24v (20 x 1.2v NiFe 250ah) batteries - many questions - experienced info or opinion appreciated

paul29690

Hi everyone,
Why would anyone who knows so little about solar in general and NiFe batteries in particular choose this battery type? Well it's a long story but after lots of research on the principal of NiFe batteries and the history, I was sold! I was researching because someone I met had the 20 batteries and the chemicals, cables etc for sale for a very good price in relation to new from a supplier, about 1/3 the price, it was too tempting to pass over. We were already planning to build an eco house on land we already own, location is Cussac 87150 France.

So far my research has led me to a 3 to 4 kW solar array 10º east of south at a height and angle optima of our location. So placement is fine, batteries are in stock (may need to source replacement chemicals as the ones I have are 5 years old, like the batteries although all are unused). So now I need recommendations, preferably from an experiential or knowledgeable standpoint although I welcome discussion in general too.

I'm concerned about the panel output in relation to NiFe charging requirements and which charging unit and inverter I should install to service reduced household requirements but include an average sized AAA fridge/freezer and probably a second small freezer along with the usual lighting and media requirements. We will probably need to power a washing machine and 1200w vacuum cleaner although these would be used during daylight hours only and could be reserved for the better sun days in the wintertime. Importantly I should say that this is an off grid system though choice. Other issues such as cable sizing, our panels will be within 5m of our ancillary equipment (inverter/battery bank etc) but the house is 30m from the inverter. I want to use as much 12/24v lighting etc as possible but the rest is likely to be 230/40v ac at 50Hz.

I'm sure someone will ask for more detail and I'm happy to oblige, any help would bevery much appreciated.

Thanks in advance, Paul

myocardia

Hi, Paul. We have had more than a few threads about NiFe batteries over the years, but this one is the one with the most replies:
http://forum.solar-electric.com/discussion/14736/compare-nickel-iron-edison-batteries-and-chinese-ni-fe-cells They seem to be very hard to use, because of how huge the voltage differential is between fully charged, and fully discharged. Solar electronics are built to be used with lead acid batteries, which only have a ~1½ volt differential between fully charged and fully discharged.

As far as the 100 feet distance between your inverter and your house, that is absolutely nothing for 240V. You'll have less than a one volt drop between the inverter and your the appliance which uses it, and likely much less. One volt is four 1/1000ths of a percent of 240V, and isn't even enough to laugh about, much less worry about. You won't be able to "ship" in 12V or 24V from that distance, though. You'd spend more money on the wiring, than you spent building the house!

To be able to use DC things in the house, you'd need to buy 2 or 4 extra 30V panels, and send one or two strings of 60V DC into your house. Inside the house, you'd need an MPPT charge controller, and a couple of 6V golf cart, or even two of the much larger L16 batteries. 24V lights and appliances, at least in the US, are very few and far between, compared to 12V lights and appliances. Good luck,and let us know how it turns out.

edit: MPPT charge controllers allow charging lower voltage battery banks with higher voltage panels, without losing power. They convert lower amperage, higher voltage to lower voltage, higher amperage, so you lose much, much less power between the panels and the batteries.

Estragon

When thinking about system design, we always first try to nail down loads. You mentioned a fridge/ freezer, and maybe a separate freezer. Is water and sewer a grid item, or does the design need to incorporate pumps for that? Cussac (near Limoges?) is a lovely part of France as I recall, but can be cool in winter. How will you heat.

Once we have a good handle on loads, we move on to batteries to support the load. You are likely to want to use a 48v bank based on what we know so far. The amp hour capacity will depend on how much you want to rely on solar alone to charge it (gloomy days need either more battery or a generator to charge)

Knowing what the bank is, we can then look at how we're going to charge it. Unless you're in an equitorial desert, an off-grid application is likely to need something to supplement solar charging, likely a generator in your location.

Going 10° east of south leads me to ask if there are afternoon shading issues? If so, to what extent will lower winter sun be an issue?

As @myocardia mentioned, running low voltage dc 150m isn't really practical. If you really want to run loads at that, you will want to put the batteries etc. close to the house and run higher voltage dc from the panels. Another way would be to use multiple inverters, with smaller inverters running lighting and other small loads, and bigger inverters dedicated to running refers, etc.

mike95490

I run a large NiFe bank, and have for 6 years.  I also have large loads (about 7Kwh winter, 15Kwh summer irrigation water)
You need to size the bank to the loads, and assume about 60% charge efficiency.
also plan for a lot of distilled water for replenishment.  I'll have to wait a couple more years to see if the Li batteries really hold up,  My driving factor was poor charging hours in winter, not being able to properly charge lead acid to prevent early death,