Re: [RE-wrenches] 120 volt grid tie inverter

[Allan Sindelar]

I have recently been dealing with a Chad Lampkin system. This is an off-grid system with a combination 120V DCnom combination inverter and charge controller. The plus side is that it works well and has been quite reliable. And the battery cables and interconnects are #10 AWG. I think he also makes inverters in the 144V and 180V DC ranges. The downsides are that it takes 24 6V batteries to make a string, so battery replacement is expensive - even golf carts (equivalent to 6 strings at 24V, or 1320 A/hr) are $3K or so. And this system badly needs new batteries, due to chronic undercharging. The integrated controller is a voltage-actuated series controller, similar to an old Trace C30A or Bobier Sun Selector. Chad prefers L16s at minimum, believing (strongly) in the Bobier school of controller logic. Also, the array is ten BP90s in series, meaning at most about 5A of charging current per array (when they were new). With L16s, that a max charge rate of C/70; with golf carts it's max C/44. But it's still only 900 watts (when new), too small to run the house it's serving, and expensive to add to. Another homeowner in this area with an early Lampkin system claims he got 17 years from a set of L16s. The difference is that he has a large array relative to his load profile, so the batteries pretty much had ideal conditions of shallow cycling and consistently high SOC. I haven't actually done anything with this system, just researched it as a consultation for the hapless homeowner. Anyway, on to the GT question: if indeed it's a Lampkin system (infinitesimally more info at Michiganenergyworks.com), it operates in the ~120-210 VDC range. It seems to me that you could make it work only by putting a 120V DC-coil relay (maybe MDI, who made the mercury contactors used in old APT/Ananda Powercenters) - they make a 120V coil model - operated by the charge control relay in the charger, connected to N.O. terminals. When the charge controller got the batteries to full and triggered the relay to open, the array energy would be diverted to a batteryless inverter with a compatible input voltage range (as others have suggested). What I don't know is whether the MEW system has a relay built in that would allow this diversion function, and what other issues would come up. And of course, there's still the 5-minute IEEE 929 wait-to-interconnect each time the controller relay opened, so if there's a load on the batteries and the voltage drops quickly, usable sell energy would end up somewhere in the range of zero... Does this help with your explanation to your customer, Bob? Allan Sindelar Allan@positiveenergysolar.com NABCEP Certified Photovoltaic Installer EE98J Journeyman Electrician Positive Energy, Inc. 3201 Calle Marie Santa Fe, New Mexico 87507 505 424-1112 www.positiveenergysolar.com On 11/16/2010 6:22 AM, bob ellison wrote: Mick, I am afraid that is what he wants to do, I am also getting the impression that his power bill is just a few bucks so I don’t see a need. He does. Later, Bob Ellison   Sent: Monday, November 15, 2010 8:44 PM To: glenn.b...@glbcc.com; RE-wrenches Subject: Re: [RE-wrenches] 120 volt grid tie inverter   Agreed, Glenn~ and that SMA unit has a nice low input voltage requirement.    Bob, might your client be wanting a "grid intertie capable" inverter which can run on a 120 volt battery bank--the medium voltage battery system which Chad Lampkin had championed? If so, it's game over for several reasons, including the NEC. Jolliness, Mick Abraham, Proprietor On Mon, Nov 15, 2010 at 6:29 PM, Glenn Burt <glenn.b...@glbcc.com> wrote: I think there is still an SMA 700W inverter available that uses 120VAC. -Glenn -----Original Message----- Sent: Monday, November 15, 2010 11:14 AM To: RE-wrenches Subject: [RE-wrenches] 120 volt grid tie inverter I have a customer who wants to grid tie a 120 volt dc system Does anyone know of an inverter that can do this? Thanks Bob ellison

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