Opportunistic PV Charging

 What should be known is for PV, it's critical to capture energy at the exact time interval that it is being produced most abundantly within any given day.

So it's widely known that solar and wind renewable energy is intermittent. While that presents a challenge, it can be overcome with engineering and process changes.

The main consideration is that on a perfectly sunny day, PV will generate it's highest amount of electricity between 10AM and 2PM. A brief 4 hour window can stand between you and a comfortable night of sleep. On an overcast day, this issue is particularly known.

Therefore it behooves all of us to generate as much electricity as possible between these hours. But there are several things that will keep your PV system incapacitated during these hours:

• Snow cover
• Inadequate wiring gauge (fire hazard)
• Inverter pulling more power than can be generated in the time window
• Batteries already at full capacity
• Break in the cloud cover comes earlier or later in the day (not between 10AM and 2PM)

If each of these things can be avoided or insulated against, it will be the difference of several kWhs on a 5 kW panel PV system.

Charging Batteries Outside

So there's plenty to say about adding more solar panels to my rooftop build. But summer really doesn't need a bunch of added solar panels since PV production is at it's highest. I will probably have more to say about how much solar and storage I have closer to winter.

This update is to say, while we still use lithium battery cells, we should probably be charging them outside. I've even heard that sodium ion cells also have a risk of shorting at the end of their cycle lifespan. So here's a picture of my outdoor enclosure I cobbled together. The batteries and inverter are in this same enclosure with electric lines coming in and going out:

Winter Solar

Since my last post, winter has come and gone, and I added another half a kWh of lithium ion battery storage. Here's the big surprise.

It's comparatively difficult to generate solar energy in the winter than the summer. I could easily charge a kWh battery in the summer months. But in the winter even on a sunny day, I would do well to generate .25 kWhs.

One of the problems is snow cover. It's right outside my window, so it's fairly easy for me to scrape snow and ice off the panels. But it was a cold winter and it's not pleasant scraping ice off solar panels in the wind chills of winter.

The sun does melt some of the snow off the panels. But the black color of the panels doesn't melt as much snow as you'd like. Essentially a small pocket of air forms off the surface of the glass which makes it an insulator from the heat that would normally melt the ice.

The moral of the story is to spec your solar array for 1/4 performance during the winter months.

12V DC Heating Elements

 This is a follow up on a previous post concerning survival level applications for PV and battery packs. The idea here is to find the lowest price to give people warmth and light using minimal circuitry.

I won't go into the weird sauce of how I connected my battery. But the big idea there is that I'm not using any inverters for me DC heaters. Inverters and even voltage regulators introduce inefficiencies and we want people to get as much bang for the buck as possible.

First of all, here is a picture of the heating elements for under 20 bucks on Amazon:

Second, these elements get very hot... like over 140 degrees F... enough to make food safe to eat.

With that out of the way, the logic of the system is this:

1. A 400 Watt solar array charges a .25 kWh battery pack in less than an hour in full sun (using a BMS circuit to step the voltage down)

2. The 12V 100W heating elements will then drain the battery overnight providing more than enough heat for a single person (not enough to heat a 12' x 12' room) for about 2.5 hours

So following this logic we could say 4, .25 kWh battery packs would be more than enough so that one person could sleep comfortably all night and even into the day (8 to 10 hours).

Let's talk money. The battery pack costs $35 for .25 kWh of energy. The heating elements cost $20. The solar panels cost roughly $250. So all in, this system cost me $310. If we wanted it to last all night, we're looking at more like $350.

So for $350 a person could sleep comfortably overnight every night for 5 years. Then it's just the cost of replacing the battery pack after that (maybe $40), for another 5 years of service.

But you may have noticed that the solar panels were only put to work for a single hour... so this person would have 7 more hours of daylight to use the panels for other systems. I'm thinking the heating elements could be plugged in directly to the solar panels during the day to provide daytime heat during colder months. Essentially this person could survive under a canopy in a sleeping bag in Yellowstone National Park all winter long... provided they had food for $350.

