Exhibit 4.4


 


WARRANT AGREEMENT


 


This Warrant Agreement (“Warrant Agreement”)
is made as of _________, 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 _________, 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.


 


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.


 






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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.


 


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


 






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(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.


 


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.


 






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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.


 


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.


 






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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.


 


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.


207 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.


 


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.


 






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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.


 


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: 	 
	 	 	Name: 	Eli Spiro
	 	 	Title:	Chief Executive Officer
	 	 	 	 
	 	CONTINENTAL STOCK TRANSFER & TRUST COMPANY
	 	 
	 	By: 	 
	 	 	Name: 	 
	 	 	Title: 	 


 


[Signature Page to Warrant Agreement]


 



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Exhibit A


Form of Warrant