Professional design, installation and service of renewable energy systems.

Building Energy 2014

The Solar Energy Course for Architects, Engineers, and Contractors

Fortunat Mueller PECo Owner

ReVision EnergyMarch, 2014

AGENDA • Introduction• Solar Basics• Solar Thermal• PV• Wrap up and Q and A

Motivation• Environmental

– Reduce CO2 emissions– Transition away from finite fossil fuels to sustainable,

renewable energy sources

• Energy Security/Geo-political• Economics

– Save money– Reduce future costs

What is Solar Energy?

– The visible, Infrared and UV radiation from the sun that can be used for heat, or electricity via the photovoltaic effect

Solar Fundamentals• Insolation: Measure of the energy striking the earth’s surface.• This energy can be collected and used

• Units are: [Energy]/[Area*time] typically: kWh/m2/day or BTU/sq ft/hr or similar

Collector Orientation• Generally South facing

– Take into account magnetic declination (Solar south is 16 deg W of Magnetic South)

– Southeast and Southwest facing is just fine in most cases((155 to 245 degrees on the compass)

Collector Installation Angle• Optimal angle depends on load profile:

– SHW: ~ 45 degrees (similar to our latitude)• Assuming balanced year round load

– Combi Systems: ~ 55-60 deg (latitude plus 10 degrees)

– GTPV: ~ pretty insensitive to installation angle for year round production

Collector Installation AngleOverall effect on annual performance

Sun Path and Insolation through the day

Shading• Shading significantly affects collector performance.• Optimal solar window is 9 a.m. to 3 p.m. year round• Important to conduct a site evaluation

– Consider the future growth of trees

Solmetric Sun Eye

Shading- PV• PV systems tend to me more affected by partial shading

than thermal systems since individual cells and modules tend to be wired in series so even cells in bright sun might show diminished performance if other sections of the collector array are partially shaded.

Solar thermal (hydronic):• Hot Water Heating• Space Heating • Pool Heating• Commercial

Components: Collectors• Collector types:

– Flat Plate– Evacuated Tube– Unglazed (pool heating)

Unglazed Collectors• Construction

– No glazing or insulation– Typically UV stabilized plastic/polymer construction

• Characteristic– High wetted area to compensate for poor heat transfer of polymer

material– Large Surface area to account for large load– Designed for high flow rate

• Applications– Seasonal pool heating systems – Temperature ~ ambient +/- 10 degrees

Glazed Flat Plate Collectors• Construction

– Metal absorber in thermally insulated sheet metal box– Transparent low iron tempered glass to minimize heat loss and maximize transmission

• Characteristics– Good mid temperature performance– More expensive than unglazed

but cheaper than evacuated tube

- Serpentine or Harp flow pattern

• Applications– Mid temperature applications

• Solar Domestic Hot Water• Low Temp process water• Preheat applications• Occasionally Combi systems

Evacuated Tube Collectors• Construction

– Single wall or double wall glass cylinder with vacuum with metallic absorber inside.

– Typically individual tubes connected to a manifold– Include barium getter to maintain vacuum

• Characteristics– Very low heat loss– Excellent performance in low light conditions– Typically a bit more expensive

• Applications– Domestic hot water systems in cold climates– Combi Systems– Higher temperature process water systems

Collectors Characteristics• Gross Area: product of outside collector dimensions• Aperture area: light entry area• Absorber area: area of the absorber itself

Efficiency• Collector Efficiency: (The ratio of usable

thermal power to the incident solar energy flux)

η = Qdota/ GoG0

G0 = Incident solar energy

G1 = reflection off glass

G2= absorber emissivity

Q1 = conduction heat loss

Q2 = radiation and convective heat loss

Qa = useable heat

G1

G2

Q1

Q2

Qa

Collectors Characteristics• SRCC and SPF and solar keymark

TYPICAL SRCC RATING

Typical SPF rating

Components: Pressurized domestic storage tanks

Pressurized domestic storage tanksdesirable attributes

• Aspect ratio: Tall and skinny is better (>2.5 to 1 ratio of H to d)– Improves stratification

• Insulation: target of 1.5 W/K total heat loss (R20+)– Minimizes heat loss

• Cold Water baffle – to minimize mixing

• Heat trap on domestic exit• Heat trap for heat exchanger connections

Components: Unpressurized thermal storage tanks (non potable)

Components: Piping• Copper (to about 1.5 inch) then Steel• Corrugated Stainless occasionally used on DIY projects

to avoid soldering/brazing• NEVER use PEX• Onyx ?

