Don’t Overcharge Your Batteries
Once you have sized your battery bank and solar panel array, determining which charge controller to use is comparatively straight forward. All we have to do is find the current through the controller by using power = voltage x current. Take the power produced by the solar panels and divide by the voltage of the batteries.Example: A solar array is producing 1 kw and charging a battery bank of 24V. The controller size is then 1000/24 = 41.67 amps. Now introduce a safety factor. Multiply the value you have found by 1.25 to account for variable power outputs: 41.67 x 1.25 = 52.09 ampsIn our example we would need at least a 52 amp controller. The Flex Max 60 MPPT Charge Controller would fit our specifications.
The Inverter Size To Use Should Not Be Calculated By Solar Panel Size
The solar panel size has nothing to do with the size of the inverter you should use for your system. You need to calculate this from the wattage of the AC appliances you want to power. Then work backwards battery size, solar array and finally solar charge controller.
With this in mind lets go back to the example of a WI-Fi and a 15 inch laptop setup..
The Wi-Fi has a rating of 7w and the laptop has a rating of 65w. Taking into account inefficiencies in the system. For example the loss of energy transferring power between the battery and inverter and inverter and appliance. Power fluctuations and surge required to initially power the load.
It might seem like overkill but it is best to over estimate by 3 times the total appliance wattage . In this case 72 watts x 3 equals 216 so a 200 watt inverter would be best. You can multiply it by 2 if you wish. But by multiplying it by 3 you will take all power inefficiencies and fluctuations into consideration.
We have already established that a 50Ah capacity battery would not be large enough. Because the total amp-hours per day this system would use would be 57.28A. You could use either 2 x 12V 100Ah deep cycle lead-acid batteries or 1 x 12V 200Ah.
If you dont already know you can only discharge a lead-acid battery to 50% of its capacity. This is because even a few discharges below that will damage it.
Solar Panel Array
100Ah x 12V = 1200Wh
1200Wh divided by 4H = 300 Watts
Solar Charge Controller
Follow The Below Guideline While Buying The 100
Ensure that the quality of the product is high. In the majority of the cases, the manufacture uses the low price to attract more customers.
The low price indicates that the product is low quality and it cannot serve the purpose. Use the product from the brand.
The brand products are manufactured with rigorous testing, which gives assurance of high quality.
2) The capacity:
Solar panels would have capacity grading mention in the specification section. Check the details and understand how much energy the whole system can generate.
Compare that with your daily use or the need for energy for the particular device. If the system cannot fulfill your requirement, it is not useful, and you may lose money on it.
Always check the size of each piece of equipment packed in the package. The solar panel output is determined based on the size of the panel.
The more the solar panel assembles into one sheet, the more energy it can produce. Also, the panels size would give you a rough estimation of how much energy it could produce in a day.
You can calculate the final output by calculating the overall production capacity of the solar panel.
Also, when it comes to assembling the solar system in your home or commercial building, the size is essential as you may have limited space for the system.
The large size solar panel would be difficult to assemble hence it would create trouble.
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Daily Energy Consumption Of An Rv
With this daily consumption estimate, we can determine the size of the PV system with Formula :
With a commercially available PV system above 985Wp, the family in the RV can easily enjoy their trip, but they need to know the size of their solar inverter. For this, we will be using Formula :
The best size inverter for an RV would be 788W. However, you may find manufacturers selling 800W solar inverters or in some instances 1,000W models.
How To Size Solar Inverter Full Guide For Beginners
In this complete guide, we show you how to size solar inverter for your power system without complicated math. Choosing the right inverter helps the system handle direct current load and convert it to AC power.
You cant just guess or ball park it, otherwise it can get dangerous. So here is how you size it properly:
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Questions Chat With Us
Wil has been a part of the solar industry for over 20 years as an electrician, solar installer, support technician, and more. He’s also been living off-grid since 1996. Wil and the rest of the Unbound Solar team are here to answer any questions you have about designing a system that will fit your needs.
Pick An Optimizer For Your Inverter
Picking the right optimizer is fairly easy when you look at the input section on the optimizer spec sheet. These optimizer models work with SolarEdge inverters:
Lets start by looking at the spec sheet for the standard optimizers:
Compare the optimizer input requirements to the solar panels spec sheet to make sure the voltage and current are within spec:
The P370 and P400 both have a high enough DC input rating to cover the 345W output of the solar panel.
