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| Q25: Some final remarks Finally some find the off grid 240V system is too costly. Getting some $20,000 is hard. Cheaper than commerical quotes, do it yourself. You do not need 500amp/hr Ni-Fe batteries. You need only power for night use. 200 Amp/hr is fine for one fridge, etc. So purchase 200amp/hr batteries, at $4,000. A second set allows you to switch over to them, if you have run the other dead flat on a cloudy or rainy day, or at the wrong time of the day. Do both auto charging and manual charging. One MPPT 100|30 controller for when you go away on holidays, auto is nice :) Add a fuse breaker to limit power in and out to a safe load, say 100Amps. This protects battery from overload charges. Purchase three Victron 1200VA inverters for $1,800. Purchase as many second hand 200W solar panels as you can, say 100 of them, at $50 each, will cost you $5,000, and provide at least 3 amps each, you switch them on until the amps reaches 80Amps. You need to source proper voltage panels, this is hard but not impossible. And all solar panels must be of similar manufacture, otherwise one amp fights another amp in parallel. Since you are manually adding distilled water weekly it's no labour issue to a grassroot person, maintaining the system. This way you get a 240V fridge, as large as you like, a 240 Water pump (700W) and another invertor to run a bore perhaps. Plus you have over in theory 300 amps available on a rainy day, actually they come in at 50amps, but who cares, no more generators, and the second hand solar panels will continue for another 20 years just fine, and the Ni-Fe batteries for 100 years. The total cost is under $9,000. Now it seems OK even to a poor person. Beware of voltage depression or Battery Memory . I suggest once a week you flatten the N-Fe bank to 20 Volts and every day use all the storage you have, so if it's 300 amp/hr make sure you consume every drop every day, and things will be fine. Or with a second battery set, run the first dead flat every day, and charge them ONLY when the cel voltage reaches 1.05V Or if you can't afford a second bank, make sure you run the bank fully flat before sunshine time, and you switch the solar panels on. DUring the day, the batteries are not used, the solar panels are used to run big loads, you only need the bank for the nght loads, from 4pm until 8 am. Make sure you can run the bank dead flat before 8 am, every day. Another saving is you do not need fuse breaker or safety switches, you cannot protect the Invertors anyhow, so do not bother wasting your money. You also don't need a BMV monitor either. And if you get stuck and want advice, just email me. Just remember I am no expert, but have wasted thousands too on learning the experience of the basics. I have just realized that my Solar Trina Solar panels are rated at a working voltage of 34.2 Volts. I am thinking of removing the wiring configuration, and building my entire system into a manual charging system, and keep Victron MPPT solar controllers as an auto back up. I can regulate the charging better myself, for summer less panels, for winter more panels, for cloudy days mlore panels and for cloudless days less panels, a solar controller cannot do all this, as a human can. And all the overcharging will do is remove too much water, but I am adding distilled water every week still anyway, so who cares? Switch on as many strings of current as required to get the batteries for bulk, from 60 Amps to 90 Amps. Come back in a few hours time and get my voltage per cell, if is 1.5 V, than switch some strings off. Come back in more hours time and switch off the strings of current and leave only a trickle running, like the auto Victron controllers. When I am using a big load, such as bore pump, water pump and distillation of water, all this is 60amps, I switch on 60 amps of current, plus another 60 amps and see if the fuse breaker holds. It should, 60 amps going out and 60 amps left passing through the 100 Amp fuse breaker into the batteries. Things to try. What does all this do? It reduces your costing by $3,500. No need for lots of solar controllers. You might keep one MPPT for when you go away on holidays. Hopefully readers will understand how Ni-Fe behaves and how different it is to Lead Acid or Lithium batteries. You also potentially save money. Nickel Iron likes to be worked hard and flogged hard. And every day you must the bank dead flat, to 1.05 Volt per cell, or 20 Volts on a 24 V system.
Or you purchase the solar panels secondhand, but all strings need to add to 30 to 40 amps at 34 Volts. You switch on manually as many strings as you need, summer, winter, cloudy or rainy. You cannot switch them all on, as it goes past the limit of the 100 Amp fuse between the battery bank and your system. But you can switch current greater than 100 amps if you pulling amps away at the same time, ie using a Inverter to run something. The 100 Amp fuse protects your battery bank, so no worries. Manually overcharging your batteries every day, no worries either. Cost for this system? Less than $12,000 If you can source 200 W 3 Amp to what used to be 5 amps when new solar panels at say $20 each A hundred of them gives 300 amps in theory and cost $2000, so you are better off. Just make each is 34V and gives the same amps (test them individually). If you have any questions, email me. This is a grass roots installation, for grass root people. If you seek bigger systems, get a commerical person to expertly do it for you. I expect my current system to run fine for the next ten years. I will design it as the above diagram. Maybe new electrolyte will restore things :) Shalom
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