Levelized cost of energy, usually shortened to LCOE, expresses a generating project’s lifecycle costs per unit of energy. For a solar proposal, it can help compare the cost of producing electricity over a defined period. It does not, by itself, tell you how much your utility bill falls or when your investment pays back.
If you are considering residential solar installation, request the calculation’s method and assumptions alongside its cents-per-kWh result. A favorable number with an unexplained denominator is difficult to evaluate.
This entry owns the definition and interpretation of the metric. Our solar quote comparison guide retains the broader purchasing checklist. Every numerical example below is fictional arithmetic for understanding the method, not a Sunburst quote, forecast, market benchmark or recommended financial assumption.
What does LCOE measure?
LCOE connects the costs assigned to a project with the electricity assigned to that same project. Its unit is typically dollars or cents per kilowatt-hour. Another presentation uses dollars per megawatt-hour; convert the units before comparing results.
The System Advisor Model distinguishes project energy cost from the value of avoided electricity purchases. It also provides separate financial measures for evaluating value. SAM explanation of LCOE.
Think of an LCOE result as a compressed model. The visible number represents many decisions about installation expense, later costs, output and financial treatment. It is informative only when those decisions match the question you are asking.
For example, a homeowner might ask, “Which of these otherwise comparable solar designs produces electricity at a lower modeled lifecycle cost?” LCOE can contribute to that answer. A different question, “Will my household spend less each month after taking this loan?” requires payments and utility bills over time. The same metric cannot fully answer both questions.
What is the discounted LCOE equation?
For a simple constant-dollar project calculation, write:
LCOE = [initial cost + sum of discounted later net costs] ÷ [sum of correspondingly discounted annual energy]
One explicit form is:
LCOE = [C₀ + Σ Cₜ ÷ (1 + d)ᵗ] ÷ [Σ Eₜ ÷ (1 + d)ᵗ]
Here C₀ is the initial included cost, Cₜ is the included net cost in year t, Eₜ is that year’s energy at the defined boundary, and d is the discount rate. The sums run over the stated analysis period. Specify when payments and energy are assigned within each year.
The comparative PV calculator documentation presents a discounted cost-to-energy calculation. Its simplified cost structure is not a substitute for every household financing or tax situation.
For the examples in this entry, annual items occur at year-end and the initial expense occurs at time zero. Other conventions can be valid, but they must be identified. A spreadsheet that changes the timing silently can change the answer without changing any equipment.
A two-year example that makes discounting visible
Use an intentionally short teaching model. It is not an estimate of a solar system’s life.
Assume an initial cost of $1,000, annual included costs of $100 in each of two years, and annual energy of 1,000 kWh in each year. Assume a 10% discount rate solely to make the arithmetic easy to see. There are no incentives, financing, replacements or terminal values in this example.
| Item | Year zero | Year one | Year two |
|---|---|---|---|
| Included expense | $1,000 | $100 | $100 |
| Energy | 0 kWh | 1,000 kWh | 1,000 kWh |
| Discount factor | 1 | 1 ÷ 1.10 | 1 ÷ 1.10² |
Discounted costs are $1,000 + $90.91 + $82.64, or approximately $1,173.55. The corresponding discounted energy quantity is 909.09 + 826.45, or approximately 1,735.54 kWh. The ratio is approximately $0.6762/kWh, or 67.62 cents/kWh.
The undiscounted ratio would be $1,200 divided by 2,000 kWh, or $0.60/kWh. Neither result describes a current residential market price. The difference demonstrates why the word “levelized” should come with a method disclosure rather than an unexplained lifetime division.
Do not round every intermediate value heavily. Keep adequate precision in the calculation and round the final display. Ask for the underlying annual schedule if you need to reproduce a proposal’s result.
Does discounting mean the panels produce fewer physical kWh?
No. Discounting is a financial treatment of timing. It does not physically remove electricity from the array.
In the teaching example, the project still produces 2,000 physical kWh over the two years. The 1,735.54 kWh denominator is a discounted quantity used in that financial calculation. Label it accordingly; it is not an alternative production forecast.
