Saturday, March 14, 2015

The Solar Power Hobbyist

I've recently started to dabble in 'hobbyist level' household solar power.
It's 'hobbyist' and not 'serious' primarily due to costs.
A solar system with enough capacity to power a household (on a sunny day), requires at least 3000 watts of power generation and maybe $20-30,000 in equipment.

My humble system generates a maximum of 450 watts and costs around $1000.

I recently added the 2 100 watt  panels on the left, boosting my power from 250 to 450 watts and wanted to see if I could run my computer system during the daytime and still have power to spare to save away in the storage battery for nighttime use.

I began my trial after the morning sun had reached a little over 1/2 the panel area

The panels are in the backyard, foregoing the expense and care needed to safely mount them on the roof.
At this exposure a quick look at the charge monitor shows that the battery is getting 8.6 Amps of current (the monitor is at the bottom of the photo, the battery is at the top):
This is good.  The battery that I have recommends a starting charge current of 8 Amps up to a maximum of 35 Amps.

The charge controller regulates the charging current to the battery and the power output when power is being consumed.   I will be simultaneously powering my computer system AND charging the battery with any left over electricity from the solar panels.  The charge controller will be managing the juggling of input and output power.

This the basic computer system that I want to power,  computer, some extra monitors, external speakers and internet modem:
I hook up a power inverter to the charge controller output.  The power inverter will take 12 volts DC power and turn it into 120 volts AC power that my computers 120 volt AC to 19 volt DC transformer expects to see. 
There is a lot of power waste lost in the inversion from 12 VDC to 120 VAC, it would be more efficient, just for the computer, to take the 12 VDC and transform it to 19 VDC instead of wasting the power sticking 120 VAC 'in the middle'.
Anyhow I turn on the inverter and feed to the 120 VAC to a real time power meter.  The power meter allows me to see how much 120 VAC power is being used.

I hook up my computer system and see that it is drawing about 1.52 Amps of AC current (the middle line in the read out):

It is interesting to go read the DC current output to see how much DC current is required to provide 1.52 Amps of AC current:
It is taking 9.6 Amps of DC current to get me the 1.52 Amps of AC current that my computer system needs.   A ratio of almost 10 to 1  !

Now, I'm drawing off 9.6 Amps for use but is there anything coming in from the panels that's leftover that we can save away in the battery ?

We do a quick check:

Yes, there is 10.1 Amps of DC current being fed to the battery.
So happily, I am both running my computer AND charging up the battery with juice that I can use to continue running the computer after dark.
This make a total of  9.6 Amps + 10.1 Amps  =  19.7 Amps of current coming in from the solar panels.
As the morning sun has covered more of the panel area, we went from  8.6 Amps to 19.7 Amps coming in !
Note:  the red box to the left is the 1000 Watt Power Inverter.

My daytime computer session ends and I check the AC power meter to find out how much AC energy I used today:
That's it..  260 watt hours  from the Sun to my computer with change leftover for the battery !

1 comment:

J Golz said...

Hi Thorick, I've been running a solar heating project here in NY for almost a decade. I have self-fabricating panels which consist mostly of oak and maple leaves situated between 30 and 50 ft. above ground on giant wooden posts ranging from 2-3 ft. in diameter, which for lack of a more technical name, I refer to as trees. There are about 60 of them in various stages of growth on a 1-acre plot of land. Once a year, I fell one of them, revealing around 60 growth rings. I split, stack and dry the rounds (interspersed with visits to the physical therapist to address back issues) and then burn these widgets over the winter in a modern EPA approved Jotul wood stove supplement heating costs. After figuring in cost of aforementioned medical attention, I just about break even on oil savings. In any case, the bigger message is the rate of growth here was suprising and these solar collectors are quite beautiful. A colleague who previously did a lot of solar cell development at Philips compared data with me and we came up with a very very rough efficiency estimate of 6:1 for single crystal Si based cells to trees. Curious if anyone has better data?