Battery energy storage (BESS): a project guide

What a BESS actually is

A BESS is a battery system plus the inverters, controls, housing and electrical works that let it charge and discharge. Capacity is usually described as power (MW) and energy (MWh), which together imply duration.

The project is the system in a place, with a connection and a reason to exist. A container drawing is not yet a project.

Commercial, standalone and behind-the-meter

Behind-the-meter (BTM) storage sits on the customer’s side of the meter, usually to serve on-site demand, solar shift or resilience. Standalone BESS is typically a grid-connected asset whose commercial life depends on the network, markets or contracted services. Commercial can mean either, or a co-located system on an industrial site.

Do not collapse these into one pitch. A 500kWh factory battery and a multi-MW standalone site need different information, counterparties and capital conversations.

Site, grid and capacity

Site control, access, flood, fire, noise and neighbouring use all matter. Grid position is often the binding constraint: existing capacity, a DNO application, an offer, or nothing yet established.

Intended power and duration should be stated as an envelope if design is unfinished. Unknown connection dates should stay unknown.

Use case before design

The use case is why the battery would charge and discharge: on-site solar shifting, peak demand, backup, a contracted service, or a merchant stack that has not been evidenced. Design follows that, not the other way around.

If several use cases are still open, say so. A revenue stack presented as fact before the connection and operating model exist is not a useful starting point.

Design and costing

Design fixes equipment envelope, electrical arrangement, civil works and controls against the use case. Costing is an EPC or installer estimate against that scope — capex, and often a view on what is excluded.

Feasibility tests whether the site and connection can support the idea. A costing is a delivery estimate. They are related and they are not the same.

Commercial assumptions and capital

Commercial assumptions are who owns the battery, who operates it, how it earns or saves, and who takes residual risk. Capital is the money to develop, build or refinance. Mixing an assumed merchant return with an uncosted connection is how a raise stalls.

Owner-funded BTM, developer-led standalone, and operator or joint-venture models are different asks. State the gap: development support, an EPC price, or construction capital.

What investors usually need to see

Site control, connection position, duration, a costing pathway, and a commercial model with labelled assumptions. They do not need a polished story. They do need known versus not yet established.

WattFund helps present that status. It does not underwrite storage, hold client money or guarantee that funding will be available.

WattFund’s role

Describe the site and what you are trying to achieve. WattFund structures that information and connects costing, delivery or capital when that is the next step. Grid uncertainty should be shown clearly rather than filled with an assumed date.