| Scenario | PV DC (kW) | Inverter AC (kW) | DC/AC | Clipping | Tariff ($/kWh) | Year-1 Net |
|---|---|---|---|---|---|---|
| Balanced | 6.0 | 5.0 | 1.20 | about 2 to 4% | 0.18 | $1,100 to $1,400 |
| Higher Oversizing | 7.5 | 5.0 | 1.50 | about 6 to 10% | 0.18 | $1,250 to $1,550 |
| Lower Oversizing | 5.0 | 5.0 | 1.00 | about 0 to 1% | 0.18 | $950 to $1,250 |
- DC/AC Ratio = (PV DC kW + Expansion kW) divided by Inverter AC kW.
- Oversizing (%) = (DC/AC minus 1) times 100.
- Year-1 DC Energy (kWh) = kW DC times 1000 times PSH times 365.
- Year-1 AC Energy = DC Energy times Performance Ratio times Inverter Efficiency.
- Net Energy = AC Energy times (1 minus Clipping%).
- Revenue = Net Energy times Tariff (with escalation each year).
- Net Cash Flow = Revenue minus O&M (with escalation each year).
- NPV = minus CAPEX plus sum(Net Cash Flow divided by (1+Discount)^Year).
- IRR = discount rate where NPV equals zero (computed numerically).
- LCOE = (CAPEX + PV(O&M)) divided by PV(Energy).
- Enter your PV DC size and any planned expansion.
- Enter the inverter AC rating you are considering.
- Pick a clipping method. Use manual if you have modeled clipping.
- Set tariff, costs, and discount rate to reflect your project.
- Press Calculate to view results above the form.
- Use the sensitivity table to compare nearby inverter sizes.
- Download a CSV or PDF report for sharing and record-keeping.
DC/AC ratio and inverter loading
The key sizing metric is the DC/AC ratio: total PV DC kW divided by inverter AC kW. For example, 6.0 kW DC on a 5.0 kW inverter is 1.20, meaning 20% oversizing. A moderate ratio can keep the inverter closer to its efficient operating band during mornings and afternoons, improving usable annual energy across more operating hours.
Clipping as an economic trade-off
Oversizing raises the chance of power clipping when sunlight drives the array above the inverter limit. If a site averages 5.0 peak-sun-hours and your ratio rises from 1.20 to 1.50, clipping might move from roughly 3% to 8% depending on orientation and temperature. The calculator converts that loss into kWh and revenue so you can compare it to inverter and BOS savings.
Tariff, escalation, and degradation
Annual value is driven by net kWh times the electricity rate. With a $0.18/kWh tariff, 9,000 kWh yields about $1,620 in year-one value before O&M. Escalation compounds: 2% per year means the rate becomes $0.22/kWh by year 10. Degradation reduces output: 0.6% per year leaves about 94% of year-one energy by year 10.
Financial metrics for sizing decisions
CAPEX is modeled as PV cost per kW DC plus inverter and other upfront items. Payback is the first year cumulative net cash turns positive. NPV discounts each year’s net cash at your chosen rate; at 8%, a $1,500 net benefit in year 10 is worth about $695 today. IRR estimates the return implied by the cashflow stream.
Sensitivity table for quick comparisons
The sensitivity section tests inverter sizes at plus/minus 20% around your input and recomputes DC/AC, clipping, year-one net value, and NPV. Use it to spot the “flat” region where NPV changes little, then pick a size that stays under your clipping limit, supports future expansion, and matches equipment availability.
FAQs
1) What DC/AC ratio should I start with?
Many residential and small commercial designs land near 1.15–1.35, then adjust for module orientation, climate, and interconnection limits. Use the sensitivity table and keep estimated clipping under your chosen limit.
2) When should I use manual clipping?
Use manual clipping when you have modeled irradiance and inverter curves (or measured data). The heuristic is a quick estimate to compare options, but it cannot capture shading, tracker gains, or detailed thermal behavior.
3) How do I model adding panels later?
Enter planned DC expansion in kW. The calculator recomputes the ratio, clipping estimate, and financial metrics using the combined DC size, helping you select an inverter that can support the future array without excessive clipping.
4) What does LCOE represent in this report?
LCOE is the discounted cost per discounted kilowatt-hour: (CAPEX plus discounted O&M) divided by discounted energy. It helps compare sizing options on a $/kWh basis, independent of the retail tariff you entered.
5) Why might a smaller inverter look better financially?
A smaller inverter can reduce upfront cost and improve loading, even if clipping rises slightly. If the value of saved capital outweighs the revenue lost to clipping, NPV can increase. Always check warranty limits and thermal constraints.
6) Which inputs move results the most?
Peak sun hours, performance ratio, tariff, and discount rate typically dominate revenue and NPV. Inverter size mainly shifts clipping and CAPEX. If you are unsure, run a few scenarios and compare the sensitivity outcomes.