Solar Panel System for Homes, Farms and Restaurants: How to Calculate Real Load Demand

To calculate the real load demand for a Solar Panel System, users must evaluate more than the wattage printed on each appliance. The essential factors are total daily energy consumption in kWh, maximum simultaneous load in kW, motor or compressor startup power, required backup duration, and local peak sun hours.

Homes use the most electricity in the morning and evening. Pumps, motors, ventilation systems, and refrigeration systems are used on farms during these times. All equipment is used in restaurants during the rush hours. Apart from farms and restaurants, all other installations can be undersized or overpriced.

What is Load Demand in the Context of a Solar Panel System?

Real load demand is the demand for power and the demand for energy.

The demand for energy is the amount of power that the solar system and batteries must create and/or store. The demand for power is the amount of appliances that the inverter can operate at one time.

Load factor	Meaning	Importance
Rated power	Appliance power in Watt (W) or kW	Load determines system operation
Daily energy use	Energy consumed in kWh	Size of PV and battery system determined
Simultaneous load	Total power of all equipment running in concert	Only continuous inverter output is applicable
Surge power	momentary demand	Problem-free starting of equipment
Backup duration	Operation duration	Size of battery system
Future expansion	Planned additional equipment or consumption	Systems will require upgrading

So, a Solar Panel System should be designed to meet both the daily energy used and the highest load that can be expected.

Step 1: List All Electric Loads

Create a list of all of your loads. To account for as much precision as possible in your listing, obtain nameplate data. Do not use rough approximations.

Appliance	Quantity	Rated power	Hours per day	Daily consumption	Startup surge
Refrigerator	1	200W	10 equivalent hours	2.0kWh	2–3×
LED lighting	10	12W	6 hours	0.72kWh	Low
Water pump	1	1,500W	2 hours	3.0kWh	2–5×
Air conditioner	2	1,200W	6 hours	14.4kWh	2–3×

Refrigerators and air conditioners cycle on and off, so their effective operating time may differ from their total connected time. Pumps, motors, compressors, welders, three-phase machinery, and electric heating equipment require separate evaluation.

Account for energy use in routers, displays, control panels, virtual security systems, and other types of electronic devices.

Step 2: Estimate Daily Energy Use

Daily Energy Use (kWh) = Rated Energy (kW) x Operating Hours

Example: 1.5 kW water pump run for 2 hours = 1.5 kW x 2 hours = 3 kWh

Calculate each appliance, and then add to find the total daily energy use.

Allow for system losses:

Adjusted Daily Demand = Total Daily Consumption / System Efficiency

A first-order estimate for the planning efficiency would be 80-90% to begin with, but the actual value will depend on:

•The efficiency of the inverter used

•The loss during the charging and discharging of batteries

•Longer lengths of cable and voltage drop

•RTM

•Solar shading due to dust, etc.

•Energy management scheduling

•Variable daily solar generation due to weather changes

Step 3: Determine Maximum Simultaneous Load

Daily energy usage and electricity usage at any given moment are different measurements.

A facility can have a daily consumption of only 25kWh, but the instantaneous load at certain times can go up to 8kW with the simultaneous operation of multiple air conditioners, pumps, refrigerators, lighting and kitchen equipment.

Use the following calculation:

Simultaneous Load = Combined Power of Appliances Likely to Run Together

The inverter in a Solar Panel System must be selected for the highest realistic simultaneous load, not only average daily consumption.

The calculation should include:

•Continuous operating loads

•Short-term peak loads

•Motor startup current

•Future equipment additions

Step 4: Account for Startup Power

Motors and compressors may require several times their normal operating power during startup. This commonly affects:

•Irrigation and water pumps

•Air compressors

•Refrigerators and freezers

•Air conditioners

•Ventilation fans

•Agricultural processing equipment

•Commercial refrigeration systems

An inverter with insufficient surge capability may cause equipment startup failure, voltage reduction, overload protection, system restarting, or excessive battery discharge current.

The required surge capacity should be verified against the appliance manufacturer's data and the equipment's startup method rather than applying one multiplier to every device.

Step 5: Size the Battery for Backup Time

Figure out how much battery capacity is required by multiplying the critical load by the backup time in hours.

Usable Battery Capacity = Critical Load × Backup Hours

If your critical load is 2kW and you need a backup of 4 hours, you need at least

2kW × 4 = 8kWh of battery capacity.

There are also many additional factors that need to be considered like the depth of discharge, the loss of energy converted to other forms of energy, battery temperature, the rate of battery aging, and if the solar will be generating during the outage.

A 51.2V, 200Ah battery has a nominal capacity of

51.2V × 200Ah = 10.24kWh

At an 80% depth of discharge, the theoretical usable energy is

10.24kWh × 80% = 8.19kWh

How much usable energy is delivered will be influenced by the inverter, how intense the load is, the battery temperature, and the battery management system.

