How big a PV system should I install?

This post is part of our “Learn About Solar” series, where we will cover common questions and answer them at a high level. These are meant as general guidelines only. For advice regarding your specific situation, please contact us directly

This is one of the most common questions we face at Oorjan.  Sometimes it is sent to us as a request for a quote for a particular size system, sometimes we find ourselves in conversations that lead to this question. Either way, sizing correctly is one of the most important decisions you get to make in your solar journey.  And like all questions worth answering, there is almost never one correct answer.

Some of the major factors that go into PV system sizing are the following:

  • Your monthly electricity consumption
  • Your specific electricity tariff rate
  • Your local utility’s solar metering rules
  • Restrictions on system size imposed by the utility
  • Financial outlay you want to make towards solar PV
  • Space available on your rooftop

This list, by the way, is not comprehensive, but is indicative.  Let us illustrate why and how each of these factors can play into the system sizing decision.

Electricity consumption: 100 sq.ft of panels (1kWp system) can generate (roughly) 4 units of electricity a day. While actual output can vary based on a variety of factors, this is a useful rule of thumb to help you calculate what size system and roof area will meet your needs.

Your specific tariff rate: Many utilities in India offer significantly cheaper tariffs for certain “slabs” under their tiered tariff regimes. For example, as of June 2016, a residential connection under Maharashtra DISCOM is charged at roughly Rs.3 per unit for the first 100 units. This is significantly cheaper than what can achieved through solar in the near future, so one might want to adjust Net Usage from the grid accordingly.

Metering rules and size restrictions from the utility: In some cases, local utilities have set up metering rules that make it attractive for rooftop owners to set up as large a system as they can. While it is not clear that these incentives will remain for the long-term, there is no reason to ignore them while they exist. Similarly, in most areas, utilities restrict the size of a solar PV system as a function of (a) sanctioned connected load on your line and (b) total load and capacity of the local distribution transformer.

Financial Outlay:  Occasionally a consumer will want to make a limited financial outlay on solar PV, and set up a small system affordable within that amount.

Roof space available: Generally speaking, you need 100 sq.ft of unshaded roof space per kW of solar PV capacity. Other characteristics of the roof such as age, material used, slope, accessibility and load-bearing capacity also play into this calculus.

In general, we at Oorjan advise our clients to “right size” their solar PV system. Essentially, this means sizing the system to serve your consumption needs, as long as it meets the constraints of your specific situation.  This removes uncertainty related to policy and tariff changes, while maximizing your benefit from going solar.

Contact us today to take the next step in your solar journey!

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