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Home My WebLink AboutCooperative Extension Solar Basics Presentation 2020The basics of solar electric systems (photovoltaics) Guillermo Metz Energy & Climate Change Team Leader Cornell Cooperative Extension of Tompkins County = energy that is derived from something that is continually being replenished (without human inputs) and is derived from natural processes = energy that is derived from something that is continually being replenished (without human inputs) and is derived from natural processes solar (electric and heat) wind hydroelectric (incl. tidal/wave) geothermal (heating/cooling and electricity) biomass (wood, agricultural waste, dedicated crops, etc. for heating and electricity) waste (natural gas from landfills, incinerated to produce electricity) Environmental concerns on a large scale: climate change fossil fuels introduce new carbon to the atmosphere (sequestered carbon is reintroduced into the atmosphere, increasing levels) renewables require fossil fuels in their manufacture, processing, transportation, but not in their energy production (even biomass combustion keeps carbon in the global carbon cycle) Environmental impacts of fossil fuels: on individual (site-specific) cases: Exxon Valdez, BP Gulf oil spill, hundreds of smaller spills each year Bureau of Safety & Environmental Enforcement Offshore Incident Statistics Environmental impacts of solar electricity: land use and habitat loss (primarily with large-scale and concentrated solar) water use (some in manufacturing, but mainly a concern for concentrated solar) use of hazardous materials in manufacturing (mainly to purify and clean the semiconductor surface) hydrochloric acid, sulfuric acid, nitric acid, hydrogen fluoride, 1,1,1-trichloroethane, and acetone, as well as silicon dust thin-film cells contain more hazardous chemicals than traditional ones (but waste is very valuable & captured on-site) Life-cycle global warming gas emissions Most estimates of life-cycle emissions for photovoltaic systems are between 0.07 and 0.18 pounds of carbon dioxide equivalent (CO2e) per kilowatt-hour Life-cycle emission rates for natural gas = 0.6-2 lbs of CO2e/kWh coal = 1.4-3.6 lbs of CO2e/kWh “Fossil fuels —coal, oil, and natural gas —do substantially more harm than renewable energy sources by most measures, including air and water pollution, damage to public health, wildlife and habitat loss, water use, land use, and global warming emissions.” Union of Concerned Scientists So, before we look at “alternative” sources of energy (to fossil fuels), we need to reduce our energy consumption Start with an energy assessment / audit Identify: areas of waste (too much) areas that could be upgraded (not enough) appliances, etc. that are old or not performing well Report details solutions, with associated costs and payback Don’t forget other benefits: improved comfort, social responsibility Energy can not be created or destroyed (the First Law of Thermodynamics = this concept for heat within a closed system) It can be transformed Two basic forms = kinetic and potential But more specifically: thermal energy, chemical energy, electric energy, radiant energy, nuclear energy, magnetic energy, elastic energy, sound energy, mechanical energy, luminous energy, mass (E=mc²) Solar panels What is silicon and what’s happening when the sun hits the panel? What are the options for solar panel types these days (readily available)? A photovoltaic system What does it mean to be grid-tied vs. off-grid? What is an inverter? Can you get power when the grid goes down? What are the options for solar panel types these days (readily available)? Photovoltaic effect-first discovered in 1830s (first patented “solar cell” = 1880s; Einstein publishes paper explaining photovoltaic effect in 1905 for which he eventually receives a Nobel) First modern silicon solar cell invented at Bell Labs in 1954 (efficiency = ~5%) Crystalline silicon is the most common technology (efficiencies reached ~15% in late 70s/early 80s) Record efficiencies = ~27% (thought that we’ve extracted just about every ounce of efficiency we can get out of crystalline silicon cells) Most panels today are 15-20% efficient Direct conversion of solar radiation to electricity Silicon crystals absorb sunlight. If the light is of the right wavelength, it can release an electron. A mobile electron is electricity –so silicon is a semi- conductor Figures from