How It Works
The amount of solar radiation received at a given location varies from year-to-year. Click on the icons at the top to see how the GlobalSolarHybrid works in average, above average and below average years for solar radiation. Click here to read about to how the GlobalSolarHybrid system works in greater detail.
How it Works
Photovoltaic systems are desirable because their impact on the environment is minimal, however, many companies have found that in going green they sacrificed reliability, which cost them money and sometimes more. GPT has learned that in some cases, a PV system can be more expensive than anticipated because of changes required to make it reliable in all circumstances.
To understand why a GlobalSolarHybrid is a no-brainer for mission critical equipment, we need to understand how a PV system works and under what circumstances it could fail. To do this, let's use a case study.
NeedEnergy Inc. is a fictitious environmentally-aware company operating mission critical equipment in Fort McMurray, Canada. It purchased a PV system to cover a 100W load and watched it for reliability and cost over time.
How PV systems generally work:
In a typical photovoltaic system the load is drawn from a bus bar connected to both the PV panels and a battery bank. During the day, sunlight hitting the panels is converted to electricity. When the PV electricity provided is greater than the 100W required, the excess is sent to the batteries that act as an energy storage device. This battery energy is then used when the PV panel electricity drops below 100W in the evenings and at night. By morning, the batteries are partially discharged from supplying the load overnight and need to be recharged by the PV panels again. As long as the PV panels supply enough energy to the batteries during daylight hours to cover the load's demands during the night, the system is able to operate continuously.
When a pure PV system can fail:
An extended run of bad weather:
Using our 100W scenario, the first complication comes when bad weather moves in and the PV panels are not able to fully recharge the batteries during the day. To remedy this situation, the engineers at NeedEnergy increase the size of the battery bank. This gives their system at least one week to operate without replenishing the battery. As long as the bad weather does not extend beyond this, the PV system should operate continuously. However, if the battery gets to the point where it is only 20% charged, the system disconnects the load to prevent severe battery damage.
An extreme drop in temperature:
A second complication with a typical PV system is the seasonal fluctuations with temperature. While the PV panels operate more efficiently in the lower winter temperatures, the batteries are negatively impacted. The battery's capacity decreases when the temperature goes down to approximately 50% of its rated capacity at 0°C and as low as 20% of its capacity at -30°C.
NeedEnergy experienced power interruptions because they failed to size the battery back-up for the lowest temperature during that week. They make another modification and their one-week room temperature battery is now 5 times larger to become a one-week cold weather battery. This means that for the majority of the year their battery actually has more than one week of backup capacity. Not a bad thing for system reliability but it obviously impacts the capital cost of the system.
If your system experiences 'solar night':
The third complication in NeedEnergy's PV equipment relates to the location of their equipment. The number of daylight hours and the angle of the sun in the sky changes throughout the year (unless you are right on the equator). This variation becomes more pronounced the further the system is from the equator to the point where extreme northern and southern locations experience night continuously for many days and months, a phenomenon called solar night. A more typical seasonal change is shown in the figure below which displays the average daily solar radiation per month in Fort McMurray, Alberta, which is at 57o north latitude. There is much more sun received daily during June than December. The reciprocal is true for a 57o south latitude location with a lot more sun in December than June.
The limited amount of daylight hours in the higher latitudes forces the PV system designer to increase the amount of PV panels used until they are able to supply the load's energy demands during the poorest solar months. Unfortunately, this means that during the majority of the year, the PV array generates more energy than the system needs. In GPT's opinion, this is a waste – the extra PV panels cost more and additional energy is required to fabricate and install them.
Variations in solar radiation from year-to-year:
The amount of solar radiation received at a given location varies from year-to-year. One December may be very clear and sunny while the next year is wet and cloudy. This year over year variation can be as little as +/- 20% in typically clear, dry and sunny location such as Calgary and be as large as +/- 40% at wet, overcast locations such as Vancouver. If the PV designer based the system on an average solar year, which is typically the way the data is gathered, then the system could fail in a below average solar year. A critical 24 hour-a-day, 365 day a year system now has to be designed for the coolest and darkest month of the poorest solar year.
