hi! looking for comments on my 'renegade' install

[JoeT]

I'm a do-it-yourselfer and I've got a partially functioning system that I've slapped together from craigslist/ebay, and it's a work in progress. Looking for any recommendations/changes.

On the roof I've built a simple 2"x4" structure that is mounted true south on a southfacing slope of my roof, it's at about 19 degrees and I've made it adjustable for spring/fall and winter modifications in 2 distinct steps. each array is a wood box-frame that itself is mounted to (3) 2"x4" that have standard simpson tie/footers that are weather-sealed/etc. and just nailed into the roof. Wind-loading calculations were not performed by me although I'm not too concerned based on some yank-testing I've performed.

array one has some old SR-90s (2) and a Sharp-165 and a Sharp-185.
array two has (2) Sharp 185s, two old 5-watt line modules (heh), and a uni-solar PVL-128 (thin film, it's like 20' long)
Right now I have (6) pairs of 12g THHN wire in a zip-tied bundle just lightly tacked to the roof (air install I guess) and all connections are either to a junction box or cleanly soldered.

I have a PV combiner box w/fuses that I got as a spare from a friends install, and that feeds the xantrex controller w/6 gauge THHN in an outdoor weatherproof box (very short run, like 8"), the xantrex then of course feeds the battery array. There I have a 40 amp DC circuit breaker really just because it seemed like as good a place as any.

Total system rated power is like 1KW.
I have a Xantrex C40 controller, and a bank of (12) DCS-100L 12v batteries wired @ 24V (everything is 24v). They are sitting in (2) of the largest big-plastic boxes that target sells, 6 fit neatly into each one with a closable cover and there are vent holes on the underside of the handle. I've punched a couple circular holes for the 10/3 extension cable on one side and the incoming power to the other. It appears to be plenty ventilated.

Every other battery has the + terminal on a 40 amp DC circuit breaker (label says it will pop at 47.5 amps) and wiring between the batts is all #2/0 600V/etc. typical wire used for PV in conduit. I divided the batteries into two seperate strings each with a ginormous connector that I found on ebay (anderson powerpole) that has #4 AWG flexible wire and it is supposedly rated at 180 amps. The two strings of 6 batteries each I connect with some Y-cables before it goes into my inverter, which is just an APC-1400RM2U UPS with the internal batteries removed, and an anderson connector installed so that I can attach it to my battery array. It's rated at 950 watts continuous, and I control it through an SNMP card (can turn on/off and monitor remotely).

It seems like it's working fine but my weak link for now is that I don't have my standby powerpanel installed yet (A siemens 100a standby power panel) so I am just running a 10/3 outdoor rated extension cord (25') from the inverter under the house and next to the house power panel. For a test circuit my living room is plugged into this extension cord.

The PV array is grounded with #6 to a ground rod, as is the inverter and charge controller outside.

OK so if you're still with me I'm going to install the standby powerpanel this weekend, and hard-wire it to the inverters incoming 10/3 cable, and have the ability to switch over a number of circuits to the inverter. Of course the 950 watt inverter will dampen my ability to do much of anything.

Anyways my average electric bill is ~300 to ~350 kwhrs/month even in the summer with central AC (rarely) needed. My goal is to cut my electric usage in half, not too concerned with the money saved just trying to be a little self-sufficient here in San Jose, CA.

Anyways I consider myself a renegade because I have a hodge-podge system. Given that I'm sure *everyone* here knows more about this stuff than I do what should I do differently?

On my to-do list:

1) Properly install the Siemens standby powerpanel (grounds, floating nuetral, etc. all)
2) Run conduit on the roof and into the weatherproof housing where the PV combiner box and charge controller reside on the side of the house (it's only a 25' run, I put the batteries as close as I could get). Replace 12g THHN w/ 10G THWN-2, since I believe UL (?) code requires 90 degree C wet rated cable on any roof installation in conduit. With my current technique of using 6 pairs, that means I'd need 150' of white and 150' of black if I'm reading the color code properly. (I always preferred black and red for DC but whatever)
3) Entertain an inspection (heh) probably hire a pre-inspection electrician to recommend any trouble-spots.
4) Get an 'official' inspection from all sources (building, electrical, etc.) to shift away from my 'maverick' status.
5) Find a better 24v capable inverter. My APC-1400RM2U seems to draw about 20 watts idle and is only rated at 950 watts continuous.

any other thoughts? Sorry for the huge 1st post.

