Dagoth Ur Does Solar
Solar Enthusiast
Hello everyone!
I have spent a couple months now doing some research on building out a very basic 12v system. My intent is to learn some about solar, and end up with a system that has some utility in the event of power outages, or maybe to reduce my electric bill some by generating power for some appliances like a few lights and a deep freezer.
When I eventually settled on was:
Some further information/my design thoughts:
Some of my questions that I'd love input/sanity checking on:
Sorry if this is too much information for one post, but I'm trying to learn as much as I can. Ultimately, if this experiment goes well, I may consider saving for a proper 48v system with higher PV in and more inverter wattage out in the future.
I have spent a couple months now doing some research on building out a very basic 12v system. My intent is to learn some about solar, and end up with a system that has some utility in the event of power outages, or maybe to reduce my electric bill some by generating power for some appliances like a few lights and a deep freezer.
When I eventually settled on was:
- MPP 1012LV-MS - All in one to handle charge controller, inverter, and automatic transfer switch as it has AC input
- LiTime 12v 230Ah LiFePO4 battery with low-temp charging protection (This model apparently has a 200A BMS)
- 4x 100W HQST 9BB monocrystalline panels
- LiTime 3000W pure sine wave inverter (debating returning this- more info below)
Some further information/my design thoughts:
- I'm intending to ground mount the panels in a south facing area that should have little to no shading. It's possible during some parts of the year a utility pole may end up partially shading one or more panel at certain parts of the day.
- I opted for the LiTime battery due to a mix of cost, and the fact that it has low temp charging protection. This system, in my climate, -should- never really be exposed to below freezing temperatures, but in rare instances it could be possible (likely only ever at night, when it wouldn't be charging anyways)- but I wanted the peace of mind.
- I have the extra LiTime 3000W inverter not for regular use (my system was designed primarily around only having 1000W of continuous max output on the AIO inverter, along with only a max of 500W of charging via solar)- however, I was considering keeping this attached to the system in the event of an emergency. Having power outages happens here more than I would like, and having the ability, in an emergency, to use a plug-in 15A cooktop to boil water and cook food for an hour per day would be nice peace of mind.
Some of my questions that I'd love input/sanity checking on:
- One of the biggest points of anxiety I'm getting surrounding this system revolves around measuring remaining battery capacity. How in the hell am I supposed to do this? What I mean is, everyone states that with LiFePO4, the voltage curve is very flat- I keep reading things like "At X voltage reading off your battery, you might be at 95% capacity, or you might be at 5% capacity and not know!" - I am being hyperbolic here and making up numbers, but how am I actually supposed to sort this out so that I can program my charge controller and have at least a ballpark idea of how much capacity I have left? I would honestly rather discharge down to something like 30% and have my AIO switch loads over to utility to conserve power so that I can float a day or two without sunlight without risking my system shutting down. Any advice on this, or even better, some suggested settings for programming my charge controller would be greatly appreciated. This is making me wish all AIOs and batteries had communication with the BMS!
- Following up on battery questions, I have been completely and utterly unable to find a good answer on this: With LiFePO4, how big of a deal is it if I were to add more batteries (in parallel to increase capacity) in say, a years time? Is the battery wear potentially adding more internal resistance actually a big deal? I have seen answers on this forum ranging from "absolutely do not do it, wastes capacity, unsafe, only use batteries literally from the exact same batch" to "it's okay if it's only been ~5 months" to "it's totally fine, mix and match anything, even different capacities as long as it's in paralell and the same voltage". I understand this could be problematic combining a bunch of random cells if you were building a DIY pack, but is this seriously an issue with a modern battery that is effectively sitting behind a BMS? The idea of being able to throw in more batteries a year from now after I save up some money so that I can have multiple days of battery backup is incredibly enticing to me.
- Considering there is the possibility of partial shading (that I currently can't avoid given space constraints), would it be advisable to simply have all four of my panels in parallel? My understand is, as long as it's within the MPPT voltage range of my charge controller, there's no real downside to this outside of having to buy fuses. Wouldn't this make it such that if one panel is partially shaded, I am still getting energy from my other three, as opposed to series where the entire array could basically output nothing? Am I missing something?
- Following on with another panel question- so long as I don't exceed the maximum PV voltage in on my charge controller (and use appropriate gauged cabling and fuses where necessary) - It's not dangerous to "overpanel," is it? As in, if I ended up with 6x 100W panels while my charge controller only supports a maximum of 500W of solar in, it won't hurt anything to have the six panels, correct? Am I correct that it could offer me advantages in terms of sun position and partial shading to ensure I'm htting my 500W max input as often as possible?
Sorry if this is too much information for one post, but I'm trying to learn as much as I can. Ultimately, if this experiment goes well, I may consider saving for a proper 48v system with higher PV in and more inverter wattage out in the future.
