Exhibit
4.1


 


WARRANT
AGREEMENT


 


This
Warrant Agreement (“Warrant Agreement”) is made as of July 14, 2021, by and between CleanTech Acquisition Corp., a Delaware
corporation (the “Company”), and Continental Stock Transfer & Trust Company (the “Warrant Agent”).


 


WHEREAS,
the Company is engaged in a public offering (the “Public Offering”) of 15,000,000 units (the “Units”) of the
Company (and up to 2,250,000 additional Units if the underwriters’ over-allotment option is exercised in full), each Unit consisting
of one share of common stock, par value $0.0001 per share (the “Common Stock”), one right to receive one-twentieth of one
share of Common Stock, and one-half of one warrant (the “Public Warrant” or “Public Warrants”), each whole Public
Warrant entitling its holder to purchase one-half of one share of Common Stock (the “Public Warrant Shares”);


 


WHEREAS,
the Company has received a binding commitment from CleanTech Sponsor I LLC and CleanTech Investments, LLC to purchase up to 7,175,000
warrants, each for a purchase price of $1.00 per warrant, pursuant to the Subscription Agreements, dated as of July 14, 2021 (collectively,
the “Subscription Agreements”), and in connection therewith, will issue and deliver up to 7,175,000 warrants (the “Private
Warrants”, together with the Public Warrants, the “Warrants”), each whole Private Warrant entitling its holder to purchase
one share of Common Stock (“Private Warrant Shares”, and together with the Public Warrant Shares, the “Warrant Shares”);


 


WHEREAS,
the Company may issue such additional warrants to purchase shares of Common Stock hereunder from time to time (together with the Public
Warrants and the Private Warrants, the “Warrants”);


 


WHEREAS,
the Company has filed with the Securities and Exchange Commission (the “SEC”) a Registration Statement on Form S-1, No. 333-256578
(“Registration Statement”), for the registration, under the Securities Act of 1933, as amended (the “Act”) of,
among other securities, the Public Warrants;


 


WHEREAS,
the Company desires the Warrant Agent to act on behalf of the Company, and the Warrant Agent is willing to so act, in connection with
the issuance, registration, transfer, exchange, redemption and exercise of the Warrants;


 


WHEREAS,
the Company desires to provide for the form, terms and provisions of the Warrants, including the terms upon which they shall be issued
and exercised, and the respective rights, limitation of rights and immunities of the Company, the Warrant Agent and the holders of the
Warrants; and


 


WHEREAS,
all acts and things have been done and performed which are necessary to make the Warrants, when executed on behalf of the Company and
countersigned by or on behalf of the Warrant Agent, as provided herein, the legally valid and binding obligations of the Company, and
to authorize the execution and delivery of this Warrant Agreement.


 




     


     


    

 


NOW,
THEREFORE, in consideration of the mutual agreements herein contained, the parties hereto agree as follows:


 


1. Appointment
of Warrant Agent. The Company hereby appoints the Warrant Agent to act as agent for the Company for the Warrants, and the Warrant
Agent hereby accepts such appointment and agrees to perform the same in accordance with the terms and conditions set forth in this Warrant
Agreement.


 


2. Warrants.


 


2.1 Form
of Warrant. Each Warrant other than a Private Warrant shall be: (a) issued in registered form only, (b) in substantially the form
of Exhibit A hereto, the provisions of which are incorporated herein and (c) signed by, or bear the facsimile signature of, the
Chairman of the Board, the Chief Executive Officer or the Chief Financial Officer of the Company. In the event the person whose facsimile
signature has been placed upon any Warrant shall have ceased to serve in the capacity in which such person signed the Warrant before
such Warrant is issued, it may be issued with the same effect as if he or she had not ceased to be such at the date of issuance.


 


2.2 Effect
of Countersignature. Unless and until countersigned by the Warrant Agent pursuant to this Warrant Agreement, a Warrant shall be invalid
and of no effect and may not be exercised by the holder thereof.


 


2.3 Registration.


 


2.3.1 Warrant
Register. The Warrant Agent shall maintain books (the “Warrant Register”), for the registration of the original
issuance and transfers of the Warrants. Upon the initial issuance of the Warrants, the Warrant Agent shall issue and register the Warrants
in the names of the respective holders thereof in such denominations and otherwise in accordance with instructions delivered to the Warrant
Agent by the Company.


 


2.3.2 Registered
Holder. Prior to due presentment for registration of transfer of any Warrant, the Company and the Warrant Agent may deem and treat
the person in whose name such Warrant shall be registered upon the Warrant Register (“Registered Holder”) as the absolute
owner of such Warrant and of each Warrant represented thereby (notwithstanding any notation of ownership or other writing on the Warrant
certificate made by anyone other than the Company or the Warrant Agent), for the purpose of any exercise thereof, and for all other purposes,
and neither the Company nor the Warrant Agent shall be affected by any notice to the contrary.


 


2.4 Detachability
of Warrants. Each of the securities comprising the Units will begin to trade separately on (i) the 90th day after the effectiveness
of the Registration Statement, or (ii) such earlier date as Chardan Capital Markets, LLC, as representative of the underwriters (the
“Representative”), shall determine is acceptable (such date, the “Detachment Date”). In no event
will separate trading of the securities comprising the Units commence until the Company (i) files a Current Report on Form 8-K with the
SEC including audited balance sheet reflecting the Company’s receipt of the gross proceeds of the Public Offering and (ii) issues
a press release announcing when such separate trading will begin.


 


2.5 Private
Warrants. The Private Warrants (i) will be exercisable either for cash or on a cashless basis at the holder’s option pursuant
to Section 3.3 hereof and (ii) will not be redeemable by the Company. The Private Warrants may not be sold, transferred, assigned,
pledged or hypothecated, or be the subject of any hedging, short sale, derivative, put, or call transaction that would result in the
effective economic disposition of, the Private Warrants (or any securities underlying the Private Warrants) for a period of three hundred
sixty (360) days following the effective date of the Registration Statement to anyone other than any member participating in the Public
Offering and the officers or partners thereof, if all securities so transferred remain subject to the lock-up restriction set forth above
for the remainder of the time period.


 




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3. Terms
and Exercise of Warrants.


