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Employee Benefit Plans | 12 Months Ended
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Dec. 31, 2023
Employee Benefit Plans |
Employee Benefit Plans | 19. Employee Benefit Plans ​ 2011 and 2021 Stock Option and Incentive Plan ​ On May 12, 2011, the Company’s stockholders approved the 2011 Stock Option and Incentive Plan (the “2011 Plan”). The 2011 Plan provided for the issuance of up to a maximum number of shares of common stock equal to the sum of (i) 1,000,000, plus (ii) the number of shares of common stock underlying any grants pursuant to the 2011 Plan or the Plug Power Inc. 1999 Stock Option and Incentive Plan that are forfeited, canceled, repurchased or are terminated (other than by exercise). The shares were issued pursuant to stock options, stock appreciation rights, restricted stock awards and certain other equity-based awards granted to employees, directors and consultants of the Company. No further grants may be made under the 2011 Plan after May 12, 2021. In July 2021, the 2021 Stock Option Incentive Plan (the “2021 Plan”) was approved by the Company’s stockholders. The 2021 Plan provides for the issuance of up to a maximum number of shares of common stock equal to the sum of (i) 22,500,000 shares, plus the 473,491 shares remaining under the 2011 Plan as of the effective date of that the 2021 Plan, plus (iii) shares underlying any awards under the 2021 Plan and the 2011 Plan that are forfeited, canceled, cash-settled or otherwise terminated, other than by exercise. In June 2023, the Company’s stockholders approved an increase in the number of shares of the Company’s common stock authorized for issuance under the 2021 Plan to 51,400,000. Stock-based compensation costs recognized, excluding the Company’s matching contributions of $12.1 million to the Plug Power Inc. 401(k) Savings & Retirement Plan and quarterly Board compensation, were approximately $150.0 million, $169.8 million and $72.4 million for the years ended December 31, 2023, 2022, and 2021, respectively, in connection with the 2011 and 2021 Plans. ​ The components and classification of stock-based compensation expense, excluding the Company’s matching contributions to the Plug Power Inc. 401(k) Savings & Retirement Plan and quarterly Board compensation, were as follows (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | Year ended December 31,
​ | 2023 | ​ | 2022 | ​ | 2021
Cost of sales | $ | 11,079 | ​ | $ | 7,259 | ​ | $ | 1,965
Research and development | ​ | 9,532 | ​ | ​ | 6,369 | ​ | ​ | 5,983
Selling, general and administrative | ​ | 129,387 | ​ | ​ | 156,127 | ​ | ​ | 64,443
​ | $ | 149,998 | ​ | $ | 169,755 | ​ | $ | 72,391
​ Option Awards ​ The Company issues options that become exercisable based on time and/or market conditions and are classified as equity awards. ​ Service Stock Options Awards ​ To date, service-based stock option awards (“Service Stock Options”) granted under the 2011 and 2021 Plans have vesting provisions ranging from one to three years in duration and expire ten years after issuance. Service Stock Options for employees issued under these plans generally vest in equal annual installments over three years and expire ten years after issuance. Service Stock Options granted to members of the Board generally vest one year after issuance. The Company estimates the fair value of the Service Stock Options using a Black-Scholes valuation model, and the resulting fair value is recorded as compensation cost on a straight-line basis over the option vesting period. Key inputs and assumptions used to estimate the fair value of the Service Stock Options include the grant price of the award, the expected option term, volatility of the Company’s stock, an appropriate risk-free rate, and the Company’s dividend yield. Estimates of fair value are not intended to predict actual future events or the value ultimately realized by employees who receive equity awards, and subsequent events are not indicative of the reasonableness of the original estimates of fair value made by the Company. The assumptions made for purposes of estimating fair value under the Black-Scholes model for the 6,849,689, 3,261,724, and 1,942,335 Service Stock Options granted during years ended December 31, 2023, 2022, and 2021, respectively were as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | December 31, | ​ | December 31, | ​ | December 31,
​ | ​ | 2023 |  | 2022 | ​ | 2021
Expected term of options (years) | ​ | 5 | ​ | 5 | ​ | 3-5
Risk free interest rate | ​ | 3.40% - 4.69% | ​ | 1.26% - 4.34% | ​ | 0.61% - 1.23%
