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Zorowatt vs REopt

Where REopt is strong, where it falls short, and what changes if you switch. Every number can be checked on their site.

REopt is a free, open-source optimiser for sizing and dispatching PV, storage, wind, CHP and more, with a web tool and an API, aimed at federal agencies, researchers and engineers. Zorowatt is a paid browser tool for consultants who sell battery studies to European businesses. (reopt.nlr.gov)

Short answer
When to pick REopt
Pick REopt if you want a free, open-source optimiser with an API, you are happy to prepare the inputs yourself, and you need technologies Zorowatt does not model, such as wind or CHP.
When to pick Zorowatt
Pick Zorowatt if you sell battery studies to European businesses and want the data checks, the bill rebuilt under a sourced Dutch, German or Romanian tariff and checked against the invoices, and a PDF report for the client in one flow.

Facts about the other tool read on 2026-10-28 from the pages linked in each cell. Prices and features change; check the vendor's page before you rely on one.

FeatureZorowattREopt
PriceFree €0 · Starter €49 / month · Pro €149 / month · Enterprise on requestFree: a no-cost online platform, an API and open-source code; REopt.jl is licensed Apache-2.0energy.gov, github.com · 2026-10-28
Runs onThe browser; nothing to installWeb tool, API and a Julia package (REopt.jl)reopt.nlr.gov, energy.gov, github.com · 2026-10-28
Battery dispatchRule-based, with the optimal (LP) dispatch as the upper bound; every saving is billed by the same bill engineOptimal sizing and dispatch as an LP or MILP (solvers such as HiGHS, Cbc, SCIP, Xpress, CPLEX); since August 2026 the web tool also shows rule-based peak shaving and self-consumption next to the optimum, which it calls the upper boundgithub.com, reopt.nlr.gov · 2026-10-28
TariffsVersioned 2026 tariffs, each with its source: Netherlands (Liander, Stedin, Enexis, plus the ACM 2028 draft as a scenario), Germany (NEW Netz, Netze BW, RheinNetz, levies and Stromsteuer), Romania (ANRE zones). Any other country: a generic template where you enter the ratesOutside the US no rates are built in: simple or time-of-use rates are entered by hand, in US dollars; detailed custom rates need a free accountreopt.nlr.gov · 2026-10-30
SolarPlanned solar modelled from PVGIS (EU Joint Research Centre) and laid on the meter data; existing PV is in the meter data (import and export)PV, wind and CHP sized together with storagegithub.com · 2026-10-28
APINo API for customers yetPublic APIenergy.gov · 2026-10-28

In short

REopt is the stronger optimiser and costs nothing; it also has an API, which Zorowatt does not offer customers yet. Zorowatt is built for a different job: turning one business's meter data and bills into a checked bill, a battery size and a client report. Researchers and engineers who want the optimisation itself will be well served by REopt; consultants who need the European bill and the report will find more of their work done in Zorowatt.

Price per year

REopt
Free
Zorowatt
Starter €588 a year (€348 at the founding price) · Pro €1,788 a year for 3 seats · single analyses €15

As each vendor's page states it; prices in other currencies are not converted.

How to switch

Upload the same load column you gave REopt: Zorowatt reads 8,760 or 35,040 values with no dates as a year from 1 January.

  1. Upload the site's meter data to the free data checker or the Workspace: every assumption made reading the file is listed.
  2. Pick the site's tariff and enter the invoices: the bill check shows whether the baseline matches before anything is sized.
  3. Size the battery, compare it with your earlier study, and send the client the PDF report.

Questions

Is REopt really free?
Yes. The US Department of Energy describes it as a no-cost online platform with an API and open-source code, and REopt.jl is licensed Apache-2.0 (read on 2026-10-28). The legacy address reopt.nrel.gov did not resolve that day; the web tool is at reopt.nlr.gov.
Is Zorowatt's optimiser the same as REopt's?
No. REopt solves sizing and dispatch together as an LP or MILP. Zorowatt sizes with a rule-based controller, the behaviour a real energy management system can reach, and computes the optimal (LP) dispatch for the chosen battery as the upper bound; the LP runs on HiGHS, one of the solvers REopt.jl supports. REopt's web tool has shown rule-based dispatch next to its optimum since August 2026, the same split. The difference is the bill: every saving Zorowatt reports is billed by its own engine under a European tariff and checked against the invoices.
Does REopt handle European tariffs?
Not built in. Its international guidance says rates for sites outside the US are entered by hand, as simple or time-of-use rates in US dollars; detailed custom rates need a free account (reopt.nlr.gov, read on 2026-10-30). Zorowatt ships sourced 2026 tariffs for the Netherlands, Germany and Romania, in euro.
Does Zorowatt have an API?
Not for customers yet. Zorowatt is used in the browser; results can be exported as CSV and printed as a PDF report.
Free tools

Try it on your own file first

Both tools run in the browser with no account; the file is not uploaded.

Looking for a REopt alternative?

Zorowatt runs in the browser, reads the site's own meter data and rebuilds its bill before it sizes anything.

REopt alternative for C&I battery studies in Europe →

Switching?

Bring a site you already studied: upload its meter data and bills, and set the result next to your old one.

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