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Ameresco Inc. 2017 EMPLOYEE STOCK PURCHASE PLAN as amended The purpose of this
2017 Employee Stock Purchase Plan (this “Plan”) is to provide eligible employees
of Ameresco Inc. (the “Company”) and certain of its subsidiaries with
opportunities to purchase shares of the Company’s Class A common stock, $0.0001
par value per share (the “Common Stock”), commencing at the time set forth in
the Plan. Subject to adjustment under Section 15 hereof, the number of shares of
Common Stock that have been approved for this purpose is 200,000 shares of
Common Stock. This Plan is intended to qualify as an “employee stock purchase
plan” as defined in Section 423 of the Internal Revenue Code of 1986, as amended
(the “Code”), and the regulations issued thereunder, and shall be interpreted
consistent therewith. 1. Administration. The Plan will be administered by the
Board of Directors of the Company (the “Board”) or by a Committee appointed by
the Board (the “Committee”). The Board or the Committee has authority to make
rules and regulations for the administration of the Plan and its interpretation
and decisions with regard thereto shall be final and conclusive. 2. Eligibility.
All employees of the Company and all employees of any subsidiary of the Company
(as defined in Section 424(f) of the Code) designated by the Board or the
Committee from time to time (a “Designated Subsidiary”), are eligible to
participate in any one or more of the offerings of Options (as defined in
Section 9) to purchase Common Stock under the Plan provided that: (a) they are
customarily employed by the Company or a Designated Subsidiary for more than
twenty (20) hours a week and for more than five (5) months in a calendar year;
(b) they have been employed by the Company or a Designated Subsidiary for at
least six (6) months prior to enrolling in the Plan; and (c) they are employees
of the Company or a Designated Subsidiary on the first day of the applicable
Plan Period (as defined below). No employee may be granted an Option hereunder
if such employee, immediately after the Option is granted, owns 5% or more of
the total combined voting power or value of the stock of the Company or any
subsidiary. For purposes of the preceding sentence, the attribution rules of
Section 424(d) of the Code shall apply in determining the stock ownership of an
employee, and all stock that the employee has a contractual right to purchase
shall be treated as stock owned by the employee. The Company retains the
discretion to determine which eligible employees may participate in an offering
pursuant to and consistent with Treasury Regulation Sections 1.423- 2(e) and
(f). 1

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3. Offerings. The Company will make two offerings in a twelve month period
(“Offerings”) to employees to purchase stock under this Plan. Offerings will
begin each June 1 and December 1, or the first business day thereafter (such
dates, the “Offering Commencement Dates”). Each Offering Commencement Date will
begin a six (6) month period (a “Plan Period”) during which payroll deductions
will be made and held for the purchase of Common Stock at the end of the Plan
Period. The Board or the Committee may, at its discretion, choose a different
Plan Period of not more than twelve (12) months for Offerings. 4. Participation.
An employee eligible on the Offering Commencement Date of any Offering may
participate in such Offering by completing and forwarding either a written or
electronic payroll deduction authorization form to the employee’s appropriate
payroll office at least ten (10) days prior to the applicable Offering
Commencement Date. The form will authorize a regular payroll deduction from the
Compensation received by the employee during the Plan Period. Unless an employee
files a new form or withdraws from the Plan, his or her deductions and purchases
will continue at the same rate for future Offerings under the Plan as long as
the Plan remains in effect. The term “Compensation” means the amount of money
reportable on the employee’s Federal Income Tax Withholding Statement, excluding
overtime, shift premium, incentive or bonus awards, allowances and
reimbursements for expenses such as relocation allowances for travel expenses,
income or gains associated with the grant or vesting of restricted stock, income
or gains on the exercise of Company stock options or stock appreciation rights,
and similar items, whether or not shown or separately identified on the
employee’s Federal Income Tax Withholding Statement, but including, in the case
of salespersons, sales commissions to the extent determined by the Board or the
Committee. 5. Deductions. The Company will maintain payroll deduction accounts
for all participating employees. With respect to any Offering made under this
Plan, an employee may authorize a payroll deduction in any percentage amount (in
whole percentages) up to a maximum of fifteen (15)% of the Compensation he or
she receives during the Plan Period or such shorter period during which
deductions from payroll are made. The Board or the Committee may, at its
discretion, designate a lower maximum contribution rate. The minimum payroll
deduction is such percentage of Compensation as may be established from time to
time by the Board or the Committee. 6. Deduction Changes. An employee may
decrease or discontinue his or her payroll deduction once during any Plan
Period, by filing either a written or electronic new payroll deduction
authorization form. However, an employee may not increase his or her payroll
deduction during a Plan Period. If an employee elects to discontinue his or her
payroll deductions during a Plan Period, but does not elect to withdraw his or
her funds pursuant to Section 8 hereof, funds deducted prior to his or her
election to discontinue will be applied to the purchase of Common Stock on the
Exercise Date (as defined below). 7. Interest. Interest will not be paid on any
employee accounts, except to the extent that the Board or the Committee, in its
sole discretion, elects to credit employee accounts with interest at such rate
as it may from time to time determine. 8. Withdrawal of Funds. An employee may
at any time prior to the close of business on the fifteenth business day prior
to the end of a Plan Period and for any reason permanently draw 2

