Posted by Scott Willing on September 25, 2005, 10:00 am
On Sat, 24 Sep 2005 09:50:34 -0700, Anthony Matonak
>Scott Willing wrote:
>> On Fri, 23 Sep 2005 22:13:16 -0700, Anthony Matonak
>>
>>>Well, one hour a day drawing 15 watts would be 15 watt-hours/day.
>>>Figure 20% off the top for panel heating and advertising effects,
>>
>> ...advertising effects?
>Advertising typically uses numbers that, while technically
>accurate, do not reflect real world conditions. This is why
>few people get the mileage shown on their cars window sticker
>and nobody considers a single can of coke two servings.
OK, just wanted to make sure I knew what you meant.
-=s
>This applies to solar PV panels in two forms. The first is the
>STC (standard test conditions) using a temperature lower than
>the panels will usually experience and, if I recall correctly,
>illumination slightly more than typically found at ground level.
>The second is that the warranties are usually only for 80% of
>that figure. Technically, they can ship panels with slightly
>less output than advertised and stay this side of the law.
>You'll see this in the case of wind turbines also. The Air-X
>is advertised as a 400W wind turbine but it only generates
>this in hurricane force winds. It's really more of a 100-200W
>wind turbine in day to day service.
>You see this in generators also. That 3kW generator may only
>be able to do 3kW for a very short time and it's continuous
>rating may only be half that.
>Advertising effects are simply the tendency of advert writers
>to stretch the truth as much as they can without going to
>jail. In the case of PV, some companies are better than others
>in this regard.
>Anthony
Posted by SpiderG on September 26, 2005, 8:31 pm
> chad@chadphillips.org wrote:
> > I have a project that would have a small embeded computer running about
> > 1 hour a day. It takes about 15 watts to run. I was thinking about
> > powering it with one of those "battery saver" solar chargers.
> >
> > Would a 5 watt or 11 watt battery trickle charger work for this?
> Well, one hour a day drawing 15 watts would be 15 watt-hours/day.
> Figure 20% off the top for panel heating and advertising effects,
> another 20% (to be on the safe side) for battery inefficiency in
> charging/discharging. That gives us (15/.80/.80=) about 24 wh/day.
> Figure you'll get an average of at least 3 'sun-hours' at your
> location even in the middle of winter (most of the USA) and your
> panel will need to be (24/3) 8 watts.
> You might squeak by on a 5 watt panel except during winter but I
> would error on the side of caution and use the 11 watt panel.
> You'll need a battery too, of course. If you want to run the
> thing 5 days without sunlight you would need (5 * 15W) 75 Wh.
> If this is a 12V battery that would be (75Wh/12V) 7 amp-hours.
Wouldn't that completely discharge the battery? Should you not consider the
Depth of Discharge calculation before using the 7 Ah as the needed capacity?
-SpiderG
> Anthony
Posted by Steve Spence on September 26, 2005, 8:44 pm
SpiderG wrote:
>
>>chad@chadphillips.org wrote:
>>
>>>I have a project that would have a small embeded computer running about
>>>1 hour a day. It takes about 15 watts to run. I was thinking about
>>>powering it with one of those "battery saver" solar chargers.
>>>
>>>Would a 5 watt or 11 watt battery trickle charger work for this?
>>
>>Well, one hour a day drawing 15 watts would be 15 watt-hours/day.
>>Figure 20% off the top for panel heating and advertising effects,
>>another 20% (to be on the safe side) for battery inefficiency in
>>charging/discharging. That gives us (15/.80/.80=) about 24 wh/day.
>>Figure you'll get an average of at least 3 'sun-hours' at your
>>location even in the middle of winter (most of the USA) and your
>>panel will need to be (24/3) 8 watts.
>>
>>You might squeak by on a 5 watt panel except during winter but I
>>would error on the side of caution and use the 11 watt panel.
>>
>>You'll need a battery too, of course. If you want to run the
>>thing 5 days without sunlight you would need (5 * 15W) 75 Wh.
>>If this is a 12V battery that would be (75Wh/12V) 7 amp-hours.
>
>
> Wouldn't that completely discharge the battery? Should you not consider the
> Depth of Discharge calculation before using the 7 Ah as the needed capacity?
>
> -SpiderG
>
>
>
>>Anthony
>
>
>
A Walmart Deep Cycle Type 27 battery costs $55 and is rated at 115ah. We
use them with our inverter/generator kits.
--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html
Posted by Anthony Matonak on September 26, 2005, 8:48 pm
SpiderG wrote:
...
>>You'll need a battery too, of course. If you want to run the
>>thing 5 days without sunlight you would need (5 * 15W) 75 Wh.
>>If this is a 12V battery that would be (75Wh/12V) 7 amp-hours.
>
> Wouldn't that completely discharge the battery? Should you not consider the
> Depth of Discharge calculation before using the 7 Ah as the needed capacity?
Sure it would completely discharge the battery and perhaps even
damage it. It would still work at least once. :) One needs to
balance this against the cost of replacing that 7 amp-hour
battery and how often you expect to get 5 days in a row with no
sunlight whatever.
The message wasn't meant to be a full system design as I clearly
left a lot of things out (charge controller, fuses, disconnects,
wires, options for tracking, mounting, grounding, boxes, etc.)
and I don't even know if the orginal posters location even gets
3 sun-hours a day (on average) in the winter.
Anthony
Posted by samc on September 25, 2005, 1:31 pm
chad@chadphillips.org wrote:
> I have a project that would have a small embeded computer running about
> 1 hour a day. It takes about 15 watts to run. I was thinking about
> powering it with one of those "battery saver" solar chargers.
>
> Would a 5 watt or 11 watt battery trickle charger work for this?
>
> Here are two I am looking at:
>
http://www.northerntool.com/webapp/wcs/stores/servlet/ProductDisplay?storeIdi70&productId 0306865&R 0306865
>
http://www.northerntool.com/webapp/wcs/stores/servlet/ProductDisplay?storeIdi70&productId 0315904&R 0315904
>
> thanks
> chad
>
some thing to think about is posably reducing the batt voltage so as to
reduce the power wasted though the voltage reg for the micro controler .
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>> On Fri, 23 Sep 2005 22:13:16 -0700, Anthony Matonak
>>
>>>Well, one hour a day drawing 15 watts would be 15 watt-hours/day.
>>>Figure 20% off the top for panel heating and advertising effects,
>>
>> ...advertising effects?
>Advertising typically uses numbers that, while technically
>accurate, do not reflect real world conditions. This is why
>few people get the mileage shown on their cars window sticker
>and nobody considers a single can of coke two servings.