What is the right size battery for a home or business?

Choosing the right size battery for a home or business can be difficult but there are a few easy ways to do this.

Battery storage is a great way of utilising any excess solar energy currently being exported back to the utility for virtually no return.  An energy storage system can store this energy for later use reducing the amount of electricity that needs to be purchased at night and hence lowering electricity bills.  Battery storage can also be used to take advantage of ‘time-of-use tariffs’ by storing energy at low-cost times for use during the high-cost times.

Sizing the battery largely depends on the amount of solar energy being exported.  If there is only a small amount of energy being exported there is no need to install a large battery system.   A large battery system would never be charged properly and hence the customer would be wasting money.

The amount of energy being exported is dependant on the size of the solar system and the energy usage during daylight hours.   The difference between the amount of energy the solar system generates and the amount of energy used during the day is what is exported and can be stored.  The more energy used during daylight hours the less energy available for storage.

Daytime energy usage in households and businesses varies dramatically, which is why it is very challenging to determine the right size battery.  Some households have no one at home using electricity during the day and some do.  There is also a variety of appliances which could be used in the home that vary from home-to-home.’

Below are three easy ways to right size a battery for a home or business to get into storage and maximize the use of solar and time-of-use tariffs:

1. Install an Enphase Envoy S Metered to calculate the right size battery

envoy_HERO_euro_ANZ_1440x600Envoy S Metered + DRM

The Enphase Envoy S Metered is a small electrical device that is installed on or near the switchboard that communicates to a website via the household WiFi.  It can monitor the solar generation of any make and model of solar system while also monitoring the household energy usage.  The Envoy has a current transformer (CT) for the solar and current transformer (CT) for the mains.  Using this data over a number of weeks or months the Envoy can accurately determine the right number of batteries for the user’s specific needs.   You are then able to confidently advise the customer on the perfect size battery system for them.


2. Install an Enphase Envoy S + one AC Battery  

The Envoy can determine the optimum number of batteries required as described above.  However, while the electrician in on site installing the Envoy they can easily install the AC cabling required for batteries and install one battery so they can get started with storing energy.  This can be more cost effective and additional batteries can be easily added when the Envoy has determined the optimum system size.


3.  Use a rule of thumb to calculate the sizing

A general rule of thumb for sizing AC battery systems is one battery per kW installed PV capacity.  For example, if a homeowner has a 3kW solar system, then three AC Batteries is a reasonable place to start.


Enphase AC Battery

If safety, performance, reliability and flexibility are important to you and your customers then the Enphase AC battery is a great solution.  The AC Battery has no dangerous DC voltages and hence no DC cabling, and no DC isolators which has been a source of fire and shock in hundreds of buildings across Australia.  The AC Battery has a performance warranty of 2 cycles a day for 10 years, depth of discharge of 95% and is warranted to 80% of the rated capacity after 10 years.  The AC battery is modular in design, so multiple batteries can be installed, as required, making it easy to add more in future, even if new models or differing battery chemistry are developed over time.  There is also no need to modify the existing solar systems on site which potentially exposes installers to warranty related issues with the existing solar system.  (i.e. poor DC wiring, underperformance of the solar system etc).

The AC battery has been designed to be small and practical.   It means that the battery management system of each AC battery manages a small number of cells resulting in a bank of AC batteries having an excellent round trip efficiency (RTC) compared to a large single equivalent sized DC battery.  The AC battery also has a relatively small inverter for discharging the battery.  This is so the battery is discharged evenly over a 4 hour period significantly increasing the life of the battery.  It is detrimental to a battery to have a large inverter to meet peaks in demand when base load energy storage is what saves consumers money.  Meeting the short term peaks in load (eg kettle, toaster, microwave oven etc) simply means your storage would discharge fast and your battery life would reduce.

The Enphase AC battery is not just a battery, it’s part of a very smart energy solution which can be perfectly sized for any home or business.

To read more about the Enphase AC Battery click here


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