Battery Storage and hybrid systems

A hybrid solar power system is a mixture of a grid connect and stand alone system. A normal grid connect solar system can be converted to Hybrid by adding a set of batteries and a smart battery inverter.

A hybrid solar power system should offer the following features;
Be able to feed excess solar energy back into the grid like a standard grid connect system.
Charge batteries from solar or grid depending on factors such as current cost of electricity.
Use the stored battery energy when the user requires it in a way that is beneficial to the user.
If the batteries become depleted the system should seamlessly switch back to mains power. Battery charging could then be started again when the sun comes up or when a suitable low cost tariff is available.

Types of Hybrid
The main difference between hybrid systems on the market today is whether or not they can provide usable power if the grid goes down. Also - can the system charge its batteries from solar during a blackout, ie - if you have an extended blackout over a few days will the batteries recharge each day from the solar or will you only get to use the power that was stored in the batteries when the power went off and then loose backup power once the batteries are discharged.
This feature of solar battery charging may not be important if you have confidence in your mains power supply. If however you live in an area where the mains power is prone to failure then it might be worth making sure that any hybrid system that you’re considering has this capability.

Any quote should specify overall battery life as well as the kWhrs of available power to a specified DOD. (Depth of Discharge)
Better batteries cost more but usually have an extended life compared to a cheap set.

Smart battery inverter
This could be the heart of a hybrid system. Control of the whole installation could be overseen by this inverter.
It should be able to charge the batteries from either the mains or solar and you should be able to choose which.
It will have a power rating that will tell you what it can run in the house from your battery bank before it needs help from the mains. If the mains has failed you will only be able to power loads in the house up to this power rating. For instance if the mains fails a 3kW inverter will run a 2.4kW kettle but it will turn off to protect itself if you plug in two 2.4kW kettles at once.
If the mains power is present then there wont be a problem as the inverter will provide 3kW from the batteries and source the missing 1kW from the mains.

This concept may be realised by using a battery inverter such as the Selectronic SP Pro, SMA Sunny Island or a an SMA Sunny Boy Storage 5.0.
These are just a few examples of what’s available on the market.