Accurate Solar System Sizing for New Custom Homes


By Tyler Michael
Director/New Solar Homes Division, HelioPower

How much solar do I need?

This is the first question that we hear when asked to design solar for a new custom home. If you get an answer to that question from someone who does not ask you at least four or five questions back, you might consider showing them the door in a hurry before either of you wastes too much of your time. A good solar contractor will always carefully prioritize the customer’s interests.

Generating more electricity for a residence than is required to run that

New solar home installation by HelioPower

New solar home installation by HelioPower

residence is not a very good way to spend money. Utilities are increasingly being called upon to pay for “over-production” by residential customers; however your best value is eliminating only the power you actually use. Most people building their “Dream Home” tend to overestimate the energy requirements of their new home because they are thinking in terms of their older home’s requirements.

Why do people overestimate electrical use in their new home?

In most cases, the new home is substantially larger than the old one. Naturally, there is good reason to assume that if the new home is twice as large, the energy required to run that home will be greater. This is not necessarily the case. In California and in most other states there are far more stringent “Energy Efficiency Requirements” in place for building new homes than were in place when the owner’s previous residence was built. Before you can get a building permit in California, you must show that some minimum energy efficiencies have been designed into the home.

For clarification, speak to your architect about your “Title-24” or CF-1-R form. Because of these design requirements, a 3000 square foot home built in 2010 is likely to require about 60% of the electricity that the same size home, with the same amenities built prior to 1985, will require. This difference is not quite as evident in the mildest climates. 

Some of the most important energy efficiency improvements in recent materials and design are:

  • Radiant barrier roof sheeting
  • Higher insulation ratings
  • More efficient HVAC Systems
  • High efficiency lighting systems, including activity sensors
  • Low ”E”  windows and doors, with better sealing
  • More efficient pool pumps

While all of the above greatly reduce electricity loads, there is still the ”Lifestyle Factor” to consider in calculating true energy usage. Your personal habits are an important factor. Just because we design homes with automated systems and better features, there is nothing that will guarantee the occupants will not override the automated controls or ignore the opportunities for energy savings built into the new home. Your energy consumption in your own home is still, and rightly so, your own business. If you choose not to take advantage of the systems in your home you may not realize the benefits of those systems.

Here are some questions that you should hear when a solar contractor discusses sizing a solar plant for your new home:

  1. How much (kWh) electricity do you use now in your current home?
  2. How many square feet is your old home?
  3. How any square feet is your new home?
  4. Are those homes in the same “Climate Zone”?
  5. Will there be the same number of occupants with the same habits?
  6. What are the ages of the occupants? (Small children will grow up to use more energy, and elderly occupants may have special comfort requirements.)
  7. Are there “guest rooms” or other parts of the home that will not be in constant use?
  8. Do you plan to occupy the home ”full time”?
  9. Is your new home serviced by the same utility company as your old home? (rates differ)
  10. Do you have or plan on purchasing a Plug-In Electric Vehicle (PEV)?
  11. Are there any other major changes in your lifestyle that you will be making in the new home?

Of course, you can see where these questions are leading. There are many other pertinent questions, depending on your specific requirements, lifestyle and design. The absence of these questions will let you know immediately that you are talking to the wrong contractor, and the presence of these kinds of questions that will at least assure you that you are speaking with someone who MAY be qualified to design an appropriate solar plant for your new home.

New homes are a very specialized sector of the solar marketplace. There are hundreds of solar contractors in California but only a small percentage of those are qualified to design and install solar for new homes, and secure the generous New Solar Homes Partnership Program (NSHP) Rebates for their customers.

For more information contact Tyler Michael at his email, [email protected]