EXHIBIT 10.2



                            STOCK EXCHANGE AGREEMENT


     THIS  STOCK  EXCHANGE AGREEMENT (this "AGREEMENT") is made and entered into
as  of  January  25,  2008,  by  and  among  The  Quercus Trust ("QUERCUS"), and
WorldWater  & Solar Technologies Corp., a Delaware corporation (the "COMPANY" or
"WWAT").

     WHEREAS,  Quercus  is  the owner of twenty-nine million ninety-two thousand
five  hundred  (29,092,500)  shares  of  Common  Stock  of the Company, of which
twenty-one  million  five hundred twenty-nine thousand five hundred (21,529,500)
shares were acquired on the public market (the "PUBLIC STOCK") and seven million
five  hundred  thousand (7,500,000) shares were acquired pursuant to a Stock and
Warrant  Purchase  Agreement dated September 28, 2007 (the "PURCHASE AGREEMENT")
(the  "PRIVATE  PLACEMENT  STOCK");  and


     WHEREAS,  the  Company  desires to exchange nineteen thousand seven hundred
(19,700)  shares  of  its  Series  E  Convertible  Preferred  Stock (hereinafter
described) for seven million five hundred thousand (7,500,000) shares of Private
Placement  Stock and for twelve million two hundred thousand (12,200,000) shares
of  Public  Stock.  Quercus  is willing to effect such exchange on the terms set
forth  herein;  and


     WHEREAS,  the  Company  intends  to  effect  the  acquisition  of  Entech,
Incorporated  in  a transaction which will require the issuance of approximately
nineteen  million  seven hundred thousand (19,700,000) shares of Common Stock to
the  shareholders  of  Entech  (the  "ENTECH  ACQUISITION").


     NOW,  THEREFORE,  in consideration of the foregoing premises and the mutual
covenants  and  agreements  herein  contained, and intending to be legally bound
hereby,  the  parties  hereto  hereby  agree  as  follows:

1.     Exchange  of  Shares.

     1.1  Exchange.  The  Company  hereby  agrees  to  issue to Quercus nineteen
thousand  seven  hundred  (19,700)  shares of its Series E Convertible Preferred
Stock  ("SERIES  E  PREFERRED"),  in  the  form,  and  containing  the  rights,
preferences  and  privileges  set forth in Exhibit "A". Quercus hereby agrees to
transfer  to  the  Company  in  exchange  for  the Series E Preferred a total of
nineteen  million  seven  hundred  thousand (19,700,000) shares of the Company's
Common  Stock,  consisting  of  seven  million five hundred thousand (7,500,000)
shares  of  Private  Placement  Stock  and  twelve  million two hundred thousand
(12,200,000)  shares  of  Public  Stock.

     1.2 The Closing. The exchange of the Series E Preferred shall take place at
the  offices  of Salvo Landau Gruen & Rogers, 510 Township Line Road, Suite 150,
Blue  Bell,  Pennsylvania  19422,  or  at such other location as the Company and
Quercus  mutually agree, concurrently with the closing of the Entech Acquisition
(the  "CLOSING").  At  the  Closing, upon transfer of the nineteen million seven
hundred thousand (19,700,000) shares of Common Stock to the Company, the Company
shall  deliver to Quercus a certificate representing the Series E Preferred (the
"PREFERRED  CERTIFICATE") against delivery to the Company of the certificate for
the  Private  Placement  Stock  and  of  twelve  million  two  hundred  thousand
(12,200,000)  shares of the Public Stock, either electronically or manually. The
obligation  of  Quercus  to consummate the exchange at the Closing is subject to
the  performance  by  the Company of the covenants set forth in Sections 2.1 and
2.2 below and to the truth and accuracy of the representations and warranties of
the  Company  in  Section  3  below.

2.     Covenants  of  Company.

     2.1  Certificate of Designation. The Company agrees to file the Certificate
of  Designation  in  the  form  of Exhibit "A" attached hereto with the Delaware
Secretary  of  State  prior  to  the  Closing.