The P400s 80V max input voltage covers the 46.37V open-circuit voltage of the panel, and its 10.1A short circuit current is enough to handle the 9.67A current from the panel. The P370 satisfies these benchmarks as well.
With those values covered, we know we can safely pair either the P370 or P400 with Astronergys 345W panels.
Next, we need to figure out our string sizethe number of panels that can be wired into a single input on the inverter.
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How To Prevent Inverter Clipping
While oversizing the solar array relative to the inverters rating can help your system capture more energy throughout the day, this approach is not without costs.
Either spend money on an additional inverter or lose energy harvest to inverter clipping.
What Figure 1 also shows is an effect called inverter clipping, sometimes referred to as power limiting. When the DC maximum power point of the solar array or the point at which the solar array is generating the most amount of energy is greater than the inverters power rating, the extra power generated by the array is clipped by the inverter to ensure its operating within its capabilities.
The inverter effectively prevents the system from reaching its MPP, capping the power at the inverters nameplate power rating.
To prevent this, its crucial to model inverter clipping to design a system with a DC-to-AC ratio greater than 1, especially in regions that frequently see an irradiance larger than the standard test conditions irradiance of 1000 W/m2 .
The US Energy and Information Administration states, for individual systems, inverter loading ratios are usually between 1.13 and 1.30.
Knowing how much energy is clipped allows a designer to understand how effective the oversizing scheme is at increasing energy harvest, and ultimately determine what system configuration is the most cost-effective.
The chart below shows three DC-to-AC ratios and their estimated losses to clipping.
How Many Watts Do You Need To Run A House On Solar
This is a good question as it ties into not only the inverter size, but how many panels you are going to need on your roof to fully power your home. At the very least, you are going to need a 1500 W inverter and a 1.5 kW system but this is really only an entry point and designed for small homes with minimal electricity usage.
There are also two figures you need to take into consideration, continuous power and peak/surge power. The continuous power rating is for the watts that your inverter will be supplying around the clock to power your home. Peak/surge is the rating required for starting up the bigger appliances like your fridge or air-conditioning which can require 3-7 times the wattage.
You can use devices like smart metres to determine your homes power needs, both continuous and peak/surge and align that data with the system you need to purchase. This is also a golden opportunity to get to understand your energy usage so you can make small changes that will make a big difference to your electricity bill as well.
Match Dc Array Size To Inverter Input Size
In our example, were going to design for an array with 30 Astronergy 345W solar panels. The array size is 10,350 watts or 10.35 kW:
30 x 345 = 10,350 watts
Once we know our desired array size, we need to pick an inverter that is large enough to handle the input from the array.
To determine which inverters are suitable, check the inverter spec sheet for the for each model. We choose 240V because that is the standard voltage on most electrical service panels installed on residential properties.
So we have a decision to make. The SE7600 would be easier to install, because it can go on a standard 200 amp service panel without derating the main breaker or doing a line side connection. On the other hand, the SE10000H would allow some room for future expansion.
Do I Need An Inverter
No! If you only use DC appliances, you dont need an inverter.
You only need an inverter if you want to use AC appliances powered by your deep cycle battery.
If you use AC appliances when hooked up and they are powered by the battery, you still need an inverter.
If you use AC appliances only when hooked up and with AC sockets on the mains circuit, you dont need an inverter.
If you also need a converter , consider installing a combined RV inverter charger instead.
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I Want A Much Bigger Inverter Than The Calculator Has Worked Out What Shall I Do
Weve included a mini calculator above to help you see the amount of battery a fully loaded inverter will use in an hour and how big the solar array would need to be to power just one hour.
The solar array shown would need 4 good hours of sun to replace the battery energy used by the inverter.
If you expect more or less peak sun hours, adjust the solar panels accordingly.
Simply enter the size of the inverter you want.
Why Do You Need An Inverter
Inverters convert the DC flowing from your battery into AC so that you can power AC home appliances with your off-grid solar setup.
The power that runs through the main power grid to supply homes with electricity flows in AC. Home appliances use AC to run.
On the other hand, the batteries connected to your solar setup flows in DC. Therefore, inverters have to convert DC to AC in order to power your home appliances with solar power.