I'm in CA, my state/local/etc. laws may be different

thanks,
-Joe

[niel]

hodge podge indeed. it's somewhat difficult to address everything and some things i'm not sure i'm reading right. now as far as the pvs go if you don't have wild voltage differences you should be ok. i am assuming too that you don't have a low current 12v pv in series with a higher current 12v pv. the pv with the lowest current is what you'd get at 24v in that case.
as to the rest you can look over some of the other posts to see if they answer any of your doubts with a recommendation that you read the one on the calculator.
http://www.wind-sun.com/smf/index.php?topic=1477.30
do note that a run of wire consists of 2 lengths of wire, one being positive and one being negative. if you have a 25ft run then you have 50ft of wire to use in the calculations. if you are getting more than 3% losses from voltage drops then you may wish to consider a change for the wiring. for lengths going from the batteries to the inverter or other loads the math stays the same as you are just substituting the batteries for the pvs. i do suspect you to have some efficiency losses above the norm for your system, but you can verify if i'm right or wrong on that.
now for you to cut your usage in half that is hard to do and some planning and conservation will be needed on your part.

[JoeT]

all my panels are 24v nominal except the two SR-90s (wired in series, for 24v) and the little dinky 5w line modules (24v wired in series).

agreed it's a mismatch cluster*%, but my observation by using a PWM controller is that beyond the voltage of the battery bank (25-27v typically) it doesn't seem to matter as that power is completely lost anyways. The sharp 185s seem to be throwing power way up there (35 ish), the 165 pretty close too, and every pair of wires I've tested are all outputting 30+ volts when the sun is shining.

I would be more inclined to care about the PV array mismatch if I was using a MPPT controller ($470 ish range for an MX-60 seems a logical choice eventually)

6 pairs of 12GA THHN were selected simply because I had a spare spool lying around. Now that I have read some posts around here I think I may go with a #8 THWN-2 run as it's available at home depot (?)

Anyways I know it isn't pretty I'm just trying to make it safe/effective at this point. Mainly I'm looking at any/all inspector related issues. I'm planning on a 2-2.5kw inverter eventually so I'll need to go through the PV disconnect (just a 40a breaker right now) and everywhere else with decisions that are appropriate for a higher-rated inverter.

anyways thanks for your $0.02

I have been powering my living room with only about a 20% discharge from my batteries every day for a week or two now including a power usage of around 2-3 KW/hrs/day which means I am already off-loading approximately 1/3 of my electric bill.

I have some outdoor DC lighting (~100 watts) that I run for a couple hours, lights/hallway lights, TV/entertainment center, and I run my laptop/wifi out there and I've rounded up most of my vampire loads to run from that circuit.

I'm sure I'll be much happier with the install when I can just switch entire household circuits betweent the grid and my inverter in the basement. That was basically my goal anyways. Rolling blackouts were fairly annoying in my area the past couple summers.

[mike95490]

I'd have suggested skip the batteries, and use a grid tie. The losses you will see with discharge and recharge of the batteries, will be in the 20% or higher range, plus your inverter lossses. Maybe set your LVD fairly high, and try running your fridge off it daytimes, keeping the batteries full, and trying to use the power daytimes when the panels are lit up.

[JoeT]

I was considering it, but there don't seem to be any (?) lower end grid tie inverters, and the cost of a grid-tie inverter would roughly double my budget.

Am I correct in that? Last time I checked a Sunny-Boy inverter is around $2k

Maybe in the budget in future years, but I definitely would want a hybrid grid-tie/battery arrangement if I were to go grid-tie.