     2.2  Condition  of Closing. Quercus' obligations hereunder shall be subject
to the concurrent consummation of the Entech Acquisition. Quercus may waive this
condition  in  its  sole  and  absolute  discretion.

     2.3  Amendment  to  Certificate  of  Incorporation. Quercus and the Company
agree  and  acknowledge  that (i) the Company does not have currently authorized
sufficient  shares  of  unissued Common Stock to allow for the conversion of the
Series  E  Preferred,  (ii)  the  Company's board of directors (the "BOARD") has
approved  an  amendment  ("AMENDMENT")  to  the  Company's  Certificate  of
Incorporation  to increase the authorized number of Common Stock to four hundred
twenty-five  million  (425,000,000),  which would authorize sufficient shares of
Common  Stock  to  allow the conversion of the Series E Preferred in full, (iii)
the  Board has approved the holding of a meeting of Shareholders to consider and
approve  the  Amendment,  and  has  voted  to recommend to Shareholders that the
Amendment  be  approved,  and  (iv)  the  Company  has  authorized "blank check"
preferred  stock  with respect to which the Board has the power to designate the
rights,  preferences  and  privileges.  In  light  of the foregoing, the Company
agrees  (x)  to  use  best  efforts  to  cause  the  Amendment to be approved by
Shareholders  and  filed  with  the  Delaware  Secretary  of  State  as  soon as
practicable,  and  to  thereafter  at  all  times  cause  there to be sufficient
authorized and unissued shares of Common Stock and other securities to allow the
Series  E  Preferred  to  be  converted  in  full.

     2.4  Filing Amendment. The Company agrees to use best efforts to obtain SEC
approval of its proxy statement, to obtain shareholder approval of the Amendment
and  to  file  the  Amendment  with  the  Delaware Secretary of State as soon as
practicable  following  the  Closing  (the  "FILING  DEADLINE").

     3.  Representations  and  Warranties of Company. Except for compliance with
the  requirements  contained  in  Sections  2.1  and  2.3,  the  Company  hereby
represents  and  warrants  to  Quercus  that:

     3.1  Organization,  Good  Standing  and  Qualification.  The  Company  is a
corporation duly organized, validly existing and in good standing under the laws
of  the State of Delaware. The Company has full corporate power and authority to
own  and  hold  its  properties and to conduct its business. The Company is duly
licensed or qualified to do business, and in good standing, in each jurisdiction
in  which  the  nature of its business requires licensing, qualification or good
standing,  except  for  any  failure  to  be so licensed or qualified or in good
standing  that would not have a material adverse effect on (i) the Company, (ii)
its  consolidated  results  of operations, assets, or financial condition, (iii)
its ability to perform its obligations under this Agreement or (iv) the Series E
Preferred  (a  "MATERIAL  ADVERSE  EFFECT").

     3.2  Consents  and  Approvals. No consent, approval, order or authorization
of, or registration, qualification, designation, declaration or filing with, any
federal,  regional,  state  or  local  governmental authority on the part of the
Company  is  required  in  connection  with the consummation of the transactions
contemplated  by  this  Agreement  except for filings with the State of Delaware
relating  to  the  Entech  Acquisition.

     3.3  Authorization.  The  Company has full corporate power and authority to
execute,  deliver  and  enter  into  this  Agreement  and  to  consummate  the
transactions  contemplated  hereby.  All  action  on  the  part  of  the Company
necessary  for  the  authorization,  execution, delivery and performance of this
Agreement  by the Company, the authorization, sale, issuance and delivery of the
Series  E  Preferred,  and  the Common Stock issuable upon the conversion of the
Series  E  Preferred  (the  "CONVERSION  SHARES")  and  the  performance  of the
Company's  obligations hereunder has been taken. The Conversion Shares have been
duly authorized and, when issued and paid for in accordance with this Agreement,
will be validly issued, fully paid and non-assessable and will be free and clear
of  all  liens imposed by or through the Company other than restrictions imposed
by  this  Agreement and applicable securities laws. This Agreement has been duly
executed  and  delivered  by  the  Company,  and  constitutes a legal, valid and
binding obligation of the Company, enforceable against the Company in accordance
with  its  terms  except  (i)  as  limited by applicable bankruptcy, insolvency,
reorganization,  moratorium  and  other  laws  of  general application affecting
enforcement  of creditors' rights generally and by general equitable principles,
or (ii) as limited by laws relating to the availability of specific performance,
injunctive  relief,  or  other  equitable  remedies.