Components: Insulation• High temperature capable insulation needed

near collectors• Typical Armaflex HT or similar or Fiberglass• Use ¾ -1 inch wall insulation outside and ½ to ¾

wall insulation inside conditioned spaces– European Standard EN 12976 calls for 20 mm of

insulation up to 22 mm pipe diameter and 30 mm for anything larger

Components: Insulation

• Insulation should be protected outside from UV damage by metal or PVC wrap

Components: pumps

• Residential– Wet Rotor Circulator with

hydraulics optimized for closed loop solar.

– Typical multiple speed pump for universal use and to minimize parasitic power

Components: pumps

• Commercial– Energy saving– Variable speed – Need to calculated

required flow and head pressure

Components: Heat Exchangers

• Internal– Plain coil or finned tube

– Vertical or Horizontal• Vertical preferred because it promotes stratification

• External– Flat plate– Shell and tube

External heat exchangers tend to be desirable in larger systems because a single hex can serve multiple tanks.

Components: Solar Fluid

• High thermal capacity• High thermal conductivity• Low viscosity• Resistance to freezing• Non toxic

Propylene Glycol/Water Mix is typical

Components: expansion tank

• Required in closed loop systems

• Check material compatibility with antifreeze

• Sized not only for thermal expansion but usually also for possible vapor volume from collectors

Components: otherCheck Valve, Air elimination, flow meter, PRV, fill and drain ports, mixing valve

Pump Station• Pump• Temperature Gauge• Pressure Gauge• PRV• Check valve• Flow meter• Fill and Drain ports

Components: Controller

Basic differential control

Components: ControllerMultiple tank system, multiple collectors, variable speed , data logging, remote display, etc

Residential Domestic Hot Water• Average American Household

consumes 64 gallons per day of hot water (20gal./person/day)

• Often best solar load because it is low temperature and year round.

• Savings multiplied by keeping oil boiler off in the summer and thus eliminating the boiler standby losses

Typical Maine Residential Oil Use

domestic hot water9%

space heat64%

boiler standby losses27%

Single Tank Solar Solution with integrated boiler backup

Single Tank with integrated electric backup (external hex)

Flush Mounted to Pitched RoofTakes the orientation and tilt of the roof

Pitched ArrayFaces south on east/west facing roof

Awning MountedFor south facing gable ends

Ground MountedRoof space may not be available

Solar Combi System Examples

Solar combi-system design

• Design for 30-40% of annual heat load or based on available roof space/budget

• The cooler the collector array operates, the lower its thermal losses and thus the higher its efficiency.

• Optimize system performance for shoulder season.• Don’t heat the solar tank with the boiler. EXCEPTION: Single

tank systems with good tank stratification.• Always provide means of dealing with excess collector heat in

summer (ideally a pool or other summertime load can use the heat).

• Steep collector angle minimizes overheating and optimizes winter time performance

• Simple is good• Solar system failure should not prevent heating system from

maintaining the house at a comfortable temperature.

Solar Combi System 2: Return water re-heating with low mass boiler

Overheat protection

• Required on all Combi systems but also a good idea on all systems

• Types of overheat protection:– Collector installation angle– Controller settings– Active pumped dump zone– Pool– Collector integrated dump zone– Controlled stagnation (steamback)

Controlled Stagnation behavior

• Expansion tank sizing• Check Valve location• Collector piping layout• Collector emptying behavior• Component location• Glycol quality

Collectors with Bad Emptying Behavior

Collectors with Good Emptying Behavior

Commercial• Any application with

substantial DHW load.

Bed and Breakfast

Assisted living facility

Farm

Hotel

Commercial DHW system design

• Multiple loads• Multi story buildings are often roof constrained which makes

it difficult to reach 100% solar fraction so systems are designed as ‘preheat’

• Low SF systems can use less storage if the demand is steady and early in the day (Restaurants).

