Suggestions for 48v PV system

mac

I want to build a 48v system and looking for suggestions. At this point it will be to learn about PV for hopes that someday in 10yrs, go off-grid with a larger more capable system and better technology. My goal is not to save money on my electric bill but it is to use less metered electricity. I want to charge the 48v battery bank using the panels and backed up by the grid. It will be used to power my office consisting of my ham radio, small DC devices, 5v USB chargers, iMac, cable router, switch and external monitor. Everything else in the house will be on the grid.

The panels will be temporarily ground mounted. It would be great if the system can be expanded at a later time but that's not a big concern. The batteries will be used only when sufficiently charged to supply power to an inverter and handle the needs for my office. Should the batteries drop too far down, it would switch back to the grid. The electronics to do all that will be added later.

So what would be the optimal configuration of panels - charge controller - inverter and batteries for a 48v system?

Minimal price is not the goal but a well balanced DIY 48v system is. Start with the best panels and design down from there.

Thanks.

lkruper

I

mac wrote: »

I want to build a 48v system and looking for suggestions. At this point it will be to learn about PV for hopes that someday in 10yrs, go off-grid with a larger more capable system and better technology. My goal is not to save money on my electric bill but it is to use less metered electricity. I want to charge the 48v battery bank using the panels and backed up by the grid. It will be used to power my office consisting of my ham radio, small DC devices, 5v USB chargers, iMac, cable router, switch and external monitor. Everything else in the house will be on the grid.

The panels will be temporarily ground mounted. It would be great if the system can be expanded at a later time but that's not a big concern. The batteries will be used only when sufficiently charged to supply power to an inverter and handle the needs for my office. Should the batteries drop too far down, it would switch back to the grid. The electronics to do all that will be added later.

So what would be the optimal configuration of panels - charge controller - inverter and batteries for a 48v system?

Minimal price is not the goal but a well balanced DIY 48v system is. Start with the best panels and design down from there.

Thanks.

If you want to expand later get a brand of solar panel from someone who will still be around like Kyocera, Sharp or Panasonic in 200, 225 or 250w. Get a good MPPT controller like Midnight Solar 150 which can start small and grow. You can put 3 or 4 200w panels in series and add groups to match as you grow.

Plan cable runs and wire sizes for your expanded system with a combiner and you won't need to scrap the wire and start over.

That being said you need to start with calculating your loads and hours of use before you decide on battery to meet those loads and panels to charge. You will need a generator to keep your batteries happy in Cloudy weather along with a charger.

You should also be aware that the cost of your solar power will be 5 to 10 times the cost of grid power.

mac

Thanks for the quick reply. I was looking at [FONT=Arial, sans-serif]Renogy 250 Watts 24 Volts Monocrystalline Solar Panel - getting two of these panels. [/FONT]

[FONT=Arial, sans-serif]Is it an issue if the total output of the panel's voltage is greater than the battery? For example two 30 volt panels?

I have a 3500w generator for emergency backup. Don't want to kill the batteries but grid power will always be available.[/FONT]

mac

I currently am using an AGM 12v 100ah battery with a Triplitte 750w charger/inverter for battery backup purposes. My kill-o-watt meter will arrive this week so I can get a better idea what my various device are using.

I want to be able to run 500 watts which is what I based my current inverter to comfortably supply. The time period of use would be adapted as needed but a target goal of 8 hours at 250w continuous use, which is what I estimate the Mac, 2nd monitor, router / switch / vonage phone / LED light will use on idle.

lkruper

mac wrote: »

Thanks for the quick reply. I was looking at [FONT=Arial, sans-serif]Renogy 250 Watts 24 Volts Monocrystalline Solar Panel - getting two of these panels. [/FONT][FONT=Arial, sans-serif]Is it an issue if the total output of the panel's voltage is greater than the battery? For example two 30 volt panels?

