The Solar Coaster and Why I Got Off

Before you all show up on my door with pitch forks and torches let me start by saying I do believe that solar power has a place.  There I said it.  Everybody take a deep breath and put the kerosine and your favorite mob weapon away.  What I don't believe is that solar is the solution to the world's energy or greenhouse emissions problem.  To be sure it is a part of it but it is not the answer.

A while back I wrote on our need to have an energy policy and it should include solar.  As it stands to today solar can provide up to about 20% of our current peak, daytime energy needs.  We should be using that energy.

Put your rake down and listen to some math.  In very limited regions (usually high deserts) you can get up to 1,100 Watts of solar radiation per square meter and you only get that for about a third of the day.  Most of the time it is significantly less.  Most areas have a peak insolation (solar radiation) of 900 to 1,000 Watts for limited portion of the day.  But that is not the whole story...  The basic efficiency of converting the suns radiant energy into electricity is about 15%.  Despite the investment of billions of dollars we have managed to increase that number for terrestrial cells a scant few percent over the last 30 years.  Yes, there are military space grade cells that are capable of 40% but we are decades from those being affordable for the terrestrial market.  So, every square meter yields about 150 Watts peak power for your typical rooftop systems for a few hours per day.

Worse yet, there are cosine losses associated with suns angle relative to solar panel.  Solar cells work by high energy photons hitting the cell and knocking an electron off.  This is most efficient when the photon hits the cell dead on and rolls off as the collision angle increases.   This accounts for the biggest variation of power output throughout the day.  Yes, you can fix this by putting a tracker which keeps the panel pointed at the sun throughout the day but these are costly to build, costly to maintain and often unreliable.

So, the bottom line is that you get a fraction of the available energy out any solar system under the best of all conditions.  You can fix this by adding lots of capacity and with the dramatic fall in solar equipment prices, you can size the system to support your load.  There is however, still one teensy little problem you can't fix...  The sun takes most nights off and calls in sick many days during the year.  That's right Ol' Sol just isn't all that reliable.

The fact that the sun does not show up for work can be a real problem.  Worse yet passing clouds shading parts of a solar supplied grid can cause real problems because the grid has a hard time compensating for large amounts of supply fluctuations and that can cause some real problems ranging to brownouts to blackouts.  Further, solar doesn't help at all with night time energy demands.  Currently, storage technology just can't scale to the grid level.  Yes, I know that some of you have home systems that have battery storage...  Call me during a prolonged winter storm.. We'll have a nice warm place for you.

I spent 3 years in the solar industry and walked (ok ran) away pretty discouraged.  The same hucksters that were peddling solar as the solution to the world's problems in the 1970's came back 40 years later and resold that same story.  We poured billions of investment down a rat hole.  Sure we got better inverters and racking systems and the systems are easier to manage and install but there really haven't been any fundamental break throughs in the technology.  What lowered the prices so dramatically is our old friend supply and demand.  The Chinese developed gigaWatts of solar cell manufacturing capacity and with cheap labor they can crank out very cheap panels.  This has resulted in solar prices dropping from about $3/W to around $0.50/W in the last 5 or so years.  Manufacturing not technology drove that price decrease.

I think we should continue to invest in solar installation and basic research.  Just don't fall from some guy in VW mini-van's story that solar will save the world.  It will help but it is only part of a balanced energy solution.  So, by all means go put those panels on your roof if you feel so inclined but just understand what your system can and can't do.   Before you run out and buy some guys story about quantum tunneling flux cells, just realize that like speaker wire, all commercial solar cells are pretty much the same and no matter what, your solar power system will always put out 0 Watts at night.