IV: Designing a Photovoltiac System:
Analyze Electrical Loads:
To begin with it is important to understand the meaning of the word, 'load.' A load in the electrical sense means a circuit that is closed (i.e. switch flipped 'on') and is drawing electricity from a source (i.e. battery or power grid). In this sense, a light bulb is a load on a battery because it is drawing power from the battery. However there are other meanings of the word 'load' that are used in the solar industry. In the context of construction, a load is a weight that weighs down and/or lifts up on a structure. In this sense, the complete solar array is a load that the structure of a roof must be able to support. In addition, the maximum rate of wind speed recorded for the geographical location of the site must be considered as an upward load that could cause the modules to fly off the roof!
The first phase of design for a photovoltaic system involves researching the precise electrical usage of a residence or business. Utility companies usually have data online for consumers to look up. "For reference, a typical inefficient North American home uses 25-30kWh/day... Highly efficient homes may use 6-10kWh/day." (Home Power Magazine p.156, Aug-Sept 2013). At this stage, decisions can be made to change habits that will conserve energy, and a photovoltaic system may not be necessary. Examples include changing light bulbs and appliances, as well as turning off entire power strips when leaving the house.
The chart below is an example of a load analysis for a highly efficient home:
| Load | Qty. | xWatts | xHrs./Day | xDays/Wk. | ÷7=Avg. Daily Wh |
| Refrigerator | 1 | 507 | 3 | 7 | 1,521 |
|
Fans |
2 | 100 | 8 | 5 | 571 |
| Computers | 2 | 80 | 8 | 5 | 457 |
| Lights | 8 | 25 | 6 | 5 | 107 |
| Clothes Washer | 1 | 320 | 1 | 2 | 91 |
|
Total Power |
1,032W | Total Energy | 2,747Wh |
As an ecological designer, it is important to become familiar with holistic goal formation, and to be able to comfortably and comprehensively discuss complex issues with clients. There is an omnipresent realm of psychological ecology on the job site that ought not be ignored. Perhaps there is an electric dryer that consumes a large amount of electricity in an otherwise energy efficient household. The recommendation would be to hang dry clothes in the sun rather than install a costly photovoltaic system. However, discontinuing the use of a dryer may be a personal issue for a client allergic to pollens, or for any other reason. I am developing a model of Mindfulness in Business that I describe in further detail in the output packet on business design.
In addition to shining a light on the patterns and behaviors of household electrical consumption, the data also gives us a number to design for. In this sense, we build a solar energy system backwards, starting with the electricity that is needed, and then proceeding to choose the right modules, racks and balance of system (B.O.S.) components. PV systems are usually measured in kilowatt hours (kWh). We can easily convert the number above to kWh by moving the decimal over 3 places, which gives us 2.74kWh/day.
The Importance of Metering:
The ability to measure and understand our electrical consumption is invaluable. In fact, metrics of special details can have a large effect on our actions and behaviors. For example, when drivers have an MPG meter in real time, they immediately change driving habits. The inability to see this information in real time "can decrease fuel economy by as much as 33%."
Unfortunately, PG&E does not provide it's residential customers with a breakdown of household electrical usage data. Therefore, we only have a generalized version of the net usage, without the ability to see a graph showing which appliances are using the most energy. Other utility companies may or may not provide this information. This alludes to another interesting topic in the solar industry, that of the dialogue between "public" utility companies and the people.
I found it very intriguing to witness the electrical metering take place in Costa Rica and Panamá during my travels. Even places with the most extreme poverty have electrical meters for the houses, sometimes seeming to pop out of the jungle. It is clear that utility companies understand the utmost importance of metering, and that they expect to be paid for every penny of energy sent to the people. In fact it is illegal to tamper with an electrical meter, which entails that the dialogue between the utilities and the public involves government.
Cost Payback Analysis
It is very important as a designer to be able to explain the cost payback analysis for the client. For example, in Palo Alto, CA residents are not under the jurisdiction of PG&E and have the option of purchasing energy from a 100% renewable source. For residents who have bought into the Palo Alto Green program, it is hard to justify a cost effective analysis. Why would a homeowner spend $10,000 on a solar system that will not be paid back for years when they could simply choose to pay for energy from a renewable source? The solar energy system may not pay for itself for 30 years or more with this sort of a relationship between the utilities and the city.
Anyhow, the cost payback analysis is based on the kWh/year AC output of the system multiplied by the cost per kWh. The cost per kWh fluctuates drastically from place to place. It is important to be familiar with the general sizes of systems, and the general cost per kWh in your area, so that you could quickly provide numbers to potential clients.
Even more so, to reach the point to be able to ask an interested client how many square footage their site location is and to mentally take that square footage to determine the number of modules that could fit in the space. The end goal being to be able to do the mental math to determine the kWh/year rating of a system and to provide an estimate of a payback analysis for a client on the spot.
