A gell cell battery has from 13.2V-13.4V therefore more CCAs. Use one of these in a very hot or cold environment. So your not waisting money. Everything is made to last a certain time including transmissions ect... It just happens to fail out-of-warranty as we call it. In our shop we repair CNG systems, Hybrrids, and EVs (Electric Vehicles). Though fewer problems, when they do happen it is much more expensive to replace than your regular car. A EV or HEV battery pack can cost up to $23,000 for the most expensive (Ex: Fisker Karma Coupe or Mercedes Benz S-400 Hybrid). So love your cheap stuff now and hate the dealers now: Honda, Lexus/Toyota, Kia... ect, Ford, Chevrolet, and Dodge, because they are set to fail after warranty. Your best bet is a foreign car like Fiat, Jaguar, Benz... ect. UK cars in general (Better economy where based). Though Fiat has brought back the 500 with Jeep/Dodge (The companies they own). We needed a small turbo deisel not gasoline powered. With a motor generator and a deisel to charge a pack we would be set. But we are afraid :(. Boo hoo America. We have almost no polution from some deisels now. Lets see your paying an extra dollar to gain a extra 25-35 mpgs its worth it trust me. We are not ready for this innovation, for even i drive a souped up 1994 940 Turbo that uses premeium gasoline. Thanks, The Hybrid guru. JKSully

400kwh a week is excessive, you would stroke if you had my house! prior to slowly making efficiency changes, our house used on average about 160kwh A DAY! we changed to almost all CFL, got rid of the 30+ year old HVAC system fro the front and installed a new high efficiency HP. all appliances are energy star, with the exception of the deep freeze. i did finally get rid of the 2nd deep freeze, or rather quit using it and unplugged it. it was made inthe early '70's and after unplugging it we saw a drop of around 400kwh per month! our usage this month was less than 1800kwh. our average now is less than 2800kwh a month, with a our highest period inthe last 13 months being Feb, the month before the new HP went in. i could get my usage lower, but my wife and 3 yr old think that if they are in acertain part of the house that ALL lights in that area must be on. i will get the usage down further, i still have a 15yr old HVAC system for the back of the house that must be replaced when money allows, but i cannot see possibly getting our usage below 1500-1800 kwh a month on average.

Sorry this post is long. If you get too bored, just skip to the next-to-last paragraph. So far nobody has yet found the perfect battery. All of them are balances of cycle life, cost, safety, temperature range tolerance, specific energy (Wh/kg), energy density (Wh/l), specific power (W/kg), charge efficiency, and probably some factors I've forgotten about.. No one battery type has them all nailed down, and probably none ever will. The battery that might make its way into a home power system today would most likely be lead or lithium ion. A few others have been used but are now mostly on the sidelines. These include nickel cadmium, nickel iron, and nickel metal hydride (which is really just improved nickel iron). Lead is the traditional battery for home power systems, but it has significant downsides. Specific energy and energy density are low. Flooded types need watering and periodic testing. Cycle life is good for heavy, expensive tubular plate types, not so great for conventional flat plate batteries. Lead used to be the uncontested leader in cost per watt-hour delivered, but in recent years lead metal prices have increased and it's no longer as competitive as it once was. Nickel iron is legendary for extremely long cycle life. I've read that some of the original NiFe cells built by Thomas Edison are still in service! Their specific energy and energy density are better than lead, but not dramatically so. Efficiency is a weak point because they gas too freely (too much energy going into electrolysis), and this also requires careful ventilation. The few NiFe manufacturers charge nosebleed prices, which limits their use. Nickel cadmium has long cycle life and decent specific energy and energy density. Their big problem is that cadmium is nasty, toxic stuff. Because of this they face severe restrictions in the EU. Nickel metal hydride batteries have sort of been lost in the lithium shuffle in recent years. They have long cycle life and quite good specific energy and energy density. The problem has been that they're encumbered by restrictive terms issued by the patent holder, but I think the relevant patents may expire later this year. The other big negative with NiMH, as with other nickel chemistries, is that nickel is expensive. If given a chance, I think NiMH could still become competitive, but don't hold your breath. Recently lithium ion batteries have grabbed the spotlight almost to the exclusion of any other type. Note though that they aren't all alike. There are several different chemistries with different balances of those concerns I mentioned above. Beyond that, each chemistry is optimized differently by different manufacturers with different design goals. In general I'll agree that lithium ion can be a bit touchy about temperature, certainly more so than lead. Some lithium ion cells shouldn't be charged below freezing (0C / 32F). Others can accept a charge down to -10C, and a few are OK as low as -30C. Again, it depends on what the battery manufacturer is optimizing for. In most home power systems this isn't a problem, especially if the battery is located in conditioned space. The battery's own internal resistance will keep it warm with any normal current use. Insulation and controlled ventilation will keep the temperature in the acceptable range. OTOH very warm temperatures can reduce lithium batteries' cycle life. The more fully charged they are, the more they suffer. So you limit the charging rate at low temperatures, charging slower and slower as the temperature falls, and eventually not at all. On the upper temperature end, you don't charge the battery completely if you expect, or already have, very hot temperatures. Because lithium batteries are fussier than other types about over-charging and over-discharging, they almost always are sold with battery management systems (BMSes). Good lithium ion BMSes know what their batteries are capable of. They monitor the cells' state of charge (or at least their voltages, which is not quite the same thing) and usually also temperature. They control the charging and discharging functions to suit, for a compromise between capacity and cycle life. To cut to the chase, based on Tesla's track record (no pun intended) with their cars, I expect that they'll be more than competent when it comes to their Powerwalls' battery management. As for whether a Powerwall or two can store enough energy for your household needs, that depends on many factors, including how you heat and your overall energy efficiency. Most off-grid folks have to make some lifestyle adjustments when they're no longer drawing their energy from an apparently bottomless source (the grid). If they don't, it probably means their pockets are pretty much bottomless. :-\

jellytoast since our solar was part of a new build, we have no prior electric use with this house to gauge a pay back period. That wasn't a huge consideration for us - kind of like buying a hybrid or electric car, part of the motivation is 'doing the right thing' and stepping into a new dynamic of fuel use. Our system is sized to (hopefully) supply all our power needs with little to no overage (net zero) and so far, 19 months in that's what we're getting. DH engineered and installed our system from components he sourced so we don't have those costs to recoup - and contractor pricing for materials helps as well. Like beagles, we got a tax credit but I don't remember what it was and pay 13.65/month for the privilege of doing business with Duke energy and be connected to the grid. If our use exceeds what we produce during a billing period and we don't have credits banked to cover it, then we'd see that cost on our electric bill - hasn't happened yet. Our credits roll over month to month for a year, (May to May) and any unused credits at that time get washed away so the goal is to have as few as possible at that point. Because our panels are on towers instead of a roof, they are adjusted throughout the year to get full value of the sun as the angle of the rays change. So close to the summer solstice they are almost flat and during winter solstice at their most vertical adjustment. We have a 2400 sq ft single story house with a full unfinished basement. Summers are hot - our AC was on non-stop this year from May into early Oct. Winters aren't brutal like the midwest can be but we certainly see our share of single digit mornings before a warm up into the teens, but average more in the 30's to 40's. New build, well insulated, good windows/doors, efficient appliances, good HVAC etc all contribute to our system being able to cover our needs. On an older house the benefit is still there but it's not as integrated so first make the house as efficient as possible, then do the solar.