rectangularBuilding

OK sounds good. I was thinking too much about my 4 kW sustained inverter.

Just a reminder, the geyser will (or at least should) not involve the inverter or the batteries no matter what kind it is. For the air conditioning it would be very helpful to have an idea how much is consumed during (future) solar production and how much would be on the (future) batteries. And preaching again: You can start small with the solar modules and the batteries and add more as you learn. But your current 15 kWh daily are an OK baseline even if you're currently in a flat. If we only knew how much of that is AC.

Never mind, I misunderstood you. You wrote cells, not battery. I can't delete my last reply. Edit: We also typed at the same time.

Looks like this is just the voltage that the BMS uses for sensing the wake-up. Surely, internally the cells are above 12V (assuming it's a 12V block) or what do you think?

Thanks. The main motivation for my topic was the permanent sleep mode. Either send in the battery or cut the enclosure open. Can't say I regret it. It was easy to do and BlueNova could still have refused the warranty, claiming abuse.

I hope this might help someone some day. I use this battery for my touring bakkie. But it's a new build and I was only in the testing phase. When left alone, the battery had gone to sleep numerous times and I always woke it up, either by bridging the terminals with the included 6.8 Ohm resistor or by connecting a charger. Normal behavior of the BMS. One day, after I think three months of inactivity, it didn't wake up. I thought I had disconnected everything but I believe a temperature sensor that I had forgotten drained the battery a little more each time it woke up. Some emails later, BlueNova support concluded that the BMS was in "permanent sleep mode" and that I should claim warranty. Then I learned that this would involve me paying for a courier no less than four times. From my town to the seller, from the seller to BlueNova, from BlueNova to the seller and from the seller to my town. I'm in Namibia. Voltage on the terminals was 3.8 V at this point. I looked at the battery and removed the maintenance plug on the right side. There is a connector below the hole labeled PC2, with pins A and B. I measured the voltage between these pins and saw 0 Volts. I shorted the pins hoping to wake up the BMS. I cut a rectangular hole into the battery enclosure (remember the 4 courier fees) to see more of the BMS. BMS uses two stacked PCBs. BMS is labeled XT4BA0971. You can't find this string on the internet search. I now had access to the internal cells voltage. Disappointingly, it was also only 3.8 V. LiFePo can be damaged below 2V per cell (8V) but 3.8 V should not totally kill it. I applied 13 Volts to the internal negative wire on the BMS using a lab supply limited to 2.5A. After about 30 seconds, the voltage was 8 Volts and I guessed the BMS should be awake. I connected a Ctek 7A charger to the external terminals and charged the battery fully. After two full charge and discharge cycles, I got 1.2 kWh out of the battery and 96 Ah with a 180-140 Watt load. No idea what a new battery should deliver. Either my battery has degraded by the over-discharge to 3.8 V or the battery specs are too high. Low-voltage disconnect by the battery was at 10.7 V. I am guessing that BlueNova could wake up the BMS on the PC2 connector but I'm sure they wouldn't tell anyone how to do it. Also, "permanent sleep mode" seems to be a non-standard term and sometime I want to research if other BMSs have this feature. Anyway, I plan to continue using the battery now. It's good enough for use.

78 kWh seems about 10x too much for a residence excluding room heating or room cooling. Although I don't know what daily "pool" consumption is and do you mean swimming pool? What is "cooking AC"? Cooking air conditioning? Don't you have existing electricity bills? My daily consumption is about 6 kWh per day but it's a one person house. A small fridge uses about 1 kWh per day. Peak power on all those appliances that cycle using thermostats has not much to do with daily consumption.

OK good to know. Without myself having any experience, Bosch claims that their heaters need especially low pressure to switch on (and presumably stay on) and provide stable temperature. Example: Bosch WRD11B23 11 Litre Battery Ignition NG Gas Water Heater, https://www.sustainable.co.za/bosch-wrd11b23-11-litre-battery-ignition-ng-gas-water-heater.html I was once very impressed with an electric Stiebel inline heater in a guesthouse. Stable temperature. I vaguely remember it might use 5 kW. Too high for solar but just an example of instant heating. Benefit obviously not needing a giant water tank. Edit: Small Stiebel electric inline heaters seem to start at 11kW.

