Hybrid Car – More Fun with Less Gas

solar in CA? where to start? - Page 2

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Posted by N9WOS on March 14, 2007, 10:59 pm
 

You want to take off a percentage for battery efficiency. The only time you
can base the load off of 100% of solar panel output is if you are using the
power when it's being generated. Batteries are not 100% efficient.

Their true efficacy depends upon day depth of discharge, rate of discharge,
and rate of charge.


I would highly suggest a laptop that will run right off the 12V DC supply.

If you already have a laptop (Likely because of the 50W consumption rate)
then it most likely already can run off of 12V DC. All you need to buy is
the cigarette lighter adapter for it.


The 100AH battery would give you two days of autonomy with the computer
load, which sounds reasonable for your application. At a 30% daily depth of
discharge, you would be looking at a life span of about 1000 cycles for a
low cost marine deep cycle battery, or an AGM battery. Basically three years
of life before it gets down to 60% of original capacity.


The only things that i can see that you are overlooking a bit is TV usage,
and lost generation recovery time.

How much TV watching are you planning on? How many watt hours, or amp hours
will that total up to? You will pretty much be using all the available panel
generation to run the computer. If you do much TV watching, you will be
running a deficit from day to day. Suggestion, Try to find a TV that will
run off of 12V DC directly. The type that they sell for using in a vehicle
or motor home.

And how many days is acceptable for your system to recover from one cloudy
day, or some other problem that will cause a day of missed generation. If
you run the computer as normal, (ignoring TV load) you will only be able to
make up 8AH of lost generation a day (assuming 100% battery efficiency) It
would take you about four days to make up for one lost day of generation. It
would take about four days for you battery to get back to almost 100%
charge. But considering battery efficiency, I would say it would take over a
week or more to catch up. If you have a couple of closely spaced poor, or
cloudy days, you will be bottoming out.


That is a good price for 15W panels


That sounds like a good deal, but be careful of the inverter. Not all are
created equal. Some can have a no load idling curring in the 80 to 100mA
range(for 200W to 400W). Some have idling currents up to 250 to 500mA(for
the same wattage range). That can eat away at your power budget if it is
left on all the time. About 3 to 6AH worth a day. That is why I was
suggesting that you find equipment that will run off of 12V directly. That
will do away with a lot of total system losses.

If I was you, at minimum I would throw two more 15W panels into the mix.
With your figures, that would be an additional 10AH a day. That would bring
the surplus budget up to about 15Ah and give you a missed day recovery time
of about two days of good generation. And it would give you a bit of power
to run the TV with. IF I was wanting a comfort zone, I would push it to an
even 10 panels, that would give me a 20Ah budget before you calculate in
battery efficiency..

That way, you can be a little bit piggish on computer/TV usage once in a
while without constantly looking over at the battery voltage gauge, worrying
that you are going to run the battery flat.

And if you begin to learn that your 100AH of battery storage isn't holding
out to well against your occasional computer rampages, then the panels will
easily support another 100AH battery which will give you much more computer
pounding action on those days when outdoor activities just don't seem to be
that inviting.

As a general rule, no mater how adequate the battery capacity appears to be,
it always seems lacking when you put it together in the real world. No mater
how big you build the battery bank, you always seem to need a little bit
larger one.


I wish you luck.



Posted by Brian Graham on March 15, 2007, 3:33 pm
 

panel<<

7 * 15W = 105W * 5 Hrs = 525 WH  Daily production


400W * 8 = 3200 WH

Of course, if you meant 400W total over the 8 hrs, I don't know of any computer
that runs on 50W. The power supplies in computers are 350W-500W. Of course,
you're not often at full load. But even with a conservative 150W figure
(including monitor), that's 1200W over 8 hrs. Still more than the 525 produced.


maybe it use 32 amps hrs.  With a 100 Amp hour battery as a buffer. <<

Don't forget that watts consumption by the AC load will translate directly to
watts consumption on the DC side. In other words, since Watts = Volts * Amps, a
12V system will have current flow 10 times higher on the DC side than the AC
side.  So if your computer used 120W (for easy math) for 8 hrs, that would be 8
AH AC. On the DC side, you'd use 80 Ah and your 100AH bank would be at 80% DOD
(Depth of Discharge). Not counting inefficiencies in conversion.

If you're wanting to power your computer, I'd guesstimate - use your kill-a-watt
for an accurate consumption reading - that you'd need one 200W panel and could
run the computer for as many hours as you have full sunshine in the day. To run
it at night, you'd need 32 AH of battery storage (AH @ 50% DOD) for every
hour you'd like to run it (200W/120V=1.6A @ 12VDC = 16AH /50% DOD2AH), which
should be the same as the number of hours of daylight - or add another panel and
more batteries. 5 hrs @ 32AH = 160 AH battery bank - if you want to discharge to
50% DOD. 320AH if you only want to go to 25%.

