The sun is the most important energy source on Earth. It provides our daily warmth and light and the rotation and orbit of the earth turn its steady output into fluctuating day and night, summer and winter. Solar energy powers the growth of all trees, grasses, herbs, crops and algae; it creates the clouds and powers the storms; it is the source of all hydro, photo-voltaic (PV), solar-thermal, bio-mass and wind energy; and, over geological time, it also creates coal.
PV solar panels are useful in remote locations, for some portable applications and, with enough panels and batteries, stand-alone solar can even power homes.
But solar energy has five fatal flaws for supplying 24/7 grid power.
Firstly, sunshine at any spot is always intermittent and often unreliable. Solar panels can only deliver significant energy from 9am to 3pm – a maximum of 25% of each day. Solar can often help supply the hot afternoon demand for air conditioning, but demand for electricity generally peaks at about 6.30pm, when production from solar is usually zero.
Secondly, to be a stand-alone energy supplier, PV solar needs batteries to cover those times when solar is not producing - about 75% of the time under ideal cloudless skies. To charge the batteries for continuous power, while also supplying usable power, a solar plant can only deliver a theoretical maximum of 25% of its day-time capacity. The chance of cloudy days will greatly increase the battery storage needed, and the generating capacity absorbed in charging the batteries. Currently, only pumped hydro storage could possibly supply the storage capacity needed and then only at massive cost, in a few suitable locations.
Thirdly, solar energy is very dilute, so huge areas of land are needed to collect industrial quantities of energy.
If it were possible to anchor a solar collector one meter square at the top of the atmosphere, aligned continuously to face the sun, and never shadowed by the earth or the moon, it would receive solar energy at the rate of 1,366 Watts per square metre (W/m2) – that would power 13 light bulbs each using 100 watts.
If that panel were located on the surface, at the equator, under clear skies, aligned continuously to face the sun, and never shaded by the earth or the moon, solar energy dissipated by the atmosphere would reduce energy received to 1,000 watts.
In the real rotating world, where sunshine only reaches usable intensity for about 25% of the time, the best located panel would have a capacity factor of about 17% - it would receive 170 watts of energy – not quite 2 light bulbs.
PV solar panels convert solar energy to electrical energy at an efficiency factor of about 15%. Thus our panel, at the equator, year round, should deliver 25.5 watts of electrical energy – one very dim light bulb.
Away from the equator, solar energy hits the Earth’s surface at an angle, thus delivering less energy per panel. This useful site shows how solar intensity varies with latitude in Australia.
Shift that panel to Melbourne, add clouds, shading, urban air pollution and dirt on the panels, and fix it to a sloping roof often aligned poorly to collect sunshine, and it is time to start the diesel generator in the car port.
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