I just "discovered" the LPG tankless (inline) water heaters. These seem to be extremely cost effective once you have committed to LPG. Are these just great or are there problems?

Sorry, no experience with any of the PV geyser kits. They just might use 24 V panels rather than 37 V. They might say no to dual-purpose panels because of liability and warranty. I can not provide a sure solution. I just mentioned an experiment that I would try. Under the roof solar geyser is possible and can be done with thermosiphon effect. But you would worry about leaks or overflowing catch trays and access for maintenance would be hard. It would keep the geyser warm, which is good.

I had my geyser wall mounted (outside) opposite the bathroom and it took five seconds for the hot water to arrive in the shower. Wall mounting keeps the geyser warmer because there is less wind. I could hot shower all night long and had usually lukewarm to pleasant water in the morning, depending on previous day usage and night temperature. Wall mounted geyser means you either need a circulating pump for a solar collector on the roof or you use PV power to heat. I had a circulating pump hoked up to a tiny 15 Watt panel but the constant hum of the pump at various pitches drove me crazy. This sound goes through the pipes and walls, not primarily through the air. Structure-borne sound is extremely hard to get rid of. It was the best and most expensive pump available. I had to get rid of the whining pump so I moved the geyser from the wall onto the roof so that it is higher than the solar collector. In that case, thermosiphon effect is available and the noisy pump is unneeded. Then I installed thermal lagging onto all the pipes (PEX, and copper only near the geyser) and two, not one geyser blankets. Now I have huge amount of hot water day and night and lukewarm to pleasant water in the morning. Hot water now takes 15 seconds to arrive. If I had photovoltaic geyser heating, which notably does not involve an inverter nor a battery, I could move the geyser back to the best spot, the outside wall. Those PV geyser kits seem overpriced because you only get two or three panels but they make you buy a controller box and a MPPT box. If I had to do it again, I would try a normal geyser and 6x PV panels in series connected directly to the standard heating element. The voltage is about right and the loss because of lack of MPPT is more than offset by money savings. Then I would make these 6 panels available to the main solar system with a switchover. But this would be experimental and is not sure to work. If it wouldn't work, I would get a solar upgrade kit for the standard geyser. Then the financial risk would be low because I needed 6 panels anyway and the standard geyser could be used. I'd rather have 30 meters of wire than 30 meters of pipe by the way 🙂.

Thanks for quick reply, that's motivating. About cooking, be sure that it really takes those giant kWh values for a big meal. These hot plates have high peak consumption but they cycle on and off, same with the oven. But I would agree that hot plates (not inductive) and solar are not the best match. Hot water depends a lot on local weather and if the users accept the occasional waiting for the shower. If they don't, they're spoiled brats 🙂. In my super sunny region, I have a giant surplus of hot water for one person and plenty for two person having long showers. Look, I'm running a mini kettle, toaster, and a mini pressure cooker in my touring bakkie every day and I could easily run a microwave if I had space. I'm also running a heating blanket on the lowest setting all night long. But I'm not claiming that this stuff is cheap to do. I'm usually not posting on forums a lot at all so I'm not sure what possessed me this time. But don't let that bother you. Best regards.