 


3.1 Warrant
Price. Each Warrant shall, when countersigned by the Warrant Agent, entitle the Registered Holder thereof, subject to the provisions
of such Warrant and of this Warrant Agreement, to purchase from the Company the number of shares of Common Stock stated therein, at $11.50
per full share, subject to the adjustments provided in Section 4 hereof. The term “Warrant Price” as used in this
Warrant Agreement refers to the price per whole share at which shares of Common Stock may be purchased at the time such Warrant is exercised.
The Public Warrants may only be exercised for a whole number of Warrant Shares by a Registered Holder.


 


3.2 Duration
of Warrants. A Warrant may be exercised only during the period (“Exercise Period”) commencing on the later to
occur of (i) the completion of the Company’s initial business combination and (ii) 12 months following the closing of the Public
Offering, and terminating at 5:00 p.m., New York City time, on the earlier to occur of (i) (A) five years following the completion of
the Company’s initial business combination with respect to the Public Warrants, and (B) five years from the effective date of the
Registration Statement with respect to the Private Warrants purchased by CleanTech Sponsor I LLC and CleanTech Investments, LLC, provided
that once the Private Warrants are not beneficially owned by CleanTech Sponsor I LLC and CleanTech Investments, LLC or any of its
related persons anymore, the Private Warrants may not be exercised five years following the completion of the Company’s initial
business combination, and (ii) the date fixed for redemption of the Warrants as provided in Section 6 of this Warrant Agreement (“Expiration
Date”). Except with respect to the right to receive the Redemption Price (as set forth in Section 6 hereunder), each Warrant
not exercised on or before the Expiration Date shall become void, and all rights thereunder and all rights in respect thereof under this
Warrant Agreement shall cease at the close of business on the Expiration Date. The Company may extend the duration of the Warrants by
delaying the Expiration Date; provided, however, that the Company will provide written notice of not less than 10 days to Registered
Holders of such extension and that such extension shall be identical in duration among all of the then outstanding Warrants.


 


3.3 Exercise
of Warrants.


 


3.3.1 Cash
Exercise. Subject to the provisions of the Warrant and this Warrant Agreement, a Warrant, when countersigned by the Company, may
be exercised by the Registered Holder thereof by surrendering it at the office of the Warrant Agent, or at the office of its successor
as Warrant Agent, currently being:


 


Continental
Stock Transfer & Trust Company

1 State Street, 30th Floor

New York, New York 10004

Attn: Compliance Department


 


with
the subscription form, as set forth in the Warrant, duly executed, and by paying in full, in lawful money of the United States, by certified
or bank cashier’s check payable to the order of the Warrant Agent or by wire transfer to the Warrant Agent’s bank account,
the Warrant Price for each whole Warrant Share as to which the Warrant is exercised and any and all applicable taxes due in connection
with the exercise of the Warrant, the exchange of the Warrant for the Warrant Shares, and the issuance of the Warrant Shares (such exercise,
a “Cash Exercise”). A Cash Exercise in accordance with this Section 3.3.1 is available to the Registered Holder only
during such times that there is an effective registration statement registering the Warrant Shares, with the prospectus contained therein
being available for the resale of the Warrant Shares.


 




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3.3.2 Cashless
Exercise. Subject to Section 2.4, notwithstanding anything contained herein to the contrary, if there is no effective registration
statement registering the Warrant Shares on any day the Registered Holder desires to exercise the Warrants and more than 120 days have
passed since the Company complete its initial business combination, the Registered Holder may exercise the Warrants in whole or in part
in lieu of making a cash payment for whole numbers of Warrant Shares, by providing notice to the Chief Financial Officer of the Company
in a subscription form of its election to utilize cashless exercise, in which event the Company shall issue to the Holder the number
of Warrant Shares determined as follows:


 


X
= Y [(A-B)/A]


 


where:


 


X
= the number of Warrant Shares to be issued to the Holder.


 


Y
= the number of Warrant Shares with respect to which this Warrant is being exercised.


 


A
= the fair market value of one share of Common Stock.


 


B
= the Warrant Price.


 


The
Registered Holder may not exercise any Warrants in the absence of a registration statement except pursuant to this Section 3.3.2.
For purposes of this Section 3.3.2 and Section 4.1, the fair market value of one share of Common Stock is defined as follows:


 


(i)
if the Company’s shares of Common Stock are listed and traded on the New York Stock Exchange, the NYSE American, the NASDAQ Global
Select Market, the NASDAQ Global Market or the NASDAQ Capital Market (each, a “Trading Market”), the fair market value
shall be deemed the average of the closing price on such Trading Market for the 10 trading days ending on the third trading day immediately
prior to the date the subscription form is submitted to the Company in connection with the exercise of the Warrant; or


 


(ii)
if the Company’s shares of Common Stock are not listed on a Trading Market, but is traded in the over-the-counter market, the fair
market value shall be deemed to be the average of the bid price on such Trading Market for the 10 trading days ending on the third trading
day immediately prior to the date the subscription form is submitted in connection with the exercise of the Warrant; or


 


(iii)
if there is no active public market for the Company’s shares of Common Stock, the fair market value of the shares of Common Stock
shall be determined in good faith by the Company’s board of directors.


 


3.3.3 Fractional
Shares. Notwithstanding any provision to the contrary contained in this Warrant Agreement, the Company shall not be required to issue
any fraction of a Warrant Share in connection with the exercise of Warrants, and in any case where the Registered Holder would be entitled
under the terms of the Warrants to receive a fraction of a Warrant Share upon the exercise of such Registered Holder’s Warrants,
issue or cause to be issued only the largest whole number of Warrant Shares issuable on such exercise (and such fraction of a Warrant
Share will be disregarded); provided, that if more than one Warrant certificate is presented for exercise at the same time by the same
Registered Holder, the number of whole Warrant Shares which shall be issuable upon the exercise thereof shall be computed on the basis
of the aggregate number of Warrant Shares issuable on exercise of all such Warrants.


