Glossary

Listed are terms applied in customer reports and studies.

1. General terms

Quantity Full name Measure unit Definition
DER - Distributed energy resources (DERs) are electricity-producing resources or controllable loads that are directly connected to a local distribution system or connected to a host facility within the local distribution system.

2. Technical terms

Full name Measure unit Definition
Estimated life time a (years) Total time of system/technology during which it can technically perform/function before it must be replaced
Operational Power kW Amount of electric or thermal generation capacity (rated values)
Nominal capacity - maximum value kW Highest power allowed in operation
Nominal capacity - minimum value kW Minimum power allowed in operation
Conversion efficiency % Ratio between useful output of an energy conversion machine and the input, in energy terms
Maximum (positive/negative) power gradient 1/h The time needed for a system to go from 0% to 100% power output (viceversa, when negative). 1/h means that the systems needs 1 hour to reach rated capacity, 0.5/h means 2 hours, 4/h means 15 minutes, etc.
Self-discharging ratio 1/d The energy losses of a (heat/cold/electric) storage that occur independently from its operation, expressed as daily rate. 1/d means that the storage loses 100% of the stored energy per day, 0.5 means 50%, etc.
Minimum SOC % An expression of the minimum energy of a storage system, as a percentage of its nominal capacity
Roundtrip efficiency % Round-trip efficiency is the fraction of energy put into the storage that can be retrieved
Heat loss kW The wasted heat or power
Start-up wind speed m/s Rated (minimum) start-up speed of a wind turbine
Rated wind speed m/s The wind speed at which the turbine can generate electricity at its maximum, or rated, capacity
Inverter efficiency (Euro efficiency) % The "European Efficiency" is an averaged operating efficiency over a yearly power distribution corresponding to middle-Europe climate

3. Financial terms

Quantity Full name Measure unit Definition
CAPEX Capital expenditures Investment costs for building project-related assets. Those can be upfront costs (at project begin), as well as costs related to hardware substitution along the project lifetime
OPEX Operational expenditures €/a Opex means operational expenditure i.e. the expenses incurred yearly after the system/technology has been commissioned (e.g. fuel costs). This does not include replacement costs, which are part of the CAPEX
Grants Grants or funds available from state or government which do not have to be paid back
Debt term a (years) Pay back payment schedule over several months or years for the loan
ROI Return on investment % On a single system:

$$ROI = \frac{Rev - OPEX - \left( CAPEX - Res \right) } { CAPEX } \cdot \frac{1}{100}$$

When comparing two systems:

$$ROI = \frac{Rev_{S2} + Sav - \left( CAPEX_{S2} - Res_{S2} \right) } { CAPEX_{S2} } \cdot \frac{1}{100}$$

Break-even a (years) The year when the cumulative benefit (OPEX savings against reference case) exceeds the cumulative effort (CAPEX increment). ROI at break-even is 0 %.
Rev Revenues Profit earned from system operation (e.g PPA)
Res Residual Value The residual value is the estimated value of a fixed asset at the end of its lease or at the end of its useful life or project lifetime
Sav Savings Given two systems S1 and S2:

$$Sav = \left( OPEX_{S1} - OPEX_{S2} \right) + \left( CAPEX_{S1} - Res_{S1} \right) - Rev_{S1}$$

LCOE €/kWh The net present value of the unit-cost of electricity over the lifetime of a generating asset
Cash flow Incomings and outgoings of cash, representing the operating activities of a system in a given time period
Net present value The difference between the present value of cash inflows and the present value of cash outflows over a period of time
Inflation % The annualized percentage change in a general price index over time
Price change rate % The percentage change in a price between two periods
Internal interest rate % The internal rate of return is a discount rate that makes the net present value (NPV) of all cash flows from a particular project equal to zero
Equity share % A main source of finance for a project giving investors rights to vote, share profits and claim on assets