House battery maintenance

My solar electric system is old school in a lot of ways. There have been upgrades. I updated the charge controller and the inverter. Some parts, like the panels themselves, have been in service for over 20 years. 

While I’ve changed out the battery bank a couple of times I keep going back to lead acid. I would have thought by now that I would have something better. Lithium batteries are an upgrade but the price is prohibitive. 

Besides price lead acid has some other advantages. They can take a fair amount of abuse. I made a lot of mistakes with my first battery bank and still got 10 years out of them. The big thing to remember with lead acid is to keep the cells topped off with distilled water. Never let them get to the point where the plates are exposed to the air. That one simple item is critical for years of service.

Another big battery saver is to never let them sit in an uncharged condition. Ideally, never let the charge get below 50%. If it gets to that level but it’s early morning I’ll let the panels charge them up. If it’s dark or very cloudy I’ll top off the battery bank from the grid. Should the grid be down I’ll go into serious conservation mode. Eventually the panels will bring the batteries out of the danger zone. 

I’ve just topped off the distilled water so the batteries won’t have to be checked for three or four months.

-Sixbears

100 Year Old Battery Technology

Lead acid batteries have been around for over a hundred years. So how come with all the new lithium batteries out there are they still in common use? Odds are very good that the battery in your car is a lead acid battery -unless you drive a Tesla. There are good reasons a gas or diesel vehicle has a lead acid starting battery and a Tesla has lithium.

In short, price, weight and energy density. The battery in a fossil fuel vehicle has one major job, to start the vehicle. A lithium battery could do the job, but why spend the money on a much more expensive battery? Lead works. A Tesla has a huge battery bank. Lead acid is heavy as . . . well, lead. It also lacks the energy density of lithium. For electric cars to make any sort of sense at all a lighter and more energy dense battery is the way to go.

Lithium works great in power hand tools. The power and light weight make sense in something you have to lug around all day. Who wants to use a 50 pound cordless drill? Cell phones and other electronics benefit from compact and energy dense batteries. 

For a while Elon Musk’s power wall was going to be the big thing for off grid houses. You don’t hear that much about it lately. One model was discontinued and they’ve been tweaking the designs. They are  kinda spendy. Personally, I’m still using lead acid batteries with my house solar electric system. It’s a  huge price savings and the weight isn’t an issue since the house isn’t driving down the road at 80 mph. 

My small solar electric systems that I use for camping are still using lead acid. They are heavy, but the systems are small and only use one deep discharge battery. The weight penalty is acceptable. 

However, I did consider using a lithium battery for a 50 watt solar electric system I was going to bring on a long canoe trip. Weight was an issue in a canoe, especially when it came time to do a portage. As it turned out the trip didn’t come together so I never spent the money. 

Lithium batteries are pretty good, but expensive enough that you have to decide if your application really needs them or not. Industrial scale production brings the price down and that helps. In the long run lithium will probably be replaced with some cheaper and even more energy dense. There’s a lot of incentive to engineer in that direction.

-Sixbears

Battery Shopping

The battery bank on my solar electric system finally died over the winter while we were away. That came as no surprise as the batteries were pretty much shot last fall. However, ten years is a pretty good run for flooded lead acid batteries.

I was thinking of putting off buying new ones, but changed my mind. While it's tempting to pay down debt, it makes no sense to pay higher electric bills either. Buying batteries and getting the system up and running again is a good return on investment.

Battery development has been rapid in recent years. My hope was that they'd be economical for my storage needs. It turns out that good old fashioned lead acid is still the best bargain. While lightweight lithium batteries make sense in cars, light weight isn't necessary for a house. The only time when the weight of the house batteries matters is when they are installed. After that they just sit there.

Getting the solar electric system up and running makes sense economically, but it's more important to have them for grid down situations. Storms in the mountains still knock out power often enough to be a pain. Only makes sense to concentrate on getting the system sorted out once more.

-Sixbears

Good old lead acid batteries

There are two common types of home solar electric systems. There's totally grid connected. They are pretty straight forward. Solar panels are directly connected to grid. The energy generated is credited towards your monthly bill. Once it's installed the homeowner doesn't have to think about it. It just works.

The other common type is for off-grid systems. The solar panels feed your own battery bank. You are responsible for managing your power use and storage. It's more hands on, but you are independent from the grid and never get a utility bill.

There are some hybrids of the two major systems. Some grid-tied systems have small battery banks for emergency use during blackouts. Otherwise, even though their panels were generating power, they could not use it.

I've got a simple system that's set up to be mostly off-grid. The solar panels cannot back feed into the grid. However, I can change the battery bank from the grid. My configuration normally uses the grid like a backup generator.

Lately I've been using the grid a bit more than I'd like. My house battery bank is on its last legs. It's been in service for almost 11 years, a long time for golf cart batteries. Now a smart person would have put a little bit of money aside over the last 11 years for when the replacement comes due. Yep, that's what a smart person would do. I wasn't that smart.

By spring I should have the funds to replace the battery bank. I'm using 12, 6 volt golf cart batteries. They are wired up to provide 24 volts which supplies an inverter that makes normal house AC. The advantage of golf cart batteries is that they are common and can be carried by one person -a strong person, but not a freakishly strong person. They can be swapped out in a day.

There have been some advances in battery technology. Batteries have always been one of the big limiting factors of alternative energy. When I first put in solar electric I'd hoped batteries would have improved by now. They have, but not at a price point that makes sense to me. Maybe Tesla's gigafactory will eventually bring the prices down low enough for me to consider them in the future.

For now I'll be going back to good old fashioned flooded lead acid batteries. They lack the energy density of the new batteries, but it doesn't really matter. It's not like in an electric car that has to haul the weight of the batteries. My battery bank sits quietly in a box in the basement. Every few months I pop the cover and check the water level in the batteries and top them off if necessary.

Even though I've had to use the grid a bit more, my bills are still very low. Since my house was designed for off-grid power it uses energy efficiently. That being said, it will be nice to have a full power battery system once more.

-Sixbears

Battery decisions

I just pulled the dead 12 volt deep discharge battery from my sailboat. It got me thinking. Well, the first thing I thought was: darn, those things are heavy. The second thing that came to mind was the fact that my household battery bank is getting on in years.

My household solar electric system is of moderate size. Storage consists of 12 golf cart sized batteries. Currently I'm using good quality Interstate brand. Trojans are good too, but since Interstate has local dealers that's what I went with. The big advantage of dealing locally is that I don't have to pay for shipping. Since shipping is based on weight and batteries are mostly lead, it would get pricey quickly.

Lead acid batteries are really old technology. They haven't advanced all that much in the last 100 years or so. Battery storage has always been the Achilles heel of alternative energy. While lead acid battery storage is adequate for off-grid homes, it doesn't scale well to power grid size. There are some massive battery bank systems out there for things like phone and Internet systems, but there are none large enough to power a big city.

At least, not until fairly recently. Battery technology is making some huge leaps. There's always been interesting things invented in laboratories, but those technologies never made it out of the lab. Now there are huge factories turning out high capacity batteries for everything form cell phones to electric cars. There's real economic incentives for cheap battery storage. Those clever ideas from the labs are starting to show up in factories.

It's almost at the point where it would make sense to replace my 19th century electrical storage system with something from the 21st century. Almost.

The house system should be able to last for another year or two. By then it might make economic sense to try something new. Of course, there's also the possibility that as new battery technology takes hold, lead acid will be deeply discounted. That would be fine too, as leas acid has proven to be good enough for my needs.

-Sixbears