under finance leases and our finance obligations. Interest expense for the three months ended September 30, 2022 decreased $0.5 million compared to the three months ended September 30, 2021, primarily related to a decrease in long-term debt and an increase in capitalized interest, offset by an increase in finance obligations. Interest expense for the nine months ended September 30, 2022 decreased $4.7 million compared to the nine months ended September 30, 2021, primarily related to a decrease in long-term debt and an increase in capitalized interest, offset by an increase in finance obligations.
Realized loss on investments, net. Realized loss on investments, net consists of the sales related to available-for-sale debt securities. For the three and nine months ended September 30, 2022, the Company had a loss of $0 and $1.3 million, respectively, of net realized loss on investments. For the three and nine months ended September 30, 2021, the Company had a gain of $0.3 million and $0.2 million, of realized loss on investments, net.