The Units Commonly Applied to Renewable Energy Are WRONG!

A case in point, the New York Time says in http://www.nytimes.com/2007/12/18/technology/18solar.html?_r=1&ref=business&oref=slogin
Nanosolar's founder and chief executive, Martin Roscheisen, claims to be the first solar panel manufacturer to be able to profitably sell solar panels for less than $1 a watt. That is the price at which solar energy becomes less expensive than coal.

It is true that if you could build a PV plant for $1/W, the plant would be cheaper than a coal plant of the same rated capacity. However, the PV plant will typically produce less than one third the energy in KWH in a year than the coal plant, and the cost of the electricity in cents/KWH will be significantly higher for the PV plant than for the coal plant. This is the frustration.

-Carolyn L,
proud rooftop PV owner

While you agree with Rob on some points, you seem to have missed his point almost entirely. He did not say that renewable energy sources were unpredictable, yet you went after that like a strawman.

It doesn't matter if you could predict solar output of PV system with 100% accuracy a day ahead or even 1 million years ahead. It's capacity factor on earth will still be about 20%, maybe 25% at best in the Mohave desert. So it can be misleading to compare the rated peak capacity of a PV plant to the peak rated capacity of a coal plant that runs at closer to 70% capacity factor.

Peak Power is a practical measure, for PV anyway. Stating an average energy would give too high an average error since given a particular array, the annual energy output would depend on amny things besides the particular PV system, such as average temp, orientation of the array and whether it is tracking- one or two axis - geographic location, etc. But using an NREL table for the approximate location, the known average temp, etc, a relatively simple calculation can give reasonably accurate results. The NREL table as I recall gives +/- 11% error bars. This error would be much lower than using a stock 2000 kWh, say, energy rating in NH or AZ where the geography and conditions are so different.

It is like trying to rate how many gallons it takes to go on a trip with your car; you can easily calculate based on your car mpg and the distance your trip is with much more accuracy than just using a national trip average fuel use in gallons!

Peak generating capacity is also important, but as we move to a renewable future we can expect to have most of our energy come from renewables and be supplemented with battery and hydro storage to smooth out the inherent intermittency of wind and solar. Wind is even cheaper to install than solar, and is somewhat complementary to solar - on days with no wind there tends to be sun and on days with no sun there tends to be wind. Peak output is important to know, but you get paid back on the average MWh/yr generated. The amount of electricity that can be generated from wind is 2 1/2 times what we use, and that is not counting any offshore wind generation. Solar is by far our biggest resource though.

Peak generating capability (capacity) under optimal conditions is a fairly straightforward way to compare similar technologies.  Another method is to measure energy production under a variety of ambient conditions, which is how solar thermal collectors are rated by the Solar Rating & Certification Corporation.  SRCC also publishes solar thermal system performance estimates (in total kWhs and/or BTUs produced annually) for numerous cities around the US.  Using these tools, the performance of solar thermal systems can be predicted with good accuracy.  See: www.solar-rating.org for more information.

This is a bit silly- are you really assuming that the public is that dumb?

  Of course renewables are inherently INTERMITTENT resources (other than geothermal and hydroelectric maybe)

 More important are RATE STRUCTURES that the utilities offer

 kWh charges -  good for RE, especially peak / off peak variables for solar

 demand charges-  no good for RE- measures 15 min when RE not present

 thermal is basic- gas replacement

 

 

In California, almost all our peak power is used for air conditioning. It's in use exactly when the sun's insolation is at its peak. In this one case, at least, capacity does mean something. Solar thermal troughs can even be more efficient if the hot liquid is used directly to heat and cool, by using heat exchanger technology.

In the strictest sense, there is no 100%, absolutely dependable, power source. There are trade-offs for every source of energy.

A coal plant can work as long as the mines dig up the coal and deliver it to the factory, and as long as the air is breathable.

A nuclear plant can work as long as nuclear fuel is delivered and the nuclear plant is working safely.

A gas or diesel engine will drive a generator as long as there is a source of fuel, and until the engine wears out, and the atmosphere becomes full of exhaust.

There are limitations and trade-offs with every energy source. The point is that for too long renewables have been ignored and/or actively blocked from development.

 

Scott is right, despite the sensationalism of the article title, when you buy solar panels, you buy them by rated peak PV, when you sell electricity, you sell it by MWh/yr. The conversion between the two depends on many installation factors, and will vary by 20% from year to year, just like almost any other type of energy producer. There is a calculator at http://www.findsolar.com/ which allows you to calculate how big a panel to install to offset your electric bill and how long it will take for it to break even. For the first time, in 2007, the typical break even period is shorter than the warrantee period of 25 years for most locations in the United States. Investors have recognized this and are willing to install solar panels for free in exchange for a long term power purchase agreement.

