Harvesting clean energy in cities

There is a new technology that can convert both solar and wind energy into electricity in such a way that it is suitable for use on urban rooftops.

Here’s the abstract from the paper describing this work:

To realize the sustainable energy supply in a smart city, it is essential to maximize energy scavenging from the city environments for achieving the self-powered functions of some intelligent devices and sensors. Although the solar energy can be well harvested by using existing technologies, the large amounts of wasted wind energy in the city cannot be effectively utilized since conventional wind turbine generators can only be installed in remote areas due to their large volumes and safety issues. Here, we rationally design a hybridized nanogenerator, including a solar cell (SC) and a triboelectric nanogenerator (TENG), that can individually/simultaneously scavenge solar and wind energies, which can be extensively installed on the roofs of the city buildings. Under the same device area of about 120 mm × 22 mm, the SC can deliver a largest output power of about 8 mW, while the output power of the TENG can be up to 26 mW. Impedance matching between the SC and TENG has been achieved by using a transformer to decrease the impedance of the TENG. The hybridized nanogenerator has a larger output current and a better charging performance than that of the individual SC or TENG. This research presents a feasible approach to maximize solar and wind energies scavenging from the city environments with the aim to realize some self-powered functions in smart city.

The paper is “Efficient Scavenging of Solar and Wind Energies in a Smart City” by Wang, Wang, Wang and Yang. You can see the abstract and download a PDF file here.

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10 thoughts on “Harvesting clean energy in cities

  1. Now that is what I need, we do have sun in Stockport UK, but my rooves are not ideally placed to harvest it given the latitude, however wind we have a lot of.

  2. But of course the question is is distributed generation really that much better than long distance HVDC transmission. Ignoring the political realities Europe has just south of the Mediterranean a very large area that would be excellent for solar power. HVDC cables could span the straits of Gibraltar at a minimum. Likewise in the US if you built the HVDC lines from the Southwest you could get solar east and also solve some of the problem of peak off peak because of the 2 hour or so difference in sunrise sunset times. Building the HVDC lines further north would also enable wind energy to participate.
    It is not clear with prices we see with solar power today at about .04/kwh at the delivery point to the network that distributed solar really makes economic sense. Note that from the integrated utilities perspective net metering should be at the wholesale route. (Which it would be in de-vertically integrated, or deregulated areas). Essentially the home system is treated just like a generator in this model.

  3. @Lyle 2

    The question is “better for whom?”

    1. What is the argument for “utilities” being retailers at all rather than common carriers?

    2. You lose the resiliency of local generation in a “stormier” world.

    3. You lose the economic benefit of local jobs.

    Here’s my suggestion: Along with pricing carbon, require “utilities” to act as common carriers only, and operate a marketplace that equitably enables buyers and sellers to make transactions. (a combination of UPS, FedEx,… and Amazon Marketplace, EBay, … .

    Then, if you want to invest in an HVDC line from the Southwest to the Northeast, that can be your market decision.

  4. I wonder about the failure rate of those vibrating membranes in the TENG, and about the cost of the whole thing. Also the angle of the solar cells to the sun looks less than optimal. I would prefer to keep solar and wind separate and as simple as possible, for cheapness and ease of servicing. You could put a row of conventional wind generators along the ridge line.

  5. @jazzlet

    What you need in Stockport is a kinetic energy generator to convert the energy stored in raindrops!

  6. Re #3 in one sense that is what the non vertically integrated model has already done. The distribution utility is a common carrier that will move power from the substation to the consumer. It is open to all comers and bills them for usage of the local grid. There is no longer a utility in the old model. For example if you want to buy wind or solar power you have the option to buy that from a retailer who provides that service.
    Just like in Europe with the feed in tarrif which is fading away roof top solar would not make sense with netmetering at the wholesale price level. (i.e. the payout would exceed 20 years). Note this is what payout times in Tx look like for solar right now. If the Ca public utility commission set cost appropriate rates solar would not catch on in Ca either, but they are extracting excess money from the public because they could not get the non vertically integrated model right.

  7. @lyle 6,

    Can you provide any detail of what you are talking about or a reference to any actual system that follows the model I have suggested?

    And explain what “extracting excess money from the public” means?

  8. “But of course the question is is distributed generation really that much better than long distance HVDC transmission.” #2

    Maybe not if, but when. I don’t think there’s a one size fits all answer, and any answer has to depend on the resources that are available. In any case, a geographically diverse renewable energy supply provides greater stability than a geographically limited one.

    The technology here is interesting, but perhaps more interesting than useful. The best winds are at higher altitudes than roof level, and as not all areas have good winds, the additional material and money resources might not make sense. There’s a good reason why wind turbines have gotten larger, and why they tend to be erected in areas with winds that actually can produce energy.

    As far as solar is concerned, utility scale solar tends to be located in sunny places. It can produce electricity at a considerably lower price than rooftop, and would probably also necessitate the use of fewer material resources.

    (From my vantage point, the policies and prices of American utilities are of no interest.)

  9. http://conservationmagazine.org/2016/01/current-technology-could-give-u-s-an-affordable-clean-grid/

    “Our results show that when using future anticipated costs for wind and solar, carbon dioxide emissions from the US electricity sector can be reduced by up to 80% relative to 1990 levels, without an increase in the levelized cost of electricity. The reductions are possible with current technologies and without electrical storage. Wind and solar power increase their share of electricity production as the system grows to encompass large-scale weather patterns. This reduction in carbon emissions is achieved by moving away from a regionally divided electricity sector to a national system enabled by high-voltage direct-current transmission.”
    Future cost-competitive electricity systems and their impact on US CO2 emissions
    http://www.nature.com/nclimate/journal/v6/n5/full/nclimate2921.html

    “The need for new energy storage is often seen as an obstacle to integrating renewable electricity into national power systems. Modelling shows that existing technologies could provide significant emissions reductions in the US without the need for storage, however.”
    Energy modelling: Clean grids with current technology
    http://www.nature.com/nclimate/journal/v6/n5/full/nclimate2926.html?WT.ec_id=NCLIMATE-201605&spMailingID=51246683&spUserID=ODQ1NzA3NTc4NDcS1&spJobID=903435134&spReportId=OTAzNDM1MTM0S0

  10. You need to do the back of the envelope math. The amount of power generated per unit area is minuscule, maybe 1% of a standard solar panel. So this may be interesting from a scientific perspective, but unless the efficiency can be scaled up by orders of magnitude, it isn’t a realistic alternative.

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