This is part of a larger project to eliminate propane (LPG) use and was installed in the timeframe of February 2020 - May 2020. My goal is to show you that we can solve the climate change / greenhouse gas problem without giving up our lifestyle. In fact, we can improve our quality of life and save money at the same time by switching to renewables. If I can inspire you to also make the switch, then we will all benefit.

Here's the old system, there's a propane boiler crammed into a tiny space where it is difficult to work and will often overheat components (such as zone valve actuators and transformers) to the point of failure, resulting in a cold shower. I lost count of the number of mornings when I shuffled disgruntledly down to the boiler room with tools in hand to fix the hot water problem.

The boiler indirectly heated this hot water tank via circulating fluid:

Since the water heater is in plain sight in the house, where I walk past it multiple times a day, I decided to make it into functional artwork. I was thankful to receive this picture for inspiration:

When the tank arrived via a freight shipment, the shipping box looked perfect. However, after opening it up, we saw that it had a big dent. The tank is a Bradford White 50 gallon unit. Here's the dented area after pulling out most of the dent:

Interesting thing about water heaters - they have sacrificial anodes and some of them are made from aluminum - good reason not to drink out of the hot water tap. This one came with a magnesium anode. Another consideration is that the failure mode for hot water tanks is generally to spring a leak and flood your house. So after much deliberation, a WAGS valve was installed to shut the water off automatically the day that happens.

Here are some flood protection devices:

Floodstop
http://www.getfloodstop.com/

Taco's version of Floodstop
http://www.tacocomfort.com/products/leakbreaker/index.html

Watt's version of Floodstop which also kills power to the water heater:
https://www.watts.com/products/plumbing-flow-control-solutions/leak-detection/lfwds

Here's what I used - it's purely mechanical, very simple, and needs no maintenance until the day it activates:
https://www.wagsvalve.com/

I went with stainless pipe because I did not want to look at oxidized copper every day, and my pipe sweating skills suck. However, this adds a substantial amount of cost and it requires dielectric unions. You generally don't want to be combining different metals together in plumbing or wiring systems, or they will corrode and you'll have problems.

Stainless pipe doesn't come all nice and shiny, you have to polish it. A wire wheel on a bench grinder is not a very good way to polish pipe - takes a long time and doesn't provide a very good finish:

This, however, is a great way to polish a pipe: a drill + a rollerblade wheel jig + sandpaper:

Finally the big swap day arrived! It was a real pain removing the old tank because it had no drain valve so I had to siphon out the water. It reminds me of Sputnik!

And here's the new unit in place with just a few little leaks to fix:

In that picture, the tank is running off grid power. The big idea here is that this is a dual-element heater. The top element will be connected to the power grid, and the bottom element will be connected to the photovoltaic (PV) panels. This makes it into a hybrid system, where most of the heat is provided by the sun, but it still has a backup power source when needed.

If you look closely, you will see a knob on the top which is part of a Honeywell mixing valve. You dial it to get your desired output temperature and it mixes in cold water to achieve that. This lowers the delta T in the pipes for less heat loss and lets you store more energy in the tank without worry about scalding.

With that tank in place, we canceled our propane service and burned off the remaining 350 gallons with the hydronic heating which we don't normally use.

In order to prepare for the PV panel installation, I cleaned up some surface rust on the roof and replaced roof screws (the rubber gaskets go bad after a while). Look, it's a cow:

The other consideration was some lightning protection. Why? Because this house is in the sky:

Here is the trusty Hilti sitting on the end of a 5/8" diameter, 8' long ground rod after driving it into the ground:

Now you could just use ground clamps to bond the lightning conductor to the ground rod. However, there's a much better way to do it: thermite! This is one such product - it is a disposable mold and thermite kit. It can be a little tricky to get right but generally does a great job and is like lighting off fireworks:

I found that you can take a giant step up from the CADWELD one-shot mold and get reusable graphite molds such as this:

These reusable Erico molds produce excellent results and they are easier to set up:

This beats a mechanical ground clamp any day:

The solar panels arrive via a freight shipment and they are (amazingly) completely undamaged:

These are REC panels for a combined total of 1220W nameplate capacity. Not 1.21 jiggawatts but 1.22 kilowatts. The price was $0.61/W before any tax credit, although the shipping cost was substantial. Remember to take into account your region's capacity factor when calculating how many panels you need.

