Off the grid power for a server

[9mmMike]

The last time I ran a set of servers and a set of disks it ended up doubling my electric bill. I have decided to try and power my equipment off grid using solar. I will only be using the servers and disk during working hours. I have about 1000 watts worth of solar panels with a 80 amp charge controller, 200 ah of 12 volt batteries, and a 3.5 kw true sine inverter to power a 160 ah load (20 ah over 8 hours a day). I plan on putting the panels in an accordion style array on top of a 16 foot tower. I may make it a flat panel array wit XY positioning, not sure yet. Some preliminary sketches.

[RWS]

If it was me doing the design,  I would use an inverter that would do both grid tie and off grid.  Then when there was cloudy weather power would come from grid.  When solar was available power would come from solar.  The inverter will do the switch automatically.  That would reduce your power bill.

Alternatively, servers can have redundant power supplies.  One powers from grid and another powers from solar.  I ran into trouble with that one as the server did not like two different phases.  So inverters syncronize to the incoming power which keeps them in phase.  For redundant power supplies use the power line that powers the inverter to power one of the power supplies.  Same phase.

Hope that helps.

[9mmMike]

Yes, I was thinking of that. I have to check the inverter

[John Galt 1]

I'm a little confused by your power description.       Assuming your 20 amp requirement is at 12v that's 240 watts while the servers are running which is a small load, roughly 2.6 pennies per hour @ 11 cents per kwh price.      Something your 1000 watts in panels can handle and also charge the batteries and so small a load that it wouldn't double your power bill.

If instead you're using 20 amps at 120v then that's 2400 watts continuously which your 1000 watts in panels can't handle, not even is strong sunlight.

If the servers double your electricity requirements I suspect you're using 120v when calculating your amp load.     That would be a large load which at the national average cost of .11 per kwh for electricity is about 26 cents per hour.

GA power has residential electricity rates at 8 cents per KWH so perhaps less than the 11 cents for the national average price.

I'd suggest using a Kill A Watt meter (about $30) and measure what those servers actually draw before you set up that solar system.          Solar tends to be a lot more expensive than grid electricity.

It sounds like you're setting up some coin miners.      I did the math for a friend who was running some miners and wanted to use solar and it was a losing proposition.      If instead you want the solar setup for a grid down event than it's worth it in my opinion.

[9mmMike]

The original servers were less efficient and the disk farm I was using was horrible, 22 -5 inch disks. My new set up is more energy efficient

[John Galt 1]

Then I'd suggest that you use a Kill A Watt meter and run those servers for 24 hours and measure their power requirements per hour.     

You'll need at least a 80 amp charge controller (you might get by with a 60 amp controller since panels rarely put out at full power).      But even if you're only putting out at 60 amps that's enough power to charge those batteries at about a C/3.2 rate which is way too fast and will shorten the battery's life unless your servers are pulling a lot of power as the batteries charge.       
To avoid overheating those batteries (I'm assuming LA batteries, AGMs will bulge if charged that fast) you need at least 500 amp/hr worth of batteries with that 12v setup.      If charging that fast be sure to keep those batteries watered every 2 weeks.      FTI.      Lithiums can handle being charged that fast.

Solar is fairly easy but there are some basics you need to conceder when designing a system.

[RWS]

To avoid overheating those batteries (I'm assuming LA batteries, AGMs will bulge if charged that fast) you need at least 500 amp/hr worth of batteries with that 12v setup.      If charging that fast be sure to keep those batteries watered every 2 weeks.      FTI.      Lithiums can handle being charged that fast.
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For that size of a system you should seriously consider 48 VDC.  It reduces the current with the same power.
 A 60 Amp charge controller is still subject to the 80% load factor per NEC.  It makes the inverter choice easier concerning grid tie capeability.  As long as you do not turn on the "Sell" parameter you can be synchronized and switch back and forth without signing a power company contract.

[John Galt 1]

A 60 Amp charge controller is still subject to the 80% load factor per NEC.

True,     I've been posting the last few answers "on the fly" and without a calculator so I'm just running with rough numbers here.      I forgot abput the 80% load factor.

[RWS]

A 60 Amp charge controller is still subject to the 80% load factor per NEC.

True,     I've been posting the last few answers "on the fly" and without a calculator so I'm just running with rough numbers here.      I forgot abput the 80% load factor.

Yeah.  I run about 45Amps @ 50VDC thru a 60 amp charger.  P=ExI  2250W = 50V x 45A, that's for a 48 VDC battery.  At 12 VDC battery 450W = 12 x 45 so you can see you loose at 12 Volt and must use larger wire to boot.  It just makes sense to go up in voltage for larger systems.  Consider the new 600VDC charge controllers.  One string of 10 panels is 8Amp @ 340VDC =2700 watt and double that for two strings.  With 2 strings you would need to keep the watts down to 4800.  Use #10 wire to the combiner and #6 to the battery bank which can be 150ft away.  Very versitile when selecting a PV array location.

[9mmMike]

Ok, I am trying to site the array properly. According to the references for western NC they should point due south at between 2 and 65 degrees depending on the season. When I point my test array south it gets less exposure than when I point it North. Look at the picture. The test array is pointing due north. The sun as at about 11 o’clock right off the top of the photo (just a bit off to the left from center). If the array was pointing due south it would be facing away from the sun....

[RWS]

All I can say is point it South within a few degrees.  Tilt it back 45 degrees. 

With that said I have an East facing array, a South facing arrray and a West facing array.  That way I have more in the early morning and late afternoon that I would with a South facing array only.

Start out with a South array.  Then later you can decide how to expand.

[John Galt 1]

To maximize your year round power average tilt your panels to match your latitude which for NC is about 36 degrees.        Since solar days are shorter during the winter (sun is lower in the sky) many people set their panels at a slightly higher angle, maybe 42 degrees.       This will increase you winter output a bit and reduce your summer output a bit.

[RWS]

To maximize your year round power average tilt your panels to match your latitude which for NC is about 36 degrees.        Since solar days are shorter during the winter (sun is lower in the sky) many people set their panels at a slightly higher angle, maybe 42 degrees.       This will increase you winter output a bit and reduce your summer output a bit.

After a few years experience at Latitude 32Deg I set all of mine at 45 Deg.  They work well, but the main reason is cleaning.  Those panels at 45 Deg stay cleaner as the rain washes them better.  The 32 Deg panels need washing each year after the pine pollen is gone.  Washing is a problem as mine are way up high.   Up high they not only get the sun earlier or later in the day, but you can't get to them to carry them away in the night.  It takes a man lift or scaffold to get to them.

[9mmMike]

Tried working outside. Got the post holes augured, the posts cut to length and the side supports cut. Started fitting the posts so the plywood sheets would fit properly and the sun decided to come out. Too hot for this 62 year old out there. Going to wait until evening...building a platform for small solar array (4-255 watt panels) and solar generator (5.5 kw peak AC true sine) battery (8-12 volt, 55 ah deep cycle) unit.

Went back out at 6 pm and drilled the pilot holes in the frames and started assembling. At 7:30 the thunderstorms moved in and I figured out in field, high on a hill working with metal tools probably could get me into the Darwin awards so I stopped.

[RWS]

Warning !Building your own solar system can be addictive !!!