Some lessons I have learnt over the last year after having to replace one or two components…
- Save now, and you will replace later. Also, you need to decide if you want a full system to power everything, or just want something to power the lights and some essential equipment. Changing your mind later can mean completely replacing the inverter.
- Try go for 24V or 48V as it is more efficient, and the cabling is cheaper too. So buy batteries in pairs so that you can create a 24V system. Four batteries in parallel or four batteries in serial still give the same storage capacity. But 24V will allow cheaper cabling costs and better efficiency.
- If you want remote management, make sure what system each device can report to. It won’t help to buy one Victron inverter but use an Ellies solar charge controller as you will have to go to two or three places to look at what is happening. I’ve moved all my components over to Victron now as the remote monitoring and dashboard views are great to use (my opinion), their engineers are also very responsive, their code is open source, and they are involved with beta testers.
The heart (and biggest expense) of your system is the batteries as they determine the ultimate storage capacity, can be very expensive and need to be replaced sooner than other components:
- You only get to use 50% of the stated capacity as you should not run the batteries down to below 50% (for lead-acid) – so a 300Ah battery capacity is going to give you 150Ah of real use.
- Work out what you want to power – the max load (peak) at any time, will determine what size inverter you need. The total amount of power used during the night for everything with some spare left will determine what capacity of batteries you need.
- Lead-acid (and AGM) is fine for backup or UPS functionality, but if you intend to cycle the batteries down to 50% daily, you will need better batteries. You will need deep discharge batteries. Without deep cycle / discharge batteries, you have to keep those batteries charged at 100% for emergencies (like a UPS) and won’t be using them for overnight use. It must state Deep Cycle on the batteries. The newer Lithium type technology batteries will allow the system to use far more of the stated capacity without such ill effects. So for example a 100 Ah lead acid will only have a usable 50 Ah (50%) capacity usage, whilst a run-flat type LiPo battery can use it’s full 100% capacity ie. 100 Ah. So whilst both batteries are listed as 100 Ah, the lead acid is not really 100 Ah usage at all. So do not just compare price against stated capacity.
- You can wire batteries in serial and parallel to get your 24V and enough capacity – but total capacity is determined by the total number of batteries you buy.
- You are not supposed to mix different capacities, brands, and old/new batteries, otherwise, you stand to kill your newer batteries. So try to buy the right number to start with.
- Don’t connect the inverter and solar charge controller all to a single battery’s terminals. Connect their negative to one battery, and connect their positive to a battery on the other end of a parallel setup – this spreads the load more evenly across a parallel setup.
- Consider also where you will store the batteries, as their lifetime as well as performance is affected by temperature (extreme cold as well as heat). Batteries will likely need to be changed after 7+ years.
Solar panels can also be wired in parallel to get more current, and for a 24V system you can even put them in serial to get 24V. You need to buy enough so that it can run your daytime usage (normal current used for a sunshine day, plus to charge your batteries. So four 120W panels are charging my 300Ah batteries and running other stuff in the day. But 600Ah batteries will likely require 8 panels. Obviously, an extra panel or two is going to help on overcast days. Panels are normally good for at least 20 years and will just start to degrade in performance over time. Newer panels also generate even more power, so my latest panels installed in 2019 are 330W rating each.
The solar charge controller regulates the power from the solar panels to be safe for the system and the batteries:
- Luckily they are often dual 12/24V output so you only have to consider their maximum Amps and Volts they will handle, and the type of controller. Of course when I moved to 48V I had to replace my previous charge controller too!
- Maximum Amps will determine how many solar panels you can add to it (look at the maximum output of the panels). This also means if you want to add a few panels later, you may have to also replace your charge controller if you did not buy one with enough capacity.
- Maximum Voltage input is important because it also determines how many panels you can connect in serial (as the Voltage is higher, which is more efficient and cheaper cabling again).
- The PWM controllers are cheaper but are also slower to respond to partly cloudy weather so you lose efficiency (as clouds come and go over the panels). The MPPT controllers cost more but are much faster and more efficient (and recommended that you wire the panels in a 24V configuration for MPPT controllers, as they will start charging quicker in the mornings).
The inverter converts the 12V or 24V battery voltage to 110V or 220V for use in the house.
- They are often a set input voltage (12V or 24V) so your battery setup helps determine this choice and then you stick with it unless you want to replace the inverter later on.
- Continuous power rating (in Watts) – this is the constant load it will support. In my house, the LED lighting, a pond pump, lounge TV, a computer, and the Internet modem and router all draw about 300 Watts at 220V. But kettles, geysers, etc are going to be at least 2kW each and remember they can run together. Someone did say that electricity is not the best way to cook and heat – and gas may actually be better for them, which lowers the cost of your solar system (requiring less peak capacity).
- The peak power rating (this handles short spikes like for a fridge motor switching on – if not high enough, a fridge will trip your system). So often you will see 600/1200 as a spec which implies 600 Watts continuous power and short peaks of 1200 Watts can be handled.
- You get standard inverters (just invert the power to 220V) and you get inverter/chargers (where the latter will also supply from 220V grid to charge the batteries on say cloudy days, and they will often also act as an automatic UPS where they will switch to batteries if the grid power is off, or vice versa. It all depends on the battery type and how the inverter/charger can be setup and programmed, so it is worth discussing these expectations to be sure of what is possible. The Victron I use allows for quite advanced programming in this regard, so you can mix the various inputs.
- You do need a registered electrician for any 220V that connects to the house. Get an electrician who has experience with solar as, from the above, you will appreciate there are nuances over and above what an electrician knows about 110/220V systems.
- You do want a separate distribution board installed so that any circuits running from the inverter, are separate from any direct grid fed 220V circuits.
- If you are mixing grid and inverter power, you may find that some of your plugs and lights share common negative, and these will need to be separated by the electrician.
- You do need to have fuse/isolator switches fitted to isolate power from the solar panels, from batteries, from inverter, and also for any power going into the sub-DB.
- There is also usually a switch fitted to select between inverter and grid power supplying the new sub-DB so that if there is any fault on your solar setup, you can switch to just using normal grid power to those circuits (in other words a full bypass).
- ALWAYS also first consult your local authority, as in my case they only approve certain inverter makes and models for grid-tied systems. This meant I had to also rip out and replace my inverter (luckily I quickly found a buyer for it) even though it was the same brand.
With systems like the Victron you may also want something like a Color Control GX (CCGX), which is essentially small Linux computer with a status display – it pulls the data together and transmits the data to Victron’s cloud (where you can monitor it remotely or have alarms sent to you). Some individual devices will connect via Bluetooth devices but a single central monitor is better.
I hope these tips will help newbies before they start out, to ask the correct questions when planning a system. If anyone else has additional tips, or corrections, please add them in the comments.