mpoweruk.com Silicon crystals are “doped” with atoms with different numbers of valence electrons –Silicon itself has 4 –Phosphorus has 5 –Boron has 3 Electric power is measured in watts. A kilowatt (kW) is 1,000 watts. You buy electricity in kilowatt-hours (kWh), which is energy (as opposed to power). If you run a 100-watt light bulb for an hour, you’ve used 100 watt-hours of energy. If you run it for 10 hours, you’ve used 1 kWh. A 1-kW PV array can produce 1 kW in direct sun. If sunlight falls on it five hours a day, it may produce 5 kWh that day. Single crystal (monocrystalline) Multicrystalline Thin film Polycrystalline silicon is purified and modified to make monocrystalline silicon. Polycrystalline silicon is generally cheaper and less efficient than monocrystalline. An inverter changes DC voltage to alternating current (AC) for household electric circuit powering wall outlets and all AC appliances. Grid-tied: the home generates its own electricity but can draw power from the utility company at night Off-grid: not connected to the grid and must generate its own power, storing energy in batteries for use at night •You own the panels •Need good orientation, clear of obstructions •High up-front cost but good investment over time •Power is net-metered: credits build up and are used up over course of year (no monetary refunds) 0.00 5.00 10.00 15.00 20.00 25.00 February March April May June July August September October November December January February kWh Daily average PV produced kWh Daily average bought kWh Daily average PV kWh sent to grid •Roof condition •Roof orientation •Shading •Budget •Flexibility for PV placement •Easily scrape off snow •Can adjust array angle seasonally •Poles increase cost of installation CALCULATION: dWh/PSH/W/CF dWh = daily watt hours PSH = peak sun hours: average daily sunshine for our latitude in the US W = wattage of solar panels CF = correction factor CALCULATION: dWh/PSH/W/CF dWh = daily watt hours (taken from 2 yrs electric bills averaged & divided by 365): 12,000kWh/yr/365 = 32.877kWh/day = 32877wH/d PSH = peak sun hours: average daily sunshine for our latitude in the US (=~5 h/day) W = wattage of solar panels (average = 320W) CF = correction factor (due to energy loss inverting DC to AC power = ~15%, so multiply total by this amount and add it to total or divide the total above by 100 minus this amount) Take your results and round up to the next panel. CALCULATION EXAMPLE: e: 32877/5/320/0.85 = 24.17 = 25 panels (can size system for 110% of need) Photovoltaics State rebates (through NYSERDA): $1.40/W subject to change and only guaranteed upon acceptance of application systems may not exceed 110% of demonstrated energy demand maximum determined by sector, incentive level; may not exceed 40% of costs residential: $9,800 non-residential: $70,000 State tax credits 25% of system cost after rebate capped at $5000 maximum system size = 25kW Property tax incentive 100% tax exemption for increase in property tax value due to installation of PV system Federal tax credit: 30% Average price of installed residential PV in Tompkins County in last 12 months (4/12-4/13) = $5.37/W (< incentives) (2003 price = $7.94/W; 2013 price = $5.37/W) 5kW system = ~$26,850 After incentives = ~$9398 (= total savings of ~65-70%) Ground-mount (pole-mount) systems are ~25-60% more expensive State credits require installation by a NYSERDA- qualified installer http://www.nyserda.ny.gov/Contractors/Find-a- Contractor/Photovoltaic-Installers.aspx •Available for purchase and “subscription” •Net-metered back to any residence in same utility •Opens up solar for renters, people whose sites are shaded, etc. •Can take “your panels” with you if you move anywhere in Load Zone Purchase: •You own the panels •Solar credits build up and are drawn down seasonally •Credits expire after 20 years (same as residential) Subscription: •You purchase your power from a developer •No up-front costs, can cancel without penalty •Savings of 5-10% on supply of electricity •Solar credits build up and are drawn down seasonally •You can select to purchase your power (supply) from an Energy Service COmpany (gas & electric) (still pay through utility, which controls the delivery of the power) •Can choose “green” power (solar, wind, hydro) •May begin with savings but rates can increase unexpectedly •Usually carry an early termination fee Guillermo Metz Energy & Climate Change Team Leader CCETC gm52@cornell.edu 607-272-2292