Levelized cost of energy turns a solar project’s lifetime costs and electricity production into one comparable figure. The formula is straightforward, but the result is only useful when installed cost, degradation, maintenance, replacements, financing assumptions, and usable energy are modeled consistently.
A solar quotation normally emphasizes the initial project price and expected annual generation. Those figures are important, but they do not show the complete cost of electricity over a 20-, 25-, or 30-year analysis period.
A project with a higher installation cost may produce electricity more efficiently, experience less downtime, require fewer repairs, or remain productive for longer. A cheaper project may develop a higher lifetime energy cost if its production estimate is optimistic or important operating expenses have been excluded.
The levelized cost of energy, or LCOE, helps place these factors into one calculation. The result is usually expressed in dollars per kilowatt-hour or dollars per megawatt-hour.
Key idea: LCOE estimates the average lifetime cost of generating electricity. It does not automatically show project profit, bill savings, payback period, investment return, grid value, or the timing of revenue.
What LCOE Measures
LCOE compares the present value of project costs with the present value of the electricity expected to be generated. Discounting is used because a cost or unit of energy occurring many years from now is not treated identically to one occurring today.
In this formula, t is the year and r is the discount rate. Costs may include capital expenditure, operation and maintenance, replacements, insurance, leases, decommissioning, and other expenses included within the study boundary.
A simple undiscounted calculation can help explain the concept:
This version is useful for a quick first look, but a commercial investment model should normally represent the timing of costs, degradation, replacements, and financing assumptions.
LCOE Is Not the Same as Other Financial Metrics
LCOE is useful for comparing different generation designs under a consistent boundary. It does not measure the hourly value of solar production, tariff savings, demand-charge reduction, avoided outages, capacity value, or contract revenue unless those questions are addressed through separate analysis.
Do not compare LCOE directly with a retail electricity bill without context. Retail tariffs may include delivery charges, demand charges, taxes, fixed fees, time-of-use pricing, and compensation rules that are not part of a generation-only LCOE.
Information Needed Before Calculating
Use one inflation basis throughout the model. A real-dollar model uses costs stated in today’s purchasing power with a real discount rate. A nominal model applies inflation or cost escalation and uses a nominal discount rate. Mixing the two can distort the result.
The Calculation Process
-
Define the calculation boundary.
Decide which project costs and energy flows are included. Apply the same boundary to every design or project being compared. -
Record the complete initial investment.
Include more than modules and inverters. Engineering, mounting, electrical equipment, labor, site work, permitting, interconnection, commissioning, and development costs may all be relevant. -
Estimate first-year AC production.
Use location-specific solar resource data and a production model that represents orientation, shading, temperature, inverter behavior, wiring losses, soiling, availability, and other system losses. -
Select the analysis period.
The project lifetime should be consistent with equipment expectations, land or roof rights, power contracts, warranties, and investor assumptions. -
Apply annual degradation.
Reduce electricity production year by year rather than multiplying first-year production by the project lifetime. -
Add recurring operating expenses.
Include realistic costs for monitoring, maintenance, cleaning, repairs, insurance, leases, vegetation control, security, and administration when applicable. -
Add major expenses in the year they occur.
Inverter replacement, transformer work, communication upgrades, roof removal and reinstallation, and other scheduled costs should be assigned to their expected year. -
Choose and document the discount rate.
The selected rate should be consistent with the model’s inflation basis, cost of capital, project risk, and financial purpose. -
Discount annual costs and energy.
Divide each future amount by one plus the discount rate raised to the relevant year. -
Divide total discounted costs by total discounted energy.
The result is the estimated LCOE. Confirm whether it is expressed in dollars per kWh or dollars per MWh.
Worked Commercial Solar Example
The following example is hypothetical and is intended to demonstrate the method rather than represent a market quotation.
Example Assumptions
With these assumptions, the model produces approximately:
| Calculated Value | Approximate Result | Meaning |
|---|---|---|
| Present value of lifetime costs | $128,960 | Initial investment plus discounted operating, replacement, and end-of-life costs |
| Present value of lifetime energy | 1,711,110 kWh | Annual degraded production discounted over 25 years |
| Estimated LCOE | $0.0754 per kWh | Approximately 7.54 cents per kWh |
| Equivalent unit | $75.37 per MWh | One megawatt-hour equals 1,000 kilowatt-hours |
The example is not a prediction. Changing production, financing, replacement timing, degradation, project life, curtailment, taxes, incentives, or operating costs can materially change the result.
Solar LCOE Calculator
Use the calculator below for an educational real-dollar estimate. All future costs are treated as today’s dollars, and no annual cost escalation is applied.