Physical reductions belong in the energy model. Those might include modeled shading losses, equipment losses, downtime or solar panel degradation. Financial discounting belongs in the economic calculation. Combining these steps without clear labels can make it impossible to see why a result changed.
For your own worksheet, keep three separate lines: predicted physical annual energy, the discount factor applied in the financial method, and the resulting discounted denominator contribution. That separation makes a model easier to audit and avoids presenting discounted energy as actual meter output.
Is lifetime purchase price divided by lifetime output still useful?
It can be a rough screening ratio if clearly labeled. Its limitations depend on what the purchase-price numerator and lifetime-output denominator omit.
Suppose a fictional cash purchase costs $24,000 and an assumed physical lifetime output is 240,000 kWh. The purchase-only, undiscounted ratio is $0.10/kWh. Add $6,000 of undiscounted ownership costs over the same period and the ratio becomes $0.125/kWh. The difference is caused by scope, before any discounting is applied.
Calling both numbers simply “the solar electricity price” hides that change. A more useful label is “purchase-only undiscounted cost per modeled lifetime kWh” for the first result. It tells the reader exactly what has been calculated.
The laboratory’s simple LCOE calculator explicitly identifies limitations involving financing, replacements and degradation. A reputable tool can still answer a narrower question than a complete household decision requires.
Use a simple ratio to identify questions, then request the fuller calculation where the omitted items could change your choice. There is no benefit in a complicated model that conceals its inputs, but simplicity should not conceal exclusions either.
Which lifecycle costs belong in the numerator?
Start by defining the project and financial perspective. A solar-only generating-system calculation, an owner’s financed investment calculation and a combined solar-plus-storage calculation need different disclosures.
An original cost inventory can separate initial equipment and labor, permits and related project work, ongoing maintenance, planned replacement scenarios, incremental insurance or other applicable ownership costs, and terminal costs or values. Include an item only when it belongs to the stated scope and has a defensible basis.
Do not quietly include the battery in the cost numerator while using solar-only output as though the two proposals had identical functions. Likewise, distinguish necessary solar-related roof work from a broader roof replacement that the owner would undertake anyway. Explain the allocation rather than declaring all roof expenses free or all expenses solar costs.
Our solar maintenance cost guide helps frame the ownership-cost discussion. It cannot supply a guaranteed expense for an uninspected property.
If a future repair cost is uncertain, use a clearly labeled scenario. A model can show the consequence of an assumed replacement without asserting that every inverter fails in a particular year. Keep that distinction visible in the assumptions sheet.
How do replacements and terminal values change the result?
A later expense belongs in the year when the model assumes it is paid. Its contribution depends on the timing and discount method.
For an isolated fictional example, a $2,000 expense at the end of year five contributes $2,000 ÷ 1.05⁵, approximately $1,567, at an assumed 5% discount rate. The physical payment remains $2,000 in the stated dollar basis; the discounted contribution is different.
A terminal value is also an assumption. If the calculation credits remaining equipment value at the end of the analysis, ask who could realize that value and how it was estimated. A spreadsheet entry is not a promised sale price or a buyer’s commitment.
Test an alternative case without that credit. If the preferred proposal changes solely because of an unsupported residual value, the comparison needs more evidence. Treat removal or disposal costs with the same care: define the scope and basis rather than assigning a universal charge.
What energy boundary should the denominator use?
The denominator must describe the output being costed. Possible boundaries include modeled AC solar generation, electricity delivered to a home and grid, or a defined combined-system output. They are not interchangeable.
Consider a fictional project with $30,000 of discounted included costs. Using 200,000 discounted kWh gives $0.15/kWh. Using 150,000 discounted kWh gives $0.20/kWh. That difference could arise from a changed output boundary rather than a changed purchase price.
Ask whether the denominator includes exports, excludes curtailed energy, accounts for system losses, or measures only a subset of household supply. A number restricted to self-used energy answers a different question from one covering all generated energy.
The energy-offset definition explains another ratio often printed beside LCOE. Neither annual offset nor a favorable cost denominator proves that all consumption occurs while solar is available.
For fair comparisons, use the same energy boundary or explain the difference explicitly. Do not reward a proposal merely because it counts a broader quantity of electricity beneath an otherwise similar cost.
