Dear Prospective Inverter Supplier:

As you can see from this web site, I am trying to obtain an inverter for my PriUPS project.  To save you from wading through the verbiage (although you might find it interesting,) I am providing this specification.  The inverter will be used to provide domestic power, just as would a typical emergency generator.  Please let me know if you can supply anything appropriate. 

Or (perhaps) Dear Prospective UPS Supplier:

Although this specification is written with the traditional inverter in mind, it appears that some "computer room" UPS units also run on battery voltages much higher than the 6 / 12 / 24 / 48 volts I expected them to use.  Below is my possibly naive comparison of what I expect the benefits of a UPS vs. inverter unit.  I am willing and even eager to be disabused of any of these notions!

Inverter Vs. UPS Comparison

Characteristic Inverter UPS
Battery Input Voltage Range Wide - general purpose Probably narrow - Batteries supplied with UPS
Continuous Duty? Yes Maybe not - typically used for only a few minutes until equipment can be shut down
External Battery Of course May need modification
Grid Tie Maybe, with luck Almost certainly not
Stand-By Efficiency 100% - turned off when not needed 9x% - Used to buffer AC line, with some inherent losses
Operating Efficiency Approximately same as UPS Approximately same as Inverter
Transfer Switch Necessary Not necessary - designed to automatically transfer load

Although both systems have their advantages, UPS killers would be the first two:  If it won't work continuously or with the battery voltage available, then it's not usable.

Cost and Market

In addition to the technical specifications, another critical one is cost.  Of course I am aware that a custom inverter will cost a fortune, and I trust you are aware that I won't spend a fortune.  So, in addition to the rather routine (other than the grid-tie/non-grid tie issue) specs, please seriously consider how this requirement fits in with your business plans.   Prius sales in the United States alone were 20,000 in 2002, 24,000 in 2003, 47,000 in 2004, and there is about a six-month order backlog at present.  2004 worldwide sales were 125K.  Of course these figures are for the Prius alone.  I have no doubt that there will be millions of hybrid vehicles on the road in a few years.  They don't all use the same battery voltage as the Prius, so flexibility in input voltage will increase sales.  For example, the Toyota Highlander Hybrid uses a 288V battery (probably requiring a 280 to 330VDC input range) and appears to deliver twice the power of the Prius. 

Inverter Specification

Characteristic Required Desired
INPUT 200-240VDC 200-400VDC
INPUT SOURCE NiMH battery pack (25A continuous, 75A peak, recharged from vehicle generator)
OUTPUT  230VAC (center tapped for 115VAC)  
OUTPUT WAVEFORM Suitable for routine household use Sine wave
POWER 5-6KW, with surge ability sufficient to start typical appliance motors. >6KW, and/or provision for parallel operation of additional inverters.
FREQUENCY 60Hz, +/- 3Hz selectable 50Hz/60Hz +/- .1Hz
EMI FCC Class A FCC Class B probably required for mass sales
LOAD CHARACTERISTICS Typical household load - refrigerator, some incandescent lamps, some entertainment equipment, etc.  Nothing exotic.
MONITORING Contact closure for alarm conditions - overtemp, excessive current, etc. Control/monitoring over internet connection would be great!  (USB or RS-232 OK, too)
TRANSFER SWITCH   Included transfer switch
GRID TIE Very desirable, but inverter MUST be able to provide power to the house regardless of whether the grid is up or not.  Ideally it would handle both UPS for House and Grid Tie with anti-islanding all by itself.  See these discussions.
TEMPERATURE Think suburban garage, mid-winter to hot summer.  Maybe -10C to +45C -20C to +55C
SIZE For fixed application, not too important The smaller the better
WEIGHT For fixed application, not too important, Light would be a bonus since it could then provide portable power with the vehicle.
COOLING If it doesn't have its own cooling provisions, should not require plumbing or special ducts.
COST Cheap - See "Cost and Market " above Even cheaper

I am interested in the immediate purchase of an inverter or UPS for this project.  Even better would be a working arrangement with a manufacturer who sees a business development possibility after reading this web site.  If one were interested in "partnering" with me, I would supply the Prius, the house, the "licensed electrician" to make sure I don't die in my sleep, and arguably valuable publicity, as well as a "story" for application notes, advertisements, etc.   You, of course, would supply the inverter or UPS hardware and, if necessary, any modifications to suit the application.

If you are interested in either arrangement, please contact me.

Thanks in advance!