Storing the sun / Almacenando sol

The amount of solar energy that reaches Earth’s surface is enormous and is naturally one of the main reasons why this is a habitable place for humanity. Because the planet is round the surface receives the solar rays at different angles at different locations. As the Earth’s axis towards the sun is tilted by 23.5°, places further away from the equator receive more solar energy in some parts of the year than others. At the latitude of 40° (like for example in Madrid) the surface receives three times as much radiation in June than in December.

The lower the angle, the further the radiation has to travel through the atmosphere, and the less of it is left when it reaches the surface. So at the poles the angles are so low that very little energy gets through, and in wintertime there are long periods without light.

The suns elliptical course around the sun during year (it is closer to sun when it is summer in the southern hemisphere) does not amount to enough difference for making the southern hemisphere hotter than the northern during their respective summer periods, as this difference is mostly absorbed by the oceans.

When we use fossil fuel we are really using the energy from the sun that reached us millions of years ago. That energy was first stored in organic form, like for example plants, by a process of photosynthesis and then decomposed deep below the surface into energy forms like coal, oil or gas. That process is still going on, but is so slow and our outtake of fossil fuels so vast that it can’t be considered a renewable energy source.

The problem with not having the same amount of solar energy all the time is that you would want to store the received energy on a sunny summer day and keep it for a cold winter night, which is of course much easier said than done. First you would need a very big storage capacity (which is expensive) to able to retain enough energy for when you need it and can’t get it and, secondly that storage should be absolutely stable so that what you captured is not slowly leaking away.

A very interesting on-going research project at the University of Chalmers in Sweden is trying to use chemical solar capture with the help of an artificial molecule (made up of carbon, hydrogen and nitrogen) as a way of creating a durable energy storage. This molecule has different forms (isomers) with different energy levels and when it is exposed to sunlight in a solar collector it changes from a low-energy form to a higher energy form, storing the energy inside its chemical bindings.

The molecule can then be stored for up to 18 years without loosing it’s new form and when the energy is needed the liquid containing the molecules is passed through a catalyser, where heat is produced and the molecules turn back to their original form. The good thing is that the system works as a closed circuit as the molecular liquid can be passed through the solar collector again and again to store new energy.

Aeroponics

Aeroponic farming is growing plants in air without any substrate or other growing medium. The plants are sustained in place and their roots are sprayed with a  “mist” to provide them with the necessary nutrients. The support enters in minimal contact with the plant holding it at the stem with the leaves and crown growing above and the roots hanging free in the air below. If the environment is kept free from pathologies the plants can grow quicker and healthier than they do in soil as the roots are better oxygenated having direct contact with the air.

There are many cases in nature where plants grow like this with air roots under humid conditions, for example orchids have a natural tendency of aerial roots and cling onto other plants and get their nutrients from them. Recent research has shown that a great number of plants can be used to grow in this way and not only the ones with a natural tendency for it.

Potato plants are grown using aeroponics as a means of getting more and same-sized tubers for planting. The method improves productivity as one plant hanging in the air yields up to 20 small potatoes instead of 3 or 4 for with the traditional soil-based method. The roots are normally kept in darkness but are accessible and can easily be harvested in the right moment without moving the plant. The method saves water, not because an aeroponic plant need less of of it, but because all excess water is recycled back to the plants again.

One part of the ongoing preparations and investigation for future space travel to planet Mars is looking into aeroponic growing as part of the survival strategies. The red planet has very adverse conditions indeed with the highest temperatures around -25 °C and the lowest below  -100°C and very little water, why growing plants naturally seems out of the question. In one experiment at the Czech University of Life Sciences, the scientists are experimentally growing lettuce, mustard, radishes and herbs using aeroponics, proving that they can survive almost without water.

On the Spanish island of Ibiza one of the first vertical gardens in Europe using aeroponic towers to grow food naturally while saving 95% water in comparison to conventional organic farming. Besides saving water the method also save space and improves crop yields. The tower structures have a separate slot for every plant where the mineral bases nutrients are circulated internally. A great variety of plants are being grown, like tomatoes, cabbage, lettuce and even melons.

