Renewable energy and sources

1. Yashoda Shikshan Prasarak Mandal’s
YASHODA TECHNICAL CAMPUS, SATARA
FACULTY OF ENGINEERING
NH-4, Wadhe Phata, Satara., Tele Fax- 02162-271238/39/40
Website- www.yspmsatara.co.in Email-admin@yspmsatara.co.in
Approved by AICTE- New Delhi, Govt. of Maharashtra (DTE, Mumbai)
Affiliated to DBATU Lonere,
Renewable energy sources
 Faculty name: Mr. S. S. Mohite.
 Class: S. Y. Robotics and AI
 Subject code:
 Credits: 3

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4. Solar energy application
• Air / Water heating
• What it is (overview).
Solar collectors absorb incoming solar radiation and transfer that heat into a working
fluid (air or water) for domestic hot water, process heat, space heating or pre-heating
boiler feedwater.
• Main collector types & how they work.
• Flat-plate collector (FPC): insulated box with absorber plate, selective coating, one or
more glass covers. Heat transfers from absorber to fluid in tubes or channels. Good for
low–medium temperature (30–90 °C).
• Evacuated tube collector (ETC): cylindrical glass tubes with vacuum insulation, higher
stagnation temperature and lower losses — better for colder climates or where higher
ΔT is required.
• Concentrating collectors (parabolic trough, CPC, etc.): reflectors focus direct normal
irradiance (DNI) onto a receiver — used for high temperature process heat or power
generation. Not used with diffuse light.

5. • System configurations & components.
• Direct (open) thermosiphon: water circulates by density difference — simple, no pump.
• Indirect (closed) with heat exchanger: glycol or other HTF in collector loop to avoid
freezing/corrosion.
• Active systems: pumps, controllers, sensors, expansion tanks, heat exchangers.
• Storage: well-insulated hot water tanks (sensible storage), sometimes stratified tanks.
• Design considerations / selection criteria.
• Local solar resource (GHI/DNI), orientation (south in northern hemisphere), tilt, shading.
• Required outlet temperature and collector type (ETC for higher ΔT).
• Flow rate: trade-off between temperature rise and collector efficiency. Use proper .
• Freeze protection (glycol or drainback) and overheat protection (dump loads or
thermosiphon).
• Material compatibility (copper, stainless steel recommended in potable loops), scale
prevention.
• Insulation of pipes and storage to reduce losses.

6. • Metrics & maintenance.
• Collector efficiency curve: .
• Solar fraction = fraction of load met by solar.
• Routine maintenance: glazing cleaning, leak checks, antifreeze checks, controller
testing, descaling heat exchangers.
• Space heating & cooling
• Space heating — passive & active approaches.
• Passive solar design: building orientation, thermal mass, glazing, night insulation
— reduces heating demand without active collectors.
• Active solar space heating: solar air heaters (air flows through absorber and into
living space), or hydronic distribution (solar thermal to radiators or underfloor
heating). Low ΔT systems (underfloor) are efficient when coupled to solar
thermal.

7. • Solar cooling — converting heat to cooling. Main technologies.
• Absorption chillers (heat-driven): use a heat source to separate refrigerant/absorbent pair
(common pairs: water–LiBr for chilled water; ammonia–water for lower temperatures). Solar
thermal provides generator heat; condenser/evaporator produce chilled water for AC. Typical
thermal COP (cooling output / thermal input) is ~0.6–1.2 for single-effect machines (depends on
temperatures).
• Adsorption chillers: use solid adsorbents; slower but can be driven by lower-grade heat and are
robust.
• Desiccant cooling: uses solar heat to regenerate desiccant (moisture removal) and then
evaporative cooling — useful for humid climates.
• PV + electric compression: PV array powers a conventional electric chiller or heat pump; simpler
integration and modular.
• Key design challenges.
• Mismatch of timing and temperature: hot hours ≠ peak cooling demand always; storage or PV
hybridization often needed.
• Storage options: chilled water tanks, ice storage, or thermal batteries (PCM) to shift cooling supply.
For heating, seasonal thermal energy storage (see later) is often desirable for high solar fraction in
winter.

