need 24 volt applinaces [RE-wrenches]

John Raynes john at raynes.com
Mon Mar 24 09:03:22 PDT 2008


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Let's not forget that there is currently another reason to look at 24 volt 
battery banks for smaller systems.  It has to do with the increasing lack 
of competitively-priced 12 volt panels.  There are lots of relatively 
inexpensive PWM charge controllers that will do either 12V-12V or 24V-24V 
configurations, but it's still a big step up in price to anything that will 
do 24V-12V.  The least expensive step-down option that I know of is the 
SolarBoost 3024.  Morningstar's 15A MPPT is supposed to be out any day now, 
but it only knocks the price point down a little, and 15A at 12V doesn't 
take one very far.

Even with the situation that I just described, I still agree that small 24V 
battery banks usually aren't compelling,   I looked at designing some 
recently, in order to utilize some 24V panels I had available, but got 
stopped even before looking for 24V appliances and lights.  Take a look at 
the options for small inverters - there just aren't any small (300-800W), 
value priced 24V inverters that I can find.  And with the nice small 12V 
sine-wave inverters available now, it's easy to talk a customer into some 
type of inverter, even for a small system.  So yes, I say go with 12 volts, 
use a small inverter.

It doesn't appear that we're going to have any really useful small 
inexpensive step-down charge controllers for the near future, unless one of 
the manufacturers has something that they're keeping under wraps.

The situation with 12 volt panels just seems to keep getting worse, and I 
don't understand as there is definitely still a need for panels in the 
70-110 watt range.  Most of the distribs still carry something, but it 
either is way expensive and/or there's no commitment to supply anymore.  If 
I had to guess, I'd say that the distribs have chosen to abandon this 
segment of the market to the large internet retailers, who now have to buy 
70-100W panels in quantity and stock themselves.  The rest of us are on our 
own, it seems, and we have to charge through the nose or offer no-name, 
non-UL Chinese panels if we can find them.  Any of the distrib 
representatives on the board care to comment on this situation?

John Raynes
RE Solar
Torrey, UT


At 04:43 PM 3/23/2008 -0700, you wrote:


>I agree with others who have suggested avoiding a 24 V system, and I live 
>with one. I went with 24 V on RE guru Windy Dankoff's advice in the early 
>1980s. It was good advice then, before high-efficiency inverters were 
>readily available, 48 V systems were almost unheard of, and PVs were much 
>more expensive. Today's RE guru advice is usually to go with AC loads, 
>unless we're talking about a very small system, in which case 12 VDC makes 
>more sense.
>
>That said, it's possible to find LED and CFL lighting in 24 V, as well as 
>fridge/freezers, motors, and occasional audio stuff (especially from 
>long-haul truck suppliers). But there are many things that you won't find 
>in 24 VDC, which led us to use 12 VDC and 120 VAC as well, leading to a 
>very complicated system.
>
>Today I recommend to almost all people that they decide between 12 VDC and 
>120 VAC, and keep it simple.
>
>Ian
>
>
>>>I am working a a full time art studio home, off grid.
>>>I have selected a 24 volt system.  where is a source
>>>of 24 volt DC appliances such as audio system, in
>>>particular amplifier, CD player, led fixtures?  am
>>>using Outback for AC source, on switch when not
>>>needed.
>
>--
>Ian Woofenden <ian.woofenden at homepower.com>, Senior Editor, Home Power 
>magazine
>Subscriptions: $24.95 per year PO Box 520,Ashland, OR 97520 USA 
>800-707-6585 (US), 541-512-0220
>or download free sample issue at <http://www.homepower.com>
>
>
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