Volatility | ​ | 80.02% - 92.55% | ​ | 73.38% - 85.97% | ​ | 72.46% - 76.60%
​ There was no expected dividend yield for the Service Stock Options granted. ​ The estimated stock price volatility is derived from the Company’s actual historic stock prices over the expected term, which represents the Company’s best estimate of expected volatility. ​ The following table reflects the Service Stock Option activity for the year ended December 31, 2023: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | ​ |  | Weighted |  | ​ | ​
​ | ​ | ​ | ​ | Weighted | ​ | Average | ​ | ​ | ​
​ | ​ | ​ | ​ | Average | ​ | Remaining | ​ | Aggregate
​ | ​ | ​ | ​ | Exercise | ​ | Contractual | ​ | Intrinsic
​ | ​ | Shares | ​ | Price | ​ | Terms | ​ | Value
Options outstanding at December 31, 2022 | ​ | 12,078,269 | ​ | $ | 14.34 | ​ | ​ | 7.57 | ​ | $ | 42,835
Options exercisable at December 31, 2022 | ​ | 6,661,969 | ​ | ​ | 8.41 | ​ | ​ | 6.40 | ​ | ​ | 42,182
Options unvested at December 31, 2022 | ​ | 5,416,300 | ​ | ​ | 21.63 | ​ | ​ | 9.01 | ​ | ​ | 653
Granted | ​ | 6,849,689 | ​ | ​ | 7.08 | ​ | ​ | — | ​ | ​ | —
Exercised | ​ | (716,581) | ​ | ​ | 2.25 | ​ | ​ | — | ​ | ​ | —
Forfeited | ​ | (875,015) | ​ | ​ | 26.27 | ​ | ​ | — | ​ | ​ | —
Options outstanding at December 31, 2023 | ​ | 17,336,362 | ​ | $ | 11.37 | ​ | ​ | 7.86 | ​ | $ | 11,391
Options exercisable at December 31, 2023 | ​ | 8,288,944 | ​ | ​ | 11.84 | ​ | ​ | 6.18 | ​ | ​ | 7,250
Options unvested at December 31, 2023 | ​ | 9,047,418 | ​ | $ | 10.94 | ​ | ​ | 9.39 | ​ | $ | 4,141
​ The weighted average grant-date fair value of the Service Stock Options granted during for the years ended December 31, 2023, 2022 and 2021 was $4.88, $13.39, and $19.80 per share, respectively. The total intrinsic fair value of Service Stock Options exercised during the years ended December 31, 2023, 2022, and 2021, was approximately $5.3 million, $15.1 million, and $115.5 million. The total fair value of Service Stock Options vested during the years ended December 31, 2023, 2022, and 2021 was $33.1 million, $22.6 million, and $11.0 million, respectively. ​ Compensation cost associated with Service Stock Options represented approximately $31.5 million, $27.5 million, and $17.4 million of the total share-based payment expense recorded for the years ended December 31, 2023, 2022 and 2021, respectively. As of December 31, 2023 and 2022, there was approximately $53.1 million and $59.8 million of unrecognized compensation cost related to Service Stock Options to be recognized over a weighted average remaining period of 2.10 years. ​ Performance Stock Option Awards ​ The Company grants performance-based stock options awards (“Performance Stock Options”) under the 2021 plan to the Chief Executive Officer and certain other executive officers. These Performance Stock Options are subject to both performance-based conditions, tied to the achievement of stock price hurdles, and time-based vesting; therefore, a Monte Carlo Simulation was utilized to determine the grant-date fair value with the associated expense recognized over the requisite service period. Up to one third (1/3) the Performance Stock Options will vest and become exercisable on each of the first three anniversaries of the grant date, provided that the volume weighted average price of the Company’s common stock during any 30 consecutive trading day period in the three-year performance period following the grant date of the stock options (“VWAP”) equals or exceeds certain levels. ​ The Company granted 6,405,000 performance-based options in May 2023. Options that meet the performance-based conditions will vest 1/3 on each for the first three anniversaries of the grant date. The performance based conditions are as follows, 33.33% of the performance stock options will be deemed to have satisfied the performance-based condition and will be eligible to be exercised if the VWAP equals $9.84; an additional 33.33% of the options will be deemed to have satisfied the performance-based condition and will be eligible to be exercised if the VWAP equals $11.81; and the remaining 33.34% of the options will be deemed to have satisfied the performance-based condition and will be eligible to be exercised if the VWAP equals or exceeds $13.77. There will be no interpolation for the Performance Stock Option granted on May 18, 2023 if the VWAP falls between any two stock price hurdles, unless in the event of a change in control. ​ Failure to achieve any of the stock price hurdles applicable to a Performance Stock Option during the three-year performance period will result in the applicable