8. • Solar drying (agricultural & industrial)
• Overview.
Solar drying uses solar energy to remove moisture from products (grains,
fruits, timber). Better control and hygiene than open sun drying; preserves
quality and reduces contamination.
• Drying modes & common dryer types.
• Direct (sunlight onto product) — simplest but exposure to contamination
and UV can damage quality.
• Indirect (solar air collector + drying chamber) — air heated in collector
then forced through product; better control of temp & humidity.
• Greenhouse (solar tunnel) dryers, cabinet dryers, mixed-mode dryers
(combine direct and indirect) — widely used in smallholder agriculture.
• Drying theory — moisture content & drying curve.

9. • Moisture content by mass (wet basis): .
• Moisture ratio (MR): where initial, equilibrium moisture.
• Drying typically has a constant-rate period (surface evaporation) followed by falling-rate period (internal diffusion
limited).
• Energy required — example with step-by-step numbers.
Suppose you must remove 40 kg of water from product (practical example): latent heat (approx) (near 100 °C; for
lower-T drying the energy per kg will be somewhat higher when accounting for sensible heating and inefficiencies).
• Heat to evaporate:
(kJ for 4 kg), then times 10 → kJ for 40 kg.
• Convert to kWh: kWh ≈ 25.08 kWh of latent heat (plus extra for heating the product and air, and accounting for
dryer inefficiencies — actual required solar energy will be higher).
• Design variables that strongly affect dryer performance.
• Air temperature, air flow rate, and relative humidity — controlled flow and moderate temperature (40–70 °C for
many foods) give good quality.
• Layer thickness, stacking, uniform flow distribution.
• Pre-treatment (blanching, slicing) changes drying kinetics.
• Avoid over-drying, protect nutritional and organoleptic properties.
• Quality & economics.
• Indirect dryers provide better quality and faster drying; capital cost higher than open sun but reduce postharvest
losses and fetch higher market prices.

10. • Solar still (small-scale desalination)
• Principle (single-basin still).
Solar energy heats saline or brackish water in a black basin; water evaporates, condenses on
a sloped transparent cover and drains into a collection trough as distilled water.
• Variants.
• Single-basin still: simplest but low yield.
• Multi-stage and multi-effect stills: use latent heat recovery between stages to multiply fresh
water yield per solar input.
• Wick and enhanced stills: use capillary wicks to increase surface area and evaporation, or
use reflectors to augment irradiance.
• Typical performance numbers & simple sizing.
• Yield depends strongly on insolation, cover temperature, and design. Typical single-basin
yields are roughly 2–6 L/day·m² under average sunny conditions; multi-effect systems can be
several times higher. (Actual yields vary with climate and design.)
• Example: A family needs 20 L/day and single-basin yield is 4 L/m²/day → area ≈ m² of basin
area.

11. • Design influences on yield.
• Water depth (shallower heats faster), basin color (high absorptivity), cover slope and
cleanliness, insulation, wind speed (increases convective losses). Using multiple effects
or heat recovery greatly improves productivity.
• Limitations & maintenance.
• Low productivity per unit area, scaling and salt deposition in basin, biofouling — periodic
cleaning needed. Best suited for small community or household use or remote areas.
• Photovoltaic (PV) conversion
• Basic physics.
PV cells convert photons to electrical energy using the photovoltaic effect in a
semiconductor PN junction. Photons with energy ≥ bandgap create electron-hole pairs;
an internal electric field separates charges and produces current through an external
circuit.

12. • Cell / module types.
• Monocrystalline silicon: high efficiency, higher cost.
• Polycrystalline (multicrystalline) silicon: moderate efficiency, lower cost.
• Thin-film (a-Si, CdTe, CIGS): lower cost per area, better performance at high temp for some
types.
• Emerging: perovskites, tandem cells (silicon + perovskite) — high lab efficiency but
commercial stability still improving.
• Key electrical parameters (IV curve).
• short-circuit current, open-circuit voltage, , at maximum power point.
• Fill factor (FF) = .
• Module efficiency measured at STC (1000 W/m², 25 °C, AM1.5).
• System components & BOS (balance of system).
• Modules, mounting, inverter (for grid-tie), MPPT charge controller, wiring, fuses, DC/AC
disconnects, batteries for off-grid, backup generator optional.

