Solar System Plans, Goals and Concerns for 48V Solar System

Sundog

I have 24 panels rated at 6120 watts total STC which is perhaps 5400 watts PTC.

Plan to use Xantrex XW MPPT 80 600 which is a 4800 watt CC at 48 volts.
This makes the array PTC 600 watts more than the CC rating.
I could use 18 panels or 4050 PTC putting me 750 watts less than the CC rating.
Recommendation?


Plan to use the Xantrex XW6048 6000 watt inverter for essential loads.

Goal:
An emergency power backup system that will work off grid for lights and recepticles etc.
And a grid-tie system to feed the grid when power is up. (Let’s not waste sunlight)


What is needed:
Battery storage with emphasis on long life. I understand that it is important to use the correct battery size for the system so charge current would be right. To much charge current and the plates deteriorate quickly but too little and sulphation occurs. Would about 800 AH (20H) be about right? Better a little too much or a little too little?

I have read that some recommend a forklift battery. (Considering a rebuilt) Others say ‘solar’ batteries last 5-15 years. I want 20-25 years. Would something like the Trojan IND13 be better than a forklift battery? Sure costs more. Are rebuilts available for these?

Concern:
It is expected that in a system of this type the batteries are used only on the rare occasion of a power outage. The rest of the time the batteries are just sitting there being maintained at full charge.

How does this effect battery life?

Do the batteries need a periodic 25% or 50% DOD so a significant charge current can be realized to maintain their health?

Thanks for your help.

K4HW

niel

Re: Solar System Plans, Goals and Concerns for 48V Solar System

i'm not sure why you'd have need of the 600v model mppt cc. too expensive for something you really don't need. you do need more controllers though as you don't want too much power going to waste or why have mppt at all. go with more cheaper in price, but still quality mppt controllers. xantrex has been having some troubles, but there's others like the midnite classic or the mornigstar line of mppt ccs. midnite has a string calculator you can use so you can see how many controllers to have and what configuration of the pvs will work best as all pvs in series is not necessary unless you are sending power out for a quarter mile or something, which i don't recommend doing. the classic even comes in a model that can go 250v if need be.

as to the batteries we often advise cheap batteries to start a system off with just in case something goes wrong or isn't optimally configured correctly.

the occasional 25% to 50% dod may be a good idea for most batteries, but if you picked up used telecom agm batteries this may not need to happen. fork lift batteries are very inefficient, but may still suit you. any battery you get will be a big investment no matter the type or even if used. it's no easy decision and the choice is up to you.

bill von novak

Re: Solar System Plans, Goals and Concerns for 48V Solar System

Sundog wrote: »

I have 24 panels rated at 6120 watts total STC which is perhaps 5400 watts PTC.
Plan to use Xantrex XW MPPT 80 600 which is a 4800 watt CC at 48 volts.
This makes the array PTC 600 watts more than the CC rating.
I could use 18 panels or 4050 PTC putting me 750 watts less than the CC rating.
Recommendation?

Wire for about 100 volts then use a Classic 150. Cheaper, more efficient, more power.

It is expected that in a system of this type the batteries are used only on the rare occasion of a power outage. The rest of the time the batteries are just sitting there being maintained at full charge. How does this effect battery life?

You probably want telecom/UPS batteriies in that case. Good telecom AGM batteries can hit 20 year lifetimes if you cycle them only rarely. They are designed for backup applications.

Cariboocoot

Re: Solar System Plans, Goals and Concerns for 48V Solar System

I'd say the first thing you should do is figure out exactly how much power you'll need to supply when the utility goes down. Quite simply you do not need full household power during an outage; just enough to keep the critical loads going. In most places black outs are infrequent and short-lived so why invest big money in batteries to cover them?

You might be much better off with a small battery-based system for outages and put all the panels on GTI to get full benefit when the grid is up. You could either have the battery system a GTI type or use SMA equipment and AC couple the GTI(s) to a Sunny Island in case of outages.

Or you could forget the batteries altogether and buy a generator for when the power goes out. No sense in investing big money in something that isn't going to get used most of the time.

n4wff

Re: Solar System Plans, Goals and Concerns for 48V Solar System

+1 on the cheap starter batteries until you get it tweaked. I scrounged and found some old forklift batteries a plant was selling for scrap value. I bought 3 for around $150 each. I am a newbie when it comes to solar, and if I kill a battery bank, I am not really out anything. I had to bypass the bad cells, and one pack was too far gone, but with equalizing, cycling, and constant water checking, I have been able to slowly bring the bank back to life. I hope to get by for a couple of years so I can save some money up for a battery bank that requires less maintenance.

Sundog

Re: Solar System Plans, Goals and Concerns for 48V Solar System

Cariboocoot wrote: »

I'd say the first thing you should do is figure out exactly how much power you'll need to supply when the utility goes down.