I have a 3500w generator for emergency backup. Don't want to kill the batteries but grid power will always be available.[/FONT]

The MPPT controller reduces the voltage and increases the amps to what the battery bank needs while the PWM chops the power to fit the battery but wastes what is above the battery bank charging voltage.

mac

lkruper wrote: »

The MPPT controller reduces the voltage and increases the amps to what the battery bank needs while the PWM chops the power to fit the battery but wastes what is above the battery bank charging voltage.

OK, that's good to know. I assume then it's best to match them as close as possible for best performance. That Midnight Solar look like it will scale well and handle my needs and isn't a throw away when I expand.

lkruper

mac wrote: »

OK, that's good to know. I assume then it's best to match them as close as possible for best performance. That Midnight Solar look like it will scale well and handle my needs and isn't a throw away when I expand.

It's best to use matching panels which is one good reason to buy panels from companies that will be in business years from now for warranty purposes.

bill von novak

mac wrote: »

So what would be the optimal configuration of panels - charge controller - inverter and batteries for a 48v system?
Minimal price is not the goal but a well balanced DIY 48v system is.

I wouldn't bother with the "well balanced system" part; your system won't be well-balanced; it will be an experimental system. I'd start with cheap batteries (T105's are pretty cheap) because you'll quickly destroy them. Most people do. I'd get some big-name panels (Kyocera, Sanyo) since it will be easy to match them later. Might as well also get a good charge controller like an FM60 or Midnite Classic since they are very reusable.

For what you want to do now you can go with a cheap inverter and separate charger. A better inverter like the Outback FX line is nice but pricey, and since you aren't sure what you want to do with the system yet you will likely end up with more inverter than you need. Spend the money on a decent battery monitor like the Trimetric or the Flexnet. (The Flexnet isn't all that accurate but is probably OK for what you want to do with it.)

Overall I'd treat the system you are putting together as a learning tool; you'll probably destroy the batteries pretty quickly but will learn about them in the process. It will help you make better decisions about the next system you buy. Try not to get too attached to anything you buy now - even if you buy an "expandable" system now it is very likely you will throw out (or sell, or trade) a lot of it as you learn.

mac

bill von novak wrote: »

I wouldn't bother with the "well balanced system" part; your system won't be well-balanced; it will be an experimental system. I'd start with cheap batteries (T105's are pretty cheap) because you'll quickly destroy them. Most people do. I'd get some big-name panels (Kyocera, Sanyo) since it will be easy to match them later. Might as well also get a good charge controller like an FM60 or Midnite Classic since they are very reusable.

For what you want to do now you can go with a cheap inverter and separate charger. A better inverter like the Outback FX line is nice but pricey, and since you aren't sure what you want to do with the system yet you will likely end up with more inverter than you need. Spend the money on a decent battery monitor like the Trimetric or the Flexnet. (The Flexnet isn't all that accurate but is probably OK for what you want to do with it.)

Overall I'd treat the system you are putting together as a learning tool; you'll probably destroy the batteries pretty quickly but will learn about them in the process. It will help you make better decisions about the next system you buy. Try not to get too attached to anything you buy now - even if you buy an "expandable" system now it is very likely you will throw out (or sell, or trade) a lot of it as you learn.

Thank you for your reply.

I was hoping there was such a thing as a well balanced system, or as best one could do.

Interesting about the batteries as that was my one of my main concerns, after reading of so many that did exactly that, foo-bar their batteries. I would rather spend the money on a decent charge controller, as you say they're reusable.

Right now I am having a hard time convincing my SO of putting the panels on a small pole outside my office. So all of this may be wishful thinking. I knew I should have kept my home for these kind of projects, along with big ham antennas. I digress.

I am going to check out the Trimetric battery monitoring system as I think this is one of the more vital pieces for longevity.

Do you have a favored source for the panels?

mac

Would you recommend T105 AGM or the deep cycle flooded?

bill von novak

mac wrote: »

Would you recommend T105 AGM or the deep cycle flooded?

For your first battery set I would recommend flooded. They are far more tolerant of overcharging; you won't lose all the electrolyte if you equalize them for too long. (Or to be accurate you will still lose it, but can add more.) You can measure their state-of-charge with a hydrometer and see them outgassing. You'll get firsthand experience with what happens to other things in the battery compartment. All in all you can learn a lot more from them.

lkruper

mac wrote: »

Would you recommend T105 AGM or the deep cycle flooded?

