I love solar power, but in reflecting carefully on a couple of high profile datacenter deployments of solar power, I’m really developing serious reservations that this is the path to reducing data center environmental impact. I just can’t make the math work and find myself wondering if these large solar farms are really somewhere between a bad idea and pure marketing, where the environmental impact is purely optical.
The first of my two examples is the high profile installation of a large solar array at the Facebook Prineville Oregon Facility. The installation of 100 kilowatts of solar power was the culmination of the unfriend coal campaign run by Greenpeace. Many in the industry believe the campaign worked. In the purest sense, I suppose it did. But let’s look at the data more closely and make sure this really is environmental progress. What was installed in Prineville was a 100 kilowatt solar array at a more than 25 megawatt facility (Facebook Installs Solar Panels at new Data Center ). Even though this is actually a fairly large solar array, its only providing 0.4% of the overall facility power.
Unfortunately, the actually numbers are further negatively impacted by weather and high latitude. Solar arrays produce far less than their rated capacity due to night duration, cloud cover, and other negative impacts from weather. I really don’t want to screw up my Seattle recruiting pitch too much but let’s just say that occasionally there are clouds in the pacific northwest :-). Clearly there fewer clouds at 2,868’ elevation in the Oregon desert but, even at that altitude, the sun spends the bulk of the time poorly positioned for power generation.
Using this solar panel output estimator, we can see that the panels at this location and altitude, yield an effective output of 13.75%. That means that, on average, this array will only put out 13.75 killowatts. That would have this array contributing 0.055% of the facility power or, worded differently, it might run the lights in the datacenter but it has almost no measurable possible impact on the overall energy consumed. Although this is pointed to as an environmentally conscious decisions, it really has close to no influence on the overall environmental impact of this facility. As a point of comparison, this entire solar farm produces approximately as much output as one high density rack of servers consumes. Just one rack of servers is not success, it doesn’t measurably change the coal consumption, and almost certainly isn’t good price/performance.
Having said that the Facebook solar array is very close to purely marketing expense, I hasten to add that Facebook is one of the most power-efficient and environmentally-focused large datacenter operators. Ironically, they are in fact very good environmental stewards, but the solar array isn’t really a material contributor to what they are achieving.
Apple iDataCenter, Maiden, North Carolina
The second example I wanted to look at is Apple’s facility at Maiden, North Carolina, often referred as iDataCenter. In the Facebook example discussed above, the solar array was so small as to have nearly no impact on the composition or amount of power consumed by the facility. However, in this example, the solar farm deployed at the Apple Maiden facility is absolutely massive. In fact, this photo voltaic deployment is reported to be largest commercial deployment in the US at 20 megawatts. Given the scale of this deployment, it has a far better chance to work economically.
The Apple Maiden facility is reported to cost $1B for the 500,000 sq ft datacenter. Apple wisely chose not to publicly announce their power consumption numbers but estimates have been as high as 100 megawatts. If you conservatively assume that only 60% of the square footage is raised floor and they are averaging a fairly low 200W/sq ft, the critical load would still be 60MW (the same as the 700,000 sq ft Microsoft Chicago datacenter). At a moderate Power Usage Efficiency (PUE) of 1.3, Apple Maiden would be at 78MW of total power. Even using these fairly conservative numbers for a modern datacenter build, it would be 78MW total power, which is huge. The actual number is likely somewhat higher.
Apple elected to put in a 20MW solar array at this facility. Again, using the location and elevation data from Wikipedia and the solar array output model referenced above, we see that the Apple location is more solar friendly than Oregon. Using this model, we see that the 20MW photo voltaic deployment has an average output of 15.8% which yields 3.2MW.
The solar array requires 171 acres of land which is 7.4 million sq ft. What if we were to build an solar array large enough to power the entire facility using these solar and land consumption numbers? If the solar farm were to be able to supply all the power of the facility it would need to be 24.4 times larger. It would be a 488 megawatt capacity array requiring 4,172 acres which is 181 million sq ft. That means that a 500,000 sq ft facility would require 181 million sq ft of power generation or, converted to a ratio, each data center sq ft would require 362 sq ft of land.
Do we really want to give up that much space at each data center? Most data centers are in highly populated areas, where a ratio of 1 sq ft of datacenter floor space requiring 362 sq ft of power generation space is ridiculous on its own and made close to impossible by the power generation space needing to be un-shadowed. There isn’t enough roof top space across all of NY to take this approach. It is simply not possible in that venue.
Let’s focus instead on large datacenters in rural areas where the space can be found. Apple is reported to have cleared trees off of 171 acres of land in order to provide photo voltaic power for 4% of their overall estimate data center consumption. Is that gain worth clearing and consuming 171 acres? In Apple Planning Solar Array Near iDataCenter, the author Rich Miller of Data Center Knowledge quotes local North Carolina media reporting that “local residents are complaining about smoke in the area from fires to burn off cleared trees and debris on the Apple property.”
I’m personally not crazy about clearing 171 acres in order to supply only 4% of the power at this facility. There are many ways to radically reduce aggregate data center environmental impact without as much land consumption. Personally, I look first to increasing the efficiency of power distribution, cooling, storage, networking and server and increasing overall utilization and the best routes to lowering industry environmental impact.
Looking more deeply at the Solar Array at Apple Maiden, the panels are built by SunPower. Sunpower is reportedly carrying $820m in debt and has received a $1.2B federal government loan guarantee. The panels are built on taxpayer guarantees and installed using tax payer funded tax incentives. It might possibly be a win for the overall economy but, as I work through the numbers, it seems less clear. And, after the spectacular failure of solar cell producer Solyndra which failed in bankruptcy with a $535 million dollar federal loan guarantee, it’s obvious there are large costs being carried by tax payers in these deployments. Generally, as much as I like data centers, I’m not convinced that tax payers should by paying to power them.
As I work through the numbers from two of the most widely reported upon datacenter solar array deployments, they just don’t seem to balance out positively without tax incentives. I’m not convinced that having the tax base fund datacenter deployments is a scalable solution. And, even if it could be shown that this will eventually become tax neutral, I’m not convinced we want to see datacenter deployments consuming 100s of acres of land on power generation. And, when trees are taken down to allow the solar deployment, it’s even harder to feel good about it. From what I have seen so far, this is not heading in the right direction. If we had $x dollars to invest in lowering datacenter environmental impact and the marketing department was not involved in the decision, I’m not convinced the right next step will be solar.
James Hamilton e: firstname.lastname@example.org w: http://www.mvdirona.com b: http://blog.mvdirona.com / http://perspectives.mvdirona.com
Disclaimer: The opinions expressed here are my own and do not
necessarily represent those of current or past employers.