How should production, degradation and the analysis period be handled?
A lifecycle calculation needs a year-by-year energy schedule. Year-one output multiplied by a long period can conceal assumptions about later performance.
Ask for the production model’s site inputs, loss assumptions and treatment of later years. Identify whether degradation is linear, compounded or applied through another documented model. Do not apply a second degradation adjustment if the supplied annual schedule already includes it.
For a hypothetical compounded example, year-one energy of 10,000 kWh and an assumed 1% annual decline give year-two energy of 9,900 kWh and year-three energy of 9,801 kWh. Those assumptions are invented for arithmetic, not equipment expectations.
The analysis period is a chosen modeling horizon. It is not automatically the module warranty, the loan term, your ownership period or a guaranteed operating life. A project modeled for a longer period can show a lower cost per kWh because more output is counted. That added output also requires credible operation and cost assumptions.
Ask what changes if you expect to own the property for a shorter time. LCOE alone does not settle resale value, contract transfer or remaining loan obligations. Those are separate transaction questions.
Why must real and nominal calculations stay consistent?
A real-dollar calculation removes general inflation from the dollar basis. A nominal-dollar calculation uses the dollar amounts associated with the modeled years. Inputs and the selected financial method must agree.
SAM publishes both forms and cautions against comparing one project’s real LCOE with another project’s nominal LCOE. SAM real and nominal LCOE guidance.
For a proposal worksheet, request the dollar base year, inflation assumption, discount-rate basis and handling of future cost escalation. A statement such as “5% discount rate” is incomplete if it does not identify the basis.
Do not choose whichever format produces the more attractive display. Apply the same basis to the alternatives you are comparing. If a worksheet mixes today’s replacement price with inflated future operating costs, ask the modeler to reconcile it.
This is a method question, not a recommendation for a particular household discount rate. Different owners can have different financial circumstances. A transparent sensitivity range is more informative than an unexplained default treated as universally correct.
Can financing costs be counted twice?
Yes, if the model combines incompatible perspectives. An owner cash-flow model must distinguish the owner’s initial contribution, loan proceeds, debt payments and other included costs. A project-cost model may use a different structure.
For an original bookkeeping illustration, a $20,000 purchase is financed entirely by a loan whose total principal and interest payments are $25,000. Simply adding $20,000 and $25,000 as owner outflows, without representing the borrowed funds or a coherent project perspective, counts the principal twice.
That is not a full discounted loan calculation. It is a warning to reconcile the ledger before computing a ratio. Ask which cash flows appear, when they occur, and whether dealer fees or financing-related price differences are already embedded in the purchase amount.
Compare a cash case and a financed case separately using the same equipment and production assumptions. A lower monthly payment can involve a longer repayment period. LCOE does not substitute for the actual payment schedule, prepayment terms or transfer obligations.
How should incentives be included in a current model?
Include only applicable benefits with documented eligibility, amount and timing. A benefit expected later should not silently become cash received on installation day.
As verified October 6, 2026, the IRS states that the homeowner Residential Clean Energy Credit is unavailable for property placed in service after December 31, 2025. Do not apply an assumed 30% homeowner credit to a new 2026 system. Current IRS homeowner clean-energy credit guidance.
That federal statement does not determine every state, business or third-party ownership circumstance. Those require their own current eligibility review. This definition does not supply a tax opinion or a state-credit calculation.
If a model includes a conditional benefit, request a second case without it. Record when any benefit is expected to become usable and who receives it. The homeowner’s price under a lease or PPA is not automatically the project owner’s cost model.
Keep the benefit schedule separate from utility savings. Combining credits, export compensation and reduced purchases into one unexplained discount makes the result harder to inspect.
Why can equal LCOE produce different utility savings?
Generation cost and the financial value of generation are different quantities. The household’s use timing and tariff help determine value.
