renewable energy Exam Prep

What happens to hydrogen at the anode of a hydrogen fuel cell?

It is separated into protons and electrons

Why can individual fuel cells be combined into a stack?

To obtain a larger electrical output

Hydrogen is an energy carrier rather than a primary renewable-energy source.

True

Why is insulation important in a thermal storage system?

It reduces heat loss from the storage material

What is the purpose of the catalyst in a hydrogen fuel cell?

To help the electrochemical reactions occur

Why are storage and careful system sizing especially important in grid-independent systems?

There is no utility backup available

Two identical 24 V, 150 Ah batteries are connected in series. What is the total stored energy of the bank?

7.2 kWh

Which is an example of a thermal storage medium?

Molten salt

Which renewable source may use hot underground water or steam to drive a turbine?

Geothermal

Why might a PV system require an inverter when supplying conventional building loads?

PV modules produce DC electricity

Which feature makes a flywheel useful for power-quality support?

Very fast response

What occurs during the charging stage of compressed-air energy storage?

Electrical energy is used to compress and store air

Which component accelerates a flywheel during charging?

Electric motor

A battery is at 25% depth of discharge. What is its approximate state of charge?

75%

Which system uses the regular rise and fall of ocean water caused mainly by gravitational forces?

Tidal

Connecting identical batteries in series increases their total amp-hour capacity.

False

Which condition can result from charging a battery outside manufacturer requirements?

Overheating or cell damage may occur

Which characteristic of a fuel-cell stack reduces mechanical wear?

It has few moving parts

A fuel cell produces electricity through an electrochemical reaction rather than combustion.

True

A renewable-energy system requires 48 V using identical 12 V batteries. How many batteries are required in each series string?

Four

Where does the useful electrical current of a hydrogen fuel cell flow?

Through the external circuit and connected load

How does an MPPT help to find set the maximum power point?

Adjusts the load to maximize power

A fuel cell produces ______ electrical output.

Direct-current

Why can marine renewable-energy equipment be difficult to maintain?

It operates in corrosive and harsh conditions

Stored thermal energy may later be used to produce steam that drives a ______.

Tur­bine

Which system would be the best example of grid-dependent renewable generation?

A home with PV operating alongside utility service

All renewable generating systems use a rotating shaft and generator to produce electricity.

False

Renewable and non-renewable generation can operate together within the same energy system.

True

Four identical 12 V, 80 Ah batteries are arranged as two series strings, with the two strings connected in parallel. What is the resulting battery-bank rating?

24 V, 160 Ah

Which feature can make geothermal generation useful compared with variable solar or wind generation?

It can provide relatively continuous output

Why can nearby buildings or trees reduce wind-turbine output?

They disturb and reduce useful airflow

What distinguishes biomass from wind and solar as an energy source?

Biomass requires a physical fuel material

What is the primary purpose of cell balancing in many lithium battery systems?

To keep individual cells at similar states of charge

Which factor can limit the overall efficiency of compressed-air energy storage?

Energy is lost during compression and expansion

A grid-independent renewable system may import electricity from the utility when renewable generation is insufficient.

False

Tidal movement is generally more predictable than changing wind conditions.

True

What is the stored energy of a 24 V, 160 Ah battery bank?

3.84 kWh

A renewable water-energy system that uses naturally moving river or ocean currents is called __________.

Hydrokinetic

In a hydrogen fuel cell, hydrogen enters at the ______.

Anode

Which process is one possible method of converting biomass into useful energy?

Direct combustion

What is the primary advantage of a utility connection for a grid-dependent renewable system?

It can supply power when renewable generation is insufficient

The same 2,400 W load is supplied from a 24 V battery system. Ignoring losses, approximately how much current is required?

100A

A device commonly needed to supply AC building loads from a solar PV array is an __________.

Inverter

Hydrokinetic generation always requires a dam to create water flow.

False

Which statement best describes the relationship between a battery and a fuel cell?

Both use electrochemical reactions, but a fuel cell uses externally supplied reactants

What happens to a flywheel as it releases stored energy?

Its rotational speed decreases

Which statement best explains why renewable energy does not necessarily eliminate the need for conventional generation?

Renewable generation may vary with resource availability

A battery bank stores 7,200 Wh at 48 V. What is its amp-hour capacity?

150 Ah

The amount of battery capacity already removed is called the ______.

Depth of discharge

Which situation would most likely require stored energy in a stand-alone solar system?

Loads continue operating after sunset

A flywheel normally stores energy for longer periods than hydrogen storage.

False

The silicon layer containing electrons is the __________ layer.

N-type

Compressed-air energy storage stores electrical energy directly inside conductors.

False

Biomass can only be converted to biogas.

False

In a hydrogen fuel cell, oxygen is supplied at the ______.

Cathode

Multiple batteries connected together to meet system voltage and storage requirements form a battery ______.

Bank

Why is shading an important consideration when locating a PV array?

It can reduce electrical production

The combination of a wind turbine's blades and hub is called the __________.

Rotor

Why must equalization procedures be matched to battery chemistry?

Some battery types are not designed to be equalized

Which water-energy system typically uses gravitational potential energy created by a difference in water elevation?

Hydroelectric generation

What does MPPT Stand for?

Maximum Power Point Tracker

Which material would most likely be used as a biomass fuel source?

Wood waste

A 36 V battery bank rated at 150 Ah stores approximately how much electrical energy?

5.4 kWh

Which operating consideration applies particularly to biomass generation?

Fuel transportation and storage

A 2,400 W load is supplied from a 48 V battery system. Ignoring losses, approximately how much current is required?

50 A

Which practice is important when working around batteries that may release gas during charging?

Provide ventilation as required

Which statement best describes thermal energy storage?

It stores energy as heat or cold for later use

Which installation best represents hydrokinetic generation?

An underwater turbine placed in a flowing river

The front metal grid of a photovoltaic cell helps collect electrical current from the cell.

True

A pumped hydro-electric system stores energy by moving water to a higher elevation.

True

A 24 V battery rated at 200 Ah is at approximately 75% state of charge. About how much of its rated charge capacity remains?

150 Ah

The device that uses electricity to separate water into hydrogen and oxygen is an ______.

Electrolyzer

Renewable energy can be used to produce heat and fuels as well as electricity.

True

What passes through the membrane in the fuel-cell process ?

Protons

When renewable generation exceeds the building load in an eligible grid-connected system, excess energy may be __________.

Exported to the utility

Which hazard makes battery-bank short circuits particularly dangerous?

Battery banks can deliver very high fault current

Changing the height of a wind turbine can provide access to stronger and more consistent winds.

True

Energy stored in an upper reservoir is stored as ______ energy.

Gravitational

The wind-turbine component that changes the angle of the blades is the __________.

Pitch system

What is the primary purpose of the rear contact of a photovoltaic cell?

Provide an electrical return path