By Andrew Gong, research engineer, Aurora Solar
Here at Aurora, we like to tackle hard questions. One question we see often is: “Given that electricity rates are higher from 4 to 9 p.m. in California, should I place my solar panels facing west instead of south to maximize savings?”
In this post we will dive into why west-facing panels might be more advantageous than south-facing ones, and provide recommendations based on your location and how your peak time-of-use (TOU) rate works.
Context: Moving West in California
Aggregate Demand and the Duck Curve
The three main investor-owned utilities in California have been utilizing peak TOU rates from 4 to 9 p.m. since late 2017; customers are charged more for the electricity they use during the late afternoon and evening hours. Prior to this, peak hours in the middle of the day — between 11 a.m. and 6 p.m. — were most common.
The peak hours shift was driven by aggregate demand on California’s grid. Prior to the early 2010s, homeowners and businesses used the most energy in the middle of the day and early evening. Midday peak-pricing provided the financial incentive to reduce energy usage or shift loads to non-peak hours. Since then, the falling cost of solar has drastically shifted the total demand on the grid as seen in the infamous duck curve, pushing the peak demand, and moving peak-pricing to early evenings.
Source: CAISO. California’s “Duck Curve” shows the low mid-day net demand on the California electricity grid after solar and wind generation is accounted for. The low mid-day trough and steep afternoon ramp are part of why time-of-use rates have peak pricing between 4 p.m. and 9 p.m.
No mention of storage here. Nor of lattitude differences. Follow-up perhaps? It does not seem this would work the same everywhere in California. Do the utilities oppose islandable microgrids and separating generation, storage, and transmission? I forget what that is officially called in power-speak. Oh wait, is it de-coupling? It has been a while since I paid attention, after a move.
The official term for grid tied only solar PV systems is “anti-islanding”. The system shuts down if the grid fails, this keeps from back feeding into the grid and killing a lineman. With solar PV prices per panel now, it is possible to overdesign one’s systems, so latitude is not that big of problem anymore. If two homes need approximately the same kWh average system over a 24 hour period. In Southern California one might need only a 8kWp system when 6 to 8 sun hours are available. In Northern California one might need a 12 to 14kWp solar PV system to meet the same requirements with less sun hours a day. The company SolarEdge has ancillary components that can take one of their grid tied systems and add energy storage and add a off grid inverter that can be wired to a “secondary” A.C. critical circuit panel that would be isolated from the primary house circuit breaker panel and allow these “critical circuit loads” to be powered off grid for days using the solar PV and ESS battery. Since 2015 the technology has been introduced to have solar PV and smart ESS that can “communicate” with a smart home system that can control house circuits by using a smart phone app and control page.
I live on the East Coast (NH). I have a south facing solar array on my house and am contemplating expanding it with an supplementary easterly oriented array. What I have observed is that many of the mornings are fine, cloudless/thin clouds but by 2.00pm clouds have started to form and the array yield drops off significantly. An easterly alignment of the expansion, with a Battery Storage system will provide the afternoon/evening power boost that is needed for the planned future electric vehicle.
I had a home with a split system where the roof pitch was East facing and West facing. The system was grid tied and although I didn’t get a big solar PV generation spike a South facing roof would generate, the East/West orientation allowed on average 2 hours more of usable solar PV generation a day. That system was installed in 2005. Now we have the option of smart ESS technology. The high end models are expensive, but give packaging and programmable options to address the electric utility’s varied and sundry pricing schemes throughout the day. With programmability, hybrid inverter(s) one can store East facing, West facing, South facing energy excess during the day and use it at night during utility induced TOU rate spiking or demand charges or during the morning wake up hours where solar PV is not generating good usable power just before and just after sunrise. Today one can actually overbuild their solar PV installation to take into account, output loss due to high ambient temperatures, “dusting”, even long term panel degradation sometimes called LID, (light induced degradation). This has been said to be for mono crystalline panels of 3% output loss the first year in service and from 0.5% to 0.7% degradation per year thereafter. Many of the panel manufacturers are manufacturing panels with a +5% to – 0% rating, taking care of the first year of use degradation. With a smart ESS one can do with less solar PV and use the programmable energy storage for more self consumption, arbitrage and perhaps in the near future, could be called upon to “provide” ancillary grid services to the local utility. The ancillary grid services could be “very” lucrative in merchant markets where demand charges rule.
“The three main investor-owned utilities in California have been utilizing peak TOU rates from 4 to 9 p.m. since late 2017; customers are charged more for the electricity they use during the late afternoon and evening hours. Prior to this, peak hours in the middle of the day — between 11 a.m. and 6 p.m. — were most common.”
Also in California, the PSPS is pushing home owners and early solar PV adopters to install their own ESS for more self consumption and the ability to time shift peak solar PV generation and spread out this energy to later in the day, 4 to 9 PM during the TOU rate spiking period.