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

AC in small SHS Solar home system topologies Mixed AC/DC SHS: • More complex/mixed network R DC AC • Commonly poor quality inverter • Uncontrolled LVD on AC • Poor overall efficiency • Not cost effective over the lifetime DC SHS + Inverter Simple AC SHS G R R DC AC R DC AC DC AC (MPPT) Integrated/hybrid R Integrated AC SHS Wired AC SHS AC SHS

AC in small SHS Efficiency in DC SHS Usually negligible losses in the regulator (> 1%) but… • Can reaches heavy losses in lines Line transmission efficiency (12V) • Have a limited transmissible power 110% • Require large wiring cross section 100% to reach acceptable efficiency 90% • Limited to short distribution 80% distances ( Efficiency 70% • Efficiency of loads sometimes 60% Inverter poorer than AC loads (I.E. CFL 50% 10m/2,5mm2 • Battery life time can be drastically 10m/1,5mm2 40% by reducing system abuse 20m/2.5mm2 30% 20m/1,5mm2 20% 0 50 100 150 200 250 300 P load [W]

AC in small SHS DC or AC SHS: Not a trivial decision, which have to take in account the power level to be distributed and the area (distances) to be covered. kWh/day [W Wp DC 2,5mm 2 ~3 ~540 900 DC 1,5mm 2 800 700 AC 1mm 2 ~2 ~360 600 500 400 ~1 ~180 300 200 ~60 100 0 0 0 100 150 50 Lengh [m] DC SHS TBD AC SHS

AC in small SHS 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 Peak Stand-by No-load 1 day no 6 h 25W eff. topology/power @ 300W efficiency power power load load 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% Be careful when Inverter efficiency comparison interpreting very sexy 100% 95% curves from manufacturer: 90% this could hide some other 85% Efficiency [%] 80% key parameters like no- 75% 70% load consumption and 65% stand-by consumption . 60% 55% 50% 0 50 100 150 200 250 300 350 400 Pout [W] HF inverter AJ350 24V

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 An efficient and sensible standby system is a must to insure a reasonable system efficiency in “small” AC SHS Integration of losses for a 610 Wh/day simulated load profile Efficiency [%] Integration of losses over a load profile: energy losses 300 Load [W] 250 250 User load Energy losses Inverter BF 200 200 Energy losses Inverter HF Energy [Wh] 150 150 Inverter-BF 100 100 Inverter-HF 50 50 0 100% 90% 80% 70% 60% 24 time [h] 0 2 4 6 8 10 12 14 16 18 20 22

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) 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. 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.

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 The standard LVD strategy can play his role Advanced battery protection algorithm Battery SOC [%] 100 Safe area 75 Enhanced Battery protection 50 25 LVD Hi lead sulfate cristallisation 0 DC regulator by-pass Time AC systems allow advanced battery protection algorithm to be fully efficient No LVD bypass mean a “learning session” non destructive for the battery, improving considerably the battery life.

AC in small SHS 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) • Lighting efficacy usually better due to higher AC CFL efficacy • 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 • 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