my first 400 watt system

bcolebuild

Hello everyone,

I'm out in taos nm about to build an earthship and need some power, im going to set up a 400 watt solar trailer to run a cement mixer, table saw and some good blues music.

Im looking at buying
2) 200 watt sun electronic panels $1.74/watt
1) C40 or BZ MPPT 500 both around $200 although i hear the bz is a pos
4) L16 375 amp/hr batteries
1) Aims 2500 watt inverter

Questions:

I planning on having a 24v system because i hear running batteries in parallel wears them unevenly and series will help the L16's last longer, is that true? i do know that higher voltage will be more efficient in long runs.

Are there any other cheap MPPT charge controllers that people would recommend over the BZ? and what size of charge controller do i need? 400watts/24v = 16.66 amps, a charge controller between 15 and 25 to 30?

Does anyone have any recommendation in general panels, batteries? im on quite a small budget so if anyone has any used equitment i would be very interested, thanks a lot for any info you can through my way.

-Ben

Kamala

Re: my first 400 watt system

BZ ALERT!

Don't! Check other threads here. Do a search. And look out for more warnings.

BTW, is there any bad blues music?

K

myocardia

Re: my first 400 watt system

Hi Ben, welcome to the forum. If you are talking about a Xantrex C40, you don't need one. It would be a complete waste of your money, unless you had plans on running a 48V system. As you can see here: http://store.solar-electric.com/xachco.html a Xantrex C35, which will also handle 24V, is only ~$100.

I can tell you for sure that a table saw will deplete 375Ah worth of batteries in a few cuts (and I don't mean 8' rips, either), and a cement mixer uses more power than a table saw. 400 watts worth of panels and two L16 batteries won't get you anywhere with either. Sorry.

Kamala

Re: my first 400 watt system

Nice sig, myocardia.

icarus

Re: my first 400 watt system

First,

I wouldn't use a BZ controller if you gave me one! (In fact someone did, and it harvested less than no controller at all!)

Second, whether or not you run 12 or 24 volts doesn't really make much difference net/net. 12 vdc hardware is a bit easy to get however. (Music etc).

Ideally you should have charging capacity of at least ~5% of battery AH capacity. So your 375 ah of L-16 would need ~ 17 amps just to get to 5%. (5-15% is the target range). Your 400 watts might put ~ 10-11 amps into 24 vdc under ideal conditions. Consider adding PV.

Finally, people all too often over estimate their solar capacity and underestimate their loading. My best suggestion is to get a good handle on your loads, and tailor your system to suit these loads.

My rule of thumb is that a typical PV system will deliver power like this: For simple math, if you take the name plate rating of the PV, divide that number by to to account for all system loses, then multiply that number by the hours of "good" sun you can realistically you can expect (seldom more than ~4)

So in your case, 400/2*4-1600 wh available out the inverter on an "average" day.

You will also need to figure in how you are going to charge your batteries when there is a period of poor sun. Most folks consider that if you draw your batteries down more than ~50% and if they are not FULLY recharged quickly, you will quickly kill a set of batteries. Personally, I prefer not to discharge my batteries more than ~20% and then fully charge them (with a generator if need be) with in three or at most 4 days.
So you will need to figure out a generator.

Just for the record, we have ~400 watts of PV, and we use ~600 wh/day. That is a number that requires that we run the generator rarely, and most days the batteries get fully charged each day by ~noon.

You might consider using your generator for your tools. A few minutes of saw time might equal your entire days production. Depending on your usage you might find it is more cost effective to build a system for your lighting and entertainment , and leave the big, but rare loads to the genny.

I would consider the Rogue MPPT controller ~$250 or the new Morningstar MPPT. Here is one more "rule" of PV. Your loads will grow with time, and indeed most systems do as well. Don't skimp on the CC. As my systems have grown, I have had to replace controllers twice since I have outgrown the. The Rogue will handle 30 amps into 12 or 30 into 24, so it is plenty big if you are going to go with 24vdc. You are about it's limit at 12. I run 454 watts into it into 12 so every once in a while I exceed it's capacity, but the only result is a small bit of waste. Those times are very rare however.



Good luck and welcome to the forum,

Tony

niel

Re: my first 400 watt system

aside from the bz controllers being junk, you will find 3 things to be true.
1> the charge rate to the batteries will be too small as it is under a 3% charge rate and i don't recommend under 5% with the acceptable range being between 5% and 13%.

2> you will most likely find that running high power items like those you list will draw far more than those 2 pvs can replace in a day. i recommend you find what kind of kwh over the course of a day you will typically need by buying a meter such as a kill-a-watt meter. due to losses and inefficiencies you may need to add up to another 50% to the kwh you find you average to come up with the solar stc watts you may need.

3> as to the inverter you will want it to be the pure sine wave type as some items will overheat (any with motors will heat and draw more power) or blow out on modsine. even if you live with that risk you will need up to another 28% more power yet from pvs due to the losses from modsine inverters.

bobdog

Re: my first 400 watt system

icarus wrote: »

....My rule of thumb is that a typical PV system will deliver power like this: For simple math, if you take the name plate rating of the PV, divide that number by to to account for all system loses, then multiply that number by the hours of "good" sun you can realistically you can expect (seldom more than ~4)

So in your case, 400/2*4-1600 wh available out the inverter on an "average" day.....

I'm confused on the math. Shouldn't that be 800 wh available?

BB.

Re: my first 400 watt system

• 400 * 0.50 sys eff * 4 hours per day average = 800 WH per day

Note that hours of sun per day is variable--it may be 2 hours per day in winter and 5+ hours per day in summer.

And yes, we take turns at faking the math. :roll:

Just seeing if you where paying attention.

-Bill "hellooo--anyone out there????" B.

icarus

Re: my first 400 watt system

Jeez you guys,

How many times do I have to tell you don't trust my math! I think I must be dyslexic (not to mention careless when I get in a hurry!)

400 divided by 2 equals 200 times 4 hours equals 800!!!

Just remember to do as I say, not as I do!

Tony

Sorry!