 




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3.3.4 Issuance
of Certificates. No later than three (3) business days following the exercise of any Warrant and the clearance of the funds in payment
of the Warrant Price pursuant to Section 3.3.1 or cashless exercise pursuant to Section 3.3.2, the Company shall issue, or cause to be
issued, to the Registered Holder of such Warrant a certificate or certificates representing (or at the option of the Registered Holder,
deliver electronically through the facilities of the Depository Trust Corporation) the number of full shares of Common Stock to which
he, she or it is entitled, registered in such name or names as may be directed by him, her or it, and, if such Warrant shall not have
been exercised or surrendered in full, a new countersigned Warrant for the number of shares as to which such Warrant shall not have been
exercised or surrendered. Notwithstanding the foregoing, the Company shall not deliver, or cause to be delivered, any securities without
applicable restrictive legend pursuant to the exercise of a Warrant unless (a) a registration statement under the Act with respect to
the shares of Common Stock issuable upon exercise of such Warrants is effective and a current prospectus relating to the shares of Common
Stock issuable upon exercise of the Warrants is available for delivery to the Registered Holder of the Warrant or (b) in the opinion
of counsel to the Company, the exercise of the Warrants is exempt from the registration requirements of the Act and such securities are
qualified for sale or exempt from qualification under applicable securities laws of the states or other jurisdictions in which the Registered
Holder resides. Warrants may not be exercised by, or securities issued to, any Registered Holder in any state in which such exercise
or issuance would be unlawful. In addition, in no event will the Company be obligated to pay such Registered Holder any cash consideration
upon exercise or otherwise “net cash settle” the Warrant.


 


3.3.5 Valid
Issuance. All shares of Common Stock issued upon the proper exercise or surrender of a Warrant in conformity with this Warrant Agreement
shall be validly issued, fully paid and non-assessable.


 


3.3.6 Date
of Issuance. Each person or entity in whose name any such certificate for shares of Common Stock is issued shall, for all purposes,
be deemed to have become the holder of record of such shares on the date on which the Warrant was surrendered and payment of the Warrant
Price was made, irrespective of the date of delivery of such certificate, except that, if the date of such surrender and payment is a
date when the stock transfer books of the Company are closed, such person shall be deemed to have become the holder of such shares at
the close of business on the next succeeding date on which the stock transfer books are open.


 


3.3.7 Maximum
Percentage. A holder of a Warrant may notify the Company in writing in the event it elects to be subject to the provisions contained
in this subsection 3.3.7; however, no holder of a Warrant shall be subject to this subsection 3.3.7 unless he, she or it makes such election.
If the election is made by a holder, the Warrant Agent shall not effect the exercise of the holder’s Warrant, and such holder shall
not have the right to exercise such Warrant, to the extent that after giving effect to such exercise, such person (together with such
person’s affiliates), to the Warrant Agent’s actual knowledge, would beneficially own in excess of 9.9% (the “Maximum
Percentage”) of the shares of Common Stock outstanding immediately after giving effect to such exercise. For purposes of the
foregoing sentence, the aggregate number of shares of Common Stock beneficially owned by such person and its affiliates shall include
the number of shares of Common Stock issuable upon exercise of the Warrant with respect to which the determination of such sentence is
being made, but shall exclude the shares of Common Stock that would be issuable upon (x) exercise of the remaining, unexercised portion
of the Warrant beneficially owned by such person and its affiliates and (y) exercise or conversion of the unexercised or unconverted
portion of any other securities of the Company beneficially owned by such person and its affiliates (including, without limitation, any
convertible notes or convertible preferred shares or warrants) subject to a limitation on conversion or exercise analogous to the limitation
contained herein. Except as set forth in the preceding sentence, for purposes of this paragraph, beneficial ownership shall be calculated
in accordance with Section 13(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). For purposes
of the Warrant, in determining the number of outstanding shares of Common Stock, the holder may rely on the number of outstanding shares
of Common Stock as reflected in (1) the Company’s most recent annual report on Form 10-K, quarterly report on Form 10-Q, current
report on Form 8-K or other public filing with the SEC as the case may be, (2) a more recent public announcement by the Company, or (3)
any other notice by the Company or the Warrant Agent setting forth the number of shares of Common Stock outstanding. For any reason at
any time, upon the written request of the holder of the Warrant, the Company shall, within two (2) business days, confirm orally and
in writing to such holder the number of shares of Common Stock then outstanding. In any case, the number of outstanding shares of Common
Stock shall be determined after giving effect to the conversion or exercise of equity securities of the Company by the holder and its
affiliates since the date as of which such number of outstanding shares of Common Stock was reported. By written notice to the Company,
the holder of a Warrant may from time to time increase or decrease the Maximum Percentage applicable to such holder to any other percentage
specified in such notice; provided, however, that any such increase shall not be effective until the sixty-first (61st) day after such
notice is delivered to the Company.


 






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4. Adjustments.


 


4.1 Stock
Dividends, Splits. If, after the date hereof, and subject to the provisions of Section 4.5 below, the number of outstanding shares
of Common Stock is increased by a stock dividend payable in shares of Common Stock, or by a forward or reverse split of shares of Common
Stock, or other similar event, then, on the effective date of such stock dividend, split or similar event, the number of shares of Common
Stock issuable on exercise of each Warrant shall be increased or decreased in proportion to such increase or decrease in outstanding
shares of Common Stock. A rights offering to all holders of the shares of Common Stock entitling holders to purchase shares of Common
Stock at a price less than the Fair Market Value shall be deemed a stock dividend of a number of shares of Common Stock equal to the
product of (i) the number of shares of Common Stock actually sold in such rights offering (or issuable under any other equity securities
sold in such rights offering that are convertible into or exercisable for the shares of Common Stock) multiplied by (ii) one (1) minus
the quotient of (x) the price per share of Common Stock paid in such rights offering divided by (y) the Fair Market Value. For purposes
of this subsection 4.1, if the rights offering is for securities convertible into or exercisable for shares of Common Stock, in determining
the price payable for the shares of Common Stock, there shall be taken into account any consideration received for such rights, as well
as any additional amount payable upon exercise or conversion.


 


4.2 Aggregation
of Shares. If, after the date hereof, and subject to the provisions of Section 4.6, the number of outstanding shares of Common Stock
is decreased by a consolidation, combination or reclassification of shares of Common Stock or other similar event, then, on the effective
date of such consolidation, combination, reclassification or similar event, the number of shares of Common Stock issuable on exercise
of each Warrant shall be decreased in proportion to such decrease in outstanding shares of Common Stock.





