Generally, if you asked us how much solar you should put on your roof we would say, “As much as you can.” (Of course, after necessary approvals and proper budgeting and you have sufficient roof space too J). Because rooftop solar power is often the best investment households can make, we recommend installing as much as will easily fit on your roof or your budget allows.

OK! You might also ask why people go solar with smaller system size. Like you may have seen a home with only a 4kW of system size. Let us answer in the shortest way possible:

  1. Insufficient roof space.
  2. Limited Financing or Insufficient Budget.
  3. Spirit of environmental solidarity.

Bigger Is Better

For better understanding we must do it by numbers:

The annual electricity consumption of an average Californian household range between 12,000 to 14,000 kWh which implies to 1,000 – 1,200 kWh every month.


4kW System

So, what will the typical 4kW on grid system save? In California, we average around 5 hours of solar insolation per day year-round. A 4Kw system x 5.8 hours of sunshine x 365 days x the efficiency of the system (Performance ratio ~~0.75) will equal the total amount of kwh you produce, in this case say 6,351 kWh i.e. only around 529 kWh every month.

Similarly, a 7kW System will produce 11,114 kWh i.e. around 925 kWh every month. This is best system size one can choose. Because bigger system comes with an additional cost. If money is not a constraint and authorities allow it, you should go with bigger one.

On the other hand, a 10kW system x 5.8 hours of sunshine x 365 days x the efficiency of the system (Performance ratio ~~0.75) will generate around 15,877 kWh every year i.e. more than 1,320 kWh every month.

Such a huge amount of energy. We don’t have such energy usage. Maybe not today but may in future. It should be noted that energy usage in households tends to rise over the course of time, not decrease.

  • What if you think to add an EV to your lifestyle in the future?
  • Number of persons in your home increases.
  • Electricity usage will start to increase as more electronic devices start to come into play.
  • Switching from a gas stove to an electric.
  • A spike in electricity rates (the average year-to-year increase is generally 4-5%).

There is no doubt that the major costs are inverters and panels. The more you increase the system size, the cost of system increases. We should remember though smaller inverters cost more per watt than larger ones. Also, for relative system size, the sales, design, and labour costs are the almost same.

There is the also paperwork involved with the solar installer’s inspection and compliance department, the time of the salesperson, and all of the general office activities that a business has to conduct. These activities are nearly fixed costs. In order to achieve an economy of scale, you have to go bigger.

Regardless, by going with a bigger solar power system, you do accrue an economy of scale. It also should be reiterated: this is a perfect time to go solar. The costs of the components have decreased by more than 70% since 2010.