James Hamilton – Solar at Scale: How Big is a Solar Array of 9MW Average Output?

I frequently get asked “why not just put solar panels on data center roofs and run them on that.” The short answer is datacenter roofs are just way too small. In a previous article (I Love Solar But…) I did a quick back of envelope calculation and, assuming a conventional single floor build with current power densities, each square foot of datacenter space would require roughly 362 sq ft of solar panels. The roof would only contribute roughly 1% of the facility requirements. Quite possibly still worth doing but there is simply no way a roof top array is going to power an entire datacenter.

There are other issues with roof top arrays, the two biggest of which are weight and strong wind protection. A roof requires significant re-enforcement to support the weight of an array and the array needs to be strongly secured against strong winds. But both of these issues are fairly simple engineering problems and very solvable. The key problem with powering datacenters with solar is insufficient solar array power density. If we were to believe the data center lighting manufacturers estimates (Lighting is the Unsung Hero in Data Center Energy Efficiency), a roof top array wouldn’t be able to fully power the facility lighting system. Most modern data centers have moved to more efficient lighting systems but the difficult fact remains: a roof top array will not supply even 1% of the overall facility draw.

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