Buying Better (Big) Batteries: Part Three
In California, 20% of solar installations are now paired with home batteries.
This action guide helps you buy big batteries to power your electric car or home, an essential step to a clean energy future. On the energy pathway to sustainability, we’ve been exploring steps to become better battery buyers. If you’ve read parts one and two of our “buying better batteries” action guides, you know that the sustainability score of a battery depends mostly on the chemistry of its electrodes, which determines the power, the energy storage, and the number of charging cycles batteries can deliver.
For small batteries, we can choose NiMH or lithium-ion chemistries so that a single rechargeable battery can do the work of hundreds of disposable alkaline or lithium batteries. For medium-sized batteries, like the ones in power tools and fuel-burning vehicles, we can start replacing toxic and heavy lead-acid or NiCad batteries with non-toxic and lighter lithium-iron-phosphate (LFP) chemistries for better sustainability. But what about bigger batteries, like the ones in electric cars and home energy storage systems?
While most of us have been buying small and medium-sized batteries all our lives, batteries big enough to drive cars and power homes are a new idea. These big batteries are still prohibitively expensive but evolving quickly in terms of affordability, safety, and value. The most important steps to take now are
- Educate yourself so you can make an informed decision as a battery buyer for your own car or home or as a resource for friends and family.
- Prepare your home for an electric car and electric heating.
- Prepare your home for battery backup so you don’t have to worry about the power going out.
- Prepare your home for solar power so you can make your own electricity and store it in your big batteries.
- Choose big batteries wisely if you have the financial resources to be an “early adopter” who can help bring new technology to market faster.
The “Big Two” Requirements for Batteries
The “big two” requirements for batteries are your power and energy needs. A “big” battery is one that can power an electric car or home, but it takes translating to understand power requirements because the United States (unlike the rest of the world) uses the imperial system. Here’s how Yanks measure power:
- “Horsepower” for cars — an average car is 180 horsepower.
- “Amps” for homes — older homes have 100 amps; new homes have 200 amps.
- “BTUs per hour” for fuel-burning furnaces — an average furnace is “90,000 BTU.”
- “Tons” for air conditioning — an average central AC unit is rated at four tons.
This can all be better done in watts, the scientific unit. Then you can just add ’em up and buy a battery that can deliver enough power. Here’s a translation table:
- 1 horsepower = 746 watts = 0.746 kilowatts — the average car is 135 kW.
- 200 amps at 240 volts = 48,000 watts — the average home is 48 kW.
- 1 BTU/hr = 0.293 watts (approximately) — the average fuel-burning furnace provides 26.4 kW of heating power (at 85% to 98% efficiency this requires 31 kW).
- 1 refrigeration ton = 3,516 watts (approximately) — the average AC unit provides 14 kW of cooling power (at 400% to 500% efficiency this requires 3.5 kW).
Here’s a fact that might leap out at you from this table: cars are powerful! The battery pack in a Ford F-150 Lightning electric truck can provide 432 kW to the motors (more than three times as much as the average car). That’s nine times as much power as the average new home can get from the power grid. Knowing this, the people at Ford came up with a clever idea: why not power your home from your truck?
If you buy an electric truck, its battery can probably supply far more power than your home can use. However, getting the power from that battery into your home is a bottleneck. When Ford’s engineers tackled that problem, they decided that 19.2 kW from their truck to your home is enough. (And they also built in a 9.6 kW electric outlet in the truck for power tools.) While an electric truck battery can provide enormous power, limiting output makes it easier and cheaper to design and build a mobile connection system that consumers can use safely.
When you buy a home battery energy storage system, make sure the kW rating can handle all the loads you put on battery power. Here’s a rough estimate of the power needs of various systems in your home that use electricity; add up the kW to know how much battery power you need.
- Mini-split heat pump (heating mode): 7.5 kW
- Electric car charger: 7.2 kW
- Electric oven: 5 kW
- Electric hot water heater (240 V): 5 kW
- Electric clothes dryer: 5 kW
- Central air conditioning (heat pump in cooling mode): 3.5 kW
- Electric stove top: 3 kW
- Heat pump electric hot water heater (120 V): 2 kW
- Coffee maker: 1.2 kW
- Refrigerator: 1 kW
- Microwave oven: 1 kW
- LED lighting (entire home): 1 kW
Power is only half the requirement for a battery; energy is the other half. Power determines how fast you can use energy; energy determines how long.
