Off-Grid Solar Power Simplified
Physical Copy:
By: Nick Seghers
Rating: C
Continuing the immersion into solar panels on the quest to find a business model that makes sense in commercial multifamily real estate.
This book was an overview of the science behind them, pieces of the system, and why certain models are used and others are not. It was pretty enlightening if you are looking for blindspots for the business model.
Practical Definitions:
Voltage: the pressure required to move the electrons from one point (A) to a second point (B) within an electrical circuit. The greater the voltage, the greater the flow of electrons through an electrical conductor.
Current: the intensity of the flow of electrons per second through a conductor.
Energy Cost
Energy Cost = Energy in kWh x Rate in cents per kWh
A solar panel is a DC power source. Meaning it needs to be converted to AC to work with most equipment.
At the residential level, there are typically 3 possible types of RMS values for AC voltage:
120V single phase
120/240V split phase
208V three-phase
The solar panels, the batteries, and the charge controller will always work in DC. The inverter will transform the DC signal coming from the battery into an AC signal to power specific loads.
No-name Safety Equipment:
Buy fuses and breakers from well-known brands. It only has to fail you once, and you are in trouble.
Common Electric Loads:
The following is a table for typical loads of common residential appliances:
Appliance
Running Watts
CD/DVD Players
35-100
Clock Radio
50
Desktop Computer
60-200
Laptop
20-50
Printer
30-50
Coffee Maker
650-1,200
Hair Dryer
1,000
Blender
1,200
Electric Water Heater
1,500
Fan
30-100
Iron
1,000-1,500
Microwave
1,200
24" TV LED
40-50
Air Conditioner 5000 BTU
500
Electric Stove
2,000
Electric Fry Pan
1,200
Electric Blanket
200
LED Lights
6-20
What do I do with this information? Focus on the big energy users that you provide your residents. Water heater, microwave, HVAC, Stove, and lights. How can you choose more energy efficient models for replacement? Research those models now!
Batteries:
Batteries work through an electrochemical process that involves a double conversion of energy. The first conversion is done to charge the battery and consists in passing from electrical to chemical energy. The second conversion process is developed by passing from chemical energy to electrical energy. This is done during the discharge process.
Deep Cycle Batteries:
These batteries can endure many deep charge and discharge cycles. Lead-acid and Lithium batteries are used for solar power storage.
Lithium Batteries are superior to Lead-acid but they are more expensive.
Lead-Acid vs. Lithium
Comparison
Lead-Acid
Lithium
Discharge Rate
50%
80%
Weight
Heavy
Half the weight of lead-acid.
Cycles
1,000 if discharged to 50% max.
3,000-5,000 if discharged to 20% max.
Maintenance
Self-discharges over time.
Can be stored longer without charging.
Venting
Needs to be able to vent gases, even if sealed.
Doesn't vent gases.
Efficiency
80%
95-99%
Types of Solar Panels:
Monocrystalline
Monocrystalline solar panels are the top or premium type of PV module available in the market. These modules have the highest light to electrical energy conversion efficiency in the market with values that range between 19-22%.
Polycrystalline
These solar panels have lower efficiency values (between 16-19%). Their greatest advantage when compared to monocrystalline is their price.
Thin-film
Thin-film modules can be divided into 4 types:
Amorphous-silicon (a-Si)
Cadmium-Telluride (CdTe)
Copper Indium Gallium Selenide (CIGS)
Organic Photovoltaic (OPV)
Temperature Influences:
Hot ambient temperatures will add to the thermal effect of the module. Therefore, increasing the temperature of the cell. This is an undesirable condition as excessive temps decrease voltage, and therefore, reduce the power output of the modules.
On the contrary, low ambient temperatures favor the thermal cooling of the cell due to ohmic effects. Therefore, cool temp locations are always desirable for solar panels.
Placement of Panels:
First option: Roof mounting
Second option: Ground mounting
Ground mounting: Orientation and tilt angle variability is much wider with ground-mounting than with roof-type. Also, maintenance procedures are easier since the modules are placed in an accessible location for the homeowner. It is very important at the time to clean the modules of any dirt or removing snow.
These systems usually have a better electrical grounding system since there is a less resistive path. They also have a better cooling system since air circulation on the backside is more than roof types as well. You won’t need to make any modifications to your house to install the modules and from an expansion perspective, ground-mounts are much easier to expand.
On the negative side, ground-mounts are generally more affected by shade than roof-mount types since more objects can project shade over the modules. Besides, the installation procedure is oftentimes more complicated than the roof-mount and probably more expensive.
Panel Maintenance
The Effect of Soiling:
In most cases, with regular maintenance procedures, this PV energy loss (commonly called soiling) would not be bigger than 2% of the annual energy yields.
Never use laundry detergents, bleach, or any other product to clean panels. All that needs to be used is distilled water, and if desired, a little bit of dishwashing soap.
The ideal time for maintenance is during the early morning (6:00 AM) or later afternoon (5:00 PM).
Note: I have yet to see maintenance costs or considerations in any financial modeling for solar panels.
Lifespan of a Typical Solar Panel:
25-year life warranty performance.
Note: The payback period I have seen for a large commercial project is around 20-25 years. If the system is no longer functional after 25 years, we have a problem!
Inverters:
What is the task of an inverter?
To convert the DC power generated by the solar panels into AC power to be used in the market.
Grid-Tied:
The most common type of inverter available in the market is the grid-tied model. This inverter is used when the power grid is available for connection and when no storage device will be used.
Hybrid-Inverter:
It is capable of using this energy to be stored into a battery, combining the advantages of available power from the grid with energy storage.
Hybrid inverters have other functionalities, such as:
Backups: isolating operation from the grid when there is a blackout.
Grid Zero: Does not allow selling energy to the utility. The inverter tries to avoid consuming power from the grid, only using the renewable energy source and the batteries.
UPS: intended to increase the response speed to support specific loads (important for data banks).
Mini-Grid: Operates as an off-grid system, using the utility grid as a backup generator.
Time-of-Use: Inverter set to take advantage of low-cost electricity rate periods to consume power from the grid and use high-cost electricity periods to sell power back.
Conclusion:
The technology for solar panels has gone through several iterations. It continues to get better and better. You do need to use the right equipment for your system and make sure it is properly maintained.
It has to make business sense. It has to benefit all stakeholders (residents, staff, owners, investors, environment). Not there yet.
Next Actions:
Talk to other owners that have implemented solar.