These are connected in series for a maximum voltage of about 159v and maximum current of 9.17A. The wiring I'm using is 10AWG, which can handle 30A or more. With these panels, the circuit could be fully shorted out when the panels are putting out peak power, and the wires would take the current like it's nothing, so no fuse or circuit breaker is needed to protect the wiring, which also means less worry about fire from this system than a standard grid-powered circuit. The oversized wire will allow future upgrades without needing to pull new wires.

There's one more trick to making this system safe, and that is this DC-DC converter / MPPT tracker board: http://techluck.com/

That board converts straight DC into "pulsed DC" which provides a zero-voltage interval, allowing the standard water heater thermostat to be used. Using a straight DC input into your water heater thermostat will burn out the contacts. Electric water heaters are made to be powered with AC voltage. AC switchgear depends on that zero-crossing to quench the arc.

Normal electrical switches use air to insulate the open contacts from each other. When the switch opens, there is an arc/spark across the contacts. That spark is ionized air, and when air is ionized it is actually a good conductor. So as those contacts move farther apart, the spark gap grows and it allows the ionized air to stretch out and maintain current flow - until we hit the zero-crossing of the alternating current waveform and the arc is extinguished, thus opening the circuit. Well, with DC (direct current) there is no zero-crossing. So DC switchgear has to account for this, and usually that means a larger spark gap between switch contacts.

The "techluck" board provides the zero crossing by pulsing the DC output so that the standard AC thermostat can be used. It also provides MPPT or MPPT-like capability to help match panel output with the load, which optimizes the system.

Originally, I wanted to wire the panels straight to the water heater element with no electronics, but couldn't come up with a reliable and practical way to switch the DC voltage. Panels are cheap enough now that the efficiency loss of having no MPPT can probably be made up for by adding one or two more panels on a system this size, and a single one of these panels is cheaper than the "techluck" board itself.

Why does safe switching matter? Because if the water heater overheats and the T&P valve fails, the water heater will explode and launch itself through the roof of your house. See the Mythbusters "water heater rocket" episode. Don't think for a moment that you can just size the system so that it never has to switch off because one day nobody will take showers and it will overheat. You're dealing with a lot of stored energy, so don't screw around.

A bit more electrical:

The bottom heating element is PV and the top element is grid backup for cloudy days. The top thermostat is set to a tolerable limit and the bottom thermostat is set as high as it will go (seems to be about 140F). The heating elements in a water heater are simply resistors, and a resistor is a resistor, it doesn't matter whether it's powered by AC or DC. The standard 240v elements come in a variety of resistances. These are 4500W.

Ohms's Law:

I=P/E = 4500/240 = 18.75A when powered from the grid.
R=E/I = 240/18.75 = 12.8 ohms fixed resistance of the heating element.

Remember that volts "push" amps. If we apply 150v from the panels, assuming infinite current available, I = E/R = 150/12.8 = 11.7A maximum current that can flow. The panels put out about 9.17A max, so in theory we will be pushing max power through the heating element at peak voltage even without MPPT.

OK, on to mounting systems. It is amazing how far PV has evolved from 2010 to 2020. Several incremental changes to panels and racking systems/mounts were made over the years that add up to much lower costs, easier installation, and higher quality results. For this system, I used S-5! roof mounts and aluminum extruded rails from IronRidge. You basically add the roof mounts for your type of roof, mount the rails to them, and screw the panels down from the top. You never need to get behind the panels. The panels just plug together in series (wires hanging off the back) so there's no need for splicing and there's no junction boxes on the panels like the old days. This is also good because you can safely plug the panels together during the day.

If you have a standing seam metal roof, you can get brackets that mount the panels flat directly to the standing seams so you don't even need rails! In this case, we have an exposed fastener roof so the mounts are screwed right down to the rafters:

This roof is pretty flat, so in order to approach the desired 40 degree angle for this latitude, I bought tilt-mount brackets. I had to shorten one side - for some reason if you buy a 10" tilt leg kit, it comes with an 8" or so leg on the other side which defeats the purpose. Here is a picture of my shortened version:

I ended up with a 25.5 degree tilt, which is not optimal, but we also regularly get 100mph wind gusts in the winter so I am OK with this for now. The roof is also not completely south facing (it's a bit southwest):

Here are a couple of cool little bits of hardware. The screw-like things are called "UFOs" - Universal Fastening Objects. Notice that they have sharp little edges under the head to bite through the oxide layer on the panels, which provides electrical bonding capability so that you don't have to run an extra wire to ground the panels. They have loc-tite preinstalled. The UFOs tie the rails and the panels together so you only need one ground lug attached to one of the rails. The black parts are for the ends where there is a panel on only one side of the UFO. These are installed from the top, you don't need to slide them into the extruded aluminum slots from the side.

