00:00:05.040 welcome back in this block I shall 00:00:08.45900:00:08.469 discuss a vital component of not only PV 00:00:11.33900:00:11.349 system but also renewable energy systems 00:00:14.69900:00:14.709 in general as we discussed in the solar 00:00:17.70000:00:17.710 fuels block there is a great need for 00:00:20.07000:00:20.080 energy storage at both small and large 00:00:23.15900:00:23.169 skills to tackle the intermittency 00:00:26.51900:00:26.529 of renewable energy sources in case of 00:00:29.88000:00:29.890 PV systems the intermittency of the 00:00:33.00000:00:33.010 source is of two kinds diurnal 00:00:36.87000:00:36.880 fluctuations the difference of 00:00:38.87000:00:38.880 irradiance during the 24-hour period and 00:00:42.21000:00:42.220 the seasonal fluctuations the difference 00:00:44.70000:00:44.710 of the irradiance across the summer and 00:00:46.50000:00:46.510 winter months 00:00:48.77000:00:48.780 there are several technological options 00:00:51.45000:00:51.460 to fulfill the storage requirements how 00:00:54.54000:00:54.550 do we make an optimal choice for the 00:00:57.78000:00:57.790 storage system let us go back to the 00:01:01.74000:01:01.750 Ragan plot again for solar applications 00:01:04.96900:01:04.979 depending on the skill of implementation 00:01:07.59000:01:07.600 we need a high energy density and 00:01:10.43000:01:10.440 unreasonable high power density we 00:01:14.39900:01:14.409 cannot use capacitors because of their 00:01:17.10000:01:17.110 very poor energy density for short term 00:01:20.61000:01:20.620 to medium-term storage the most common 00:01:23.19000:01:23.200 kind of storage in use is of course the 00:01:25.86000:01:25.870 batteries they have just the right 00:01:28.56000:01:28.570 energy density and power density to meet 00:01:31.29000:01:31.300 the daily storage demand in the PV 00:01:33.60000:01:33.610 system of course the seasonal storage 00:01:36.93000:01:36.940 problem at large kills is yet to be 00:01:39.99000:01:40.000 solved convincingly for now batteries 00:01:43.56000:01:43.570 still seem to be the most reliable 00:01:45.57000:01:45.580 option for PV systems in the small to 00:01:48.60000:01:48.610 medium scale the ease of implementation 00:01:52.23000:01:52.240 and efficiency of the batteries is still 00:01:55.52000:01:55.530 unbeatable when compared to other 00:01:58.53000:01:58.540 technologies like Pumped hydro 00:02:00.98000:02:00.990 compressed air energy storage conversion 00:02:04.50000:02:04.510 to a hydrogen and converting back into 00:02:07.32000:02:07.330 electricity and others I will therefore 00:02:10.67900:02:10.689 focus on the battery technology in this 00:02:12.72000:02:12.730 block as a viable storage option for PV 00:02:16.11000:02:16.120 systems bad 00:02:17.97000:02:17.980 our electrochemical devices that convert 00:02:20.76000:02:20.770 chemical energy into electrical energy 00:02:23.18000:02:23.190 they are mainly classified as primary or 00:02:26.79000:02:26.800 secondary batteries primary batteries 00:02:30.77000:02:30.780 irreversibly convert chemical energy 00:02:33.00000:02:33.010 into electrical energy 00:02:35.18000:02:35.190 examples include sink carbon batteries 00:02:38.25000:02:38.260 and the alkyne batteries secondary 00:02:42.44900:02:42.459 batteries or as they are more commonly 00:02:44.46000:02:44.470 called with chargeable batteries 00:02:46.72900:02:46.739 reversibly convert chemical energy to 00:02:49.67000:02:49.680 electrical energy that is they can 00:02:53.34000:02:53.350 recharge when the chemical reaction is 00:02:55.74000:02:55.750 reversed using an over potential in 00:02:59.67000:02:59.680 other words the excess electrical energy 00:03:02.55000:03:02.560 is stored in these secondary batteries 00:03:05.49000:03:05.500 