Calculator inputs
Use realistic values for your location and operations. For residential users, set downtime cost to estimated inconvenience or spoilage cost.
Example data table
Sample scenarios to show how inputs change results.
| Scenario | Events/yr | Avg hours | Backup (cov × rel) | Adjusted outage hours | Expected annual cost | Risk band |
|---|---|---|---|---|---|---|
| Residential baseline | 3 | 1.5 | 0% × 100% | 5.94 | $475.20 | Moderate |
| Small business w/ partial backup | 5 | 2 | 60% × 90% | 16.20 | $8,942.40 | Moderate |
| Critical facility w/ strong backup | 8 | 3 | 90% × 98% | 37.91 | $22,365.72 | High |
Example costs assume different critical loads and hourly interruption impacts.
Formula used
1) Base outage hours
BaseHours = EventsPerYear × AvgOutageHours
2) Adjusted outage hours
AdjustedHours = BaseHours × GridMultiplier × WeatherMultiplier × PreparednessMultiplier
3) Effective backup coverage
EffectiveCoverage = (Coverage% ÷ 100) × (Reliability% ÷ 100)
4) Unserved fraction
Unserved = 1 − EffectiveCoverage
5) Expected annual downtime cost
AnnualCost = AdjustedHours × DowntimeCostPerHour × Unserved
6) Energy not served
ENS(kWh) = AdjustedHours × CriticalLoad(kW) × Unserved
7) Risk score
RiskScore blends normalized frequency, adjusted hours, unserved fraction, and multipliers into a 0–100 index for comparisons.
How to use this calculator
- Enter typical outage frequency and average duration for your site.
- Provide critical load and realistic downtime cost per hour.
- Set current backup coverage and reliability to estimate today’s risk.
- Adjust grid, weather, and preparedness ratings for local conditions.
- Optional: model a planned upgrade and review payback and NPV.
- Download CSV or PDF after running the calculation for reporting.
Article
Outage frequency translates directly into exposure
Organizations commonly experience 2 to 8 outage events annually, with durations from 0.5 to 4 hours. In the calculator, base outage hours equal events per year multiplied by average duration, then adjusted by grid, weather, and preparedness multipliers. A site moving from 2 events to 6 events, holding duration constant at 2 hours, triples base exposure before any mitigation.
Backup coverage and reliability reduce unserved impact
Effective coverage is the product of coverage and reliability. For example, 70% coverage with 90% reliability yields 63% effective coverage, leaving 37% of critical load unserved. If adjusted outage hours are 18 per year and downtime cost is $500 per hour, expected downtime cost is 18 × 500 × 0.37 = $3,330 annually. Small changes in reliability materially affect cost.
Risk score supports consistent comparisons across sites
The risk index blends normalized frequency, adjusted hours, unserved fraction, and stress multipliers into a 0–100 scale. A moderate band often indicates either high interruption hours or weak backup, not necessarily both. Use the driver chart to isolate whether frequency, duration, or unserved fraction is dominating your score so you can target the right mitigation.
Scenario analysis quantifies the value of upgrades
Planned coverage and reliability produce a new unserved fraction and an updated annual cost. The avoided cost is the difference between current and planned expectations. If current cost is $9,600 and planned cost is $1,800, avoided cost is $7,800. Subtract annual O&M to estimate net annual benefit used for payback and discounted value.
NPV, payback, and reporting keep decisions finance-ready
NPV discounts annual net benefits over the selected analysis years and adds salvage value at the end. If CAPEX is $20,000, net benefit is $4,000 per year, discount rate is 8%, and salvage is 10%, the calculator estimates whether the upgrade creates value today. Export CSV or PDF to share assumptions and results with stakeholders. carefully carefully carefully carefully carefully carefully carefully carefully
FAQs
What does the risk score represent?
It is a 0–100 index that combines outage frequency, adjusted outage hours, the unserved fraction after backup, and site stress multipliers. Use it to compare sites and scenarios consistently, not as a guarantee of any specific future event.
How should I estimate downtime cost per hour?
Use your best operational estimate: lost production, labor inefficiency, spoilage, penalties, and recovery time. For small offices, you can proxy with revenue per hour or the cost of idle staff. Keep the value consistent when comparing scenarios.
Why do grid, weather, and preparedness change hours?
The multipliers approximate how local conditions influence outage exposure. Poorer grid condition and higher weather exposure increase expected interruption hours. Stronger preparedness reduces the adjusted hours through faster response, maintained equipment, and practiced procedures.
How is effective backup coverage calculated?
Effective coverage equals coverage percentage multiplied by reliability percentage. A 80% coverage system that succeeds 95% of the time yields 76% effective coverage. The remaining 24% is treated as unserved during adjusted outage hours for cost estimation.
What does the upgrade NPV include?
NPV discounts annual net benefits, defined as avoided downtime cost minus annual O&M, across your chosen analysis years. It then adds a salvage value percentage at the end. A positive NPV indicates value creation under your assumptions.
Can I use this for residential planning?
Yes. Enter outage frequency and duration from your utility history, set a realistic inconvenience cost per hour, and estimate critical load such as refrigeration and lighting. The results help compare backup options, but they remain planning-level estimates.