Anyways I'm kind of excited to do the standby panel cut-over this weekend. I'm wondering if my inverter can power my frig? Probably not, it's a fairly big unit, I remember the tag on it says expected power use/yr of 720 kw/hrs or so. My inverter has a peak cont. rating of only 950 watts I'm thinking when the compressor kicks in it's done for.

[BB.]

JoeT,

$2k should get you somewhere around a 4kW grid tie inverter--They seem to be running around $0.50 per Watt... You will just have to look around for a small(er) unit.

There are other types of units that are inverters/chargers/on-grid/off-grid units like the Xantrex SW series talked about on another thread... If you wanted, basically, a Gird-Tied inverter with UPS type function, it seems to be a good place to start.

Of course, there are many other brands out there and I am sure somebody here can give you better sources for what you want (a 600 watt Grid-Tie?)...

Powering your fridge, get yourelf a kill-a-watt meter for $25-$40... It will give watts, VoltAmps, Power Factor, KWhours, and Elapsed Time (as well as frequency)... Unfortunately, the kill-a-watt does not do a good job on peak power/current (only updates about once per second).

Your fridge probably is around a 200-400 watt unit when running, and motors take 2-5x (or more) starting current. You should not damage the inverter if it cannot handle the load (although, if it does not start the fridge, prepare to quickly unplug the motor as it can stall and overheat within a few minutes).

720 kWhrs per year is not an overly expensive refrigerator to run (~$70-$80 per year, or $7-$8 or so a month)... My old fridge from 20 years ago was 3x that amount (much less efficient).

Make sure you know what you are doing with your Grid-Tied system--I would be wondering if your local building inspector would approve the roof-top installation (I think it is required that the mounting system supports 125lbs per square foot), is your grounding correct, do you have metal conduit from your roof to your JBOX/Inverter, that your solar inverter + panels are rated at 20% or less (IIRC) of your main service/circuit breaker box ratings, and I don't believe that THHN/THWN insulation is UV resistant.

All the above will have to be inspected, and you will need a lockable switch by the meter to disconnect the solar inverter, and to fill out the utility's forms (insurance, building inspection sticker, inverter identification).

If you connect all of this yourself without approval, the utility will probably cut your service, may sue you, and if somebody is injured or killed, you will probably have to prove that it was not your fault.

Not trying to scare you out of having Grid-Tied Solar--but it is almost the same cost and work to do it right as to do it wrong. It is not that hard to do the second time--However, how to do it right it right the first time without any help or direction is not always obvious.

Since I am not an expert in NEC and other codes, take what I am saying as guidance as to where and what to look for... Others here (and locally) will be able to better answer your questions.

-Bill

[JoeT]

gracias, much appreciated. Unfortunately I don't have $2k in the budget for an inverter right now, maybe next year. For now I'll concentrate on getting the proper inter-panel wiring (the THHN was just temporary, it's only been up since Sunday), outside disconnect, proper battery connections/breakers/etc. and sub-panel wiring.

I've seen some roof-installation guidelines on the internet and I'll look into that, it might be the easiest part to get signed-off by the city I'm thinking. It's really a simple wood frame made of 2"x4" pressure-treated lumber bolted to the panels that is then bolted to (3) 2"x4" that lie along the roof on a true-south orientation that can be raised in two tiers (summer=flat, etc), it's definitely not going anywhere, quality simpson-ties and sealant used on any through-roof holes.

Anyways my meter was reading a peak of 30.2 amps @ 27 volts around 1:45 yesterday afternoon, I am pretty happy about that. I wasn't expecting to make that kind of power at this latitude so late in the season (I'm in San Jose).

[mike95490]

My inverter has a peak cont. rating of only 950 watts I'm thinking when the compressor kicks in it's done for.

Is it a pure sine wave inverter, or a modified sine ? Magnetic thingies do not like modified sine inverters, transformers, motors, ballasts ...

[JoeT]

yeah I hear you on that. it's a modified sine, intended for electronics/PC/systems backup (a UPS , APC-smart-UPS 1400RM2U)