What kW, kWp, MW and MWh measure in a Romanian project file

Power and energy

A kilowatt (kW) measures power, the rate at which electricity flows at a given moment. A kilowatt-hour (kWh) measures energy, the amount delivered over time: one kilowatt for one hour. A megawatt (MW) is 1,000 kW and a megawatt-hour (MWh) is 1,000 kWh.

A solar or wind project is sized in power and earns from energy: its installed power is given in kW or MW, its yearly production in MWh or GWh. A battery needs both figures. MW says how fast it can charge or discharge, MWh says how much energy it holds, and MWh divided by MW gives the hours it can run at full power.

The 2025 environmental memorandum for a battery project in Medgidia, published by ANMAP, shows why the two are read together. Its title gives 189,1 MW. Its technical table, on page 16 and again on page 28, gives the power and the energy:

The 74 battery containers of 4.472 MWh each, listed on page 15, add up to 330.9 MWh. Two other paragraphs of the same memorandum, on pages 15 and 27, describe the system as “122.7 MWac/214.7 MWhdc”. Both pairs give a nominal ratio of about 1.75 hours, so they read as two sizes of one design, and the memorandum does not say which one is current. A reader should ask for the current configuration rather than choose one.

The table also calls the MWh figure “putere instalata in acumulatori”, installed power in the batteries. The unit shows that the figure is an amount of energy, whatever the label says.

Energy stated on the direct current side, at the batteries, is more than the energy delivered at the connection point, because of conversion, transformer and auxiliary losses. The usable energy is lower again, because of the depth of discharge, the round-trip efficiency and the batteries’ degradation over time.

kWp and kW: the panels and the inverters

A PV module’s rating in watts-peak (Wp, kWp, MWp) is its direct current output under standard test conditions: an irradiance of 1,000 W/m², a cell temperature of 25 °C and an AM 1.5 spectrum. The feasibility study for a 200 kW solar plant in Gurghiu states the same conditions on page 29. Real output is usually lower, and on cold, clear days it can be higher.

Inverters turn the direct current into alternating current, and their rating is in kW. Panel and inverter totals differ by design, and many plants have more panel power than inverter power.

Which of the two is the plant’s installed power? Romania’s connection regulation defines installed power, for a generating unit, as its rated active (or apparent) power, as indicated in the manufacturer’s technical documentation, on its nameplate or by the manufacturer. It defines total installed power as the sum of the installed powers of the generators at a production site. The regulation does not say whether a solar plant’s installed power is the power of its panels or of its inverters. The two ATRs cited here list both, in separate tables.

The ATR for a 400 kW solar plant in Arad, issued by Rețele Electrice România on 15 April 2025, is an example. Its panel table gives 666 panels of 0,6 kW, 399,6 kW in direct current (page 1). Its inverter table gives four inverters of 100 kW, 400 kW in alternating current (page 2). Page 8 says it in words:

The Gurghiu study mixes the two on page 25. It adds up the inverters’ rated power, calls the total the alternating current power, and writes it in kWp:

Page 29 of the same study gives 200,00 kWp for the panels, and page 58 calls the plant “capacitate 200,00 kW”. A figure labelled as alternating current and written in kWp cannot be checked from the sentence alone. The inverter table in the ATR, the inverter datasheets or the single-line diagram settle it.

The power the grid accepts

The same regulation defines approved power as the maximum simultaneous active (or apparent) power that a user may draw from or export to the grid through the connection installation covered by the ATR. The ATR records this figure. For export, the network operator sets it at no more than the power the user requested.

Both ATRs cited here give the approved power for the situation when the ATR was issued and for each stage up to the final one, each valid from a date, in kVA and in kW, with export and draw on separate lines.

In the Arad ATR, the approved export for the final stage, valid from 15 April 2025, is 387,608 kW, or 430,676 kVA (page 2). That is less than the 399,6 kW of panels and the 400 kW of inverters. The ATR also has a line for the export allowed before grid reinforcement works are done, and in this ATR it is empty.

For a buyer, the export figure in the ATR, at the stage in force, limits what the plant may deliver at the connection point, whatever the panel total.

An ATR issued in Târgoviște in August 2024, for a school with a solar installation, shows another arrangement. Its panels add up to 179,280 kW in direct current and its inverters to 186,400 kW (page 2), and the approved export is 179,280 kW (pages 3 and 4). Here the inverters are larger than the panels, and the approved export equals the panel total.

kW and kVA

kW measures active power, the part that does useful work. kVA measures apparent power, which also counts the reactive power the network has to carry. The ratio of kW to kVA is the power factor.

Both ATRs give the approved power in kW and in kVA. In the Arad ATR, the export at the final stage is 387,608 kW and 430,676 kVA, a ratio of 0.90. The power drawn from the grid is 1.557 kW and 1.692,3913 kVA in the situation when the ATR was issued, and 500 kW and 543,478 kVA at the final stage, a ratio of 0.92 (page 2). In the Târgoviște ATR, the power drawn is 452,520 kW and 502,800 kVA at each stage, a ratio of 0.90 (page 4). Neither ATR states a power factor.

A kVA figure should therefore not be turned into kW with an assumed factor. When a document gives only kVA, the kW figure is a question for the network operator or the project’s designer.

How the numbers are written

Romanian documents usually mark decimals with a comma and group thousands with a dot. In the Arad ATR, “1.557” kW is one thousand five hundred and fifty-seven kilowatts, not a little over one and a half. The Medgidia memorandum uses the dot the other way: its containers hold “4.472 MWh” each, and 74 of them make 330.9 MWh only if the dot marks the decimals. Its title says 189,1 MW and its table says 189.1 MW.

The Târgoviște ATR prints its approved power as “179,280” kW. Read with English conventions, that is 179 thousand kW. Read with Romanian ones, it is 179.28 kW. The ATR’s own panel table settles it: on page 2, 240 panels of 0,250 kW give 60,000, and the five rows add up to 179,280. The arithmetic works only with a decimal comma, so the approved power is 179.28 kW.

Units are sometimes joined to the number. A 2022 memorandum for a wind farm in Pecineaga describes the turbines this way:

Eight turbines of 6 MW make 48 MW. The model name carries digits too, and they are not quantities.

What to check for each figure

• Is it power (kW, MW) or energy (kWh, MWh)?
• Where is it measured: at the panels in direct current (kWp), at the inverters in alternating current (kW), or at the connection point (the approved power in the ATR)?
• Is it active power (kW) or apparent power (kVA)?
• Which stage of the ATR does it belong to, and from which date is it valid?
• Is there a lower export figure until grid reinforcement works are done? If so, who pays for the works, and when will they be finished?
• For a battery, what power is approved for drawing from the grid (charging), as well as for export?
• Is the ATR still valid, and have the connection contract (contract de racordare) and then the connection certificate (certificat de racordare) followed?
• Do the ATR, the connection contract, the building permit (autorizație de construire) and the set-up authorisation (autorizație de înființare) give the same installed power?
• Does the document mark decimals with a comma or a dot, and does its own arithmetic confirm the reading?
• If two figures in one document disagree, which configuration is current? Ask, and keep the page of each figure.

How ELARID reads these figures

ELARID records each figure with its unit, its page and the words it was read from. It keeps kVA apart from kW, and kWp apart from kW. When a number can be read in two valid ways, it shows both readings and waits for a person to choose. When a sentence gives a figure in a unit that contradicts what the sentence says it measures, such as an alternating current total in kWp, the reading is marked “contradicts itself” and no value is recorded.

See the 179,280 example on the home page →