Greening Datacenters Through Self-Generation of Renewable Energy

(Software defined datacenter power management. And they build a real system: hardware + software on a small size datacenter)

Thu Nguyen,   Rutgers 

Motivation: 
Datacenters uses lots of energy.....Most of it consumed by small datacenters.
Can we use renewables?

Approaches:
1. Buy renewable energy from other power plants off-site. (Google buys wind power from NextEra) --- not stable enough, transmission loss.
2. Self-generation, co-location (Apple built 40MW solar array in NC) --- location may not be ideal for DC or power plant.

Trends in solar energy:
Current PV efficiency (solar energy to electricity) ~15%, expect to grow to ~40% in 10 years.
Capacity efficiency (this largely depends on location) ~15-25%
Cost of solar energy system installation decreasing in time, expect to go down by 40%-60% in 10 years (DOE data)

Main Challenge: power supply is variable, and it may not match your workload consumption

Idea: Match world to energy supply, instead of matching energy supply to workload demands.
         (And you can use net metering to sell the power your battery can't store to your grid electricity provider)

Solution: 
Hardware (Parasol):
Steel structure on the roof + Backup power (battery + grid)  + IT equipment + Cooling
(Actually we don't need cooling that much, even though they are really energy consuming)
Software:
Use Hadoop workload scheduling to predict energy availability (based on weather forecast). Schedule jobs on renewable energy first, then low-price grid electricity, then peak-price electricity, as long as we can meet the job completion deadline.
Also, make sure we don't draw a lot of power from grid at any particular time (high peak usage adds up to bills!)
GreenSwitch: keep keys on jobs, servers on/off, battery lifetime management, peak time power and total power consumption, then output an energy source schedule and a workload schedule.

Results:
Parasol (use polar energy) without software: 60% cost save, amortize in 7 years.
Parasol + GreenSwitch: 75% cost save, but batteries are too expensive to amortize...
Parasol + GreenSwitch + Deferrable Workloads: 96% cost saving, solar + battery amortized in 7.6 years.
(But they did the experiment in summer, so might be too optimistic.....)

Aside:
They have a year of datacenter energy profile data (for every minute, the power efficacy at each inverter, the temperature and the humidity, etc)