A colleague sent this to me yesterday. I’m warmed (pun intended) to see Walmart take a bold move toward energy efficiency. Using the roof space on it’s massive buildings to host solar arrays may make some sense. Certainly Google thinks so and Federal Express (Oakland, CA sorting facility) has had solar cells on the roof for some time now.

Independent of this specific proposal, it’s great to see some large corporations make concentrated efforts to lead in this area.

Note to Mr. LaMonica (author of the CNet piece) – the largest proposed single instance of solar generation is in China at 100MW and Germany has a 12MW plant in production now. While Walmart could aggregate into 100MW size, it’s not quite the same thing. Still beneficial, no doubt.


Technorati Tags: Renewable | Energy | Solar

A follow-up story from yesterday’s entry, there is a report out today that China intends to build the world’s largest solar electricity generation plant, 100MW. To put that in perspective, it’s about 1/2 the size of a traditional coal fired generation plant and about 10x the largest solar installations on the planet. If you’ve ever wondered why we don’t see more solar plants, the clues are in the report.

A year has 8,760 hours in it. In this report the selected site has an outstanding 3,362 hours of sunlight. That would yield a capacity factor of a little over 38% (good compared to the 25% normally achieved by solar.) To translate that into something more tangible, the system is rated at 100MW x the 38% capacity factor means that around 38MW output can be expected from the installation. Each MW provides enough electricity for about 600 households per year (US – I’m sure China is substantially different due to lower electricity demand per capita.)

The announced cost for this installation is $766M, or $7.6M per nameplate MW, or $20.1M per capacity factor constrained MW. Even amortized over decades, it’s difficult to see the economic payback from such an installation. To put solar cost in perspective, one would expect to pay $1M/MW for wind, $750k/MW for natural gas, and $3M/MW for geothermal. My sense is we’re still a technology generation or two away from economically viable solar electric generation at utility scale.

I think solar energy generation is great and I laud China for stepping up with an audacious plan, but I do believe there are more economically viable ways to achieve the same result. I’ll watch this project with interest as it unfolds.


Technorati Tags: Energy | Renewable | China

If you’re into way off the grid living, this is an interesting way to get some light. The University of Michigan has done some prototyping on a “light bag” – effectively a solar textile that charges 6 individual lamps and/or a central battery.




Technorati Tags: Solar | Light | Energy

You might recall “Aquarius/Let the Sunshine In” as a catchy little tune from the musical Hair, but that’s not what this entry is about…

It turns out that the energy in sunlight is measured at 250 watts/square meter on average across the US, or 3 KWh/square meter/day. See the NREL map below for details.



Now don’t go out and buy solar panels for your roof just yet, not all of that available energy can be directly translated into electricity, the best solar panels are about 15% efficient which means that one might harvest as much as 0.45 KWh/square meter/day into direct current, during day time. Obviously the amount of energy produced is related to location, hours of direct/indirect sunlight, and weather. So just what are these solar panels (photovoltaic cells) anyway?

Photovoltaic (PV) cells are a semi-conductor that absorbs sunlight (photons) into charge carriers (electrons) then directs them to a conductor. Typically, PV cells are grouped into arrays and placed on sheets or panels which in turn are arrayed to generate a desired amount of electricity. Solar panels have been in use for years in space applications, remote sensors, pocket calculators, and increasingly, for individual home power generation (or co-generation.)

There have been some efforts to get to utility scale with PV technology, but the cost remains prohibitive (~$0.20/KWh competing against $0.03-0.07/KWh for other technologies.) Japan and Germany have the most installed PV technology with the largest single installation rated at 12 MW peak production. To put this in perspective, the average fossil fuel plant in the US is rated at 219 MW peak production and the average nuclear plant in the US at 2,000 MW. As costs for PV continue to drop (as they have around 3% per year over the past few years) coupled with fossil fuel cost increases, the point at which PV becomes profitable at scale will likely happen in the next 15 years.

PV power generation does have some distinct advantages including $0 fuel costs, zero-emission power generation, long equipment lifespan, relatively low maintenance costs, and modular application scaling from micro-installations up to small utility size. The disadvantages to solar are in capacity factor, it’s only light so many hours per day and power demands are 24/7. Relatively speaking, it’s expensive to procure and install. And finally, the resulting power is direct current which further degrades efficiency as the power must be “inverted” to use on the grid or in typical AC household power systems. I’ve heard there may be some breakthrough research happening on the production of PV cells that radically change the costs of PV; if this happens, solar may become mainstream faster than any of us would expect.

Google is certainly making a go of it. Recently, the company announced a plan to install solar panels on its buildings (1.6 MW) and that the resulting power would satisfy up to 30% of the company’s energy requirement. Aside from being good for the planet, I presume someone ran the numbers to see this would at least be a slightly positive return on investment.


Technorati Tags: Energy | Solar | Photovoltaic