Solar Power Beyond the Rooftop

Solar electricity can lift water, illuminate a road, operate remote communications or help keep food cold. These applications look different from a rooftop system serving a home, yet they share one design rule: define the service and its timing before choosing the panel, battery or backup source. A panel rating alone cannot tell you how much water will reach a field, how many nights a camera will work or whether produce will remain within its required temperature range.

Start with the service, not the solar array

Every useful design has two separate requirements. Power, measured in watts or kilowatts, describes the maximum rate of energy use and determines whether an inverter, controller or source can start and run the equipment. Energy, measured in watt-hours or kilowatt-hours, combines power with time and helps size the solar array and storage. Motors and compressors may also demand a brief starting current higher than their normal running current.

Open full image

Diagram description

The teaching graphic presents solar lighting, remote equipment and standalone power as three separate applications. Each has its own photovoltaic module. The small building visibly includes a charge controller or inverter and a battery, while the drawing does not specify the internal storage of the streetlight or remote-equipment system.

Solar water pumping: move water when light is available

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Diagram description

Sunlight reaches a ground-mounted photovoltaic array. An electrical arrow leads to a surface pump, and blue pipes carry water upward into a labelled storage tank. A gravity-fed outlet then supplies a network of irrigation lines. The arrangement illustrates energy flow and water storage; it does not provide pump, tank or pipe dimensions.

A pumping design begins with the required water volume and the total dynamic head. Head includes vertical lift, the change in source level while pumping, pressure needed at the outlet and friction through pipes, filters, valves and fittings. The designer also checks the source's sustainable yield, seasonal water level, water quality, irrigation method, daily solar resource and the pump-controller-motor operating range. A pump selected only by kilowatts can deliver too little flow, cycle inefficiently or draw the source down too far.

Screen the electrical energy needed to lift water

Epump ≈ (ρ × g × V × H) / (3.6 × 10⁶ × ηtotal)

This relationship gives an initial energy estimate when SI units are used. It does not replace a pump curve, pipe-loss calculation, source test or an hour-by-hour solar simulation. Combined efficiency changes with operating point and includes the pump, motor, controller and other applicable losses.

Epump

estimated electrical energy delivered to the pumping system, in kilowatt-hours

ρ

water density, approximately 1000 kilograms per cubic metre for a screening calculation

g

gravitational acceleration, approximately 9.81 metres per second squared

V

water volume moved, in cubic metres

H

total dynamic head, in metres

ηtotal

combined decimal efficiency at the relevant operating condition

Example

Moving 20 cubic metres through 30 metres of total dynamic head requires about 1.64 kWh of hydraulic energy. At an assumed 50 percent combined efficiency, the screening electrical energy is about 3.27 kWh; pipe, pump and solar design still require detailed calculations.

When irrigation can be scheduled flexibly, pumping into a correctly designed reservoir or elevated tank during sunny hours can be simpler than charging a battery and running the pump later. Water storage needs adequate usable volume, overflow and drainage, structural support, level controls, contamination protection and safe access. Raising a tank also adds head, so unnecessary height makes the pump and array work harder. If constant high pressure is required, gravity storage alone may not provide it.

Standalone power: design around a measured load profile

An off-grid system has no utility supply available to correct a sizing mistake. Begin with an inventory that records each device's running power, start-up behavior, operating hours, duty cycle, AC or DC supply, season and importance. Measure existing loads when possible. Then create a time-based profile: ten watt-hours used at noon is not operationally equivalent to ten watt-hours required at midnight.

Build the daily electrical-energy budget

Edaily = Σ(Pi × ti × fi)

Use measured input power where available and keep units consistent. Add conversion, wiring and standby losses after defining the load-side energy. A margin may address forecast uncertainty, but an unexplained percentage should not replace a proper inventory.

Edaily

electrical energy used by all loads during a representative day

Pi

input power of load i

ti

scheduled operating time of load i

fi

fraction of that time the load actually runs, from zero to one

Example

A 40 W communications unit running continuously uses 0.96 kWh per day. A 20 W lamp operating for 10 hours uses 0.20 kWh per day. Their combined load-side energy is 1.16 kWh before controller, battery and wiring losses.

1. 1. Separate critical and deferrable loads.Protect essential communications, safety or control functions first. Schedule pumping, charging or other flexible tasks when solar production is available.
2. 2. Check peak and starting power.Add loads that can run together and verify motor or compressor starting demand against the inverter, controller, battery and cabling.
3. 3. Set an autonomy target.State how long critical loads must operate without useful solar input and which loads will be disconnected as stored energy falls.
4. 4. Model the design period.Use location-appropriate irradiance and temperature data for the difficult season, not only an annual average or a best clear day.
5. 5. Include ageing and recovery.Check usable capacity, allowed state of charge, temperature, degradation, recharge time after a poor-sun period and any replacement plan.

Solar refrigeration: electricity is only one part of the cold chain

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Diagram description

The conceptual drawing shows photovoltaic panels feeding electrical equipment and a packaged refrigeration unit. Blue piping connects refrigeration equipment, a vessel labelled thermal storage and an open cold room containing stacked produce. Labels identify solar electricity, refrigeration, thermal storage and cold storage; no capacities or temperature guarantees are shown.

A cold room must remove heat entering through the insulated envelope and door openings, heat from warm incoming product, people, lights and fans, and heat associated with defrost or other processes. Product type, arrival temperature, required cooling rate, storage temperature, humidity, daily throughput, ambient conditions and door traffic all matter. A nominal room volume or compressor rating by itself is not a cooling-load calculation.

