Solar PV + Battery Sizing and Co-optimization

Why size solar and storage together

Size solar alone and midday generation spills to the grid at low export rates; size storage alone and you miss the cheap daytime energy that makes arbitrage and evening peak-shifting work. Co-optimising the two lets the battery soak up surplus PV and release it into the evening peak, lifting the share of solar you actually consume on site — where it is worth retail rates, not export rates.

How the tool models it

PV generation is modelled from the site's latitude and longitude with weather-aware output, then subtracted from your interval load to give the residual profile the battery sees. The tool sizes storage against that residual, capturing self-consumption, evening peak shifting and demand-charge reduction in a single yearly dispatch.

It distinguishes new PV from existing PV: new capacity adds capital cost and, where applicable, new-solar incentives; existing capacity already in your load data adds neither. That keeps the payback honest whether you are adding solar, adding storage to an existing array, or building both at once.

Export, feed-in and incentives by market

Malaysia — NEM 3.0 nets exported solar against consumption for eligible C&I customers. Australia — feed-in tariffs vary by retailer and region, and small-scale certificates (STCs) can offset new PV capital. The tool applies the relevant export and incentive logic per market so self-consumption is valued correctly against export.

Assumptions you control

Battery cost per kWh, round-trip efficiency, degradation, discount rate and price escalation are all inputs you set, so the case reflects your procurement and your view of the market. A sensitivity view shows how payback moves with battery price and energy prices — the two variables that matter most to an investment decision.

New PV carries its own capital cost and, where applicable, incentives; existing PV adds neither. That separation keeps the economics honest across the three cases people actually face: adding solar, adding storage, or building both at once.

Self-consumption is where the value sits

Solar exported to the grid usually earns far less than solar consumed on site, so the point of co-optimisation is to raise the self-consumed share — storing midday surplus and releasing it into the evening. The report highlights self-consumption rate alongside payback, not just installed capacity.

Export caps and network limits

Many C&I sites face an export limit — the network caps how much solar can flow back to the grid, sometimes to zero. That changes the economics: value shifts away from export and toward self-consumption and storage, because surplus that cannot be exported is only worth anything if the battery captures it.

The tool can model limited or zero export, so a constrained site is sized for what it can actually do rather than an unachievable feed-in assumption — and the battery is credited with the surplus it rescues from being curtailed.

From co-optimisation to a report

Once a solar-plus-storage configuration clears your hurdle rate, EWISER EStack produces an investment-ready report — PV and battery specification, savings by value stream, capital cost and the NPV / IRR / payback case — ready for a client or investment committee.

Frequently asked questions