 


4.3 Extraordinary
Dividends. If the Company, at any time while the Warrants (or rights to purchase the Warrants) are outstanding and unexpired, shall
pay a dividend or make a distribution in cash, securities or other assets to the holders of the shares of Common Stock on account of
such shares of Common Stock (or other shares of the Company’s capital stock into which the Warrants are convertible), other than
(a) as described in subsection 4.1 above, (b) Ordinary Cash Dividends (as defined below), (c) to satisfy the conversion rights of the
holders of the shares of Common Stock in connection with a proposed initial Business Combination or vote to extend the time period to
complete an initial Business Combination, (d) as a result of the repurchase of shares of Common Stock by the Company in connection with
an initial Business Combination or as otherwise permitted by the Investment Management Trust Agreement between the Company and the Warrant
Agent dated of even date herewith or (e) in connection with the Company’s liquidation and the distribution of its assets upon its
failure to consummate a Business Combination (any such non-excluded event being referred to herein as an “Extraordinary Dividend”),
then the Warrant Price shall be decreased, effective immediately after the effective date of such Extraordinary Dividend, by the amount
of cash and the fair market value (as determined by the Company’s board of directors, in good faith) of any securities or other
assets paid on each share of Common Stock in respect of such Extraordinary Dividend. For purposes of this subsection 4.3, “Ordinary
Cash Dividends” means any cash dividend or cash distribution which, when combined on a per share basis with the per share amounts
of all other cash dividends and cash distributions paid on the shares of Common Stock during the 365-day period ending on the date of
declaration of such dividend or distribution (as adjusted to appropriately reflect any of the events referred to in other subsections
of this Section 4 and excluding cash dividends or cash distributions that resulted in an adjustment to the Warrant Price or to the number
of shares of Common Stock issuable on exercise of each Warrant) does not exceed $0.50 (being 5% of the offering price of the Units in
the Offering). The foregoing adjustment shall not apply to the Private Warrants.


 






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4.4 Adjustments
in Exercise Price. Whenever the number of shares of Common Stock purchasable upon the exercise of the Warrants is adjusted, as provided
in Sections 4.1 and 4.2 above, the Warrant Price shall be adjusted (to the nearest cent) by multiplying such Warrant Price, immediately
prior to such adjustment, by a fraction, (a) the numerator of which shall be the number of shares of Common Stock purchasable upon the
exercise of the Warrants immediately prior to such adjustment, and (b) the denominator of which shall be the number of shares of Common
Stock so purchasable immediately thereafter.





 


4.5 Replacement
of Securities upon Reorganization, etc. In case of any reclassification or reorganization of the outstanding shares of Common Stock
(other than a change covered by Sections 4.1, 4.2 or 4.3 hereof or one that solely affects the par value of such shares of Common Stock),
or, in the case of any merger or consolidation of the Company with or into another corporation (other than a consolidation or merger
in which the Company is the continuing corporation and that does not result in any reclassification or reorganization of the outstanding
shares of Common Stock), or, in the case of any sale or conveyance to another corporation or entity of the assets or other property of
the Company as an entirety or substantially as an entirety, in connection with which the Company is dissolved, the Registered Holders
shall thereafter have the right to purchase and receive, upon the basis and upon the terms and conditions specified in the Warrants and
in lieu of the shares of Common Stock of the Company immediately theretofore purchasable and receivable upon the exercise of the rights
represented thereby, the kind and amount of shares of stock or other securities or property (including cash) receivable upon such reclassification,
reorganization, merger or consolidation, or upon a dissolution following any such sale or transfer, that the Registered Holder would
have received if such Registered Holder had exercised his, her or its Warrant(s) immediately prior to such event (the “Alternative
Issuance”); provided, however, that in connection with the closing of any such consolidation, merger, sale or conveyance, the successor
or purchasing entity shall execute an amendment hereto with the Warrant Agent providing for delivery of such Alternative Issuance; provided,
further, that (i) if the holders of the Common Stock were entitled to exercise a right of election as to the kind or amount of securities,
cash or other assets receivable upon such consolidation or merger, then the kind and amount of securities, cash or other assets constituting
the Alternative Issuance for which each Warrant shall become exercisable shall be deemed to be the weighted average of the kind and amount
received per share by the holders of the Common Stock in such consolidation or merger that affirmatively make such election, and (ii)
if a tender, exchange or redemption offer shall have been made to and accepted by the holders of the Common Stock (other than a tender,
exchange or redemption offer made by the Company in connection with redemption rights held by stockholders of the Company as provided
for in the Company’s amended and restated certificate of incorporation or as a result of the repurchase of shares of Common Stock
by the Company if a proposed initial Business Combination is presented to the stockholders of the Company for approval) under circumstances
in which, upon completion of such tender or exchange offer, the maker thereof, together with members of any group (within the meaning
of Rule 13d-5(b)(1) under the Exchange Act (or any successor rule)) of which such maker is a part, and together with any affiliate or
associate of such maker (within the meaning of Rule 12b-2 under the Exchange Act (or any successor rule)) and any members of any such
group of which any such affiliate or associate is a part, own beneficially (within the meaning of Rule 13d-3 under the Exchange Act (or
any successor rule)) more than 50% of the outstanding shares of Common Stock, the holder of a Warrant shall be entitled to receive as
the Alternative Issuance, the highest amount of cash, securities or other property to which such holder would actually have been entitled
as a stockholder if such Warrant holder had exercised the Warrant prior to the expiration of such tender or exchange offer, accepted
such offer and all of the Common Stock held by such holder had been purchased pursuant to such tender or exchange offer, subject to adjustments
(from and after the consummation of such tender or exchange offer) as nearly equivalent as possible to the adjustments provided for in
this Section 4; provided, further, that if less than 70% of the consideration receivable by the holders of the Common Stock in the applicable
event is payable in the form of common stock in the successor entity that is listed for trading on a national securities exchange or
is quoted in an established over-the-counter market, or is to be so listed for trading or quoted immediately following such event, and
if the Registered Holder properly exercises the Warrant within thirty (30) days following the public disclosure of the consummation of
such applicable event by the Company pursuant to a Current Report on Form 8-K filed with the Commission, the Warrant Price shall be reduced
by an amount (in dollars) (but in no event less than zero) equal to the difference of (i) the Warrant Price in effect prior to such reduction
minus (ii) (A) the Per Share Consideration (as defined below) minus (B) the Black-Scholes Warrant Value (as defined below). The “Black-Scholes
Warrant Value” means the value of a Warrant immediately prior to the consummation of the applicable event based on the Black-Scholes
Warrant Model for a Capped American Call on Bloomberg Financial Markets (“Bloomberg”). For purposes of calculating such amount,
(1) Section 6 of this Agreement shall be taken into account, (2) the price of each share of Common Stock shall be the volume weighted
average price of the Common Stock as reported during the ten (10) trading day period ending on the trading day prior to the effective
date of the applicable event, (3) the assumed volatility shall be the 90 day volatility obtained from the HVT function on Bloomberg determined
as of the trading day immediately prior to the day of the announcement of the applicable event, and (4) the assumed risk-free interest
rate shall correspond to the U.S. Treasury rate for a period equal to the remaining term of the Warrant. “Per Share Consideration”
means (i) if the consideration paid to holders of the Common Stock consists exclusively of cash, the amount of such cash per share of
Common Stock, and (ii) in all other cases, the amount of cash per share of Common Stock, if any, plus the volume weighted average price
of the Common Stock as reported during the ten (10) trading day period ending on the trading day prior to the effective date of the applicable
event.If any reclassification also results in a change in shares of Common Stock covered by Sections 4.1, 4.2 or 4.3, then such adjustment
shall be made pursuant to Sections 4.1, 4.2, 4.3 and this Section 4.5. The provisions of this Section 4.5 shall similarly apply to successive
reclassifications, reorganizations, mergers or consolidations, sales or other transfers. In no event will the Warrant Price be reduced
to less than the par value per share issuable upon exercise of the Warrant.