How time can affect PV panels:
Now let's look at how the system's components degrade over their operational life. High-grade mono or polycrystalline PV panels are warranted to provide 80% of their original power rating in 20 years, so a 1% per year degradation can be assumed. Lead acid batteries have a 5 to 10 year design life, so lose capacity over their life. This performance degradation results in the system needing to be upsized again to ensure high reliability operation at the end of their design life.
What this means for NeedEnergy's PV system
Without any of the complications, NeedEnergy requires a PV system consisting of a 1,620W PV array and the equivalent of 24 car sized batteries. If the first three complications (extended bad weather, drop in temperature and solar night) were all factors in our scenario, the 100W continuous load in Fort McMurray would need a 2,160W PV array and the equivalent of 32 car size batteries to operate full time during a normal year. Even though this system may cover NeedEnergy's requirements in December, it would throw away 200W in June when that power just isn't required. Furthering this discussion, adjusting the system size for year-to-year radiation variation and PV panel degradation, the system ends up being a 2,940W PV array and the equivalent of 52 car sized batteries.
The cumulative result of all of these site dependent complications grew NeedEnergy's 100W system in Fort McMurray from 1,620W and the equivalent of 24 car sized batteries, to a system that is nearly twice its PV array and battery size at 2,940W with the equivalent of 52 car sized batteries.
How the GlobalSolarHybrid™ works:
GlobalSolarHybrid™ combines two sources of electricity, PV panels and thermoelectric generators (TEGs) to decrease the size and cost of the PV and battery requirements while keeping the system reliability at the highest level. If the designer accepts that at least 80% of the load's demands should be provided by a PV system but not 100%, the size of the system drops substantially. Continuing with our 100W Fort McMurray scenario, the PV system required to deliver greater than 85% of the energy in an average solar year drops back down to 1,080W from the peak of 2,940W – this is a 60% reduction! The battery size also decreases by half.
The GlobalSolarHybrid™ controller monitors the battery bank's state of charge and starts the generator when the battery starts to drain too low. As long as the battery stays above a 50% state of charge with the PV array delivering enough energy to the load, the generator never starts. However, as a backup power source, the generator is able to deliver enough energy to the system as and when required to keep the load fed. The generator does not necessarily recharge the batteries much but holds them in a healthy condition such that they are able to accept PV energy as the sunlight returns. If the generator runs any more than as a backup, the fuel consumption increases which is a waste. The GlobalSolarHybrid™ minimizes waste while ensuring reliability. The PV system size is shrunk and the generator's fuel consumption is minimized.
Battery operation: GlobalSolarHybrid™ versus a pure PV system
The role of the battery in a GlobalSolarHybrid™ system is different than in a pure PV system. In a pure PV system, the battery is sized to provide energy to the load in the event of extended shady periods. In the GlobalSolarHybrid™ system, the battery size determines how often the generator starts and how much fuel is consumed. If the battery is small, a 50% state of charge will be reached quickly, forcing the generator to start frequently. A larger battery bank gives the PV array more opportunity to provide the load's needs by covering a shady period and preventing unnecessary generator operation. If this is the case the battery still does not need to be the size of a pure PV system. Through system size modeling, and taking seasonal and year-over-year sunlight and temperature variations into account, optimal battery sizes were calculated for GPT's PV system.
Finally, NeedEnergy decided to switch their pure PV system to a GlobalSolarHybrid™. Their 100W load in Fort McMurray now consists of 1080W PV array, a battery equivalent to 24 car batteries and a 100W thermoelectric generator. The amount of energy derived from the PV array ranges from 83% to 92%, and the fuel consumption is 15% to 30% of a normal 100W generator's consumption, depending on the actual sunlight received at the site. This switch gives them what they were looking for in the beginning, an environmentally friendly system that minimized waste and the consumption of fossil fuels, while generating reliable and predictable power to their equipment.