Grid & off-grid

Grid tie vs off grid comparison tool

See the cost difference between staying connected to the grid and going fully off-grid. Adjust every variable, from battery chemistry to depth of discharge, for a precise side-by-side estimate.

Your numbers

1 Project details Optional
Shown on your exported report. Leave blank to skip.
2 Your system and usage
Use your quoted or planned system size.
Monthly usage divided by 30 gives a rough daily figure.
Off-grid systems must be sized for your worst season, not your average.
Off-grid homes often trim usage first, since every kWh saved reduces battery cost directly.
3 Off-grid battery sizing
Off-grid systems typically size for 2 to 5 days of cloudy-weather backup.
Depth of discharge and cost per kWh vary significantly by chemistry.
Off-grid systems need a beefier inverter setup than a standard grid-tie inverter.
Most off-grid systems still keep a generator for the rare worst-case stretch.
4 Cost assumptions Optional overrides
National average is roughly $2.50 to $3.50 per watt before incentives.
Covers application, equipment, and inspection fees for a grid-tied system.
Off-grid sites often need extra electrical permitting and site prep versus a standard grid-tie install.
This context doesn't change the math below, but shapes which option applies to you.

How it works

Three steps to your result

Step 1

Enter your system size and usage, adjusted for season

Use a system size you already have quoted, or your panel count times each panel's wattage divided by 1,000. Add a winter usage increase if you use electric heat, since off-grid systems must be sized for your worst season.

Step 2

Set your battery chemistry and autonomy target

Lithium, lead-acid, and saltwater batteries all price and perform differently. Off-grid systems need enough usable battery capacity to cover multiple cloudy days without running out.

Step 3

Compare the two totals side by side

The result shows the full installed cost of both paths using your exact equipment choices. If the gap looks larger than expected, the grid tie with battery backup tool shows a middle option: staying grid-tied while adding a smaller battery for outage protection.

Weighing grid-tied against fully off-grid

Why off-grid systems cost so much more

A grid-tied system only needs enough solar to offset your usage, since the grid absorbs excess production and supplies power at night. An off-grid system needs a battery bank large enough to survive multiple cloudy days in a row, which is why the battery bank, not the panels, usually drives the bulk of the extra cost. A 7 kW system sized for 3 days of autonomy can need over 100 kWh of battery storage, more than 10 times what a typical grid-tied backup battery holds, which is why the off-grid battery bank sizing calculator is worth checking against your own usage before you commit to a chemistry and autonomy target here.

Why battery chemistry changes the math so much

Depth of discharge, the share of a battery's rated capacity you can use without shortening its lifespan, varies enormously by chemistry. Lithium LiFePO4 batteries allow 90 to 95% usable capacity, while older lead-acid technology is typically limited to around 50%, meaning a lead-acid bank needs roughly double the rated kWh to store the same usable energy, even though its price per kWh is lower upfront. The U.S. Department of Energy's overview of solar-plus-storage covers why lithium has become the default choice for most new residential systems. The grid tie with battery backup comparison tool uses the same chemistry logic at a much smaller, more affordable scale. If any term on this page is unfamiliar, the buy-all sell-all entry in our Glossary explains it in plain English.

Why off-grid systems still need a generator

Even a well-sized battery bank can run low during an unusually long cloudy stretch, particularly in winter when both solar output drops and heating loads rise. A generator, whether portable gas, standby propane, or a whole-home automatic unit, provides a lower-cost backstop than oversizing the battery bank further to cover a rare worst case. The Consumer Product Safety Commission warns that portable generators must run outdoors, at least 20 feet from the house, since their exhaust can build lethal carbon monoxide indoors within minutes. Winter is also when the gap is most likely to show up, since lower solar output and higher heating loads stack together, and the winter vs summer savings comparison tool shows how much that swing costs across both paths.

What to check before committing to off-grid

Before ruling out grid-tied, get a quote for what a grid connection would cost at your specific site. The grid interconnection cost estimator breaks down typical application, equipment, and study fees, which are almost always far lower than a full off-grid battery bank. The winter vs summer savings comparison takes the same inputs and works through the next step.

Questions

Frequently asked

Staying grid-tied is almost always cheaper, often by tens of thousands of dollars. In this calculator's example, a 7 kW system with 30 kWh of daily use, a 15% winter increase, and 3 days of lithium battery autonomy costs roughly $97,000 more off-grid than the same system grid-tied, since off-grid batteries need to cover worst-case cloudy stretches, well beyond daily cycling.

Chemistry affects both usable capacity and price. In this calculator, lithium LiFePO4 batteries run 90 to 95% usable depth of discharge at $800 to $950 per kWh, saltwater batteries run 85% usable at $1,100 per kWh, and lead-acid batteries run about 50% usable at $300 per kWh, which means a lead-acid bank needs close to double the rated capacity to store the same usable energy.

Most off-grid homes size for 2 to 5 days of autonomy to ride out a cloudy stretch without a generator running constantly. Locations with more consistent sun can size closer to 2 days, while cloudy climates often plan for 4 or 5, and winter usage increases should be factored in separately.

Off-grid makes sense when a grid connection would require an expensive line extension, often $15,000 or more per mile in rural areas, or when no grid access exists at all. The grid interconnection cost estimator can help you check what a standard connection would cost first.

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