Step 6: Size the Solar Array

A planning formula is

Required PV Capacity = Daily Energy Demand ÷ Peak Sun Hours ÷ System Efficiency.

Peak sun hours are the solar hours with full output. The total number of daylight hours is something that people often confuse these with.

•Temperature

•Line of sight to the sun

•Season

•Shade

•Roof direction, incline, and surface

•Dust

•PV modules degradation

•The inverter output

•The battery state of charge

Monocrystalline panels of high energy output can give more installed capacity within restricted roof space, but they cannot guarantee consistent daily solar production.

Solar Panel System Load Calculation by Application

Homes

Residential loads include refrigerators, lighting, computers, WiFi equipment, pumps, air conditioners, washing machines, water

Demand tends to increase after the sun goes down and battery storage becomes more important. Refrigerators, lighting, internet, security system, and essential circuits can all be provided critical-load panels and prioritized during blackouts.

Farms

A farm Solar Panel System may operate irrigation pumps, livestock water systems, ventilation, refrigeration, electric fencing, feed-processing machinery, and monitoring equipment.

The major hurdles are startup demand, seasonal operation, long cable distances, voltage drops, dust, moisture and corrosion, and storage of energy in batteries. Energy can be stored by running pumps and other flexible loads during peak times of solar energy production.

Restaurants

Typical loads in a restaurant include: freezers, refrigeration, AC, lighting, ventilation, POS equipment, coffee equipment, ice making equipment, and heating equipment.

Careful consideration must be given to the size and the placement of the sat system due to the nature of refrigeration and continuous and overlapping peak loads. A 10kW system may be sufficient to support critical or partial loads in a restaurant; however, it may not be sufficient to support loads in restaurants with large ovens, electric cooktops, and large water heaters.

Application	Main load characteristic	Common challenge	Recommended priority
Home	Morning and evening peaks	Nighttime consumption	Refrigeration, lighting, and internet
Farm	Pumps and motor loads	Startup demand and cable distance	Pumps, ventilation, and refrigeration
Restaurant	Multiple simultaneous loads	Peak demand and continuous cooling	Cold storage, lighting, and POS
Mixed-use property	Complex load combinations	Overlapping demand	Circuit separation and staged expansion

Is a 10kW Solar Panel System Large Enough?

Given that high-power appliances do not all operate at the same time, and critical circuits are separate, then a 10kW system could be sufficient for a given installation. However, if multiple electrical motors start at the same time, there are large loads of electrical energy for cooking, full off-grid operation is necessary, solar resources are limited during the winter months, or three-phase loads are necessary, then a different or larger configuration would be required.

The answer to the question really depends on the load profile and not the type of use case alone.

Start with an Accurate Load Assessment

Accurately sizing a Solar Panel System requires consideration in both kWh and kW. There are also differences in the nature of operation, startup loads, and environmental considerations as well as backup priorities in homes, farms, and restaurants.

If you need to design a Solar Panel System for a home, farm, or restaurant, send JSDSolar your load lists, operating hours, and installation plus your backup requirements to obtain an optimal combination of PV, battery, and inverter systems.

FAQs

Q1. How does JSDSolar determine battery storage capacity?

Battery capacity utilization calculation by JSDSolar involves factors such as critical load, backup time duration, depth of discharge, inverter losses, aging, temperature, solar input, and battery storage capacity. Battery sizing is done by utilizing the energy stored rather than nominal capacity of a battery.

Q2. Is it possible for JSDSolar to extract the capacity for a solar system from an electricity bill?

An electricity bill provides an estimate of the energy consumed on a monthly basis and it can't evaluate the capacity for a solar system. JSDSolar analyzes the peak power, operating schedules for appliances and loads, seasonal demand, back up requirements, and solar hours as well.

Q3. Do JSDSolar offer farm, home and restaurant solar systems?

Yes, JSDSolar offer solar and battery systems for homes, farms and businesses. Each system is custom made based on unique needs. The variations in the use of the systems and the demand at different times of the day such as a farm and restaurant requires different types of equipment and determines the priority of backup power.

Q4. How does JSDSolar evaluate the need for a 10kW solar system?

JSDSolar evaluates the rated output of the inverter and confirms if it is capable of managing that load. JSDSolar also evaluates the energy consumed on a daily basis, the surge of capacity for the motors, available solar generation, backup time for battery, and also if high power appliances can be placed on a dedicated circuit or have a separate schedule for operation.

Q5. Will a JSDSolar system accommodate 120V and 240V devices?

Yes, some of our JSDSolar systems can use a split-phase inverter to provide 120V (or 240V) to support the split phase electrical needs. This would depend on the system configuration, market, local electrical codes, voltage/frequency of appliances, wiring design and installation.