AGMs cost about 2X more than FLAs and last about 1/2 as long. With FLAs you can measure the specific gravity of the liquid and know exactly the State of Charge. With AGMs there is really no way to know for sure. Being able to add water to FLAs is a big advantage and one of the reasons that AGMs don't last as long. AGMs have their place. Some don't like to store FLAs indoors. AGMs have a much higher rate of charge and discharge allowable than FLAs, but the T105 FLA is a hybrid which has less internal resistance and allows for quicker charger and discharging, however the manufacture still recommends C/10 for charging.

You already have one AGM. Are you looking forward to being more involved with battery maintenance and chemistry? If so, learning to measure specific gravity is a good skill. Get a temperature compensated hydrometer.

BB.

And you will need to look at 48 volt system or some other voltage... Smaller AC inverters tend to be in lower voltages. And depending on your solar panels (Vmp~30 volt are common), you would need 3 in series to get high enough charging voltage for charging a 48 volt battery bank.

There are Vmp~36 volt panels where you can put two in series for a 48 volt battery bank, but they are not always easily available (at a good price).

Suggest that you start with your loads--Then design the system around the loads.

-Bill

mac

Thanks everyone for the suggestions.

mac

lkruper wrote: »

You already have one AGM. Are you looking forward to being more involved with battery maintenance and chemistry? If so, learning to measure specific gravity is a good skill. Get a temperature compensated hydrometer.

The one AGM that I have is used for a UPS emergency backup on my computers and won't be part of the system, should I build it and I will use FLAs.

mac

BB. wrote: »

And you will need to look at 48 volt system or some other voltage... Smaller AC inverters tend to be in lower voltages. And depending on your solar panels (Vmp~30 volt are common), you would need 3 in series to get high enough charging voltage for charging a 48 volt battery bank.

There are Vmp~36 volt panels where you can put two in series for a 48 volt battery bank, but they are not always easily available (at a good price).

Suggest that you start with your loads--Then design the system around the loads.

-Bill

So the output of the panels should be greater than the battery bank?

My loads would be adjusted to whatever the system I purchase provides. If the load is too great, the device will be kept on the grid.

The load that I would like to support is ~ 500w for 6-8 hours.

mac

One of my goals is to be able to get enough battery power for this load value so that they never get discharged below 30% of full charge in hopes to greatly extend their service life. The batteries are the biggest expense and learning how to care for them is critical.

At some point I will incorporate the gas generator so when the power is needed and the batteries are getting low, it is used to charge them and provide power for the load requirements.

mac

If I start with a minimal 3 12v 159AH batteries to give me 48v, how do I calculate the run time to reach the 30% discharge value of the batteries at 500 watts? These batteries will cost $1000 shipping included with 3 yr warranty. 300 complete discharge cycles and 10 year standby.

mac

I found this calculation for a 12 Volt System: to a 50% discharge ???
(10 x (Battery Capacity in Amp Hours) / (Load Power in Watts)) / 2 = Run Time in Hours

10 x 477 / 500 = 9.54 / 2

4.77 hrs

Approximately 3 hrs to 30% discharge rate with no solar input charging and assuming full charge on the batteries. I would assume this accounts for typical conversion losses in the inverter. This is worse case usage to run my office needs at idle usage.

vtmaps

mac wrote: »

If I start with a minimal 3 12v 159AH batteries to give me 48v, how do I calculate the run time to reach the 30% discharge value of the batteries at 500 watts?

First of all, you need 4 (not 3) of those batteries to make 48 volts.

159 amphours X 48 volts = 7632 watthours

30% of 7632 watthours = 2290 watthours

2290 watthours consumed at a 500 watt rate will last 4.58 hours

BUT that assumes no Peukert factor. You will be discharging at greater than the 20 hour rate, so therefore your battery's capacity is less than the 159 amphours that I used in the calculation.

