Renewable Energy Technologies: Fundamentals, Solar PV, Solar Thermal, Geothermal, and Hydropower

Comprehensive practice flashcards defining essential terminology, units, governing laws, and engineering systems across Renewable Energy Fundamentals, Solar PV, Solar Thermal, Geothermal, and Hydropower.

First Law of Thermodynamics

The principle stating that energy can neither be created nor destroyed, but can only change forms; in a system, energy output equals energy input minus the energy stored.

Second Law of Thermodynamics

The law stating that it is practically impossible for any process to be perfectly ($100\%$) efficient, meaning that entropy in any practical process is always greater than zero.

Entropy

The physical state of disorderliness in a thermodynamic system that contributes to unavoidable energy dissipation and losses during energy conversion processes.

Joule ($\text{J}$)

The standard unit of energy or work done by a force of $1\,\text{N}$ exerted through a distance of $1\,\text{m}$, defined equivalently as $1\,\text{J} = 1\,\text{N}\cdot\text{m} = 1\,\text{W}\cdot\text{s}$.

Erg

A unit of mechanical energy defined as the work done by a force of $1\,\text{dyne}$ ($10^{-5}\,\text{N}$) exerted through a distance of $1\,\text{cm}$, equivalent to $10^{-7}\,\text{J}$.

Foot-pound

A unit of work defined as the work done by a force of $1\,\text{lb}$ ($0.4536\,\text{kg}$) acting through a distance of $1\,\text{ft}$ ($0.3048\,\text{m}$ or $12\,\text{inches}$), equal to $1.3826\,\text{J}$.

Calorie (cal)

The amount of heat required to raise the temperature of $1\,\text{g}$ of water by $1^\circ\text{C}$, equal to $4.1855\,\text{J}$ ($1\,\text{Cal} = 1000\,\text{cal} = 1\,\text{kcal}$).

British Thermal Unit (BTU)

The amount of heat required to raise the temperature of $1\,\text{lb}$ of water by $1^\circ\text{F}$, equivalent to $1055\,\text{J}$, $10^{-15}\,\text{quad}$, or $10^{-5}\,\text{therm}$.

Watt hour (Wh)

The unit of electrical energy produced when $1\,\text{W}$ ($1.3410 \times 10^{-3}\,\text{hp}$) of power flows continuously for $1\,\text{h}$, equivalent to $3600\,\text{J}$.

ElectronVolt (eV)

The amount of energy gained by an electron that accelerates under the action of an electric potential difference of $1\,\text{V}$, equivalent to $1.602 \times 10^{-19}\,\text{J}$.

Tonne of Oil Equivalent (toe)

The standardized unit of energy representing the heat released when one metric ton ($1000\,\text{kg}$) of crude oil is burnt, equal to $41.868 \times 10^9\,\text{J}$.

Renewable Energy Source

An energy resource that is replenished naturally over short timeframes and is virtually inexhaustible, including hydro, solar, wind, biomass, geothermal, and ocean energy.

Non-Renewable Energy Source

A depletable energy resource formed over geological timescales that cannot be replenished on human time horizons, such as crude oil, natural gas, coal, peat, and radioactive metals.

Ocean Thermal Energy Conversion (OTEC)

A renewable power generation method that uses heat engines to produce electricity by exploiting temperature differences between warm surface seawater and cold deep ocean water.

Irradiance

The instantaneous solar power delivered by sunlight per unit surface area, measured in watts per square meter ($\text{W/m}^2$).

Insolation

The cumulative solar energy received per unit area over a specified time duration, expressed in units of $\text{kWh/m}^2/\text{day}$ or $\text{kWh/m}^2/\text{year}$.

Photovoltaic (PV) Cell

A solid-state p-n junction semiconductor device typically fabricated from doped silicon wafers that directly converts incident sunlight photons into DC electricity.

Monocrystalline Silicon PV Cell

A photovoltaic cell constructed from silicon possessing a single, continuous crystal lattice, characterized by uniform dark coloration, rounded corners, higher efficiency, and higher cost.

Polycrystalline Silicon PV Cell

A photovoltaic cell composed of multiple smaller silicon crystal grains, characterized by a speckled or patchy appearance, perfectly rectangular edges, lower efficiency, and lower production cost.

PV Array Arrangement

The structural hierarchy of photovoltaic power systems where individual solar cells are connected into modules, and multiple modules are combined into strings and arrays.

PV String

A series-connected group of photovoltaic modules wired together to increase the total operating voltage to the required system level.

Blocking Diode

A diode wired in series with a PV module or string to prevent storage batteries from discharging backwards through the array during dark periods or low module voltage.

Bypass Diode

A diode wired in anti-parallel with a group of PV cells within a module to provide an alternative current path, mitigating voltage collapse and localized overheating caused by shading.

Thermal Voltage ($V_{\text{T}}$)

A temperature-dependent voltage parameter in the semiconductor diode equation defined as $V_{\text{T}} = \frac{kT}{q}$, evaluating to approximately $25.68\,\text{mV}$ at standard test temperature ($25^\circ\text{C}$).

Standard Test Conditions (STC)

Standardized laboratory reference conditions for rating PV modules: solar irradiance of $1000\,\text{W/m}^2$, cell temperature of $25^\circ\text{C}$, and air mass spectral distribution of $\text{AM} = 1.5$.

Nominal Operating Cell Temperature (NOCT)

The open-circuit cell junction temperature reached under standard operating conditions ($800\,\text{W/m}^2$ irradiance, $20^\circ\text{C}$ ambient temperature, $1\,\text{m/s}$ wind speed, and $\text{AM} = 1.5$).

