Report of Foreign Issuer (6-k)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of August, 2020

Commission File Number 001-36487

Atlantica Sustainable Infrastructure plc

(Exact name of Registrant as specified in its charter)

Not applicable

(Translation of Registrant’s name into English)

Great West House, GW1, 17th floor

Great West Road

Brentford, TW8 9DF

United Kingdom

Tel: +44 203 499 0465

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F:

☒ Form 20-F

☐ Form 40-F

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1): ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7): ☐

This Report on Form 6-K is incorporated by reference into the Registration Statement on Form F-3 of the Registrant filed with the Securities and Exchange Commission on August 6, 2018 (File 333-226611).

Q2 2020 Earnings PresentationAugust 3, 2020

DISCLAIMER Forward Looking StatementsThis presentation contains forward-looking statements. These forward-looking statements include, but are not limited to, all statements other than statements of historical facts contained in this presentation, including, without limitation, those regarding our future financial position and results of operations, our strategy, plans, objectives, goals and targets, future developments in the markets in which we operate or are seeking to operate or anticipated regulatory changes in the markets in which we operate or intend to operate. In some cases, you can identify forward-looking statements by terminology such as "aim," "anticipate," "believe," "continue," "could," "estimate," "expect," "forecast," "guidance," "intend," "is likely to," "may," "plan," "potential," "predict," "projected," "should" or "will" or the negative of such terms or other similar expressions or terminology.By their nature, forward-looking statements involve risks and uncertainties because they relate to events and depend on circumstances that may or may not occur in the future. Forward-looking statements speak only as of the date of this presentation and are not guarantees of future performance and are based on numerous assumptions. Our actual results of operations, financial condition and the development of events may differ materially from (and be more negative than) those made in, or suggested by, the forward-looking statements. Except as required by law, we do not undertake any obligation to update any forward-looking statements to reflect events or circumstances after the date hereof or to reflect the occurrence of anticipated or unanticipated events or circumstances.Investors should read the section entitled "Item 3D. Key Information—Risk Factors" and the description of our segments and business sectors in the section entitled "Item 4B. Information on the Company—Business Overview", each in our annual report for the fiscal year ended December 31, 2019 filed on Form 20-F, for a more complete discussion of the risks and factors that could affect us.Forward-looking statements include, but are not limited to, statements relating to: expected amounts, payments and closing timelines for investments; business synergies from investments; project growth strategy; accretive investment opportunities; strategic business alternatives to ensure optimal company value; estimated returns and cash available for distribution (“CAFD”) estimates, including from project debt refinancing; net corporate leverage based on CAFD estimates; debt refinancing; ESG initiative improvement; the quality of our long-term contracts; self-amortizing project debt structure and related debt reduction; the use of non-GAAP measures as a useful predicting tool for investors; the possibility to extend asset life; cost improvements from debt refinancing; the impact of COVID-19 and the ongoing economic crisis; dividends; and various other factors, including those factors discussed under “Item 1.A—“Risk Factors” in our Quarterly Report for the six-month period ended June 30, 2020 furnished on Form 6-K on the date hereof and “Item 3.D—Risk Factors” and “Item 5.A—Operating Results” in our Annual Report for the fiscal year ended December 31, 2019 filed on Form 20-F.The CAFD and other guidance incorporated into this presentation are estimates as of February 27, 2020. These estimates are based on assumptions believed to be reasonable as of the date Atlantica published its FY 2019 Financial Results. Atlantica disclaims any current intention to update such guidance, except as required by law.Non-GAAP Financial Information This presentation also includes certain non-GAAP financial measures, including Adjusted EBITDA including unconsolidated affiliates, Adjusted EBITDA including unconsolidated affiliates as a percentage of revenues (margin) and CAFD. Non-GAAP financial measures are not measurements of our performance or liquidity under IFRS as issued by IASB and should not be considered alternatives to operating profit or profit for the period or any other performance measures derived in accordance with IFRS as issued by the IASB or any other generally accepted accounting principles or as alternatives to cash flow from operating, investing or financing activities. Please refer to the appendix of this presentation for a reconciliation of the non-GAAP financial measures included in this presentation to the most directly comparable financial measures prepared in accordance with IFRS as well as the reasons why management believes the use of non-GAAP financial measures in this presentation provides useful information.In our discussion of operating results, we have included foreign exchange impacts in our revenue and Adjusted EBITDA including unconsolidated affiliates by providing constant currency growth. The constant currency presentation is not a measure recognized under IFRS and excludes the impact of fluctuations in foreign currency exchange rates. We believe providing constant currency information provides valuable supplemental information regarding our results of operations. We calculate constant currency amounts by converting our current period local currency revenue and Adjusted EBITDA using the prior period foreign currency average exchange rates and comparing these adjusted amounts to our prior period reported results. This calculation may differ from similarly titled measures used by others and, accordingly, the constant currency presentation is not meant to substitute for recorded amounts presented in conformity with IFRS as issued by the IASB nor should such amounts be considered in isolation.