options not becoming exercisable. The Performance Stock Options have a maximum term of seven years from the grant date. ​ Key inputs and assumptions used to estimate the fair value of Performance Stock Options include the grant price of the awards, the expected option term, VWAP hurdle rates, volatility of the Company’s stock, an appropriate risk-free rate, and the Company’s dividend yield. Estimates of fair value are not intended to predict actual future events or the value ultimately realized by employees who receive equity awards, and subsequent events are not indicative of the reasonableness of the original estimates of fair value made by the Company. ​ The following table presents key assumptions used to estimate the fair value of the Performance Stock Option awards granted in 2023, 2022 and 2021: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, | ​ | ​ | December 31, | ​ | ​ | December 31,
​ | ​ | 2023 | ​ | ​ | 2022 | ​ | ​ | 2021
Remaining VWAP performance period (years) | ​ | 3 | ​ | ​ | 3 | ​ | ​ | 3
Risk- free interest rate | ​ | 3.60% | ​ | ​ | 3.10% | ​ | ​ | 1.12%
Expected volatility | ​ | 75.00% | ​ | ​ | 75.00% | ​ | ​ | 70.00%
Closing stock price on grant date | $ | 7.87 | ​ | $ | 26.38 | ​ | $ | 26.92
​ For the 2022 and 2021 Performance Stock Option awards, the expected term was determined based on term features within the grants that decreases the overall grant pool if options are exercised early (0-3 years) reducing the maximum future payout and the Company’s historical experience with employee early exercise behavior. There was no such early exercise option for the 2023 Performance Stock Option award. The estimated stock price volatility was derived from the Company’s actual historic stock prices over the past five years, which represents the Company’s best estimate of expected volatility. ​ The following table reflects the Performance Stock Option activity for the year ended December 31, 2023. Solely for the purposes of this table, the number of shares is based on participants earning the maximum number of shares underlying the Performance Stock Options (i.e., 200% of the target number of shares). ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | ​ |  | Weighted |  | ​ | ​
​ | ​ | ​ | ​ | Weighted | ​ | Average | ​ | ​ | ​
​ | ​ | ​ | ​ | Average | ​ | Remaining | ​ | Aggregate
​ | ​ | ​ | ​ | Exercise | ​ | Contractual | ​ | Intrinsic
​ | ​ | Shares | ​ | Price | ​ | Terms | ​ | Value
Options outstanding at December 31, 2022 | ​ | 15,520,000 | ​ | $ | 26.87 | ​ | 5.81 | ​ | $ | —
Options exercisable at December 31, 2022 | ​ | 1,391,000 | ​ | ​ | 26.9 | ​ | 5.7 | ​ | ​ | —
Options unvested at December 31, 2022 | ​ | 14,129,000 | ​ | ​ | 26.86 | ​ | 5.82 | ​ | ​ | —
Granted | ​ | 6,405,000 | ​ | ​ | 7.87 | ​ | 6.38 | ​ | ​ | —
Exercised | ​ | — | ​ | ​ | — | ​ | — | ​ | ​ | —
Forfeited | ​ | — | ​ | ​ | — | ​ | — | ​ | ​ | —
Options outstanding at December 31, 2023 | ​ | 21,925,000 | ​ | $ | 21.32 | ​ | 5.27 | ​ | $ | —
Options exercisable at December 31, 2023 | ​ | 2,782,000 | ​ | ​ | 26.92 | ​ | 4.73 | ​ | ​ | —
Options unvested at December 31, 2023 | ​ | 19,143,000 | ​ | $ | 20.50 | ​ | 5.35 | ​ | $ | —
​ The weighted average grant-date fair value of Performance Stock Options granted during the years ended December 31, 2023, 2022 and 2021 was $4.32, $9.73 and $12.70, respectively. There were no Performance Stock Options exercised during the years ended December 31, 2023, 2022 and 2021. The total fair value of the performance stock options that vested during the years ended December 31, 2023, 2022 and 2021 was $20.8 million, $20.8 million and $0, respectively. ​ As of December 31, 2023, there were 5,661,000 unvested shares underlying Performance Stock Options for which the employee requisite service period has not been rendered but are expected to vest. The aggregate intrinsic value of these unvested Performance Stock Options was $0 as of December 31, 2023. The weighted average remaining contractual term of these unvested Performance Stock Options was 5.97 years as of December 31, 2023. ​ Compensation cost associated with Performance Stock Options represented approximately $64.0 million, $95.7 million and $27.8 million of the total share-based payment expense recorded for the years ended December 31, 2023, 2022 and 2021, respectively. As of December 31, 2023, there was approximately $34.2 million of unrecognized compensation cost related to Performance Stock Options to be recognized over a weighted average remaining period of 1.55 years. ​ Restricted Common Stock and Restricted Stock Unit Awards ​ Restricted common stock and restricted stock unit awards generally vest in equal installments over a period of one to three years. Restricted common stock and restricted stock unit awards are valued based on the closing price of the Company’s common stock on the date of grant, and compensation cost is recorded on a straight-line basis over the vesting period. ​ A summary of restricted common stock and restricted stock unit activity for the year ended December 31, 2023 is as follows (in thousands except share amounts): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ | ​ | Weighted |  | Aggregate
