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A 300 watt solar panel with full irradiance will run a constant AC load of 270 watts, taking into account inverter losses of 10%. This includes appliances such as blenders, desktop PCs, vacuum cleaners and treadmills. A 300 watt solar panel will also run a small fridge with 120Ah lithium battery.
- How much power does a 300 watt solar panel produce?
- 300 watt solar panel specifications
- How many kwh does a 300 watt solar panel produce?
- What can a 300 watt solar panel power?
- 300 watt solar panel how many amps?
- 300 watt solar panel size
- How much does a 300 watt solar panel cost?
- Can a 300 watt solar panel run a refrigerator?
- Related Questions:
- How many batteries do I need for a 300 watt solar panel?
- What size charge controller for 300 watt panel?
How much power does a 300 watt solar panel produce?
Before working out what a 300 watt solar panel will run we need to understand how much energy in watt-hours it can produce and under what conditions.
I’ll be focusing on the energy in watt-hours a 300 watt solar panel can generate, rather than instantaneous power in watts . It’s a much more useful value for matching panel output to load.
Before moving on to how many kilowatt-hours a 300 watt solar panel produces, let’s take a look at the basic specifications of some commercial panels.
300 watt solar panel specifications
Important solar panel electrical specifications are:
- Open circuit voltage (Voc) – measured by multi-meter across the + and – leads
- Short-circuit current (Isc) – measured by multi-meter inline with leads shorted together
- Maximum power voltage (Vmp) – the volts at which maximum power is generated
- Maximum power current (Imp) – the currrent that flows when maximum power is generated
Vmp and Imp occur at the panel Maximum Power Point (MPP) and is normally the panel’s stated rating in watts at STC (Standard Test Conditions).
Table – 300 watts solar panel brand specifications compared
Grape Solar GS-M60-300-FAB1-USA
GoGreenSolar Phono Solar 310W
# of cells
Vmp (volts max power)
Price guide ($)
Power at MPP
kWh/day at 4 peak-sun-hours
kWh/yr 4 peak-sun-hours
65.6*39.5*1.4 in (1666*1002*35 mm)
1640mm x 992mm x 40mm (64.57” x 39.06” x 1.57”)
1640mm x 922mm x 35mm (64.57” x 39.06” x 1.38”)
40.8 lbs (18.5kg)
39.9 lbs (18.1kg)
Video – Can a 300 watt solar panel run an RV?
How many kwh does a 300 watt solar panel produce?
With an average irradiance value of 4 peak-sun-hours a 300 watt solar panel produces 1.2 kilowatt-hours (kWh) of electrical energy per day, or 438kWh per year, The exact amount will vary according to location irradiance. If supplying AC appliances, deduct at least 10% for inverter losses, which depends on inverter size and efficiency.
You’ll come across the term Maximum Power Point again and again as you research solar power generation. This is when the panel volts and current are at optimum values for maximum power.
Power (watts) = volts x amps
This only happens under certain conditions:
- when irradiance is sufficient (how much sun energy is available)
- when the load characteristics match the panel requirements
Solar irradiance and power output
Solar panel output is heavily dependent on irradiance and varies a lot during the day – maximum in a few hours around mid-day and very low in early morning/evening.
Because of this, solar professionals talk in terms of average hours of maximum irradiance in a day and use this to calculate the average power a panel delivers over time.
The value varies by location and is taken from historical data from sites such as https://globalsolaratlas.info/ The screen-shot below shows the irradiance value in kWh/m2/day for Houston, Texas.
The daily value is also called peak-sun-hours and this value is used to determine solar panel power.
Solar panel internal resistance
Every electrical component has an internal resistance and in the case of a solar panel it’s called the Characteristic Resistance. For most solar panels it’s around 3 ohms.
Maximum power transfer from panel to load occurs when the load resistance matches the panel resistance, which is obviously not always the case.
Luckily, devices do exist that automatically adjust to simulate maximum power conditions. They are called MPPT chargers and MPPT inverters.
How much energy will a 300 watt solar panel produce?
In terms of energy, the amount of power can be calculated in this way:
Maximum panel rating x peak-sun-hours/day = watt-hours per day
If we take Houston as an example, then a 300 watt solar panel would generate:
300 watts x 4.254 = 1.276kWh/day = 465.7kWh/year
What can a 300 watt solar panel power?