13. • Performance factors to consider.
• Temperature coefficient: power falls as cell temperature rises (typically ~ −0.3 to −0.5 %/°C).
• Shading: even small shading on a cell string can reduce output unless bypass diodes or
module-level power electronics (microinverters, optimizers) are used.
• Orientation & tilt: for fixed arrays, tilt ≈ latitude (with seasonal adjustments) and azimuth
south (in NH) for max annual yield.
• Degradation rate: modules degrade ~0.5–1%/yr depending on technology; warranties
commonly 25 years.
• Example — sizing PV to supply the 6.98 kWh/day thermal requirement above (approximate
teaching example).
Assumptions: average daily insolation = 5 kWh/m²/day, module efficiency = 18%.
• Energy produced per m² per day = kWh/m²/day.
• Required PV area = . Compute:
≈ 7.7556 m² → round ≈ 7.76 m².
• Add system losses (inverter, wiring, soiling) typically 20–30%; so practical area ~10 m² for the
same delivered energy.

14. • Grid-connected vs off-grid.
• Grid-tie: simpler, no batteries (unless backup desired), export/import with net
metering possible.
• Off-grid: requires battery sizing and charge controllers; system design more
complex and costly.
• Advanced PV topics.
• Bifacial modules capture reflected radiation from the ground.
• Tracking systems increase energy yield (single-axis or dual-axis) but add complexity
and cost.
• PV-T (photovoltaic-thermal) hybrid recovers waste heat from PV modules,
increasing overall system exergy.
• Environmental & economic notes.
• Energy payback time typically 1–4 years depending on technology and location;
lifetime 25+ years. Recycling of modules is increasingly important.

15. • Thermal energy storage — cross-cutting (brief)
• Types:
• Sensible heat storage: water tanks, rock beds — store by raising
temperature of bulk material. Simple and cost-effective.
• Latent heat (PCM): store energy at phase change (e.g., paraffin waxes, salt
hydrates) — higher energy density, useful for space or short term storage.
• Thermochemical: reversible chemical reactions that store heat — very
high energy density and long term/seasonal potential.
• Seasonal storage: large water tanks, pit storage or underground thermal
energy storage (UTES), or borehole thermal energy storage for shifting
summer heat to winter — important for high solar fraction heating
systems.

16. • Practical selection guidance & tradeoffs
• If you need hot water for a household and you have moderate climates: a flat-plate or thermosiphon system with a well-insulated
storage tank is practical and cost-effective. For very cold climates or high temp demand, choose evacuated tubes or a hybrid with a
backup heater.
• For space heating at low temperatures (underfloor): solar thermal + low-temperature distribution with seasonal or short-term
storage is very effective.
• For cooling: consider PV + electrically driven heat pumps for simplicity or absorption chillers if you have abundant low-grade heat
and can manage thermal storage.
• For agricultural drying: indirect solar dryers (solar air collectors + drying chamber) give quality and reduce losses — often best ROI
for smallholders.
• For potable water in remote areas: solar stills are simple but low yield—use multi-effect or hybrid (solar + RO or membrane) for
larger yields.
• For electricity needs: PV is generally the most modular and rapidly deployable solution; combine with batteries or grid connection
per requirements.
• Quick checklist for designing any solar system
• Define the load precisely (energy/day, temp, profile).
• Obtain local solar resource (average daily insolation, seasonal variation).
• Choose appropriate technology (collector type or PV) for temperature and scale.
• Size collectors/modules and storage (perform energy balances).
• Add controls, freeze/overheat protection, backup.
• Consider installation orientation, shading, mounting strength, and maintenance needs.
• Evaluate economics: capital cost, running cost, payback, incentives.

17. Solar drying

18. Need of solar energy

19. Construction of solar dryer

20. Principal of solar dryer

21. Advantages

22. Working

23. Improvement/ advancement

24. Limitations