Comparing storage quotes

Two quotes for the same request can rarely be compared line by line. Different kilowatt-hour figures, differently defined power values and a different scope of supply make a direct comparison hard, even though both quotes appear to answer the same question. Comparing only the stated numbers therefore often sets figures side by side that describe different things.

Why quotes are not directly comparable

One supplier states the nameplate capacity of the battery cells, another the usable capacity after reserve and depth-of-discharge limits. One supplier gives continuous power, another the briefly available peak power. Both figures appear in the quote but describe different things. Without normalising to a common basis, comparing the raw numbers is misleading.

Normalising: establishing a common basis

A proper quote review first converts every quote to the same figures: usable capacity instead of nameplate capacity, continuous power instead of peak power, round-trip efficiency under the same test conditions, guaranteed cycle count at a defined depth of discharge, and the promised remaining capacity at the end of the warranty period. Only once every quote stands on this common basis can you judge which one actually delivers more for the same requirement.

Scope gaps that are easily missed

Beyond the technical figures, the scope of supply often differs substantially between quotes. Is the grid connection, including any change to the metering setup, included, or does it need to be commissioned separately? Is fire protection technology part of the delivery, or organised separately by the client? Is commissioning with a full record part of the quote, and who takes on O&M (operation and maintenance) after handover, for how long? A quote that looks cheaper can result simply from one supplier leaving these items out and another including them.

Checking plausibility before price

A quote can only really be judged once its sizing has been checked against the company’s own load profile. Does the offered power match the actual peakiness of the company’s load, or is the system sized for a load profile that has little to do with its own? An oversized system ties up resources unnecessarily; an undersized one fails to deliver the intended peak-shaving effect. Both only show up once checked against the real quarter-hour values.

A low-priced quote can result because a supplier genuinely works more efficiently, or because it has left out services, cut safety margins, or shortened warranty periods. Without prior normalisation to common figures, this distinction cannot be made. A price comparison carried out before normalisation really only compares each bidder’s own interpretation of the request, not their actual performance.

A complete quote review therefore assigns the same normalised figures to every quote first, and only then looks at the respective price. This shows whether a lower price rests on genuinely lower performance, on excluded items, or on real efficiency in the supplier’s offer. Only the last case justifies favouring a quote on price alone.

References and locking terms into the contract

Beyond the technical figures, it is worth looking at a bidder’s reference projects: how many comparable systems has it already built, at what scale, and can the operators of these systems actually be reached? A quote with impressive figures but no solid references carries a different risk than one with less striking numbers but demonstrable experience with comparable projects. A short conversation with the operator of a reference system often delivers more reliable information about a supplier’s actual reliability than any further figure in the quote itself.

By the end of the quote review, every relevant commitment, usable capacity, power, round-trip efficiency, cycle life and warranty periods by component, should carry over word for word into the contract. A quote that promises good figures without those figures reappearing exactly in the contract does not bind the supplier the way it appears to. This last step, from quote into contract, is often underestimated in practice, and is frequently the point where a careful quote review loses its real value.

Questions to ask bidders

• What usable capacity is committed at what depth of discharge and what ambient temperature?
• What cycle count and depth of discharge is the stated cycle life based on?
• Is the grid connection, including registration with the grid operator and the metering concept, included in the quote?
• Which components are covered by which warranty period, and what applies to a defect outside that period?
• How is commissioning documented, and which capacity test is carried out at acceptance?

At the end of this review stands a recommendation that can be justified item by item, rather than a general impression drawn from several differently worded documents. A structured quote review brings exactly this normalisation, and the comparison against the company’s own load profile, into a traceable format. The grid connection itself, which a complete quote should specify, follows VDE-AR-N 4105 on the low-voltage grid and VDE-AR-N 4110 on the medium-voltage grid; a quote that does not clearly state this assignment defers a technical check that really belongs before the contract is signed. As of September 2026.

Sources

1. VDE-AR-N 4105, low-voltage technical connection rule, vde.com
2. VDE-AR-N 4110, medium-voltage technical connection rule, vde.com