In an ideal world (one without load shedding that is) the decision by homeowners to go green and save money would be an easy one – install grid tie only and zero your consumption.
But, in South Africa today most consumers are knee jerking and insisting on a hybrid system (with batteries) as they cannot do without power for more than 2.5 hours. Personally I think that they are then pricing themselves out of the market.
Batteries are a consumable and only last for the rated number of cycles given by the manufacturer. Batteries also add cost to a system.
What occurs now is that the consumer asks for a hybrid quote and then faints at the price.
Two main options are normally explored by consumers:
- Grid Tie Only or
It is vital that you examine your reasons for wanting to use Solar Power or equipment:
- If your main priority is not to reduce your electricity consumption but to survive load shedding using technology that is seamless and quiet then use a large solar power inverter with the number of batteries you require to continue your lifestyle. You can always add Solar Panels to it later or use that as a selling point for your home. Solar inverters from reputable manufacturers and installers can carry a 10 year extended swap out guarantee.
- If your priority is to save electricity and ‘lock in’ your electricity price to around R0.80 per unit for the next 20 years then install Grid Tie only and take the pain with load shedding – the addition of a small UPS to run your computer, router and energy saver light will not break the bank and work out cheaper than a full blown hybrid system.
Any battery backup system will consist of the following:
- Main Power Unit: This is what most people understand to be the “inverter”. The power unit, or controller if you like does contain an inverter which is the part that converts the battery power to mains power but it also contains a battery charger to charge your batteries when the mains is connected. Beside this, is a bunch of clever electronics which handle the transfer from mains to battery and back again and usually some form of display to give the user useful information about the system.
- Batteries: This is your “fuel tank”. The batteries store charge to be used when the mains power fails. So basically they are “filled up” or charged by the charger when there is mains power connected and then when the mains fails this charge supplies your equipment until it runs out or until the mains returns at which point they start to fill up again.
A Solar Power Inverter will be hardwired to your Distribution Board and provide power to selected circuits whenever there is no municipal load.
Hardwired units require the services of an electrician to install
Frequently asked Questions
How big an inverter do I need?
Inverters are sized in Watts (power) and the rating indicates the maximum power that it can deliver. So the best way to size your inverter is to make a list of all the things you want to be able to run through it, then write down the power rating on all of the equipment and add all these values together. The total is how big the inverter should be, but always go to the next standard size up. Remember that things like kettles, geysers, stoves, hair-dryers, tumble dryers, heaters, some washing machines, vacuum cleaners are all very high power devices and you should try to avoid putting these onto a backup system.
How many batteries do I need?
The batteries are your fuel tank so the bigger your fuel tank, the longer you can run without mains power. Different Inverter’s have different rated Battery voltage inputs usually in multiples of 12 so 12V, 24V, 36V, 48V etc. This means that the inverter you select will require a minimum number of batteries to get to the input voltage. For example – for a 12V input a single battery will do, but if it has a 96V input then you will need a minimum of 8 x Batteries for it to work. Batteries are rated in Amp Hours or Ah. This is the number of amps it can deliver for 1 hour before the battery is flat. For example then a 100Ah battery can theoretically deliver 100A for 1 hour before going flat. The number of batteries you need is a function of the equipment you want run when the power fails and how long you want to be able to run for.
Which is better – Hardwired or plug n play?
This is more of a personal preference and a budgetary issue but here are some of the pro’s and cons of each system.
Plug n play
These are usually smaller systems so they are comparatively easy to move around
They are usually less expensive than their hardwired counterparts and don’t require expensive.
Using them can be a bit messy as you need to run extensions to the various appliances.
They usually are limited to under 1500W
They have limited charging capability so you can’t put really big batteries onto them.
Hardwired systems can go be daisy chained into really big systems
They are installed in garages, storerooms etc. so that they are out of the way.
This is true seamless operation as the circuits connected to them just keep operating without the need to run extension leads etc. (There is literally nothing one needs to do once they have been installed.)
They can accommodate really large battery banks making very long backup times possible.
They are relatively costly especially when you factor in the installation costs
Installation can be complicated as old houses especially do not have very well defined circuits so isolating specific plugs can be difficult.
Why can’t I just put my whole house onto the inverter?
Firstly it can be extremely costly.
Space is an issue. A system this large requires a lot of batteries which obviously need to be put somewhere.
It would be cheaper to convert your cooking to gas and your geysers to solar or heat pumps than to invest in the extras batteries
Batteries need to be replaced periodically so the fewer you can get away with the lower these replacement costs will be.
How often do I have to replace the batteries?
Batteries unfortunately do not last forever so replacement is inevitable.
Standard locally manufactured batteries can last from 3 to 5 years – provided the batteries are not abused.
All batteries are rated by their manufacturers in cycles and maximum rate of discharge.
How long do my batteries take to recharge?
This depends on how far they discharged during the power outage. If they completely discharged then you will need 10hrs to recharge them to 90% and proportionally less than that if they did not discharge completely. Using an intelligent Solar Inverter will allow you to pre-determine the maximum level of discharge and help preserve battery life.
Do I use more electricity when the batteries are recharging?
For the time that the batteries are recharging you will use more electricity but it’s not much more than what you saved while you were running on batteries so you should not really see any difference on your electricity bill.
I have a 3-phase supply to my house. Are Inverter’s available for this?
There are 3-phase Inverters’s available which are comparatively more expensive than the standard single phase systems.
What if a draw more power than my inverter is rated for?
All Inverter’s have overload protection so you probably won’t damage it if it only happens now and then but try to avoid it.
If the power is out for an extended period, can I recharge my batteries from a generator?
Yes – Hybrid Solar Inverters can accept Generator and other inputs from Solar Panels and Wind Generators.
Can I mount the Inverter outdoors?
How much space will an inverter installation take up?
You will need around 4 square metres of flat wall space for a hybrid inverter plus space for a battery rack.
Can I mount the batteries outdoors?
Yes, but ensure they are out of direct sun and the elements. Ensure that the batteries are at most 3 metres from the Inverter and safe from being pilfered.
More info: Straton Solar
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