Because renewable energy is now recognized as one of our most important future energy sources, if not in fact, the most important one, I think that speaking in energy terms will eventually win more respect than just using the peak power rating.  I don't think we need any longer to skirt probable energy production from renewables because the smart decision-makers that will end up buying renewable energy plants are going to figure out pretty soon or know already that capacity factors MAY be less than a comparable conventional power plant.  We need to meet people's objections head on rather than dance around them.

One of the problems with using average generation kWh/yr, ect. to compare generation capacity is that results can vary widely based on location or weather alone.  Rating in peak power is the only controllable common demoninator manufacturers can use to compare and warranty their products or technology to others.  As Scott notes, fueled generator technologies (coal, gas, nuclear) also have widely varying capacity factors between technologies and even between plants.

That said, I think we need a common cost denominator of $/kWh that includes all of the life cycle costs, such as maintenace, carbon/pollution output, and clean up at end of life.  Let's also include the health and environmental cost for fuel gathering.

I have a problem understanding the issue when math formula are given.  Nothing personal here, I just am not that good at math. What I would like to see is a simple example.  Something like: (for you average house you need a 6-8k peak power system if you run your air conditioner. This will provide an average daily output of approximately 2-3k watts. This provides the maximum power you need when you need it, that is, when the air conditioner will run the most at peak sunlight, and you PV system will be producing peak power at the same time). This is an example those of us who are mathamatically challenged can sometimes understand.  Its not perfect and I am sure can be improved on. It provides more relivent reference to how we use power every day.

Interesting...

  But poorly stated, Rob L. has a 'little' trouble with units.  He fails to understand that we have to rate our systems in terms of peak POWER, otherwise we risk damaging the infrastructure.  Our 200kW can deliver 200kW under full sun, but It I called it a "35kW avgerge", I'd find myself at the pointy end of a lot of lawsuits.  The only real purpose of the peak rating is to determine the initial cost of the hardware. 

  Now when I quote ENERGY, he's correct the numbers aren't nearly as impressive... Blame the 19th century scientists on that. Solar can operate about 4-6 hours per day, and on average we expect about 2300J of total 'flux' per m^2 per day.  That's an awfully boring number.  Worse yet, when you multiply by the system efficiency you get electricity at 1/3 kWh * m^-2 * day^-1... Woot woot!

  So what can we do? Educate the public!  What else?

Remember, the average educational level of the U.S. is around eighth grade.

That being the case, perhaps we should label renewable consumer products  similar to energy star. Energy star clearly shows the number of reference dollars saved per year in energy costs by a particular device.  I know, it's dumbing down.  But we need a way to connect with technotards.  Solar energy should be for the masses.  The masses, on average, don't have a college education, and don't like math.

For most of us on this site, units are not a problem.  But then, we're all pretty smart, aren't we?

Er, maybe I should have said "solar thermal" plant instead of "PV" in that last comment.

"aMW", thanks! I hadn't heard of that one before, though now that you mention it, it seems obvious. As others pointed out, aMW is going to vary a lot depending on installation and location. It still feels like there's some other thing missing. A gas plant and a PV plant might have the same peak power rating, same capacity factor, same availability factor, same aMW, yet one has a different dispatchability. What units do you use for dispatchability?

Tempest in a teapot, folks.

 The power units are important, as one commenter pointed out, because electrically you need to know the peak power of the generator.  Natural Gas peaking units run for far less time than wind and solar units, and still have a nameplate rating.

 If you really want a way to name something that takes into account its annual capacity factor, use the "aMW" nomenclature - for average MW.  THe PNW has used this for years due to its heavy reliance on hydro.  So a 100 MW solar project would be 20 aMW, a 100 MW wind project, 30 aMW, etc.

In all thiis discussion I didn't read a word about hydrogen.  I do know about Calisoria going back on hydrogen, but I still beleive instead of electricity going to waste it should be stored to be used during  peak times.

With all the wonderfull grid intertie inverters to smoothly "inject" the up and down power from a wind charger into the national grid,  has anybody ever considered an "outverter" (??) to smoothly adapt conumption to supply??

My idea:  A House is upplied with 3 different breakers:  one for most urgent consumption (lights, Tv, radio, one small fridge, say 1 Kw together)  This supply is never to be disconnected.  Number two is  for heavy loads not so urgent (stove, freezer, household appliances) This is disconnected when load shedding in cases of short supply.  The third breaker is for the geyser, heater, air con, dish washer, dryer, etc. (the customer will net even realize when power is supplied to these) and is switched ON  only when there is enough power from the grid.....And this is where your wind chargers' power goes.

    

Units applied to hydrogen can really confuse some people. There would be a claim that so many liters or cubic meters of hydrogen is needed to run a car a certain distance. Then someone gets confused and says that volume won't even fit in the car. However, the numbers listed are at 1 atmosphere, while the hydrogen is actually stored in the car compressed to a much smaller volume. But that doesn't mean the units are wrong there either.