Short-Circuit Current Temperature Coefficient ($\alpha_i$)

A parameter quantifying the percentage increase in short-circuit current per Kelvin or degree Celsius rise in PV cell operating temperature.

Open-Circuit Voltage Temperature Coefficient ($\alpha_v$)

A parameter quantifying the percentage reduction in open-circuit voltage per Kelvin or degree Celsius rise in PV cell operating temperature.

Maximum Power Point (MPP)

The operating point along a PV cell or module I–V characteristic curve where the product of voltage and current ($V^* \times I^*$) achieves its peak output power.

Solar Collector

A specialized heat-absorbing device that intercepts incoming solar radiation and converts it into thermal energy conveyed to an internal circulating working fluid.

Concentration Ratio

The ratio of the planar aperture opening area receiving incident sunlight to the absorber or receiver surface area of a solar thermal collector.

Flat Plate Collector (FPC)

An insulated, stationary non-concentrating solar thermal collector (concentration ratio of $1$) consisting of a dark absorber plate under glass glazing, operating between $30^\circ\text{C}$ and $80^\circ\text{C}$.

Evacuated Tube Collector (ETC)

A solar thermal collector using parallel double-walled glass tubes with an evacuated annular vacuum space to minimize conductive and convective losses, operating between $50^\circ\text{C}$ and $200^\circ\text{C}$.

Parabolic Trough Collector (PTC)

A single-axis tracking concentrating solar thermal collector using long, U-shaped curved parabolic mirrors to focus sunlight onto an axial tubular receiver, operating between $60^\circ\text{C}$ and $300^\circ\text{C}$.

Parabolic Dish Reflector (PDR)

A two-axis tracking solar concentrator that focuses solar rays onto a focal point receiver (often integrated with a Stirling engine), operating between $100^\circ\text{C}$ and $500^\circ\text{C}$.

Heliostat Field Collector (HFC)

A solar thermal electric generation system utilizing an array of two-axis tracking flat mirrors (heliostats) to focus sunlight onto a central receiver atop a tower, reaching $150^\circ\text{C}\text{ to }2000^\circ\text{C}$.

Solar Chimney Power Plant (SCPP)

A solar power facility that uses a wide canopy to heat ground-level air, which rises by natural convection through a tall vertical chimney to turn an air turbine and generator.

Geothermal Gradient

The rate at which the Earth's subsurface temperature increases with depth, averaging approximately $0.03^\circ\text{C/m}$ ($30^\circ\text{C/km}$).

Dry Steam Geothermal Power Plant

A geothermal generating station that extracts underground vapor directly from production wells to spin steam turbines without needing a phase-separation flash tank.

Flash Steam Geothermal Power Plant

A geothermal power plant that extracts high-pressure hot water ($>180^\circ\text{C}$) into a reduced-pressure separator flash tank, causing it to rapidly vaporize into steam to drive a turbine.

Binary Cycle Geothermal Power Plant

A geothermal plant where hydrothermal fluid transfers heat through a heat exchanger to boil a secondary organic working fluid with a lower boiling point (such as butane or pentane) to drive a turbine.

Hot Dry Rock (HDR)

Deep subterranean hot rock formations within $10\,\text{km}$ of the Earth's surface ($90^\circ\text{C}\text{ to }650^\circ\text{C}$) that possess high thermal energy but lack water or natural interconnected permeability.

Hydropower

The harnessing of the potential and kinetic energy of flowing or falling water through hydraulic turbines to generate useful mechanical or electrical energy.

Run-of-the-River Hydro Scheme

A hydroelectric facility that generates power directly from the natural flow of a river without constructing a large water-impounding reservoir dam.

Pumped Hydroelectric Storage Facility

A hydroelectric energy storage configuration that pumps water from a lower reservoir to an elevated upper reservoir during low-demand periods and releases it through turbines during peak demand.

Micro Hydro Power (MHP)

A small-scale hydroelectric system designed to produce between $5\,\text{kW}$ and $100\,\text{kW}$ of electricity, commonly utilized for decentralized or rural mini-grid power.

Pelton Turbine

An impulse hydraulic turbine designed for high head ($300\text{ to }1800\,\text{m}$) and low flow rates, utilizing high-velocity water jets fired through nozzles against split buckets on a runner wheel.

Francis Turbine

A reaction hydraulic turbine suitable for medium head ($40\text{ to }600\,\text{m}$) and medium flow conditions, where water enters radially through a spiral volute and guide vanes before discharging axially through the runner into a draft tube.

Kaplan Turbine

An axial-flow reaction hydraulic turbine designed for low head ($2\text{ to }70\,\text{m}$) and high flow rates, equipped with adjustable propeller-like runner blades and movable wicket gates.

Penstock

A high-pressure pipe or enclosed conduit that conveys water under pressure from a dam reservoir or forebay to a hydroelectric turbine.

Draft Tube

A gradually expanding conduit connecting a reaction turbine outlet to the tailrace that decelerates discharge water and recovers kinetic energy as a pressure drop.

Total Head ($H_{\text{T}}$)

The total hydraulic energy per unit weight of water upstream from a hydro turbine, calculated as the sum of velocity head ($\frac{v_w^2}{2g}$), elevation head ($h$), and pressure head ($\frac{p_w}{\rho_w g}$).

Effective Head ($H_{\text{E}}$)

The net usable hydraulic head available to perform work across a hydro turbine, determined by subtracting friction and pipe head losses ($H_{\text{L}}$) from the gross total head ($H_{\text{E}} = H_{\text{T}} - H_{\text{L}}$).

Turbine Specific Speed

A characteristic parameter derived from developed mechanical power, rotational speed, and effective hydraulic head used as the primary engineering criterion for selecting hydraulic turbines.