Small/medium AC solar home Systems: preconceived ideas, benefits and - - PowerPoint PPT Presentation

AC in small SHS

Small/medium AC solar home Systems: preconceived ideas, benefits and limits

AC Solar home (individual) system topologies Some prejudices about AC SHS

• Poor efficiency
• More expensive
• Hazardous for people
• Harmful for battery life

Criteria to select between AC or DC system Some of other benefit of AC SHS

R R

DC AC G

Integrated/hybrid AC SHS

R

DC SHS

DC AC

+ Inverter

(MPPT)

DC AC

Wired AC SHS

R

Simple AC SHS

Integrated AC SHS

R

DC AC

Mixed AC/DC SHS:

• More complex/mixed network
• Commonly poor quality inverter
• Uncontrolled LVD on AC
• Poor overall efficiency
• Not cost effective over the

lifetime

Solar home system topologies

AC in small SHS

Efficiency in DC SHS

20% 30% 40% 50% 60% 70% 80% 90% 100% 110% 50 100 150 200 250 300

Efficiency

P load [W]

Line transmission efficiency (12V)

Inverter 10m/2,5mm2 10m/1,5mm2 20m/2.5mm2 20m/1,5mm2

Usually negligible losses in the regulator (> 1%) but…

• Can reaches heavy losses in lines
• Have a limited transmissible power
• Require large wiring cross section

to reach acceptable efficiency

• Limited to short distribution

distances (

• Efficiency of loads sometimes

poorer than AC loads (I.E. CFL

• Battery life time can be drastically

by reducing system abuse

AC in small SHS

Wp 900 800 700 600 500 400 300 200 100 Lengh [m] 100 150 50 ~3 ~2 ~1 kWh/day

DC 1,5mm2 DC 2,5mm2

AC 1mm2

~540 ~360 ~180 [W ~60

DC or AC SHS:

AC in small SHS

Not a trivial decision, which have to take in account the power level to be distributed and the area (distances) to be covered.

AC SHS DC SHS TBD

Inverter topology/power Efficiency @ 300W Peak efficiency Stand-by power No-load power 1 day no load 6 h 25W load eff. HF 350 W nom. 90% 92% 9,5W 9.5W 228 Wh 371Wh 40% BF 300 W nom. 78% 90% 0.3W 3W 7Wh 176Wh 83%

Inverter efficiency in AC SHS

The efficiency of a system is the sum of efficiency of systems parts. The inverter efficiency is one key part of it.

Inverter efficiency comparison

50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% 50 100 150 200 250 300 350 400 Pout [W] Efficiency [%]

HF inverter AJ350 24V

Be careful when interpreting very sexy curves from manufacturer: this could hide some other key parameters like no- load consumption and stand-by consumption.

AC in small SHS

Efficiency in AC SHS

The efficiency at partial load is a key point to obtain an acceptable system

• efficiency. The no load consumption is a good indicator of this key point

50 100 150 200 250 2 4 6 8 10 12 14 16 18 20 22 24 time [h] Load [W] 50 100 150 200 250 300 Energy [Wh]

60% 70% 80% 90% 100%

Efficiency [%] Integration of losses over a load profile: energy losses

Inverter-HF Inverter-BF Energy losses Inverter BF User load Energy losses Inverter HF

Integration of losses for a 610 Wh/day simulated load profile An efficient and sensible standby system is a must to insure a reasonable system efficiency in “small” AC SHS

AC in small SHS

Efficiency /reliability in AC SHS

The efficiency and reliability of AC SHS depend on efficiency and reliability of inverter but also on efficiency and reliability of all other parts on the system. Lighting efficacy: AC CFL are usually better in efficacy (10 to 30%) comparing to DC CFL (but difficult to have third part data for DC CFL) Most of appliances are more cost effective and often with a better price/quality ratio in AC than DC appliances thanks to the mass production, high competition and well developed quality standards. Thanks to a well developed third part survey bodies, high quality AC products are well highlighted and a real large choice of good quality products is offered by the market.

AC in small SHS

Battery are often abused by AC loads

The presence of AC may push users to experiment heavy load like rice cooker or refrigerator ect. Choosing inverter with limited power will reduce the risk: a 300W inverter will not accept a rice cooker or iron This risk is as well true in DC. (keeping the light or TV on all the day long will also abuse the battery). Whatever DC or AC solution is used, the user must and will learn how to cope with the limited resource of solar. The point is: The battery must not be not be destroyed during these learning session. The AC system has a very important and neglected intrinsic features: In an In an AC SHS, all the loads are AC and can’t be connected directly to the battery There is no way to bypass the LVD (low voltage disconnection) in an AC SHS.

AC in small SHS

There is no way to bypass AC SHS

No LVD bypass mean a “learning session” non destructive for the battery, improving considerably the battery life.

Battery SOC [%] 75 100 50 25 Time Hi lead sulfate cristallisation Safe area LVD DC regulator by-pass Enhanced Battery protection

The standard LVD strategy can play his role AC systems allow advanced battery protection algorithm to be fully efficient

AC in small SHS

Advanced battery protection algorithm

Some other good reason to choose AC for small/medium solar home

• Easy installation using standard installation material
• Larger choice of high efficient appliances (qualified by third parts bodies)
• A full reliable control on battery management
• Sustainable investment ready for the future coming grid
• Installation compatible with a back-up generator
• Reduced risk of fire
• Compatible with much longer wiring
• Lighting efficacy usually better due to higher AC CFL efficacy
• Cost effective over lifetime of the system

AC in small SHS

Thank you for your attention, And enjoy all benefits of small AC SHS … with suited AC inverter tailored for particular requirement of rural electrification. And let’s discuss about!

Photos : Energiebau

AC in small SHS