If you buy an electric truck from Ford, you can choose between two batteries that can deliver the same power but store different amounts of energy. With a standard range battery, at max power, a Ford F-150 Lightning can send 432 kW to the motors to accelerate up a steep hill, but only for 14 minutes. At normal power, you can drive 70 miles an hour for three hours and twenty-five minutes — covering 240 miles. An extended-range battery can still send a maximum of 432 kW of power to the motors for acceleration, but can keep it up for 18 minutes. At normal power, more energy in the battery allows you drive at 70 miles an hour for four hours and thirty-four minutes — covering 320 miles. The difference between a 98 kWh standard range and 131 kWh extended range battery is not the power of the battery but the energy storage.
The amount of energy a big battery can store should be reported in kWh (i.e. kW times hours). Some vendors feature the amp-hour (Ah) rating instead. To convert an Ah rating to kWh, multiply Ah by the voltage (V) of the battery. For example, a 400 Ah 12-volt battery can only store 4.8 kWh of energy, whereas a 400 Ah 48-volt battery can store 19.2 kWh of energy. Both batteries have the same 400 Ah rating, but one can store four times as much energy as the other because it operates at four times the voltage, allowing each amp to do four times as much work.
Convenience is the main reason to measure battery energy in kWh rather than the scientific unit of joules. Your electric bill reports how many kWh your home uses — the average home in Maine, for example, uses less than 20 kWh per day. So, a battery that can power the average Maine home for a week needs about 140 kWh of energy storage (20 kWh/day times seven days).
Preparing to Go Electric
The people who built homes with 100-amp electrical services did not foresee electric vehicles and electric heat pumps. They assumed that everyone would burn fuel to move and to keep warm. If you get all your electricity from your power company, it has to squeeze through one small wire that can only safely send 24 kW in older homes. (Compare this to the 432 kW that a battery in an electric truck can send to its motors: 24 kW is not a lot of power in today’s electrifying world.) Even if you have a newer home with a 200-amp service, your power company can only send you 48 kW — and that might not be enough, either.
One solution is to pay to upgrade your electrical service from 200 amps to 400 amps so your local utility can safely send you up to 96 kW of electric power. A more sustainable solution is to go solar, make your own electricity, and store it in batteries. Whichever solution you choose, there is one thing you can do now to prepare for the day when your vehicles and your home are fully electric: get efficient.
The more efficient you are, the less power you need. Consider these steps now:
- Replace all of your lights with LED.
- Unplug and recycle all freezers and refrigerators that are not essential. You can’t afford the power to keep an old freezer plugged in.
- Upgrade essential refrigerators and freezers to Energy Star models.
- Upgrade to a 120 V heat pump hot water heater. (Do not upgrade to a 240 V heat pump hot water heater, because that demands more than twice the power. We’ll explore the topic of water heating in a future action guide.)
- Upgrade to an induction electric stove that uses less power than a standard electric one.
- Upgrade to a ventless clothes dryer.
- Air seal your home.
- Insulate your home.
Reduce the total kW your home demands to make it more likely that you can generate all the electricity you need with solar panels and store it in batteries.
Battery Back Up
In the future, you’ll be able to install batteries to power everything in your fully electric home for months. But that day could be far in the future. Today, for financial reasons, you’ll probably need to carefully decide which loads in your home you want to put on battery backup.
The cheap way to do battery backup (a few hundred dollars) is an extension cord. When the power goes out, plug an extension cord into your battery backup and power your refrigerator, your WiFi router, cell phone charger, and a few lights.
More expensive (a few thousand dollars) is to install a separate electrical panel, put your critical loads in that panel, and have your big battery switch on to power those loads when it detects a power outage.
If price is no object, install batteries to power every load in your home. Be prepared to spend tens or hundreds of thousands of dollars to do this with 2023 technology. Technically, it’s now possible to install enough energy storage in a backyard shed to keep the average home on battery power for a whole year. You could be completely off grid with an all-electric home anywhere in the world.
400-Amp Electrical Service?
