Residential Solar Systems: Part II: Getting Started

Identify Your Objectives, Set Priorities

Residential solar systems can be fairly complex or fairly simple. Complexity is driven by the objective or set of objectives the systems are being built to meet. Even though there are numerous issues to weigh, those issues should fall under one or more basic objectives. Generally, the best place to start is by identifying and separating your residential solar systems "wants" from "needs". Doing so will serve as a guide for the decisions you'll need to make about the size, capabilities, features and options for your home installation. Also, it will help keep the solar project focused on the priority items when questions or conflicts arise. For instance, consider the following set of residential solar systems objectives below. Each could fall into a "want" or "need" category depending on circumstance:

1) Must be able to live completely independent of commercial energy supply (off-grid)

2) Must be able to lower commercial energy bills by 75%

3) Must have a noiseless electrical back-up system in case of commercial power outages

4) Must be able to reduce home carbon (CO2) footprint to near zero

5) Must be able to heat the pool and/or spa to 85 degrees using solar

6) Must cost no more than $20, 000 dollars out of pocket, after all rebates and incentives

7) Must lower current energy bill by 50% and not be visible from the street

8) Must be a no maintenance system

9) Must be a do-it-yourself installation design and kit

10) Must be able to use (switch to) commercial energy supply as a back-up automatically

11) Must be able to recover the cost of system in 5 years

Each of the listed items as stated may be of sufficient importance to drive the project. However, notice how quantifying and prioritizing (as much as possible) each objective can give a better understanding of the systems feasibility in those terms. For example, item 11 implies that residential solar systems generate a certain amount of financial return on an annual basis. To really know if objective 11 (and probably objectives 6 and 2, for that matter) can be met, a detailed financial analysis will be required. Otherwise, the likelihood of reaching those objectives is just a shot in the dark. The point is, identifying a specific, quantified set of objectives will provide a much better position from which to guide the project. With your initial list of objectives in hand, it's time to start designing your system and refining your objectives.

Residential Solar System Design

Residential solar systems design is a process that involves starting with an initial set of objectives and translating them into the systems specifications that will precisely support those objectives. Typically, a successful finished design requires specific knowledge and expertise about residential solar systems technology and its application. Even so, a preliminary design effort is advisable to work out the technical and financial feasibility of meeting the objectives. When complete, the overall process should produce a final systems diagram and/or schematic along with basic component specifications.

Also during the process of design, the initial objectives are scrutinized again for feasibility and modified, if required. Note that this is a back-and-forth process where changes in design can necessitate changes in the objectives which may then require further changes in the design and so forth. This typically continues (iteratively) until a balance is reached between expected functionality, technical feasibility and cost. System features may have to be scaled back because of cost considerations or dropped altogether because the needed technology is not currently available. For example, to meet objective #1 we need to know how much power is consumed by the home and its appliances (referred to as electrical load). Once we understand how much load is presented by the home, we have a pretty good idea of how much power needs to be generated by our system to meet that load without the help of a utility company. Assuming that we use photovoltaic technology, we next need to understand the average amount of solar energy that will be available to the system to convert into electricity. Using this information, a calculation is made to find the optimal PV panel configuration (a.k.a. solar array) that meets the power generation requirement. It could be that the site is in a location where the monthly average amount of solar energy is so low that numerous solar panels are needed for the array to generate the required electrical energy. This could increase the initial cost well beyond that set in objective #6. It will also impact objective #11. A decision will have to be made to resolve the conflict between the objectives (off-grid independence vs. cost). Prioritizing your objectives will help. If cost is a priority, set a budget and stick to it, no matter what. If, on the other hand, reaching objective #1 is more important, then the over budget expense for the array configuration may be be justified and acceptable. This underscores the importance of understanding the priority of your objectives relative to a residential solar systems design.