Solar v2 – choosing the components

Since my first attempt at solar, I have learnt a few things and several new bits of tech have been introduced into the market. Some of the new tech include; all-in-one inverters, bigger “better” batteries, shingled solar panels and micro-inverters…

Time to take the learnings from my first solar project and scale-out

New Parts

An all-in-one solar inverters can include the following functions in a single device;

  • Solar Controller – MPPT (2x string inputs)
  • Inverter – Converts DC (48v) to AC (pure sine wave @230v, 50 hertz)
  • Battery Charger –
    • from Grid (AC -> DC)
    • from Solar Panels (DC -> DC)
  • ATS / Line mode – Flicks over to Grid if solar or batteries are low
  • BMS, Timers and Controls – Can program battery types, priorities and timers depending on how you want to power your loads and utilize your batteries.
  • Stats / Alerts – WIFI enabled

I have committed to an 8kW PV all-in-one inverter. My house doesn’t have a north-facing roof, but it has a NE and NW facing roof which isn’t too bad, the bonus of having 2 string feeds on the inverter means that each side of the roof will act independently without dragging down the total power output.

I’m currently running a few lead-acid batteries on my solar. I’ve been in two minds about whether I continue with batteries or go with a hybrid system that effectively uses the grid as a battery. I ended up deciding to go with batteries one last time, here in NZ the solar rebate is not really worth the effort of exporting – we typically get wholesale prices which can be 1/3 of the cost of power. I’ve also been pretty excited about how quickly the new LiFePO batteries can charge and discharge, so I’ve committed to a couple of 48v PylonTech batteries in a stack, totaling 7kWh.

Us3000 48v/74ah 3.5kwh Lithium Battery Solar Battery Pylontech 48v  Residential Battery - Buy Pylontech Us3000,3.5kwh Lithium Battery,10kwh  Lithium Battery Product on Alibaba.com

They can peak at 100A (15s) but the recommended rate is 37A each. At 48v this will give me a charge / discharge power rate of 3.55kW (37A x 48V x2) in total. In some cases it may be beneficial to charge with cheaper off-peak power from the grid.

Singled solar panels are pretty nice, with more surface area and better resiliency. I found a 480W mono Hyundai panel which I’ll use to build 2 strings of 4 panels. In total, this gives me 3.84kW (480W x 4 x 2)

In terms of power, for my next venture I decided to stay with the more traditional DC solar panels. There is however another choice thanks to the introduction of micro-inverters. These little devices convert power on each panel direct to AC, which includes several advantages (higher voltage, operate in parallel (independent of other panels). Each also has its own sensors if you want to see stats!

The next sections – powering things, ROI, the build, safety

lead acid battery “state of charge” chart

Lead acid batteries do not like being completely discharged. I have used the following chart for reference, in most cases i only discharge my battery to 50% DOD (depth of discharge).

Even deep cycle lead acids life (max charge cycles) will be extended if it is not completely discharged. It is also generally recommend to completely charge your battery after use – i.e. take the battery back to full charge in a single cycle.

My battery is a deep cycle 24v bank, so i generally only discharge (under load) to about 24.0v (see ATS post)

ATS – 24/7 power loads on solar!

By hooking up my ATS in my solar system, I’m nearing the end of my solar experiment. I cannot recommend the ATS (automatic transfer system) more, such a brillient device.

By installing the ATS i am keeping my solar power generated off grid, but with on grid backup for any loads i attach to it. Also keeps me away from any danger introduced by back filling the grid

So i can run a 24/7 load which will automatically flick over to main power when the batteries are low. At the moment i am powering my attached server (the load) approx 33% of the day. I could power my server for longer if i had a larger battery attached to solar. Its currently winter, so sunlight hours are also limited.

Check out this video for more – https://www.youtube.com/watch?v=ni0A_ZdH7aU.

ATS on Ali Express – https://bit.ly/2O63Hq4

I’m running a 24v lead acid (yuck) battery. I have setup the LV (low voltage) cut over to 24.0V. Keep in mind that under load there is a voltage drop so when the ATS flicks back to mains the battery actually jumps back to about 24.5V (over 50% DOD).

My HV (high voltage) is set to 29.0V, this is voltage when not under load. Again lead acid batteries like to be fully charged, so i have to take this quite high to ensure longer life of my battery.

Note : Running UNRAID server also helps, each disk while not being used will power down reducing my power draw. The unique RAID also means that all disks do not need to spin up on data access (non distributed parity). Friken cool!

Disclaimer : This dabbles with high voltage, please do NOT attempt install without certified assistance. Electricity is dangerous!