Discounted Solar LCOE Estimate
Replace the example values with project-specific assumptions. Negative values and incomplete inputs are rejected.
How the Spreadsheet Should Be Structured
A spreadsheet gives each project year its own row. Year zero normally contains the initial investment, while electricity production begins after the system enters operation.
| Column | Typical Formula or Entry | Purpose |
|---|---|---|
| Year | 0 through the end of the analysis period | Shows when each cost and production event occurs |
| Annual energy | Year-one energy × (1 − degradation)year − 1 | Applies the annual production decline |
| Operating cost | Annual O&M and other recurring costs | Captures expenses after construction |
| Replacement cost | Entered in the expected replacement year | Prevents major future costs from being omitted |
| Discount factor | 1 ÷ (1 + discount rate)year | Converts future amounts into present-value terms |
| Discounted cost | Annual cost × discount factor | Builds the numerator of the calculation |
| Discounted energy | Annual energy × discount factor | Builds the denominator of the calculation |
Audit tip: keep the raw assumption, formula, unit, source, and date visible. Avoid embedding unexplained values inside long formulas, because hidden assumptions are difficult to review and update.
Production Assumptions That Change LCOE
Energy production is the denominator of the calculation. When lifetime cost remains constant, higher usable production lowers LCOE and lower production raises it.
- Local solar irradiance and weather variability
- Module orientation and tilt
- Near and far shading
- Module temperature losses
- Inverter conversion efficiency
- DC and AC wiring losses
- Soiling and cleaning strategy
- Module mismatch and tolerance
- Equipment availability and downtime
- Grid curtailment or export restrictions
- Annual module degradation
- Transformer and auxiliary consumption
The production estimate should clearly identify whether energy is measured on the DC side, at the inverter output, at the project meter, or after additional losses. Commercial comparisons should use the same measurement boundary.
Module nameplate capacity is not annual energy production. A 1 MW solar plant does not generate 1 MW continuously. Its annual output depends on solar resource, design, losses, availability, curtailment, and operating conditions.
Costs Commonly Forgotten
| Cost | Why It Matters | How to Model It |
|---|---|---|
| Interconnection and grid upgrades | Can materially increase project cost or delay operation | Add confirmed studies, fees, equipment, and construction costs |
| Inverter replacement | Inverter service life may differ from module life | Add expected replacement cost in the relevant year |
| Insurance | Creates a recurring operating expense | Include annual premiums within O&M |
| Monitoring and software | Some platforms require recurring subscriptions | Add annual service and communication costs |
| Cleaning and vegetation | Site conditions may require repeated work | Use location-specific frequency and labor estimates |
| Land or roof lease | May continue throughout the project life | Add the payment schedule and escalation method |
| Decommissioning | Large projects may have removal or restoration obligations | Add net end-of-life cost after residual value |
| Construction delay | Costs may occur before electricity production begins | Use a more detailed model with construction timing |
Run More Than One Scenario
Conservative Case
Lower production, higher installed cost, greater degradation, higher O&M, earlier replacement, or a higher discount rate.
Base Case
The assumptions considered most reasonable using current engineering, supplier, financing, and operating information.
Optimistic Case
Higher production, controlled cost, lower downtime, longer equipment life, or more favorable financing assumptions.
Scenario analysis is more useful than presenting one number as certain. It shows which assumptions have the greatest influence and where stronger information is needed.
High-Value Sensitivity Tests
- Installed cost above and below the base case
- First-year production uncertainty
- Different solar-resource years
- Higher and lower discount rates
- Alternative degradation assumptions
- Early or late inverter replacement
- Different project lifetimes
- Higher maintenance and insurance
- Curtailment and export limitations
- Downtime after major equipment failure
Common Calculation Errors
| Error | Possible Consequence | Better Practice |
|---|---|---|
| Using module price instead of total installed cost | Major project expenses are omitted | Use the full cost required to reach commercial operation |
| Multiplying first-year production by project life | Lifetime energy is overstated | Apply degradation and realistic downtime year by year |
| Mixing nominal and real assumptions | Future costs are valued inconsistently | Use one inflation and discount-rate basis |
| Ignoring replacement expenses | Lifetime cost appears artificially low | Add major repairs and replacements in expected years |
| Mixing kWh and MWh | The result can be wrong by a factor of 1,000 | Control units throughout the spreadsheet |
| Assuming zero curtailment | Delivered energy may be overstated | Use interconnection and operating studies |
| Changing boundaries between alternatives | The comparison becomes unfair | Use equivalent cost and energy boundaries |
| Treating a low LCOE as guaranteed profit | Revenue, tariffs, timing, and market value are ignored | Combine LCOE with a complete cash-flow analysis |
When LCOE Is Not Enough
| Decision Question | Useful Metric | Why |
|---|---|---|
| What is the average lifetime generation cost? | LCOE | Compares discounted cost with discounted electricity production |
| How quickly is the investment recovered? | Payback | Focuses on cumulative project recovery time |
| Does the project create financial value? | NPV | Compares discounted benefits and costs |
| What return does the investment produce? | IRR | Estimates the return implied by project cash flows |
| How much does discharged battery energy cost? | LCOS | Represents storage charging, losses, degradation, and discharge |
| What is electricity worth at the time it is produced? | Hourly value analysis | Recognizes that electricity value changes by time and location |
Two projects can have similar LCOE results while producing very different financial outcomes. One may receive a strong long-term contract while another faces curtailment, weak compensation, or expensive grid upgrades.
