As we begin to look at power, the first thing we need to do is to determine the desired availability.  In some models (and certainly the most inexpensive, Tier 0) there simply isn't any.  This essentially relies on the utility provider and the general utility practices (GUP) for power without any additional support means.  I don't know anyone who is doing this yet, but there are a couple of folks that are looking at it.  (Note: their availability is managed at a higher level even  with duplicate data centers (geographically separated) that can take over and deliver their service if one of the data centers goes down ... and yes there may be a reduction in their service, but it will stay up.)  If your business model allows you to do this, you can see some very interesting advantages.  Your centers can be very low frills which can save you a lot of money and the duplication can not only provide the availability but also serve to provide a data backup function, fulfilling another major objective. (I believe this will become a standard practice in the future as building blocks become even less expensive ...More on this later.)

(A good reference for all this is the Tier definition from the Uptime institute which can be found at http://uptimeinstitute.org/.)

The next step in availability is type  N (Tier 1), N+1 (Tier 2), etc.  (This is probably a rehash of Power Availability 101 for some, but it is kind of nice to see it all put together.)  Here, there is a backup source (equal to what is considered the critical power part of N ... and this is probably not everything) for power in the event that the utilities go away.  Most folks in this space seem to be providing some form of N+1 (Tier 2 - a backup source and 1 additional source in the event that some of their primary backup fails).  You may be able, depending on your circumstance and your utility provider, to create a model for the maximum duration of backup power that doesn't require you to cover a prolonged outage. (This can save a lot of money especially if you can shift load to an alternate locations as I mentioned above.)  Your planning should look something like this: 

• 1. Determine the amount of power needed to back up only the essential systems. (BTW, don't forget to isolate this from the general power which will likely include some things you don't want to pay to backup, but don't forget about cooling. We'll discuss that in the next installment.) This is "P_critical KVA" or the critical load and you will need to outfit this amount of alternate power. If you have the space, I favor a simple diesel or LP generator for the backup power (Generation_Diesel). (Also note, this may be the longest lead time item you need to procure as you are building a data center and in some cases approaches 48 weeks.) Depending on the size (usually bigger is better), these retail for about $150 to $200 / KVA. (Note: this is just a rule of thumb for the materials and does not include installation cost. Plus, the actual prices may vary from your suppliers.) For example, if your P_critical is 3MVA, you could use four 1000KVA generators (M x UPS_KVA). This covers your P_critical and provide an additional unit giving you N+1. For each generator, you will need a transfer switch which will move your load from the utility power to your generators. As a rule of thumb, these retail for about $20 - 30 per KVA. This example would cost you somewhere around $800K for the generators and $30K for switching equipment (not including installation).
  
  Generator sets require two things that you need to consider. These are the storage of fuel on site which will determine the "T_BUP (Hrs)" or the duration of backup power will last without intervention; (With today's environmental rules, this is not something that can be taken lightly) and monthly maintenance. Once a month or so, the generators will need to be checked to ensure they are properly working and are setup correctly for the current season. There is a lot of automation here, but it is pretty expensive and some of it can be avoided by simply having a "trusted" human :o) perform these regular checks.
  
  
• 2. Now let's focus on the UPS. Some form of UPS is required to hold the load up while the generators are becoming operational. This is the sequence of events occurs something like this: It can take about 4.5 seconds for a generator to crank up and become stable. (This is one of the main reasons for monthly maintenance. ) If it fails, there may be a pause / purge of about 3 seconds followed by an additional 4.5 second start up time. This is just under 15 seconds to bring them up. Most folks add some margin here but this is one place where time is money and 30 seconds for "T_UPS (Sec)" for the duration of power provided by ups seem appropriate. By this point, it you are not up, you have a bigger problem. If you are planning to use a conventional UPS with VRLA type batteries (UPS_VRLA), you should expect to pay something around $50to $75 per KVA for each 30 seconds of backup time. For the example configuration of 3MVA, if you use 500KVA UPS systems, you will need 6 of them (M x UPS_KVA) and at $75 / KVA, this will cost you somewhere around $225K for the UPS systems alone. (Note: This is a very soft estimate and not all sizes and durations are available. So you will have to work in the constraints of you vender when you are sizing/estimated the UPS. All estimates are just to give you an idea about some of the cost. These will vary as technology changes and with specific vendors.)
  
  There is a lot of other material required to hook this up. I would add 10% to the total to give you are good rule of thumbs for materials cost. At this point, our stack and model look like the following with configuration guidelines to come.
  
  There are a couple of other good resources I would refer to at this point and both come from the uptime institute. They are: Cost Model: Dollars per kW plus Dollars per Square Foot of Computer Floor and A Simple Model for Determining True Total Cost of Ownership for Data Centers. Note: These are created along the lines of conventional data center, but they do contain some good information.