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out the balance accumulated in the employee’s account and thereby withdraw from
participation in an Offering. Partial withdrawals are not permitted. The
employee may not begin participation again during the remainder of the Plan
Period during which the employee withdrew his or her balance. The employee may
participate in any subsequent Offering in accordance with terms and conditions
established by the Board or the Committee. 9. Purchase of Shares. (a) Number of
Shares. On the Offering Commencement Date, the Company will grant to each
eligible employee who is then a participant in the Plan an option (an “Option”)
to purchase on the last business day of such Plan Period (the “Exercise Date”)
at the applicable purchase price (the “Option Price”) up to that number of
shares of Common Stock determined by multiplying $2,083 by the number of full
months in the Plan Period and dividing the result by the closing price (as
determined below) on the Offering Commencement Date; provided, however, that no
employee may be granted an Option which permits his or her rights to purchase
Common Stock under this Plan and any other employee stock purchase plan (as
defined in Section 423(b) of the Code) of the Company and its subsidiaries, to
accrue at a rate which exceeds $25,000 of the fair market value of such Common
Stock (determined at the date such Option is granted) for each calendar year in
which the Option is outstanding at any time; and, provided, further, however,
that the Committee may, in its discretion, set a fixed maximum number of shares
of Common Stock that each eligible employee may purchase per Plan Period which
number may not be greater than the number of shares of Common Stock determined
by using the formula in the first clause of this Section 9(a) and which number
shall be subject to the second clause of this Section 9 (a). (b) Option Price.
The Board or the Committee shall determine the Option Price for each Plan
Period, including whether such Option Price shall be determined based on the
lesser of the closing price of the Common Stock on (i) the first business day of
the Plan Period or (ii) the Exercise Date, or shall be based solely on the
closing price of the Common Stock on the Exercise Date; provided, however, that
such Option Price shall be at least 85% of the applicable closing price. In the
absence of a determination by the Board or the Committee, the Option Price will
be 95% of the lesser of the closing price of the Common Stock on (i) the first
business day of the Plan Period or (ii) the Exercise Date. The closing price
shall be (a) the closing price (for the primary trading session) on any national
securities exchange on which the Common Stock is listed or (b) the average of
the closing bid and asked prices in the over-the-counter-market, whichever is
applicable, as published in The Wall Street Journal or another source selected
by the Board or the Committee. If no sales of Common Stock were made on such a
day, the price of the Common Stock shall be the reported price for the next
preceding day on which sales were made. (c) Exercise of Option. Each employee
who continues to be a participant in the Plan on the Exercise Date shall be
deemed to have exercised his or her Option at the Option Price on such date and
shall be deemed to have purchased from the Company the number of whole shares of
Common Stock reserved for the purpose of the Plan that his or her accumulated
payroll deductions on such date will pay for, but not in excess of the maximum
numbers determined in the manner set forth above. 3

