Answering a Solar question from Allan

This posting is about a question from a reader, Allan, wishing to know a bit about the solar system. I was going to write him a reply but then it seemed easier to jot it down here for all.

The majority of my components was purchased online. Simpleray.com and EVTV.ME 

Date : 06/20/2013

Simple Ray Invoice : (Links to website)

 $1774.16     8 - Canadian Solar 250 Watt Polycrystaline Solar panel - CS6P-250P $240.12/$1920.96
$144.25        1 - Midnite-Solar-2-String-MC4-Combiner-Box  - MNPV2-MC4 $144.25
$95.81          1 - 300 Volt Lightening Arrestor - MNSPD300  $95.81
$659.00        1 - Midnight Solar 200v Charge Controller - C200 $659.00
$1877.43      1 - Outback VFX 3600 watt inverter - VFX 3648 $1781.86

Shipping $223.01 (to Colorado)

Total : $4773.66      Current : $4601.68

EVTV  (Based in Missouri)

$2384           16 - CALB LiFePO4 100aH Cells $149

Shipping   $116,16

Total:  $2500.16 (To Colorado)


There you have it, Allan.

Links to where I picked them up and the exact components used. There are of course missing pieces. Your wire runs will be different. Also how you decided to mount them. I used unirac rails you can easily get at the hardware store rather than expensive racking systems.

The 8 panels (2000watts) would be able to power the 1500SF house I had in Michigan. We used 10kwh a day. Here in the mountains I use a fraction of it. Which allows me to get away without needing a larger battery bank and a genny.

I am not sure what you need as far as daily power. I imagine your battery bank would be quite different than mine. Those 16 100ah cells in my case are 5kwh.

LiFePO4 are nice in that you can use 80 percent of their capacity daily and still get >3000cycles.

This saves (even though Lead is much cheaper) you having to over size a battery bank. Lead you have to essentially double capacity as they do not like to be routinely discharged more than 50% without a huge degrade of cycle life.

Colorado, even at this mountain altitude, is very sunny. Rarely do we have cloudy days. So I get away with a small bank. IE not sizing for multiple days of bad weather. Plus even in overcast I get 500watts or about 1/4th. 

The thing with these chemistry batteries is you need a good charge controller. One in which you can modify all the voltages. They are completely different to Lead. The Midnite Solar is a very good controller. At this point, I would say the top choice.

The cells are a nominal 3.2v. I have 16 for a "48v" bank. In actuality, they are charged to 55v. When it reads 48v, you have used most of the pack.

That is why I purchased the Midnite solar. It can be modified to essentially any chemistry voltage parameters. Also. It handles high voltage. 200v, whereas most other controllers are limited to 150v.

This allows me to connect 4 panels together and then those two strings into one, which is carried to the house. Higher voltage, lower loses for longer runs, cheaper and thinner cabling.

I am using a mindset of, no active cell balancing. Instead, I bottom balance the pack to within milivolts of each other at 2.75v each. Then charge the whole pack up to 55v. (Which keeps them from the very top of their voltage curve. Basically not using the top end, which is little, and saving me the headaches)

My parameters are : (These apply to 100aH cells  EDIT: The voltages would remain the same if you use 16 cells of LiFePO4 batteries. The Endamps would change based on aH. A 180aH battery for instance would have EA of around 9amps)

No equalize
55v (3.473 per cell) Bulk (Gives all the amps it can based on conditions until reaching 55v then moves to Absorb phase)
55v Absorb until it reaches 5.5amps (starts giving as many amps as needed to hold 55v then lowers them to maintain 55v as it fills up (End Amps - 0.05C of the Cell Capacity) then switches to Float
53.5 Float. (3.34v per cell)

3.34 is the resting actual open voltage of the cells.

I think that gets most of what you asked, Allan. You'll have to let me know if I missed anything.

Basically I have a system large enough for my weather and two days usage if the sun blew up and all went dark. 2000w/5kwh bank

Many electric kettles of tea, led lights, computers, and 5 hours of 42inch HDTV per day.

All for $72-$7500. In your case, if you doubled the bank to 10 for an additional $2500 you would be well set.

Let me know how it goes!

- Cloud

ps. Note how the cost of the 8 panels was $1774. A nice number for electrical independence!