A year ago I built my first house and my first solar system which is off-grid. I'm writing this also for my own reference so don't be offended if it's all said before or if the post is too long. Just some thoughts: Keep it simple! (As simple as possible, but not simpler 🙂). Start with a big inverter and solar charger for future proofing. Be sure to have monitoring of state of charge, solar production and AC consumption with graphs. Start with the bare minimum of solar panels and battery capacity. For a new install, Lithium and 48 V is nearly mandatory. Make sure that on your roof, more modules can be installed easily without moving the existing ones. After having moved in, learn your usage patterns. See if you can adapt your usage to what's available during day and night. If you can not adapt, add modules and batteries as needed. Increase solar production until you get 100% state of charge before sunset most of the time. (Depending on weather patterns). Increase battery capacity until you get a comfortable, not too low SOC (state of charge) before sunrise most of the time Long term high power loads at night are the most difficult. AC or heating. Every degree less of AC or heating for a full night makes a big difference. Use as little cooling or heating as you can bear, then determine the kWh needed and add battery capacity as long as it makes sense. The cost of battery power per kWh is important but it must be related to the cost of the whole house. If you have a luxurious or large house, it does not matter if you spend a 20'000-40'000 ZAR on more batteries. I would hate to juggle gas bottles for the rest of my life. If still designing the floorplan, put your sleeping room on the shady side in the afternoon. Rooms in the same house can vary a lot in night time temperature. Find out if you can build a cooler roof than standard. I distinguish 4 kinds of loads: Low power, short duration: TV, music. Irrelevant. Low power, long duration or always on: Alarm, cameras and NVR, phone and notebook chargers. Base load. High Power, short duration: Microwave, electric kettle, bread making machine, toaster, electric pressure cooker, induction counter-top hot plate, washing machine, hair drier. Stick welder. The electric kettle, electric pressure cooker, microwave and induction hot-plate are extremely efficient. See if you can move some of these into solar production hours. High power, long duration: AC or heating. Comfort vs. battery cost. If I had solar panels for geysers, I would surely make them switchable to the main system. If your water is fully hot by noon or sooner, might as well use that solar production elsewhere. I can't imagine two different orientations for the panels to be more good than bad. Simplicity means quality of life. AC or heating means quality of life. Both can be a luxury worth money. The garage is only semi-secure. Normal garage doors are easy to pry open. Burglars will steal your entire solar system if nothing stops them. It would be not trivial to come up with a secure garage door. Consider security and fire hazards in your planning. Personally, I would not enjoy having three separate solar systems (two geysers and the house). What I did: - I bought expensive Victron inverter and solar charger because I hoped for above average reliability and durability. I wish I knew which of the less expensive brands are also good and reliable. - I bought a high power inverter because I wanted the ability to stick-weld. - I bought the bare minimum of 6x 300 Watt panels because we have extremely reliable sunshine in desert Namibia. That turned out to be more than enough. A local solar salesman wanted to sell me 18 panels, lol. - Bought 7 kWh of Pylontech batteries because I thought 5 kWh Lithium to be the bare minimum and the next size modules were not much more expensive. - Without any special projects, I get average of 50% state of charge each night. Lowest I ever had was 10% after two exceptionally dark days. - I get 11 kWh of solar production daily, half of it unused most days. - I run heaters in the cold season, but for now only during solar production and only for one room on modest power. - I'm going to add another battery (total of three Pylontech, 10.5 kWh) to have modest heating power all night and to have very shallow charge cycles when not heating. - My solar equipment is in a semi-strong-room along with the camera NVR and alarm system plus two safes for documents and pistol. Burglars should not be able to snatch the NVR easily. The top of the room has steel mesh. I built my own strong doors of steel with the help of a welder. Our local neighborhood watch reports fairly frequent burglaries but fortunately (almost) no home intrusions with people inside and assaults. The strong room provides some fire-separation. - My cooking and washing just don't make a serious dent in battery capacity. But I make simple meals and I have efficient appliances. - I don't run a fridge and having no TV is great. - My house is exactly rectangular and includes the garage. Trespassers can not sneak up without being captured by four cameras and they can not hide behind anything. - My bakkie including touring equipment cost more than the house. - I aligned the house exactly east-west for the solar panels. I specified a steeper roof than normal, 25%, exactly north facing for better production during the winter. This was silly though because the difference is small and solar panels are cheap. - My geyser is working with a 2 square meter water solar collector but I regret that. It took me three attempts to get the piping right myself (plumber was an idiot). I should have used a normal geyser and more solar panels that I can switch over between water heating or battery charging. It's working fine now though. - A geyser placed closely to the kitchen and bath will give much quicker hot water. Question: How many kWh does a stove and oven combo consume for a big cooking event? With my simple cooking, I just don't consume much at all.