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."

Comments

Efficiency?

[mdsolar]

I read though the site and found many calculations but I'm trying to figure out the actual efficiency of converting solar energy to electricity. I don't mind if the hot water out gets counted at 100% but I'm guessing that per unit area this does not do as well as silicon PV at 15%. If there is a table that gives this kind of comparison, can someone please point it out? Thanks.
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Re:Efficiency?

[rohar]

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.

Re:Efficiency?

[mdsolar]

Thanks. I'm looking for a number though. For a solar tower you might expect 0.5% http://en.wikipedia.org/wiki/Solar_updraft_tower but this project is tweaked. If the heat is being stored, it is still solar power, but delta T may not be so favorable. For corn ethanol, the efficiency is about 0.06%. At this level of efficiency for energy production/storage competes with food production so it is not all that feasable. But, algae get close to PV efficiency http://mdsolar.blogspot.com/2007/02/photosynthesis .html. So, in terms of land use, I'm trying to figure out where this falls.

I wonder how this would be for growing winter crops as well: is the ground warmed eough? And, if it is, what kind of losses might be expected owing to water evaporation from soil?

Re:Efficiency?

[rohar]

For a solar tower you..

Convection tower performance is very poor and the convection tower portion of the SHPEGS system accounts for less than 10% of the system output. It is still clean renewable power, but the convection tower wind turbine output is trivial. The chimney is there to allow a large volume of air to move across the heat exchangers efficiently and the wind turbine takes a slight advantage of the effect, but it isn't significant.

I wonder how this would be for growing winter crops as well

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.

Thanks. I'm looking for a number though.

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.

Re:Efficiency?

[bussdriver]

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

Re:Dupe

[weighn]

Isn't this just the Energytower renamed?

renamed, but the original article was based around the premise of a discussion into whether or not it would work.

The SHPEGS (Shit-Hot Power or Electricity Generation System) project "just works".

Re:looks OK. one question bothers me...

[rohar]

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.

Let's see a prototype

[Animats]

That thing has an incredibly complex cycle, with losses all along the chain. There's ammonia, water, steam, air, and hot oil involved, with heat exchangers all over the place. The paper attached to it doesn't describe the basic thermodynamics in any real detail. It's sort of like a solar-powered Rankin cycle system. But much more complex, and without solid justification for the extra complexity.

This might be credible if they had a working prototype, even a little one. A prototype in the 1 KW range would be about right. That's a backyard project. A 1KW plant would need about 10 square meters of collector mirror, which isn't too hard. Then they'd have something. All they have now is hype.

Re:Let's see a prototype

[rohar]

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.

Developing World Application

[FromTheHorizon]

I currently live in Indonesia, where people commonly burn rubbish - including farmers who burn the husks from rice production. Although this certainly isn't the most environmental form of waste management, I feel that if they are already burning rubbish, at least they could collect the energy from the burning?

Would it be possible to build a simple generator to convert the energy into electricity?

Re:Developing World Application

[rohar]

This is a very interesting project by a group of MIT grads that implemented a very cheap solar thermal system out of salvage automotive components (power steering pump, alternator, etc) for low cost deployment in developing countries.

The SHPEGS additions to this type of system (thermal storage, convection tower) could also be implemented cheaply from common materials and salvage parts.

Re:hold on

[Dunbal]

Using geothermal power will speed up the cooling of the earths core.

????????

      Seriously do you have any kind of idea of the amount of energy required to cause any sort of noticeable impact on the earth's core? It's like a colony of ants saying they will destroy all the buildings in Manhattan.

Can anyone help with the math?

[Bodhammer]

I recently read an article about solar power in Wired magazine: http://www.wired.com/wired/archive/13.07/solar.htm l

The article mentions a new design for a concentrator that only uses two motors. To quote the article -

"Then, in a weekend flash of inspiration, a young Caltech physics grad named Kevin Hickerson figured out how to reduce the number of motors needed to move 25 mirrors independently, a major cost factor. Instead of two motors for each mirror - the traditional approach - Hickerson's solution requires only two motors for any number of mirrors. The key is a mathematical curve known as the conchoid of Nicomedes (named for the ancient Greek mathematician, who discovered it). A grid of ball bearings arrayed to match the conchoid is attached to a frame inside the Sunflower. As the motors move the frame, the bearings control each mirror's position individually."

I have found this but it is not helping me much:

http://nvizx.typepad.com/nvizx_weblog/2005/08/conc hoid_of_nic.html

I have been unable to locate a more detailed explanation of the system and I'm not sure if this basic math is patentable. My advanced math skills are very rusty and I'm not quite sure where to start to understand this. I have an idea that this technique might be useful and I want to understand how to design such a frame. I did look at the concentrator page here: http://www.sandia.gov/pv/docs/PVFarraysConcentrato r_Collectors.htm but it was not much help.

These articles as well also have some implications for the benefits of a simple energy source:

http://science.slashdot.org/article.pl?sid=05/09/1 2/1621204&tid=126&tid=14

http://www.time.com/time/magazine/printout/0,8816, 1101299,00.html

Also, this today triggered my interest again:

http://www.renewableenergyaccess.com/rea/news/stor y?id=46765

I want to understand how to make a spreadsheet or something that would allow me to input number mirrors, focal length, size and it tell me shape, size a location of pivots. Can you explain it to someone who hasn't touched calculus in 18 years? I want to build a cheap one on my roof!

Re:Likely not worth it...

[mdsolar]

It is true that heat retention improves with scale linearly and delta T can be increased with scale, but the cost goes up with volume (linear scale^3). One nice aspect of this system is that you might build it to last a few centuries in the below ground hardware so that the cost per unit time is low. It is difficult though to arrange multi-generational financing of this duration so the first users have to carry the install costs.

PV scales as you say, but the cost comes down a lot with large scale manufaturing, and the cradle-to-cradle-to-cradle aspects of recycling the PV look pretty positive so it carries reduced costs forward but in a way that spreads them without having to work out new finacial instruments.
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