Solar output often overlaps with hot daytime conditions, but the cold chain may have to continue through evening, cloud and equipment downtime. Electrical storage can run the compressor later. Thermal storage can operate refrigeration when solar is available and retain useful cooling in ice, chilled water or a purpose-selected phase-change material. The grid or a generator can provide backup. These options may be combined, and each has conversion losses, limits, controls and maintenance needs.

Choose storage by asking what may safely wait

Water and thermal storage can avoid repeated electrical conversions when the final service is water delivery or cooling. They can also make operation easier to inspect: tank level or stored-cold state relates directly to the service reserve. They are not universally superior. Tanks occupy space, require safe structures and can affect water quality; thermal stores need heat exchangers and controls; batteries can serve several electrical loads and respond quickly. Compare complete architectures at the same service level.

A practical feasibility and sizing workflow

1. 1. Define the useful output.State cubic metres of water at pressure and time, watts of electrical service by hour, or product quantity and temperature performance—not merely panel capacity.
2. 2. Measure the resource and load.Use source tests and crop demand for pumping, time-based electrical measurements for off-grid loads, and a thermal load assessment for cooling.
3. 3. Set the continuity rule.Document permissible interruption, autonomy, critical functions, load shedding and the conditions that start backup.
4. 4. Compare complete architectures.Model direct operation, service storage, battery storage and hybrid backup with the same weather, demand, losses and reliability target.
5. 5. Check every power boundary.Verify steady and starting power, voltage range, controller limits, conductor and protective-device ratings, pump curve or refrigeration duty and simultaneous loads.
6. 6. Cost the lifecycle.Include civil work, distribution, storage replacement, fuel or grid charges, inspections, cleaning, water treatment, refrigerant service, monitoring and end-of-life responsibilities.
7. 7. Commission the delivered service.Test flow and pressure, load priority and autonomy, temperature distribution, alarms, safe shutdown, backup transfer and recovery under documented conditions.

What should the monitoring record?

• Water system.PV energy, pump run time, flow, pressure, tank level, source level or drawdown, irrigation delivery and controller faults.
• Standalone electrical system.PV production, load by priority, battery state and temperature, low-energy events, curtailed loads, backup operation and communication gaps.
• Cold store.Representative air and product temperatures, door events, compressor and fan operation, stored-cold state where applicable, alarms, backup operation and excursion response.
• Common context.Time-synchronized weather, maintenance, configuration changes and sensor-quality flags so an apparent performance problem can be investigated.

To understand why solar and load vary through a full operating day, read Solar Generation During Day, Night and Bad Weather. For the choices available when daytime production exceeds immediate use, continue with What Happens to Solar Electricity You Do Not Use?.

One-minute questions

Questions to answer before you apply this lesson

What should I select or check first for Solar Power Beyond the Rooftop?

1. Separate critical and deferrable loads. Protect essential communications, safety or control functions first. Schedule pumping, charging or other flexible tasks when solar production is available.

Which assumption can change the conclusion?

Irradiance, weather, module construction, wiring, orientation and measurement boundary match the case being discussed.

What can go wrong if I copy the example directly?

Product temperature is the acceptance boundary. Do not assume that a cold room is safe because the compressor ran or an air sensor looks normal. The required range depends on the product and applicable food, medicine or process rules.

How do I verify the result in the real system?

5. Include ageing and recovery. Check usable capacity, allowed state of charge, temperature, degradation, recharge time after a poor-sun period and any replacement plan.

Sources and further reading

1. Solar Pumping: The BasicsWorld Bank Water Global Practice · 2026-10-12Reviewed for solar-pumping components, water demand, source assessment, total dynamic head, storage, solar resource and system-sizing considerations.
2. Solar-Powered Irrigation Systems: A Clean-Energy, Low-Emission Option for Irrigation Development and ModernizationFood and Agriculture Organization of the United Nations · 2026-10-12Reviewed for component matching, solar pumping configurations, irrigation scheduling, water storage as an alternative to battery storage and sustainable water governance.
3. Positive Prospects for Solar-Powered Irrigation SystemsFood and Agriculture Organization of the United Nations · 2026-10-12Reviewed for the need to assess well depth, soil, configuration, water storage and economics together, and for groundwater-overextraction risk.
4. Procedures for Determining the Performance of Stand-Alone Photovoltaic SystemsNational Renewable Energy Laboratory · 2026-10-12Reviewed for stand-alone PV design verification, array-to-load balance, charge-controller function, usable battery capacity, design month and hours-of-autonomy concepts.
5. Solar and Resilience BasicsU.S. Department of Energy · 2026-10-12Reviewed for the distinction between solar generation and resilient electrical supply, and the need for properly configured inverter and storage equipment for islanded operation.
6. Solar Energy and the Cold Chain: A Guide for Small-Scale Fisheries InterventionsFood and Agriculture Organization of the United Nations · 2026-10-12Reviewed for the role, limitations, feasibility assessment, operation and maintenance of solar-powered refrigeration and ice-making in cold chains.
7. Innovation Outlook: Thermal Energy StorageInternational Renewable Energy Agency · 2026-10-12Reviewed for cold thermal storage using ice and phase-change materials, and for shifting cooling production from generation time to later demand.
8. Freezing and Refrigerated Storage in Fisheries: Cold StoresFood and Agriculture Organization of the United Nations · 2026-10-12Reviewed for insulation, vapour barriers, air ingress, door operation, cold-air distribution, defrosting, temperature control, reliability and specialist design.
9. For an Energy Efficient and HFC-Free Retail Refrigeration SectorUnited Nations Industrial Development Organization · 2026-10-12Reviewed for solar-refrigeration intermittency and the use of thermal storage, electrical storage or conventional backup to maintain cold-chain continuity.