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(d) Return of Unused Payroll Deductions. Any balance remaining in an employee’s
payroll deduction account at the end of a Plan Period will be automatically
refunded to the employee. 10. Issuance of Certificates. Certificates
representing shares of Common Stock purchased under the Plan may be issued only
in the name of the employee, in the name of the employee and another person of
legal age as joint tenants with rights of survivorship, or (in the Company’s
sole discretion) in the name of a brokerage firm, bank, or other nominee holder
designated by the employee. The Company may, in its sole discretion and in
compliance with applicable laws, authorize the use of book entry registration of
shares in lieu of issuing stock certificates. 11. Rights on Retirement, Death or
Termination of Employment. If a participating employee’s employment ends before
the last business day of a Plan Period, no payroll deduction shall be taken from
any pay then due and owing to the employee and the balance in the employee’s
account shall be paid to the employee. In the event of the employee’s death
before the last business day of a Plan Period, the Company shall, upon
notification of such death, pay the balance of the employee’s account (a) to the
executor or administrator of the employee’s estate or (b) if no such executor or
administrator has been appointed to the knowledge of the Company, to such other
person(s) as the Company may, in its discretion, designate. If, before the last
business day of the Plan Period, the Designated Subsidiary by which an employee
is employed ceases to be a subsidiary of the Company, or if the employee is
transferred to a subsidiary of the Company that is not a Designated Subsidiary,
the employee shall be deemed to have terminated employment for the purposes of
this Plan. 12. Optionees Not Stockholders. Neither the granting of an Option to
an employee nor the deductions from his or her pay shall make such employee a
stockholder of the shares of Common Stock covered by an Option under this Plan
until he or she has purchased and received such shares. 13. Options Not
Transferable. Options under this Plan are not transferable by a participating
employee other than by will or the laws of descent and distribution, and are
exercisable during the employee’s lifetime only by the employee. 14. Application
of Funds. All funds received or held by the Company under this Plan may be
combined with other corporate funds and may be used for any corporate purpose.
15. Adjustment for Changes in Common Stock and Certain Other Events. (a) Changes
in Capitalization. In the event of any stock split, reverse stock split, stock
dividend, recapitalization, combination of shares, reclassification of shares,
spin-off or other similar change in capitalization or event, or any dividend or
distribution to holders of Common Stock other than an ordinary cash dividend,
(i) the number and class of securities available under this Plan, (ii) the share
limitations set forth in Section 9, and (iii) the Option Price shall be
equitably adjusted to the extent determined by the Board or the Committee. (b)
Reorganization Events. 4

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(1) Definition. A “Reorganization Event” shall mean: (a) any merger or
consolidation of the Company with or into another entity as a result of which
all of the Common Stock of the Company is converted into or exchanged for the
right to receive cash, securities or other property or is cancelled, (b) any
transfer or disposition of all of the Common Stock of the Company for cash,
securities or other property pursuant to a share exchange or other transaction
or (c) any liquidation or dissolution of the Company. (2) Consequences of a
Reorganization Event on Options. In connection with a Reorganization Event, the
Board or the Committee may take any one or more of the following actions as to
outstanding Options on such terms as the Board or the Committee determines: (i)
provide that Options shall be assumed, or substantially equivalent Options shall
be substituted, by the acquiring or succeeding corporation (or an affiliate
thereof), (ii) upon written notice to employees, provide that all outstanding
Options will be terminated immediately prior to the consummation of such
Reorganization Event and that all such outstanding Options will become
exercisable to the extent of accumulated payroll deductions as of a date
specified by the Board or the Committee in such notice, which date shall not be
less than ten (10) days preceding the effective date of the Reorganization
Event, (iii) upon written notice to employees, provide that all outstanding
Options will be cancelled as of a date prior to the effective date of the
Reorganization Event and that all accumulated payroll deductions will be
returned to participating employees on such date, (iv) in the event of a
Reorganization Event under the terms of which holders of Common Stock will
receive upon consummation thereof a cash payment for each share surrendered in
the Reorganization Event (the “Acquisition Price”), change the last day of the
Plan Period to be the date of the consummation of the Reorganization Event and
make or provide for a cash payment to each employee equal to (A) (1) the
Acquisition Price times (2) the number of shares of Common Stock that the
employee’s accumulated payroll deductions as of immediately prior to the
Reorganization Event could purchase at the Option Price, where the Acquisition
Price is treated as the fair market value of the Common Stock on the last day of
the applicable Plan Period for purposes of determining the Option Price under
Section 9(b) hereof, and where the number of shares that could be purchased is
subject to the limitations set forth in Section 9(a), minus (B) the result of
multiplying such number of shares by such Option Price, (v) provide that, in
connection with a liquidation or dissolution of the Company, Options shall
convert into the right to receive liquidation proceeds (net of the Option Price
thereof) and (vi) any combination of the foregoing. For purposes of clause (i)
above, an Option shall be considered assumed if, following consummation of the
Reorganization Event, the Option confers the right to purchase, for each share
of Common Stock subject to the Option immediately prior to the consummation of
the Reorganization Event, the consideration (whether cash, securities or other
property) received as a result of the Reorganization Event by holders of Common
Stock for each share of Common Stock held immediately prior to the consummation
of the Reorganization Event (and if holders were offered a choice of
consideration, the type of consideration chosen by the holders of a majority of
the outstanding shares of Common Stock); provided, however, that if the
consideration received as a result of the Reorganization Event is not solely
common stock of the acquiring or succeeding corporation (or an affiliate
thereof), the Company may, with the consent of the acquiring or succeeding
corporation, provide for the consideration to be received upon the exercise of
Options to consist solely of such number of shares of common stock of the
acquiring or succeeding corporation (or an affiliate thereof) that the Board
determines to be equivalent in 5

