How Many Solar Panels Do I Need For 1500kwh Per Month?

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The average American home uses about 900kwh a month, and for that you need 30 solar panels. But what if you require 1500kwh monthly? Perhaps you have a large house or a shed and want to run your workshop on solar? How many will you need?

It takes 27 x 375 watt solar panels to generate 1500kwh a month. Under ideal conditions this solar power system is going to produce about 10,000-11,500kwh a year.

How to Calculate Solar Panel Size For 1500kwh

Your solar system panels do not have to be 375 watts. As long a the total output is 50000 watts (5kw) a day, the system is going to generate 1500kwh a month.

For instance, you can use the Eco Worthy 1000W Of Grid Kit and add a few ore panels s o the output reaches 5kw a day. This kit is good for 1kw a day so you need another four of these to produce the required power.

If you want to try other solar panel sizes you have to understand how we came up with 27 x 375 watt solar panels .The math is actually simple.

One kilowatt is 1000 watts, so 1500 kilowatts is 1.5 million watts.

1.5 million / 30 = 50000

You need a solar array that produces 50000 watts (5kw) a day to reach 15000kw a month. Now wee need to know the solar panel size you will use and number of sunlight hours you have..

Let us say there are 5 hours of sunlight and you want to use 375 watt solar panels.

375 x 5 = 1875

A 375 watt solar panel can produce 1875 watts a day. With 27 of these you get 50000 watts or 5kw a day.

1875 x 27 = 50625

This is based on the assumption there are 5 hours and the panel produces 375 watts each hour. If there are more hours this array will produce more power. The opposite will happen if sunlight is limited.

If you live in a place with limited sunlight, increase the solar panels to 28 or even 30. A larger solar array can compensate for limied hours of sun.

You can use these same step for other solar panel sizes. Replace 375 watts with whatever solar panel size you have chosen. We chose 375 watts because anything smaller would require more space. You would need about 50 x 250W solar panels to produce 5kwh a month for instance.

How Many Batteries Do I Need For 1500kwh Solar Power?

if you home is on the grid you do not need batteries. But if you are off the grid a battery bank or generator is required because the solar panels will not be able to power your home at night.

If you are on a grid tie system, calculate how much power you want to run on solar and how much on electricity. You could for instance, let the grid run your fridge, AC and heater, while your stove runs on solar, as well as other appliances. With the grid you can be more flexible in how you manage your resources.

If you are off the grid, you must have backup power available in case of cloudy or winter days. Those solar panels will get you 1500kw on clear days. But during the cold season there may not be enough sun hours available.

Make sure your generator and / or battery can supply at least 700kw or more of power. This is assuming solar production goes down by 50% during winter.

Large batteries are the best for large solar systems. 700kw is equal to 14583 amps

You will need 15 Mighty Max 1000ah 12V AGM batteries to back up half of a1500kwh solar system. Alternatively you can get a generator but the capacity should be similar.

If you think production will be lower, then get a bigger battery or generator. Some would say even have 70% or 100% of your total wattage requirements, though it is unlikely solar power will completely stop producing even during winter. You should also prepare ahead by topping the battery before winter comes. For off grid systems we suggest lithium or AGM as they are more efficient than regular lead acid batteries.

Why is My Solar Array Not Producing Enough Power?

Solar panel performance is affected by efficiency, the angle of the sun, the climate in your area and how many sun hours are available. The inverter you install also affects how much energy your system can use. If you are off the grid, you also need a battery bank to store the energy produced by the panels.

Solar Panel Wattage

As pointed out in our guide for solar panels for 1000 sq ft homes, the solar panel wattage determines how many you will need. If you install 250W panels, you will need 50 or so to generate 1500 kilowatts. That is going to take a lot of space on your roof and require a longer, complicated installation.

Does it make a difference if you install 250W, 300W or 400W? If the total output is 1500kw per month, maybe not. However, higher wattage panels have a higher efficiency rating, and that is significant. When it comes to high demand systems, you have to be as efficient as possible, and every little amount makes a difference.

