Solar Energy for Engineers, Architects and Code Inspectors Specialization: Solar Energy Systems Overview
Gay E Canough, Partner, Direct Gain Consulting
Week 1: Solar Power
Week 2: The Nature of PV
Week 3: Solar Power ROI
Week 1: Solar Power
Solar Industry History
1950's Silicon solar cell invented at Bell Labs
1960-70s Off grid homesteaders began using PV, all space craft are outfitted with solar cells
1980's Nuclear fission reactors used
2000's Mass production increased and costs decreased, China entered solar panel market, 1MW system was cutting edge
2010's Solar power plants begin producing 100+ MWs
Cost of the thing will go down when you start mass producing it.
If you double the production, the cost will go down 20 percent.
201,480 Trillion kWh/year on Earth's land
The Value of Solar Energy
National Renewable Energy Lab collected data for 30 years using 250 stations around US, Southwest US has more than Northeast and is increased by 40%. Kilowatt hours per square meter per years aka. full sun hours per year.
Germany (1250) is the leader in solar deployment and use. Phoenix, AZ (2336), New York City (1642).
Total installed capacity 2018 China (176k), All other (118k), US (62k), Japan (56k), Germany (45k), Italy, UK, India, France, Aust range from 9-20k.
PV Watt per Capita Germany (500), Japan (368), Italy (325), US (156), China (94).
0.07% of Earth's land needed to power the entire planet with solar, but we need storage
Solar Cells - Origins and Proliferation
Majority are made of silicon solar cells, copper for wiring, aluminum for frame, no toxic chemicals.
Simple PN junction (holes and electrons).
Growth of Solar PV in US (MW) 2021 (1k) 2021 (18k), residential is linear 15deg, non-res is 20deg, utility is 45deg.
1977 ($300 / 4W cell), 1988 ($10), 2010 ($3), 2018 ($1.20)
Optional How a solar cell works
Clean Energy Incentives
Net metering - generate solar electricity, unused electricity rewards a credit from the retailer
Small grants for solar energy systems at home and in commercial.
Need to streamline process.
Week 2: The Nature of PV
How PV Works
Photovoltaic - light to electricity
2022 - efficiency at 23%, spacecraft 25%
Silicon crystalline material, lattice of atoms, adding impurities like boron lead to deficit of electors in lattice, material is positively charged, Phosphorus leads to extra electrons for negatively charged, upon light, the pos-neut-neg layer has a electrical field going through. Sun hits cell, and the impurity (neut), has the electrons moving, as DC, then inverter.
Solar Electric System Anatomy
Take solar cell and make it into a module or panel, and the current that you get out of it depends on its area. modern cells produce 0.5 volts at 9 amps. Put it into a panel and wire them in series to increase voltage. Wire those in series for a higher voltage. A grid connected system has solar panels, an inverter, switches. Inverter converts DC to AC, located in the circuit breaker. Micro inverter takes 40 volts out of a panel converting it to 240 volts, more efficient than a string inverter. Stand alone has a solar array, charge controller, battery bank, and inverter.
[RE system DC generation Device (Solar PV modules)] -> [DC Disconnect Switch]-> [Grid-Tie inverter (UL/IEEE), DC Power to AC Power (~92-96% Efficiency)] -> [AC / Utility Disconnect Switch] -> [REC Generation Meter (Utility Grade)]
Optional Size and weight of solar panels
PV System Components
Shows what you imported/exported, but not what you generated/used.
PV modules: produce direct current
Inverter: converts direct current into alternating current
Rack and mounting structure: metal rails and cross-members, L brackets or stand-offs for roofs, ground mounts or pole mounts
Types of Solar Cells
Monocrystalline Silicon: More expensive
Polycrystalline Silicon: Cheaper, melt and pure
Trina Allmax 60 Cell Module Specs
Peak power watts: Pmax (Wp)*: 320
Power output tolerance: Pmax (W)
Max power voltage(under load): Vmpp (V) 33.3
Max power current: Impp (A): 9.6
Open circuit voltage(no load): Voc (V): 40.6
Short circuit current: Isc (A): 10
Module Efficiency (%): 19.3
*Standard test condition (STC) @ cell temp (25 C) & irradiance (1000W/sqm)
When temp goes down (resistance goes down), voltage goes up.
