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Digged deeper and thought along

At this point statements, thoughts and comments concerning different topics of energy supply will be published in loose sequence.

2013.06.24

Space and Energy - Real Estate!

What does account primarily for the value of real estate? - Space provided on earth cannot be enlarged.

Similar does happen to energy, too: Energy may be converted between different forms, but will never increase by conversion.

Regenerative energies like solar and wind energy are quite comparable to agricultural cultivation: They are harvested. The larger the area, the more extensive the yield.

Thus, most efficient usage of the rare asset "space" has to be considered. Is it advisable to cultivate energy crop for production of biogas? Which technology will provide for more energy output from existing ground, wind power plants or photovoltaic installations?

The result is unexpected, but explicit and unambiguous: Per square meter of ground, photovoltaic systems in Germany will provide for 50-150 kWh of electrical energy, annually. Most important to consider is slope: South oriented  slope or roof top maybe plated full faced by modules, while solar parks on plein ground require for some distance between elevated rows modules - otherwise row will shade each other. Efficiency of modules is of second importance. Additionally, energy demand for production is amortizised in between 2-4 years - at operational life time of 25 years. For this reason, photovoltaic prove to be the most efficient technology for harvesting regenerative energy from a given area.

Renewable energy crop for biogas or biofuel tend by annaul yield of 1 kWh (biodiesel) and 4-5 kWh from biogas at the lower end of scale. In addition it is to be considered that these values represent thermal energy from combustion. When biogas and biodiesel are converted by motors into propulsion or electricity, above values decrease to just one third. Anyway, energetical effort  for cultivation is already included..

And how about wind power? Well, physical requirements of space even for large wind power plants of some Megawatts of power and annual yield of several million Kilowatthours is just a few hundedred square meters - for foundation. It is obvious that rotors of adjacent located turbines need not clash. Therefore adequate distance between single wind power plants has to be kept. For aerodynamic aspects, minimum distance is a multipleof rotor diameter. For actual turbines of 2-3 MW class separation distance is in the order of 300-600 m. Related to windpark's total area, annual yield is around 20-60 kWh per square meter, half of photovoltaic. Although there is immense material effort, wind power plants bring in their total energy effort in about half a year, providing for the highest energy harvest of all technologies. - Coastal sites may energetically amortize already after 2-3 months. Offshore turbines provide for a less favorable energy balance: Energetical amortization requires several years of operation. The cause are large fundaments and foundations!

Wind parks at coastal sites typically provide for more yield than at locations in the interior, but therefore to dispense with wind turbines in teh interior? Even farmland is of different fertility, but nevertheless will we cultivated. And usage of wind energy provides for an additional advantage: Ground may be still used as farmland and for forests - or by solar photovoltaic installations.

Consequences of this compilation are clear: Handling of ground has to be considered carefully; replacement of fuel, diesel and heating oil by renewable energy crops and "business as usual" is not feasible just by restrictions of space. Otherwise it is premature to bet unilateral on photovoltaic. All reweable energy carriers provide for a right to exist, in particular when considering seasonal balance effects. Furthermore biomas and biogas possess notably properties: They are inherent energy storages.

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