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A 400 watt solar panel with full irradiance will run an AC load (constant) of 360 watts. This value takes into account 10% inverter losses. This includes a combination of appliances like televisions, laptops, slow cookers and ceiling fans. A 400 watt solar panel can run a small fridge using a 120Ah battery.
- How much electricity will a 400 watt solar panel produce?
- 400 watt solar panel electrical specifications
- How much electricity does a 400 watt solar panel produce?
- What can a 400 watt solar panel power?
- 400 watt solar panel how many amps?
- How big is a 400 watt solar panel? Dimensions
- Will a 400 watt solar panel run a refrigerator?
- Related Questions:
- How many batteries would I need for a 400 watt solar panel?
How much electricity will a 400 watt solar panel produce?
Before finding exactly what a 400 watt solar panel can run we should calculate how much energy in watt-hours it generates and under the best conditions.
Energy output of in watt-hours instead of instantaneous power in watts is a much more useful value to use when matching loads to solar panels.
400 watt solar panel electrical specifications
The main solar panel specifications are listed below:
- Open circuit voltage (Voc) is the voltage measured by a multi-meter when connected across the positive and negative and leads
- Short-circuit current (Isc) is the amps that flow when the leads are shorted together
- Maximum power voltage (Vmp) Maximum power occurs at this voltage
- Maximum power current (Imp) Maximum power is achieved when this current flows
The Maximum Power Point (MPP) of a solar panel is when the voltage and current combine to generate most power in watts. This is a panel’s rated watts at STC (Standard Test Conditions).
The chart below shows specifications for several commercially available 400 watt solar panels:
Chart – 400 watts solar panel specifications comparison
# of cells
Vmp (volts max power)
Price guide ($)
Power at MPP
kWh/day at 4 peak-sun-hours
kWh/yr 4 peak-sun-hours
2,067mm (81.4in) x 1,046mm (41.2in) x 54mm (2.1in)
1,644mm (64.7in) x 1,204mm (47.4in) x 40mm (1.6in)
2,008mm (79.1in) x 1,002mm (39.4in) x 40mm (1.6in)
2000 X 992 X 35 mm
22.5 kg (49.6 lbs
Video – Can a 400 watt solar panel run power tools?
How much electricity does a 400 watt solar panel produce?
Assuming average irradiance of 4 peak-sun-hours a 400 watt solar panel generates 1600 watt-hours (Wh) of energy a day, or 584kWh per annum. The precise energy value will change according to the location’s peak-sun-hours. Deduct at least 10% to account for inverter losses, which will depend on inverter size and load.
You might have heard of the term Maximum Power Point as you read about solar power generation. This is the point when the panel volts and amps are at just the right values to generate the panel’s maximum power.
Power in watts = voltage x current
Maximum power is generated when:
- the sun’s energy (irradiance) is strong enough and,
- the characteristics of the load resistance match the panel’s internal resistance
Solar irradiance to power output – the relationship
Solar panel output depends on the sun’s strength and and changes across the day. It’s strongest those few hours either side of noon and weakest in the early morning and evening.
Solar installers talk in terms of average hours sunshine per day and they use this value to estimate the average watt-hours a panel can generate over time.
Peak-sun-hours varies according to geographical location and can be found sites such as https://globalsolaratlas.info/ which has a database of historical solar data. The image below shows the value of irradiance in kWh/m2/day for Houston, Texas.
The daily value is usually known as peak-sun-hours and this number is useful when sizing domestic solar panel power.
Solar panel characteristic resistance
Every electrical device has an internal resistance. For a solar panel it’s known as the Characteristic Resistance. Most solar panels have an internal resistance of it’s about 3 ohms.
Maximum power generation occurs when load resistance is the same value as the panel’s characteristic resistance.
Some devices (solar chargers and inverters) automatically adjust their internal resistance to create maximum power output. These are called MPPT devices, which stands for Maximum Power Point Tracking.
How much energy can a 400 watt solar panel produce?
The amount of energy generated can be found in this way:
Solar panel rating x irradiance (peak-sun-hours/day) = energy in watt-hours/day
Taking Las Vegas as an example, a 400 watt solar panel could produce:
400 watts x 5.701 = 2.28kWh/day = 832kWh/year
What can a 400 watt solar panel power?
