Assessing Customer Energy Demand
The first thing you need to understand to design a system for a customer is their energy demand. Most customers will not understand how to read their electric bills to determine their energy usage. So the first step is to determine their annual energy use in kWh. To do this you will need a years worth of energy bills. The customer should be able to access this online through their account and just print them out. This information will allow you to determine if there are any peaks in energy demand during the year. Examples of a peak are during summer when the air conditioner gets used a lot or during winter when the heater gets used.
Once you have an average annual kWh energy demand you will have a reference as to how large a photovoltaic system the customer will need. Many utilities now provide tools online through accounts to perform energy audits and view energy usage which can be helpful.
Make sure to discuss with the customer any plans they may have for future changes to their home that would affect energy usage. Examples are additional rooms which would add additional heating requirements during winter and cooling requirements during summer along with lights and other electrical use in the room. Changing out of appliances for energy efficient models or changing over to gas from electric are all major factors on the energy demand so these need to be known.
You will want to also discuss with the customer what they would like to generate from the system. Do they want to offset the grid energy use by 50% or maybe more. A major factor in this is the customers budget so keep that in mind also. Often times between the budget and available space for a system their are already going to be limitations on the system that will be installed. If your customer wants to offset 75% of their energy demand with the solar electric system but only have space for a system that would produce 50% then this is a factor that must be considered. Once you know the information discussed up to this point you can use anyone of the dozens of online solar calculators to get a quick run down on the size of the system needed and even square footage required in some cases and more advanced ones will give you a rough cost.
Next you will determine essential loads. These are loads such as lighting, refrigerator, heating and air, computer systems and security systems. These critical systems may need to be backed up in case of a power outage from the grid. You will need to discuss options with the customer and determine if they need a backup for these systems. If they decide they want backup then you need to determine the amount of power these systems will require. Then determine if storage batteries are an option or if a generator or other method would be more efficient. If storage batteries are to be used you will need to determine how much capacity is needed and how long they will have to backup the essential systems for.
Battery backup systems work great with photovoltaic systems and can provide great backup. These types of systems are rated by autonomy which is the length of time the system can operate on battery power alone. A battery system with three days of autonomy can support the essential loads for 3 days without dropping below the allowable discharge. The longer system autonomy you want the more batteries you will need which add further cost. Not only do they raise the cost but you have to have the storage space for the batteries.
This covers the basics of customer energy demand. With this information you can give a rough system size and cost to your customer then go back and get a specific system detailed out. This energy demand assessment is usually done with the solar site analysis which provides the other pertinent information to create a detailed system design. For information on steps that should be taken prior to coming out to a site and to save you a little time on site read the Pre Solar Site Assessment Inspection article.
