Saturday, February 11, 2012

PV versus Heat Pumps ---------- Read my Book ----

The news is full of how Solyndra failed and how China is winning the Photovoltaic (PV) war. The US installed approximately 1.8 million kilowatts of peak PV systems in 2011. The Germans installed 7.5 million kilowatts peak of PV systems in 2011. For the layperson a kilowatt is about the instantaneous power a hairdryer requires. Given the amount of sunshine, average generation in the US is approximately 2,000 kilowatt hours a year for each kilowatt peak of PV installed. Again for the layperson, as the sun only shines a certain number of hours in year and other daylight hours are cloudy, we do not get all the hours in a year (8,760 hours) multiplied by the 1 kilowatt. We only get a fraction of this total. Now we know we get 2,000 kilowatt hours of electricity in a year for each kilowatt of PV cell installed, we will correspondingly get 3.6 billion kilowatt hours each year going forward for the 1.8 million kilowatts of PV installed in the entire US during last year.

This sounds like a lot of power for the $9 billion that was spent to install those 1.8 million kilowatts of PV. Actually had we spent the $9 billion on another alternate many more kilowatt hours of fossil fuel power generation could have been saved and the $9 billion would have been better spent by saving average citizens money and correspondingly saving the planet a lot more carbon dioxide emissions. What is the alternate? Is it some unproven new high tech gizmo? Actually the device is simple and very well proven. The device is a heat pump hot water heater.

The US has approximately 20 million homes where the hot water heater is powered by an old fashioned electrical resistance heater. The old fashioned hot water heaters do convert more than 95% of the electrical energy into heat in the hot water. This seems to be highly efficient and a good use of the electricity? Well for each kilowatt of electricity used by the home owner for hot water heating only 0.95 kilowatt hours of heat was imparted into the water. A heat pump extracts heat from the ambient air, even in winter, and a single kilowatt hour of power used by the heat pumps compressor can impart as many as 3 to 5 kilowatt hours of heat into the water by conveying heat from the air into the water. The warmer the ambient temperature of the air the higher the advantage of energy imparted from the air to water. Think of the heat pump as the thermodynamic lever or a set of pulleys that gives you advantage. Just like a crowbar gives you added mechanical strength, the heat pump give you added heat over and above the simple electricity that is used by the system.

By coincidence the state of Florida has a significant portion of its homes that use electricity as the fuel for hot water heating. Florida has a warm climate and is perfect for year round heat pumping. I estimate that for each kilowatt hour of electricity used on average in a hot water heat pump in Florida (year round) approximately 3.8 kilowatt hours of heat will be imparted into the hot water. The average household used about 4,000 kilowatt hours a year of electricity to impart 3,800 kilowatt hours of heat into their hot water with the old fashioned resistance heater. The same household will only need to purchase 1,000 kilowatt hours a year of electricity with a heat pump hot water heater. Therefore, they will save 3,000 kilowatt hours of electricity purchases each year. The added first cost for the heat pump system versus a traditional electric resistance heater is about $1,200 as compressors are more expensive than resistance heaters. The cost of residential electric power in Florida is approximately 11 cents per kilowatt hour hence the yearly electricity savings will equal $330. The added initial cost for the heat pump system will be recovered in three and two thirds years (44 months).

Had we as a country spent the $9 billion on heat pumps we could have bought 7.5 million heat pumps versus the same number of traditional hot water heaters and saved 22.5 billion kilowatt hours of power each year in heating the hot water used in these 7.5 million homes. This savings is much more than the 3.6 billion kilowatt hours a year of electricity the $9 billion that was spent on PV systems will generate. The added 18.9 billion kilowatt hours of electricity (22.5 – 3.6 billion) have carbon dioxide emissions that are approximately 12.3 million tons a year. Hence by a misallocation of scarce capital in our economy we actually caused carbon dioxide emissions to increase by some 12.3 million tons and did not help the common householder to make a prudent investment that would have provided them a handsome return and a rapid payback. Approximately 50% or $4.5 billion of the $9 billion for PV installations was provided by the Federal and State government. Had our government simply directed their $4.5 billion gift to poorer households to install heat pump hot water heaters, 3.75 million households could have benefited from the program and 11.25 billion kilowatt hours of power could have been saved.
I ask why oh why do we place so much hope on PV when simpler and more immediate alternates yield far better results? Let the Chinese win the PV war. We can better spend the money they loan us and then let them take a hot bath on the write-down of the debt when we pull a Greece on them.


  1. Great piece. Only objection is that we shouldn't cede PV to China as we may be able to drive down cost over time. There are other advantages of PV not available to heat pumps. We need all of the above strategy. Did you notice that new nuke plant was just authorized for first time in 30+ years?

  2. Hey, I don't own a Kindle. Is there another format one can obtain the copy of your book?

  3. there are free Kindle aps for iPads, iPhones, Androids, and other smart phones. down load the free ap and then you can get the book on your device

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