# Factory Solar and Diesel Hybrid Payback Calculator for Unreliable Grids

> Source: https://netray.co/tools/africa-factory-solar-diesel-hybrid-payback-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Estimate the diesel saved, capital cost, running cost and simple payback of adding solar PV to a factory that relies on generators.

## Category

cost-finance

## Region

Africa

## Industry

Manufacturing

## Audience

- Plant manager
- Finance director
- Energy manager

## Tool

**Kind:** calculator

**Currency:** $

**Inputs:**

#### Annual electricity from generators

**Key:** annual_kwh

**Type:** number

**Default:** 900000

**Min:** 0

**Step:** 10000

**Unit:** kWh

#### Share of that energy replaced by solar

**Key:** solar_share

**Type:** slider

**Default:** 35

**Min:** 5

**Max:** 80

**Step:** 5

**Unit:** %

**Help:** Without batteries, solar usually cannot replace more than a fraction of generator output because generators need a minimum load.

#### Diesel use per kWh

**Key:** lpk

**Type:** number

**Default:** 0.3

**Min:** 0.2

**Max:** 0.5

**Step:** 0.01

**Unit:** L/kWh

**Help:** Typical large sets run near 0.25 to 0.35 L/kWh depending on load.

#### Delivered diesel price

**Key:** diesel_price

**Type:** number

**Default:** 1.05

**Min:** 0

**Step:** 0.05

**Unit:** USD/L

#### Annual solar yield

**Key:** yield_kwp

**Type:** number

**Default:** 1550

**Min:** 800

**Max:** 2200

**Step:** 25

**Unit:** kWh/kWp

**Help:** Depends on site irradiance, tilt and losses.

#### Installed cost per kWp

**Key:** capex_kwp

**Type:** number

**Default:** 720

**Min:** 0

**Step:** 10

**Unit:** USD/kWp

#### Annual O&M as share of capex

**Key:** om_pct

**Type:** number

**Default:** 1.5

**Min:** 0

**Max:** 10

**Step:** 0.25

**Unit:** %

**Outputs:**

#### Solar energy used

**Key:** solar_kwh

**Expr:** annual_kwh * solar_share / 100

**Format:** integer

#### PV capacity required

**Key:** kwp

**Expr:** solar_kwh / yield_kwp

**Format:** integer

#### Installed capital cost

**Key:** capex

**Expr:** kwp * capex_kwp

**Format:** currency

#### Diesel cost avoided per year

**Key:** diesel_saved

**Expr:** solar_kwh * lpk * diesel_price

**Format:** currency

#### Annual O&M cost

**Key:** om

**Expr:** capex * om_pct / 100

**Format:** currency

#### Net annual saving

**Key:** net_saving

**Expr:** diesel_saved - om

**Format:** currency

**Primary:** true

#### Simple payback

**Key:** payback

**Expr:** if(gt(net_saving,0), capex / net_saving, 0)

**Format:** years

**Primary:** true

**Chart:**

#### Simple payback as diesel price changes

**Type:** line

**X:** diesel_price

**From:** 0.6

**To:** 1.8

**Steps:** 25

**Series:**

- payback

**Disclaimer:** Simple payback ignores financing, degradation, tax allowances and battery costs. Use it for screening, then ask an installer for a full yield study.

## Content

**Intro:** Where grid supply is unreliable, a generator is often the real price setter for power. This calculator estimates what adding solar PV to a diesel-backed factory saves, what it costs, and how long it takes to pay back on a simple basis.

**Sections:**

#### How to use it

**Body:** Enter the energy your generators supply each year, the diesel price you actually pay delivered to site, and the fuel use per kWh. Set the share of that energy you want solar to replace, then enter yield and installed cost per kWp. The tool sizes the array, estimates diesel avoided and net saving after O&M, and returns simple payback in years.

**Bullets:**

- Use metered generator kWh, not nameplate capacity.
- Use delivered fuel price including transport and losses.
- Keep the solar share realistic for a no-battery design.

#### The method

**Body:** Solar energy used equals generator energy times the replaced share. Capacity equals that energy divided by annual yield per kWp. Diesel avoided equals solar kWh times litres per kWh times price. Payback is capital cost divided by net annual saving. It is deliberately simple so a finance team can reproduce it in a spreadsheet and then compare it with an installer proposal.

#### Reading the result

**Body:** Short paybacks are typical where diesel is the marginal source, but the result depends heavily on fuel price, which the chart sweeps for you. Check that the array fits roof area and structure, and that your generator controller can run in parallel with PV without reverse power or minimum load trips. If you also buy grid power, the saving per kWh is lower than diesel, so model that mix separately.

**Bullets:**

- Treat battery storage as a separate costed option.
- Add inverter replacement to long-term cost views.
- Check insurance and landlord consent for roof systems.

#### Common mistakes

**Body:** Overestimating the solar share, using the grid tariff instead of diesel cost, ignoring annual degradation, and assuming perfect yield are the usual errors. Another is forgetting that production patterns matter: if most load runs at night, daytime PV saves less. Match the sizing to your actual load profile from a meter log.

**Cta:** If you track generator hours, fuel and downtime in an ERP or spreadsheet, Netray can pull those figures into a monthly energy cost report with the query shown.

**Faq:**

#### How much diesel does a generator use per kWh?

**Answer:** Many large diesel sets use roughly 0.25 to 0.35 litres per kWh at reasonable load, and more at light load. Use your own fuel and meter records for the best estimate.

#### Can solar run a factory without batteries?

**Answer:** Partly. PV can reduce generator fuel during the day, but generators need a minimum load and the system needs controls to avoid reverse power. Full replacement normally needs storage.

#### What is simple payback?

**Answer:** It is capital cost divided by net annual saving. It ignores financing, tax and degradation, so it is a screening measure rather than a full investment appraisal.

#### Is this the same as the load shedding generator cost calculator?

**Answer:** No. That tool prices the cost of running generators during outages. This one estimates the benefit of adding solar to offset generator fuel.

## Search terms

solar diesel hybrid payback calculator, factory solar payback africa, diesel generator cost saving solar, solar roi calculator manufacturing, cost of generator power per kwh, load shedding solar factory, commercial solar payback period, diesel savings calculator

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