Voltage drop musings [RE-wrenches]

[Joel Davidson]

Bill, by this climate do you mean low elevation north and south California?

Bill Brooks wrote:

> To all,
>
> Lots of numbers are being thrown around about MPPT controllers without a lot
> of good test data. Beware of manufacturers claims. Having lived with a
> battery-based grid-tied system for over two years with lots of operating
> experience, I believe that an MPPT controller would provide no benefit in
> this climate.
>
> Not necessarily so in other climates, but MPPT controller are really better
> suited for stand-alone systems. Be very careful about using higher voltage
> battery strings. C-40s and other controllers have a very real upper voltage
> limit that will bite you. Just returned from check a 54 volt system that was
> experience controller voltage issues.
>
> It's nice to throw around a lot of numbers, but until you constrain the
> application, it is way to broad of a statement to say that MPPT controllers
> are the way to go. When are they going to get UL? The controller does not
> exist in my book until that happens.
>
> Bill.
>
> > -----Original Message-----
> > From: jay peltz [mailto:jay at asis.com]
> > Sent: Wednesday, May 02, 2001 9:11 PM
> > To: RE-wrenches at topica.com
> > Subject: Re: Voltage drop musings [RE-wrenches]
> >
> >
> > Hi Joel,
> >
> > One way is to increase the number of batteries in the system.
> > This increases the
> > operating voltage ( more watts) without the need for a MPPT
> > controller.  48v systems
> > are pretty easy as you add another 6v ( if you are using 6v
> > batteries.  If you are
> > using 2v cells, then maybe 8v would work better?) battery to the
> > system, works
> > pretty slick- cell voltage is lower, overall voltage is higher=
> > more watts to the
> > grid.
> >
> > And yes many people are using the MPPT controllers to get around
> > this problem called
> > "batteries".
> >
> > Jay
> > Peltz Power
> >
> > Joel Davidson wrote:
> >
> > > Yes, I have 32 each 70-watt modules 4 in series for nominal 48
> > volts. The C40 is
> > > set at 54.8 volts so that voltage flows downhill to the
> > inverter which is set at
> > > 54.4 volts.
> > >
> > > Note that this is a grid tied net metered PV system with
> > batteries - not a stand
> > > alone or standby PV system.
> > >
> > > The problem with a net metered PV system using the SW-series
> > inverter with
> > > batteries is that the inverter operates at the nominal battery
> > voltage, not the
> > > optimum PV array max power point. Since the batteries are just
> > sitting there
> > > being float charged and power passes through the inverter to
> > the load and grid,
> > > can the SolarBoost send max power from the array to the
> > inverter? Has anyone
> > > used a SolarBoost to get around this SW inverter shortcoming?
> > >
> > > "Travis Creswell, Ozark Solar" wrote:
> > >
> > > > Joel,
> > > >
> > > > Are you trying to say you have thirty two 70 watt modules?  8
> > strings x 4.?
> > > > amps = 30 + amp array.  You will need two Solar Boost 3048's.
> >  Better yet
> > > > put 16 on the C40 and 16 on the SB3048 (you'll need a DVM
> > option for it too)
> > > > and compare the outputs.   Do you have a Fluke 36 ammeter?
> > If you don't
> > > > borrow/buy one (~$250 and you really should have one) and
> > compare it's amp
> > > > rating to your C40's.  I almost always find the C40 DVM's to
> > read amps ~10%
> > > > low.  I have found the SolarBoost products to be very
> > accurate.  (Never pass
> > > > a chance to beat up on Trace, just kidding, maybe)
> > > >
> > > > Oh yeah, your question,  you should produce up to 30% more
> > amps when its
> > > > colder, say less than 40F.  In the summer you will only see a
> > 10% (maybe)
> > > > difference when the batteries are under 50 volts in the
> > cooler mornings
> > > > which you won't see since you are grid tied.
> > > >
> > > > Travis Creswell
> > > > Ozark Solar
> > > >
> > > > ----- Original Message -----
> > > > From: "Joel Davidson" <joeldavidson at earthlink.net>
> > > > To: <RE-wrenches at topica.com>
> > > > Sent: Wednesday, May 02, 2001 6:51 PM
> > > > Subject: Re: Voltage drop musings [RE-wrenches]
> > > >
> > > > > Is the SB3048 a current boosting battery charger or a PV
> > array max power
> > > > point
> > > > > device? I have 8 each 4-module series strings of Siemens
> > SP70 modules
> > > > feeding
> > > > > into a C40 and then into a net metered SW4048 with a small
> > backup battery
> > > > bank.
> > > > > The batteries just sit there (pulling the inverter off max
> > power point),
> > > > but the
> > > > > net metered load is the grid so it can take all the PV I
> > produce. Right
> > > > now
> > > > > (4:30PM) my C40 digital meter says 16 amps at 54 volts
> > equals 864 watts.
> > > > Will I
> > > > > produce 19.2 amps at 54 volts or 19.2 amps at 45 volts with
> > the SB3048?
> > > > >
> > > >
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