Using a maximum power of 270 watts as a guideline, the table below gives some indication of the type of common household appliances that could be run with the output from a 300 watt solar panel:
Table: Appliances that can be powered using a 300 watt solar panel
What can a 300 watt solar panel Power? (Renogy Price)
Electric Can Opener
Home Sound System
Electric Fence (25 miles)
300 watt solar panel how many amps?
The maximum amps of a 300 watt solar panel is called Imp (Current at Maximum Power) and is provided on the specification sheet by the manufacturer. An average current is 9.5 amps DC for a 300 watt solar panel with Voc 42 volts. The equivalent AC appliance current (USA) is about 3 amps.
The easiest way to find how many amps a 300 watts solar panel can deliver is to read the specification sheet. An average value is about 9.5 amps DC.
In terms of AC current, we need to take away inverter losses of at least 10% and assume the panel is delivering maximum power.
If Vmp is 36 volts, then for an AC load in USA we need to reduce the DC current by the difference in the DC/AC voltage. A simple equation could be:
AC amps = DC amps x 36/120 = 9.5 x o.3 = 2.85 amps AC
Remember that the inverter efficiency varies according to load and I’m guessing at 90% when fully loaded. However, this also depends on the size of the inverter used.
Final maximum AC load current = 2.85 – (2.85*10/100) = 2.56 amps AC
300 watt solar panel size
The physical size of a 300 watt solar panel is determined by the size and number of solar cells used in its manufacture, and the cell efficiency.
The most common area is 1640mm x 922mm (64.57” x 39.06”) while the thickness can vary according to manufacturer. The solar cells are a similar thickness across the industry but the layers of EVA, panel backing and the thickness of the glass cover can vary.
Most panels lay between 35mm (1.38”) and 40mm (1.58”) thick, and weigh between 18kg (39lbs) to 19kg (42lb).
How much does a 300 watt solar panel cost?
Check Renogy 300 watt solar panel kit price.
As you can see from the table presented previously, there is a wide variation. Generally, as in most things, price reflects quality and country of manufacture.
Renogy is based in USA and their 300 watt panel is very expensive at $1199 while at the other end of the spectrum, many Chinese manufacturers are churning out good quality solar panels at well under $200 per unit.
Of course, shipping must be taken into account but these panels still represent very good value for the power. It remains for the customer to make a shrewd judgement about quality and panel output over it’s lifetime.
In general, the price of solar per watt has been tumbling down for some years now to something like $0.85/watt, so there is little need to go for the most expensive panels. In my own experience, in the Chinese market – buyer beware!
Can a 300 watt solar panel run a refrigerator?
300 watts is probably the minimum size needed to run a small to medium fridge, in combination with a 120Ah lithium iron phosphate battery and a 500 watt pure sine-wave inverter. It’s calculated like this – we know that a 300 watt panel puts out about 465kWh/year on average and a small fridge uses between 200kWh to 400kWh/year.
It seems a match, it seems the panel could power a 400kWh/yr fridge – but can it? Let’s assume our fridge takes 400kWh/year.
A fridge runs over 24 hours, while solar panels only generate power during daylight hours. This means the battery has to provide night-time energy equivalent to 200kWh/year i.e. half the energy required.
During the daytime the solar panel has to supply 200kWh over the year to run the fridge and another 200kWh to fill up the battery for night-time running.
It should be OK, but it may be tight, but there are cloudy days …
Can I use solar panel without battery?
It’s possible to use solar panels without batteries, and this is exactly how grid-tie home solar works. The solar system feeds in to the national power grid when there is a surplus of production.
When using a solar panel separately to power appliances, it is possible but not recommended. If a cloud passes over the power output will drop and disrupt the supply to your appliance.
Some appliances, such as fridges, don’t draw a constant load but cycle on and off. During starting, a fridge needs 3 times more power than when running – perhaps more than the solar panel can supply.
For this reason energy storage in the form of a battery is needed to act as a ‘power reservoir’ to absorb the extra demands of cycling compressor motors.
How many 300 watt solar panels to run a house?
The average amount of electrical energy used per household in the US is about 11,000kWh/year.
Each 300 watts solar panel can generate 465kWh/year on average, but we also need to take into account solar system losses. These can be up to 23%.