 






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4.6 Notices
of Changes in Warrant. Upon every adjustment of the Warrant Price or the number of shares issuable upon exercise of a Warrant, the
Company shall give written notice thereof to the Warrant Agent, which notice shall state the Warrant Price resulting from such adjustment
and the increase or decrease, if any, in the number of shares purchasable at such price upon the exercise of a Warrant, setting forth
in reasonable detail the method of calculation and the facts upon which such calculation is based. Upon the occurrence of any event specified
in Sections 4.1 – 4.5 the Company shall give written notice to each Registered Holder, at the last address set forth for
such Registered Holder in the Warrant Register, of the record date or the effective date of the event. Failure to give such notice, or
any defect therein, shall not affect the legality or validity of such event.





 


4.7 Form
of Warrant. The form of Warrant need not be changed because of any adjustment pursuant to this Section 4, and Warrants issued after
such adjustment may state the same Warrant Price and the same number of shares as is stated in the Warrants initially issued pursuant
to this Warrant Agreement. However, the Company may, at any time, in its sole discretion, make any change in the form of Warrant that
the Company may deem appropriate and that does not affect the substance thereof, and any Warrant thereafter issued or countersigned,
whether in exchange or substitution for an outstanding Warrant or otherwise, may be in the form as so changed.


 


4.8 Notice
of Certain Transactions. In the event that the Company shall (a) offer to holders of all its shares of Common Stock rights to subscribe
for or to purchase any securities convertible into shares of Common Stock or shares of stock of any class or any other securities, rights
or options, (b) issue any rights, options or warrants entitling all the holders of shares of Common Stock to subscribe for shares of
Common Stock, or (c) make a tender offer, redemption offer or exchange offer with respect to the shares of Common Stock, the Company
shall send to the Registered Holders a notice of such action or offer. Such notice shall be mailed to the Registered Holders at their
addresses as they appear in the Warrant Register, which shall specify the record date for the purposes of such dividend, distribution
or rights, or the date such issuance or event is to take place and the date of participation therein by the holders of shares of Common
Stock, if any such date is to be fixed, and shall briefly indicate the effect of such action on the shares of Common Stock and on the
number and kind of any other shares of stock and on other property, if any, and the number of shares of Common Stock and other property,
if any, issuable upon exercise of each Warrant and the Warrant Price after giving effect to any adjustment pursuant to this Section 4
which would be required as a result of such action. Such notice shall be given as promptly as practicable after the Company has taken
any such action.


 


5. Transfer
and Exchange of Warrants.


 


5.1 Transfer
of Warrants. Prior to the Detachment Date, the Warrants may be transferred or exchanged only together with the Unit in which such
Warrant is included, and only for the purpose of effecting, or in conjunction with, a transfer or exchange of such Unit. Furthermore,
each transfer of a Unit on the register relating to such Units shall operate also to transfer the Warrants included in such Unit. From
and after the Detachment Date, this Section 5.1 will have no further force and effect.


 


5.2 Registration
of Transfer. The Warrant Agent shall register the transfer, from time to time, of any outstanding Warrant into the Warrant Register,
upon surrender of such Warrant for transfer, properly endorsed with signatures properly guaranteed and accompanied by appropriate instructions
for transfer. Upon any such transfer, a new Warrant representing an equal aggregate number of Warrants shall be issued and the old Warrant
shall be cancelled by the Warrant Agent. The Warrants so cancelled shall be delivered by the Warrant Agent to the Company from time to
time upon the Company’s request.


 


5.3 Procedure
for Surrender of Warrants. Warrants may be surrendered to the Warrant Agent, together with a written request for exchange or transfer,
and, thereupon, the Warrant Agent shall issue in exchange therefor one or more new Warrants as requested by the Registered Holder of
the Warrants so surrendered, representing an equal aggregate number of Warrants; provided, however, that, in the event a Warrant surrendered
for transfer bears a restrictive legend, the Warrant Agent shall not cancel such Warrant and shall issue new Warrants in exchange therefor
until the Warrant Agent has received an opinion of counsel for the Company stating that such transfer may be made and indicating whether
the new Warrants must also bear a restrictive legend.


 


5.4 Fractional
Warrants. The Warrant Agent shall not be required to effect any registration of transfer or exchange which will result in the issuance
of a warrant certificate for a fraction of a warrant.


 




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5.5 Service
Charges. No service charge shall be made for any exchange or registration of transfer of Warrants.