Key Messages Adjusted EBITDA including unconsolidated affiliates includes our share in EBITDA of unconsolidated affiliates (see reconciliation on page 29).This amount includes the ~$143 million of one-off cash generated in the second quarter 2020 referred to above. Adj. EBITDA incl. unconsolidated affiliates1 decreased by 7.4% mostly due to FX and lower solar radiation in EMEA No material impact from COVID-19 situation as of today; health and safety remains our first priority Continued executing on accretive growth strategyRaised a total of $489 million2 for growthExercised option to buy out Solana’s tax equity investor. Closing expected in August, subject to customary conditionsClosed the acquisition of Chile PV I, a 55MW solar asset through the Renewable Energy Platform created in Chile 3% year-over-year CAFD growth in H1 2020 up to $97.3 million Q2 2020 dividend of $0.42 per share Additionally generated ~$143 million of one-off cash through a non-recourse refinancing in Q2 to finance growth

1. Financial Results Sustainable Infrastructure

First Half US $ in millions 2020 2019 ∆ Reported ∆ Excluding FX impact Revenue 465.7 504.8 (7.7)% (6.1)% Adjusted EBITDA incl. unconsolidated affiliates1 380.1 410.5 (7.4)% (5.5)% Margin2 82% 81% CAFD 97.3 94.5 +2.9% Cash generation fromproject debt refinancings in the period 143 HIGHLIGHTS+3% CAFD Growth in H1 2020 Adjusted EBITDA including unconsolidated affiliates includes our share in EBITDA of unconsolidated affiliates (see reconciliation on page 29).Adjusted EBITDA Margin including unconsolidated affiliates is defined as Adjusted EBITDA including unconsolidated affiliates divided by revenue (see reconciliation on page 31).

WATER H1 2020 H1 2019 ∆ 15.6 11.9 +31% 12.9 11.2 +15% 83% 94% RENEWABLES H1 2020 H1 2019 ∆ 344.7 380.1 (9)% 275.1 301.4 (9)% 80% 79% EFFICIENT NATURAL GAS H1 2020 H1 2019 ∆ 52.0 61.7 (16)% 47.8 54.3 (12)% 92% 88% TRANSMISSION H1 2020 H1 2019 ∆ 53.4 51.1 +5% 44.3 43.6 +2% 83% 85% By Sector US $ in millions Revenue Adjusted EBITDA incl. unconsolidated affiliates1 Margin2 EMEA NORTH AMERICA H1 2020 H1 2019 ∆ 157.9 164.5 (4)% 142.6 147.2 (3)% 90% 89% SOUTH AMERICA H1 2020 H1 2019 ∆ 232.8 271.2 (14)% 177.7 205.8 (14)% 76% 76% By Region US $ in millions Revenue Adjusted EBITDA incl. unconsolidated affiliates1 Margin2 Adjusted EBITDA including unconsolidated affiliates includes our share in EBITDA of unconsolidated affiliates (see reconciliation on page 29).Adjusted EBITDA Margin including unconsolidated affiliates is defined as Adjusted EBITDA including unconsolidated affiliates divided by revenue (see reconciliation on page 31). H1 2020 H1 2019 ∆ 75.0 69.1 +9% 59.8 57.5 +4% 80% 83% HIGHLIGHTSPerformance by Sector and Region