Here you can see there are just 4 UFOs per panel:

Now for wiring... I used 1/2" EMT conduit because it looks neat and provides some lightning protection. Here, 3 LBs saved the day to get around this crazy corner:

Here is an Eaton DC disconnect switch rated to 600VDC. This provides a reliable way to turn off the power without entering the same room as the water heater (for example, when the tank fails and spills water). It was overkill, but will allow me to upgrade this system later if I want:

The wire used from the panels to the disconnect switch is PV wire. Here's what 10awg PV wire looks like compared to standard 10awg THHN - the PV wire is the thicker one:

These panels use a connector that is called "MC4" and in order to get a good connection, you should use a proper crimp tool. They aren't cheap though, but when you use one, it's an absolute delight and the results speak for themselves:

Here's a look at the wiring clips and MC4 connectors:

Here's the conduit with single gang junction boxes. Each box has raintight EMT connectors, and sealing strain relief units for the PV wire to exit through:

Here's the inside of the box above the water heater. It contains the DC-DC converter board, disconnects, a gauge, and ground splices. The big box functions as a heatsink for the DC-DC converter board, and provides space for future upgrades such as additional control systems.

Surplus voltmeter from eBay:

Here's where the magic happens:

The photovoltaic panels provide the power to heat slowly over the whole day (much less power than the 4500W from the power grid) and then the water stores the heat energy until the next day. If there isn't enough stored energy in the tank, the top grid-powered element will kick on to help out.

Now you might be thinking "why PV, what about solar thermal systems, such as evacuated tubes?" Solar thermal isn't cost effective anymore since PV is so cheap. PV also has no moving parts, no fluid to change or leak, and no pumps to wear out.

OK, now let's dive into performance and costs...

When I originally calculated how much this would cost, I didn't realize how quickly the costs of all the little bits of hardware and stuff add up. The figure thrown around is that the panels are 1/3 of the system costs and I found that to be roughly the case here. It takes about the same amount of work to wire up one panel vs. many panels so it makes the most sense to go as big as you can. In this case, I was limited by the DC-DC converter board - it can't handle much more than 1200W.

With the 2020 tax credit, you can deduct the cost of all parts of a complete and working system including shipping costs, and this will get you a maximum of 26% of your tax money back. How often do you get to choose how your tax money is spent?

Another idea is that you can pick up pallets of used PV panels that still have plenty of life left in them. Most seem to go for $0.50/watt which is way too much money but I've seen asking prices of $0.25/watt on craigslist - at that price, if you have the space for those older lower efficiency panels, then it might make sense to get some of those.

For electricity costs, we pay $0.11/kWh which is pretty cheap. As far as the propane costs go - check this out - these are the most recent propane bills that we have where the boiler was mostly heating water:

That's $753 in a time when propane was cheap. And propane prices are quite variable; we have paid upwards of $4/gallon in the past. Electricity prices are very stable by comparison. The propane use also translates to an absolutely ridiculous amount of emissions. Compare the $753 for only 4 months of propane-fired water heating to the estimated $411 for a full year of electric water heating (below) and the estimated $109 for a full year with this hybrid PV system (below). Compared to propane, this system will pay for itself in less than 3 years. For those who already have an electric hot water heater, I included break-even estimates below.

By the way, we had other propane-fueled appliances that we switched out for electric in 2019. Simply switching from fossil fuels to electric already results in less greenhouse gas emissions, and that improves daily as more renewables are added to the grid.

This chart gives you an idea of the energy consumption - the new water heater was on purely grid power for about a month, then the PV went live on May 10^th, and you can see how that reduced the rate of energy use from the grid:

Benefits summary:

• Much lower greenhouse gas emissions.
• No propane means no potential for gas leaks or CO poisoning, no exhaust smell outside, no noise, and no propane tank eyesore.
• Reliable, low maintenance.
• Redundancy (hot showers when the power is out).
• Lower cost.

Cost Summary in USD:

Cost details / approximate Bill of Materials: