New off-grid system advice

MTnate · March 2015

Hello all,

I was hoping to hear some of your opinions and get some advice on my current plan. We are looking at about 2500 watt hours of use each day, I sized it using my own calculations in addition to http://www.solarelectricityhandbook.com/solar-calculator.html. So right now, the plan is to buy:

14-136 watt panels (4.1 amps, 33 volts) for a total of 1904 watts
The plan is to wire them in series and parallel (7 sets of 2) for a total of 66 volts at 28.7 amps. The reason for wiring them in series is that from the garage there will be about a 30 meter run to the house where the rest of the system will be, and the higher voltage means less loss and cheaper wire, right? Does it make sense to go for an even higher voltage?

So then there will be a combiner box immediately following the panels and from there a positive and negative wire that will then lead to the house underground in conduit (any suggestions on combiner box type or conduit?).

Once in the house it will be received by the charge controller (Tri-star TS-60 amp MPPT or Xantrex XW 60 amp MPPT- any suggestions?) The charge controller will then connect to the DC disconnect box (any suggestions?) and from there to the battery bank.

The battery bank will be 16 6v Trojan t-105s (225 ah) wired to 48 volts, which will give me 8 strings of 2 and 450 ah of 48v storage. From there it will go to a 3000 watt 24v Cotek pure sinewave inverter (any suggestions?). I also would like the option of charging with a generator that we have, but haven't looked into it yet- where does this fit in? From the inverter, the load will then go to a main breaker box.

So, thank you for sitting through all of that, and sorry for being such a beginner. Any other small details that I've missed? Also, any general thoughts or criticism on my approach from you experienced folks would be greatly appreciated!

Thanks guys!
Nate

westbranch · March 2015

Welcome, a few things to correct before we can go further... Once you have it clear in your minds eye, a lot of comments that we can make will be easier to understand...

MTnate wrote: »

The battery bank will be 16 6v Trojan t-105s (225 ah) wired to 48 volts, which will give me 8 strings of 2 and 450 ah of 48v storage.

Nope. your will have 2 strings of 8, in series, for 48 volts... 8 x 6v = 48v...

MTnate wrote: »

From there it will go to a 3000 watt 24v Cotek pure sine wave inverter (any suggestions?

you can NOT use a 24 Volt, inverter, good choice for a starter though, on a 48 volt battery.

MTnate wrote: »

for a total of 66 volts at 28.7 amps

the 2 panels in series may be a bit light on the output for a 48 v bank, the ratio for a 12 v bank is you need ~ 17 - 18 volts fro a full charge, 4 x 17 = 68 volts and you have 66 V, you may have to go with 3 in series for 99Vmp Voc will be higher... yoour battery amnufacturer may have different specs for charging

MTnate wrote: »

which will give me 8 strings of 2 and 450 ah of 48v storage

Correct, strangely, BUT, you will have 2 strings of 48V @ 225Amps each , so 450Amps in total... in series the voltage is added, in parallel the amps are added...

hth

MTnate · March 2015

Thanks for clearing up some of my terminology and the suggestion of 3 panels in series, definitely something I missed. Is there a downfall to wiring more panels in series?

Photowhit · March 2015

MTnate wrote: »

Thanks for clearing up some of my terminology and the suggestion of 3 panels in series, definitely something I missed. Is there a downfall to wiring more panels in series?

No you will actually have to do it over the long distance if you intend a 48 volt system. In general MPPT type charge controllers work best at around 2x the system voltage coming from the array. So 4 in series would work so long as you didn't have problems with too high a VOC.

Just off the top of my head, I'd guess you have a normal operating incoming amperage of about 6-7% of your battery capacity. I would consider this low for a system in daily use, so you might consider increasing the size of your array or decreasing the size of your battery bank.

MTnate · March 2015

The VOC is 46.2 V so a series of 4 would be ~176.8 V. So I believe that would surpass my current choice of charge controller which is rated at up to 150 V. So, I think 3 in series would be best for the current plan, unless it'd be more wise to change charge controllers. If I decrease the battery bank to 48 V 260 ah and go with 3 strings of 5 panels for 99 V at 20.5 amps, I'll be looking at a normal incoming amperage of ~12.7% of the battery capacity- would this be better, or am I looking for some sort of sweet spot like 10%? Is this an issue affecting battery longevity?

Photowhit · March 2015

MTnate wrote: »

The VOC is 46.2 V so a series of 4 would be ~176.8 V. So I believe that would surpass my current choice of charge controller which is rated at up to 150 V. So, I think 3 in series would be best for the current plan, unless it'd be more wise to change charge controllers.

No the Morning star is a fine stand alone unit, there might be some reasons if you wanted to run 'opportunity loads' loads that would be signaled by the charge controller to start once the batteries have been fully charge. Things like water heaters, air conditioning.

MTnate wrote: »

If I decrease the battery bank to 48 V 260 ah and go with 3 strings of 5 panels for 99 V at 20.5 amps, I'll be looking at a normal incoming amperage of ~12.7% of the battery capacity-

2040 watts /48v = 42.5 amps x .75(%) = @32amps That looks a lot better to me. It should help maintaining.

Much depends on your life style, if it's all new and you're not use to living under such minimal energy usage, you may find 2.5 kwh to be very little electric, in a warm climate even a very efficient fridge may use over 1 kwh a day and that's AC so add 20% for converting through an inexpensive inverter.

MTnate wrote: »

...would this be better, or am I looking for some sort of sweet spot like 10%? Is this an issue affecting battery longevity?

More depends on the battery usage. Ideally you would like to stay in the top 50% of capacity only dipping below 75-80% after cloudy days and reach full charge once a week.