in the form of chemical energy 00:03:08.69000:03:08.700 examples include lat acid batteries and 00:03:12.78000:03:12.790 lithium-ion batteries it is the 00:03:17.25000:03:17.260 secondary batteries that we are 00:03:18.96000:03:18.970 interested in to explore as a possible 00:03:21.63000:03:21.640 storage option there are several kinds 00:03:24.00000:03:24.010 of secondary battery technologies 00:03:25.80000:03:25.810 available that could be used for example 00:03:29.06000:03:29.070 lat acid batteries these are the oldest 00:03:33.93000:03:33.940 and the most mature battery technology 00:03:36.21000:03:36.220 available till date I will go deeper 00:03:40.02000:03:40.030 into this widely accepted PV storage 00:03:42.19900:03:42.209 option later another secondary battery 00:03:45.96000:03:45.970 type is nickel metal hydride and nickel 00:03:48.78000:03:48.790 cadmium batteries make a metal hydride 00:03:51.87000:03:51.880 have a good energy density comparable to 00:03:55.50000:03:55.510 that of the lithium ion batteries but 00:03:58.28900:03:58.299 the nickel metal hydride batteries 00:04:00.75000:04:00.760 suffer from a high rate of self 00:04:02.58000:04:02.590 discharge nickel cadmium batteries have 00:04:05.78900:04:05.799 much lower energy densities due to the 00:04:08.94000:04:08.950 environmental impact of cadmium the SIL 00:04:11.58000:04:11.590 of nickel cadmium batteries for consumer 00:04:14.37000:04:14.380 use is largely banned in the European 00:04:16.37900:04:16.389 Union further nickel cadmium batteries 00:04:20.31000:04:20.320 suffer from what is called as memory 00:04:23.01000:04:23.020 effect the batteries lose their usable 00:04:25.89000:04:25.900 energy capacity if they are repeatedly 00:04:28.89000:04:28.900 charged after only a partial this 00:04:32.39000:04:32.400 these demerits make the nickel cadmium 00:04:36.00000:04:36.010 and the nickel metal hydrides unlikely 00:04:40.02000:04:40.030 candidates for storage in a PV system 00:04:43.07000:04:43.080 next we go to the lithium ion and 00:04:46.62000:04:46.630 lithium-ion polymer batteries these are 00:04:50.67000:04:50.680 being heavily researched currently as 00:04:53.01000:04:53.020 storage alternatives in various 00:04:55.08000:04:55.090 applications their high energy density 00:04:59.04000:04:59.050 has already made them a favorite in 00:05:01.50000:05:01.510 light weight storage applications but 00:05:05.67000:05:05.680 for their cost and low maturity they 00:05:08.52000:05:08.530 would have been instant favorites for 00:05:11.13000:05:11.140 storage and PV systems note that you 00:05:14.58000:05:14.590 shouldn't confuse lithium batteries with 00:05:17.13000:05:17.140 lithium ion or lithium-ion polymer 00:05:19.74000:05:19.750 batteries lithium batteries are 00:05:22.62000:05:22.630 disposable primary batteries while 00:05:24.63000:05:24.640 lithium ion and lithium-ion polymer are 00:05:27.12000:05:27.130 secondary batteries the last and the 00:05:31.08000:05:31.090 most upcoming category is that of the 00:05:33.06000:05:33.070 redox flow batteries the two main 00:05:36.36000:05:36.370 storage options for PV storage let acid 00:05:40.56000:05:40.570 and lithium ion batteries are similar in 00:05:43.32000:05:43.330 the sense that their electrodes 00:05:44.82000:05:44.830 on-the-go chemical conversion during 00:05:47.67000:05:47.680 charging and discharging therefore the 00:05:52.29000:05:52.300 electrodes tend to degenerate with time 00:05:55.13000:05:55.140 adding to the inevitable aging of the 00:05:59.79000:05:59.800 battery redox flow batteries are a very 00:06:04.32000:06:04.330 new technology which seem to combine the 00:06:07.29000:06:07.300 properties of both the batteries and the 00:06:09.87000:06:09.880 fuel cell the different reactants