I have just returned from the Intel sponsored Eco-Technology Great Debates where I was slotted into the topic of Thin vs. Thick Client Energy Efficiency. I had the opportunity to weigh in on the side of "Thick" clients as the most energy efficient. The bad news is that our team lost; the good news is that we didn't lose by much (29 to 24)! The best news is that all of the teams had some very strong arguments (and even several very entertaining exchanges).
Being a simple data center guy, I learned a lot, especially as it relates to thin client architecture and energy impacts. No contest, thin clients consume less energy at the device level than do thick clients (PCs and Laptops). But is that really the energy efficient answer?
For thin clients, compute and storage are necessarily displaced to the data center. Data centers with thier concentrated IT equipment are typically inefficient to power and cool relative to laptops and PCs which are distributed by nature and cooled by ambient air. Generally data centers require 1 watt of power for cooling and electrical distribution (house load) for 1 watt of IT load (newer data centers are more efficient but still incur additional power costs simply to power and cool). Therefore, every kW of power that is shifted from distributed thick client use to a data center causes more or less 2 kW of impact in the data center! Wow!
With the majority of the world's data centers facing power or cooling capacity constraints and some with no additional grid power available at all, total energy costs extend beyond the simple house load + IT load equation. Expansion and upgrade of facilities increases energy consumption, as well. There are too many areas to detail here but needless to say the total power consumption for extracting and manufacturing data center components, transporting them to a site and construction of new facilities is non-trivial and likely larger per unit of compute than for the typical laptop. This collateral consumption is not comprehended in any calculations of alternative client model power efficiencies of which I am aware..
I also have no specific data on the power efficiency of PCs or laptops to provide rigorous comparison to data center power utilization efficiency. The above arguments, however, do appear to be logical. More work needs to be done to collect the data and analyze these concepts in detail.....
If you want to see the instant replay of all of the debates (including the client debate, liquid vs. air cooling and ac power vs dc power in the data center), click on the web link above and look for the embedded webcast URL at the bottom of the resulting page. There are also a couple of links to other articles on the subject that are well worth reading.