Yeah, computers get expensive to run..

FYI, I have a 24V 1800W pure sine inverter, an 880AH battery bank on order. I'm
planning on slowly adding panels to run non-critical lighting until I get
sufficient production to run critical equipment (fridge etc). The bank will be
available to run fridge/freezer/microwave - 1 at a time - during an outage, and
panels to recharge after the outage. With no real rebates in Canada, it'll be a
long time to take my home off-grid. But I'll move in that direction gradually.

I'd like to get get my computers and AV off-grid since Quebec Hydro has toasted
2 computers on me in 2 years. But as you can see, it'll take a few good panels
to do it.
--
Brian

Posted by jeremy_ho on March 15, 2007, 6:35 pm
 
computer that runs on 50W. The power supplies in computers are 350W-500W. Of
course, you're not often at full load. But even with a conservative 150W figure
(including monitor), that's 1200W over 8 hrs. Still more than the 525 produced.


watts consumption on the DC side. In other words, since Watts = Volts * Amps, a
12V system will have current flow 10 times higher on the DC side than the AC
side.  So if your computer used 120W (for easy math) for 8 hrs, that would be 8
AH AC. On the DC side, you'd use 80 Ah and your 100AH bank would be at 80% DOD
(Depth of Discharge). Not counting inefficiencies in conversion.


kill-a-watt for an accurate consumption reading - that you'd need one 200W panel
and could run the computer for as many hours as you have full sunshine in the
day. To run it at night, you'd need 32 AH of battery storage (AH @ 50% DOD)
for every hour you'd like to run it (200W/120V=1.6A @ 12VDC = 16AH /50%
DOD2AH), which should be the same as the number of hours of daylight - or add
another panel and more batteries. 5 hrs @ 32AH = 160 AH battery bank - if you
want to discharge to 50% DOD. 320AH if you only want to go to 25%.


I'm planning on slowly adding panels to run non-critical lighting until I get
sufficient production to run critical equipment (fridge etc). The bank will be
available to run fridge/freezer/microwave - 1 at a time - during an outage, and
panels to recharge after the outage. With no real rebates in Canada, it'll be a
long time to take my home off-grid. But I'll move in that direction gradually.


toasted 2 computers on me in 2 years. But as you can see, it'll take a few good
panels to do it.


You are correct, I did something wrong in my calculation and used amp
for amp, this is wrong and resulted in 10 times less amp hours :X    I
did mean 400W per hour of computer use.

Thanks for correcting this.  So calculating by watts will yield the
correct calculation instead.
So a system with a few 15W panels isn't going to work very well except
to power some cell phone chargers and LED lights at night..










Posted by Brian Graham on March 15, 2007, 7:22 pm
 
calculation instead. <<

I like to change to AH since the bats are rated as such. But yeah, I read in a
book that the biggest mistake people make is to forget the current multiplier
when you go to the DC side.


power some cell phone chargers and LED lights at night.. <<

Yeah, not much. Even when I plan on my upstairs lighting, I'm looking at 10x15W
CFs (Ceiling fixtures, bedside lamps, bathroom fixtures), for an hour in the
morning and an hour in the evening during the winter when the avg daylight is
only 2.4Hrs. So basically it'll take a 150 watt panel to produce the power
needed to run those lights while getting ready for work/bed. Since I'm at 24V,
I'll need 150W/120V*2H*5ac-dc = 12.5Ah per day of battery storage. If I needed
to get through a week of discharge before recharging from the grid on the
weekend before I get the PV panel online, I'd need a 12.5*7.5/50%= 175AH bank.

It adds up fast.












Posted by N9WOS on March 15, 2007, 10:10 pm
 

computer

course,

produced.

I had assumed that he was probably trying to run a laptop computer, and that
he meant 400W of usage over the entire 8 hours. Or 50 watts an hour. That
would be consistent with a 50W consumption and it would be consistent with
the figures for battery usage that he posted.

The fact that it's now evident that he is running a full size computer with
a consumption of up to 400W an hour. At that consumption, you would kill a
100AH battery in a couple hours. You would barely get an hour of operation
from a full day of sunshine.

As far as full size computers that run on 50W...... I have a few full size
computers that will run on less than 50W. They are not the new fangled
things that you have now, but they are "computers". One of them, an old
zenith, has a 20W power supply in it. An 8088 processor, 640K of ram, and
two floppy drives. :-)

On the more realistic side. A computer with a late generation P133, late
generation mother board, with 64M of ram, and a single hard drive running
win 95, would be running around 50W with an LCD display. It wouldn't be the
top end of entertainment, but it would work for internet browsing. On the
new product front, you can get micro motherboard running high efficiency
processors that would easily run in that range. They are designed to be able
to be run off 12V in a car or remote application. It would probably be
easier to buy a low end lap top though.



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