What Size Solar Generator Do I Need?
Solar generators are a significant investment, and this article guides you on choosing the right unit tailored to your energy needs.
Many face the dilemma of overspending on oversized units or underspending and ending up with inadequate power. How do you strike the right balance?
Drawing from extensive research and industry data, we’ve observed that the key to maximizing your investment lies in understanding your daily power consumption and battery storage needs.
For those of you diving into the world of solar power, it’s crucial to make informed decisions that align with your energy requirements.
I remember my first solar generator purchase – the excitement, the confusion, and the lessons learned. Let’s embark on this journey together, ensuring you buy the best solar generator for your needs.
Power Requirements Of Different Appliances And Electronics
Several common mistakes are made when sizing a solar generator (or any other solar system). Considering these three points will help you decipher which generator you need.
Adding Too Much Capacity
As we discuss in the next point, one of the methods used to size a solar generator is to add up the power requirements of each item and arrive at a total.
The reality is that, apart from power consumers such as fridges and air conditioners, most appliances are not used simultaneously. An example is that it may not be necessary to cater for a hair dryer being used simultaneously with a coffee maker.
As a result, it is vital that when you calculate the power the system will consume, you are realistic regarding what equipment will draw in the system simultaneously. It may take some coordination with the family members, but it is straightforward to apply these rules later.
Adding Too Little Capacity
It is very frustrating to turn the kettle on only to find the solar generator trips. But too much capacity is a waste, and a balance must be struck to ensure the system can run the equipment as required.
This applies very strongly to batteries in a solar generator. A battery has to be sized correctly to provide sufficient power for immediate use (kW) and have adequate storage “volume” to keep giving power when there is no sun.
Surge Capacity Is Not Provided For
All appliances that use induction motors have two power requirements. Running and Starting (surge) power.
Examples of appliances that require starting (surge) power are listed below.
| Appliance | Average surge power |
|---|---|
| Refrigerators | up to 3,000W |
| Freezers | up to 1,800W |
| Washing Machine | up to 2,000W |
| Air Conditioners | 10,000 BTU surges @ 1800W/ 12,000 BTU surges @ 3950W. |
| Swimming Pool Motors | |
| Borehole (well) pump | |
| Pressure (Sump) Pump | |
| Circular Saws | |
| Electric Chain Saws | |
| Air Compressor |
Appliances like refrigerators, freezers, washing machines, and air conditioners start and stop erratically. Therefore, it is important to ensure that the solar generator has sufficient capacity to provide power when required.
How To Calculate the Total Amount Of Energy Needed
There are two ways (Method 1 and Method 2) to calculate energy needs.
Method Two is the correct method to apply if the solar power generator is being used off-site (camping, etc) or to power specific equipment.
Method One
Take a look at your electric utility bill and check the kWh usage. The value shown on the utility bill is the total kilowatts used for the period the bill applies.
The average electricity used in American households per month is 975 kilowatt-hours. To break this down to the size solar generator that would be needed, the number of kilowatt hours is divided by the number of hours in the billing period.
For example:
- kWh used in a month – 975 kW
- Days in a month – 30 days
- Hours in a day – 24 hours
The average kW usage per hour is, therefore, 975/30/24 = 1.35kW.
This figure is an average for each month, so before deciding upon a 1.35kW solar generator, it is crucial to assess when the realistic peaks in consumption occur. For example, the following equipment items are being used around meal times:
- Stove (If electric)
- Microwave
- Toaster
- Kettle
- Lights (if in the evening)
- Fridge (always on)
- Freezer (always on)
These may consume more than 1.35kW so that value should be adjusted for these peak periods.
The average includes nighttime when consumption may be meager, reducing the average.
Method Two
Once you know how much power is consumed on average, listing all the electrical consumers used at home or on camping trips is valuable.