--vtMaps

mac

vtmaps wrote: »

First of all, you need 4 (not 3) of those batteries to make 48 volts.

159 amphours X 48 volts = 7632 watthours


--vtMaps

What the heck was I thinking?

mac

Needed more coffee, or something. I was thinking of the 3 panels mentioned earlier. 4 batteries and 3 panels!

What's the best case for recharging those batteries with 3 panels? Can it be done? If the sun wasn't available and a 3.5kw generator is available to recharge, how long to get the batteries back to full?

Two 36v panels would be better suited in this test setup. I haven't checked the dimensions of either.

mac

With 3 ~ 250w panels it wouldn't be enough to recharge the batteries from the previous day's usage with no sun or generator recharge?

mac

So Two of these LG panels would be sufficient to charge a 48vdc system ? How much above 48v should the panels be at minimum?


System Rating: 260 Watts
Max Power Voltage (Vmpp): 31.1 Volts
Max Power Current (Impp): 8.38 Amps
Open Circuit Voltage (Voc): 38.1 Volts
Short Circuit Current (Isc): 9.05 Amps
Max System Voltage: 1000 Volts
Module Efficiency: 15.9%
[h=2]LG MONO X LG260S1C-A3[/h]

bill von novak

mac wrote: »

So Two of these LG panels would be sufficient to charge a 48vdc system ?

For flooded batteries you want to be able to equalize at 2.5 volts per cell so you'd want to be able to hit 60 volts. With a max voltage at 62.2 volts you are cutting it pretty close, but with a good CC and good (large gauge) wiring you should be OK.

mac

bill von novak wrote: »

For flooded batteries you want to be able to equalize at 2.5 volts per cell so you'd want to be able to hit 60 volts. With a max voltage at 62.2 volts you are cutting it pretty close, but with a good CC and good (large gauge) wiring you should be OK.

Thanks Bill. It looks like I will be using AGM batteries at this point, does that matter? Shipping FLAs increases my costs considerably and any local sources are much higher.

mac

I will look for two panels that output higher voltages, 36v perhaps

mac

Received my Kill-o-Watt meter and found my iMac and Airport Express to be consuming ~ 90w under light load, less than 1/2 WATT I thought With the LCD backlight off it drops down to 60w. Time to measure all my toys.

bill von novak

mac said:

bill von novak wrote: »

For flooded batteries you want to be able to equalize at 2.5 volts per cell so you'd want to be able to hit 60 volts. With a max voltage at 62.2 volts you are cutting it pretty close, but with a good CC and good (large gauge) wiring you should be OK.

Thanks Bill. It looks like I will be using AGM batteries at this point, does that matter?

AGM's generally are not equalized so you can live with lower voltages (57 volts or so for bulk)

vtmaps

bill von novak said:

mac wrote: »

So Two of these LG panels would be sufficient to charge a 48vdc system ?

For flooded batteries you want to be able to equalize at 2.5 volts per cell so you'd want to be able to hit 60 volts. With a max voltage at 62.2 volts you are cutting it pretty close, but with a good CC and good (large gauge) wiring you should be OK.

I disagree.  Two of those 60 cell panels in series will USUALLY not work on a 48 volt bank.  That Vmp of 62.2 volts is at STC, it will be lower at NOCT.   If it can work at all, it might work better with a PWM controller because the PWM controllers need less headroom than the MPPT controllers. 

Even with so called 'true 24 volt' panels (Vmp about 36 volts), there may not be enough headroom for an MPPT charger to charge a 48 volt battery with two panels in series (Vmp about 72 volts). 

Over on the Midnite forum it is acknowledged that sometimes trading in a PWM for an MPPT can lead to performance degradation if there is not enough headroom for the MPPT to function.

If you are using 60 cell panels, put three in series for a 48 volt battery.

--vtMaps

postscript: I see in a later post that you will be using AGM batteries.  That will probably shave a couple of volts off your need for charging volts, but it does not change my advice which is to put the panels 3 in series.

mac

Thanks bill and vtMaps for your suggestions and advice.