A storage developer calls and says they need three to five acres. You have three hundred. It sounds like the easy part of the conversation, and it is — but not for the reason most landowners assume.
The acreage is almost never what decides whether a battery project gets built on your ground, or how big it is. The grid decides. And the tools available to check the grid from the outside are, by the operators' own written admissions, not good enough to rely on.
How much battery actually fits on an acre
Start with the equipment, because the numbers surprise people.
The U.S. Department of Energy's environmental assessment for a roughly 100-megawatt battery project in Arizona sets out the footprint in a table: 4.5 acres of permanent disturbance for the battery facility itself, plus 0.67 acre for the high-voltage substation, on a ten-acre parcel. The equipment was 37 battery cores and 37 inverter and transformer skids. (DOE/EA-2123, Table 2-2.)
Manufacturers are denser still. Fluence advertises that its Smartstack product occupies "just 32,000 square feet (3,000 square meters) for a typical 100 MW/400 MWh project." That is under three-quarters of an acre of equipment.
For scale at the individual-unit level, Tesla's published Megapack 2 XL datasheet rates each unit at 3,916 kWh and 979 kW in a four-hour configuration, so a nominal 50 MW / 200 MWh system is about 52 units before you account for auxiliaries or degradation. (Megapack 2 XL datasheet, Rev. 1.5.1, February 2023 — Tesla has since announced newer products, and you should not assume these figures describe current equipment.)
The practical range most often cited for utility-scale storage is 0.03 to 0.1 acres per megawatt, which a 2025 study prepared for the Indiana Office of Energy Development reports while noting that natural gas plants run about 0.343 acres per megawatt. That range traces back to a University of Michigan planning guide rather than a national laboratory, so treat it as a planning heuristic, not a standard.
Run the arithmetic and a 100-megawatt project wants somewhere between three and ten acres. On a quarter section, land is not the scarce input.
What is actually inside the fence
Vendor footprint figures describe equipment. A permitted site has to hold considerably more, and this is where quoted acreage and real acreage diverge:
- Battery enclosures and their required separation
- Inverters and medium-voltage transformers
- Collector switchgear and the project substation
- Fire lanes and equipment spacing
- Property-line and dwelling setbacks
- Stormwater detention
- Control building and auxiliaries
- Construction and maintenance access
- Space held back for augmentation — replacement capacity added as cells degrade over a twenty-year contract
If a lease or option quotes an acreage, it is worth requiring the developer to state in writing which of those it includes. A number that covers containers but not the substation, the fire lanes and the augmentation reserve is not the number that ends up fenced.
Fire code drives the layout more than zoning does
The International Fire Code's energy-storage chapter is usually the binding constraint on how equipment sits on a pad. Under IFC § 1207, electrochemical storage is segregated into groups not exceeding 50 kWh with a minimum three-foot separation between groups, unless large-scale fire testing to UL 9540A shows fire will not propagate from one unit to the next. Outdoor installations must sit at least ten feet from lot lines, public ways, buildings and stored combustibles — reducible to three feet with a one-hour fire barrier — and an installation more than 100 feet from those exposures is treated as "remote" and escapes several of the limits entirely. Combustible vegetation must be cleared ten feet around the equipment.
One caution that matters in central Illinois: NFPA 855, the stationary energy storage standard, is not adopted statewide in Illinois. The State Fire Marshal's rules at 41 Ill. Adm. Code Part 100 incorporate NFPA 101 and several other standards; NFPA 855 does not appear in them. Whether it applies to your project is a question for the local authority having jurisdiction and whichever code that body has adopted. Do not let anyone tell you it is automatic, and do not assume it is absent either.
The real constraint: what the wires can take
Here is the part that decides project size. In Ameren Illinois territory the system comes in tiers, and Ameren defines them in its own interconnection policy:
| Tier | Voltage | What it realistically supports |
|---|---|---|
| Distribution | 4 kV to 15 kV | Ameren recommends screening projects of 5 MVA and below |
| Subtransmission | 34.5 kV and 69 kV | Ameren recommends 5 MVA and above |
| Transmission | 138 kV and above | No public hosting capacity map exists at all |
That last row is the one to sit with. A utility-scale battery interconnects at transmission voltage, and there is no free public map that will tell you what is available there.
