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 300 Ah battery capacity is going to give you 150 Ah of real use. In fact, if you regularly run your lead-acid batteries down to 50% or even 65%, expect only about 3 years of useful life, before it drops the power whenever anything like a kettle gets turned on. With Li-Ion, or better still LiFePO4, you can use right down to 0% of the stated capacity. So bear this in mind when deciding on capacity versus price.
- 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 LiFePO4 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. In fact, for lead-acid batteries even running down to 50% is not ideal, as they they prefer to stay in a fully charged state (more like UPS batteries). So after three years I was finding I had to set them for a minimum charge level of 80% unless the grid failed, and even with that setting, when they dropped to about 75% they sometimes tripped the power if I put something heavy on like a kettle. On a steady usage of about 800 W they had seemed to be carrying the load OK down to 70% charge. But it was clear that the lead-acid batteries lost their usable capacity quite rapidly.
- You can wire batteries in serial and parallel to get your 24 V, or 48 V, 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, or even less if you’ve run them harder (ie. to lower charge levels, or with heavier draw appliances such as kettles, heaters, etc).
- In conclusion on batteries, and considering now the lower cost in 2022 of LiFePO4 and similar Li-Ion batteries, it is honestly a better proposition to go for the Lithium based batteries. The Lithium based batteries cost only slightly more than lead-acid, but give a good 3x the usable capacity, and often have a 10-year guarantee with 4,000 full cycles, vs lead-acid that will probably only last 3 to 4 years (load shedding really ages lead-acid batteries more quickly than usual). In 2019 Lithium based batteries were a lot more expensive so it was a compromise many of us made with lead-acid batteries.
- I’m currently using a 10.7 kWh Balancell LiFePO4 battery (made in Cape Town). It has intelligent battery management built-in to manage minimum and maximum charge levels, temperature, etc.
Solar panels can also be wired in parallel to get more current, and for a 24 V system you can even put them in serial to get 24 V. 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 120 W panels are charging my 300 Ah batteries and running other stuff in the day. But 600 Ah 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 330 W rating each, and in 2022 single panels are often now 400 W to 500 W 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 12/24 V 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 48 V 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 24 V configuration for MPPT controllers, as they will start charging quicker in the mornings).
The inverter converts the 12 V or 24 V battery voltage to 110 V or 220 V for use in the house.
- They are often a set input voltage (12 V or 24 V) 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 220 V. But kettles, geysers, ovens, etc are going to be at least 2 kW each and remember they could run together at times. 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). But bear in mind too that gas does give off fine particulate matter so is not the healthiest way to cook indoors. Induction top stoves are the lightest current draw, and most efficient way to cook. But be sure it is a proper induction top (requiring specific metal-type pots and pans), and not just a glass top stove with elements inside. I decided not to have the geysers on the solar/battery power so I am getting away with a constant power rated inverter of 5kW.
- A tip for higher draw devices like a geyser or oven, is to consider having a 3-way switch fitted on the distribution board. I did this for our oven so the oven can be switched of, to battery/solar, or to mains grid power. In this way your geyser could run off mains by default, but there is an extended blackout, you could temporarily switch it to solar/battery to use it. In my case the oven defaults to solar/battery but if there is excessive load on the battery, I can switch it over to use grid power if available.
- 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 220 V) and you get inverter/chargers (where the latter will also supply from 220 V 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 Multiplus II inverter which I use allows for quite advanced programming in this regard, so you can mix the various inputs. It can be programmed any way you want, but I went for a priority for using solar power if available, then switch to using battery until it runs down to 35% (it’s the LiFePO4 battery, and then revert back to using grid power. If there is a grid outage, or load shedding and no solar, the battery will continue to run down to 0%. As soon as the grid power is restored, the inverter/charger charges the battery back up to the minimum of 35% capacity, unless there is solar as then the solar will charge it up to 35% or all the way to 100% if enough solar.
- You do need a registered electrician for any 220 V 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 110/220 V systems.
- You do want a separate distribution board installed so that any circuits running from the inverter, are separate from any direct grid fed 220 V 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.