REGISTRATION RIGHTS JOINDER

Exhibit 99.18

REGISTRATION RIGHTS JOINDER

THIS REGISTRATION RIGHTS JOINDER is made as of the 11th day of June, 0000,

X X X X X X X:

BROOKFIELD BRP HOLDINGS (CANADA) INC., a corporation incorporated under the laws of the province of Ontario

(“BRPHC”)

– and –

ORION US HOLDINGS 1 L.P., a limited partnership incorporated under the laws of the State of Delaware

(“Brookfield”)

– and –

TERRAFORM POWER, INC., a corporation incorporated under the laws of the State of Delaware

(“TerraForm”)

RECITALS:

Brookfield and TerraForm entered into a Registration Rights Agreement dated October 16, 2017 (the “Registration Rights Agreement”); and

BRPHC has agreed to purchase 29,878,048 shares of Class A common stock, par value $0.01 per share, of TerraForm (the “Class A Shares”) in a private placement (the “Private Placement”).

NOW THEREFORE in consideration of the premises and mutual agreements herein contained, and other good and valuable consideration (the receipt and sufficiency of which are hereby acknowledged), the parties hereto agree as follows:

1. Registration Rights Joinder

Upon the consummation of the Private Placement, (a) BRPHC shall be added as a “Holder” under the Registration Rights Agreement and (b) BRPHC shall be subject to and bound by all the terms and conditions of the Registration Rights Agreement as a “Holder”.

Except as modified hereby, the terms of the Registration Rights Agreement remain in full force and effect. TerraForm acknowledges and agrees that the Conflicts Committee of the TerraForm Board of Directors has agreed to and approved this Registration Rights Joinder.

2. Further Assurances

Each of the parties hereto shall promptly do, make, execute or deliver, or cause to be done, made, executed or delivered, all such further acts, documents and things as the other party hereto may

reasonably require from time to time for the purpose of giving effect to this Registration Rights Joinder and shall use its best efforts and take all such steps as may be reasonably within its power to implement to their full extent the provisions of this Registration Rights Joinder.

3. Governing Law

This Registration Rights Joinder shall be governed by and construed in accordance with the laws of the State of New York.

4. Counterparts

This Registration Rights Joinder may be executed in one or more counterparts, and by different parties hereto on separate counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument. Execution and delivery of this Registration Rights Joinder may be made and evidenced by facsimile transmission or other means of electronic transmission.

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IN WITNESS WHEREOF the parties hereto have executed this Registration Rights Joinder as of the date first written above.

	BROOKFIELD BRP HOLDINGS (CANADA) INC.,
	by	/s/ Xxxxxxxx Xxxxx
		Name: Xxxxxxxx Xxxxx
		Title:   Senior Vice President and Secretary

	ORION US HOLDINGS 1 L.P.,
	by	ORION US GP LLC,
		by	/s/ Xxxxxx Xxxxxxxxxxxx
			Name: Xxxxxx Xxxxxxxxxxxx
			Title:   Senior Vice President

	TERRAFORM POWER, INC.,
	by	/s/ Xxxxxx Xxxxxxxxx
		Name: Xxxxxx Xxxxxxxxx
		Title:   General Counsel