With a maximum power output of 360 watts, the table underneath gives an idea of the type of home appliances that you could comfortably run from a 400 watt solar panel in full sunshine:
Table: Appliances that can be powered using a 400 watt solar panel
Electric Can Opener
Home Sound System
Electric Fence (25 miles)
Electric Hedge Trimmer
400 watt solar panel how many amps?
The maximum currents of a 400 watt solar panel is known as Imp (Maximum Power Current) and is indicated on the specification sheet by the supplier. Average current is 9.5 amps DC for a 400 watt solar panel with Voc 49 volts. The equivalent current (US) to run AC appliances is about 3.3 amps.
By far the best way to know the maximum amps a 400 watts solar panel can generate is to read the amps from the specification sheet.
When converting to AC current, inverter losses of at least 10% should be deducted.
If Vmp is 42 volts, we should reduce the DC current valuer by the ratio of the DC to AC voltage. A simple looks like this:
AC current = DC current x 42/120 = 9.5 x o.35 = 3.325 amps AC
Inverters are not very efficient if not loaded to 100% and drops sharply as the load decreases. Let’s assume 95% if fully loaded. This depends on the inverter size and in practice, the load won’t remain constant so the efficiency will change dynamically.
Final AC load current =3.325 – (3.325*5/100) = 3.16 amps AC
How big is a 400 watt solar panel? Dimensions
The exact size of a 400 watt solar panel is determined by how many solar cells are used in its production. Most panels are somewhere between 40mm and 55mm thick, and can weigh 20kg to 25kg.
A common surface area is 2050mm x 1050mm and the thickness varies across manufacturers. The solar cells are all about the same thickness across the board but the extra layers of EVA plastic, solar panel backing and the glass cover thickness varies, but not a lot.
Will a 400 watt solar panel run a refrigerator?
A 400 watt rated panel will run a medium size refrigerator, combined with a 120Ah lithium iron phosphate (LiFeP04) battery and a 500 to 600 watt inverter (pure sine-wave type). If a 400 watt solar panel produces about 584kWh/year and a refrigerator needs between 2ookWh to 400kWh/year, then it seems a comfortable match.
Let’s take a closer look – assume the fridge in question consumes 400kWh/year.
A fridge runs continuously day an night, but solar panels only produce power during the day. This means some kind of battery is needed to power the refrigerator during the night equivalent to about 200kWh/year or 50% of the energ needed.
In daylight hours the solar panel has to generate 200kWh per year to power the refrigerator and an additional 200kWh to charge the battery back up for running during the night.
If there are not too many cloudy days a 400 watt panel should generate enough energy to run a medium sized fridge.
Can a solar panel work without a battery?
A solar panel can work without a battery – this is how a grid-tied solar system works. Solar panels supply power to the grid when there is over-production. It is not recommended to power appliances without a battery. If clouds pass over the solar panels reduces output and appliances may not work.
Some home appliances, like fridges, freezers and AC units, don’t pull the same current all the time but turn on and off.
When a motor starts, a fridge will pull up to 3 times more current than when running constantly. This extra power may well be too much for the solar panel.
This is why energy storage in the form of deep-cycle lead-acid or lithium phosphate batteries are needed to provided the surge current of compressor motors that cycle on and off.
How many 400 watt solar panels to power a house?
Nineteen 400 watt solar panels are needed to power the average house. The average American household uses about 11,000kWh of electrical energy per year. A 400 watt solar panel produces 584kWh per year with irradiance of 4 peak-sun-hours. Dividing 11000kWh by 584kWh results in 19 solar panels (ignoring losses.)
Let’s assume a very lean overall PV system loss of 10%:
Number of 400 solar panels = home energy needs/solar system production
Each panel generates annually 584kWh-(584kWh*10%) = 465 = 525.6kWh
Number of 400 watt solar panels to power a home = 11000kWh/525.6kWh = 21 panels
The precise number of solar panels you will need for your home depends on how much energy you use and where you live.
