Hello.

[Colaman]

A diary thingo? Cool.

Well, seeing as it's here, I'll start using it I guess! So this post is a biggy, leading up to what I'm working on.

I've a block of land (2.5 acres) on a hill near the ocean at Cow Bay, Far North Queensland (EffenQue), Australia. Surrounded by world heritage listed rainforest and national park, about 3500mm a year rainfall. Climate is tropical and generally just has a typical monsoonal 'wet' and 'dry' season. I've plans for a house to go on there - a two storey 4 bedroom pole house that juts out over the slope on the block. There's no power/water/sewage, but curiously, the phone is on. All development has been stopped by the local council, so the only work left is the ones who have already got building permits, like me. Mine expires in 2008, so I've got to get a move on - once it lapses, that's it.

Solar input is highly variable, with a week of overcast conditions seperated by a few days of scattered clouds/sunshine quite likely for months at a time in summer. So the battery bank's going to cop a bit of abuse at times. Probably only abuse it 6-8 months of the year :-D I'll likely put in a decent logging weather station and if it's suitably windy over a 12 month period, I might invest in a wind generator to supplement the solar/genset.

So, after much head-scratching and back-of-an-envelope calculations, I've come up with:

• About 1500-2000W of kyocera 120W panels. 2000W is about the maximum I can fit on the northen sides of the roof. The roof pitch is 14 degrees or so and seeing that I'm pretty close to the equator at 16 deg S, the sun does come from the south by a few degrees or so in summer. I could probably mount panels on the much bigger southern side as well anyway without it being too much of an eyesore.
  
• A MX60 MPPT to match the 72V panel voltage to the batteries.
  
• Twin 2kW 240V outback power inverters, tied together for about 9kW surge and about 100A of charging capacity. And the extra redundancy of twin inverters is always good too.
  
• A 24V 800Ah nickel-iron battery bank (probably). Reasons for this cell type is given in this posting. But it's mainly for it's ability to handle regular deeeep discharges, as that's probably going to be it's main mode of operation there.
  
• A lister 6HP diesel driving a 5KVA alternator, running at 3KVA continuous.
  
• A pentametric energy meter, with shunts wired on inverter, batteries and panels.
  
  

All this is in the ballpark of $45,000 australian to source the bits, plus installation work. The rebate for solar here in Australia was totally oversubscribed and it's been discontinued due to lack of funds. You needed to use an accredited installer to get the funds anyway, so I'll probably just end up installing it myself, with an electrician to do the 240V wiring.

There's little info on NiFe cells around, and I intend to go and collect some decent data. All I seem to find on the internet are either just whispers, a cut and paste of a single 20 year old battery FAQ or references to the original edison battery. The logging spreadsheets I've seen on the site that sells the pentametrics look excellent - you can do a lot with that system. I'm going to try and pin down overall cycling efficiency of the NiFe cells and experiment a bit with charging regimes. For example, is it the last 20% of capacity that causes the ineffeciency when charging? What happens to overall efficiency when you only charge to 80% 6 days a week with a top-off to 100% with the genset once a week? How does a slow charge to 1.5V float voltage without boosting to 1.7V go with regards to efficiency capacity available? Stuff like that. If it all goes hideously wrong with the NiFe cells, I've enough cash/resources to go save up and get a lead-acid set to replace it in a few months.

But anyway, that's a pretty good start for a first diary post :-)

[Flux]

I don't think much of the battery data for lead acid is relevant to NiFe.

Most of the effort with lead acid is directed at obtaining a reasonable life.

In the days when Nife were common they were not often floated. They were generally hammered up to gassing point when power was available and discharged until you couldn't live with the low volts.

Efficiency is low normally and probably dreadful if you mess about keeping them above 80% at all times. If you have enough power to keep them up there then efficiency doesn't matter.

If you have to run a generator I would suggest you do so when you need big loads and charge the batteries as far as you can when it is running. When running the generator it will be more sensible to run big loads direct, not via battery and inverter ( You can do it via inverter on sunny days).

At best I think the overall efficiency power wise for NiFe is below 50%. AH efficiency perhaps 60%.

[PaulJ]

   3500mm rainfall - drool. We've had about 100mm so far this year (North central Victoria) and we're on tank water. Summer is looking iffy, stage 4 restrictions are in force already for those on town water - no outside watering at all, only allowed to wash car windows/lights/mirrors for safety reasons.

   Without knowing the specifics of your location, I would hazard a guess that a hill in tropical FNQ near the ocean would be a prime location for windpower. Just make sure you build/buy something robust enough to cope with the extremes of tropical weather! The logging weather station will give you the numbers on that anyway.

   We live quite comfortably on 700W of solar (half of it on a tracker) and a 2.7 metre diameter windmill (tops out at about 1.4kW, on a windy day it probably averages 400 to 500W). The wind is rarely enough to run the house by itself, but it will often make up for the drop in solar output on a cloudy day. I can't back this up with numbers, but I reckon it cuts our generator run time by at least 80%, possibly 90 to 95%.

   Different climate though, you'll probably get a bit less than me per nominal Watt of solar, a bit (or a lot) more per nominal Watt of wind.

   I did the installation myself back when the rebate was available - it simply wasn't worth going through the hoops to obtain it, the conditions were so strict, and I was using some secondhand parts that disqualified me anyway. Got a licensed sparky to wire the 240V like you're planning to do.

   Good luck, and let us know how the NiFe's go if you use them.

   Paul.

[Colaman]

I think the "hammer with genset until gassing and run them flat" approach is generally what will be happening a lot - with the amount of cloud cover in winter it'll be rare in summer for them to reach float. Might be able to do it in winter a bit though.

Will probably run the genset for 8 hours or so once a week to charge to 100% - will be using all the larger loads then as well. Apart from that, it will usually/hopefully stumble along on solar unless things get bad enough that I can't go overnight without running out of power.

But anyway, the pentametric will tell all I guess :-)

[Colaman]

I actually haven't had a chance to experience any decent rain there yet - I still live in Mount Isa, with 450mm/year rainfall, so I'm looking forward to living somewhere a bit less arid. Once I manage to pay it off I'll pull up stumps and move to the coast.

I'll have to have a sniff around for some decent weather stations and logging stuff. Get some pretty good breezes off the ocean - it's only about a kilometer or so to the beach and it's about 150ft up a hill, so wind power could be a good option down the track. Cyclonic weather might be a bit too much power though :-P The house will have to be built to handle 60m/s wind gusts - about 210kph.

I've an architect and a builder doing all the dirty work in Cairns as it's a little bit out of my way to visit too often at the moment. I gave them a fairly specific rundown on what I wanted in a RAPS - basically, what I've set out here, dictating NiFe cells, twin inverter/chargers, MPPT,etc - they put out a request for quotes, so I'll see what the local RAPS guys up there think. Pretty much every commercial RAPS installer I've talked to has no idea about NiFe cells and wants to sell me sungels or sonneschein(sp?) gels. Which are fine - don't get me wrong - but I think that they might be a bit mismatched for the area. I've a report on RAPS in the Daintree area done in 2003 and one of the major issues is battery damage and sulfation due to undercharging, and generally trying to keep a system operational in such an environment. There's a couple of hundred systems in the area and batteries are a real bugbear, so anything that might alleviate that is good idea. It's a pretty large system and gels running at 50% DoD cost double that of NiFe's running at 100%, so (in theory) the savings in the battery area can be directed towards more charge capacity to offset the lousy efficiency.

I guess I'll just have to see how things go.