Smart Home Energy Storage

Smart Home Energy Storage

One of the biggest challenges and most costly components of our experiment was the smart home energy storage.

For a home to truly be “smart”, it needs the capability of generating renewable energy and reducing its dependency on the grid.  Because renewable energy can be heavily dependent on the sun and wind, you’ll need some storage capacity to help you balance energy supply and demand.

There are several ways that energy can be stored:  elevated weights (Ex:  A water tower); compressed gases; Ice (stored cooling); and the most popular means, in the form of potential chemical energy,  batteries.

Our homes typically measure energy use in kilo-watt hours (kWh), so we will be measuring our smart home energy storage options in kWh or watt-hours.  1000 watt hours = 1 kWh.


Smart Home Energy Storage:
Rechargeable Batteries!

From a 3 watt-hour AA battery to a 1.2 kWh AGM battery to Tesla’s incredible 14 kWh Powerwall, there are several means to store energy for our home’s use!  You’ll want to take a close look at your smart home’s energy profile and balance the estimated energy generation vs. the energy expenditure need.  For our smart home experiment, we started with the small requirement of running our landscape lights and eventually grew this into our home Wi-Fi and automation, rechargeable batteries, and emergency lighting.  As we grow our capacity to generate energy, we’ll look to add larger household requirements such as the 500W HVAC fan motor and our 1200W refrigerator.

Part of our smart home experiment was determining means and methods to live more sustainable.  One of the most unsustainable things that we use is disposable batteries.  Going around the house, we counted over 50 AA batteries that we used for smoke detectors, remote controls, our wall clock, thermostats, battery-powered candles, flashlights, and more.  We researched various rechargeable options and chose Eneloop batteries to gradually replace our disposable batteries.  With 1,000+ charging cycles and the added capability to use C & D sleeves, rechargeable batteries are a great smart home energy storage options.  In the 2+ years since we’ve started this experiment,I estimate that we’ve avoided sending more than 200 disposable batteries to a landfill.  And we’re just one home!

Rechargeable batteries are a great way to keep necessary smart home functions going with or without grid power.  Battery operated candles with 4 & 8 hour auto-timers provide nice ambiance and practicality.

The safest and most economical battery available for smart home energy storage when we started this experiment (in 2014) was the high-capacity, sealed AGM battery.  These batteries are safe for indoor use; need no maintenance; and are deep-cycle and chainable.  Each battery weights 70-90 pounds and can store 1.0 – 1.25 kWh of energy.  At 12V, these can be chained together easily store additional capacity.  For a few dollars, I purchased a bright green LED voltmeter that displays battery voltage and allows us to keep the batteries in a safe voltage range.

Sizing Your Smart Home
Energy Storage:

This can be the greatest challenge.  Initially, I was running our landscape lighting only on renewable energy which worked out nice.  The landscape lights used approximately 75 watts an hour.  The challenge is that on a summer day, the solar panels would take in anywhere from 1-2 kWh of energy and the landscape lights would only use 300 watt-hours (or 0.3 kWh).  And on a winter day, I would be lucky to get 0.3 kWh of energy from the solar panels and the landscape lights would use 500 watt-hours because of the shorter daylight?!

Over the course of 2 years, we expanded and modified our energy use to more steady (around-the-clock) requirements such as cable boxes, computers, chargers, and WiFi hubs.  We also added in a “summer only” cord for running the basement rec. room TV-area electronics.  And finally, I added a utility battery charger to help pull in grid-energy to charge the batteries on cloudy days and help stabilize the battery drain.

Ideally, I did not want to dip below 75% of our battery bank’s capacity so that I could maximize the life of the batteries.  That made our goal for average generation and usage to be approximately 0.5-1.2 kWh per day.

The above graph depicts our plan.  Like all good plans, some things don’t work out, as estimated.  (Example:  Actual wind power is much lower)

Smart Home Energy Storage:
The Next Steps

Today, my string of AGM batteries can hold just 4 kWh of energy and support some minor requirements if we were to lose power, such as emergency lights, security, and communication.  But, it is sustainable and clean, off-the-grid energy.  Our set-up grew from a 200W of solar and the Goal Zero Yet1 1250 as the charge controller, energy storage and inverter to a larger set-up that requires more capacity and has messier wiring.

If we were to continue the growth of this concept to encompass additional requirements, our smart home energy storage would need to grow with it.  AGM batteries would be cumbersome, heavy and take up a significant amount of living space (i.e. 20 kWh of capacity would be 17-20 batteries?!).  Tesla, Novele, and other manufacturers are quickly seizing this opportunity and you can buy flat lithium-ion batteries in the 7-10 kWh range that weigh only 200-300 pounds and can be hung like a sheet of drywall and carry your entire home load!  For people with larger renewable generation, this could be the answer to getting completely off of the grid.

Starting to get messy – next step will include sub-panel; larger inverter; and lithium-ion battery bank.

Is Off-the-Grid the Future?

For where we live, the “grid” is the PJM network of generation plants and distribution lines.  The capacity of this grid peaks at over 145,000 MW during the hottest summer days.  Our home’s peak is probably around 12 kW (120V x 100A) or 0.012 MW.  Therefore, 145,000 MW is equivalent to over 12 million homes!  Power plants have entire turbines maintained in reserve to meet these summertime peaks.  These auxiliary plants are expensive and costly to maintain (we, the consumer, ultimately pay) and for our environment and lungs that has to endure the pollution.

Years ago, an industry evolved to coordinate and reduce these peaks – called “Demand Response” (DR).  In DR, large users and consumers of electricity are incentivized to reduce energy use during peak times.  They can do this by reducing air conditioner use (high electricity consumer) or other high loads.  In exchange for their reduction, power companies need less emergency generation capacity and they share their savings to create these incentives.  If you had the capability to store energy during low-use times (overnight) and dip into that storage during peak hours, we could level out our usage curve and we’d have a far lower need, as a society, for auxiliary power generation plants!

While I love the idea of off-the-grid living, I think the answer may be in our ability live harmoniously and sustainably with the grid.  Perhaps community-sized smart grids clustered through larger interconnections.  Time will tell what the future holds, but I think it’s exciting.