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Choosing panels, inverter and batteries

An experienced PV installer will be able to advise you on the different options available to you that will fit your requirements.

Individual companies tend to work with specific products and brands so discussing the choice of component brands and types with different companies is always a good idea.

Solar panels for grid-tied systems come in two main sizes, depending on the number of solar cells they are made from. 60 cell panels are about 1.6m tall and 1m wide, 72 cell panels area about 2m tall and 1m.

Larger panels are not better because they are bigger, they will generate the same energy on the same area of roof as smaller panels.

The choice is about which size of panel will best fit the available roof space

The choice is about which size of panel will best fit the available roof space

A solar panel is made using solar cells. Each cell is about 6 inches, 125mm, square. The cells are made using one of two different materials, monocrystalline or polycrystalline. Polycrystalline is slightly cheaper but is less efficient so a solar panel made with monocrystalline cells will generate more energy than one made using polycrystalline cells, but will be more expensive.

There are a number of good quality PV panels to choose from however Tier 1 panel producers are advisable due to their warranty provisions, performance guarantees and company stability prospects (in order to honour guarantees and warrantees).

A solar PV inverter is needed in every grid-tied solar PV system to convert the DC power generated by the solar panels into AC power that can run the devices in the property.

Most residential properties have a single-phase connection and most commercial buildings and farms will have a three-phase connection. This factor normally determines if you need a single or three phase inverter.

You can however use one, two or three single-phase inverters on a three-phase supply, especially if you have different loads on each phase.

Some inverters work in combination with optimisers that are fitted to each individual, or pair of solar panels. These ensure that every panel in the system will operate at its maximum capability for the life of the system. These are especially useful where there is some shading during a part of the day or where you want to monitor the performance of every module over the life of the system.

For inverters that are not supplied with optimisers the solar panels are wired in series on one or more strings, each strings acts as if it is a single very large solar panel. The inverter has one or more built-in Multiple Power Point Trackers (MPPT) that take the power from one or more strings. This is an intelligent electronic circuit that automatically extracts the most possible energy from each string of solar panels.

Lithium ion batteries for use in PV solar systems have come down in price significantly in the last 2-3 year. 

A good quality lithium-ion battery may have a lifetime of 5,000 – 7,000 cycles which is considerably more than 10 years of normal usage.

The built-in battery management system will ensure that the battery condition is always maintained in optimum condition and a full 10 year life may be expected. Compared to this the number of cycles that a lead-acid battery can be used for is directly related to the amount of energy charged and discharged in each cycle.

With a system configured to utilise 50% of the gross storage capacity (DoD) on a daily basis a typical lead-acid battery will have a lifetime of 2,000 – 2,500 cycles. Allowing for some degredation over the life of the battery a useful lifespan of about 5 years in a well designed system may be expected.

The initial investment cost of a lithium-ion battery may be 2.5 – 3 times more expensive per kWh of gross capacity compared to a similar sized lead-acid battery but when comparing the Rand per kWh over a 10 year period the lithium-ion will be a cheaper option with no need to renew the battery after 5 years.