Imagine two otherwise identical fictional systems producing 10,000 kWh annually with equal LCOE. Assume each self-used kWh avoids $0.20 of purchases and each exported kWh earns $0.05. These are invented values, not South Carolina tariff quotations.
| Scenario | Self-used solar | Exported solar | Assumed annual energy value |
|---|---|---|---|
| Household A | 6,000 kWh | 4,000 kWh | $1,200 + $200 = $1,400 |
| Household B | 3,000 kWh | 7,000 kWh | $600 + $350 = $950 |
The $450 value difference does not require a change in LCOE. It arises from different self-use under the assumed compensation structure. Actual bill modeling must also apply the tariff’s other relevant terms.
The solar self-consumption definition, export-rate definition and net-billing definition explain those separate inputs. A generation-cost result cannot replace them.
Likewise, bill total divided by purchased kWh is a historical whole-bill average. It can include charges that remain after solar reduces imports. Using that average as the avoided value of every generated kWh needs justification.
How does LCOE differ from other proposal metrics?
Keep each measure attached to its own question.
| Measure | Main question | What it does not establish alone |
|---|---|---|
| Cost per watt | What is the purchase price relative to stated capacity? | Lifecycle output or bill value |
| LCOE | What is the modeled lifecycle cost per energy unit? | Actual household savings or outage capability |
| Payback period | When do cumulative modeled benefits cover costs? | All later returns or ownership risks |
| Net present value | What is the modeled discounted net financial value? | Certainty that assumptions occur |
| Monthly payment | What scheduled payment is due? | Total ownership cost or bill reduction |
| PPA price | What does the contract charge for applicable energy? | The provider’s project LCOE |
A low cost per watt can coexist with a less favorable LCOE if the output assumption is lower or later costs are higher. A favorable LCOE can coexist with weak bill value if much generation earns a low export credit.
Request the metrics together with their definitions. The purpose is to understand the proposal, not to select a single number that makes every remaining question disappear.
What changes when a battery is included?
Storage adds cost, losses and operating choices. It also changes when electricity can reach the household. Define whether the calculation concerns solar generation, storage throughput or combined delivered energy.
Do not count a solar kWh once when generated and again when discharged from storage as two newly generated kWh. For an invented physical ledger, 10 solar kWh enter a battery and 9 emerge for later delivery. Those 9 kWh are shifted energy, not 9 additional solar kWh.
The round-trip efficiency definition explains why energy boundaries matter. If a combined output forecast already reflects storage losses, applying another blanket loss factor can understate the denominator.
Grid charging also needs clear treatment. Charging purchases are not free solar generation. SAM’s documentation treats charging costs within its specified model structure; another tool may use a different structure. Ask the modeler to identify the boundary and prevent omitted charging costs or double-counted benefits.
Evaluate backup function separately. A battery can provide a useful resilience benefit without reducing the generation-cost ratio. Conversely, an attractive ratio does not establish supported loads or runtime during an outage.
Why are utility-scale benchmarks not rooftop prices?
A published power-plant LCOE describes a project type and methodology. It does not quote installation on your roof.
Scale, site development, equipment configuration, finance, output assumptions and included costs can differ. Before importing any benchmark, identify its publication year, geography, project scale, dollar basis, subsidy treatment and energy boundary.
The comparative PV calculator illustrates cost and performance trade-offs between defined cases. Its presets are modeling inputs, not contractor offers for a particular property.
Our commercial solar cost guide retains the commercial purchasing discussion. Even within commercial projects, a rooftop and a ground-mounted system should not be assumed equivalent because both produce electricity.
Use broad benchmarks to formulate questions about a model. Use a site-specific scope and proposal to evaluate an actual purchase.
How should South Carolina buyers use the metric?
Keep the definition generic and the decision inputs local. Identify the serving provider from the account, then confirm the applicable tariff and export arrangement through the utility information hub and the provider’s current documents.
Use the property’s production model rather than a statewide yield substituted for its roof. Use household timing data where available; the load-profile definition explains how an annual total can conceal different import and export patterns.
Request three distinct outputs: the generation-cost calculation, the utility-bill comparison, and the owner payment or cash-flow schedule. Each should use compatible system and timing assumptions. If one output assumes cash purchase and another assumes financing, disclose that difference.
