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SHPEGS — DIY Solar/Geothermal Electricity
rohar writes "SHPEGS is an open design not-for-profit project to design and prototype a base-load renewable electrical generation system suitable for moderate climates and built from common materials. The design centers around creating a local geothermal source with an efficient solar thermal water heater system and can be scaled from single residence to mega-scale. The heliostat system used in Europe's first solar thermal plant could be used in a scaled-down SHPEGS system with Practical Solar's small scale heliostats."
Isn't this just the Energytower renamed?
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Solar PV is a different system. The SHPEGS design focus is base load electricity, cheap collectors and enhancing the solar thermal output with additional ambient heat from the air which will mean the collectors scale in a non-linear fashion. There is also a prevailing wind enhancement potential with the convection tower. I would think that both for simplicity and summer daytime operation in arid locations that Solar PV or a classic Solar Thermal system would be a better solution for output/m2 of collector. At night or for most of the winter in Canada, Solar PV has little or no output and there isn't a comparison between systems.
It's fractional distillation and the heat is recovered from both the water and the ammonia. This is a good document on GAX Absorption Heat Pumps and the wikipedia Gas Absorption Refrigerator entry.
The step-by-step detail PDF outlines what is happening in the SHPEGS cycle along with the Flow Animation.
Ammonia/water is also not the only possible working pair, but it is commonly used in heat pumps and Industrial Heat Transformers and was used in the system to simplify explaining the concepts. A commercial absorption heat pump powered by a geothermal source with images and diagrams.
There are plans to prototype it, actually as soon as I finish coaching my kids softball. :)
Questions I am hoping the prototype will answer:- The theory is that by using a Absorption Heat Transformer/heat pump to "upgrade" additional heat from the air, it will lower the amount of solar collector required for a given output and scale in a non-linear fashion. This adds a lot of complexity to a solar thermal system and although the absorption heat pump has been around for 100 years, it isn't that common of a technology and it's difficult to find experts in the area.
- By using the heat transformer concept, the temperature can be raised to use a water steam turbine as opposed to a lower temperature and a organic rankine system. Water is more dense than lower boiling point fluids and in theory the turbine power output is higher. The question is whether the power going into the solution pump to pressurize the aqueous ammonia to raise it's temperature that high justifies the increased power out.
- The negative buoyancy caused in the convection tower and it's fluid dynamics are difficult to model for someone that isn't a fluid dynamics engineer. In theory, the air intake of the tower can be orientated to prevailing winds, the heat exchangers can angle the air and a vortex can be created in the tower which will increase the angle of attack against the wind turbine. It's difficult to picture how this will work without a working prototype.
- A dozen other things.
As far as complex, the cycle isn't much more complex than an absorption refrigerator found in most RV's. I have one in my camper that is 30 years old, never been serviced and works fine.The thermal storage would be deep enough to not interact with the surface or shallow groundwater. The Drake Landing project has some information. This is another research document on thermal storage.
There is a lot of potential for integrating bio-methane which requires a very constant temperature as well as this Solar Hydrogen from methane production system. Algae farming also has a potential integration with the solar thermal storage.
I don't mean to avoid the efficiency question. Again, in an arid location with the majority of electrical usage for AC, Solar PV or Solar Thermal is simpler and probably more suitable. The cost/m2 of collectors is substantially cheaper in a thermal system, so I'm not sure what you are comparing. Marginal and poor land that isn't suitable for crop production or the roof of a Walmart isn't the cost factor, the solar collector is. The MIT group was able to get 1kW from 14m2 of trough collectors on a straight thermal system and the SHPEGS additions should improve on that.
There are also 2 heat sources in the SHPEGS system, solar and hot summer air along with two power generation systems, thermal and the wind turbine. In theory, the absorption system should improve not degrade the straight solar thermal system, so I would expect something better than 10% efficiency on the solar portion if you include the additional heat from the air. The conversion efficiency of the heat being extracted from the air is difficult to calculate. The energy cost is the energy going into the solution pump to pressurize the aqueous ammonia and there isn't the same direct cost in the volume of air being moved, in fact the more air that is moved the better the output of the wind turbine portion.
