Learn & Understand

The Duck Curve: Why Solar Timing Doesn't Match Your Usage

The companion calculator computes a net-metering bill by netting the electricity a solar home imports from the grid against what it exports, often at different rates. The reason net metering exists at all is a fundamental timing problem: a solar array generates most of its power at midday, while a household uses most of its electricity in the morning and evening, so a solar home is constantly both buying and selling power at different hours. Understanding this timing mismatch, how net metering reconciles it, why import and export rates differ, and how it connects to the grid-wide "duck curve" turns a net-metering calculation into an appreciation of the timing dance between solar production and demand.

Production and Usage Don't Line Up

Solar production and household electricity usage rarely match hour by hour: a solar array generates most of its power in the middle of the day when the sun is highest, but household consumption typically peaks in the morning (before work) and evening (after work), so the two are out of sync. This means a solar home is often producing more than it uses at midday (exporting the surplus to the grid) while using more than it produces in the morning and evening (importing from the grid), so at different hours it's simultaneously a power seller and a power buyer, as the calculator's premise explains. The mismatch arises because the sun's schedule (peaking at noon) doesn't align with human activity patterns (peaking at the day's ends), so even a solar system that produces enough total energy over a day may not produce it when the home needs it, creating the constant give-and-take with the grid. This timing problem is central to how residential solar works: without perfect alignment or storage, the home relies on the grid to absorb its midday surplus and supply its morning/evening deficit, which is exactly what net metering manages. Understanding that production and usage don't line up is the foundation for understanding why net metering exists and what it does. Understanding that production and usage don't line up is the starting point: solar peaks midday while homes use power morning and evening, so a solar home both exports surplus and imports deficit at different hours. The calculator nets these flows; understanding the mismatch is what reveals why net metering is needed, production and demand are out of sync, so the calculator reconciles the exporting and importing the timing mismatch creates.

How Net Metering Reconciles the Mismatch

Net metering reconciles the timing mismatch by netting the two flows over a billing period: it charges for the electricity imported from the grid and credits for the electricity exported to it, so the bill reflects the net of buying and selling.

Net metering treats the grid as a kind of battery or clearinghouse: when the home exports surplus solar (midday), it earns a credit, and when it imports (morning/evening), it's charged, and over the billing period these are netted, so the bill is the import cost minus the export credit, as the calculator computes (net bill equals import kWh times import rate minus export kWh times export rate). This lets the home effectively "use" its midday surplus later by offsetting its later imports with the credits earned, so net metering makes the timing mismatch manageable without requiring on-site storage, by using the grid to balance the flows. If exports exceed imports (a surplus month), the net bill can be negative, meaning the utility owes a credit, and if imports dominate (a deficit month), the home owes, as the calculator's examples show. This netting is the mechanism that makes residential solar practical despite the timing mismatch: the home doesn't need to consume its solar exactly when produced, because the grid absorbs the surplus and returns the value through credits. Understanding how net metering reconciles the mismatch, by netting charged imports against credited exports, reveals what the calculator computes and why it's the key to solar economics without storage. Understanding how net metering reconciles the mismatch reveals the mechanism: it nets charged imports against credited exports over a billing period, letting the grid balance solar's timing mismatch. The calculator nets import cost against export credit; understanding net metering is what reveals how the bill works, exports offset imports, so the calculator computes the net of buying and selling that net metering enables.

Why Import and Export Rates Differ

A crucial detail is that many utilities credit exported power at a lower rate than they charge for imported power, so the import and export rates are entered separately, which significantly affects the economics of a solar system and how large it should be. As the calculator's premise notes, utilities often pay a lower rate for exported power than they charge for imported power, so a kilowatt-hour you export earns you less credit than a kilowatt-hour you import costs you, meaning the netting isn't one-for-one in value, which is why the calculator lets you enter import and export rates separately, as its formula shows. This rate difference matters because it changes the value of surplus solar: if export credit is much lower than the import rate, then exporting surplus is worth less than using solar directly or offsetting imports, so oversizing a system to export a lot may pay back more slowly than sizing closer to your actual consumption (to maximize self-use), as the calculator's context notes. The reason utilities pay less for exports varies (reflecting the grid's costs, the value of the power at that time, and policy), but the practical effect is that export-heavy solar is less valuable when the export rate is low, so understanding the rate structure is essential to sizing and evaluating a system. Comparing utilities' net-metering policies, running the same generation and consumption against different rate structures, shows how much a utility's specific policy affects the bottom line, as the calculator's context describes. Understanding why import and export rates differ reveals a key economic factor, so the calculator's separate rates capture the real value of imports and exports. Understanding why import and export rates differ reveals a key economic factor: exports are often credited less than imports cost, so surplus is worth less, affecting sizing. The calculator uses separate rates; understanding the difference is what reveals why it matters, low export rates make oversizing less valuable, so the calculator's separate rates capture the real, often asymmetric, economics of net metering.

The Duck Curve and the Bigger Picture

The household timing mismatch mirrors a grid-wide phenomenon, the "duck curve": as many solar systems produce midday surplus and demand peaks in the evening, the net demand the grid must serve dips at midday and ramps up sharply in the evening, shaping solar's value and policy. The duck curve is the shape of net electricity demand (total demand minus solar production) over a day in regions with lots of solar: it dips low midday (when solar floods the grid) and rises steeply in the evening (when solar fades but demand peaks), resembling a duck's silhouette, so the grid faces a glut of solar midday and a steep ramp in the evening. This grid-level mismatch is the aggregate of the household mismatch, and it explains why midday solar exports may be worth less (there's often a surplus of solar then, so the grid values it less) and why evening power is more valuable, which underlies the lower export rates and the growing interest in storing solar (batteries) to shift midday surplus to the evening. So the household net-metering situation, exporting cheap midday power and importing valuable evening power, reflects the broader duck-curve dynamics of solar-heavy grids, and understanding it illuminates why net-metering policies and rates are structured as they are, and why storage and time-of-use pricing are increasingly relevant. The calculator's netting, with separate rates, captures the household side of this larger timing story. Understanding the duck curve and the bigger picture reveals the grid-wide mismatch: midday solar surplus and evening demand peaks shape a duck-shaped net-demand curve, driving lower midday export values and the push for storage. The calculator computes the household net bill; understanding the duck curve is what reveals the broader context, the timing mismatch is grid-wide, so the calculator's net metering reflects a household version of the duck-curve dynamics shaping solar's value.

Understanding Net Metering

Use the calculator to compute your net-metering bill, and understand the timing problem behind it: solar produces most power at midday while homes use most in the morning and evening, so a solar home constantly exports surplus and imports deficit, and net metering reconciles this by netting charged imports against credited exports over a billing period. The calculation nets import cost against export credit at separate rates; understanding the timing mismatch, why export rates are often lower, and the grid-wide duck curve is what reveals how net metering works and why sizing and rates matter, so the calculator captures the household side of the timing dance between solar production and electricity demand.