Do I Need Batteries?

Do you need batteries?  Maybe!  it depends what you want to accomplish.  Let’s have a look at batteries and how we can use them in our home energy strategy.

What do batteries do?

Batteries store electrical energy.  We’re all familiar with many kinds of common batteries, such as:

• Small, portable, general use batteries like AA, AAA, 9V, coin cells, etc.
• Special use batteries like those in our phones, laptops, and cordless tools
• Automotive batteries used for engine starting
• Batteries for EVs (electric vehicles)

Basic net metering:  No batteries needed

A basic net metered solar energy system displaces grid energy with locally generated clean energy.  This does not require batteries.  Because there are no batteries, there is no energy storage and no backup power in the event of a grid outage.  These systems generate energy in conjunction with the grid; the grid will soak up any excess generation and supply any shortfall.  When the grid goes down, so do net metered solar energy systems.  Most net metered solar energy systems are battery-less.

Applications for which you will need batteries

• Off grid power – if there is no utility grid present and you need to store electricity, you will need batteries. 
• Backup power – If you want power when the grid is down, you will need batteries.  Some people use propane or natural gas generators for backup power; batteries can be used in addition to, or instead of, these generators.
• Solar shifting – this is the practice of charging batteries during the day from a solar array and then discharging them in the evening, shifting the solar benefit from day time to evening.  With a net metered solar energy system, solar shifting offers no tangible benefit but some folks like the notion of ‘using their own solar energy at night.’ 
• Arbitrage – this is the practice of ‘buying low and selling high’ (ie charge the batteries from the grid at night, during off-peak electricity pricing, and discharge them during the day, during peak electricity pricing.)  The economics of arbitrage depend on the spread between the on-peak and off-peak electricity pricing vs the cost of the equipment.  At this time in Ontario, the spread is low and the cost is proportionally high, making arbitrage economically unattractive.
• Peak Shaving – If you pay demand charges for your electricity, you can use batteries to shave off the top of your demand peak, reducing demand charges.  In Ontario, this is applicable to some business utility accounts but does not apply to residential accounts.

Backup power: Bridging nuisance grid outages

The vast majority of grid outages are short in duration: usually from a few minutes to several hours. but sometimes up to 24 or 48 hours. These short duration outages pose little risk to our lives and are mainly just a nuisance.  Battery based backup power excels at bridging these short duration outages and reducing the nuisance factor.

Backup power:  Whole home vs partial home

When using any energy storage technology for backup to the grid, a decision must be made about the scope of the backup service.  Should backup power be available for the entire home, and all its appliances?  Or should the backup power be focused on just essential loads?  Naturally, a whole home backup power system will be larger and more expensive than a partial home (essential loads only) backup system. Common essential loads include:

• well pump
• sump pump
• fridge
• freezer
• furnace air handler
• lights
• device charging
• network, computers
• etc.

Some appliances consume large amounts of energy and require a correspondingly large energy storage system for backup power.  These include:

• any electric home heating system (baseboard heaters, electric furnace, heat pumps, etc)
• electric cooking: stoves, ovens
• EV charging
• air conditioning
• Electric clothes dryer
• and others

Smaller battery based backup power systems can be configured for whole home backup, however large loads must be automatically disabled during a grid outage so as to not overload the backup power system.  This adds complexity to the system.  For most residential and small commercial battery based backup power systems we strongly recommend partial backup to keep the system simple and to reduce system cost.

Net metered solar with batteries

A net metered solar energy system can be designed to work with energy storage.  As long as the grid is present, the system will generate clean energy and feed it into the house, like any basic net metered solar energy system.  Batteries will be kept full, ready in the case of a grid outage.  During a grid outage, the batteries and solar will work together to provide power to the home (whole home or partial), much like an off-grid energy system.   When grid power returns, the battery bank will be recharged, ready for the next outage.  Solar generation will return to regular net metered operation.

Batteries now or later?

Either!  We can design a system that includes batteries from the start, that will accommodate batteries with little effort over the near term, or that can accommodate batteries at some point in the future.  Our recommendations will depend on your short term vs long term objectives and your expected timeline. 

Battery technologies for home energy storage

The most common types of batteries for off-grid home energy storage are flooded lead acid and lithium-ion.  For on-grid applications we recommend sealed lead acid or lithium-ion.  Each has its own advantages and disadvantages and we will recommend based on your application.  Far and away the technology that attracts the most interest is lithium-ion.  Compared to lead acid technologies, lithium technologies are smaller and longer lived, but they are also more expensive.

How much does it cost?

As you may have figured by now, there are lots of factors that drive system design and therefore price.  That said and based on our experience, a roof mounted net metered solar energy system with partial home backup using lithium-ion batteries will cost in the range of $45,000 to $85,000 +HST depending on the size of the solar array, the size of the battery bank, the complexity of the essential loads, and the complexity of the installation.