Solar-plus-storage requires additional analysis. Battery cost, charging energy, round-trip losses, usable capacity, cycle degradation, replacement, controls, dispatch strategy, and revenue sources are not represented adequately by a basic solar-only LCOE.
Before Using the Result for an Investment Decision
- Confirm the installed-cost boundary
- Use an AC production estimate for the delivery point
- Document degradation and availability
- Confirm whether curtailment is included
- Check the real or nominal basis
- Review replacement and end-of-life costs
- Verify the selected project lifetime
- Test at least three scenarios
- Compare LCOE with cash-flow metrics
- Confirm current tax and incentive treatment separately
- Review grid and contract limitations
- Have significant projects independently checked
Engineering review is particularly important for commercial, industrial, and grid-connected projects because a small change in production, interconnection cost, availability, or curtailment can affect millions of kilowatt-hours over the project life.
Final Recommendation
LCOE is most useful when it is transparent. A reviewer should be able to see where every cost came from, how electricity production was modeled, why the discount rate was selected, when replacements occur, and which expenses or benefits were excluded.
Begin with a clear calculation boundary and a realistic first-year production estimate. Apply degradation annually, place future expenses in the correct years, discount costs and energy consistently, and test conservative as well as optimistic scenarios.
Use the resulting LCOE as one part of the decision. A complete commercial solar evaluation should also consider cash flow, financing, tariffs, contract terms, interconnection, hourly electricity value, operational risk, and professional technical review.
Frequently Asked Questions
What does LCOE mean for a solar project?
LCOE estimates the average lifetime cost of generating one unit of solar electricity. It compares the present value of included project costs with the present value of expected electricity production.
Should incentives be included?
A model may calculate LCOE before or after incentives, but the treatment must be clearly labeled and applied consistently. Eligibility, timing, tax treatment, transferability, and current rules should be verified separately with qualified professionals and official sources.
Why is degradation included?
Solar production generally changes over time. Applying the selected degradation assumption annually prevents the model from assuming that every future year produces exactly the same amount as the first.
Does a higher discount rate increase solar LCOE?
It often does because much of the solar project cost occurs near the beginning while electricity is generated over many future years. A higher rate reduces the present value assigned to later production. The exact effect depends on the timing of costs and energy.
Is lower LCOE always the best project?
No. A project with low LCOE may still have weak revenue, poor cash flow, curtailment exposure, difficult interconnection, limited grid value, or unacceptable technical risk. LCOE should be used with other financial and operational measures.
Can rooftop and utility-scale solar LCOE be compared?
They can be compared only when the boundaries and intended purpose are understood. Rooftop solar may be evaluated against a customer’s retail tariff, while utility-scale solar is normally connected to wholesale markets or long-term power contracts.
What is the difference between $/kWh and $/MWh?
One megawatt-hour equals 1,000 kilowatt-hours. An LCOE of $0.075 per kWh is equivalent to $75 per MWh.
When should a professional model be used?
Professional support is appropriate for financed, commercial, industrial, utility-scale, tax-sensitive, battery-integrated, or grid-constrained projects. These projects may require detailed engineering, financing, tax, tariff, contract, and interconnection analysis.
Official Tools and References
- National Renewable Energy Laboratory — PVWatts Calculator
- National Renewable Energy Laboratory — System Advisor Model
- National Renewable Energy Laboratory — Annual Technology Baseline
- U.S. Energy Information Administration — Levelized Costs of New Generation Resources
- U.S. Energy Information Administration — Levelized Cost Definition
The Ogumex Editorial Team creates practical, research-based content about commercial solar energy, battery storage, clean technologies, and sustainable industrial solutions. Our goal is to explain complex topics clearly, helping professionals, businesses, and informed readers make better decisions. Each article is reviewed for clarity, accuracy, and usefulness using reliable industry and official sources.