Micro: common for residential or small commercial roof top, each pv module has its own inverter, no DC wiring
String: common for ground mounts and larger installations, PV modules wired in series (450 to 850V),
Are connected via racks, or are built into the roofing.
Alternatives to Rooftop Systems
Post driven, if using a tracker will cost more.
Week 3: Economics of Solar Power
Economics of Solar Power
Climate change drives costs, power purchasing agreement, leasing, direct own.
Benefits of Solar PV Ownership
- Outright purchase and ownership attributes all the financial benefits and risks to the owner
- Maximize financial benefits if grants and investment tax credit can be used
- Renewable energy credits can be sold
- Businesses can depreciate the solar system asset
Benefits of Purchase Power Agreements (PPA) and Leasing
- Both assign risk and major portion of the financial benefits to a 3rd party
- Usually no money down
- Pay per kilowatt-hour
- Increasing in popularity with community solar projects
- Lease: agree that electricity prices will escalate annually
Reasons for Solar Adoption
- Homeowners want to go solar because they
- Feel beholden to the utility company (lack of control)
- Want to be green
- Want the latest gadget
- See that neighbors have it
- Want electricity when the utility power is out
- Business owners want to save money by controlling energy costs
Solar PV System Cost
- New equipment (fuse box upgrade)
- Post installation
- Locally licensed electrician
- Large equipment (materials lift or excavator)
- Tax credits
- Accelerated depreciation
- Tax exemption: per municipality
Calculating System Cost to End User
- Installed cost
- Federal tax credit
- State tax credits
- Depreciation (commercial only)
- Estimated maintenance costs
- = System cost to end user
Silicon goes down half a % per year.
Calculating kWh Production
System cost to end user / 25 year production = cost per kWh
- ex. with incentives $0.05/kWh, without $0.10
- Residential utility rates
- Rural $0.08
- Mid-size cities $0.14/kWh
- Large metros $0.20/kWh
- Property tax exemptions for solar?
Calculating ROI - Example Calc
Trina 385 W PV modules (50.82 kW)
SMA TriPower 3-phase inverter
Fixed cost per kWh of PV for next 25 years: $0.04
PV life expectancy is 40 years
PV modules have a 25 year warranty
Inverters have a 20 year warranty
Generates 53,893 kWh/year, PWWATTS and 1.2 GWh/25 years
Total job cost 138k
Nyserda grant 22k
After nyserda cost 115k
Estimated fed tax credit 30k
MACRS (modified accelerated cost recovery system over 5 years) 34k
End cost 50k (25 -30% of total job cost
And look at cost of no change (cost of increasing utility at 3% inc a year)
year 1 $0.065, what pv saves 3.5k
year 10, $0.085, what pv saves is 4.2k, running total savings 38.8k
year 15, $0.098, what pv saves is 4.8k, rts 61k
Ex2 initial cost 27k, incentive 0.30/w tot 1.8k, federal energy credit 8k, NY credit 0, actually install cost 17k
Anual savings/income, energy 7.5mWh@0.14/kwh 1k, other saving 4k, income 0, tot savings 5.8k
Savings pays for system in 2.9 years 17k/5.8k = 3 years
ROI is 34%, (1/7 * 100) 1/2.4)*100 = 34%
Note: Need to add energy rates, interest and depreciation costs
Solar Plant Advantages
500 MW solar can produce electricity at $0.04/kWh, 2 cents cheaper than coal. Nuclear is comparable but startup costs are high, and doesn't include spent fuel at $8/wat to install.
[RE System DC Gen Device(solar PV module, Wind Turbine, Micro-Hydro Turbine] -> [DC Disconnect Switch] -> [Grid-Tie Inverter (UL/IEEE) & DC Power to AC Power (96% EFF)] -> [AC/Utility Disconnect Switch -> [REC Generation Meter (Utility Grade)] -> [Breaker Box] -> [Utility Distribution Meter]