 


5.6 Warrant
Execution and Countersignature. The Warrant Agent is hereby authorized to countersign and to deliver, in accordance with the terms
of this Warrant Agreement, the Warrants required to be issued pursuant to the provisions of this Section 5, and the Company, whenever
required by the Warrant Agent, will supply the Warrant Agent with Warrants duly executed on behalf of the Company for such purpose.


 


6. Redemption.


 


6.1 Redemption.
Subject to the second sentence of this Section 6.1, all (and not less than all) of the outstanding Warrants may be redeemed, in whole
and not in part, at the option of the Company, at any time from and after the Warrants become exercisable, and prior to their expiration,
at the office of the Warrant Agent, upon the notice referred to in Section 6.2, at the price of $0.01 per Warrant (“Redemption
Price”); provided that the last sales price of the shares of Common Stock has been equal to or greater than $16.50 per share
(subject to adjustment for splits, dividends, recapitalizations and other similar events), for any twenty (20) trading days within a
thirty (30) trading day period ending on the third business day prior to the date on which notice of redemption is given and provided
further that there is a current registration statement in effect with respect to the shares of Common Stock underlying the Warrants for
each day in the aforementioned 30-day trading period and continuing each day thereafter until the Redemption Date (defined below). For
avoidance of doubt, if and when the warrants become redeemable by the Company under this Section, the Company may exercise its redemption
right, even if it is unable to register or qualify the Warrant Shares for sale under all applicable state securities laws.


 


6.2 Date
Fixed for, and Notice of, Redemption. In the event the Company shall elect to redeem all of the Warrants, the Company shall fix a
date for the redemption (the “Redemption Date”). Notice of redemption shall be mailed by first class mail, postage
prepaid, by the Company not less than 30 days prior to the date fixed for redemption to the Registered Holders of the Warrants to be
redeemed at their last addresses as they shall appear on the Warrant Register. Any notice mailed in the manner herein provided shall
be conclusively presumed to have been duly given, whether or not the Registered Holder received such notice.


 


6.3 Exercise
After Notice of Redemption. The Warrants may be exercised in accordance with Section 3 of this Warrant Agreement at any time after
notice of redemption shall have been given by the Company pursuant to Section 6.2 hereof and prior to the Redemption Date; provided that
the Company may require the Registered Holder who desires to exercise the Warrant to elect cashless exercise as set forth under Section
3.3.2, and such Registered Holder must exercise the Warrants on a cashless basis if the Company so requires. On and after the Redemption
Date, the Registered Holder of the Warrants shall have no further rights except to receive, upon surrender of the Warrants, the Redemption
Price.


 


6.4 No
Other Rights to Cash Payment. Except for a redemption in accordance with this Section 6, no Registered Holder of any Warrant shall
be entitled to any cash payment whatsoever from the Company in connection with the ownership, exercise or surrender of any Warrant under
this Warrant Agreement.


 


 


7. Other
Provisions Relating to Rights of Registered Holders of Warrants.


 


7.1 No
Rights as Stockholder. A Warrant does not entitle the Registered Holder thereof to any of the rights of a stockholder of the Company,
including, without limitation, the right to receive dividends, or other distributions, exercise any preemptive rights to vote or to consent
or to receive notice as stockholders in respect of the meetings of stockholders or the election of directors of the Company or any other
matter.


 




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7.2 Lost,
Stolen Mutilated or Destroyed Warrants. If any Warrant is lost, stolen, mutilated or destroyed, the Company and the Warrant Agent
may, on such terms as to indemnity or otherwise as they may in their discretion impose (which terms shall, in the case of a mutilated
Warrant, include the surrender thereof), issue a new Warrant of like denomination, tenor and date as the Warrant so lost, stolen, mutilated
or destroyed. Any such new Warrant shall constitute a substitute contractual obligation of the Company, whether or not the allegedly
lost, stolen, mutilated or destroyed Warrant shall be at any time enforceable by anyone.


 


7.3 Reservation
of shares of Common Stock. The Company shall at all times reserve and keep available a number of its authorized but unissued shares
of Common Stock that will be sufficient to permit the exercise in full of all outstanding Warrants issued pursuant to this Warrant Agreement.


 


7.4 Registration
of shares of Common Stock. The Company agrees that as soon as practicable, but in no event later than thirty (30) business days after
the closing of a Business Combination, it shall use its best efforts to file with the SEC a registration statement for the registration
under the Act of the shares of Common Stock issuable upon exercise of the Warrants, and to cause the same to become effective and to
maintain the effectiveness of such registration statement, and a current prospectus relating thereto, until the expiration of the Warrants
in accordance with the provisions of this Warrant Agreement. In addition, the Company agrees to use its best efforts to register the
shares of Common Stock issuable upon exercise of the Warrants under state blue sky laws, to the extent an exemption is not available.


 


8. Concerning
the Warrant Agent and Other Matters.


 


8.1 Payment
of Taxes. The Company will, from time to time, promptly pay all taxes and charges that may be imposed upon the Company or the Warrant
Agent in respect of the issuance or delivery of shares of Common Stock upon the exercise of Warrants, but the Company shall not be obligated
to pay any transfer taxes in respect of the Warrants or such shares.


 


8.2 Resignation,
Consolidation, or Merger of Warrant Agent.


 


8.2.1 Appointment
of Successor Warrant Agent. The Warrant Agent, or any successor to it hereafter appointed, may resign its duties and be discharged
from all further duties and liabilities hereunder after giving sixty (60) days’ notice in writing to the Company. If the office
of the Warrant Agent becomes vacant by resignation or incapacity to act or otherwise, the Company shall appoint, in writing, a successor
Warrant Agent in place of the Warrant Agent. If the Company shall fail to make such appointment within a period of 30 days after it has
been notified in writing of such resignation or incapacity by the Warrant Agent or by the Registered Holder of the Warrant (who shall,
with such notice, submit his, her or its Warrant for inspection by the Company), then the Registered Holder of any Warrant may apply
to the Supreme Court of the State of New York for the County of New York for the appointment of a successor Warrant Agent. Any successor
Warrant Agent, whether appointed by the Company or by such court, shall be a corporation organized and existing under the laws of the
State of New York, in good standing and having its principal office in the Borough of Manhattan, City and State of New York, and be authorized
under such laws to exercise corporate trust powers and subject to supervision or examination by federal or state authorities. After appointment,
any successor Warrant Agent shall be vested with all the authority, powers, rights, immunities, duties and obligations of its predecessor
Warrant Agent with like effect as if originally named as Warrant Agent hereunder, without any further act or deed; but, if for any reason
it becomes necessary or appropriate, the predecessor Warrant Agent shall execute and deliver, at the expense of the Company, an instrument
transferring to such successor Warrant Agent all the authority, powers, and rights of such predecessor Warrant Agent hereunder; and,
upon request of any successor Warrant Agent, the Company shall make, execute, acknowledge, and deliver any and all instruments in writing
for more fully and effectually vesting in and confirming to such successor Warrant Agent all such authority, powers, rights, immunities,
duties and obligations.