• Larger systems require more attention to design details (pump sizing, HEX sizing, pipe sizing, overheat protection etc)

• Large tank size (>400 G) favors unpressurized storage for reasons of cost.

Commercial DHW system design

Commercial Example: Country Inn

Solar Domestic Hot water, pool and spa heating system

• Other considerations– Variable speed control of circulation pump– Remote display and data logging

– Hot water recirculation lines– Collector layout

• Reverse return (Tichelman)• Balance valves

BREAK 3 min

SHW system design processI. Site Analysis:

– Determine the Load– Evaluate the roof space and exposure– Evaluate the storage tank space– Identify design goal

II. System Design– Choose system type (drainback, closed loop, etc)– Size collectors– Size Tanks /heat exchanger– Determine flow rate/ size pipe run– Select pump– Size expansion vessel– Specify other components– Physical Layout

Design Step 1: Determine the load

First determine the load in gallons of hot water per day:– Residential: 15-20 G per person per day – Hotels: 15-20 G per occupied hotel room – Restaurants: 2.4 G per meal – Assisted living: 18.4 G Per bed – Office: 1.0 G Per person per day – School: 0.5 to 1.0 G per person per day – Salon: 80.0 G Per basin – Laundromat 50.0 G Per top-loading washer 30.0 G Per front-loading washer (3)

Then convert that to BTUs:

(Gal/day) * (deg F rise) * (8.4 BTU/G deg)= BTU per day

…add to that the expected heat loss from pipes and tanks etc

Design Step 2: Solar Resource Assessment

• Measure the available roof space

• Check for obstacles– Vent pipes, chimneys, etc

• Check shading

Shading Analysis

• Use Sunchart, Pathfinder, Suneye etc

• Look for year round sound 9 AM-3PM

Design Step 3: Boiler room assessment

• Measure the available space (footprint, height, entry doors!)

• Note existing water heater type and capacity

• Existing plumbing size

• Mixing valve

• Location of electrical equipment

Design Step 4: Identify the Design Goal

• Maximum fossil fuel displacement?• Quickest payback?• Something else?

Solar Fraction: Fraction of load met by solar energy.– Typical DHW systems are most cost effective when shooting for

a SF of 100% in summer (non heating months).• Larger means wasted energy much of the year• Smaller means missed opportunity for savings (especially where the

backup may have very low efficiency)

Step 5: Choose system type

• Closed loop vs drainback

• Preheat vs integrated

• Internal vs External HEX

• Choose collector type (flat plate, vacuum tube, unglazed)

Step 6: Sizing the Collectors

• Use rules of thumb– Flat plates : 800-1000 BTU per SF on good summer day– Evacuated tubes: 900-1200 BTU per SF on good summer day

• Use ratings from SRCC or SPF or others– Between ‘Clear Day-C’ and ‘Mildly Cloudy-C’ is a good average

number from SRCC for summertime production

• Use a model– RETscreen, Polysun, F chart, T sol etc

Step 7: Tank/HEX Sizing

• Tank sizing:– Roughly 2 Gallons of storage per SF of collector yields roughly 60-80 degree

temperature rise on a sunny day.– If designing for 100% summer SF, typically 1-2 times the daily hot water

consumption to bridge the gaps– If designing as a preheat (low SF) then size storage for volume of hot water

produced each day.– If the load is regular and well understood size based on necessity

• Heat Exchanger sizing:– Design for a 20 deg F temp rise in collector loop with peak sun and full flow– Use manufacturer’s modeling tools– Rules of thumb:

• Plain copper tube: 20% of collector surface area• Finned copper tube: 35% of collector surface area

Step 8: Flow rate and pipe sizing

• Flow Rate:– Max flow rate should result in ~20 degree rise through collector array

with peak sun.– Follow manufacturer’s recommendations– Rules of thumb:

• 0.03- 0.06 GPM per sq ft of collector area• Pipe sizing:

– Like any hydronic system, keep flow velocity 4 ft per second to minimize flow noise and abrasion in pipe.

– But to minimize wasted pumping power, between 2-3 ft/second is a good rule.

