A REopt alternative for European battery studies
If REopt doesn't fit your sites or your budget: what Zorowatt does differently, what it costs per year and how to move a site over.
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)
Five reasons consultants pick it.
- 01
The bill is checked against the invoices
Zorowatt rebuilds the bill from the meter data and sets it against each invoice, line by line, before it sizes anything. None of the tools we compared says it does this (checked 30 October 2026).
- 02
Dutch, German and Romanian tariffs, with sources
The 2026 tariffs of Liander, Stedin, Enexis, NEW Netz, Netze BW, RheinNetz and the Romanian ANRE zones are built in, each linked to its source. US tools leave European tariffs to you, in dollars.
- 03
Batteries from any maker
A database of 44 commercial products, every spec with its source. The free tools of Sungrow, SMA, Huawei and Victron size their own hardware only.
- 04
Prices on the page, from €0
A free analysis and free tools that need no account; Starter at €49 a month. Furo, Tibo, Gridcog and Energy Toolbase show no price before a call.
- 05
In the browser, in your language
A year of quarter-hours is simulated in about a second, with nothing to install, in English, Dutch, German and Romanian. HOMER, PVsyst and PV*SOL run on Windows.
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.
- Upload the site's meter data to the free data checker or the Workspace: every assumption made reading the file is listed.
- Pick the site's tariff and enter the invoices: the bill check shows whether the baseline matches before anything is sized.
- Size the battery, compare it with your earlier study, and send the client the PDF report.
- 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.
| Feature | Zorowatt | REopt |
|---|---|---|
| Price | Free €0 · Starter €49 / month · Pro €149 / month · Enterprise on request | Free: 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 on | The browser; nothing to install | Web tool, API and a Julia package (REopt.jl)reopt.nlr.gov, energy.gov, github.com · 2026-10-28 |
| Battery dispatch | Rule-based, with the optimal (LP) dispatch as the upper bound; every saving is billed by the same bill engine | Optimal 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 |
| Tariffs | Versioned 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 rates | Outside 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 |
| Solar | Planned 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 |
| API | No API for customers yet | Public 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.
Try it on your own file first
Both tools run in the browser with no account; the file is not uploaded.
Meter data checker
Gaps, duplicates, daylight saving time, kW vs kWh and coverage in a meter export, before the study starts. No account, nothing uploaded.
Peak-shaving battery calculator
Battery size and payback for cutting a site's peak charges — from four numbers or your own load profile. No account, nothing 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.
Switching?
Bring a site you already studied: upload its meter data and bills, and set the result next to your old one.