Number of 300 solar panels = home energy requirements/solar production-10% losses
465kWh*23% = 465-107 = 358kWh
Number 300 watt solar panels to run a house = 11000kWh/358kWh = 31 panels
The exact number of panels you need for your home depends on your energy consumption and your location. Us the following calculator to find out how many solar panels to need to run your house:
How many solar panels do you need to run your home calculator
How many amps does a 300 watt solar panel produce?
The electrical specifications for a 300 watt solar panel produced by Renogy are as follows:
- Maximum Power at STC: 300W
- Maximum System Voltage: 1000VDC
- Optimum Operating Voltage (Vmp): 32. 20V
- Open Circuit Voltage (Voc): 38. 80V
- Optimum Operating Current (Imp): 9. 32A
- Short-Circuit Current (Isc): 9.71A
The details given on the the label at the back of the panel gives a lot of useful information, but we need to make sense of what the different parameters mean.
For this panel the maximum working current (Imp) is 9.32 amps, but this only occurs when the panel voltage is at 32.20 volts (Vmp). Why is that?
These values of volts and amps that produce maximum power occur at what is called the Maximum Power Point (MPPT) – if you multiply 32.2 volts x 9.32 amps you get 300 watts.
If you come across a 300 watt panel or any other solar panel with no label, then as a general rule Imp is about 96% of Isc.
Simply short the leads together with a multi-meter in ammeter mode and read the short-circuit current. Multiply by 96% and you have the maximum working current (Imp) in full irradiance.
What size inverter for 300 watt solar panel?
At first sight you would think the answer is obviously 300 watts, but it’s always best to over-estimate your needs for a couple of reasons.
Let’s say for example you were running a fridge or freezer. It might run quite comfortably in full sunshine as the average refrigerator has a continuous running watts of 40 to 100 watts.
However, when the compressor cycles, and the motor starts ups, it draws up to 3 times more power due to the surge current.
The 300 watt solar panel output may not be enough to supply this load, particularly if if the panel isn’t operating at maximum output, which is mostly the case except for 4 or 5 hours around mid-day.
In that case a battery is essential and would be coupled to the 300 watt solar panels using a solar charge controller.
Solar PV losses
Unfortunately, every element in a solar circuit loses a little power. In fact, a complete domestic solar system can lose up to 23% of generated watts!
If we just assume 10% losses, then the safest bet is to use a 300 watt continuously rated inverter. This would normally allow up to 50% over-current for short periods, so would have enough capacity.
Why not just use a 500 watt inverter, or bigger?
Inverter efficiency goes down the more lightly loaded it is. A 500 watt inverter running at 50 watts (10%) would have a much lower efficiency than when fully loaded.
In addition, an inverter with no load at all will consume between 10 to 40 watts.
Inverter efficiency curve
How many batteries do I need for a 300 watt solar panel?
Batteries used for energy storage purposes in solar applications are either lead-acid deep-cycle type (leisure batteries) or lithium iron phosphate.
Lead acid can be discharged 80% of rated capacity but 50% is recommended to maximize battery life. This means that you can only use 50% of a lead-acid deep-cycle battery.
LiFPo4 batteries have a different chemistry and can be discharged to 95% without damage, but 80% is often recommended to extend battery life.
The average energy output of a 300 watt solar panel is:
4 peak-sun-hours x 300 watts = 1200 watt-hours
So this is the maximum charging energy available each day.
Assuming you’ll be charging a 12 volt battery, then charging amp-hour capacity supplied from the panel:
1200 watt-hours/12volts = 100Ah
Assuming this amount would also be discharged overnight, then the following battery capacity would be required for a 300 watt solar panel setup:
What size charge controller for 300 watt panel?
The average current produced by a 300 watt solar panel is between 9 and 9.5 amps, so a solar charge controller rated at 10 amps do nicely.
However, it would be prudent to upgrade to a 30 or even a 60A model in case you want to increase solar capacity later.
Most MPPT controllers have an input voltage rating of 60 volts, so a 300 volt solar panel with Voc of between 40 to 44 volts will work.
RENOGY are fast becoming the preferred source for solar panels, kits, batteries and solar control accessories. Based in the US, where the products are manufactured, they are widely known and respected for innovation and quality.