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This thread is inspired by the work of Kris DeDecker on the Low Tech Magazine. I raise it here to explore the potential for using energy produced by renewable energy sources (as electrical, mechanical or thermal energy) as it is being generated, either entirely without storage or with minimal storage. This avoids both the energy losses associated with storage and energy conversion and the very considerable capital costs and embodied energy costs of energy storage systems. But living in this way obviously requires deep changes to how our society operates. I want to explore exactly what those changes need to be.
This article concerns direct use of solar power.
https://solar.lowtechmagazine.com/2023/ … batteries/
DeDecker is talking about the direct coupling of low voltage DC producing solar panels to low voltage DC loads. Transmission distances will be just a few metres, as the panels would be on the roof of the building that they power. We would have a number of DC electricity consuming applications within a building. As power production rises and falls, we would adjust our electricity demand accordingly. With machine tools powered by DC motors, lower current from solar cells results in the motors running more slowly. We could accept a slower work rate, or we could prioritise more urgent applications and switch off other power uses to allow the motors to speed up. Obviously, when the sun goes down, power supply goes to zero. And peak power will be lower and available for far fewer hours in winter than in summer. Is there any way that we could adjust to living like this? Adjusting our demand to match supply?
Similarly, we can use wind power to produce mechanical power without going through the intermediate step of generating electricity. We just use mechanical power to drive mechanical loads. There are a very great number of applications in society that use mechanical power. But this works best if we can cluster mechanical loads arouhd a wind machine and do not attempt to store mechanical energy. We vary work rate according to the power available. Traditionally, this is exactly how wind power has been used and could be again.
The simplest power transmission arrangement is the line shaft. A wind machine is coupled to a rotating shaft running along the ceiling of a factory building. Individual machines take off power by belts connected to the shaft. The number of machines operating or their running speed would need to vary with wind speed. There are other mechanical power transmission technologies as well. Hydraulics and compressed air are the most promissing examples. But rope, chain and rod drives have applications as well.
I would like to use this thread to explore how a direct renewable energy economy would work in practice. Our illustrous leaders have made nuclear power unworkable and are intent on limiting our access to fossil fuels as well. Whilst I have no interest in enabling these moronic people, as an engineer I will look for ways of operating within available parameters.
Last edited by Calliban (2023-12-05 15:45:16)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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Additional: One very cheap way of storing energy which might actually be affordable long term, is thermal energy storage. This involves storing thermal energy either as sensible heat in liquud and solids, or as latent heat of melting in phase change materials. Electrical power can be stored as heat by activating heating elements within an insulated thermal mass. Heating elements can be used as dump loads when power production exceeds demand.
Wind or wave power could be used generate heat without electricity. Mechanical energy couod be used to compress air, which can generate extremely high temperatures. Simple friction brakes in water could generate low grade heat. Mechanical windmills could also drive heat pumps, dumping heat into underground hot water tanks which supply a large local heat load or a distributed load via a district heating system.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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A wind driven saw mill in the Netherlands.
https://m.youtube.com/watch?v=axSBSul8vXo
Living energy farm. This is a good example of how DC from PV panels can be directly coupled to DC motors. No charge controllers, inverters or batteries needed.
https://m.youtube.com/watch?v=xXvgp1q8Rfw&pp
I wonder if a system like this could be operated with banks of resistance heaters in water tanks serving as dump loads. Essentially, you switch these off when you want to operate other equipment. This means that no solar electricity is wasted, as anything not used for mechanical or electrical purposes is captured as high quality heat. We could do something similar with cooking. Build well insulated ovens containing a lot of thermal mass. When there is excess power, we use the oven as a dump load. It will store heat that can be used for cooking on demand. If temperatures happen to be lower on a particular day, we extend cooking times accordingly. In the winter we could favour energy cheap cooking methods like the slow cooker.
Some other applications that can be carried out intermittently if necessary.
1. Brick baking. Once ovens are loaded, a baking cycle must be finished. But the batch nature of brick ovens allows them to plan a run depending upon the abundance of power. The ovens could be powered by resistance heaters.
2. Cement manufacture. This requires very high temperatures, but could be driven by heating elements in batch kilns.
3. Ammonia production using the Haber process. This is typically a batch process. Hydrogen could be produced when power is available. This is less than ideal, because electrolysus stacks are capital intensive equipment. But ut could be done.
4. Crude iron production. Iron oxide could be reduced in batch kilns. Iron oxide could be mixed with reduced iron powder in an insulated batch kiln. The mixture is heated to 1000°C by induction heaters and hydrogen gas is passed through the mixture reducing iron oxide to iron metal. The crude iron metal can then be seperated from iron oxide powder by milling and magnetic seperation. Iron powder can then be turned into steel in an arc furnace.
Last edited by Calliban (2023-12-05 17:14:39)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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There are distinct advantages if you can integrate the renewable directly into the supply for grid-supplied devices. An example has to do with domestic hot water heating.
You put the solar thermal panel on the roof, and let it keep an insulated tank of water as hot as it can. About 190 F in the summer is an upper bound. You also put a water pipe coil in the tank, connected to the domestic water supply at its inlet, and to the hot water heater's inlet at its exit. That way, you are solar pre-heating the water that goes into the water heater. As long as that supply to the water heater is hotter than the thermostat setting, the grid (or gas) connection to power the heater never gets used. Works with either electric or gas-fired water heaters. Their power types make no difference to this concept.
The only downside is a variable hot water delivery temperature from the water heater. It should be easy enough to learn how to live effectively with that.
With hot water a substantial fraction of home energy use, this is a fairly large effect. Bigger solar panels and bigger tanks cost a bit more, but that extends the longest time-without-sunlight you can deal with, in cold winter weather. Not usually much of a problem in the summer.
GW
Last edited by GW Johnson (2023-12-05 17:10:23)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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