The power delivered by the sun is free indeed but it cannot be harvested without relatively expensive equipment. Things like solar cells etc makes it possible to use the solar power but they come at a cost. The cost can be recovered over time by savings on Eskom payments. After that you have to budget and save for replacement of batteries and other items that might fail.
If only this was true. Some components of every system needs replacement from time to time. Some items might be replaced due to failure and others due to reaching end of life. Batteries are one of those items that WILL need replacement at a regular interval. The endurance of your batteries will be determined by a number of factors.
1) The life cycle specified by the supplier. This is the number of charge cycles that the battery will endure. There are varied specifications for the varied number of batteries that are available on the market.
2) The number of cycles are in turn dependent on how deep the discharge cycle might be. The more often a deep discharge cycle is applied, the less the total amount of cycles that the battery will endure.
3) The more power you draw from the battery the sooner it will fail.
4) The type of battery has a huge influence on the endurance. The following figures are only indicative as it will vary between products and suppliers. A GEL battery could last from 300 cycles (90% discharge) to 3000 cycles (10% discharge) whereas a Lithium battery could be 3000 cycles to 6000 cycles at 90% discharge.
This must be one of the greatest misconceptions that has caused many people to be disallusioned with solar power and it's usefulness. It's like this, if you have a ladder that is 1m long you can assume that you can use it to get onto your roof. But when you get to the roof you find out that the roof is 3m high. So having a ladder does not mean that you can climb onto a roof. Similirly, if you have a solar system it does not mean that you have infinite amount of power. If you have a 3KW/h system you can draw 3KW's for one hour and no more. If your needs are greater than that, you need a system that is specified to deliver what your needs are. Don't blame the solar system for being inadaquite if it was not specified correctly.
Unless you have spent a huge, and I mean huge amount of money, you can never say that. You need to apply some dicipline and management to your power usage habits. Some of your appliances or machines need to have either Eskom or a generator attached to the system to provide for a higher demand of power. You may have to manage the usage of those items manually.
Going off-grid requires a lifestyle change and a mindset change. It is pleasant though when all the neighbours are wrapped in darkness and your life carries on as per usual. The "as per usual" might not be the same as the neighbour's, but it's a small price to pay to be power independent.
Batteries will need replacement at the end of their life cycle. As lithium batteries will last ten years on average, the comparison is made over a ten year cycle.
The following tables intends to compare the average KW/h cost of a household that uses 1500KW/h's per month. They installed a 10KW system that has a lithium battery capacity of 30KW/h. A similar system using GEL batteries would have to have 60KW/h batteries to compare. The Eskom column includes the sundry charges that appear on the monthly account that is included to make up the full monthly cost from Eskom.
|Lead-Acis AGM||Lithium-ION||Eskom Monthly|
|Lifespan – years||1.37||10.9||454.5|
|Number of installations||6||1||7.27|
|Cost per usable KWh per cycle||R2.57||R1.47||R2.73|
Service and Admin charge
Network Capacity Charge
Network Demand Charge
Ancillary Service Charge