Includes curtailment in wind assets for which we received compensation.Represents total installed capacity in assets owned at the end of the period, regardless of our percentage of ownership in each of the assets.GWh produced in the first half of 2020 includes 30% production from Monterrey since August 2019. Major maintenance overhaul in ACT held in Q1 and Q2 2019, as scheduled, which reduced production and electric availability as per contract. Electric availability refers to operational MW over contracted MW.Includes 43MW corresponding to our 30% share of Monterrey since August 2, 2019.Availability refers to actual availability divided by contracted availability. WATER RENEWABLES TRANSMISSION EFFICIENT NATURAL GAS H1 2020 H1 2019 Availability6 102.0% 100.6% Mft3 in operation2 17.5 10.5 H1 2020 H1 2019 GWh produced1 1,482 MW in operation2 1,551 1,496 H1 2020 H1 2019 GWh produced3 1,268 Electric availability4 101.7% 88.5% MW in operation5 343 300 H1 2020 H1 2019 Availability6 99.9% 100.0% Miles in operation 1,166 1,152 1,651 866 KEY OPERATIONAL METRICSSteady Operational Performance

Adjusted EBITDA including unconsolidated affiliates includes our share in EBITDA of unconsolidated affiliates (see reconciliation on page 29).Includes proceeds for $7.4 million and $14.8 million for the six-month period ended June 30, 2020 and June 30, 2019 respectively, related to the amounts received by Solana in relation to the consent with the DOE. Consolidated cash as of June 30, 2020 increased by $226.0 million vs December 31, 2019 including FX translation differences of $(11.1) million. First Half Second Quarter US $ in millions Q2 2020 Q2 2019 H1 2020 H1 2019 Adjusted EBITDA incl. unconsolidated affiliates1 214.1 229.3 380.1 410.5 Share in Adjusted EBITDA of unconsolidated affiliates (4.0) (2.0) (7.5) (4.1) Net interest and income tax paid (119.5) (129.4) (131.0) (143.3) Variations in working capital (24.7) (37.4) (84.0) (91.9) Non-monetary adjustments and other (3.2) (8.3) (9.2) (22.1) OPERATING CASH FLOW 62.7 52.2 148.4 149.1 INVESTING CASH FLOW2 17.6 (97.1) 16.8 (119.4) FINANCING CASH FLOW 12.1 (39.8) 71.9 (84.4) Net change in consolidated cash3 92.4 (84.7) 237.1 (54.7) CASH FLOWIncreasing Operating Cash Flow

NET DEBT POSITION1 Net debt corresponds to gross debt including accrued interest less cash and cash equivalents.Corporate Net Debt defined as indebtedness where Atlantica Sustainable Infrastructure plc. is the primary obligor minus cash and cash equivalents held at Atlantica Sustainable Infrastructure plc. Project Net Debt is defined as indebtedness where one of our subsidiaries is the primary obligor minus cash and cash equivalents held by one of our subsidiaries.Net corporate leverage calculated as corporate net debt divided by midpoint 2020 CAFD guidance before corporate debt service. US $ in millions As of Jun. 30,2020 As of Dec. 31,2019 Corporate Net Debt2 558.3 657.8 Project Net Debt3 4,497.5 4,355.6 NET DEBTConservative Corporate Leverage Corporate net debt / CAFD pre corporate debt service4 2.3x

2. Strategic Update Sustainable Infrastructure

GROWTH STRATEGYRaised over $400 million for growth Exercised Solana option. Closing expected in AugustClosed Chile PV IOther opportunities Weighted average cost of new financings and refinancings closed in 2020. Average cost of new financings: 3.9%1 Cash generated from Project Debt Refinancings (non-recourse) Total Funds Raised NIFA 2020 Million USD