What Is a Watthour - Whole House Solar Generator

A watthour (Wh) is a unit of energy that measures the total amount of electricity used over time. It refers to using one watt of power for one hour.

Watts measure the rate of energy use or power draw at any instant. A watthour measures the total energy used over a time period. The key difference is that watts are instantaneous, while watthours measure accumulated energy usage over time.

The relationship between watts and watthours is analogous to that between speed and distance traveled. For example:

Power (watts) is like the speed of a car
Energy (watthours) is like the distance traveled by the car

If a car is traveling at 60 mph, that is its instantaneous speed or power draw at that moment. But over the course of an hour, the car will cover 60 miles, so its energy usage over that time period is 60 miles or mile-hours.

In the same way, if a 100W light bulb is turned on, it has an instant power draw of 100 watts. But over the course of 1 hour, it will use 100 watt-hours of electricity (100W * 1h = 100Wh).

So in summary, watts measure instant power whereas watthours measure accumulated energy usage over time. This makes watthours a useful unit for calculating total electricity consumption.

Watts vs Watthours

The key difference between watts and watthours is that watts measure instantaneous power draw, while watthours measure total energy usage over time.

Watts tell you how much electricity an appliance is consuming at any given moment. For example, a 100W lightbulb uses 100 watts of power when turned on.

Watthours measure the total energy used by an appliance over time. To calculate watthours, you multiply the wattage by the number of hours used. For example, a 100W lightbulb used for 10 hours consumes 1000 watthour (100W x 10hrs = 1000Wh).

An analogy is the difference between speed and distance traveled. Watts are like speed (mph), while watthours are like distance (miles). Driving at 50mph for 2 hours covers 100 miles. The 50mph is the instantaneous speed, while 100 miles is the total distance traveled over time.

In the same way, knowing an appliance’s wattage tells you its instantaneous electricity usage. But to know the total energy consumed, you need to calculate based on time used – the watthours. This is key for properly sizing solar power stations and generators.

Calculating Watthours

To calculate the watthour (Wh) energy consumption of an appliance, you need to know the wattage rating and the number of hours it is used.

The formula is:

Watthours = Watts x Hours

Where:

Watthours is the total energy used over a time period, measured in Wh
Watts is the power rating of the appliance
Hours is the amount of time the appliance is used

For example, if you use a 60W light bulb for 5 hours:

Watthours = 60W x 5h

= 300 Wh

So the 60W bulb uses 300 Wh over the 5 hours.

Here are some more examples of calculating watthour usage:

A 300W microwave used for 15 minutes (0.25 h) per day:
- 300W x 0.25h = 75 Wh
A 2000W electric heater used for 2 hours:
- 2000W x 2h = 4000 Wh
A laptop rated at 65W used for 3 hours:
- 65W x 3h = 195 Wh

As you can see, by taking the wattage and hours used, you can calculate the total watthour consumption to understand the energy needs and usage patterns of appliances and devices. This becomes very useful when determining the capacity needed for a solar generator.

Usage for Sizing Solar Generators

Knowing your electricity usage in watthours is key for properly sizing a solar generator. Most manufacturers of portable power stations like Jackery list the battery capacity in watt-hours (Wh). So you want to make sure your expected power needs match the battery capacity to avoid running out of power.

The basic process for sizing your solar generator is:

Calculate the watthour usage for the essential appliances and devices you want to run. If uncertain, measure actual usage with a kill-a-watt meter.
Add up the watthour needs over a given period of time, such as a day. This gives your total estimated daily watthour consumption.
Choose a solar generator with a battery capacity well above your total watthour needs. Allow for some excess capacity as a buffer.
Select appropriate solar panels to be able to replenish your battery capacity each day.

As an example, here are some of the solar generators offered by Jackery and their capacities:

Jackery Explorer 240 – 240 Wh capacity
Jackery Explorer 500 – 518 Wh capacity
Jackery Explorer 1000 – 1002 Wh capacity
Jackery Explorer 1500 – 1512 Wh capacity

The Explorer 1000 or 1500 would power most essential appliances for an off-grid setup or emergency backup. For more extended outages, additional solar panels can recharge the battery each day.

Properly sizing your solar generator using expected watthour consumption ensures you get the right system to meet your energy needs. Check the battery capacity before purchase and calculate your watthour usage.

Importance of Understanding Watthours

Knowing how to calculate and understand watthour usage is very important for several reasons:

It helps you determine your household’s total electricity consumption. By adding up the watthour needs of all your appliances and devices, you can get a clear picture of your home’s energy appetite. This allows you to size your solar power system appropriately.
Watthour calculations are essential for properly sizing a solar generator. Solar generators are rated by their capacity in watthours. To choose the right solar power station, you need to know your total watthour needs so you select a model with enough capacity. Undersizing can lead to a power shortage, while oversizing is an unnecessary expense.
Thinking in terms of watthours helps balance electricity supply and demand. With solar generators, the number of watthours the battery can store determines how long devices can run. Knowing your watthour usage allows you to predict how long a solar generator’s charge will last before needing a recharge. This helps you effectively manage your power consumption.
Understanding watthours gives you better insight into an appliance’s electricity appetite over time versus simple watts. Watts only tell instant power draw. Watthours better reflect the impact of sustained energy use for tasks like cooking, cleaning, entertainment, etc. This helps make informed energy decisions.
Conceptualizing usage in watthours provides a more accurate picture than vague wattage ratings alone. Knowing that your laptop uses about 20-40 watthours per hour helps estimate actual electricity needs versus a simple 60W adapter rating.