• For flow rates of 1.6 GPM to 3.2 GPM use 0.5 inch • For flow rates between 3.2 GPM to 6.5 GPM use 0.75 inch • For flow rates between 5.5 and 10.9 GPM use 1 inch • For flow rates between 8.2 and 16.3 use 1.25 inch

Step 9: Pump Sizing• At the design flow rate determine circuit head loss from:

– Tables or other methods for pipe run.– Manufacturer’s published data for collectors– Manufacturer’s published data for heat exchangers

• Draw the system curve then look for a pump with an appropriate pump curve

Step 10: Expansion tank sizingExpansion Volume = Volume required for thermal expansion of the fluid AND possible steam volume

from collectors.

= (Total Volume of Glycol * Expansion Factor) + Volume of collector*

(Expansion factor ~ 0.05-0.1 for glycol/water)

Tank Volume = Expansion Volume * [(Pmax +1) / (Pmax –Po)]

Where: Pmax = Maximum allowable pressure (absolute pressure)Po = initial system pressure (at prv location) (absolute pressure)

To avoid air leaking into the system, pressure in a closed loop system should be 7-10 psi minimum at the highest point of the system so:

P0 = .5 * system height(ft) + 10 psi

Step 11: Other Components• PRV• Mixing Valve• Domestic Expansion Tank• Air Elimination• Fill and Drain Ports and valves• Insulation• Controls• Sight Glass, flow meter• BTU meter

Step 12: Physical Layout of components

• Roof Layout:– Roof loading– Collector piping– Aesthetics– Service access– Ease of Install

• Boiler room Layout– Service access to solar and other components– Minimize distances for solar and domestic piping

• Pipe Run planning:– Minimize total length– Minimize high points– Ease of install

And then…Install it

SHW system design processI. Site Analysis:

– Determine the Load– Evaluate the roof space and exposure– Evaluate the storage tank space– Identify design goal

II. System Design– Choose system type (drainback, closed loop, etc)– Size collectors– Size Tanks /heat exchanger– Determine flow rate/ size pipe run– Select pump– Size expansion vessel– Specify other components– Physical Layout

Sample using RETscreen and Polysun: Blueberry Commons

Building 14Load: 10 Senior apartments roughly 16 people (240 G per day)Roof: Pitched, 35 degrees 180 deg TrueBackup system: Propane indirect hot water heater from boiler

Simple Payback =System Cost / Annual Savings

– Savings estimates?– At what fuel cost?– Cost of capital?– Incentives?

SHW Economics

• Federal tax credit– 30% of system cost – Requires SRCC rating for residential (not commercial)– Pool heating doesn’t qualify

• State Rebate– Varies by state

• Accelerated depreciation– MACRS 5 year accelerated depreciation– Bonus depreciation– Section 179

• Utility Rebate• Low interest loans

– Small business low interest loan program– HELP loan for residential

• USDA REAP grants• Other grants (CBDG, VRRF, etc)

Solar Hot Water Incentives

$11,000 Typical Solar Hot Water system gross cost - $2,000 (conventional indirect tank you don’t have to buy) - $3,300 (Federal Tax Credit) - $1,000 (State Rebate)----------------------------------------------------- $4,700 net cost

Financed on 30 year mortgage at 6% this is an extra $28 per month.Average Savings (250 G per year at 3.50 per Gallon) = $73 per month

Total COST SAVINGS = $540 per year

It costs less to have SHW than it does NOT to have it…how many of your products can you say that about?

Residential SHW Economics

Commercial Solar System Economics

Discussion/Questions

Contact us: Fortunat Mueller fortunat@revisionenergy.com (207) 221-6342

Photovoltaic (PV) Applications• Solar Electric systems can be designed to meet up to

100% of our residential annual electrical needs• Average 5 kW PV array uses approximately 350 sq’• Net metering allows excess energy produced during the

day to be stored at retail with the grid, indefinitely

How a GTPV System Works

Grid-tied Photovoltaics (PV) Components

Photovoltaic modules convert sunlight into Direct Current (DC) electricity, which flows through cable to the inverter.