Critics to aeroponics argue that, as the plants are fed with artificial nutrients, they don’t have access to the microbiology of healthy soil. In that sense aeroponic farming can be compared to feeding humans directly through an intravenous solution. In that sense, the role of soil is as important as the role of the stomach, to break down organic matter and provide micronutrients and other things that are associated with organic food production. Still, if we want to make a living in such a hostile environment as the red planet, the method seems rather promising.

 

Future batteries / Baterías futuras

One of the really limiting factors for the technological development of alternatives to fossil fuel solutions is the energy storage, whether it’s for solar powered homes or for electrical cars. Even though there are other ways of storing energy than electricity, this is perhaps one of the most important methods and most crucial to future technological development.

The normal way to store electricity is using batteries. A battery is a device composed of one or more electrochemical cells, where electrons will flow between two electrolytes, from the negative terminal (anode) to the positive terminal (cathode) when connected to a electrical circuit. This is done due to a chemical reaction that will turn a high-energy chemical component into a low-energy component while freeing up energy as electricity.

Today the most commonly used battery types are lead-acid and lithium-ion. Lead-acid batteries were the first rechargeable battery ever invented and have been around since mid 19th century and, despite being very heavy and therefore having a relatively low energy-to-volume ratio, their ability to supply high surge currents make them useful for providing the high current needed for vehicle starter motors. Modified versions, so called deep-cycle batteries, are much less sensitive to degrading from frequent discharges, and are often used in photovoltaic systems.

Lithium-ion batteries are commonly used for electrical vehicles and portable electronics and were developed and came into commercial use during the end of the 20th century. They have high energy density, low self-discharge and maintain their capacity over time. One issue with these batteries is the limited availability of lithium and other heavy metal elements that are used in them, which could cause geopolitical conflicts and other environmental problems, though recycling could partly solve this. Another issue is the risk of overheating which could cause a fire or explosion.

Numerous research projects are ongoing to find viable battery alternatives that would cost and weigh less while having a higher energy density. Another important goal is to reduce the charging time, which is especially important for electrical vehicles as long stops for charging makes these vehicles less attractive compared to their fossil fuel counterparts.

Dual-carbon or dual-graphite is a solution where both electrolytes (anode and cathode) are based on graphitic carbon. This battery type can be fully discharged without risk of short-circuiting and damaging the battery. It operates at room temperature without the risk of overheating. Its electrolytes are made of pyrolyzed cotton and the battery is fully recyclable. It is claimed that this battery type can be charged 20 times faster than lithium-ion batteries.

IBM Research is currently working on a battery type that is free of heavy metals, which use three new materials that can be extracted from seawater and said to be able to surpass lithium-ion. IBM states that initial test has shown lower costs, faster charging time, higher power and higher energy density as well as low flammability. IBM is working together with Mercedes-Benz and a battery manufacturer to make the new technology commercially available.

The startup company Sila Nano is developing a version of lithium-ion batteries where the graphite is replaced by silicon in one of its electrolytes. The silicon is extracted from sand and the new technology promises to achieve a much better performance than conventional li-ion batteries, through higher density and lower cost.

Uno de los factores realmente limitantes para el desarrollo tecnológico de alternativas a las soluciones de combustibles fósiles es el almacenamiento de energía, ya sea para hogares con energía solar o para coches eléctricos. Aunque hay otras formas de almacenar energía que la electricidad, este es quizás uno de los métodos más importantes y más cruciales para el desarrollo tecnológico futuro.

La forma normal de almacenar electricidad es usando baterías. Una batería es un dispositivo compuesto por una o más células electroquímicas, donde los electrones fluirán entre dos electrolitos, desde el terminal negativo (ánodo) al terminal positivo (cátodo) cuando se conecta a un circuito eléctrico. Esto se hace debido a una reacción química que convertirá un componente químico de alta energía en un componente de baja energía mientras libera energía como electricidad.

Hoy en día, los tipos de baterías más utilizados son el ácido de plomo y el ion de litio. Las baterías de plomo-ácido fueron la primera batería recargable que se hayan inventado y han existido desde mediados del siglo XIX y, aunque sean muy pesadas y, por lo tanto, tener una relación energía-volumen relativamente baja, su capacidad para suministrar altas corrientes de sobretensión las hace útiles para proporcionar la alta corriente necesaria para los motores de arranque del vehículo. Las versiones modificadas, llamadas baterías de ciclo profundo, son mucho menos sensibles a la degradación de las descargas frecuentes, y a menudo se usan en sistemas fotovoltaicos.