Use the solar calculator below to calculate how many solar panels you would need to power your house:
How many solar panels do you need to power your home calculator
How many amps does a 400 watt solar panel produce?
The electrical specifications for a typical 400 watt solar panel might be:
- Max Power at STC: 400W
- Max System Voltage: 1000VDC
- Optimum Operating Voltage (Vmp): 72.9V
- Open Circuit Voltage (Voc): 85.3V
- Optimum Operating Current (Imp): 5.49A
- Short-Circuit Current (Isc): 5.74A
The electrical specifications provide a lot of valuable information, but we need to be sure of what the different numbers mean.
For this 400 watt panel the maximum working current (Imp) is 5.29 amps, and this happens when panel voltage is 72.9 volts (Vmp).
The values of voltage and current that generate maximum power are optimum at the Maximum Power Point (MPPT). This is how the panel rating is calculated – multiply 72.9 volts x 5.49 amps you get 400 watts.
If you happen to have 400 watt panel that has no label, then multiply Isc by 96% and that will be the maximum current the panel can generate.
You just short the leads through a multi-meter on the ammeter setting to find Isc. Multiply this number by 96% to find the maximum working current (Imp) in full sunshine.
What size inverter for a 400 watt solar panel?
As a general rule, an inverter should be sized closely to the actual power rating of the solar panels. This is because inverters are most efficient when fully loaded. Most inverters have a continuous load rating and a surge power rating. A 500 watt pure sine-wave inverter would be a good choice.
Your first thought might be that it’s obviously 400 watts, but a good ruel-of-thumb is to over-estimate the inverter rating.
A fridge or freezer with a running watts between 40 to 100 watts might run in full sunshine, but the power drawn by this type of appliance is not constant.
Motor surge current can be 3 times more than it’s running current, and as a fridge compressor stops and starts in normal operation the power demand will fluctuate.
The 400 watt solar panel may well supply this load, but perhaps not if the panel isn’t operating at maximum output – solar panels don’t output their maximum power for much of the time.
Power output reduces due to a host of factors – time of day, cloud coverage, seasonal changes, temerature and dirt.
A battery is essential to supply power if the solar panel power drops
Solar system PV losses
It’s a sad fact that every part of a solar circuit loses some power. In total, a domestic solar power installation loses up to 23% of the rated power output!
Assuming 10% to 15% losses, then you should use a 400 watt continuously rated inverter. This rating allows up to 50% over-current for a limited time, so would be big enough to provide power during motor surge current.
Why not just use a bigger inverter?
Inverters become more inefficient as they are lightly loaded. A 600 watt inverter with a 60 watts load (10%) will have a very poor efficiency compared to full load.
Unfortunately, inverters also draw power in their own right, and may consume between 10 to 50 watts even with no external load connected.
Image – Power inverter efficiency curve
How many batteries would I need for a 400 watt solar panel?
A 400 watt solar panel would need a 166Ah lithium iron phosphate battery with 80% Depth of Discharge (DoD). A lead acid deep-cycle would need a capacity of 266Ah, with recommended DoD of 50% i.e. half the actual capacity can be used. A 400 watt solar panel can charge 133Ah at 12 volt.
Energy storage solutions for solar systems can be lead-acid deep-cycle type, often called leisure batteries, or lithium iron phosphate (LiFeP04).
Although it’s easily possible to discharge a deep-cycle battery to 80% of its rated capacity 50% is recommended so that battery life is maximized. In this case only 50% of a leisure battery is usable in practice.
LiFPo4 batteries are a little different and you can discharge them to 95% without harming them. However, 80% is normally recommended if you want the batteries to last a long time.
The average Wh output of a 400 watt solar panel is:
4 peak-sun-hours x 400 watts = 1600 watt-hours
This is the maximum charging energy you have available each day.
If recharging a 12 volt battery, then the charging amp-hour capacity available from the solar panel:
1600 Whs/12volts = 133Ah
If the same amount were to be discharged during the night, then this battery capacity would be needed for a 400 watt solar installation:
- Lead-acid leisure battery @50% DoD= 266Ah
- LiFeP04 battery @80% DoD = 166Ah
Read about 300 watt solar panel power.
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