3.4     Compliance With Other Instruments.

     (a)  The  execution  and  delivery by the Company of this Agreement and the
consummation  of the transactions contemplated hereby will not (i) result in the
violation of any provision of the Certificate of Incorporation or By-laws of the
Company,  (ii)  result  in  any violation of any law, statute, rule, regulation,
order,  writ,  injunction,  judgment  or  decree  of  any  court or governmental
authority to or by which the Company is bound, (iii) trigger the increase in the
rights  of  any  holder  of the Company's outstanding debt or equity securities,
including  securities  converted  with  such  securities, (iv) conflict with, or
result  in  a  breach  or  violation  of,  any of the terms or provisions of, or
constitute  (with  due  notice  or  lapse  of time or both) a default under, any
lease,  loan  agreement,  mortgage, security agreement, trust indenture or other
agreement  to  which  the Company is a party or by which it is bound or to which
any  of  its  properties  or  assets  is  subject, nor result in the creation or
imposition  of  any lien upon any of the properties or assets of the Company, in
the  cases  of  clauses  (ii) and (iii) above, only to the extent such conflict,
breach,  violation,  default  or  lien  reasonably could, individually or in the
aggregate,  have  or  result  in  a  Material  Adverse  Effect.

     (b)  No  consent,  approval, license, permit, order or authorization of, or
registration,  declaration  or  filing with, any court, administrative agency or
commission  or  other  governmental  authority  remains  to  be  obtained  or is
otherwise  required  to  be  obtained  by  the  Company  in  connection with the
authorization,  execution  and delivery of this Agreement or the consummation of
the  transactions  contemplated  hereby, including, without limitation the issue
and  sale of the Series E Preferred and the Conversion Shares, except filings as
may  be required to be made by the Company with (i) the United States Securities
and  Exchange  Commission  ("SEC") and (ii) state "blue sky" or other securities
regulatory  authorities.

     3.5  Material  Adverse Changes. Since June 30, 2007, there has not occurred
any  event  or  events  which,  singly  or  in  the  aggregate,  have had or are
reasonably  expected  to  have,  a  Material  Adverse  Effect upon the business,
operations  or  financial  condition  of  the  Company.

     3.6  Issuance  of Securities. Since September 28, 2007, the Company has not
issued  any  capital  stock, or any securities convertible into, or exchangeable
for,  capital stock, or entered into any written or oral commitment with respect
thereto,  except  for  its  agreement  of  merger  in connection with the Entech
Acquisition.

     4. Representations and Warranties of Quercus. Quercus hereby represents and
warrants  to,  and  agrees  with,  the  Company  that:

     4.1  Restricted  Securities.  Quercus  understands  that  (i)  the Series E
Preferred and the Conversion Shares are characterized as "restricted securities"
under  the  federal securities laws inasmuch as they are being acquired from the
Company  in  a transaction not involving a public offering, (ii) under such laws
and  applicable  regulations  such securities may be resold without registration
under  federal  and state securities laws only in certain limited circumstances,
and  (iii)  the  Company  may  require  a legal opinion of Quercus' counsel with
respect  to  unregistered  transfers.

     4.2  Accredited  Investor.  Quercus  represents  that  it is an "accredited
investor"  within  the  meaning of Regulation D promulgated under the Securities
Act.

