Suggestions for 48v PV system

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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 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 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.

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

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.