 




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8.2.2 Notice
of Successor Warrant Agent. In the event a successor Warrant Agent shall be appointed, the Company shall give notice thereof to the
predecessor Warrant Agent and the transfer agent for the shares of Common Stock not later than the effective date of any such appointment.


 


8.2.3 Merger
or Consolidation of Warrant Agent. Any corporation into which the Warrant Agent may be merged or with which it may be consolidated
or any corporation resulting from any merger or consolidation to which the Warrant Agent shall be a party shall be the successor Warrant
Agent under this Warrant Agreement without any further act on the part of the Company or the Warrant Agent.


 


8.3 Fees
and Expenses of Warrant Agent.


 


8.3.1 Remuneration.
The Company agrees to pay the Warrant Agent reasonable remuneration for its services as Warrant Agent hereunder and will reimburse the
Warrant Agent upon demand for all expenditures that the Warrant Agent may reasonably incur in the execution of its duties hereunder.


 


8.3.2 Further
Assurances. The Company agrees to perform, execute, acknowledge and deliver, or cause to be performed, executed, acknowledged and
delivered, all such further and other acts, instruments and assurances as may reasonably be required by the Warrant Agent for the carrying
out or performing of the provisions of this Warrant Agreement.


 


8.4 Liability
of Warrant Agent.


 


8.4.1 Reliance
on Company Statement. Whenever, in the performance of its duties under this Warrant Agreement, the Warrant Agent shall deem it necessary
or desirable that any fact or matter be proved or established by the Company prior to taking or suffering any action hereunder, such
fact or matter (unless other evidence in respect thereof be herein specifically prescribed) may be deemed to be conclusively proved and
established by a statement signed by the Chief Executive Officer, Chief Financial Officer or Chairman of the Board of the Company and
delivered to the Warrant Agent. The Warrant Agent may rely upon such statement for any action taken or suffered in good faith by it pursuant
to the provisions of this Warrant Agreement.


 


8.4.2 Indemnity.
The Warrant Agent shall be liable hereunder only for its own gross negligence, willful misconduct or bad faith. The Company agrees to
indemnify the Warrant Agent and hold it harmless against any and all liabilities, including judgments, costs and reasonable counsel fees,
for anything done or omitted by the Warrant Agent in the execution of this Warrant Agreement, except as a result of the Warrant Agent’s
gross negligence, willful misconduct or bad faith.


 


8.4.3 Exclusions.
The Warrant Agent shall have no responsibility with respect to the validity of this Warrant Agreement or with respect to the validity
or execution of any Warrant (except its countersignature thereof); nor shall it be responsible for any breach by the Company of any covenant
or condition contained in this Warrant Agreement or in any Warrant; nor shall it be responsible to make any adjustments required under
the provisions of Section 4 hereof or responsible for the manner, method or amount of any such adjustment or the ascertaining of the
existence of facts that would require any such adjustment; nor shall it, by any act hereunder, be deemed to make any representation or
warranty as to the authorization or reservation of any shares of Common Stock to be issued pursuant to this Warrant Agreement or any
Warrant or as to whether any shares of Common Stock will when issued be valid and fully paid and non-assessable.


 




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8.5 Acceptance
of Agency. The Warrant Agent hereby accepts the agency established by this Warrant Agreement and agrees to perform the same upon
the terms and conditions herein set forth and, among other things, shall account promptly to the Company with respect to Warrants exercised
and concurrently account for, and pay to the Company, all moneys received by the Warrant Agent for the purchase of shares of the Company’s
shares of Common Stock through the exercise of Warrants.


 


8.6 Waiver.
The Warrant Agent hereby waives any right of set-off or any other right, title, interest or claim of any kind (“Claim”) in
or to any distribution of the Trust Account (as defined in that certain Investment Management Trust Agreement, dated as of the date hereof,
by and between the Company and the Warrant Agent as trustee thereunder) and hereby agrees not to seek recourse, reimbursement, payment
or satisfaction for any Claim against the Trust Account for any reason whatsoever.


 


9. Miscellaneous
Provisions.


 


9.1 Successors.
All the covenants and provisions of this Warrant Agreement by or for the benefit of the Company or the Warrant Agent shall bind and inure
to the benefit of their respective successors and assigns.


 


9.2 Notices.
Any notice, statement or demand authorized by this Warrant Agreement to be given or made by the Warrant Agent or by the Registered Holder
of any Warrant to or on the Company shall be delivered by hand or sent by registered or certified mail or overnight courier service,
addressed (until another address is filed in writing by the Company with the Warrant Agent) as follows:


 


CleanTech
Acquisition Corp.

West 25th Street, 9th Floor

New York, NY 10001

Attention: Eli Spiro, Chief Executive Officer

with a copy (which shall not constitute notice) to:

Loeb & Loeb LLP

345 Park Avenue

New York, New York 10154

Attn: Giovanni Caruso


 


Any
notice, statement or demand authorized by this Warrant Agreement to be given or made by the Registered Holder of any Warrant or by the
Company to or on the Warrant Agent shall be delivered by hand or sent by registered or certified mail or overnight courier service, addressed
(until another address is filed in writing by the Warrant Agent with the Company), as follows:


 


Continental
Stock Transfer & Trust Company

1 State Street, 30th Floor

New York, New York 10004


 


Any
notice, sent pursuant to this Warrant Agreement shall be effective, if delivered by hand, upon receipt thereof by the party to whom it
is addressed, if sent by overnight courier, on the next business day of the delivery to the courier, and if sent by registered or certified
mail on the third day after registration or certification thereof.