So in summary, grasping watthour consumption is very useful for determining total household electricity needs, properly sizing solar power systems, balancing supply and demand, and truly understanding appliance energy use over time. It provides a more complete and practical view of electricity consumption.

Compare to Amp-Hours

Amp-hours and watthours are two different ways to measure battery capacity. While watthours measure total energy, amp-hours measure the flow of electric charge.

There is a direct relationship between amp-hours and watthours that allows converting between the two units. The conversion depends on the voltage of the battery.

For a 12V battery:

Amp-hours x 12 = Watthours
Watthours / 12 = Amp-hours

For example, a 100 Ah 12V battery would have:

100 Ah x 12V = 1,200 Wh

And a 1,000 Wh 12V battery would have:

1,000 Wh / 12V = 83.3 Ah

For other battery voltages, you just replace the 12V in the formulas above with the battery’s voltage.

So for a 24V battery:

Amp-hours x 24 = Watthours
Watthours / 24 = Amp-hours

And for a 48V battery:

Amp-hours x 48 = Watthours
Watthours / 48 = Amp-hours

The voltage acts as the conversion factor between amp-hours and watthours.

Knowing how to convert between the two units allows you to work seamlessly with battery capacity ratings that use either unit.

Battery Capacities

When looking at batteries for solar generators or other applications, their capacity is typically measured in watthours (Wh). This allows you to easily compare the energy storage potential of different battery chemistries and technologies.

The two most common types of batteries used in solar generators are lithium-ion and sealed lead acid. Here is a comparison of their typical capacities:

Battery Type	Typical Capacity Range
Lithium-ion	1,000 – 3,000 Wh
Lead acid	500 – 1,500 Wh

As you can see, lithium-ion batteries tend to have a higher capacity or energy density compared to lead acid for a battery of the same physical size. Some key advantages of lithium-ion are:

Higher capacity in a smaller, lighter package
Longer lifespan (more cycles)
Better performance in cold weather

However, lead acid batteries can still be a cost-effective option despite their lower capacity. When selecting a solar generator, make sure to consider the battery capacity in watthours to ensure it can meet your energy needs. A capacity of 1,000+ Wh is recommended for most emergency backup applications.

FAQs

What’s the difference between watts and watthours?

Watts measure instantaneous power, while watthours measure energy usage over time. A watt is like measuring speed, while a watthour is like measuring distance traveled. For example, a 100W lightbulb uses 100 watts of power at any moment when turned on. But over 1 hour, it consumes 100 watt-hours of energy (100W * 1hr = 100 Wh).

How are watthours calculated?

Watthours are calculated by multiplying the power rating in watts by the usage time in hours. For example, a 500W microwave oven used for 30 minutes would consume 250 watthour (500W * 0.5hr = 250 Wh). The formula is:

Watthours = Watts x Hours

Why are watthours important for solar generators?

Knowing an appliance’s watthour consumption helps properly size a solar generator. Totaling the watthour needs of devices you want to power ensures your solar generator has sufficient battery capacity and panels to operate them. Watthours determine how long a solar generator will last.

What’s the difference between watthours and amp-hours?

Amp-hours measure battery charge capacity. Watthours measure energy consumption and usage. To convert between them, you need to know the voltage. For example, a 100Wh battery with a 12V system would be around 8.3 amp-hours (100Wh / 12V = 8.3Ah).

How many watthours are lithium batteries versus lead acid?

Lithium batteries store more watthours in a given size and weight compared to lead acid. For example, a 100lb lithium battery may store 2000-3000 watthours, while a 100lb lead acid would store 500-1000 watthours. Lithium is much more energy dense.

What are typical watthour consumptions for appliances?

Some examples: Refrigerator = 720Wh/day, Clothes Washer = 500Wh/load, LED Light Bulb = 10Wh/day, Laptop = 50Wh/day, Smartphone = 5Wh/day. Knowing typical watthour usage helps size solar generators and estimate your needs.

Quiz

Test your knowledge with this short quiz to recap the key learnings about watthours:

What is the main difference between watts and watthours?

A. Watts measure power, watthours measure energy
B. Watts measure energy, watthours measure power
C. There is no difference
If an appliance is rated for 1000 watts, how much energy would it use in 2 hours?

A. 1000 watthours
B. 2000 watthours
C. It depends on actual usage
How are watthours calculated?

A. Amps x volts
B. Watts x hours
C. Amps / volts
Why are watthours important for solar generators?

A. To properly size the solar capacity
B. To compare with amp-hour battery capacity
C. Both A and B
What unit is typically used for battery capacity?

A. Watt
B. Watt hour
C. Amp hour

Check your answers below:

How did you do? Understanding key concepts like watts vs. watthours is important for energy literacy and using solar power effectively.

Conclusion

Understanding watthours is key to properly measuring electricity usage and sizing solar generator systems. By calculating the watthour rating of appliances and devices, you can determine the total energy demand in your home or office. This helps select a solar generator with sufficient battery capacity to meet your needs.

Watthours provide a way to quantify electrical energy consumption over time, as opposed to instantaneous power draw in watts. The conversion between watts and watthours depends on the time period. With the simple formula of Watthours = Watts x Hours, you can calculate your total usage.

Knowing the energy consumption in watthours is necessary for an appropriately sized solar power station. Undersizing can lead to battery drain and power shortfalls, while oversizing adds unnecessary costs. Proper watthour sizing ensures your solar generator can handle peak demand.

By understanding watthours and energy consumption over time, you’ll be equipped to choose the ideal solar generator and utilize solar energy more effectively. Measuring usage in watthours is essential for balancing supply and demand. Take time to calculate your watthour needs for clean, renewable solar power.