Avoid city-specific LCOE claims without actual local inputs. A city name does not establish the serving utility, roof exposure, installed price or financing terms. The useful local question is which verified property facts change the calculation.
A sensitivity worksheet for comparing assumptions
Begin with the disclosed base case. Change one assumption at a time so that the effect remains understandable.
| Input to test | Alternative case | Question the comparison resolves |
|---|---|---|
| Energy forecast | Lower modeled output | How dependent is the result on production? |
| Analysis period | Shorter period | How much output is counted beyond your horizon? |
| Ownership cost | Additional documented scenario | Do omitted later costs change the choice? |
| Financial basis | Consistent alternative discount assumption | How sensitive is the result to timing treatment? |
| Conditional benefit | Benefit excluded | Does eligibility drive the apparent advantage? |
| System scope | Same included equipment and work | Are the alternatives actually comparable? |
For simple isolated arithmetic, $30,000 of discounted costs divided by 200,000 discounted kWh gives $0.15/kWh. Holding cost fixed and reducing that denominator by 10% to 180,000 kWh gives about $0.1667/kWh. A 10% output reduction increases this ratio by approximately 11.1%, not 10%.
That example is a ratio sensitivity, not a complete forecast. Do not change actual production inputs solely to make a proposal look better or worse. Use a documented alternative and explain why it is worth testing.
What should you request before accepting an LCOE claim?
Ask for the cost schedule, energy schedule, analysis period, dollar basis, discount method, output boundary and treatment of finance, benefits and terminal values. Request enough detail to reproduce the result.
Then ask how the calculation connects to the bill model. Which energy avoids purchases? Which energy is exported? Which charges remain? What assumptions change if household consumption shifts? A response that repeats the displayed LCOE has not answered those questions.
Bring Sunburst the proposal, recent electricity records and any available production or financing worksheet. Request an assessment of the design, cost scope and utility assumptions so the next discussion starts with identifiable inputs. A useful review can uncover a missing item or clarify a boundary without promising that a particular financial outcome will occur.
Sources and methodology
The primary references checked October 6, 2026 are SAM’s LCOE help, the laboratory’s simple LCOE tool and comparative PV calculator documentation, and current IRS homeowner-credit guidance. They support the defined method, tool limitations and the dated federal-credit statement. Numerical examples and proposal worksheets here are original teaching scenarios.
No market LCOE range, utility rate, installation price, equipment life or savings guarantee is supplied. Current project economics require the property’s actual scope, model and applicable written terms.
Frequently asked questions
What does LCOE stand for?
LCOE stands for levelized cost of energy. In an electricity-generation discussion, it is also called levelized cost of electricity. Read the calculation method and energy boundary alongside the acronym.
Is LCOE the same as the price on my utility bill?
No. It is a project lifecycle-cost metric. Your tariff prices purchases and may include fixed or other charges. A historical whole-bill average also differs from the marginal value of each purchase avoided by solar.
Can I calculate LCOE from the purchase price alone?
You can calculate a purchase-only ratio if you also assume an energy quantity. Label its omissions. A fuller lifecycle calculation needs the selected cost schedule, output schedule, analysis period and financial treatment.
Does a lower LCOE guarantee faster payback?
No. Payback depends on the costs and financial benefits over time. Different self-use, export value, financing or benefit timing can change payback even when two systems have similar generation costs.
Why does the discount rate affect LCOE?
It changes how later costs and energy enter the specified financial calculation. Initial costs and later output occur at different times. It does not change physical generation, and the appropriate financial assumption needs explicit disclosure.
Should I use the panel warranty as the analysis period?
Do not substitute it automatically. A warranty is a coverage agreement; an analysis period is a modeling choice. Explain operation, later costs and your ownership horizon separately.
Is battery discharge added to solar generation in the denominator?
Only within a clearly defined energy accounting method. Stored solar is shifted energy, so counting generation and its later discharge as two independent generation events can overstate output. Charging costs and losses also need coherent treatment.
What is the best next step if a quote only gives cents per kWh?
Request the underlying annual costs and energy, method, boundaries and assumptions. Then compare the bill-value and owner cash-flow calculations. The displayed ratio is a starting point for review, not sufficient evidence of savings.