Solar Power System Design – Part III

In Part III of Solar Power System Design, I like to discuss the wiring diagram of my new off-grid photo voltaic system in some detail. I disclaim once again: This, following articles and downloadable material to which I link to, shall NOT be treated as advice, instruction or a form of guideline for any sort of power system. The reason why I share my experience with you is basically because I found it difficult to find similar articles that were comprehensive enough. Furthermore, my intention is to offer useful information to anybody who is interested in setting up an off-grid solar power system, so that they can make better informed decisions and understand concepts involved. After all, a sound working knowledge of your off-grid power system is required even if you don’t do it yourself.

My friend Sinclair gave me a hand installing the panels on the roof. This was certainly not a thing I could have done on my own. Other than being given the wrong battery temperature sensor, the system is completely installed and active. The following diagram depicts how I wired the components. I have purposefully omitted details about cable diameters and specifications about fuses, circuit breakers etc., as this is something that will depend on individual power system components and cannot be generalized.

off_grid_pv_diagramAt some stage I will install another DC bus through the shunt to be able to access 24 VDC directly for some appliances. Apropos shunt, another word for it is ammeter, this component is often optional, but without it you cannot measure current drawing into and out of the battery bank. You definitely need one for LixxPO4 batteries though.

I got very confused talking and reading about grounding and earthing, and chose to follow the wiring diagram of the charge controller (rtfm; read the f**** manual) and also ground the chassis of solar panels, inverter and controller. The physical earth is a conductor that I hammered a meter and half into the ground, and everything is earthed via its own line.

I mentioned in previous articles that I couldn’t find any information about possible noises the inverter and charge controller could make, and am glad that they operate so far without making any. The inverter cooling fans will certainly kick in when applying larger loads, but there is no humming or otherwise irritating noises coming from those units.

We also experienced strong winds from southerly directions with gusts up to 50 knots and I was very glad to see the panels not shaking or being affected in another form.

mppt_charge_controller2The charge controller has a battery monitor built in, but requires a shunt to achieve optimal operation levels. Some controllers have a remote monitor which comes very handy if you want to install the controller outside or in a power shed.

inverterMy pure sine inverter can provide a continuous load of 1200 W with  a capacity to handle surge loads of up 2400 W. Inverters are most efficient under full load and as I in general do not require large loads, I chose this one. I’ve seen small chest freezers with peak power of about 150 W and washing machines with about 380 W. I might buy a TV one day, something about 50-70 W. The inverter should, therefore, be able to handle all my requirements.

deep_cycle_agm_batteryI’ve got four of these 6 V batteries in series to provide a bank of 24 V. They are sealed and of AGM type, and their actual capacity can arguably only be tested once I’ve got a chest freezer running for a period.

In the following some manufacturer’s specifications.

Batteries:

  • 390 Ahr C100, 300 Ahr @ 24 V and 20 deg Cel.
  • 475 NZD each (times 4)

Solar Panels:

  • 4×295 W @ 1000W/m^2, two pairs in series
  • Voc=45 VDC
  • Imax=8.65 A
  • Vmax @ Imax = 32.75 VDC
  • 366 NZD each (times 4)

Charge Controller:

  • Power Master SCC 80AM
  • Imax out=80A
  • Imax in=70A
  • Input voltage=16-112VDC
  • Shunt=50mVDC/500A
  • 1100 NZD excluding shunt and battery temperature sensor
  • This component is oversized for my setup but I think it is a good idea to future-proof yourself on the controller.

Inverter:

  • Power Master 1200W 24V
  • Surge Power 2400W
  • Pure Sine Wave
  • 850 NZD

Total cost:

  • About 6500 NZD including all necessary and optional components, wiring, circuit breakers, fuses and so on. I picked the components up myself and can now understand why such a system can cost more than 10000 NZD if you get someone else to order and install it.

And kids, if you are looking for a way to earn money and have your own business, do something in import and export. It is ridiculous how much small connecting bits can cost… I also kind of like the renewable energy trade. So yeah, a clean and straight-forward trade for the future. You can even combine it with import & export…

2 thoughts on “Solar Power System Design – Part III”

  1. Oh Wow!

    So it looks like you have got a decent solar system together Ben. A far cry from the vipers’ nest of the “A”-Frame (see your early posts if you’ve forgotten!). And you might even get a freezer? And a Washing Machine! You are seriously Living The Dream now my friend!

    Sorry the long silence – I have been very distracted by an even bigger project than yours which although nowhere near how we want it is starting to look like something. I can tell you all about it in due course! For now I have a lot of reading to catch up on…..

    This is good stuff – keep it up xxxxx

    1. Hey Paul,

      had a look at chest freezer and washing machine, within my budget and power limitations. So yeah, those and an enclosed decking addition to the new cabin should be, as I like to say – on the start – when you get here. Oh boy, I can see you already lounging on the site doing 4 loads of washing a day, spending quality time with the chicken, eating frozen fish, going for a pick-nick with Amy
      at the million dollar spot and forgetting all about those kingis…

      Project sounds exciting. Yupp, unfortunately, there won’t be much about fishing. Haven’t been out there in two months. But yeah, it’s the
      quiet time anyway…

      And brace yourself, I’ll even install one of the old power systems into the A-Frame for yous. There’ll be lights upstairs and downstairs,
      a small inverter and charging points for phones etc.

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