Q&A: renewable energy quiz, questions PLUS answers for schools, universities education, fun, etc.

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Q1 – How many types of renewable energy are there normally said to be?

A – Seven: solar, wind, hydro, biomass, waves, tidal, deep geothermal.

Q2 – How many types of renewable energy are solar in origin?

A – All of the above except for tidal and deep geothermal. Tidal energy is captured from the energy of the moon’s orbit. Deep geothermal is actually heat from nuclear reactions (fission, not fusion, as in the sun) in the rocks under the earth. Why are the remaining five all solar? Wind is mainly solar in origin since it is caused by differential solar heating of the earth’s surface. Hot air rises and cold air blows into replace it. Hydro is really solar in origin because it is the heat of the sun which evaporates water such as the sea which blown by winds (mainly solar) then condense into rain which falls on mountains. Biomass is really solar too, thanks to photosynthesis in plants. It is sunlight which powers the conversion of CO2 (carbon dioxide) and H2O (water) back into O2 (oxygen) and (CH2O)n (carbohydrates). Wave power is derived from the wind, which is originally a solar-derived energy.

Q3 – Why is solar sometimes termed the primary renewable energy?

A – Because it is the origin of many other energies as explained above. It is the most abundant renewable energy resource. Converting it into other forms is inefficient. Solar panels rarely exceed 50% efficiency over a year. Photosynthesis is typically under 1% efficient over a year.

Q4 – Why is solar energy really a form of nuclear energy?

A – Because the solar energy which arrives on earth is part of a spectrum of radiation types emitted by thermonuclear fusion (not fission) reactions which take place on the sun. This is the hydrogen bomb nuclear reaction, where deuterium (heavy hydrogen) atoms are combined to make helium plus energy. Of course, a tiny amount of light and heat also arrives from other stars than the sun. But this is a very tiny amount. So to say all light is solar energy, or hat all of the power of a solar panel comes from our sun is not strictly true. But that is splitting hairs (and atoms).

Q5 – What is the difference between renewable energy and renewable energy technology?

A – Renewable energy technology is what collects, converts, (= transduces), sometimes stores, and delivers the renewable energy. For example (a) solar water heater converts solar radiation energy into heat energy, from one form into another, then it stores the heat in a hot water store and delivers it to your taps; (b) a solar PV panel converts solar radiation energy into electrical energy, from one form into another, then delivers it to your electricity supply, often without storing it. There are lots of renewable heat technologies such as: solar thermal panels which heat water, solar photovoltaic electric panels which make electricity, wind and water turbines which make electricity or sometimes heat, wood stoves, biodiesel car engines, biogas electric generators, tidal stream turbines and tidal barrages and geothermal power stations. It can be interesting to make a table of all the options!

Q6 – What is the difference between renewable energy inputs and outputs?

A – To state the obvious, inputs go in and outputs come out. Sometimes things also happen in between. For example for solar thermal hot water energy systems, the input is solar radiation energy, while the output is heat, in the form of heated water with not much in between. For photovoltaic systems, the outputs are electrical energy instead. Heat and electricity are the main outputs. With some biofuels the heat of combustion is converted again into movement, such as in vehicles, or again into electricity as in biogas powered electrical generators. In this case there is an in-between (intermediate) form of energy: movement.

Q7 – What is the difference between stored and instantaneous renewable energy?

A – one gets used right away and the other has a degree of storage in it. For example, grid-connected PV’s are instantaneous since they inject energy straight into the electric grid. But off-grid PV systems with batteries can have over a day of storage involved. Solar hot water systems also have storage, typically for a day or so. Wood is stored renewable energy. Storage is often useful. It can help to smooth out the intermittent nature of renewables, delivering the energy when you want it, hours, days or years after nature supplies it. Some large solar hot water systems use underground year-long hot water stores so the summer heat can be used in winter.

Q8 – Why are heat pumps defined as renewable energy?

A – Because (a) of a European Directive and (b) they collect heat from the environment derived from solar energy. A recent Energy Saving Trust showed that some have a worse carbon-saving capability than gas boilers. Perhaps condensing gas boilers should be classified as renewable energy.

Q9 – What is coefficient of performance?

A – It is the ratio of electricity in to energy out for mains electric powered renewable energy technologies. For heat pumps, you can put one unit of electricity in an get out, say 3 units of heat. This would be a 1:3 CoP. In a mains pumped solar water heating system the CoP is typically 1:10 for evacuated tubes, which is not bad, and 1:15 for flat plate collectors which is even better. PV pumped solar water heating systems have a CoP of 1: infinity, which is better still since they use no mains electricity at all in operation. More on CoP here.

Q10 – What are photovoltaics?

A – Technologies which converts solar radiation directly into electricity. More here.

Q11 – What is solar thermal electricity?

A – Solar technologies which usually heat water which then drives steam turbines to generate electricity.

Q12 – What is solar thermal heating?

A – Solar technologies which heat. They usually heat a moveable fluid. This may be a liquid such as solar water heating, (or sometimes which heat air). Plenty more here.

Q13 – How can renewable energy technologies be compared?

A – Phew   – in all sorts of ways. What’s your bottom line? By costs benefits, with and without subsidy, by the types of energy the take in and give out, by their coefficient of performance, by their reliability, by years to carbon or energy breakeven, and so on. Here is some further discussion.

Q14 – What types of biofuels are there?

A – Biosolids, more commonly known as biomass, bioliquids, biogas. These are the three phases of matter!

Q15 – Is wood a renewable energy?

A – Er, it is defined as such in Europe. But if growing it, cutting and chipping it, compressing it, drying it, transporting it and operating its boiler so on use more energy than it actually delivers, then it can not be renewable. Best to choose local, naturally dried wood.

Q16 – Do biofuels have any social impact?

A – Yes and here are two. First they can take land for food crops out of food production, which can increase food cost, cause disease and social unrest. There are some arguments that biofuels need to be based on wastes and not occupy food land or newly cleared forests. Second, in cities, smoke from wood burning can increase PM10 (particulate) pollution, which leads to respiratory disease and can worsen asthma.

Q 17- What is the difference between biofuels and fossil fuels?

A – Time. Both are mainly stored products of photosynthesis. Fossil fuels were created longer ago.

Q18 – Are fossil fuels renewable?

A – Arguably. They are solar in origin. But unlike biofuels they can be burnt faster than they are created.

Q19 – Is peat biomass or a fossil fuel?

A – Technically it is neither. It is a picked fuel because it is plant remains which have been pickled in plant-produced acids. It is usually viewed as a fossil fuel. There is a degree of continuous graduation between live peat moss, dead peat, brown coal and black coal.

Q20 – Do people buy renewable energy without subsidies?

A – Usually not, unless they are dedicated environmentalists.

I hope this renewable energy quiz stimulates debate!

Sunny regards from Barry and colleagues at Solartwin.