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value (as of the date of such determination or another date specified by the
Board) to the per share consideration received by holders of outstanding shares
of Common Stock as a result of the Reorganization Event. 16. Amendment of the
Plan. The Board may at any time, and from time to time, amend or suspend this
Plan or any portion thereof, except that (a) if the approval of any such
amendment by the shareholders of the Company is required by Section 423 of the
Code, such amendment shall not be effected without such approval, and (b) in no
event may any amendment be made that would cause the Plan to fail to comply with
Section 423 of the Code. 17. Insufficient Shares. If the total number of shares
of Common Stock specified in elections to be purchased under any Offering plus
the number of shares purchased under previous Offerings under this Plan exceeds
the maximum number of shares issuable under this Plan, the Board or the
Committee will allot the shares then available on a pro-rata basis. 18.
Termination of the Plan. This Plan may be terminated at any time by the Board.
Upon termination of this Plan all amounts in the accounts of participating
employees shall be promptly refunded. 19. Governmental Regulations. The
Company’s obligation to sell and deliver Common Stock under this Plan is subject
to listing on a national stock exchange (to the extent the Common Stock is then
so listed or quoted) and the approval of all governmental authorities required
in connection with the authorization, issuance or sale of such stock. 20.
Governing Law. The Plan shall be governed by Delaware law except to the extent
that such law is preempted by federal law. 21. Issuance of Shares. Shares may be
issued upon exercise of an Option from authorized but unissued Common Stock,
from shares held in the treasury of the Company, or from any other proper
source. 22. Notification upon Sale of Shares. Each employee agrees, by entering
the Plan, to promptly give the Company notice of any disposition of shares
purchased under the Plan where such disposition occurs within two years after
the date of grant of the Option pursuant to which such shares were purchased.
23. Grants to Employees in Foreign Jurisdictions. The Company may, to comply
with the laws of a foreign jurisdiction, grant Options to employees of the
Company or a Designated Subsidiary who are citizens or residents of such foreign
jurisdiction (without regard to whether they are also citizens of the United
States or resident aliens (within the meaning of Section 7701(b)(1)(A) of the
Code)) with terms that are less favorable (but not more favorable) than the
terms of Options granted under the Plan to employees of the Company or a
Designated Subsidiary who are resident in the United States. Notwithstanding the
preceding provisions of this Plan, employees of the Company or a Designated
Subsidiary who are citizens or residents of a foreign jurisdiction (without
regard to whether they are also citizens of the United States or resident aliens
(within the meaning of Section 7701(b)(1)(A) of the Code)) may be excluded from
eligibility under the Plan if (a) the grant of an Option under the Plan to a
citizen or resident of the foreign jurisdiction is prohibited under the laws of
such jurisdiction or (b) compliance with 6

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the laws of the foreign jurisdiction would cause the Plan to violate the
requirements of Section 423 of the Code. The Company may add one or more
appendices to this Plan describing the operation of the Plan in those foreign
jurisdictions in which employees are excluded from participation or granted less
favorable Options. 24. Authorization of Sub-Plans. The Board may from time to
time establish one or more sub-plans under the Plan with respect to one or more
Designated Subsidiaries, provided that such sub-plan complies with Section 423
of the Code. 25. Withholding. If applicable tax laws impose a tax withholding
obligation, each affected employee shall, no later than the date of the event
creating the tax liability, make provision satisfactory to the Board for payment
of any taxes required by law to be withheld in connection with any transaction
related to Options granted to or shares acquired by such employee pursuant to
the Plan. The Company may, to the extent permitted by law, deduct any such taxes
from any payment of any kind otherwise due to an employee. 26. Effective Date
and Approval of Stockholders. The Plan shall become effective on the date that
the Plan is approved by the Company’ stockholders (the “Effective Date”).
Adopted by the Board of Directors on April 26, 2017 Approved by the stockholders
on June 1, 2017 Amendment Adopted by the Board of Directors on February 2, 2018
Amendment Approved by the stockholders on May 24, 2018 Amendment Adopted by the
Board of Directors on July 25, 2018 7

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