FWIW- I'm not a fan of the thin film Unisolar 136 Watt panels, It seems thin film may deteriorate faster than mono or poly type panels, add to that that I have yet to see a flexible panel that didn't yellow or have the surface deteriorate to diminish the output and.... well... I'm just not a fan. Unisolar went bankrupt back in 2012(reorganized?), don't think these are being made anymore. While I would buy a glass panel for cheap as they tend to be very dependable, I don't think I'd risk these. I think you can find glass panels as cheap or cheaper. Perhaps you have a steel roof that you want to run these down between the groove?

MTnate · March 2015

Photowhit wrote: »

Perhaps you have a steel roof that you want to run these down between the groove?

Exactly right- we are putting a garage up and it seemed like a great way to make a building multi-task. Also, I was a bit worried about the winds we get here, with gusts over 80 mph at least a couple times a month in the winter.

mike95490 · March 2015

MTnate wrote: »

... Is there a downfall to wiring more panels in series?

YES. When you get to array Vmp is much more than 2x the battery voltage, the MPPT controllers start to loose efficiency. So you have to trade that with losses in the PV wire and find the sweet spot for your install.

MTnate · March 2015

Photowhit wrote: »

No the Morning star is a fine stand alone unit, there might be some reasons if you wanted to run 'opportunity loads' loads that would be signaled by the charge controller to start once the batteries have been fully charge. Things like water heaters, air conditioning. 2040 watts /48v = 42.5 amps x .75(%) = @32amps That looks a lot better to me. It should help maintaining.

Much depends on your life style, if it's all new and you're not use to living under such minimal energy usage, you may find 2.5 kwh to be very little electric, in a warm climate even a very efficient fridge may use over 1 kwh a day and that's AC so add 20% for converting through an inexpensive inverter. More depends on the battery usage. Ideally you would like to stay in the top 50% of capacity only dipping below 75-80% after cloudy days and reach full charge once a week.

FWIW- I'm not a fan of the thin film Unisolar 136 Watt panels, It seems thin film may deteriorate faster than mono or poly type panels, add to that that I have yet to see a flexible panel that didn't yellow or have the surface deteriorate to diminish the output and.... well... I'm just not a fan. Unisolar went bankrupt back in 2012(reorganized?), don't think these are being made anymore. While I would buy a glass panel for cheap as they tend to be very dependable, I don't think I'd risk these. I think you can find glass panels as cheap or cheaper. Perhaps you have a steel roof that you want to run these down between the groove?

Well, I would like to leave it open-ended for a dump load, so perhaps I'll go with either the Outback 80 amp MPPT, or the Midnite Classic 150 MPPT. I believe they both have opportunity load capabilities, but it is difficult to find in their manuals.

My plan is to now spend a bit more on n Outback Power FX3048 3000W inverter. What are the advantages of a vented vs. a sealed inverter? I've noticed some places mentioning certain charge controllers are best for certain inverters- do some play better with others...how?

And finally, as cheap as I am, you have convinced me that it would not be wise to go with the Uni-solar panels. This is a big investment for us and I would hate to see it deteriorate in a mere 10 years. I have decided to go with 9- 250w Hyundai poly panels instead. There nothing quite like changing everything about a plan! You have been great, don't hesitate to correct anything else I've missed! [h=1][/h]

MTnate · March 2015

mike95490 wrote: »

YES. When you get to array Vmp is much more than 2x the battery voltage, the MPPT controllers start to loose efficiency. So you have to trade that with losses in the PV wire and find the sweet spot for your install.

Thanks Mike- I'll keep that in mind.

Alaska Man · March 2015

For what it is worth........... I have nothing but good things to say about the Midnight 150 Amp MPPT. I think that you will find in a year or so the desire to add some more panels, as I did. With the Midnight 150 you'll still have the room to do that.

Photowhit · March 2015

MTnate wrote: »

My plan is to now spend a bit more on n Outback Power FX3048 3000W inverter. What are the advantages of a vented vs. a sealed inverter? I've noticed some places mentioning certain charge controllers are best for certain inverters- do some play better with others...how?

I think, in choosing a vented or unvented inverter would have to do with the environment they will live. If it will be dusty and or moist, consider a sealed unit. I think for the most part Outback's units are the same just lower capacity rated and controlled for the reduced cooling of a sealed unit.

I don't have my planned inverter yet, I have been using a Prosine which was originally designed for a marine environment, which only extends to having a coating over the electronics to help keep them from oxidizing. Mine have live in unheated or air conditioned space, My original unit has had a fan die, so that when the unit pulled more than @500watts it would over heat and shut down. I replaced the fan about 18 months ago (myself) and it has been running fine, though the fan has started making some noise and I suspect I will replace it some time this summer. The inverter is from my cabin and has been in use for @ 8 years now and was 5 years old though unused when I purchased it. To be fair I set up a second inverter of the same type, also used, while working on the fan and it appeared to have died shortly after I reinstalled the 1st one. I haven't tried to diagnose it's problem.

I'm not as familiar with Outback's Charge controller, but I believe it works with a 'system' approach, in which the current is measured at shunts in the charge controller and the inverter, requiring a 'Mate' to bring all the information together. I do think you can have the charge controller start items without a mate, but I DO NOT KNOW this as a fact.

Midnite's approach is to measure all the current going to and from the battery across a single shunt. This in my opinion, helps the charge controller do it's intended purpose better, which is controller the battery's state of charge. Midnite has continued to evolve the system so information might be better through it's forum. I would also be sure to check out the most current manual. One of their systems to run opportunity loads is called "waste not" and a search for such might aid your study.

The engineers at Midnite frequent this site from time to time as well. Brothers Robin and boB worked for Trace/Xantrex(now Schneider) then started Outback and Now own Midnite (they may still have some vested interest in Outback).

New off-grid system advice

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