The first step of any project is to identify what is desired to be accomplished. For my solar project, I began with the following points:
• Grid tied – I’m already on the grid, and my usage profile sits best with a grid tied solution
• Roof mounted – I have a section of roof over the garage which has a good SW exposure and is not shaded.
• Fit within a 300 sq. ft. footprint – the above mentioned section of roof. There is also a significantly larger area available, but much if it is shaded in the afternoon by a well established tree.
• Owned system – There are people who like leases; I am not one of them.
• Installed and operational within a $15,000 budget – when I purchased this property I came in that much under my budget, so I earmarked it for property improvements.
• Data rich – I like having data to work with, and data from my own projects is the best kind there is.
• Mid to top tier equipment – I’m happy to buy a bargain tarp to collect fallen leaves with, but once a certain threshold is passed I have a quickly diminishing tolerance for sub-par components. I want to be able to install the system and more or less forget about it, and that starts with quality components.
• Able to accommodate current and future needs – For example, if the system has excess capacity I’m not opposed to doing more with electricity around the house – Add a space heater to the (currently unheated) workshop, switch from the propane water heater as primary and the electric as backup to the other way around, etc…
• Capability to make use of any excess in an advantageous way
With this as a starting point, I began to look up general information on residential solar installations.
A grid-tied installation has 3 main components: solar panels (to generate DC electricity), inverter (to turn the DC electricity into AC so it can be used by the household and grid), and mounting system (to hold the panels). There are also several minor components, such as connection wiring, disconnects, etc… Within this relatively small set of components, however, there is a massive selection of parts to select from with a range of features, capacities, and capabilities. Even within a basic subset, such as 250 Watt panels, there is a large range of suppliers and options within each supplier. After a few hours of research, it became clear that I needed to either spend quite a bit of time learning all the ins and outs of solar system design or pull in outside assistance.
I opted for the later approach and contacted a couple of local solar companies for system quotes. Through them, I learned several things:
• A basic installed 3kW system in this area should run around $10k.
• The local utility limits grid-tied system size based on panel nameplate rating to 100% of the average monthly usage at the residence for the prior 12 months.
• Adding a battery backup system would assist in optimizing production and household usage, but nearly doubles the system cost.
• There are multiple factors at play when selecting components for the system. Some are fully compatible, some are mutually incompatible, and others can be compatible depending on how the system is designed – for example, the same panels can be used for a basic grid-tie system and a battery backup, but they need to be connected differently during installation.
• The basic component functions are very similar from one company to another, but they differentiate themselves in terms of longevity and support – some are designed more robustly and carry up to 25 year warranties backed by large corporations, others are targeted for a lower cost, shorter life, and their warranties are only good as long as they are still in business.
• There are a few leaders in the industry and lots of followers.
The biggest surprise from this was learning of the 100% size limitation based on the past year’s usage. Based on data from the US Energy Information Administration (http://www.eia.gov) for 2014 the average US household consumed 911 kWh of electricity per month, while the average for California was 562 kWh / month. My assumption is that the California data is not representative of the high desert environment and is likely biased to the more moderate regions of the state, so I consider Arizona as a reasonable substitute, where the average was 1013 kWh / month. Regardless of which average is used, my personal average was 390 kWh / month, which is substantially below either state’s or the national average. As ironic as it seems, having been energy efficient over the past year means that I am only allowed to install a system to meet that demonstrated usage, so I am essentially penalized in terms of solar generation capability relative to someone else who was not as efficient. More practically seen, this means that my desire to accommodate potential increased usage in the future is unlikely to be obtained.
Relative to data, there appear to be only a limited number of inverter offerings that include a data capability beyond a real-time display at the inverter. Those that do offer data typically have some form of internet based communication such that the data can be pulled up anywhere with internet access, and most have a capability to download data as well.