Table of Contents
To check business solar payback, follow the cash the project leaves after operating costs. Multiplying annual generation by a price from an electricity bill is insufficient. Establish how much solar energy actually replaces purchases during operating hours, which charges decrease, and when maintenance or replacement payments occur.
This guide sets out a review process and a reproducible hypothetical example for direct solar consumption without battery storage. Every numerical input is an educational assumption. The figures are neither a system quotation nor a current electricity price, market forecast or promised investment return.
1. Define the comparison and its inputs
Start with the question: what are we comparing? Here, the baseline is the business operating without the proposed PV installation. The project case has the same production schedule with solar generation added. If machinery, shifts or production volumes also change, identify their effects separately. Otherwise, savings from another operational change can be incorrectly attributed to solar.
Build an input register containing each value, its unit, period, origin and the person responsible for confirmation. Bills establish purchasing costs, interval meter data explain demand, and the installation proposal establishes the investment. A generation estimate needs a location, configuration and stated losses. Keep assumptions distinguishable from measurements.
Agree on currency, VAT treatment, commissioning date and analysis period. The investment cashflow must include the complete working installation. This guide examines how that total affects the result; a detailed comparison of quotation line items belongs in a separate budget review.
2. Match generation with demand over time
Matching annual totals do not establish that a business can consume all its solar output. A warehouse may operate mainly in the evening, production may stop at weekends, and a summer shutdown may coincide with strong generation. Use time series with consistent intervals and time zones. Keep missing readings and abnormal operating days visible.
Within each interval, direct consumption is limited by both available generation and simultaneous demand at the agreed electrical boundary. A simplified interval calculation takes the smaller energy quantity. Long intervals can hide brief surpluses, so accuracy depends on data resolution. Adding the results estimates the energy that can replace purchases. Dividing annual totals cannot reconstruct that timing.
Check the denominator of any self-consumption percentage. The share of potentially available output can differ from the share of actual generation after curtailment. Our example uses the former. Adding a battery requires another energy balance, covered in the guide to solar with storage and surplus energy.
3. Establish the value of avoided purchases
The avoided purchase price answers a specific question: how much does the bill decrease if the business buys one less kilowatt-hour in that interval? It may differ from the average bill divided by consumption. Fixed charges may remain, while variable components need checking against contracts and their billing method.
With hourly pricing, use the prices for hours when solar actually covers demand. An expensive evening period does not create equivalent savings from daytime generation without shifting energy. A simplified model can use one weighted average, provided the calculation behind that average is available for review.
Export has separate volumes, payment terms and costs. Do not automatically value surplus at the purchase price or count a kilowatt-hour as both a sale and an avoided purchase. If export revenue and feasibility remain unconfirmed, test a case in which surplus has no financial value. This reveals how dependent the project is on that revenue.
4. Place costs in the years they occur
Avoided electricity purchases are the starting point. Deduct applicable maintenance, monitoring, insurance and other operating payments. Give each allowance a defined scope. A percentage of investment may support an initial estimate, but it does not establish that every future service activity is covered.
Put major replacements in their expected years. Spreading a large payment evenly across the model can hide the cash needed at a particular date. Avoid counting it twice: if a service contract covers a replacement, an additional line should represent only an extra payment. A warranty period does not, by itself, establish a failure date.
Initial payment timing also matters. An advance may precede commissioning, and the first calendar year may contain only a few months of generation. Check actual dates for a real proposal. The educational model below deliberately starts with a full operating year following one initial investment payment.
5. Review a transparent hypothetical example
Assume an initial investment of UAH 2,400,000, first-year available AC energy of 120,000 kWh, direct use of 80%, and avoided purchases worth UAH 6/kWh. Annual operating costs are an assumed UAH 40,000. The remaining available energy is curtailed and produces no revenue; the example includes neither storage nor electricity sales.
