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The following image is helpful in explaining the most common solutions.
Solution 1: Back-Up
Almost everyone needs a primary inverter with a battery bank.
The inverter takes mains power (ZESA), charges the batteries with it and feeds the house. The batteries take over when the power goes.
The problem. Large enough battery banks are expensive, don’t necessarily last the entire power cut and have a short lifespan when worked hard.
Solution 2: Extended Backup.
Throw on just a couple of solar panels with a charge controller to enable solar power to top up the batteries.
Pros: Good for people on a budget, it will boost the batteries (to a limited extent).
Cons: When mains power is on, the batteries will quickly be fully charged. In this event all of your expensive solar equipment and the energy they produce simply sits idle, it has nowhere to go as the batteries are full.
Solution 3: Grid Tie
You guessed it this one’s a bit more expensive but offers far more value and will more than pay for itself if you have the budget.
The house attempts to run itself on solar power at all times regardless of whether mains power is on or not. The inverter will only provide a top up from mains / battery power if the solar energy is proving insufficient. This way, when the sun sets your batteries are fully charged and only then start supporting you. Expensive batteries last far longer as they are not being worked hard. You save by not running a generator and in addition electricity bills are reduced because the solar power is always harvested regardless of the battery state.
Zimbabwe does not presently have the legislation in place to allow for grid feeding back onto the ZESA grid, although this is being worked on. It is currently technically possible for those without a pre paid meter to back feed the grid, its technically impossible for those without pre paid meters. For this reason, on most installations there is little point in going too big on solar panels.
Diesel hybrid solutions have proven to be an option on some larger businesses installations. This means no battery banks. The business then attempts to run itself on solar but the system then automatically turns on supplementary generator power in moments when the solar coming off of the roof is proving insufficient. E.g one school that we are working with is planning to retire a 100kVA generator, run itself on solar and their smaller 30kVA one can kick on in rare moments when the solar is not proving to be enough, such as in the evenings etc. This is not the best value option but can be helpful to those lacking the up front cash for a full system with batteries.