How To Size Your Off
If you are designing a solar electricity system and don’t have access to the grid, you are going to have to deal with batteries. When you start looking at solar batteries you are going to encounter a little math. Fortunately, SolarTown is here to guide you through the calculations!The general goal when designing an off-grid battery bank is to get a system that is big enough to supply all your needs for a few cloudy days, but is also small enough to be charged by your panels. Before you get started here you may want to check out this article. It serves as a good introduction to the solar batteries I’ll be talking about:http://www.solartown.com/learning/solar-panels/solar-battery-storage-systems-if-you-cant-tell-your-agm-from-your-gelAlright let’s get started! Here are the steps to sizing your off-grid system.
Tips For Using An Inverter With Solar Panels
The following tips are for 100W solar panels, but many of them also apply to larger PV modules. Always keep these in mind before you buy and install an inverter.
- The inverter will use the battery to power whatever you connect o it. However the battery obtains its energy from the solar panel. The charge controller meanwhile, must be the right size and make certain the optimum amount of power goes into the battery. All of them must match for the system to work.
- The more watts you draw per hour, the faster the battery will drain. It is not as simple as 100 watts is good for an hour, 50 watts for 2 hours etc. The more current is drawn, the faster the battery depletes.
- The inverter capacity is limited by the amount of watts going into the battery. In our example we assume the panel draws 600 watts with six hours of sunlight. But if the sky is overcast, production will go down. So will the capacity of the inverter.
- The wires and cables you use make a big difference. The thicker the cable, the better. It will cost more yes, but energy loss is reduced. With 100 watt modules however, the losses will be quite small unless you wire these into an array.
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Real Life Experience What Will A 3500w Inverter Run
Based on our experience the 3500W inverter can easily run these appliances at the same time:
With all of our appliances plugged in at the same time, we never exceeded 75% of the inverters capacity the most powerful pumps never run for a long time .
With such an example, we can conclude that a 3500W inverter is a perfect size for the needs of a family.
Size Of Your Solar Array
The size of your solar array is the most important factor in determining the appropriate size for your solar inverter. Because your solar inverter converts DC electricity coming from the array, it needs to have the capacity to handle all the power the array produces.
As a general rule of thumb, the size of your inverter should be similar to the DC rating of your solar panel system if you are installing a 6 kilowatt system, you can expect the proposed inverter to be around 6000 W, plus or minus a small percentage.
Inverter manufacturers typically list sizing guidelines for the array capacity their inverters can be paired with on their product spec sheets. If the size of the solar array paired with their inverter is outside of the stated guidelines, manufacturers may void their warranty offering.
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What Size Inverter Do I Need For A 100 Watt Solar Panel
Converting DC to AC is necessary if you want to run household electrical appliances with a solar power system. But what size inverter do I need for a 100 watt solar panel?
You are probably thinking that a 100 watt solar panel hooked up to an inverter means I can run AC appliances. Like a fridge, a washing machine, power tools or even a cooker. But unfortunately these types of appliances require large amounts of power to run them.
A much larger solar array is required to provide enough re-charging power to a battery to keep the inverter going. The reality is that the inverter needs to be sized to the appliances you want to run. But lets look at what size inverter a 100 watt solar panel is suitable to be combined with.
Final Thoughts From Koos Mulder
To conclude this article, weve reached out to an expert in solar off-grid systems, Koos Mulder. Koos is installing micro-grid systems in remote villages throughout the Philippines for the Shell Foundation.
According to Koos:
Microinverters can be a good choice for AC coupled systems thanks to their high efficiency, however, he brought attention to two issues:
- Safety As the back of a solar panel can be very hot and the more inverters you have the higher the risk of an electric fire
- Maintenance Although you might not need to perform maintenance for years, when you eventually do, it might be complicated to figure out where the defective micro-inverter is.
He still favors central hybrids inverters as they are much easier to install, control and ultimately, they are cheaper. They might be slightly less efficient but it is balanced by all the previous advantages.
In the end, the main trend is now geared towards energy storage at home, with smart inverters and solar batteries: the Energy Storage Systems .
Electricity consumers will turn into prosumers, to sell their excess electricity to the grid when prices are high.
By doing this, we could achieve a higher amount of renewable energies in our global electricity production.
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