How to Calculate Solar Panel Battery and Inverter?

If you wish to construct a solar-powered electrical system but can’t access the grid, then you may have to consider solar batteries. Having decided on the type of battery to purchase, then the next thing is to determine the size of your system. Sizing your system involves a lot of calculations; hence, it is essential to get it right from the very beginning.

While it may seem difficult determining how to calculate solar panel battery and inverter, this has been simplified as much as possible in this article. The general concept is that your system ought to be large enough to supply the amount of energy required during a few cloudy days, at the same time they should be compact enough to be charged by your solar-powered panels.

Come along as we discover the steps involved in sizing your system. They include the following:

1. The capacity of the battery bank - How to calculate your amp needs per hour?

Inverter Size

To determine the size of the inverter, there is a need to first discover the maximum wattage of the peak load of your house. To determine this, add up the wattage of all devices and appliances which functions at the same time in your home. While doing that, add up everything, right from devices like microwaves, cooker and lights to clocks and laptops. The total sum gotten shows the size of the inverter you will need in your home.

Also, do not forget that some devices make use of their rated power during start-up of such a device. So, while calculating, there is also a need to factor in the increase in the rate of the inverter power surge.

Example:

If in a room, there are three 60 watts of light bulbs and one 300 watts of laptop. To calculate the inverter size, we have that

60 x 3 + 300 = 480 watts

Daily Use of Energy

After calculating the inverter size, the next thing to do is to determine the amount of energy used by your home daily. Before this can be done, you must first determine the duration (in hours) it takes each electronic device to run in a day. Then you multiply the wattage of the devices by the amount of time it takes to run to determine the energy used in watt-hours for each day. Sum up the watt-hour values to get a total figure for your house.

The figure gotten is likely to be very low as there are also some efficiency losses factored in. To determine a rough estimate of the real value with regards to system loses, multiply the total value by 1.5. This helps to put into account any decreasing performance gotten when there is an increase in temperature.

Example:

If a light bulb is in use for 6 hours per day and the computer is in use for 3 hours per day. The daily energy use is calculated thus:

120 x 6 + 300 x 3 = 1620 x 1.5 = 2,070 watts-hours

Autonomy Days

To determine the days of autonomy, decide the energy worth you wish to keep in a battery bank (according to the number of days). Ideally, this is always anywhere between two to about five.

The capacity of Your Battery Bank

At last, we can now calculate the minimum capacity of a battery (ΔH). This is done by multiplying the watt-hours for each day by the number decided upon in step 3 above (Autonomy Days). This represents about 50% of battery discharge. Hence, multiply the figure by two and then convert the result gotten from the kWh into amps hours (ΔH). To do this, divide using the voltage of the battery.

Example:

If you wish the battery to last for three days without the need to recharge and you intend using 1.8kwh per day. Then the capacity needed from the battery implies

1.8x 3 x 2 = 10.8kwh

To convert this to ΔH, divide the result by your system’s voltage. This could be within the range of 12, 24 and 48 (if it’s for a commercial purpose). If for instance, we choose to go with 48V, the minimum battery (ΔH) capacity is then calculated thus:

10 800/48 = 225ΔH

If this figure is then divided by the rating of your battery, then you will discover the number of cells to be used.

Note: Caution should be applied as this is only applicable to some wiring setups and not all.

2. Charge Controllers - Do not Overcharge your battery!.

The next step involved in sizing your system and also in determining how to calculate solar panel battery and inverter is to size your charge controller, But before then, we have to understand some components which you probably have not encountered and so do not understand. This will give you a better understanding of the calculation.

Overview

Charged controllers are used to control the amount of power coming into the batteries from the solar panels. They are a vital part of any off-grid system as they prevent your cells from being overcharged. There are two types of charge controllers, the PWM and then the MPPT charged controllers.

PWM (Pulse-Width Modulations): 

These charged controllers are much cheaper than their MPPT counterparts but usually create a lot of pf power loses as about 60% of energy may be lost. This is generally because PWM charged controllers do not make use of the voltage going into the batteries to its utmost capacity. This drawback makes it a poor choice for large systems. However, they function effectively in smaller systems.

MPPT (Maximum Power Point Technology): 

This, on the other hand, is a controller that optimizes the amount of voltage coming into solar panels, this way the maximum number of energy gets into the battery bank. Sometimes, the conversion voltage (optimal) or the maximum power point fluctuates as a result of a change in the intensity of light, temperature, and some other factors.

When this happens, the MPPT controller performs a digital optimization process, and this is done by locating and adjusting to the maximum power point very fast. MPPT controllers are usually used for sophisticated devices. Hence they are generally costly. Since they are about 93 to 97% efficient in the conversion of power, these high price is justified as it gives you value for your money.

Calculation

Once the size of your battery bank and solar panel has been gotten, the process of determining the type of charge controller to use is pretty straightforward. All that is required is to determine the controller by making use of the formula:

Power = Voltage x Current

Divide the voltage of the batteries by the power produced by the solar panel.

Example:

If a solar panel produces one kw and charges a battery bank of about 24v. the size of the controller is then calculated as 

1000/24 = 41.67amps

A safety factor is then introduced, and this is done by multiplying the value gotten by 1.25, this puts into consideration the variable power produced:

41.67 x 1.25 = 52.09amps

From the example, it shows that we would need at least 52amp controller.

The Flexible Maximum MPPT Charge Controller – The Flexible Maximum 60 will suit our specification.

3. Battery Wiring- Assembling All Parts

Wiring plays a significant role in the determination of the number of batteries needed and also helps you know how to calculate solar panel battery and inverter. This last stage aims at producing the target ΔH and voltage. Wiring components of a circuit can be done in two ways: parallel and series. In a series setup, the battery sums up while in a parallel configuration, the current sums up.

Both series and parallel connections can also be combined to produce voltage and ΔH required. Always note that:

Series → voltage adds up, currently doesn't

Parallel → Current adds up; the voltage doesn't

Also, it would be wise to minimize parallel connections as they tend to decrease battery life. For instance, if an already used battery is joined in parallel connection with a new one, the old battery will degrade the new one, which in turn leads to the decrease of the whole system. This feature has made many conclude that an ideal battery bank is one which consists of several batteries which are connected in series. However, this is not always the case, and this is as a result of the voltage as well as the ΔH required by each system.

Conclusion

As earlier mentioned, it is not so easy to determine the number of batteries needed to power a home. The reason is that the wiring configuration plays a massive role in the output of the battery bank. Therefore, it is best to have your storage system designed first before buying any components.

Regardless of this drawback, I believe this article has been able to teach you how to calculate solar panel battery and inverter as much as possible, and now you can calculate your home's energy requirement.

Stephen Hoffman
 

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