​ | ​ | ​ | ​ | Average Grant Date | ​ | Intrinsic
​ | ​ | Shares | ​ | Fair Value | ​ | Value
Unvested restricted stock at December 31, 2022 | ​ | 6,276,376 | ​ | $ | 21.56 | ​ | $ | 77,639
Granted | ​ | 4,131,193 | ​ | ​ | 11.55 | ​ | ​ | —
Vested | ​ | (2,851,637) | ​ | ​ | 20.40 | ​ | ​ | —
Forfeited | ​ | (823,048) | ​ | ​ | 23.60 | ​ | ​ | —
Unvested restricted stock at December 31, 2023 | ​ | 6,732,884 | ​ | $ | 15.66 | ​ | $ | 30,298
​ The weighted average grant-date fair value of the restricted common stock and restricted stock unit awards granted during the years ended December 31, 2023, 2022, and 2021, was $11.55, $20.28, and $32.35, respectively. The total fair value of restricted common stock and restricted stock unit awards that vested for the years ended December 31, 2023, 2022, and 2021 was $58.2 million, $36.7 million, and $76.0 million, respectively. ​ The Company recorded expense associated with its restricted common stock and restricted stock unit awards of approximately $54.5 million, $46.5 million, and $27.2 million, for the years ended December 31, 2023, 2022, and 2021, respectively. Additionally, for the years ended December 31, 2023, 2022, and 2021, there was $84.1 million, $110.3 million, and $74.5 million, respectively, of unrecognized compensation cost related to restricted common stock and restricted stock unit awards to be recognized over a weighted average remaining period of 1.99 years. ​ Included in the total unvested restricted common stock and restricted stock units as of December 31, 2023, there were 375,000 restricted common stock units outstanding with a performance target. The Company recorded expense associated with the restricted common stock units with a performance target of $1.1 million for the year ended December 31, 2023. Additionally, as of December 31, 2023 there was $3.1 million of unrecognized compensation cost related to the restricted common stock units outstanding with a performance target to be recognized over the weighted average period of 2.58 years. ​ 401(k) Savings & Retirement Plan ​ The Company offers a 401(k) Savings & Retirement Plan to eligible employees meeting certain age and service requirements. This plan permits participants to contribute 100% of their salary, up to the maximum allowable by the Internal Revenue Service regulations. Participants are immediately vested in their voluntary contributions plus actual earnings or less actual losses thereon. Participants are vested in the Company’s matching contribution based on years of service completed. Participants are fully vested upon completion of three years of service. During 2018, the Company began funding its matching contribution in a combination of cash and common stock. The Company issued 1,473,662 shares of common stock, 442,056 shares of common stock, and 90,580 shares of common stock pursuant to the Plug Power Inc. 401(k) Savings & Retirement Plan during the years ended December 31, 2023, 2022, and 2021, respectively. ​ The Company’s expense for this plan was approximately $12.1 million, $9.2 million, and $4.3 million for the years ended December 31, 2023, 2022, and 2021, respectively. ​ Non-Employee Director Compensation ​ Each non-employee director is paid an annual retainer for his or her service, in the form of either cash or stock compensation. This annual retainer is paid in four quarterly installments. The Company granted 59,323, 21,886, and 12,258 shares of common stock to non-employee directors as compensation for the years ended December 31, 2023, 2022 and 2021, respectively. All common stock issued related to this annual retainer that is paid quarterly, is fully vested at the time of issuance and is valued at fair value on the date of issuance. The Company’s share-based compensation expense in connection with non-employee director quarterly compensation was approximately $452 thousand, $390 thousand and $372 thousand for the years ended December 31, 2023, 2022, and 2021, respectively.

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