With the gaining popularity and awareness of the multifold benefits of solar systems, one of the questions faced by many potential users is deciding on the capacity of the solar system.

It is not wise to simply take a decision of the solar system capacity based on a general notion or just because some solar system vendor has offered you a certain capacity.
It is important to understand the factors to be kept in mind.

Major factors to be considered while deciding on solar system capacity

This decision can be taken based on the category user falls in following ways :

(A) On-grid / grid-tie / batteryless systems

In case of on-grid systems the solar system capacity decision can be based on a number of factors. Since the on-grid system works on the principle of no storage and many customers opting for on-grid systems choose to go for the net metering facility of their Electricity distribution companies (DISCOM).


The first factor is the available space for installing solar panels. The site selection for installing for solar panels should be done very carefully as this will affect the capacity and also the generation from the solar system in the long run.
The solar panels can be installed on ground or on any kind of rooftop such as flat RCC rooftops or PEB or other types of roofs also. Solar panels can also be installed in a way so as to incorporate them as part of building architecture or as part of a parking structure or storage system.

While choosing a site for installing solar panels , it must be kept in mind that the area should have clear access to sunlight throughout the day and also through the different seasons. { it must be noted that during the winter season the sun has a lower angle of incidence as compared to summer season when the sun path is much higher }
Another point to keep in mind is that there should not be any high rise buildings or other structures which may obstruct sunlight during the daytime. Eg. If you are located in the northern hemisphere, then it is important to keep in mind that the south side of the chosen site should not have any such shadow causing structures or buildings which may obstruct sunlight. It is vice-versa for people located in southern hemisphere.

As regards the space required for installing solar panels, a general thumbrule is to consider an area of 10 sq. Mtr for each KW of solar panels to be installed.
Eg. If you have around 700 sq. Mtr., then you can install around 70 KW { 700 / 10 = 70 } of solar system

It is important to bear in mind that this rule is applicable for the area which is having access to sunlight throughout the day. Although this thumbrule is a simple guide, in many cases there could be wide variations in this figure from site to site.

An important point to note is that it is possible to have a higher solar system capacity installed by using HIGHER Efficiency solar panels which are able to fit more capacity of solar system in the same space.

Eg. A solar panel of 18% or higher efficiency will require about 20% lesser space as compared to panels with 15% efficiency !!

Another factor to be considered is the electrical load for the location and available rating of the electrical infrastructure.
For example if a factory is having a connected load of 800 KVA with the DISCOM, it is not possible for this user to go for a higher capacity of 1000 KVA, since the electrical infrastructure at site might not be equipped to handle a higher power rating. Secondly in many states or regions the DISCOMs do not allow a user to install a solar system of higher capacity than the connected load or sanctioned load.
Eg. If the sanctioned load from the DISCOM is 500KVA, then you can in most circumstances not install a solar system of capacity greater than 500 KVA.

In fact many DISCOMs also have a limitation on the capacity of solar system in terms of percentage of transformer capacity which can be installed by a user.

Further we also have to consider the past electricity consumption (KWh / electric units) per month on average for the past few months. It is usually advisable to avoid being a net exporter of energy. Rather it is always preferable to be a net importer of energy from the DISCOM.

(A3) Financial and economic reasons

Of course another important criterion while choosing the capacity is the budget available. Since the on-grid technology allows to use a solar system of capacity lower than their consumption without any difficulty, hence a very important decision making criterion is the financial budget available or other economic factors such as any government benefits or Tax incentives while choosing the solar system capacity.
Also it must be borne in mind that on grid systems are modular and hence one can keep on installing them in phases to reach the final desired solar system capacity.

Let us take a scenario below :

Take the case of an industry having a connected load of 900 KW and also having a large roof space of 12000 sq. Mtr. Hence considering the above criterions the industry can install a solar system upto 900 KW { the space allows for approx 1200kw, but the DISCOM connected load is 900KW. Hence we are forced by this limiting factor. } However, due to limited budgets they may at the moment be keen to deploy 300kw {considered based on their budget available or the amount of tax incentive available} solar system capacity and then plan the next phase of the project at a later time. This way they can monitor the results of the first phase and also start getting the savings so that they are able to implement the next phase at a later date.

(A4) Government regulations or Green building requirements

There may be cases where there may be a government regulation or the user may be wanting to opt for some kind of Green building certification.
In such cases we can choose the capacity based on above criterion, but as well as keeping in mind the requirements as per the statutory requirements.

Eg. suppose the Government mandate requires a solar system of 5% of connected load from DISCOM. In that case it is advisable to get in touch with a reliable solar solution provider and try to achieve the required solar system capacity so as to be compliant with Government regulations.

(B) battery based / off-grid / hybrid/ solar genset systems

The decision making criterion differs in case of such systems.
Of course the preliminary requirement of space consideration is most important. Because without the available space, it is simply not possible to install the required solar system capacity.

But the next most important factor here is the proper computation of the solar system capacity based on the load requirements, hours of operation and other electrical consumption factor.
Subsequent to understanding the load and site requirements, a solar system must be designed carefully and then the capacity of the solar system must be computed.

Eg. Suppose after analyzing the electrical load requirements for a site it is found that the solar system must be of 47KW. Then we must have sufficient space to install 47kw of solar panels. In case we don’t have this capacity, we would be left with 2 options. First option is to reduce the electrical loads being fed through solar OR else the remaining option of not going for solar and choosing some other power source !

(C) Other types of solar systems

The decision making criterion differs in case of such systems depends on the requirements. Eg. considering the case of special architectural projects or custom designed solar systems. In such case it is better to take expert help.


The above are general basic guidelines for deciding on the solar system capacity. However, there are a number of other factors which may affect the solar system capacity criterion.
Also since it is possible to go for solar in phases {in many cases}, then it is possible to also plan the solar deployment in phases rather than opting to go for it in one shot.

Hence, the best decision is to contact a reliable and experienced solar solution providing company and take their assistance while finalizing the capacity.