Inverter

An Inverter is the heart of a PV solar system and is available in hybrid and grid connect options in single and three phase.

The primary difference between a hybrid inverter and non hybrid inverter is that a hybrid inverter can charge a battery and a non hybrid inverter cannot charge a battery. A hybrid inverter chooses where to send the usable power produced. It's main function is to send produced power to the building first and excess power to a battery if connected or hot water immersion heater via a hot water diverter or charge a car via a car charger and lastly send the remaining power to the national grid.

A non hybrid inverter will only supply usable power produced to your building and the excess produced to the national grid. It does not have the ability to charge a battery. If you have an existing non hybrid inverter and wish to charge a battery, an AC charger would have to be purchased in order for this to work.

Battery

The advantage of having battery storage installed, is that it will supplement the power to your building for the duration of the available charge when there is little sun or at night. The battery power usage can be timed and also the battery charge times from the PV system can be timed (Forced Time Use) option. The use of a battery or battery bank, dependant on the size of the PV system installed can be very useful. Various tariffs are now available and if you use a tariff with the least expensive cost per KWH (normally in the early hours of the morning), you can top up your battery inexpensively and use that power at peak times like in the evenings when the KHW cost is expensive and offset a lot of your cost of running your building.

There are a variety of battery types available:

Deep Cycle Lead Acid, Lithium Polymer, Lithium Ion, Lithium Iron Phosphate Lifepo4

High Voltage and Low Voltage options

Batteries with external BMC units or built in BMC units (battery management controllers)

Stackable and non stackable options

External or internal options

Choosing the correct battery can be somewhat confusing!

LV (Low voltage) PV batteries are generally less expensive than HV (High voltage) batteries. HV batteries offer a higher discharge rate meaning they can support much higher demand loads. The energy density is also much higher in HV batteries. The charge and discharge rates of HV batteries is much quicker.

LV batteries have a voltage no greater than 100 volts. HV batteries run up to around 500 volts. High voltage batteries have a lower amperage than LV batteries. HV batteries deliver more energy per charge cycle due to their high energy density and low discharge rate.

HV batteries also have better cooling tendencies and heat reduction properties over low voltage batteries when charged with the same current. Low charge currents which would cause low voltage batteries to overheat and degrade would have little to no effect on high voltage batteries.

These high voltage batteries could also be built and function within a system with small conductive materials whilst low voltage batteries would require larger conductive materials to increase low currents in order to charge properly without overheating. Lithium high voltage batteries also have no “Memory effect” which is a degrading process whereby a battery periodically reverts to a lower capacity as a result of partial charge and discharge cycles. Low voltage batteries are plagued with this effect and would eventually lead to early battery degradation and a short lifespan.

For off grid applications LV batteries are the preferable choice.

 

Inverter Image Below