The only large essential load is charging my Nissan Leaf which I would like to do in an outage. It is about 3kw and perhaps 4kw if charging and preheating. Otherwise it is refrig, microwave, lights etc. I could manually operate the water heater etc. being careful to avoid coincidental loads.

Sundog

Re: Solar System Plans, Goals and Concerns for 48V Solar System

n4wff wrote: »

+1 on the cheap starter batteries until you get it tweaked.

I like this idea if I can find something. Don't have the industrial connections I used to. Everyone I knew is retired or dead.

Sundog

Re: Solar System Plans, Goals and Concerns for 48V Solar System

bill von novak wrote: »

Wire for about 100 volts then use a Classic 150. Cheaper, more efficient, more power.

Well, the nearest good place I can put the panels (and it is a very good place) is about 400 wire feet away. Too shady around the house and would have to put them in the shady yard build expensive mounts etc. So I series them up to 400 to 500 volts so I can run #10 copper.

bill von novak wrote: »

You probably want telecom/UPS batteriies in that case. Good telecom AGM batteries can hit 20 year lifetimes if you cycle them only rarely. They are designed for backup applications.

Yes this sounds exactly like what I want. Where can I find these?

Sundog

Re: Solar System Plans, Goals and Concerns for 48V Solar System

niel wrote: »

xantrex has been having some troubles,

Would like to hear more about this. I am not opposed to going to something better.

niel wrote: »

the occasional 25% to 50% dod may be a good idea for most batteries, but if you picked up used telecom agm batteries this may not need to happen. fork lift batteries are very inefficient, but may still suit you. any battery you get will be a big investment no matter the type or even if used. it's no easy decision and the choice is up to you.

I like the telecom battery idea. If you have any leads...
Thanks

BB.

Re: Solar System Plans, Goals and Concerns for 48V Solar System

Remember, if you do cycle the (telecom or "float service") batteries "deeply" (some models, below ~85-75% state of charge), the phone companies would replace them.

If this is for truly "emergency use" and I had the room... I would get a good quality water cooled genset (or even a good low tech Onan or similar air colded unit if I could build it into a sound proof shed) and a large propane tank for a few weeks of storage (perhaps running the genst 6 hours in the morning and 6 hours in the evening).

I just use a small Honda eu2000i and 20 gallons of fuel (plus stabilizer, change every 6-12 months into my car). Much cheaper and more portable (we are in earth quake country--No guarantee that the home is habitual after a major quake).

Batteries and solar power tend to make for very expensive emergency backup power systems--Both initial installation and maintenance costs.

-Bill

jcheil

Re: Solar System Plans, Goals and Concerns for 48V Solar System

Grid-Tie + Generator, is going to be the cheapest (and best) solution for this in my opinion.

Cariboocoot

Re: Solar System Plans, Goals and Concerns for 48V Solar System

Sundog wrote: »

The only large essential load is charging my Nissan Leaf which I would like to do in an outage. It is about 3kw and perhaps 4kw if charging and preheating. Otherwise it is refrig, microwave, lights etc. I could manually operate the water heater etc. being careful to avoid coincidental loads.

The only thing mentioned there that isn't a big load is the lights. Even then if you have enough of them (or the 'wrong kind') it adds up.

BTW you're not looking at kilowatts, but kilowatt hours. Providing 4kW hours for occasional outages via solar is going to be a lot of money for very little return. In my opinion this is an impractical plan.

Cariboocoot

Re: Solar System Plans, Goals and Concerns for 48V Solar System

jcheil wrote: »

Grid-Tie + Generator, is going to be the cheapest (and best) solution for this in my opinion.

I second that. Unquestionably the best way to go.

BB.

Re: Solar System Plans, Goals and Concerns for 48V Solar System

You can also add a SMALL battery bank + solar (say 2-4 golf cart batteries plus a 300 - 1,000 Watt TSW inverter).

Small enough that you can throw $200-$400 worth of batteries every 3-5 years and enough power for lights, laptop, cell phone, radio/TV for night time use when you really don't want to runt the genset 24x7 (and burn up your precious fuel).

-Bill

Sundog

Re: Solar System Plans, Goals and Concerns for 48V Solar System

Everything you have told me makes sense. I think you are right and that is what I plan to do. I had already thought about the generator and that is easy to do. Perhaps micro-inverters on the panels. That will be easy to do with minimal wiring and have grid-tie that way. Or perhaps a string inverter. I don't have a shading problem and all panels face south. I have learned quite a lot researching this project and thank you all for your help.

K4HW

bill von novak

Re: Solar System Plans, Goals and Concerns for 48V Solar System

Sundog wrote: »

The only large essential load is charging my Nissan Leaf which I would like to do in an outage. It is about 3kw and perhaps 4kw if charging and preheating.

If you really have a need to do solar charging of an EV I'd recommend relying on Level 1 charging during the time of the outage. 1.5kW is a lot easier to manage than 3.6kW, whether you are using generator or solar. It also removes the need for 240VAC.