How Many Solar Panels Do I Need For 700kwh a Month?

The average American home uses 900 to 1000kwh a month, but a smaller, more energy efficient household will probably just need 700kwh. In that case how many solar panels would you need?

It takes 16 x 300 watt solar panels to produce 700kwh a month. This assumes 5 to 6 hours of sunlight are available and each panel generates 1500 watt a day. Fewer sun hours will require more solar panels to produce that power.

Calculate How Many Solar Panels are Needed For 700kwh

We say you need at least 16 x 300 watt solar panels because the output will be influenced by many factors. One of the problems with other solar power calculations is they always assume the panels produce peak power, which is not often the case.

In perfect weather a 300 watt solar panel produces 300 watts an hour or 1500 watts with 5 hours of sunlight. 16 of these solar panels gives you 24,000 watts per day or 720,000 watts / 700kwh a month.

But as we all know, perfect weather does not happen every day. There will be times when clouds cover the sky, reducing solar panel output. The sun’s position in the sky also changes throughout the day, so solar panels will not always be at peak power.

To get a more accurate estimate, we have to account for these factors plus the number of sunlight hours available per day. Keep in mind this will change too as the seasons go by.

Sample Solar Power Output Calculation 1

The following is a sample calculation. Adjust the numbers as it fits your solar system and location. This also assumes you have some basic understanding of how solar power works.

You need 700kwh a month and average 6 sun hours a day. You want to use 300 watt solar panels for your array, but don’t know how many are required. Let us find out.

Solar panel output rises and falls through the 6 sun hours, but assume an average of 280 watts an hour.

280 x 6 = 1680

The solar panel produces 1680 watts per day. If you have 16 of these in an array:

1680 x 16 = 26880

Now multiply that by 30 days:

26880 x 30 = 806400

That is 806400 watts or 800kwh, above the 700kwh you need every month. Even if we factor in the occasional cloudy sky the output should be at 700kwh or above it.

Sample Solar Power Output Calculation 2

In the example given, 16 x 300 watts is more than enough. However it assumes 6 sun hours per day and a 280 watt an hour output per solar panel.

Take this example. In some parts of the US, sun hours are limited especially during winter. Let us use the same example as above, but this time you only have 4 hours of sunlight per day. Let us keep the hourly panel output at 280 watts.

280 x 4 = 1120

Multiply that by 16, the number of 300W panels in your array:

1120 x 16 = 17920

17920 watts a day. If you multiply this figure by 30:

17920 x 30 = 537600

The monthly output drops to 537600 watts or 500kwh, below what your home needs.

This scenario can happen if you live in the northeast for example. In this case we kept the hourly output at 280 watts. But is is very possible for that figure to drop to 250 watts or more.

What Solar Panel Size is Best For 700kwh?

The standard solar panel size for homes is 300 watts, and that is what we recommend. You can also use 350 or 400 watt panels.

The reason we do not recommend solar panels under 300 watts is for space reasons. There are many instances where 250W, 100W and 50W solar panels will work. But if you need 700kwh monthly, you must use the fewest number of solar panels possible.

But you can use 300 wat solar panel kits if space is not an issue. You can start with the Renogy 300W Solar Starter Kit and add more modules until you reach 700kwh a month.

The fewer solar panels you install, the less weight on your rooftop. Fewer panels also reduces the risk of faulty wiring, installation errors and other problems. In case you need to troubleshoot the system it is easier to do so with a smaller number.

This is going to make things easier for solar repair technicians just in case. It is always easier to fix PV modules if there are less in number. It reduces the complexity and makes it easier to pinpoint the source of the problem and have it fixed.

Installing fewer PV modules also means buying fewer cables. Solar wires are not that expensive, but the cost will add up if you have to install several. So any way you look at it, 300 watt solar panels or higher is best in this case.

How to Improve Performance of 700kwh Solar Systems

If you still want that 700kwh to come from solar power, you must increase the array. How many to add depends on how many sun hours are available in your area.

In the samples here you can see how reducing the sun hours from 6 to 4 led to a drop from 8kwh to just above 5kwh.

If your location gets 4 sun hours a day and the solar panel output is 250 watts an hour, how many will you need to reach 700kwh a month?

Let us try 25 solar panels.

250 watts an hour x 4 = 1000

1000 x 25 = 25000

25000 x 30 = 750000

750000 watts or 7.5kwh. With 25 solar panels you should have enough power to cover your 700kwh need.

Adding more solar panels will help but they will take up more space on your rooftop. This is something to consider as solar panels need space from each other.

Solar PV modules are also heavy. Each one weighs an average of 40 lbs. Twenty of these and that is over 800 pounds on your roof, not including the mounting hardware. If you want to combine monocrystalline and polycrystalline solar panels, check out our guide.

This is just one of the reasons why solar powered homes have other energy sources available. Solar power production will drop during the winter so you need to be prepared for that. Fortunately there are many other options available, such as a battery bank or generator.

Do I Need Batteries For a 700kwh Solar System?

If you are on the grid no. But if you are off the grid, a battery bank or a generator is necessary.

If your home is tied to the grid, you already have a backup power source. In case the solar array does not generate enough power, your system will automatically switch to the electrical grid.

This is how majority of American solar homes are configured. it saves you the cost of buying a battery bank. But the disadvantage is you cannot use solar during a power outage.

Most people like the idea of going solar because it gives them another power source in case of a blackout. But if you are tied to the grid, your PV system shuts down automatically to protect line workers who will try to restore power.

The reasoning is sound, to protect workers from solar power electrocution. But what if you want backup power? The solution is a battery bank, which stores solar energy so you can tap into it any time.

What Battery Size Do I Need for a 700kwh Solar System?

If you have a solar array generating 700kwh, how many batteries will you need?

There is no one size fits all answer here. First of all, an off the grid mobile home should not consume that power a month. It is too expensive and setting up a battery bank for that system will be space and cost prohibitive.

If you are on the grid and want backup power, a battery bank is a good choice. List all the essential appliances you want to run in case of an emergency.

Add the watts for the total length of time you need to run them. It can be for 1 to 3 days or even a week. The more backup power you want to have, the larger the battery bank has to be.

Batteries come in various sizes, but when it comes to type most go with lithium or AGM. Lithium is the more expensive one, but it can be fully discharged, needs less maintenance and has the longest life cycle among batteries. AGM batteries are more affordable than lithium but do not last as long.

Once you have determined what battery type and capacity to use, you can connect it to your solar system. Make sure you have a charge controller installed to protect the battery from overloading, overheating and other potential system hazards.

If you are going to run AC powered appliances – and in this case it is almost 100% certain – you also need an inverter. Solar panels produce DC which most home appliances cannot use. So you must have an inverter to turn DC into AC to get those appliances running.

Conclusion

As you can tell there are a lot of factors to consider. The easiest way to set up a 700kwh solar system is to contact a solar installation service. They can tell, based on your location and power usage, how many solar panels you will need.