Tag solar

A bit of Solar

I got a message a few weeks back to see if I was still looking for old laptop batteries for 18650 harvesting, and of course I said yes. The next day, I got one or two batteries dropped off at my house:

A few crates. There were a couple of other ones too.

A few crates. There were a couple of other ones too.

Wow. Its going to take some time to crack them all open, harvest the cells, and test them all properly. Of course, I’ve got two batteries for R2 now that seem to be in a good shape and last long enough for pretty much any event. So the question is, what do I do with all the cells I’m going to have once I’ve finally gone through all these crates.

I’ve a few projects in mind that will utilise a couple of cells each, including a standby battery for R2’s brain, but a rough calculation shows that once I’m through all these crates I’ll have approx 1200 cells of varying states. So far, I’m through about half a crate and the vast majority seem to be in a good condition and over 2000mAh capacity. That means I’ve got nearly 8kWh of energy storage! Even if I assume half the cells are dead (so far only about 2% seem dead), thats still 4kWh.

The first thing that jumps out for this amount of storage is a form of power wall. Now, I’m not going to do anything grid tied, that is just too much hassle, but doing something off grid for the garage is definitely doable. If I can perhaps do enough to run the computer and other electronics, plus indoor and outdoor lighting, then I will consider it a success.

25W solar panel for testing

25W solar panel for testing

To start the project, I got hold of a few small solar cells, one 25W, and a couple of 50W ones. The 25W one will be used for experimentation and testing theories out, and the two 50W panels will be mounted on the wall of the garage for a more permanent solution. I also purchased an EPSolar MPPT charge controller, to go with a couple of spare 12V SLA batteries I had spare from initial testing of R2. I went for this model as it has a serial out port on it that will allow me to tie it into my OpenHAB home automation system and graph things like battery charge, solar power production, and any load on the system.

Fabricated a couple of brackets to mount the 100W combined solar panel

Fabricated a couple of brackets to mount the panel

Being able to graph those details will allow me to make an estimate of how much energy I can generate on a typical day, and from that calculate how much I can actually run off my system for a given amount of solar panels, and also work out just how many kWh of energy storage I need.

The charge controller however will only work with standard lead acid batteries, whilst I want to make use of the 18650 cells. To this end, I did a lot of reading and it seems that there are very few hobby level solar charge controllers that will work properly with lithium technologies. Some charge controllers can be made to work with them, but it is more of a bodge.

After much searching, I did find one chinese charge controller that said it worked with lithium batteries, and actually seemed to back that up in the details. One of the main things to look for is that it supports the typical CC/CV (constant current/constant voltage) charge methods that are required for all lithium cells. A few clicks, and it was on its way on a slow boat from china.

Solar charge controller mounted

Solar charge controller mounted

For now, I’ve got the EPSolar charge controller mounted on the wall of the garage, connected to the 100W of panels outside.

Next steps are to get some data logging from the serial port, probably using an ESP8266 based device, dumping the data into my MQTT server, which in turn will be monitored by OpenHAB to be dropped into an influxDB store for graphing with Grafana.

Along with this is the slow process of breaking open a lot of laptop batteries and harvesting the cells. Once I have enough for a decent sized test, I will be looking into various ways of mounting them and hopefully adding an individual fuse to each cell for safety. More research into BMS for making sure the battery is properly balanced is required too.

 

 

One Year of Solar

So, I’ve had my solar panels for a year now, and have just received my fourth cheque from British Gas for my Feed in Tariff and Export Tariff. So, in a year of having the panels, just those cheques alone have come to over £400, and that doesn’t take into account the money saved on my electric bills. British Gas have some nice tools for viewing usage, and from the following graph you can see just just how much my electric consumption went down compared to the previous year.

Screenshot - 050414 - 15:19:23

Summer months of course were extra good, especially July where I actually consumed next to nothing off the grid. Even the winter months show a little improvement. Rough calculations show my electric bills were approximately £300 less than the previous years.

So, what does this mean? Well, with the FiT money, Export Tariff money, and savings on my electric bill, I’m definitely on track for paying off the solar panels within the predicted 8 years. As electric prices go up, that figure may well improve somewhat too. I’m definitely glad I got them installed, I think it was a fantastic investment and certainly is going to be a better way of saving money in the long run.

Solar!

Over the last couple of years I’ve been looking at the feasibility of  getting photovoltaic cells put on the roof of my house. I’ve only got a small amount of roof space seeing as I live in a mid terrace so wasn’t sure if I could get enough panels to make it worth while. A couple of months ago I decided to take the plunge and get a few quotes in. Unfortunately, this is where I met the main hurdle with the whole project. Despite emailing half a dozen companies, I only got two visits to give me a quote, and only one of those actually sent me a quote.

Thankfully I’d done enough research into the technology and rough costs so that I knew the quote I got back was a pretty typical price. The company also seemed to be pretty decent with some good reviews and a good web site. With all that in mind, I decided to go for it and accepted the quote. I was very impressed with how quickly things went. One of the requirements for getting the feed in tariff from the government is to get an Energy Performance Certificate (EPC) and within a few days I’d had the survey done for that and the certificate in my hands. Only a little over a week later the panels were installed, commissioned and my meter was running backwards.

 

Solar install

Solar install

So, what did I actually get installed? All together, 16 panels were squeezed onto my roof across two elevations with 8 on a west facing aspect and then 8 on the south facing which gave me 4kW in total. The installation is fairly straight forward and involves the two arrays of panels going into an inverter which feeds into the main circuit breaker panel. I’ve also installed a full monitoring system that keeps track of power consumed and solar power produced, which I’ll probably write about in another blog post.

The big question however is, is it all worth it? I haven’t been running them for long enough really to give a definitive answer, but from the calculations I’ve done I think the answer is a resounding yes. The feed in tariff is index linked, so will increase over the 20 year lifespan of the panels along with inflation, and it is highly unlikely that the price of electricity is going to go down, all of which means that I should have paid off the panels totally in under 8 years. I can see that number dropping quite a bit too as electric prices increase. Also, the feed in tariff runs for 20 years, but the panels should last even longer than that and are still 80+% efficient after the 20 year mark so should be providing free electricity for many years after the feed in tariff has finished. Over a 20 year period, the initial investment should see a return of over 12% which is so much more than any bank can offer.

If you can afford to get PV installed, I’d definitely recommend it. I’ve already seen a drastic drop in my electric usage and the money is much better installed on my roof than in the bank.