Solar Glossary

Watt or "W" -- Hey, you know what this means.  Think "100 watt light bulb."  But if you want to know the nitty gritty of what a Watt is, and it's brother "Joule," click here.

- A KWH (also, kWh), or kilowatt-hour, or KW, is a measure of electricity. It describes the amount of power (kilowatts) used over a period of time (hours). Running a 100-watt light bulb for one hour uses 100 watt-hours of electricity.  This is equivalent to .10 kilowatt-hours. If it is illuminated for a half hour, the bulb will consume .050 kWh of electricity, or half as much.  Depending on location and size, a house electric consumption may vary between 20-40 kWh per day or 600-1200 kWh per month.  Source:

MWH (or MW) - A megawatt hour is one million watt hours of electricity, or one thousand kilowatt hours (KWH). According to the Department of Energy, the average home consumes 12,000 KWH of electricity annually.

GWH (or GW) - A gigawatt is a billion watt hours.  So now you can appreciate what a statement like this means: "Enertrag, a wind energy company with its base near Prenzlau [Germany], is leading the project [to  turn wind energy into hydrogen, which allows it to be stored]. The company has 440 wind installations that produce 1.5 billion kWh annually — enough to support the yearly energy needs of 1.5 million people." (Source).

TWH  (or TW) - A terawatt is a trillion watt hours. Also denominated "TW."  According to, "[t]he total power used by humans worldwide (about 16 TW in 2006) is commonly measured in this unit."  Note how the term is used here: "McKinsey estimates that the amount of PV that could be cost effectively deployed globally could exceed a terawatt (1,000 GW) by 2020 based on costs declining to below $2 per watt peak (Wp) for a fully installed system – in the process saving over a gigaton of Carbon."  Or this: "I looked up the amount of electricity used for lighing in the US - it's over 500 TWh. That's over 12% of the total electricity consumption in the United States. If the LED guys are right about LEDs taking over within 10 years it means that the electricity used for lighting will fall dramatically. Estimates vary but let's say the US could save 250 TWh per year by transitioning to LEDs.  You'd need about 200 GW of photoelecrics to produce this much electricity. Pretty crazy eh."  (Source).

Levelized Cost of Energy (LCOE) - usually expressed in cents per kilowatt-hour, LCOE takes into account not only the capital cost of building an energy-producing plant, but also the operating and maintenance expenses over time, such as the length of a power purchase agreement and the cost of the plant's fuel.  LCOE is a crucial metric for solar investors, as it is often used to compare the cost of solar energy to other sources. It is LCOE that determines the long-term profitability of a power plant.  So when someone says "that nuclear plant's LCOE is 12 cents/KWH," you now have some sense of what they mean.  Compare that to "First costs," and total operating costs (TOC).  First costs represent the costs to acquire equipment, as well as to build and commission the solar power plant. TOC include the sum of all direct and indirect costs that go into operating a solar plant. Both first costs and TOC affect when a plant ultimately becomes profitable.  (Source).  As this fellow explains, LCOE numbers can be too easily manipulated to political ends.

Here's another LCOE explanation:  

Enter “levelized cost,” or the cost of a solar PV array averaged over a number of years of production. For example, a 1-kilowatt (kW) solar array installed in Minneapolis for $6.40 per Watt costs $6,400. Over 25 years, we can expect that system to produce about 30,000 kWh, so the “simple levelized cost” is $6,400 divided by 30,000, or about $0.21 per kWh.

But people usually borrow money, and pay interest, to install solar power. And there are some maintenance costs over those 25 years. And we also use a “discount rate” that puts heavier weight on dollars spent or earned today compared to those earned 20 years from now. A 1-kW solar array that is 80 percent paid for by borrowing at 5 percent interest, with maintenance costs of about $65 per year, and discounted at 5 percent per year, will have a levelized cost of around $0.37.

That means that “solar grid parity” for this 1-kW solar array happens if the grid electricity price is $0.37 per kWh. But this calculation is location-specific.

In Los Angeles, that same 1-kW system produces 35,000 kWh over 25 years, lowering the levelized cost to $0.31. The time frame also matters.

(Source).  Here's a report on the LCOE for various renewable energy sources.

SOLAR BASICS --  Click herehere, here, and here, for basic explanations.  Here's a Suntech video of how solar panels are made.

Here's a nice piece on efficiency ratings for Solar PV.

