Every buyer asks for the payback period, every proposal contains one, and it answers a question that does not match the decision being made.
For teams coordinating research, review and follow-up work around a project, remote employee monitoring software provides a separate record of time and handoffs.
What payback measures
How long until cumulative savings equal the initial cost.
It is a liquidity measure. It answers "how long is my money tied up", which is a real concern and a different one from "is this worth doing".
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And it stops counting at the moment it is reached. A plant paying back in seven years and running for twenty-five produces eighteen further years of output that the metric ignores entirely.
What it does to comparisons
It favours smaller systems. A system sized to your minimum load has high self-consumption and short payback; a larger one exports more, pays back slower, and may produce far more total value.
Payback would tell you to build the smaller one. Whether that is right depends on your cost of capital and your export tariff — neither of which payback contains.
It also favours cheap installations over durable ones, because it counts the initial cost and not the inverter replacement or the maintenance profile.
The better questions
"What is the return on the money, against what else I could do with it?" An internal rate of return or a net present value at your own discount rate. Harder to compute and it answers the actual question.
"What is the levelised cost per kilowatt-hour?" Total lifetime cost divided by total lifetime output, discounted. Comparable directly against your tariff, and it makes the twenty-five-year horizon visible rather than truncating it.
"What happens if I am wrong about the price path?" The dominant uncertainty, and a sensitivity range is worth more than any single figure.
And "what is the worst realistic case?" P90 production, flat real prices, full excluded costs. If it still works, the decision is easy; if it only works at P50 with rising prices, that is worth knowing before signing.
Why payback survives
Being fair to it.
Everybody understands it instantly. "Seven years" travels through an organisation in a way that a discounted cash flow does not, and a decision involving non-specialists needs something that travels.
It is directionally right in the simple case.
And it does capture a real constraint. An organisation that cannot tie up capital for a decade has a genuine reason to care about payback specifically, independently of return.
What to actually do
Use payback as a screen and not as the decision.
Ask for the lifetime figures alongside it — total production, total value, levelised cost. Any supplier producing a payback calculation already has the underlying model.
And ask for the sensitivities, at P90 and at flat prices. Two additional runs of an existing model, and together with the headline they describe the range you are actually buying.
If a supplier can only produce the payback number, that is informative about the model behind it.
The short version
- Payback measures how long money is tied up, which is a liquidity question rather than a value question
- It stops counting at the payback point and ignores the remaining eighteen or so years of a twenty-five-year asset
- It favours smaller systems and cheaper installations, because it excludes export value, cost of capital and mid-life replacement
- Better questions: return against alternatives, levelised cost per kWh, sensitivity to the price path, and the worst realistic case
- It survives because it is instantly understood, roughly directional, and captures a real capital constraint for some organisations
- Use it as a screen; ask for lifetime figures and for runs at P90 and flat prices, which the supplier's model already supports