Economics and Development

Solar hour is the daylight window (roughly 9 a.m. to 4 p.m. in Nepal, wider in summer) in which solar PV plants inject energy, and which is metered, scheduled and settled as a separate time block in energy accounting, tariffs and trading. It should not be confused with the "peak sun hour", which is an insolation measure (1 kWh/m² per hour).

Significance in demand-supply balance

1. Matches daytime load. Solar output coincides with industrial, commercial and irrigation demand, so it meets part of the daytime load directly.
2. Cuts imports and peaking support. Solar energy displaces costly dry-season imports from India and diesel or other peaking supply, because run-of-river hydro falls in winter.
3. Price and settlement effect. Abundant supply lowers midday prices, which affects PPA design, time-of-day tariffs and IPP revenue. Surplus in wet-season solar hours may be spilled or exported.
4. Ramping and curtailment. Output rises sharply in the morning and drops at sunset (the "duck curve"). The grid then needs fast ramping from reservoir or peaking plants, spinning reserve and storage. Surplus midday solar may have to be curtailed.
5. Planning use. Solar-hour output is used to set capacity credit, schedule dispatch and plan evening peak supply.

In short, solar hours ease daytime scarcity, but they also require flexible resources to cover the evening peak when solar is zero.

Cash Flow

Cash flow is the actual movement of cash into and out of a project over a period of time. It is the lifeblood of project appraisal because profitability and liquidity are not the same thing — a project may show accounting profit yet fail if cash is not available when needed.

Cash flows are classified as:

• Inflows — cash receipts such as sales revenue, sale of assets, recovery of working capital, loans received.
• Outflows — cash payments such as capital expenditure, operating costs, taxes, interest, repayment of loans.

For appraisal, only incremental after-tax cash flows are relevant, and non-cash items such as depreciation are excluded (though depreciation is added back to profit to arrive at cash flow). The net cash flow of each year is:

$\text{Net Cash Flow} = \text{Cash Inflows} - \text{Cash Outflows}$

Cash flows are then arranged in a time line — an initial outflow at year 0, followed by net inflows in years 1, 2, 3 … n — which becomes the basis for all discounted and non-discounted appraisal techniques.

Time Value of Money

Time value of money is the principle that a rupee received today is worth more than the same rupee received in the future, because money available today can be invested to earn a return, and because of inflation and risk. Two concepts follow from it:

Compounding (future value): money grows when invested.

$FV = PV(1+i)^n$

Discounting (present value): future cash flows are brought back to today's value.

$PV = \frac{FV}{(1+i)^n} = FV \times DF$

where $i$ = discount rate (cost of capital) and $n$ = number of years. The factor $\frac{1}{(1+i)^n}$ is the discount factor.

Why it matters in appraisal: cash flows arising in different years cannot be compared or added directly. Discounting brings them all to a common point in time (present), so that projects of different durations and different cash flow patterns can be compared on a fair basis. This is the foundation of NPV, IRR and discounted payback.

Simple Payback Period

The simple (traditional) payback period is the time required for the cumulative cash inflows to recover the initial investment. It ignores the time value of money.

$\text{Payback Period} = \text{Year before full recovery} + \frac{\text{Unrecovered cost at start of year}}{\text{Cash flow during the year}}$

Example: Investment = Rs 1,00,000; annual cash inflow = Rs 25,000.

$\text{Payback} = \frac{1{,}00{,}000}{25{,}000} = 4 \text{ years}$

Merits: simple, easy to understand, and a good measure of liquidity and risk — a shorter payback means capital is at risk for a shorter time. Demerits: it ignores the time value of money and ignores all cash flows arising after the payback period, so it may reject a project with large later returns.

Discounted Payback Period

The discounted payback period is the time required to recover the initial investment from the present value of cash inflows, using the discount rate. It corrects the main weakness of the simple payback period by recognising the time value of money.

Steps:

1. Compute the present value of each year's cash inflow using the discount factor.
2. Find the cumulative present value.
3. Identify the year in which cumulative PV equals or exceeds the initial investment.
4. Compute the exact period by interpolation.

$\text{DPBP} = \text{Year before full recovery} + \frac{\text{Unrecovered investment at start of year}}{\text{Discounted cash flow of that year}}$

Example: Investment = Rs 1,00,000; discount rate = 10%; annual inflow = Rs 25,000.

Recovery falls in year 6.

$\text{DPBP} = 5 + \frac{1{,}00{,}000 - 94{,}750}{14{,}100} = 5 + 0.37 = 5.37 \text{ years}$

Merits: considers the time value of money and still measures liquidity and risk. Demerits: it still ignores cash flows after the payback period, and it requires an estimate of the discount rate. It is always longer than the simple payback period (4 years vs 5.37 years above), so it is a stricter test.