 




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9.3 Applicable
Law. The validity, interpretation, and performance of this Warrant Agreement and of the Warrants shall be governed in all respects
by the laws of the State of New York, without giving effect to conflict of laws. Subject to applicable law, the Company and the Warrant
Agent hereby agree that any action, proceeding or claim against either of them arising out of or relating in any way to this Warrant
Agreement shall be brought and enforced in the courts of the State of New York or the United States District Court for the Southern District
of New York, and irrevocably submits to such jurisdiction, which jurisdiction shall be exclusive forum for any such action, proceeding
or claim. The Company and the Warrant Agent hereby waive any objection to such exclusive jurisdiction and that such courts represent
an inconvenient forum. Notwithstanding the foregoing, the provisions of this paragraph will not apply to suits brought to enforce any
liability or duty created by the Exchange Act or any other claim for which the federal district courts of the United States of America
are the sole and exclusive forum.


 


Any
person or entity purchasing or otherwise acquiring any interest in the Warrants shall be deemed to have notice of and to have consented
to the forum provisions in this Section 9.3. If any action, the subject matter of which is within the scope the forum provisions
above, is filed in a court other than a court located within the State of New York or the United States District Court for the Southern
District of New York (a “foreign action”) in the name of any Warrant holder, such Warrant holder shall be deemed to
have consented to: (x) the personal jurisdiction of the state and federal courts located within the State of New York or the United States
District Court for the Southern District of New York in connection with any action brought in any such court to enforce the forum provisions
(an “enforcement action”), and (y) having service of process made upon such Warrant holder in any such enforcement
action by service upon such Warrant holder’s counsel in the foreign action as agent for such Warrant holder.


 


Any
such process or summons to be served upon the Company or the Warrant Agent may be served by transmitting a copy thereof by registered
or certified mail, return receipt requested, postage prepaid, addressed to it at the address set forth in Section 9.2 hereof.
Such mailing shall be deemed personal service and shall be legal and binding upon the party receiving such service in any action, proceeding
or claim.


 


9.4 Persons
Having Rights under this Warrant Agreement. Nothing in this Warrant Agreement expressed and nothing that may be implied from any
of the provisions hereof is intended, or shall be construed, to confer upon, or give to, any person or corporation other than the parties
hereto and the Registered Holders of the Warrants and, for the purposes of Sections 2.5 hereof, the Representative and the underwriters,
any right, remedy, or claim under or by reason of this Warrant Agreement or of any covenant, condition, stipulation, promise, or agreement
hereof. All covenants, conditions, stipulations, promises, and agreements contained in this Warrant Agreement shall be for the sole and
exclusive benefit of the parties hereto and their successors and assigns and of the Registered Holders of the Warrants.


 






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9.5 Examination
of the Warrant Agreement. A copy of this Warrant Agreement shall be available at all reasonable times at the office of the Warrant
Agent in the Borough of Manhattan, City and State of New York, for inspection by the Registered Holder of any Warrant. The Warrant Agent
may require any such Registered Holder to submit his, her or its Warrant for inspection.


 


9.6 Counterparts-
Facsimile Signatures. This Warrant Agreement may be executed in any number of counterparts, and each of such counterparts shall,
for all purposes, be deemed to be an original, and all such counterparts shall together constitute one and the same instrument. Facsimile
signatures shall constitute original signatures for all purposes of this Warrant Agreement.


 


9.7 Effect
of Headings. The section headings herein are for convenience only and are not part of this Warrant Agreement and shall not affect
the interpretation thereof


 


9.8 Amendments.
This Warrant Agreement and any Warrant certificate may be amended by the parties hereto by executing a supplemental warrant agreement
(a “Supplemental Agreement”), without the consent of any of the Warrant holders, for the purpose of (i) curing any
ambiguity, or curing, correcting or supplementing any defective provision contained herein, or making any other provisions with respect
to matters or questions arising under this Warrant Agreement that is not inconsistent with the provisions of this Warrant Agreement or
the Warrant certificates, (ii) evidencing the succession of another corporation to the Company and the assumption by any such successor
of the covenants of the Company contained in this Warrant Agreement and the Warrants, (iii) evidencing and providing for the acceptance
of appointment by a successor Warrant Agent with respect to the Warrants, (iv) adding to the covenants of the Company for the benefit
of the Registered Holders or surrendering any right or power conferred upon the Company under this Warrant Agreement, (v) providing for
the delivery of Alternative Issuance pursuant to Section 4.5, or (vi) amending this Warrant Agreement and the Warrants in any manner
that the Company may deem to be necessary or desirable and that will not adversely affect the interests of the Registered Holders in
any material respect. All other modifications or amendments to this Warrant Agreement, including any amendment to increase the Warrant
Price or shorten the Exercise Period, shall require the written consent of the Registered Holders of a majority of the then outstanding
Warrants. Notwithstanding the foregoing, the Company may extend the duration of the Exercise Period in accordance with Section 3.2 without
such consent.


 


9.9 Severability.
This Warrant Agreement shall be deemed severable, and the invalidity or unenforceability of any term or provision hereof shall not affect
the validity or enforceability of this Warrant Agreement or of any other term or provision hereof. Furthermore, in lieu of any such invalid
or unenforceable term or provision, the parties hereto intend that there shall be added as a part of this Warrant Agreement a provision
as similar in terms to such invalid or unenforceable provision as may be possible and be valid and enforceable.


 


[SIGNATURE
PAGE FOLLOWS]


 




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IN
WITNESS WHEREOF, this Warrant Agreement has been duly executed by the parties hereto as of the day and year first above written.


 


	 	CLEANTECH ACQUISITION CORP.
	 	 	 	 
	 	By:	/s/ Eli Spiro
	 	 	Name: 	Eli Spiro
	 	 	Title: 	Chief Executive Officer
	 	 	 	 
	 	CONTINENTAL STOCK TRANSFER & TRUST COMPANY
	 	 	 	 
	 	By:	/s/ Erika Young
	 	 	Name:	Erika Young
	 	 	Title:	Vice President


 


[Signature
Page to Warrant Agreement]


 




     


     


    

 


Exhibit
A


 


Form
of Warrant