I used 5% thermal to electrical efficiency for the calculations to be conservative, and generally 10% is used for binary geothermal plants.If you are comparing Solar PV, you need to account for battery cost and cut all the numbers by at least 50% to account for the daytime only output. Regardless of what is used for electrical storage, there are 3 months of the winter in Canada and the northern US where Solar PV isn't going to put out anything substantial and seasonal electrical storage isn't feasible.
The Toronto Exhibition Palace Live Solar PV Stats page has some historical data on Solar PV in winter in Canada.I've been into this stuff for 15 years (hobby) and I've not made anything large scale (yet) as far as solar. The problem is that its of minimal benefit to me because I'm so far north and its cloudy.
What is best in any problem usually depends upon its end use (like playing computer games and getting yourself hacked are uses best suited for Windows.)
HEAT
If your goal is heat, which is the #1 energy load for MANY people, then its clear solar heat is more direct.
The KEY issue with ALL power systems is the conversion losses (which includes capturing.) Storage is the next big issue after conversion.
For heating, solar heat wins hands down by a large margin except perhaps if your on mars or something (where your air can turn liquid when its cold outside.)
COOL
Cooling is big if heating is not. A clever cooling system leverages the earth's 50F temp-- just running some garden hose underground and running water thru it and a car radiator and you are already in business.
Naturally the biggest deal with hot or cold is insulation and thermal mass, those are your first priority before anything else. You can work on that today and it will save you money. Your ceiling loses the most, followed by the walls and a close third is the windows and doors.
For cooling, I'm seeing solar heat based products that claim better than PV for the whole system. I've not seen a PV cooling system-- they just use the power on a normal unit. I don't know the numbers, not much interest-- a thermal syphon is plenty for me.
Electric Power
You can store heat better and cheaper than you can electricity, generally speaking.
PV is simple, direct but costly to setup and maintain (long term-- hopefully PV prices drop in the 30-40 years before panels need replacing.) The Heat to Electricity conversion process is complex and while it is good at large scales, I've not seen anybody with a small scale setup that is seriously being used. Also something people don't think about-- is the scattered indirect light which is more common in clouds and smog. PV will handle that better than the concentrating heat based systems (and they must concentrate to get high temp.)
Exposed concentrators (as opposed to infrared blocking coverings) will use the full-spectrum while PV doesn't use much of the spectrum-- which gives them a huge edge as well. The physics of the problem dictate that dumping spectrum means less power is possible (you could do 100% but if you skip half the light energy your only getting 100% of 50% = 50% tops.)
PV panels claim to last 30-40 years, which means payback in about 20. At that time their cost or performance will be higher. The problem with "payback" is that you are still paying for it so it is STILL costing you that much money which could be saved by getting something with a better cost performance ratio. It should always come down to lifetime performance cost-- a poor PV panel which costs nothing and lasts a long time can beat out "better" PV panel. Same for solar heat, Wind, etc. (or nuclear, which I've heard has never been profitable--its heavily subsidized.)
I've focused on insulation and heating. Those will not change much and are quite good TODAY and have low cost and quick 'payback'. Electricity is a secondary concern because its not my primary cost or environmental impact. Electric generation is still quite up in the air and costs will come down. Better thinking about a wind generator if you have some wind available; it could provide a better ratio for you.
So your question is not that important for people, and as far as the answer-- you will see PV power plants that are honestly profitable popping up as soon as they can beat the other methods. (I know canada is building the biggest PV plant, but I doubt its because PV won out... if it did, its solely from the cold temps and often indirect light which PV is unaffected by.)
Getting a Grid Tie is not cheap, but it beats wasting money on batteries. Never forget that cost-- if you are
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