Energy use at your multifamily property

To properly size a solar PV system for your multifamily property, it is important to understand how much energy is consumed on-site and how it affects utility bills – and your budget. Once you understand your energy consumption, you can estimate an appropriate system size. Further considerations will include how much you want to reduce the common and/or tenant load bills and how much you want to spend on solar. Solar contractors will be able to provide a more precise estimate of appropriate system size and the associated costs and savings.

Later, we will discuss how to identify the energy usage on-site. First, here are the basics.

What’s a watt?

A watt (W) is a unit of instantaneous power. In the solar industry, this refers to the capacity or size of the system.

What’s a kilowatt-hour?

A kilowatt-hour (kWh) is a unit of energy, which is the use of power over time. You are billed by your utility company per kWh.

How can I find my past electricity consumption?

Most utility’s online service offers this information to the account holder. You will be able to retrieve your past 12 months of kWh consumption. If your utility does not offer an online service, you can add up your total kWh consumed from your past 12 electricity bills. Always look at kWh use on an annual basis, since your consumption fluctuates over each season.

For solar PV systems that will offset multiple tenant and/or common load accounts, this step will involve identifying each account’s annual energy usage.

There are multiple ways of identifying tenant annual energy consumption information.

  1. Ask tenants for the information: Tenants can identify their unit’s annual consumption from the local utility. They may use their online utility account or simply call their local utility to get information.  
  2. Do it yourself: Have participating tenants sign an authorization form allowing a designated representative to have access into past kWh consumption levels from the utility. Contact your local utility to request a copy of this form and directions on how to complete the form correctly. Release forms for California’s major investor-owned utilities (IOUs) are available online.Five or more residential accounts - Building owners in a California IOU territory can request aggregated building data for buildings with five or more residential accounts, by emailing their utility’s benchmarking office. Contact your utility’s benchmarking team for more information. 
  3. Use a rule of thumb: The on-site load can be estimated by using a calculation of 2 watts/square foot of livable space (e.g., an 800-square-foot apartment unit may benefit from a PV system up to 1,600 watts or 1.6 kW). Speak with your solar contractor to understand how this estimated system size will reduce your utility bill, depending on your applicable rate structure.

Understanding different utility rate structures

Depending on your utility company and customer type, different rate structures may be available. For multifamily residential customers, example rate structures may include flat, tiered and time-of-use (TOU).

Flat rate – You are charged the same amount per kWh no matter how much, or when, you consume.

Time-of-use (TOU) rate – The rate you pay per kWh is based on the time of consumption, with designated peak and off-peak times.

Tiered rate – You are charged the rate of various tiers. Each tier has a designated amount of kWh that can be charged for (“baseline”) before shifting up to the next higher tier. The rates increase with each tier and typically include two to four tiers.

Once you install solar, your utility may require you to change to a different rate structure required for solar customers. For example, you may be required to move from a flat rate schedule to a TOU rate.

Other charges may be included on your utility bill beyond those kWh charges for your applicable rate structure. These other charges could include demand charges and nonbypassable charges. Refer to your utility bill or speak with your local utility to further understand your bill.

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