Solar installations and electric vehicle sales are based on $/kWh. This turns the labor of the worker into a function of dollars per Watt hour, or money earned or spent per energy used over time. As a permaculture designer, I am familiar with viewing the world as energy. I am grateful to have mathematically brought the world as energy into my business, along with my greater understanding of solar energy.
I strive to reach the point where I am confident enough to create solar designs in my imagination. I feel as though photovoltaic design fits comfortably within permaculture design methodology as though they were nested bowls. When these two bowls are placed within a business philosophy of mindfulness, I feel as though I have arrived at a dynamic, functional and successful business model.
Site Assessment:
Once the decision is made to move forward with a PV system, the first thing that must be done is a site assessment. Here in Santa Cruz, California, we have a magnetic declination of 13 degrees due East. Because of this, in order to maximize the amount of sun that will hit the PV array, we need to direct the modules slightly due West of true South. We are also prone to heavy fog in the mornings, which a designer must take into account when deciding which rooftop of a building to use. These 2 factors point toward the preference of a SW facing roof over a SE facing roof for this location.
Determine Solar Harvesting Potential:
In order to figure out how much sun your site will get during each season, there are various methods. These days, this process is mostly electronic. Using a tool called the SolMetric Suneye, we can take pictures from each corner of the roof. The Suneye must be held level and pointing towards South. The Suneye prompts the user to enter a geographical location, and then directs the user to point the Suneye towards South (taking magnetic declination into account). Once a picture is taken for each corner of the roof, the Suneye then creates an annual sun profile, showing where there will be shade during which seasons, and allowing the designer to view how many peak sun hours/day the site will receive.
As a designer, it is important to also be able to estimate the solar energy that a site will receive. For example, if there is a large tree on the South side of the house, then it is not necessary to get on the roof and use the Suneye unless you have permission from the client to trim the tree. It is important to have the mindfulness to avoid unnecessary mistakes that may cost you time and energy.
Rebates & Incentives:
An important part of the design process is the knowledge of law and policy. As a professional designer, you must be aware of codes, regulations, rebates and incentives on a city, county, state and federal level.
Rebates and incentives are the most vital information to understand in order to be able to communicate with potential clients about the cost of the complete solar energy system. The states with the best rebate programs are the ones with the most solar energy, such as Germany, Japan and California. The federal rebate incentive in the U.S.A is 30%. CSI, the California Solar Initiative, is the source of information for CA state incentives.
There is a lot of specialized information and language within the framework of the solar industry. The acronym CSI stands for the CA Solar Initiative as well as crystalline silicon. Knowing what this acronym represents requires the ability to read into the context. HeatSpring Learning Institute is a great resource that offers free online courses on solar financing and solar thermal systems.
Authorities Having Jurisdiction (AHJ):
Authorities having jurisdiction (AHJ) have the ability to make solar energy very friendly and/or very distressing for home and business owners. During the NABCEP examination, there are questions on everything from the required distance between brackets supporting the conduit, proper labeling and proper wiring techniques. When the inspector comes to commission the system, it is vital that the system is up to code. If an inspector finds faults, the system will need to be remedied before you are able to provide the residence or business with the energy.
The AHJ also controls the metering agreement between the solar system and the grid. In California, there is a 'net metering' agreement wherein the meters measure the wattage going into the house from the grid, as well as the wattage going onto the grid from the photovoltaic system. The customer (or the utility company) pays the difference at the end of the month.
AHJ can make it so that the ends do not justify the means with a PV system. For example Hawaii has a lengthy and costly permitting process, towards which the most common response is for the "customer to give up on their ambitions of renewable energy."
As a seemingly inevitable answer to the hurdles put in place by the utilities, there is the concept of grid parity. This is the state of affairs in which consumers can 'go solar' for less than the amount per kWh than the grid. The following excerpt explains the concept in detail:
The solar opportunity is driven by converging economics: the installed cost of solar has fallen 10% per year since 2006 and grid electricity prices have averaged a 2% annual increase in the last decade.
If the trends continue, there may be an outbreak of economical solar. Nearly 100 million Americans could install over 60,000 megawatts of solar at less than grid prices – without subsidies – by 2021.
Institute for Local Self Reliance
While in Panamá, we encountered a juice cart with a sort of piecemeal solar system, connecting a used panel to used marine batteries with a basic charge controller. He was making tropical fruit smoothies on a trailer on the side of the road. Needless to say the AHJ in the United States are very strict in comparison. As solar energy is a relatively new technology that also happens to threaten the utility company’s control over the energy market, it is prone to stringent review by inspectors before systems are commissioned. Of course, if you have private land in a rural area in the U.S.A. or anywhere else, you can set up any system that you want and do your best to avoid the AHJ.
California has a goal of being 33% renewable by the year 2020, however PG&E has set a limit on the number of residential properties that can distribute solar energy back to the grid. As you can see, the dialogue is dynamic and never static.