The analysis covers 15 years. Available generation declines by an assumed 0.5% annually, while the direct-use share stays at 80%. A separate UAH 250,000 replacement is included in year ten. These are inputs for testing the calculation, not equipment specifications, standard cost allowances or a recommended replacement schedule.
All amounts use constant purchasing-power hryvnias. There is no inflation or electricity price escalation. Taxes, VAT, debt, grants, residual value and decommissioning costs are excluded. The result therefore describes this specified cashflow before tax and financing, rather than an owner's net income. Add applicable omitted items before using a model for an investment decision.
6. Reproduce the cashflow and recovery point
First-year direct use is 120,000 × 0.8 = 96,000 kWh. Avoided purchases are worth 96,000 × 6 = UAH 576,000. After operating costs, UAH 576,000 - 40,000 = UAH 536,000 remains. Dividing 2,400,000 by 536,000 gives approximately 4.48 years if that annual cashflow stays unchanged.
However, our assumptions already specify a change. In year t, available energy equals 120,000 × 0.995t-1. The annual cashflow is that energy × 0.8 × 6 - 40,000, with another UAH 250,000 deducted in year ten. The starting cumulative balance is minus UAH 2,400,000.
After year four, the balance is approximately minus UAH 273,222; after year five, it is plus UAH 251,344. At annual checkpoints, investment is first recovered at the end of year five. Linear interpolation gives about 4.52 years, but seasonality prevents that estimate from identifying the actual recovery month. The year-ten flow falls to UAH 260,592 because of replacement. Earlier payback does not eliminate that later payment.
7. Change one input at a time
Each row changes only the stated input. Other assumptions, including generation decline and replacement, remain at their baseline values. Recovery is measured using cumulative cashflow at each year end.
| Scenario | Year-one cashflow, UAH | Recovery year |
|---|---|---|
| Baseline assumptions | 536,000 | 5 |
| Direct use of 60% | 392,000 | 7 |
| Direct use of 95% | 644,000 | 4 |
| Avoided purchases at UAH 4.8/kWh | 420,800 | 6 |
| Avoided purchases at UAH 7.2/kWh | 651,200 | 4 |
| Investment of UAH 2,000,000 | 536,000 | 4 |
| Investment of UAH 2,800,000 | 536,000 | 6 |
Reducing direct use from 80% to 60% cuts first-year cashflow by UAH 144,000. This explains why operating schedules deserve attention before final system sizing. A higher share is not necessarily a free improvement: changing production hours can have costs of its own, which belong in the comparison.
After individual changes, combine plausible risks, such as lower generation, a more expensive installation and reduced daytime demand. Do not describe an arbitrary collection of worst-case numbers as a forecast. Record the reason for each deviation and check that the assumptions can occur together.
8. Examine the full analysis period
Net present value, or NPV, accounts for the timing of the specified cashflows at a selected discount rate. Internal rate of return, or IRR, is the rate at which NPV is zero. The handbook on payback and financial metrics explains these measures in more detail.
For this example, an assumed real discount rate of 10% and year-end cashflows produce a 15-year NPV of approximately UAH 1,466,968. Subtract the initial investment immediately and divide each subsequent flow by 1.1t. The rate is educational, and the positive result depends on all the exclusions. It cannot be transferred to a loan schedule or described as an equity return.
9. Prepare the model for a useful review
Before agreeing to a project, request a calculation file with visible formulas. A reviewer should be able to change an input and trace the effect through energy, savings and cashflow. Annual figures must reconcile with totals, and every material number needs an explanation.
- Match a full year of demand and generation, including shutdowns.
- Identify genuinely avoided charges and value surplus separately.
- Include the complete investment, operating costs and major replacement dates.
- Agree on taxes, currency, analysis period and feasible alternative scenarios.
For the next step, assemble meter data, bills, contracts and a proposal for a grid-connected business solar system. Once the economics of the installation are aligned, compare financing options using the same underlying inputs. This gives the discussion a calculation that can be checked and a clear basis for each decision.