Municipal Energy TransitionArea is valuable

Renew­able ener­gies are good — but it is also impor­tant to use them as effi­cient­ly as pos­si­ble. The con­cepts for this are already in place. An analy­sis.

Enough sun­light falls on a sur­face area of 10 square meters to sup­ply a house­hold with ener­gy for heat­ing, elec­tric­i­ty and mobil­i­ty for e‑cars. This results from a sim­ple cal­cu­la­tion: If a house­hold switch­es from con­ven­tion­al ener­gy sources to renew­able ones, its demand is reduced from an aver­age of 24 MWh for heat­ing, elec­tric­i­ty and mobil­i­ty (e‑vehicles) to a manage­able 10 MWh. The rea­son for this is that around the 50th par­al­lel, solar radi­a­tion pro­vides approx­i­mate­ly 1 MWh of ener­gy per square meter per year. This means that the solar ener­gy for such a house­hold already falls on 10 square meters.

And what about at night or when there are lulls last­ing weeks? Stor­age for hot water, bat­tery stor­age for elec­tric­i­ty, and long-term stor­age for wind ener­gy (for exam­ple, through hydrol­y­sis with recon­ver­sion via fuel cells) bring the ener­gy from wind and sun into the evening hours, win­ter, and wind­less peri­ods. A heat reser­voir in the ground can also be used as long-term stor­age for the cold sea­son in com­bi­na­tion with heat pumps and solar ther­mal ener­gy. If the effi­cien­cy of renew­ables is deter­mined by how much sur­face area they require for the same yield, pho­to­voltaics and solar ther­mal ener­gy achieve a yield of between 200 and 600 kWh/m²a of elec­tri­cal or ther­mal ener­gy, i.e. a very good 20–60 per­cent yield on the sur­face area. Wind pow­er still achieves 20–60 kWh/m²a. In the case of pure solar sup­ply with pho­to­voltaics, 50 square meters per house­hold would thus be suf­fi­cient, or 500 square meters of wind sur­face.

The best renewables

The cal­cu­la­tion shows how lit­tle area is actu­al­ly required to cov­er our needs with the solar and wind ener­gy that is avail­able free of charge. And yet we pay for ener­gy sources that for­mal­ly count as renew­ables but require immense­ly more land. We are talk­ing here about bio­gas and bio­fu­els from agri­cul­tur­al crops. To obtain sig­nif­i­cant amounts of ener­gy from these, huge areas of arable land have to be cul­ti­vat­ed at great expense, using oth­er valu­able raw mate­ri­als. This makes them by far the most inef­fi­cient renew­ables with an effi­cien­cy of only 0.6–5.9 kWh/m²a. This high land con­sump­tion is not economical—especially not in times of rapid­ly decreas­ing bio­di­ver­si­ty and glob­al­ly com­pro­mised food sup­plies. Only where bio­mass is pro­duced any­way, for exam­ple as an agri­cul­tur­al by-prod­uct, is it a valu­able ener­gy source that can sup­port munic­i­pal ener­gy sup­plies.

But it is not only the small area required that makes wind and sun the best ener­gy sources. If a house­hold switch­es from gas heat­ing, whether fos­sil or bio, to a heat pump, the ener­gy yield is tripled, because from 1 MWh of elec­tri­cal ener­gy, it achieves 3 MWh of ther­mal ener­gy for heat­ing and hot water. An elec­tri­cal­ly pow­ered vehi­cle also improves the ener­gy bal­ance by a fac­tor of about 3: For a pas­sen­ger car, 15 kWh per 100 km is cal­cu­lat­ed, which is equiv­a­lent to two liters of gaso­line. This results in the sig­nif­i­cant­ly low­er demand of 10 MWh instead of 24 MWh. Sys­tems for indus­tri­al use achieve an even high­er yield from geot­her­mal ener­gy. Switch­ing to heat pumps, for exam­ple, there­fore also sig­nif­i­cant­ly reduces ener­gy require­ments.

The self-sufficient municipality

Indi­vid­ual house­holds can hard­ly imple­ment this con­ver­sion on their own, but numer­ous projects show that munic­i­pal solu­tions can pro­vide a secure and com­pre­hen­sive sup­ply based on renew­ables. Mod­ern plant tech­nol­o­gy also con­tributes to this. In addi­tion to com­bined heat and pow­er plants, heat pumps and ener­gy stor­age sys­tems, mod­ern con­vert­er sys­tems are also part of the pow­er sup­ply. As ener­gy sources are increas­ing­ly locat­ed at the munic­i­pal lev­el, the ener­gy sup­ply will become more secure and sta­ble. This par­tic­u­lar­ly applies to the pow­er sup­ply net­works, which can also be oper­at­ed autonomous­ly or as an emer­gency pow­er sup­ply in the event of a net­work fail­ure. It fol­lows from this: A sus­tain­able ener­gy sup­ply must pro­tect raw materials—and this includes the land­scape, the raw mate­r­i­al “sur­face area”, so to speak. Solar and wind pow­er with a com­mu­nal approach are by far the most effi­cient solu­tion for this in math­e­mat­i­cal terms.


The dif­fer­ences in terms of effi­cient use of land for ener­gy pro­duc­tion are enor­mous: While solar ther­mal ener­gy in our lat­i­tudes needs about 1.7 m2 of land to pro­duce 1 MWh/year, biodiesel from canola requires 500 m2 of cul­ti­vat­ed land. The sun pro­vides 1 MWh of ener­gy per m2. And that’s how much of it can be har­vest­ed with renew­ables:




Onload 12 Christian Mayer Wind Solar energy

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