Thread Recap: The price-point of ESS to go Off-Grid
Net-Metering
If you live where there's a
good net-metering agreement you'll not want to go off-grid as the bill can be zeroed out with a relatively modest cost of increasing your PV array. But not every place has net-metering and if you do have, it is always under attack. This thread is about figuring out how to find the price-point where it makes sense to go off-grid.
In-between Cases (TOUs)
It's not always necessary to go off-grid, often you only need enough battery to cover a high Time of Use (TOU) rate. This thread isn't about that per se and a number of people (e.g.,
@GXMnow) have
blogged their experiences doing so.
Incentives
Some states (e.g., MA) already offer hefty incentives to installing ESS, it might become a federal tax credit.
Risks
Still working on identifying these and how to include them. Ideally, these are all adjustable parameters as different people will have different ideas as to the value to compensate for the risk.
How Much Storage?
Being off-grid means having a reliable backup power supply (e.g., generator). Ideally, that source only runs a few times per year to over a hump where there's insufficient power from your renewable source (e.g., solar panels).
For LFP, from the
graph in the OP we know 3 days of storage gives an average 33% depth of discharge (DoD) which should give 20 years of cycles leaving them at 80% capacity. But, due to calendar aging, they might only last a decade. If a decade is an upper limit then 90% DoD is the minimum based on cycle life.
Ultimately, how much storage is up to you. Generally, 2 to 3 days is the realistic pick for convenience and not being a slave to the generator.
Storage Alternatives
In some cases you can hedge your storage needs by altering power consumption to alter your lifestyle to using the most power while the sun is up or doing without on days you can't provide enough sunshine. You can also oversize your PV array so that sufficient power is available even on gloomy days.
What's the Value of going Off-Grid?
This one is fairly simple assuming consistent usage, it's the sum of the bills over a year. You can use an
online inflation calculator to adjust the total for future years and then sum them up for 20 years or the life of the PV array. The PV array's output will degrade over time, you can find the amount from your panel's datahseets.
What's the Cost of Energy Storage?
This is the cost of an installed system plus generator brought out to 20 years (e.g., if you think LFP lasts 10 years double the price to get to 20 years).
Example
Let's use
$0.156/wh as the price of the Energy storage installed and assume:
- The maximum kWh consumption on record is 70 kWh, but the maximum two consecutive days is only 100 kWh.
- Decide we want 2d autonomy
- The batteries will safely last a decade
Then for two days automony you might decide on 100 kWh. Sure that one day might use more, but the generator can catch the few outlier days. Or not, this is totally up to you. But for this example, we'll use 100 kWh. Then 100 kWh x $156/kWh is $15,600 for the batteries. A ~2 kW inverter generator runs about $1000 and can recharge 48 kWh of battery/d. For this example, we'll assume you already have an inverter properly sized for your off-grid needs (but otherwise you'd add the costs in).
So, $15,600 * 20 years needed/10 year-calender-life + $1000 generator = $32,200 investment.
What's the value?
Let's say your grid bill totals $1500 per year. Over 20 years with 2% inflation that's ~$39,000. From the example above the cost is $32,200, so is it good deal? The payback period is positive, but if you invested that at 1.25%, it would return $41,000 over 20 years.
Other Unknowns
- What happens if the feds offer a 25% incentive on ESS? Then that $32,200 system in the example above costs $24,150.
- LTO has a cycle life of over 50 years, if the calendar life is over two decades the economics look very positive (see #39)
- Solid-state batteries are expected to start being mass-manufactured in 5 years and in common use in 10. They may have both long cycle and calendar lives at lower prices and higher densities.
- Rather than invest in a battery, if your driving patterns permit, it might soon be possible to use your EV battery for 2nd or 3rd day emergency use, reducing the size of the main ESS.
- The argument most commonly used by those trying to get rid of net-metering is the burden it places on those without net-metering (as if they weren't charging for grid-access or that there was no value in the energy residential DERs provided), what happens when people who can leave the grid? What new legislation would need to be enacted?