How to plan a commercial solar and battery storage system

What is the business trying to fix?

A warehouse with steady daytime refrigeration may use most of its solar as it is generated. A workshop whose bill is set by a short compressor peak has a different problem. A hotel that wants refrigeration, lighting and communications during an outage has another. Starting all three with the same battery-to-solar ratio would hide the real decision.

Choose the main job first. It may be using more solar on site, reducing a monthly demand peak, moving energy away from an expensive tariff period or supporting selected loads when the grid is unavailable. Other benefits can be modelled afterwards. If every goal is treated as equally important, the proposed battery often grows while the reason for its size becomes harder to explain.

Timing is the link between the problem and the equipment. Solar can serve loads that run during daylight. Storage moves some of that energy to a later hour, clips a brief peak or keeps a defined load running. Its kW rating tells you how much power it can supply at once; its kWh rating tells you roughly how long it can do so. Keep outage value in a separate line from bill savings because the cheapest financial option may not provide the backup the owner expects.

The electricity bill does not show enough

A monthly bill tells you how much energy was bought, but it hides when the building used it. That missing timing can change both the equipment size and the return. Whenever possible, obtain at least 12 months of 15-minute, 30-minute or hourly import data. Put it beside the operating schedule and mark unusual shutdowns, seasonal production and any new machinery that will change the load.

Read the tariff instead of relying on an average cost per kWh. A commercial bill may contain energy charges, demand charges, time-of-use periods, fixed fees, minimum-import conditions or charges that onsite generation cannot remove. A battery can reduce some of these items and leave others untouched. For example, lowering the highest monthly kW may help where a demand charge is based on that peak, but it will not erase a fixed monthly fee.

The site also sets physical limits. Record the roof or ground area, shading, access, equipment locations, cable routes, grid connection and space available for the battery. For backup, make a separate list of the loads that truly need power. Keeping an entire factory alive is a very different request from maintaining controls, refrigeration, communications and a small production line.

Four numbers that people often mix up

PV capacity in kWp describes the rated solar array. Solar-inverter capacity in kW describes how much AC power the inverter can deliver under its stated conditions. Battery power in kW describes how quickly the storage system can charge or discharge. Usable battery energy in kWh describes how much stored energy is available within the proposed operating limits.

Choose each number from the job it performs. The solar array starts with usable installation area, local solar resource, expected losses and the site's daytime energy demand. Battery power starts with the peak that must be reduced or the largest group of loads it must support. Battery energy starts with how long that power is needed. A simple first screen is target battery power multiplied by discharge duration, followed by allowances for usable operating range and conversion losses. That screen is not a purchase specification.

Suppose a site wants to reduce a 150kW peak for roughly two hours. The simple energy delivered during that window is 300kWh. A preliminary model might test a 200kW PCS and around 400kWh of usable storage so it has room for losses and a changing load. The model must then check whether enough charging energy is available, how often the peak occurs, whether the battery can repeat the duty, and how its control will interact with solar and the grid. Another site with the same annual consumption could produce a different answer.

The equipment list is longer than it first appears

A first quotation often names the visible products and leaves the connecting equipment vague. That makes the price look simple, but it moves uncertainty into the construction stage. Ask for an itemised bill of materials with exact models, quantities and a note showing who supplies each part.

The battery package needs particular care. Cells or modules, racks or cabinets, battery management, PCS, energy management, metering, communications, thermal management and fire provisions may be sold as one integrated product or split across several suppliers. The quotation should show the proposed arrangement and the evidence used to confirm compatibility. A familiar brand name on each box is not enough.

Mounting, cables and protection cannot be finalised from a catalogue alone. Their specification depends on the layout, environment, electrical design and local requirements. A supplier can identify the proposed equipment and product-side accessories; the responsible project parties still have to approve the final structural, electrical and safety design for the site.

Make the savings calculation easy to challenge

Someone reviewing the proposal should be able to follow the money from the electricity bill to the final result. Solar may create value through electricity used on site and, where applicable, exported energy. Storage may add value by shifting energy, trimming a measured demand peak or reducing solar curtailment. If a revenue stream depends on a special tariff or contract, name it instead of burying it in "battery savings."

Continue the fictional sizing example from above. Assume the wider proposal combines a 400kWp array with the 200kW / 400kWh storage option and costs 500,000U installed. Modelled solar use and export create 62,000U of annual value. After charging cost, lost export value and conversion loss have been allowed for, battery energy shifting and peak reduction add 22,000U. Annual monitoring and maintenance are estimated at 4,000U. The simplified net benefit is 80,000U a year, so simple payback is 500,000 ÷ 80,000 = 6.25 years.

Now try to break the result. Reduce the expected solar output, change the load schedule, let a second demand peak appear after the battery has discharged, and include financing or a future replacement if the project expects one. Simple payback ignores when cash arrives and what happens later. NPV and IRR add useful context only when the solar, tariff, degradation, maintenance and replacement assumptions remain visible.

A good equipment plan can still fail on site

The proposed models may be sensible and the arithmetic may work, yet the job can still stall over a weak roof, a blocked service route or nowhere suitable to place the battery. Check where the equipment will go, how it will arrive and what the building can accept. Roof condition and load capacity, drainage, access paths and maintenance space matter before modules are released. A ground-mounted array brings its own survey, civil design, drainage and access work.

The battery area needs a project-specific review covering enclosure or room conditions, temperature control, service clearance, emergency access, fire strategy and the route to the electrical connection. Record the distance between the array, inverters, battery, switchboard and meter. Long or difficult routes affect design, labour and cost even when the main equipment stays the same.

Agree the work boundary early. Name who owns the site survey, detailed drawings, structural review, protection study, utility submission, permits, construction, testing and final acceptance. The delivery plan also needs unloading space, lifting access and secure storage. Production teams should know when shutdowns or temporary power will be required. At handover, the owner should receive the agreed tests, monitoring access, training, as-built drawings, settings record, manuals and warranty contacts.

What the buyer should receive

A reviewer should not have to reverse-engineer the quotation. The final proposal should show the data received, any gaps filled with assumptions, the proposed operating strategy and the calculations that connect the site to the equipment. Alternatives should be labelled. If the battery is added mainly for backup, keep its extra cost and supported-load result visible rather than folding everything into a headline return.

For an early supplier discussion, the buyer does not need a complete engineering package. A year of bills, interval load data, site drawings or photographs, the main operating goal, the backup-load list and the desired project boundary are enough to expose the important questions. The next version can then replace assumptions with verified site information instead of pretending the first estimate is final.