Insert these and their consumption values into a spreadsheet like the example below.
| Common Appliances | Continuous Watts consumed | Surge Watts (Starting) |
| Coffee Maker | 1,200 | 0 |
| Blender | 750 | 0 |
| Microwave (1000 watts) | 1,000 | 0 |
| Waffle Iron | 1,250 | 0 |
| Hot Plate | 1,500 | 0 |
| Electric Skillet | 1,500 | 0 |
| Toaster Oven | 1,200 | 0 |
| Toaster | 800 | 0 |
| Light bulbs (LED) simultaneously on | 50 | 0 |
| Hair Dryer | 1,500 | 0 |
| Vacuum Cleaner | 1,200 | 0 |
| Space Heater | 1,500 | 0 |
| Clothes Iron | 1,250 | 0 |
| Refrigerator | 750 | 1,875 |
| Chest Freezer | 600 | 1,500 |
| Washing Machine | 750 | 1,875 |
| Furnace Fan | 1,000 | 0 |
| Household Fan | 120 | 0 |
| Air Conditioner (10,000 BTU) | 1,500 | 5,000 |
| Clock Radio | 10 | 0 |
| Stereo | 50 | 0 |
| Cell Phone Charger | 10 | 0 |
| Laptop Computer | 75 | 0 |
| MacBook Pro | 85 | 0 |
| iPad / Tablet | 20 | 0 |
| Desktop with Monitor | 400 | 0 |
| Inkjet Printer | 75 | 0 |
| Laser Printer | 500 | 2,000 |
| Aquarium | 500 | 0 |
| 32 Inch LED TV | 50 | 0 |
| 42 Inch Plasma TV | 240 | 0 |
| Home Theatre System | 200 | 0 |
| Blu-Ray system | 15 | 0 |
| Satellite Dish | 25 | 0 |
| Video Game Console (Xbox / PS4 / Wii) | 100 | 0 |
| Total Watts | 21,775 | 12,250 |
| Total kW | 21.8 | 12.3 |
The equipment described in this list is fictitious, and these consumption values should not be used.
Using the first table, the equipment in the home consumes 21.8 kW continuously and 12.3 kW to start (surge).
On the face of it, a 34.1 kW (21.8 kW + 12.3 kW) system is required.
This is not necessarily true, as most appliances do not run continuously. If we assume that the items marked in blue are run simultaneously, the solar generator would need to provide 4.4kWh of power, with a surge of 3.3kWh.
As many solar generators can double the power required for starting (surge) current, a system that produces more than 4.4 – 5 kW will be sufficient.
What Size Solar Generator to Get Based on Energy Storage Capacity
To correctly size a solar generator, it is essential to understand the relationship between energy storage capacity and power output.
Each battery will have kW and kWh power levels on its datasheet.
Kilowatts Power Of The Battery
kW is the maximum amount of energy that can be stored by a battery that is available instantly. Most batteries will also have a surge value higher than the base KW.
Kilowatt Hours Capacity Of The Battery
kWh (energy storage capacity) is the energy (volume) the battery can store.
The Tesla Power Wall 2 has the following capacities:
- Battery Size – 5kW (higher rates possible for short periods)
- Storage capacity of 13.2kWh.
This means that the battery can produce 5kW of power for 2 hours and 38 minutes (13.2kWh/5kW)
Determining The Size Of Generator Based On Energy Needs
There are two power levels that you need to consider that require the battery and inverter capacity to be sized correctly.
The Solar Generator’s Inverter Capacity
The inverter’s capability (part of the solar generator) dictates the maximum power availability at any time.
This is the maximum kW rating of the inverter that can be produced. Most inverters will show an additional (higher) rating called surge power.
This power can be produced for a minimal timeframe (seconds) and is used for starting fridges and similar equipment with induction motors.
The Solar Generator’s Battery Capacity
The battery capacity (kW) must match or exceed the kW capacity of the inverter.
The battery’s storage capacity (kWh) must provide continuous power when the sun is not shining. In sunny climates, this is overnight, and in environments with little sun, this is for much longer periods.
