Energy Storage (Battery/Thermal)
Standalone without a Renewable Energy Source
Battery systems are becoming more and more popular now the technology can be delivered at a economical rate. Using low rate electricity at night to charge the battery for daytime usage is the most common application. Equally, off-grid sites can use battery power in conjunction with a generator, the battery can be charged when convenient and the generator can work at maximum output and therefore perform most efficiently.
Complimenting a Renewable Energy Source
During the day when solar panels are generating electricity, the power will automatically feed anything connected to the fuse board including machinery, appliances, lighting, etc. When the property’s power consumption is greater than the PV system is generating, i.e. peak demands or after sunset, the grid will provide the power in the traditional way. Similarly, as solar panels produce electricity when the sun is shining – which does not necessarily correlate with the building’s usage – it is sometimes necessary to ex-port the excess power back to the grid. Alternatively, a battery system can be utilised to store the excess energy and use it later in the day or at night.
It is always better to use the power on site if possible as it has more value. This assumes the electricity tariff is at least 30% higher than the export tariff (it is usually at least 200-300% higher). The reason you need this gap is that storage is not 100% efficient; you will lose 20-30% through the process and therefore the extra saving will pay for the cost of the batteries.
You can potentially improve the financial case for the battery system by charging it overnight on a lower tariff, again assuming the 20-30% rule mentioned above.
There are three types of battery storage solutions to consider:
Back Up ‘Island’ – is the best solution as it allows the PV system to completely separate itself from the grid, thus ensuring you store the maximum amount of power possible. The best percentage return on in-vestment is likely to be found with this option as you utilise all/most of the power. Before considering any battery option ensure it will physically disconnect from the grid; if you are charging the battery from a so-lar array and it is still connected to the grid there is no way of ensuring all ‘free’ electricity goes to the battery and not the grid.
Grid Assisted – means you are still permanently connected to the grid. The downside is the electricity generated will always take the path of least resistance and may end up exporting more energy when in fact it would still be beneficial to store it by charging the battery. This type of battery system is currently more common in production and therefore a wider variety and increased competition may make it economically attractive in the short term.
Off Grid – is utilised when there is no access to the national grid and allows the end users to be completely off grid. However, depending on the energy demand there may need to be additional power sources to charge the batteries to complement the solar panels i.e. a generator.