     4.3  Legends.  Quercus  understands  that  the  certificates evidencing the
Series  E  Preferred  Stock will bear substantially the following legends: THESE
SECURITIES  HAVE  NOT  BEEN  REGISTERED  UNDER  THE  SECURITIES  ACT OF 1933, AS
AMENDED.  THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN THE
ABSENCE  OF  A  REGISTRATION  STATEMENT IN EFFECT WITH RESPECT TO THE SECURITIES
UNDER  SUCH  SECURITIES ACT OR AN OPINION OF COUNSEL SATISFACTORY TO THE COMPANY
THAT  SUCH  REGISTRATION  IS NOT REQUIRED OR UNLESS SOLD PURSUANT TO RULE 144 OF
SUCH  SECURITIES  ACT.

     4.4 Investment Purposes. The securities will be acquired for investment for
Quercus'  own  account,  not  as  a  nominee or agent, an not with a view to the
public resale or distribution thereof within the meaning of the federal or state
securities  laws,  and Quercus has no present intention of selling, granting any
participation in, or otherwise distributing the same. Quercus further represents
that  he or it does not have any contract, undertaking, agreement or arrangement
with  any  person to sell, transfer or grant participations to such person or to
any  third  person,  with  respect  to  any  of  the  securities.

     5.  Certain  Covenants of WWAT. The provisions of Section 4 of that certain
Stock  and  Warrant  Purchase  Agreement  between  Quercus and the Company dated
September  28,  2007  (the  "PURCHASE  AGREEMENT")  are  hereby  incorporated by
reference  and  shall  apply  to seven million five hundred thousand (7,500,000)
shares  of  Common Stock from time to time owned by Quercus, whether such Common
Stock  constitutes  part  of the Public Shares or constitutes Conversion Shares.

     6.  Indemnification.  The provisions of Section 5 of the Purchase Agreement
are  hereby  incorporated  by  reference  and  shall  apply  to the transactions
contemplated  by  this  Agreement.

     7.  Survival  of  Representations  and  Warranties.  All  representations,
warranties  and  agreements made by WWAT and Quercus in this Agreement or in any
certificate  or  other  instrument  delivered  pursuant hereto shall survive the
Closing  and  any investigation and discovery by WWAT or by Quercus, as the case
may  be,  made  at any time with respect thereto; provided, however, that, other
than  with  respect  to  Section  3.6  (for which there shall be no time limit),
neither  Quercus  nor  WWAT  shall  have  any  liability  to  the  other for any
misrepresentation,  inaccuracy or omission in any representation or warranty, or
any breach of any representation or warranty, unless the party asserting a claim
with  respect  to any thereof gives to the other written notice of such claim on
or  before  the  date  which  is  two  (2)  years  following  the  Closing Date.

     8.     Miscellaneous.

     8.1  Entire  Agreement.  This Agreement contains the entire agreement among
the  parties  with  respect  to  the  exchange  contemplated  hereby.

     8.2  Governing Law. This Agreement shall be governed by and construed under
the  laws  of  the  State  of  Delaware.

     8.3  Counterparts.  This  Agreement  may  be  executed  in  two  or  more
counterparts,  each  of  which  shall  be  deemed  an original, but all of which
together  shall  constitute  one  and  the  same  instrument.

     8.4 Severability. The invalidity of any portion hereof shall not affect the
validity,  force, or effect of the remaining portions hereof. If it is ever held
that  any  restriction  hereunder  is  too  broad  to permit enforcement of such
restriction  to  its fullest extent, the parties agree that a court of competent
jurisdiction may enforce such restriction to the maximum extent permitted by law
against those for whom it may be enforceable, and each party hereby consents and
agrees  that such scope may be judicially modified accordingly in any proceeding
brought  to  enforce  such  restriction.

     8.5  Further  Assurances.  The  parties  hereto  shall,  without additional
consideration,  execute  and  deliver or cause to be executed and delivered such
further  instruments and shall take or cause to be taken such further actions as
are  necessary  to  carry  out  more  effectively the intent and purpose of this
Agreement.