Compatibility With Solar Panels
It is essential to ensure that the solar panels used for the solar generator are compatible with it.
The critical metric to ensure compatibility is that the power produced by the solar panels should always be within the capability of the solar generator or, more specifically, the charge controller within the unit.
In this regard, all solar generators, power stations, and inverters have a value shown in the datasheet titled – Power In (or similar).
Most units will show this value as:
- Maximum Solar Input Voltage
- The maximum wattage range from the solar panels
Choosing A Generator That Will Work With Your Solar Panel Setup
The following lists the variables to consider when choosing a solar generator.
How Do You Intend To Use The Solar Generator?
The intended use of the solar generator is the most crucial consideration.
Backup Power For The Home
Is the solar generator intended for use at home to continue supplying power when the main electricity supply is interrupted? (For example, during a power outage).
If so, what appliances do you need to keep running while the electricity is off?
You must decide how long the solar generator will need to provide power, particularly at night or when the weather is terrible. This is where the previously discussed kWh measure comes in.
This will help you determine the capacity of the chosen system.
Use While On Holiday To Power Electrical Equipment
If you intend only to use the solar generator on holiday, it needs the following characteristics:
It should be light and small enough to transport to the holiday site. A portable solar generator is essential.
It should be sized correctly to provide power for the electrical equipment. For example, if you need to power an RV, you will need the generator to power a fridge/freezer, lights, air conditioner, and other equipment.
The Available Budget
You must use the solar generator budget wisely.
Only select a system that provides the amount of power that you realistically need. There are three reasons why you should never overspend:
- Purchasing capacity you don’t need is a waste of money from which you will never recover.
- The batteries and inverters in a solar generator have a finite lifespan, so purchasing more than you need will add to the waste.
- Solar power and inverter technology are continually developing, and when you come to replace the system, a more robust system will be available at a lower cost.
How To Determine The Most Cost-Effective Option
The solar generator should fit your realistic energy requirements and budget.
To achieve this, we recommend following the decision-making process detailed below.
- Decide how much you want to pay.
- Decide on how and where the solar generator will be used.
- Calculate how much power you will need for the use you will apply it to.
- Once you have completed these exercises, review different solar generators that match your requirements.
- Choose the solar generator with the best reviews, manufactured by an established company (in business for many years), that meets your budget.
Environmental Factors
Several environmental factors affect the performance of a solar generator, as listed below.
Solar Panels
Although solar panels are designed to be used to capture sunlight, their efficiency decreases markedly when the temperature is too high.
Peak power efficiency is obtained at temperatures between 59°F (15°C) and 95°F (35°C).
The solar panel manufacturer’s data sheet will detail how much power is lost with increased temperature. This is expressed as a percentage on the datasheet and will be called the temperature coefficient (Pmax).
The percentage value is the amount of power lost for every degree increase in temperature. An example is listed below.
Pmax-0.258% means that the solar panel will produce 0.258% less power for each 1° Celsius increase in temperature.
High levels of humidity negatively affect the long-term performance of solar panels.
Solar Batteries
The performance of Lithium-ion batteries reduces as temperatures reduce. Similarly, the performance increases with temperature.
Research has found that the performance of lithium-ion batteries improves significantly with temperature. In tests, it was shown that increasing the temperature from 25 to 45 degrees centigrade led to a 20% increase in maximum storage capacity.
Unfortunately, the same study found that high temperatures reduced the battery lifespan.
The opposite is true of cold temperatures, which reduce the battery capacity while increasing the unit life expectancy.
Key Takeaways
Solar generators are useful devices with various applications, from providing you with an emergency power source to going off-grid to being essential camping equipment.
1️⃣ That the intended use of the equipment is carefully defined upfront.
2️⃣ The solar generator must be carefully sized based on its intended use.
3️⃣ Ensure that the budget availability is sufficient for the most appropriate devices.