Making Solar PV panels:

At the simplest level, there are four main steps in making a solar panel, also known as a solar module. Using molten polysilicon to grow crystals or cast blocks of polycrystalline silicon is the first step. The second step is cutting and polishing the material into thin, smooth wafers.

The third step involves chemically treating the wafer and adding electrical contacts to turn it into a solar cell. The last step involves connecting 60 or 72 solar cells together, covering them with glass, enclosing them in an aluminum frame and adding an electrical junction box.


------------------->  Now that you've learned what those terms mean, you 
can better understand statements like this from this article:  "Though the report discovered a small decline in global wind installations, down 2.3 GW to 35.2 GW, the doubling of solar and PV installations to 15.6 GW led the surge of clean energy growth."

Or this: "17 GW [of Solar PV was] installed in 2010[, which] is the equivalent of 17 nuclear power plants – manufactured, shipped and installed in one year. It can take decades just to install a nuclear plant."

Or this assertion from this site, which cites a lower installed quantity: "new solar installations reached more than 15.6 gigawatts of power worldwide in 2010, a more than doubling from 7.1 gigawatts in 2009, representing the largest year-over-year increase on record. Strong growth occurred in the U.S. solar market as well."

More, from this site: "Citing unnamed sources, China Securities Journal today reported that the country’s solar target might be raised to 10 gigawatts (GW) of PV by 2015, up from the current target of 5 GW. For comparison, global solar PV capacity was about 40 GW in 2010."

Or this, from my favorite magazine: "
The photovoltaic (PV) power sector increased annual solar cell output by 118 percent to 27.2 GW in 2010, according to a survey by PV magazine PHOTON International. This year, global cell companies plan to produce over 50 GW, which could generate as much electricity as about six nuclear reactors."

Or this statement from this site:
"Nuclear power plants typically operate at 90% of nameplate capacity while wind and solar operate at something closer to 25% of nameplate.  The nuclear reactors that have recently gone off-line in Japan and Germany accounted for roughly 125 TWh of electricity production last year. In comparison, global electricity production from wind and solar power in 2009 was 269 TWh and 21 TWh, respectively. In other words, we just lost base-load power that represents 43% of the world's renewable electricity output. The gap cannot possibly be filled by new wind and solar power facilities."

You will also be able to gain perspective, such as this statement from this site: "One megawatt has the capacity to power 250 homes or one Super Target."

And this: "Current world energy use is approximately 16 terawatts (TW) per year. According to the BP Statistical Review of World Energy 2008, the amount of direct solar energy that arrives on Earth during an average four-week period is roughly 1,853 TW/yrs., which is greater than the total remaining reserves (1,755 TW/yrs.) of all fossil fuels. The numbers speak for themselves and the technically feasible (at this time), long-term solution is renewables."

And this: "
A virtual power plant (VPP) is one of the main functions of the smart grid. A VPP matches up a variety of distributed energy systems with intelligent demand response capabilities and aggregates those resources into an asset that acts like a centralized power plant. VPPs are similar to microgrids; but while microgrids are very local in scope, VPPs can theoretically be deployed on a GW-scale at the utility level."

Here is a  useful explanation of
Concentrated Solar Thermal.  And here.

Feed-In-Tariffs (FITs): A FIT is a policy mechanism designed to accelerate investment in renewable energy technologies. Producers of renewable energy are paid a set rate for the electricity they produce, usually differentiated according to the technology used (wind, solar, biomass, etc.) and the size of the installation. It achieves this by offering long-term contracts to renewable energy producers, typically based on the generation cost of each of the different technologies.

For example, if a PV system is installed on a home in Germany it would initiate a FIT program. This creates a reciprocal energy agreement with your utility — the utility would buy the power you produce at whatever the FIT rate was at the time of the agreement for a period of 20 years. You then buy any additional power (mostly at night) from the utility. Since the FIT price is higher than the retail power price, this arrangement allows you to get a stable return on your investment and makes any borrowing of money very easy.  (Source).

More on Feed-In-Tarriffs here.

Loaded Solar: A photoelectric project or system that uses some or all of its generation to serve on-site load. 

Unloaded Solar: A photoelectric project or system that feeds all generation into the grid. 

Hydel: Shorthand for hydroelectricity 

Photel: Shorthand for photoelectricity

SRECs:  Solar Renewable Energy Certificates  - as defined by the New Jersey solar program.