On 27.05.19 20:44, Chris Albertson wrote: > The low volts significantly raise the cost. I remember buying wire (some > years ago) for a system on my sailboat and paying $5 per foot. > > OK, I just looked up the cost of wire that is suitable for a 4KW low volt > system. Home Depot sells a 12 foot run of black and red #0 wire for $93. > That is less then what I paid but the quality is not as good. And then > the size of the bus bars and the switches and fuses is also huge. Every > time you double the volts you about cut the cost of the parts in half. > until you get to about 400 to 500 volts and then you can use normal house > wiring.
Chris, what seems to be missed here is that a whole house only needs 2 or 3 metres of high current 48v wire - from the battery bank to the inverter/charger. That unit has standard 4 sq. mm PV cabling (1kV rated) up to the roof, and standard 220v mains wiring around the house for power and lights. It-is-only-the-battery-which-is-at-48-volts. Why? Because every man and his dog sells 48v battery systems for on- or off-grid solar. (Yes there are one or two at higher voltage, but they are the exception, and usually offered as integrated battery & inverter systems, depriving the user of system flexibility.) Even funny technologies such as saltwater, NiFe, and ZnBr redox are 48v. Why? Because the currents are inefficiently high at 24v, so dozens of vendor supply 48v inverters now, in the shop, on the net, delivered to my door. > Electrocution risk? We assume you are a skilled electrician or can afford > to hire one. And then after installation, the ENTIRE system is inside a > grounded metal cabinet that is locked. You don't leave something like > this on a bench with wires exposed. The regulations do not permit that, at least down under. > As it turns out for tiny system of a few KW the cost is low no matter what > you do. But if the goal is to power an entire house then you have to > design carefully to contain the cost. And if you go off-grid, so have to add batteries, thereby buying into the low voltage issue, then good luck containing cost. Good batteries with a long life are not cheap. > You find that it is hard to buy the parts for the price of a Power Wall. > In fact, you can't unless to luck into some one-time deal with salvaged > parts The problem with the Power Wall is that usable capacity is significantly less than nameplate capacity on day one, then decays like a laptop battery after that. While it's to hand at a link I think I've posted upthread, here's an independent appraisal: "In comparison, the Tesla Powerwall is a 6.4 kilowatt-hour battery and only 5.44 kilowatt-hours of that is actually warranted to be usable. But after the first 2 years that drops to 4.6 kilowatt-hours. And 3 years later it drops down to only 3.8 kilowatt-hours of warranted storage. So after 5 years it would take 3 Tesla Powerwalls to have the same warranted energy capacity as the ZCell." From: https://www.solarquotes.com.au/blog/redflows-zinc-bromide-zcell-battery-may-have-the-edge-over-lithium-ion/ These guys make a living from their reputation for telling it how it is, and are regularly quoted by our national TV broadcaster. (They're quick to update/rectify if there's a slip-up, and we post more current info.) We've been over the durability issue upthread, so I'll limit repetition to that. Erik _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