400 Watts of PV w/ Grid Inverter

 Something very news-worthy has happened in the past 6 months. There is a glut of PV panels manufactured and now the price has come down as retailers try to shed their inventory. I could at this moment go on the internet and find a 100 Watt PV panel listed for $50. So naturally I sprung for 3 new panels and put them on my roof.

As you scale up your home brew rooftop PV installation, there are problems to look out for. First of all, wires and connectors will get hot. But then the grid inverter itself will get hot. 

One thing to look out for is loose and frayed connectors. If the electrical contact surface area is small and a lot more current is pushed through that contact, it will heat up more than the rest of the wire. So essentially beef up your wires and connectors as you scale up your system.

Let's talk money. So the three new panels were a little over $180 and the first panel was $100. So $300 in and then another $200 for the grid inverter brings us to a total of $500 DIY rooftop solar installation. Now we could talk ROI which is something like 5 years, but that's a bit boring for a normal person's income.

Far more exciting is what doors 400 Watts (in the middle of the day) of electricity opens. Easily, this powers computers and laptops and TVs... but that's a 1st world problem and not very interesting. I've been looking into heated flooring and heated blankets and you can easily find a 100 Watt system like that.

What this means is to heat a room overnight, a 400 Watt system would easily charge a 1 kWh battery pack and that would heat a room for 10 hours overnight and have energy to spare to heat during the day. Presently I am working on a battery pack made from surplus cells costing $50 for a kWh and more to come on that.

Grid Tie Inverter

 The second most useful and readily available piece of equipment for those looking to generate their own electricity, is a grid tie inverter. The first most useful is just to get a couple 100 Watt solar panels.

The grid tie inverter I guess senses the frequency and phase of the AC current in your house or apartment and sends the current to the meter in reverse. Today I watched my meter go backwards after hooking one up.

Now the thing is, it will probably not be enough current to kick you back a check from the energy company. However, it will certainly reduce your electricity bill. Additionally, your account with the energy company would need to be enabled for net metering to be eligible for kick back checks. This usually comes at a monthly subscription cost. 

So up front, until you have 10 x 100 Watt solar panels or more, this piece of equipment can out of the box be used to reduce your electricity bill. The one I purchased was the "SolarEpic" 1300W grid tie inverter.

12V DC Water Pump and Solar

 One of the most visceral applications of solar power is when you watch a solar panel directly power an electric water pump. You can watch when the clouds come over and the flow lessens and then when the sunlight breaks again how it rushes the water with renewed vigor. As fun as it is to watch, let's talk about real world applications and how it might fit into your residential experience.

There are many reasons to pump water. Certainly in the more arid regions of the globe, it helps tremendously. But for the rest of us, it doesn't pay to sit there waiting on the sun to wash dishes or take a shower. Probably the most famous renewable energy application for pumping water is "pumped storage hydro". Again, this isn't on the residential level, but it can be scaled fairly easily.

Most likely, you may have a hydroponic system for growing indoor plants or perhaps an ornamental water fountain in your yard. But let's just take it from the perspective of water pressure and moving water from one elevation to another. 

New York City was famous for this issue as they would have water towers on top of the apartment buildings. This elevation of the water would allow the residents to have the water pressure they needed. In fact they still do use water pressure to move water from reservoirs into the city through underground tunnels.

Using a solar panel that produces ~40W (peak) of power at 12V, I can pump water for about 8-10 hours straight. With that much power I could move about 10 gallons of water every 30 minutes from 0 feet, to 10 feet of elevation. Let's say all that water is shower water. At the end of the day about 16 people could have water pressure for their shower they are going to take that night. And that is just running of 40 Watts of electricity. 

Now the next thing will be, "ok, having water pressure is great, but can it be warm/hot water". So then I have to get a 12V water heater and tell you how that works out and whether 40 Watts of solar panels is enough to provide enough water pressure and heat to take a comfortable shower at the end of the day.