In the future, you will not need a 400-amp electrical service if you have a powerful enough battery. California leads the country in home battery adoption — changes to their net metering rules make solar with batteries more valuable than without batteries. That situation may repeat across North America, and that could drive down battery prices to affordable levels for everyone in the world. But that hasn’t happened yet.
The key fact is that batteries allow us to fill them up when the sun shines, or when utility power is cheap and available. With a battery, you can be slowly charging from a 100-amp (24 kW) or 200-amp (48 kW) power grid connection. Then, for the few times a day when you need more power, you can get it from your battery instead of the grid.
The problem is that powerful home battery energy storage systems are simply too expensive for the average homeowner today. Batteries are getting much more affordable very quickly, but they have a long way to go before everyone can benefit.
If you are in a hurry to electrify your vehicles and your home, and you cannot afford powerful batteries, then you will probably need to increase your electrical service so you can get all of your power from your local utility and none from batteries.
Being an Early Adopter
If you have the financial resources to live in the sustainable future today, you can buy powerful batteries, and you can go solar to make your own electricity and store it in your batteries. Here are essentials to know when choosing a home battery energy storage system (BESS) today:
- LFP batteries are less likely to catch on fire than NMC batteries. NMC batteries should only be installed in fire-proof enclosures because they can spontaneously burst into flame and burn at high temperatures without any external oxygen supply. Most lithium-ion battery fires are due to NMC chemistries.
- Battery management systems are circuitry and software that control the cells in a battery pack. Check the functionality of the software provided with the BMS to make sure it will meet your needs, and be prepared to apply all security updates, feature enhancements, and bug fixes.
- If you have solar photovoltaic (PV) panels, you have the choice between a “DC-coupled” (between your solar panels and your inverter) or “AC-coupled” (between your inverter and your grid connection) BESS. Without solar PV, you will have to install an AC-coupled BESS (compatible with your grid connection). DC coupling is more efficient; AC coupling is more convenient.
- Many battery chemistries based on iron are much better than LFP or NMC for energy storage. The primary advantages are that iron-based chemistries are not flammable, so they won’t burn your house down, and they are ten to twenty times more affordable. It takes time for new chemistries to be commercialized and manufactured at scale, but over the next five years, affordable iron chemistries (and maybe affordable sodium or carbon chemistries, too) are likely to come to market, making today’s lithium LFP and lithium NMC chemistries obsolete.
Buying a big battery today is like buying a computer in the 1980s. New developments are announced daily, and you can always get a better deal if you wait. But someone has to be the first buyer. Being an early adopter puts your consumer dollars to work to help companies bring their products to market and improve them. Just take prudent steps so you don’t burn your house down!
What’s Still Ahead on the Pathway…
Earlier this year, we explored the pathway to sustainable movement; now, we’re exploring the related pathway to sustainable energy. What are the best ways to save, use, and make energy? Stay with us on the journey to sustainability as we take action to have a positive impact on the world.
References and Further Reading
- Buying Better Batteries: Part One, Fred Horch
- Buying Better Batteries: Part Two, Fred Horch
- Only Three Countries in the World (Officially) Still Use the Imperial System, Statista
- What Is The Average Horsepower Of A Car?, J.D. Power
- How to Determine Your Electrical Service Amps, The Spruce
- How Many BTUs Does a Typical Home Furnace Need?, Overland Park Heating & Cooling, Inc.
- What Size AC Unit Do I Need?, American Standard Heating & Air Conditioning
- 2023 F-150 Lightning Capability, Ford
- What are the battery specifications for the 2022 Ford F-150 Lightning?, Brandon Ford
- Electricity Prices, State of Maine Governor’s Energy Office
- California’s new net-metering policy brings batteries to forefront, PV Magazine
- Mitigating Thermal Runaway Risks and Lithium-Ion Battery Fires, Clean Energy Associates
- What is a Battery Management System?, Synopsys
- AC vs. DC solar battery coupling: What you need to know, EnergySage
- Long-Duration Energy Storage, ESS Inc.
- How sodium could change the game for batteries, MIT Technology Review
- New Flow Battery Lasts All Year On Simple Sugar, CleanTechnica
Originally published at https://sustainablepractice.substack.com.