Las baterías de iones de litio se usan comúnmente para vehículos eléctricos y dispositivos electrónicos portátiles y se desarrollaron y entraron en uso comercial a fines del siglo XX. Tienen una alta densidad de energía, baja autodescarga y mantienen su capacidad con el tiempo. Un problema con estas baterías es la disponibilidad limitada de litio y otros elementos de metales pesados utilizados en ellas, lo que podría causar conflictos geopolíticos y otros problemas ambientales, aunque el reciclaje podría resolver esto en parte. Otro problema es el riesgo de sobrecalentamiento que podría provocar un incendio o una explosión.

Numerosos proyectos de investigación están en curso para encontrar alternativas de baterías viables que costarían y pesarían menos mientras tengan una mayor densidad de energía. Otro objetivo importante es reducir el tiempo de carga, que es especialmente importante para los vehículos eléctricos, ya que las paradas prolongadas para la carga hacen que estos vehículos sean menos atractivos en comparación con sus homólogos de combustible fósil.

El doble carbono o el doble grafito es una solución donde ambos electrolitos (ánodo y cátodo) se basan en carbono grafítico. Este tipo de batería se puede descargar completamente sin el riesgo de cortocircuito y dañar la batería. Funciona a temperatura ambiente sin riesgo de sobrecalentamiento. Sus electrolitos están hechos de algodón pirolizado y la batería es totalmente reciclable. Se afirma que este tipo de batería se puede cargar 20 veces más rápido que las baterías de iones de litio.

IBM Research está trabajando actualmente en un tipo de batería libre de metales pesados, que utiliza tres nuevos materiales que pueden extraerse del agua de mar y que se dice que pueden superar el ión de litio. IBM afirma que las pruebas iniciales han demostrado menores costos, un tiempo de carga más rápido, mayor potencia y mayor densidad de energía, así como una baja inflamabilidad. IBM está trabajando con Mercedes-Benz y un fabricante de baterías para hacer que la nueva tecnología esté disponible comercialmente.

La empresa emergente Sila Nano está desarrollando una versión de baterías de iones de litio donde el grafito es reemplazado por silicio en uno de sus electrolitos. El silicio se extrae de la arena y la nueva tecnología promete lograr un rendimiento mucho mejor que las baterías de iones de litio convencionales, a través de una mayor densidad y un menor coste.

Storing solar energy / Almacenar la energía solar

In most places on earth the energy flow from the direct sunlight corresponds to more than 1,000 watts per square meter. As the sun shines, the light heats air, water, earth or whatever material that comes underneath its generous rays.

When photovoltaic panels are exposed to sunlight the energy flow is transformed into electricity, but that electricity is then automatically lost if it is not consumed directly or put into storage. Therefore most solar systems use some kind of battery bank so that the consumption of the generated energy can be postponed to when it is needed better. Typically the electricity generated by day is mostly consumed during the night.

Most photovoltaic systems are over-dimensioned to some extent to allow for a continued use during periods with less productivity (like cloudy days). With more panels you get more production capacity, and with more batteries you can store more of that production.

When looking at many off-grid systems that added capacity from over-sizing means that the systems spend most of their time with fully loaded batteries. So when the batteries are full the system just has to discard the rest of energy production.

One simple way to augment the system’s capacity is to plan the use of electricity so that it coincides with the time of the day when most of the energy is produced (around midday or early afternoon), like for example to set the washing machine to run at those hours. In this way you get added capacity as you draw both from the batteries and what is produced at that very moment. And you don’t drain the batteries as easily as you have planned the main consumption when there otherwise would have been an over-production of energy.

If you also have the on-grid option of a connection to the general electrical network, you could sell to the grid when your batteries are full and buy back from them when you need to, and use the grid as a virtual storage for all the extra electricity that you can’t store yourself. It is a virtual storage, as the energy you have put to the grid will be consumed be someone else directly, and someone else will produce the electricity you buy back later. So really you are storing energy in the form of the money you get for selling electricity, which buys you capacity to withdraw energy from the grid later.