only 00:06:13.02000:06:13.030 exchange ions in the form of 00:06:14.84000:06:14.850 electrolytes through a membrane in a 00:06:17.28000:06:17.290 Cell thus the cell reactions proceed 00:06:20.58000:06:20.590 without a physical mixing of the 00:06:23.01000:06:23.020 reactants the chemical energy in a redox 00:06:25.98000:06:25.990 flow battery is stored in its two 00:06:27.78000:06:27.790 electrolytes which can be maintained 00:06:30.27000:06:30.280 physically separate from each other 00:06:33.02000:06:33.030 redox flow batteries does have a high 00:06:35.76000:06:35.770 life expectancy let's look at a ragam 00:06:42.00000:06:42.010 plot specific to the typical batteries 00:06:44.67000:06:44.680 only 00:06:45.55900:06:45.569 this is slightly different from the 00:06:47.96900:06:47.979 Oregon plot shown earlier as this shows 00:06:50.76000:06:50.770 the comparison between the various 00:06:52.74000:06:52.750 batteries technologies in terms of 00:06:55.70000:06:55.710 gravimetric energy density and the 00:06:57.96000:06:57.970 volumetric energy density for you metric 00:07:02.15900:07:02.169 energy density is the amount of energy 00:07:04.23000:07:04.240 stored per volume of battery the typical 00:07:08.96900:07:08.979 unit of measurement is what hours per 00:07:10.80000:07:10.810 liter higher the volumetric energy 00:07:13.71000:07:13.720 density smaller the battery size 00:07:16.85000:07:16.860 gravimetric energy density is the amount 00:07:19.49900:07:19.509 of energy stored per mass of the battery 00:07:22.49000:07:22.500 the typical unit of measurement is what 00:07:25.74000:07:25.750 hours per kilogram created the 00:07:29.10000:07:29.110 gravimetric energy density lighter the 00:07:32.33900:07:32.349 battery will be as seen let acid shows 00:07:37.23000:07:37.240 the lowest volumetric and gravimetric 00:07:39.60000:07:39.610 energy densities among the batteries 00:07:43.04000:07:43.050 lithium ion batteries show ideal 00:07:45.87000:07:45.880 material properties to make it an 00:07:47.93900:07:47.949 optimal storage choice redox flow 00:07:51.51000:07:51.520 batteries have shown a lot of promise in 00:07:53.93900:07:53.949 their research faced so far however 00:07:56.24000:07:56.250 redox flow batteries and lithium-ion 00:07:58.61000:07:58.620 technologies are still being heavily 00:08:01.02000:08:01.030 researched upon consequently these 00:08:04.77000:08:04.780 technologies are also very expensive due 00:08:08.87900:08:08.889 to the unbeatable maturity and low cost 00:08:11.90900:08:11.919 of the lead acid batteries they are 00:08:14.10000:08:14.110 still the storage technology of choice 00:08:16.05000:08:16.060 and PV systems despite their much lower 00:08:19.62000:08:19.630 energy density and extremely low cycle 00:08:22.29000:08:22.300 life let's look a little bit more 00:08:25.32000:08:25.330 closely at the let acid battery here you 00:08:31.64900:08:31.659 see typical construction of a lead acid 00:08:34.19900:08:34.209 battery as with most batteries the lead 00:08:37.29000:08:37.300 acid battery is composed of several 00:08:39.75000:08:39.760 individual cells each of which have a 00:08:43.19900:08:43.209 nominal cell voltage of around 2 volts 00:08:45.63000:08:45.640 let acid batteries could have different 00:08:48.93000:08:48.940 types of assembly when built as a block 00:08:53.13000:08:53.140 assembly the individual cells share the 00:08:56.49000:08:56.500 housing and are interconnected in turn 00:08:59.79000:08:59.800 for instance to get the popular let acid 00:09:03.69000:09:03.700 battery pack of 12 volts six such cells 00:09:07.32000:09:07.330 have to be connected in series as the 00:09:11.22000:09:11.230 battery name suggests the electrolyte in 00:09:14.10000:09:14.110 this battery is made from dilute 