July 18, 2006
Auto Parts Build Solar Power Generator

MIT's Technology Review has an interesting report on how MIT graduate student Matthew Orosz, while on a Peace Corps trip to Lesotho in southern Africa, saw Africans using a parabolic reflector to bake bread. Building on this idea Orosz came up with a way to use common parts to make a solar electric generator that is cheaper than photovoltaics.

The basic design of Orosz's solar generator system is simple: a parabolic trough (taking up 15 square meters in this case) focuses light on a pipe containing motor oil. The oil circulates through a heat exchanger, turning a refrigerant into steam, which drives a turbine that, in turn, drives a generator.

The refrigerant is then cooled in two stages. The first stage recovers heat to make hot water or, in one design, to power an absorption process chiller, like the propane-powered refrigerators in RVs. The solar-generated heat would replace or augment the propane flame used in these devices. The second stage cools the refrigerant further, which improves the efficiency of the system, Orosz says. This stage will probably use cool groundwater pumped to the surface using power from the generator. The water can then be stored in a reservoir for drinking water.

Since the parts are mass produced for automobiles they are half the cost of photovoltaics for generating electricity.

As a result, the complete system for generating one kilowatt of electricity and 10 kilowatts of heat, including a battery for storing the power generated, can be built for a couple thousand dollars, Orosz says, which is less than half the cost of one kilowatt of photovoltaic panels.

But does that cost estimate include maintenance costs and replacement parts? I'd expect a much higher mean time between failure for photovoltaics. Though when this gadget fails people with fairly common auto mechanic skills would be able to fix most of it and they'd be able to get many of the parts from an auto parts store.

There's a downside to the mass-produced parts: It is unlikely that many of these parts could be made much cheaper. The design is not as amenable to cost reduction as photovoltaics. Eventually photovoltaics will drop in cost below the cost of this system. Still, it is a pretty neat idea today.

Some questions: How much heat and electricity would this device generate in winter? Would the cold air prevent it from working? Also, can the heat do anything useful in the summer? Solar hot water comes to mind.

Another question: How noisy is it?

Share |      Randall Parker, 2006 July 18 06:45 PM  Energy Solar

Engineer-Poet said at July 21, 2006 5:20 PM:

This is the sort of thing which would get solar seriously moving in the USA.  Half the cost of PV is cheaper than afternoon peak power, and a solar system which offers some electricity and absorption A/C would be worth huge amounts in any zone which gets blackouts during summer heat.

Very quickly, such arrays would be seen as responsible - even fashionable.  "Look, I'm saving electricity; if you get a blackout because of overload, I was part of the solution and not the problem."  And that would take off like crazy.

Randall Parker said at July 21, 2006 5:47 PM:


But currently the lack of dynamic pricing prevents the cost of peak afternoon power from driving investment decisions. I've said this before: We need dynamic pricing in part because dynamic pricing will incentivize the development of non-fossil fuel electric generators.

Such a device as this one could provide a lot of electricity during the spring and also heating during that period too. In the northern hemisphere during the period from March 21 to June 21 we get as much sunlight as we get from June 21 to September 21.

Engineer-Poet said at July 22, 2006 7:11 AM:

You've said it, I've said it, The Knowledge Problem has said it.  It's not news that a consumer isn't going to make an investment if the value is captured by the utility.

I think blackouts change that.  Consumers suffer from them whether they are frugal or wasteful, and taking A/C off-grid makes a huge difference.  Being able to function during blackouts benefits the consumer, and would be a huge competitive advantage to a business.  If the state requires favorable rates for people with solar A/C, it could return some of that value.

Unfortunately, it's probably going to require government action, meaning it will be done badly and late.

Satvinder virk said at August 9, 2006 12:57 PM:

I am an indian born french citizen flying in mauritania ( between morocco and senegal). I have this project of water well drilling and installing solar powered pumping stations ( if i could develop a combined electricity, refrigeration and pumping unit, like those heat and electric powerplants in scandinavia) destined to villages and camps in the desert. All previous experiences and documentation are welcome. Water levels are almost 80 metres.



richard gagne said at October 24, 2006 4:05 PM:

The Chena geothermal project in Alaska is using a large, (7KW rated input) carrier vapour compression a/c unit, running in reverse as a organic rankine cycle motor, (4Kw output, see yourownpower.com and find the paper by Holdman et al). This low temp -70C source would be insufficient at present without the available year round cold (max 5C) creek water.

Many of these large rooftop units are due for decommissioning and pressure swing adsorption, (silica gel Nishiyodo system) is due to replace vapour compression.

Sorry folks i gotta cut and paste a bit here ok? We don't have enough direct insolence up here in Saskatoon to use the trough or parabolic collectors as heat sources for left over air conditioner binary cycle motors, but the low to medium temp collectors work just fine. Nor do our rivers, (whats left of them... MR tar sands), stay very cold in the summer.

Basically, the system will produce, "waste heat",
using a parabolic cement dome as a primary batch heater/storage vessel, and an array of tracking solar
modules, (70% glazed flat panel, 30% evacuated tube).
A seasonal thermal energy production and storage
vessel, ( cement and foam dome/sphere) will be used to
provide a year round cold stack. The input is snow,
the storage medium an ice slurry, (binary ice), the
freezing point reduction brine made from CaCl and prop
Outputs of the system will be considered for their
potential as inputs for district heating and cooling,
CHP, and waste heat to power systems. Cooling
capacity/cost of the binary ice vessel as a stand
alone app. are also of interest.

OK im back ... hope the spacing in that came out ok.

Anyway the basic idea is:

SSTES, (Seasonal Superstructure Thermal Energy Storage), plus solar thermal equals CHPC - combined heat power and cooling on the district, institutional or resort scale. Canada currently spends just under half of heating costs in cooling, just under a third of total Kw costs.

Carnot is your friend, all his leftovers are prefect for humans.

Excellent site! i have one other post here somewhere but read regularly... much appreciated!

regards rg

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