Inverters accept the DC electricity produced by PV modules and convert it into Alternating Current (AC), which then feeds demand in the building or if there excess, feeds the utility grid.

Net Metering & Inverter Technology Replaces Batteries

• Suitable for locations with varying sun and/or partial shading

Micro Inverters

Mounted Flush to Pitched RoofTakes the orientation and tilt of the roof – most common application

Ground MountsRoof space may not be available

TrackersApproximately 35% more annual energy using dual axis tracking technology

Sizing

• Performance rules of thumb– 1000-1300 kwhr/kW per year

• Modeled performance– RETScreen– Pvwatts– PVSOL– Polysun

Sizing Example

• Pvwatts and RETscreen demo

• 7 kW in Portland, ME

Electrical Design

• Array sizing

• Inverter Sizing and String layout

• Wire/Conduit Sizing

• Overcurrent/Disconnect specification

• Grounding/Bonding

Electrical Design

Mechanical Design

Dead load of the Equipment onto the Structure Uplift on the array Snowfence effect of multiple rows (flat roof) Ballast if used (flat roof) Electrical Grounding Weather sealing penetrations Isolation for galvanic reaction Longevity – 50 years

All modern sloped roof-mount systems are based on extruded aluminum rails2-3 psf typical

Mounting and roof loads

Low-angle, ballasted systems dominate installations on flat, membrane roofs. (4-10 psf typical)

Mounting and roof loads

Grounding array structures is one of the most important safety issues of PV installations.Approved grounding hardware is necessary.

The WEEB (washer, electrical equipment bonding) technology is now becoming The industry standard for all hardware systems

Grounding

Weather-sealing roof penetrations requires hardware and sealants designed and built for the purpose.

In membrane flat roofing, regardless of application technique, all penetrations are provided by the roofing contractor carrying the roof warranty. Standard bootsand flashings are used. The roof warranty is intact.

Flashing and Sealing

Economics

• Purchase vs Lease vs PPA– Purchase is almost always the best deal for

the customer in the long run– Lease and PPA may be a good option for non

profits or clients without access to capital or to limit technical risk

Beyond Simple Payback: LCOE

LCOE = Total Life Cycle Cost / Total Lifetime Energy Production

usually in $/kwhr  or $/Mwhr

Full analysis includes:•Capital costs•All incentives•O and M costs•Cost of capital•Electricity price escalation

Beyond Simple Payback: Cash Flow

A calculation of the Price of Electricity offered by a PV System over a 20 Year lifetime. The formula spreads the system net capital cost (after tax credits, depreciation, rebates, and grants) over the kilowatt-hours produced. The PV investment locks in the price of

the delivered power for 20 years, unaffected by energy supply-demand conditions of the external grid. This price can then be compared to that offered by the local utility, including both energy cost and transmission cost. After the first 20 years, the solar

array will continue to generate power for an additional 30 years, for free.

Simplified COE

ReVision is working with institutions, non profits and municipalities to transition from fossil fuels using solar Power Purchase Agreements (PPA)

71 kW PV - Wilkins Meeting House(273) Suniva Solar 260 watt modules (US Made Cells)

(1)Solectria PVI 60 kW Inverter (US Made)Over 90,000 kWh produced annually offsetting over 139,000 lbs. of CO2

Power Purchase Agreements Capturing Tax Subsidies for Non-Profits Using PPAs

Investor(s)

• Tax Investor• Major Donor

Special Purpose LLC

• Build project• Own-operate 6 yrs• Sell power to host

Host 501c3

• Lease roof space• Buy power, REC• Option to buy after 6 yrs

PPA

Pass-thru tax benefits and earnings to investors

Solar PPA Structure

Investor(s)

Provide Capital, Form LLC

Build/Own/Operate ≥ 6 yrs

Recoup Investment thru: Federal Tax Credit

Depreciation & Tax Benefits

Energy Payments from Host

Grants, Rebates, REC sales

Buyout Payment Year Seven

Host

Provides Roof Space

Net Metering w/ Utility

Off-takes Energy, RECs

Can pre-pay, up to six years

Buyout Equipment ≥ year 7 at fraction of original cost

Assume remaining debt, if any

Questions