The maps that do exist disclaim themselves
Ameren publishes hosting capacity maps for distribution and subtransmission, and they are genuinely useful for small projects. But read what Ameren says about them:
"Projects in the study and interconnection queues that have not yet executed an interconnection agreement may have an impact on hosting capacity. AIC lacks certainty on whether these projects will proceed, therefore, the impacts of these potential projects are not reflected in the hosting capacity values shown on the maps."
Ameren Illinois, Hosting Capacity Map
In plain terms: the map shows capacity that may already be spoken for by projects ahead of you in line. Ameren says elsewhere on the same page that hosting capacity "is not guaranteed and/or may change at any time" and that the map "is not intended to be a substitute for the established interconnection process."
MISO's screening tool carries the same warning. Its Points of Interconnection tool lets a developer pre-screen substations, but MISO's own queue process materials state the results "are for information only and do not include voltage or stability constraints." Voltage and stability are frequently what kills a project.
Two further gaps are worth knowing. The federal Energy Information Administration states plainly that "EIA and HIFLD do not publish the location of electric substations" — so you cannot screen substation proximity on the public federal map at all. And MISO's transmission models and maps, the data that would actually answer the question, are released only under Critical Energy Infrastructure Information non-disclosure agreements.
A green square on a public map is a hypothesis. Only a completed interconnection study establishes what a site can carry.
Size determines which legal regime you are in
This is where landowners and even some developers get the citation wrong, and it matters.
Illinois has its own interconnection rules for distributed energy resources: 83 Ill. Adm. Code Part 466 for facilities of 10 MVA or less, and Part 467 for facilities larger than 10 MVA. But both parts contain the same carve-out. They apply only where the facilities being interconnected to are "not subject to the jurisdiction or interconnection requirements of either the Federal Energy Regulatory Commission (FERC) or the applicable Regional Transmission Organization" — meaning MISO or PJM.
Cross that line and the state rules step aside entirely. You are in MISO's generator interconnection queue under a federal tariff. That is a very different process, on a very different timeline, and it is not one an Illinois landowner's counsel can meaningfully influence.
Where the money actually goes
Interconnection cost is rarely about the connection itself. It is about upgrades to the wider network beyond the point of interconnection.
Lawrence Berkeley National Laboratory studied MISO interconnection costs and found that for projects that completed all studies, costs averaged $102 per kilowatt in 2019–2021. For projects that were withdrawn, the figure was $452 per kilowatt — and network upgrades beyond the interconnecting substation accounted for 85% of it. Storage projects averaged $248 per kilowatt. There is one encouraging note for this region: LBNL found projects in the eastern part of MISO, specifically Illinois and Indiana, reported the lowest costs in the footprint at $50 to $70 per kilowatt. That is a 2022 study on 2000–2021 data, so treat it as directional.
On the distribution and subtransmission side, Ameren publishes its own indicative ranges, and they explain why a "small" upgrade is not small: reconductoring a line runs $150,000 to $400,000 per mile below 15 kV and $250,000 to $1,000,000 per mile at 34.5 or 69 kV.
This is the single best explanation for a pattern landowners find baffling: a developer options your ground, pays for a few years, and then walks. They were buying time to find out whether the grid would take the project. Often it will not, at a price anyone will pay.
What this means for your lease
If interconnection is the real asset, the lease should reflect it:
- Get the option economics right. You are being paid to hold ground off the market while someone else resolves a question they cannot yet answer. Price the option accordingly, and cap how long it can run.
- Ask what stage the interconnection request is at. A queue position, a study milestone, a definitive agreement — these are wildly different levels of commitment, and they are knowable.
- Do not grant rights over ground the project does not need. A right of first refusal over your whole farm, granted for a project that will occupy five acres, hands over the scarcity for free.
- Pin down the acreage definition and require written consent before expansion.
- Watch assignment. The interconnection position is the valuable thing; the entity that ends up holding your lease may not be the one that signed it.
- Insist on real decommissioning security, sized without netting out assumed salvage value, running to you and not only to the county.
None of this requires you to predict the grid. It requires the lease to allocate the risk that the grid says no.
We review these agreements for landowners across central Illinois. See our wind, solar and battery lease practice, or start with what a battery storage project actually is and what to check before you sign.