Solar panel output is usually lower than its rating. A 250W panel may produce 250W at its peak, but as the sun angle changes and clouds move, the number drops and averages to 230 to 235W. Higher wattage panels like 315W, 375W and 400W have a higher rate, about 390W for 400W panels and 365W for 375W modules. Because their PV cells are larger, they generate more power.

Lastly, installing larger but fewer solar panels is easier than several smaller ones. It is also easier to troubleshoot solar panels. The price difference is not really that much given the total is the same (1500kw), so if you can buy a higher wattage solar panel, do so.

Solar Panel Efficiency

Solar panel efficiency indicates how much sunlight is converted into electricity. Solar efficiency ratings range from 15% to 23%. Panels made of monocrystalline are more efficient than polycrystalline, but they cost more. Poly solar panels have improved a lot, but overall mono panels still have a higher efficiency rating overall.

Do not buy solar panels with anything less than 20% efficiency. 1500kw is a lot of power and your solar system must be as effective as possible. With an efficient solar panel, expect good output even in less than ideal conditions. This is also applicable if you need 700 kwh of solar power for instance.

Angle of the Sun and Intensity

Panels that face true south (true north if you are in the southern hemisphere) are ideal, but the angles are just as important. While you cannot change the angle of your roof, knowing how and why the angle of the sun changes is important.

The sun’s angle is higher in summer compared to winter. The higher the angle, the greater the intensity that strikes your solar panels. This angle changes during the day and through the seasons, so you must know how solar energy works to prepare for it.

Region and Climate Conditions

Where you live determines how many solar panels you need. A house in the northwest may need more solar panels to generate 1500kw than a house in the Midwest. Similarly, a house in the South Atlantic will have different sun hours compared to that of the West Pacific.

The general climate in your state also plays a role. The colder it is, the longer it takes for solar panels to produce electricity. Expect solar panel production to be lower and slower in Alaska, Maine, South Dakota and Minnesota compared to Hawaii, Florida, Texas and Louisiana.

This does not mean you cannot generate 1500kw in cold states. It is possible as the seasons and the sun angle change throughout the day. But the sunlight intensity and sun hours are greater in some states. By planning for these days and seasons, you can set up a system that works well regardless of the location or time.

Inverter Efficiency

For best results, look for an inverter with 85% to 95% efficiency. The higher the efficiency, the lower the energy losses during conversion, and the more electricity will be available for use. Inverters do the same thing, convert DC to AC, but how efficiently they do it varies a lot.

An inverter must also be large enough to run all the appliances, tools and devices you need. You probably will not use 1500kw at the same time, but do account for surge watts of all your electronics. We have written about inverter sizes here, and you should check it out to find what is suitable.

There are basically two types of inverters, modified and pure sine. For small scale use, modified sine inverters will do fine. But for 1500kw, you should invest in a pure sine wave inverter. While pure sine wave inverters are more expensive, you will get better results. They are more energy efficient and lose less energy. With such a high power requirement, you have to minimize losses as much as possible.

Solar panels are only as powerful as its access to sunlight. Even the biggest solar panel won’t be effective is there is shading. Make sure there are no foliage, tree branches or anything blocking the solar panels. Microinverters can reduce energy loss due to shade, but do your part in making sure the panels have maximum sun exposure.

Do not wait for dirt, leaves or debris to accumulate. Even a few of these may impact performance. If you notice significant drops in production, check the roof or call your solar panel provider for assistance. While you are at it, don’t forget to check the other components like the battery, charge controller and inverter.

Dirt and Grime

For a solar array that produces 1500kw a month, cleaning is best left to a professional solar cleaning service. There are a lot of panels to go over and cleaning them on a rooftop will not be easy. Another benefit of calling a professional cleaning service is they will conduct an inspection to check for signs of solar panel damage.

How often should solar panels be cleaned? Probably once a year, twice at most. Rain should wash off most debris, but if you notice a dip in performance, have a professional installer check for dirt or look for signs of trouble. Your solar system monitor should be able to tell you if something is wrong, but it’s best to just show it to the professional and let them handle the matter.


To summarize briefly, you need 27 to 37 solar panels to produce 1500kwh. The higher the wattage the fewer panels you will need. Several factors will determine how much energy you can utilize, so careful planning is a must. Knowing how much power you really need and how much can be produced consistently are the most crucial elements.