Solar Systems in Practice

Alan Kiff CEng MCIBSE

Managing Director

Portsmouth SBN Meeting – 25th November 2010

Contents

• CASE STUDY - Solar Thermal Installation• CASE STUDY - Solar PV Installation• Conclusions

Solar Thermal

• Generation of Hot Water by absorbtion of solar radiation

Collector Pump Tank

With only 3 components what can go wrong???

Solar Thermal - Tank

• What’s wrong with this picture?– Blue tank is the new

solar tank– Other tank is existing

• Integration into existing systems

• Storage capacity– Matched to load?

Solar Thermal - Pump

• Is the pump powerful enough?

• How fast is the solar fluid moving?

• Has the system been correctly commissioned?

PUMP

Flow Meter

Solar Thermal - Collector

• Orientation – Taken at lunchtime so

why is the sun on the other side of the roof?

• Type– Overheating– Stagnation

• Number– Too Few / Too many

• Does Collection profile match usage profile?

What’s wrong with this picture?

Solar Thermal – Case Study

• System purchased direct from installer• No evidence of design calculations• Client questions system performance after

18 months

• 5 evacuated tube collectors on exposed South facing roof at 35° pitch.

• Good quality pump and control station

Solar Thermal – Case Study

• Collector selection and location– Good quality tubes– Correct orientation and pitch– Right number of tubes

BUT• three storeys between collector and tank

and VERY long poorly insulated pipe run• Collector had overheated due to poor

location of expansion tank

Solar Thermal – Case Study

• Pump– Flow rate set to 5 litres / minute – too fast– Pump slightly undersized for “head”

• Tank size– 315l tank used for preheat of existing 400l tank– House has 4 bathrooms but typically only 2

occupants– Any solar heat collected will never get to the

tap!

Solar Thermal – Case Study

• How we proved the system wasn’t working– Data-logging of flow-rates and temperatures– Collector had hydraulic locked – fluid short circuiting

through expansion loop– Proved no heat transfer between collector and tank

• How we fixed it– Removed original cylinder and used solar cylinder as

intended– Re-commissioned flow rates and pump speeds– Installed Auto air-vent and relocated expansion

vessels

Solar Thermal - Conclusions

• Insist on seeing design calculations– Collector type and sizes – Tank sizes

• Insist on a formal commissioning report

USE AN INDEPENDENT CONSULTANT !!

Unless the installation is small scale domestic DON’T rely on the installer.

Photo-Voltaic

• Client considering PV as an investment• Maximise payments under FIT• Installation on an outbuilding rather than

main house

Key Features• Own electricity meter• South facing, 45° roof pitch• Room in roof• 5000 kWh/yr electricity use

PV –Stage 1- Simulation

• Different panels (makes and models) and inverters• Different numbers of panels

Transient Simulation (TRNSYS16)

• Product specific performance data• NASA Weather data•10 min time steps

PV – Stage 1 – Simulation (Results)

PV – Stage 2 Financial Analysis

“Benefit” from the panel =Feed In Tariff + Export Tariff + Electricity Offset

41.3 + 3 + 12.5

Electricity Use = 5000 kWh per yearPV output = max. 1910 kWh per yearTherefore

Export = 0 kWh, Offset = 1910 kWh, FIT based on 1910 kWh

Majority of income is due to FIT

PV – Stage 2 Financial Analysis

• Done for each panel / inverter combination• Costs based on manufacturer prices +

installation costs• Lifetime analysis includes panel

degradation in accordance with manufacturer warranty

PV – Stage 2 Financial Analysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

-£30,000.00

-£20,000.00

-£10,000.00

£-

£10,000.00

£20,000.00

£30,000.00

£40,000.00

Cumulative Cash Flow - Yingli with SMA inveter

Yingli 8Yingli 6Yingli 4

PV – Stage 3 – Technical Feasibility

STRUCTURAL SURVEY

• Each panel weighs around 20kg• Mounting frames weigh around 10kg

per panel

• Survey revealed that the structure could support the additional weight BUT only if the joist fixing bolts were replaced.

PV – Stage 4 - Quotes

• To qualify for FIT the system must be installed by MCS accredited installer.

• Specify the exact makes and models

• Quotes obtained for installation + remedial work to roof.

• Recalculate the payback period

PV - Conclusions

• Selection of the panels is critical to project success• Inverter losses must be factored in• Panel degradation must be factored in• Modelling should be accurate – don’t use SBEM

– Initial feasibilty should be done in RETScreen– Detailed simulation (TRNSYS) is worthwhile

• Panels and frames are– Heavy– Increase wind sheer

have a structural survey done!

CONCLUSIONS

• There are poorly installed Solar Thermal Systems

• There are accurate modelling tools

• The FIT and RHI are significant

• Do you trust your installer to act as consultant?