00:09:16.41000:09:16.420 sulfuric acid h2so4 two plates of 00:09:22.44000:09:22.450 opposite polarity are inserted into the 00:09:25.41000:09:25.420 electrolyte solution which acts as the 00:09:27.90000:09:27.910 electrodes the electrodes contain grid 00:09:31.83000:09:31.840 shaped let carrier and the porous active 00:09:35.25000:09:35.260 material it is the porous active 00:09:38.13000:09:38.140 material that acts as a sponge-like 00:09:40.22000:09:40.230 structure providing sufficient surface 00:09:43.95000:09:43.960 area to help the electrochemical 00:09:46.05000:09:46.060 reaction reactive mass in the negative 00:09:49.74000:09:49.750 electrode is lat and in the positive 00:09:52.38000:09:52.390 electrode is lat 00:09:53.85000:09:53.860 oxide when electricity is drawn 00:09:57.06000:09:57.070 electrons flow from the negative to the 00:09:59.64000:09:59.650 positive electrode through the external 00:10:02.40000:10:02.410 circuit causing a chemical reaction 00:10:04.77000:10:04.780 between the plates and the electrolyte 00:10:07.58000:10:07.590 this forward reaction also depletes the 00:10:11.22000:10:11.230 electrolyte affecting its state of 00:10:13.41000:10:13.420 charge or SOC 00:10:16.82000:10:16.830 when the battery is recharged the flow 00:10:19.77000:10:19.780 of electrons is reversed as the external 00:10:22.44000:10:22.450 circuit doesn't have a load but a source 00:10:25.35000:10:25.360 that has a higher voltage than the 00:10:27.39000:10:27.400 battery to enable the reverse reactions 00:10:30.00000:10:30.010 in the PV systems this source is nothing 00:10:34.32000:10:34.330 but the PV module or array providing 00:10:37.56000:10:37.570 clean solar power remember that the use 00:10:40.65000:10:40.660 of storage is more common in stand-alone 00:10:44.01000:10:44.020 PV systems because there is no other 00:10:46.53000:10:46.540 source of power to support the PV array 00:10:49.82000:10:49.830 the loads are at the mercy of the 00:10:53.37000:10:53.380 availability of the Sun in such a case 00:10:56.36000:10:56.370 storage options like the battery can be 00:10:59.04000:10:59.050 very useful as an example a typical 00:11:02.79000:11:02.800 solar irradiance profile is shown during 00:11:05.88000:11:05.890 the day you can also see the low demand 00:11:08.82000:11:08.830 which is significant in the parts of the 00:11:12.15000:11:12.160 day where there is 00:11:13.24000:11:13.250 in a stand-alone system without storage 00:11:17.71000:11:17.720 even though the Sun has more than enough 00:11:19.84000:11:19.850 power during the day the system feels to 00:11:22.74900:11:22.759 utilize this excess energy to power the 00:11:25.60000:11:25.610 loads when the solar power isn't enough 00:11:28.88900:11:28.899 with the introduction of the battery 00:11:31.15000:11:31.160 storage in the pv system the excess 00:11:33.87900:11:33.889 energy from the Sun during the day can 00:11:36.24900:11:36.259 be stored in the battery the battery can 00:11:39.91000:11:39.920 then be discharged during the periods of 00:11:42.40000:11:42.410 low solar irradiance and thus the load 00:11:45.55000:11:45.560 demand can be met to summarize we have 00:11:49.11900:11:49.129 seen the different kinds of battery 00:11:50.92000:11:50.930 technologies and discussed why lat asset 00:11:54.46000:11:54.470 is the battery of choice for most 00:11:56.11000:11:56.120 current PV systems I will talk in detail 00:11:59.43900:11:59.449 about the various battery parameters in 00:12:02.41000:12:02.420 the next block we also see how managing 00:12:06.30900:12:06.319 the different battery parameters is a 00:12:08.82900:12:08.839 whole new optimization challenge on its 00:12:11.17000:12:11.180 own see you in the next block
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