Planning Your Solar Home Heating System

Solar heat energy has a lot of practical uses, including creating electricity via solar photo voltaic panels, or heating hot water via solar water collectors.  A popular use is to heat a home or a shop during the winter.  Since there are so many Instructables about building and installing different types of systems, I thought an Instructable about the planning process might be helpful for all the DIYers out there!  This Instructable is mainly geared towards people who want to install a store-bought system themselves. 

Home heating requires using good quality solar collectors.  Vacuum tube solar collectors are frequently recommended over flat plate for winter heating, because they work better and more reliably in the winter- which is when you need the most heat!  You will need to use a larger sized system for winter space heat. If winter heating is your goal, I'd recommend choosing larger collectors instead of many smaller collectors just to make the installation process easier.  For example, choose 4 x 30 tube evacuated tube collectors versus 6 x 20 evacuated tube collectors.

When you're trying to determine what size of system or what size of collectors you are going to use, remember that you probably won't fill 100% of your space heating requirements with solar, even with a huge system.  Try and target a reasonable goal, such as 50%, as that will provide a better performing system for a fraction of the cost.  There is no exact science to sizing a solar space heating system due to variables such as the insulation value of the home or shop, the outdoor temperature, and the amount of sunlight received during the winter. One 30 - tube vacuum tube collector is generally recommended for every 300 square feet of space to be heated.  In warmer climates might be able to heat 400 square feet with one collector, but colder climates might only be able to heat half that space with one collector. 

The next decision you need is make is whether or not you want to store the solar energy. Two options are Live Photo Voltaic systems, which use batteries, and solar thermal systems which use water tanks to store the heat energy.  The more energy  you want to store, the larger the water tank you'll need. Multiple tanks can also be used. The advantage of storing heat energy is that you can use it during the night or during periods of little sunlight, so you can maintain an even temperature.  Unfortunately, solar storage tanks are expensive, and can make up nearly half of the total cost of the system.  If you don't want to store heat energy and instead dump it into the home or space as it is available, you might find the temperature during the day becoming hotter than required.  Another option is to use a concrete slab to dump the heat energy, which is becoming more popular as people are adding radiant floor heating to their homes or work spaces. The solar energy can be dumped directly into the slab to be slowly released through the day, for more even heating.

To maximize your investment into solar, you should position the collectors facing south. If you are using vacuum tubes, it won’t make much of a difference if you face them south-west or south-east, since they absorb energy from all angles.  For solar heating in the winter, the optimal angle is the latitude of the location, plus 15 degrees.  In most of Canada, this would be 55-65 degrees.  However, snow can become a problem in winter heating, so one strategy to handle that is to mount the collectors on a wall instead of a roof. That way, you can mitigate the chance of snow building up on the collectors and decreasing the systems performance.

Obviously, there are a lot of important components to building a solar space heating system. Once you've decided on the basics of your heating system, some of the components you'll need to choose include piping, solar heating fluid, pump stations, controller, and expansion tank to complete you solar space heater. For this step, the best instruction I can offer is to do your research. If you want to build something yourself, there are a ton of great resources on this site. If you're buying parts of the system, make sure you're buying quality. Here's a breakdown of some of the common components: 

1. Piping- A solar system can reach get hotter than 400 F, so you should never use PEX piping on the loop. Only copper or special solar stainless steel piping should be used. Flexible solar stainless steel piping is commonly recommended because it's easy to use and comes pre-insulated with sensor wires, which makes installation much easier. This type of pipe uses special ceramic gaskets that can withstand temperatures up to 600 F. These system don’t require soldering, so they're great for people who aren't experienced with plumbing. 

2. Solar Heating Fluid- In order to move the solar energy from the collectors to the home, you need special glycol heating fluid.  Glycol heating fluid is used instead of water so that the system will not freeze in cooler temperatures.  Choose a glycol heating fluid designed for solar applications, so it can withstand the high temperatures that a solar heating system can reach.

3. Pump Stations- The pump station is the main mechanical component of the solar heating system.  The pump is use to circulate the heating fluid from the collectors into the home.  The pump station also contains other key components, such as fill and drain valves, the air purge valve, shut off valves, the flow meter, and the safety pressure release valve and expansion tank connection.

4. Expansion Tank- The expansion tank is an important part of a solar space heating system, but it often gets overlooked. The expansion tank is used to buffer the volume of heating fluid in the system as the heating fluid expands. The hotter the system, the more the fluid will expand, so it's pushed into a pressurized rubber bladder found in the expansion tank.  As the system cools off during the night, the expansion tank pushes the fluid back into the system. This way the system volume can change from hot to cold without being damaged. 

5. Controller- The solar controller is a differential controller, and measures the temperature of the system at different locations, and activates or deactivates pumps based on solar heating logic.  The controller will measure the heating fluid in the collector via a temperature sensor and compares this to another sensor in the storage tank or in the home heating loop.  If the collector is hotter than the second reference sensor, the solar pump will be activated to move the heat fluid to the heating zone. If the temperature in the collector drops below the reference sensor then the pump will stop, since there's no solar gain to be had.

Once you have your system planned out, the last step before actually building it is planning what to do with the heat in the summer.  A good solar space heating system will provide you with heat in the winter, but what about during the summer when you don't need that heat?  This can result in the system constantly being overheated, unless the heat is used up somehow.  One way is to use the space heat to heat a pool in the summer.  If you don't have a pool, the only option for space heating systems is to cover the collectors for the summer. Collector manufactures make customer covers which are designed to shut down the collectors in the summer.

That's all the tips for planning out a solar heating system I have for you; I hope you found them useful!