     8.6  Successors and Assigns. Except as otherwise provided herein, the terms
and  conditions of Section 5 of this Agreement shall inure to the benefit of and
be  binding upon the respective successors and assigns of the parties (including
transferees  of  any securities). Nothing in this Agreement, express or implied,
is  intended  to  confer  upon any party, other than the parties hereto or their
respective  successors  and  assigns,  any  rights,  remedies,  obligations  or
liabilities  under  or by reason of this Agreement, except as expressly provided
in  this  Agreement.

     8.7  Titles  and Subtitles. The titles and subtitles used in this Agreement
are  used  for  convenience  only  and are not to be considered in construing or
interpreting  this  Agreement.

     8.8  Notices.  All  notices  required  or  permitted  hereunder shall be in
writing and shall be deemed effectively given: (i) upon personal delivery to the
party  to  be  notified,  (ii) when sent by confirmed telex or facsimile if sent
during normal business hours of the recipient, if not, then on the next business
day; (iii) five (5) days after having been sent by registered or certified mail,
return  receipt  requested,  postage  prepaid; or (iv) one (1) day after deposit
with  a  nationally  recognized overnight courier, specifying next day delivery,
with  written  verification  of receipt. All communications shall be sent to the
address  as  set  forth on the signature page hereof or at such other address as
such  party  may  designate by ten (10) days advance written notice to the other
parties  hereto.

     8.9  Finder's  Fee.  Each  party  represents that it neither is nor will be
obligated  for  any  finders'  fee  or  commission  in  connection  with  this
transaction.  Quercus  agrees to indemnify and to hold harmless the Company from
any liability for any commission or compensation in the nature of a finders' fee
(and  the  costs  and  expenses  of defending against such liability or asserted
liability)  for  which  Quercus  or  any  of  its  trustees,  employees  or
representatives  is  responsible.  The  Company  agrees  to  indemnify  and hold
harmless  Quercus  from  any liability for any commission or compensation in the
nature  of  a finders' fee (and the costs and expenses of defending against such
liability  or  asserted liability) for which the Company or any of its officers,
employees  or  representatives  is  responsible.

     8.10  Expenses. The Company shall pay all costs and expenses that it incurs
with  respect  to  its  negotiation, execution, delivery and performance of this
Agreement  and,  if the Closing is effected, shall pay the actual legal fees and
costs  of  Greenberg Glusker Fields Claman & Machtinger LLP, counsel to Quercus,
in  an amount not to exceed Five Thousand Dollars ($5,000). If any action at law
or  in  equity is necessary to enforce or interpret the terms of this Agreement,
the  prevailing party shall be entitled to reasonable attorney's fees, costs and
necessary  disbursements in addition to any other relief to which such party may
be  entitled.

     8.11  Amendments and Waivers. Any term of this Agreement may be amended and
the  observance of any term of this Agreement may be waived (either generally or
in  a  particular instance and either retroactively or prospectively), only with
the written consent of the Company and Quercus. Any amendment or waiver effected
in  accordance  with  this  paragraph  shall  be binding upon each holder of any
securities  purchased  under  this  Agreement  at the time outstanding, and each
future  holder  of  all  such  securities  and  the  Company.

     8.12  Aggregation  of Stock. All shares of Common Stock held or acquired by
affiliated  entities  or persons shall be aggregated together for the purpose of
determining the availability of any rights under this Agreement.


                          [SIGNATURE PAGE FOLLOWS]


<PAGE>

IN  WITNESS  WHEREOF,  the  parties  have executed this Agreement as of the date
first  above  written.

PURCHASER:

THE QUERCUS TRUST


By:          /s/  David  Gelbaum
           ---------------------------------
           Name:     David Gelbaum
            Its:     Trustee

Address:

1835 Newport Blvd.
A109 - PMB 467
Costa Mesa, CA 92627


COMPANY:

WORLDWATER & SOLAR TECHNOLOGIES CORP.


By:          /s/ Quentin T. Kelly
          ---------------------------------
          Name:     Quentin T. Kelly
          Its:      Chief Executive Officer


Address:

Pennington Business Park
55 Route 31 South
Pennington, New Jersey 08534

<PAGE>

                                   EXHIBIT "A"
                           CERTIFICATE OF DESIGNATION