Other forms of energy storage are to produce hot (or cold) water with the surplus electricity and use that energy to heat (or cool) your building. Or some other liquid could be used for the storage (like oil), or the proper building could be looked upon as a form of storage, if it encloses heavy elements that can hold thermal energy. This could be conceived by an under-floor heating system that put energy into the floor slab. If it is water-based it could even be used for cooling down a building during hot summer days.

There are far more complex to store energy a for example using catalyzers to produce hydrogen gas from water, hydro potential storage (pump water to a higher point and let it fall through a generator) or the use of a heat exchanger to produce electricity. Most of them are just too expensive or too inefficient but of course still interesting for smaller scale experiments or for large-scale investments.


En la mayor parte de la Tierra, el flujo de energía de la luz solar directa corresponde a más de 1.000 vatios por metro cuadrado. A medida que el sol brilla, la luz calienta el aire, el agua, la tierra o cualquier material que venga por debajo de sus generosos rayos.

Cuando los paneles fotovoltaicos estén expuestos a la luz solar, el flujo de energía se transforma en electricidad, pero esa electricidad se pierde automáticamente si no se consume directamente o se almacena. Por lo tanto, la mayoría de los sistemas solares utilizan algún tipo de banco de baterías para que el consumo de la energía generada pueda posponerse cuando se necesite mejor. Normalmente, la electricidad generada por el día se consume principalmente durante la noche.

La mayoría de los sistemas fotovoltaicos están sobredimensionados en cierta medida para permitir un uso continuado durante los períodos con menos productividad (como los días nublados). Con más paneles hay más capacidad de producción y con más baterías se podrá almacenar más de esa producción.

Cuando se observan muchos sistemas fuera de la red, la capacidad agregada por estar sobredimensionados significa que los sistemas pasan la mayor parte de su tiempo con baterías completamente cargadas. Entonces, cuando las baterías están llenas, el sistema tiene que desechar el resto de la producción de energía.

Una forma sencilla de aumentar la capacidad del sistema es planear el uso de la electricidad de modo que coincida con la hora del día en que se produce la mayor parte de la energía (alrededor del mediodía o la tarde), como por ejemplo configurar la lavadora para que funcione a esas horas. De esta manera, se obtiene mayor capacidad a medida que extrae tanto de las baterías como de lo que se produce en ese momento. Y no agota las baterías tan fácilmente como ha planeado el consumo principal cuando de lo contrario habría habido una sobreproducción de energía.

Si también tiene la opción de una conexión a la red eléctrica general, podría vender la electricidad a la red cuando sus baterías estén llenas y comprarlas cuando sea necesario, y utilizar la red como un almacenamiento virtual para todos la electricidad adicional  que no puedes almacenar. Es un almacenamiento virtual, ya que la energía que ha puesto en la red se consumirá directamente por otra persona, y otra persona producirá la electricidad cuando vuelves a comprar. De modo que realmente está almacenando energía en la forma de dinero que obtiene por vender electricidad, lo que le da capacidad para retirar energía de la red más adelante.

Otras formas de almacenamiento de energía son producir agua caliente (o fría) con el excedente de electricidad y usar esa energía para calentar (o enfriar) su edificio. O se podría usar algún otro líquido para el almacenamiento (como el aceite), o se podría considerar el edificio mismo como una forma de almacenamiento, si encierra elementos pesados ​​en su interior que pueden contener energía térmica. Esto se puede conseguir por medio de un sistema de calefacción por suelo radiante que almacena energía en la losa del piso. Si el sistema radiante es a base de agua, incluso podría usarse para enfriar un edificio durante los calurosos días de verano.

Hay formas mucho más complejas para almacenar energía como, por ejemplo, utilizar catalizadores para producir gas hidrógeno a partir del agua, almacenamiento de potencial hidráulico (bombear agua a un punto más alto y dejarlo caer a través de un generador) o el uso de un intercambiador de calor para producir electricidad. La mayoría de ellos son demasiado caros o demasiado ineficientes, pero por supuesto siguen siendo interesantes para experimentos a pequeña escala o para inversiones a gran escala.