The more direct we use our sun's energy, the more efficient the complete system will be. Depending on the local circumstances the most direct source of energy can be found.
PV-Systems (Photovoltaics) are not the only way to harvest solar energy. PV consists of industrial high tech. We cannot repair a broken solar panel. Batteries are problematic as well. The lifetime of solar modules is limited. PV can be a good choice, especially in remote and mobile applications, but it is not the only, and often not the best option.
Looking at systems as a whole, we want a great lifetime and a positive impact on the whole region. Architecture, landscaping, forestry, lifestyles, etc., all of it plays together. Functional architecture is the key when it's about energy.
Passive Solar Heating is a must for each home in cold climates, and it's simple. South-facing windows are placed in a way, so that the precious winter sun warms the house. Well proportioned roof overhangs provide shade at summer. Additionally we can use Solar Chimneys for automatic ventilation. Further, cooling by vaporation is possible, e.g. by having a bond near the house.
To heat up houses, Rocket Stoves are a beautiful and simple technology. Efficient ovens save us a lot of wood.
Water heating ist a must for a modern house. Putting the hot water source below the hot water tank provides an automatic circulation of the hot water up to the tank. Thus, the need to pump is less or even zero. Using gravity for heat transportation is called Natural circulation.
Many of todays' heating systems are useless without electricity or can even explode if heated up without a working pump to transport the heat away.
Harvesting solar energy happens in many forms, e.g. by burning wood, by solar thermal modules, by wood gas, biomass composting, etc.
Usually we store our harvested heat in form of hot water. Water is an excellent heat storage and heat transport medium. It is a real gift by nature that simple water can store so much energy in form of heat. (The energy density of water is very high compared with most materials.) Water is optimal in all cases where no higher temperatures are needed than approx. 90 degree Celsius.
By burning wood or gas it is easy to achieve much higher temperatures, 200 degree Celsius and beyond. Many green ways exist to produce gas from biomass at small or big scale.
Creating high temperatures with direct Sunlight is possible as well. The so called Concentrated Solar Power (CSP) shows a simple and sustainable solution. Many types of CSP layouts exist. My favourites are the Scheffler Mirror and the Parabolic Trough.
Concentrating Solar Energy (CSP) is easy, cheap and effective. The reason, why it is not popular and used in small and big scale all round the world, keeps unknown.
On industrial scale CSP is recognized as the cheapest energy source on long term. The existing power plants show a great financial balance and run nearly risk free over decades. Many successful examples exist. See e.g. http://www.nrel.gov/csp/troughnet/power_plant_systems.html
To naturally store temperatures above 100 degrees Celsius we can use natural oils. All oils have different limits. With peanut oil gooing up to 230 degrees is poissibe, mustard oil allows up to 250 degrees Celsius. We can use synthetic oils for even higher temperatures but it is not necessary in non-industrial cases. (See http://en.wikipedia.org/wiki/Smoke_point )
The solar testfield in Tamera used the same oil (Sunflower) over several years. It is quite sustainable and relatively cheap. The energy-density of oil is incredible. Hot oil holds huge amounts of energy without pressure. Hot oil can naturally circulate like water. Hot oil is very liquid.
Heat storages containing 200 degrees Celsius inside, having outside temperatures of 10 degrees, need a good insulation. The higher the difference in temperature the trickier to build a well-insulated tank. There exists a solution: Building layers of tanks containing each other. The central hot oil tank is surrounded by another tank containing hot water. The hot water tank can be surrounded by a warm water tank. This can be done in several layers.
Combining, what was said, into a complete system we might come up with following construction:
a) Three layer heat storage (oil, hot water, warm water)
b) CSP to harvest heat into oil (up to 250 degree Celsius)
c) Additional burner to maintain high temperatures in times of little sunshine
Depending on the size of the construction a single home or a whole village can be heated with such a Layered CSP Oil System. But we also need electricity!
To produce electricity with a generator, we first need rotation. Wind and waterflow provides rotation. But...
We want rotation generated from heat. Because heat is available in abundance using CSP or burners.
A famous device to get rotation by heat is called Stirling Engine. It's mainly used for small scale applications. The industries widely gave up the research on Stirling Engines, using huge Steam Engines in general. The Stirling Engine was invented by an English priest, who wanted to help miners, who often were killed by exploding steam tanks. At the early times of steam engines they were a serious risk to life. Modern steam technology is widely risk free.
Stirling Engines use gas as the working medium, simply oxygen usually. The problem working with gas, without burning it, is its small energy density. The temperature difference between hot and cold side and the amount of used gas results in the overal efficiency of the Stirling Engine, which is not that amazing. Professional Stirling Engines work with a difference of about 700 degrees Celsius between hot and cold, to be efficient.
Older than Stirling engines, and much more in industrially use, is the good old Steam Engine. In fact, even nuclear power plants always include huge Steam Engines in their gigantic processes. The Steam Engine has a long history of technical improvement. Before the second world war, ten thousands of Steam Engines were used in Germany alone. Wherever rotation was needed, you would have found a Steam Engine. It was so common, that even farmers built their own small Steam Engines on their farms to pump water and such. Steam Engines are quite simple. They use water and steam as working medium. Steam, the result of heated water, has a far higher energy density than heated gas.
Both Stirling Engine and Steam Engine are able to transform heat into rotation. It's a choice. Though, the effectivity of Steam Engines is much higher.
Today, small scale Steam Engines became forgotten. After a lot of research, I gave up tp try to buy a modern Steam Engine with approx. 2 KW output. The only option was a Steam Engine from 1960 for 5000 Euro. It's a rattle to me, why small Steam Engines are not available on the markets, using all the nice, modern, high tech possible.
One advantage of the Steam Engine is, that it does not need a 'cold' side. Using the same water over and over in a cycled process we only have to condense the used steam after it did its work. We only have to get the used steam back into water to bring it back into the cycle. The energy output by condensing can directly warm up the warm or hot water tank.
All devices, creating rotation from heat, have a significant heat loss. The efficiency factor will be around 10% only, even using high tech. The rest is lost as 'waste heast'. Waste heat?!
Out of 100% heat energy we can produce 10% precious electricity. The rest of 90% we use for hot water and heating homes. There is little 'waste heat' in a clever combined system.
A layered CSP oil system with integrated Steam Engine can run day and night providing electricity and heat on demand. This technology is appropriate for all world regions. Some kind of heat source is found everywhere.
The company, that sells this powerful device, will be very beneficial. Also ecosteam.org will be a player in the great game of small and medium scaled CSP technology.