Solving the Intermittency Problem of Solar Energy: Ground Source Heat Pump + PVT, No More Interruptions in Household Hot Water

1. Talking about the PVT System: One Device Doing Two Jobs, but with Quite a Few Issues Let's first talk about a common device in the solar energy field — the PVT photovoltaic-thermal system. You might not have heard of this name, but its function is very practical: it generates electricity from solar energy while simultaneously collecting heat to heat water. It's like one device doing two jobs, sounds cost-effective, right? But this thing has two major problems that seriously affect daily use. The first is "weather-dependent"; it can produce heat normally when the sun is shining, but on cloudy or rainy days or at night, it can't continuously supply heat. Imagine wanting to take a hot shower at night or during several consecutive cloudy days, and it can't provide hot water — very frustrating. The second problem is more hidden: when it generates electricity, it produces heat that can't dissipate, causing the back panel temperature of the solar cells to rise. When the temperature goes up, the power generation efficiency drops. What could have generated 10 kWh might only produce 8 kWh in the end, which is a loss.
2. The "Helper" to Solve the Problem: PVT + Ground Source Heat Pump, Complementary Advantages Is there a way to solve these two problems? There really is — by combining the PVT system with a ground source heat pump. Let me briefly explain what a ground source heat pump is: it doesn't burn coal or electricity directly to heat but uses the heat stored in underground soil. The underground temperature remains relatively stable throughout the year. In winter, it extracts heat from the ground to warm the indoors; in summer, it expels indoor heat underground to cool down, making it a very energy-efficient device. Combining these two brings immediate benefits. First, it solves the PVT system's "weather-dependent" problem. When the sun is shining, the PVT system can generate electricity and heat by itself, and excess heat can be stored; when there is no sun, the ground source heat pump takes over, continuing to provide hot water or heat, ensuring you always have hot water when needed. Second, the ground source heat pump can help "cool down" the PVT system. It can promptly remove heat from the back panel of the solar cells, lowering their temperature so that power generation efficiency is not affected. Moreover, the heat collected by the PVT system can serve as the "heat source" for the ground source heat pump, making the heat pump work more efficiently — a win-win.

3. Disassembling the Combined System: Simple Structure, Flexible Modes Let me break down the working logic of this combined system for you; it's actually not complicated at all. The entire system mainly consists of a solar collector, the ground source heat pump's compressor, evaporator, condenser, and a hot water storage tank. Simply put: a special liquid refrigerant absorbs heat in the evaporator and turns into low-temperature, low-pressure vapor; this vapor is compressed by the compressor into high-temperature, high-pressure gas; then the hot gas enters the condenser, transferring heat to cold water, which is heated into hot water and stored in the hot water tank for your use. There's a particularly clever design here: the solar collector and the heat pump's evaporator are combined into one. This way, the refrigerant can directly absorb heat and vaporize inside the collector without extra heat exchange equipment, simplifying the system structure and reducing costs. Also, this system has two working modes that can automatically switch based on actual conditions, making it very flexible. The first is the constant temperature heating mode, used most of the time. When the sun is strong, the system sets a water temperature (for example, your household's preferred 50°C hot water). When the water temperature in the collector reaches 50°C, the controller automatically opens the cold water valve, letting cold water into the bottom of the collector while pushing the already heated water at the top into the storage tank; if the temperature is below 50°C, the cold water valve closes, and heating continues. This repeated operation keeps the storage tank filled with hot water at the right temperature. The second mode is the temperature difference circulation mode, generally used after the storage tank is full. If the water temperature in the collector is higher than in the tank, the circulation pump automatically starts, drawing cooler water from the tank into the collector for reheating, then sending the hotter water back to the tank. This maximizes the storage of solar heat without waste. When you use hot water and the tank water level drops, the system automatically switches back to constant temperature heating mode, making it very convenient. Also, the two devices don't always have to run together. If the weather is good, the water temperature in the collector is high enough, and your hot water usage is low, the ground source heat pump doesn't need to start; you can directly use the hot water from the collector. At this time, the system only consumes a little electricity to maintain basic operation, achieving very high thermal energy utilization efficiency. But if there's no sun, or the collector's water temperature is insufficient, or your household suddenly uses a lot of hot water and the tank water is insufficient or not hot enough, the ground source heat pump automatically starts. It heats the water in the tank to the set temperature, ensuring you have hot water; once the water level and temperature in the tank return to normal, the heat pump automatically stops. Although starting the ground source heat pump consumes more electricity, it saves much more compared to directly using electric heating, saving a lot on electricity bills in the long run.

4. Want to Use This System Well? These Issues Must Be Noted However, to use this combined system well, several points must be noted, or problems can easily arise. The first is heat storage. Solar heat is not always available — it's there during the day but not at night, more on sunny days and less on cloudy days. Therefore, the collected heat must be stored promptly. If the heat storage equipment is inadequate or the storage capacity is insufficient, the heat collected during the day will dissipate at night, increasing the burden on the ground source heat pump and reducing energy savings. So choosing a reliable hot water storage tank or designing a reasonable heat storage plan is especially important. The second is installation constraints. This system requires installing solar collectors. If you live in an old community or your building was not designed with installation space reserved, installing collectors later can be very troublesome or even impossible. So if you want to install this system, it's best to plan ahead during house renovation or when buying a new home, reserving enough installation space. The third is system parameter adjustment. During operation, parameters like inlet water temperature, collector temperature, cold water temperature, and water flow rate must be adjusted to the optimal range. For example, the inlet water temperature can't be too high, or it will affect the solar panel's power generation efficiency; the water flow rate must also be controlled properly, as too fast or too slow will affect heat collection and transfer. If these parameters are not well adjusted, the system will either have low power generation efficiency or unstable heating, possibly wasting electricity. The fourth is the underground part of the ground source heat pump. Whether the heat pump works properly depends on the underground piping and geological conditions. Before installation, you must survey your home's soil and groundwater conditions, understand the heat transfer characteristics of underground rock and aquifers; then select suitable pipe materials based on these conditions, carefully design the pipe depth and layout, and strictly follow standards during construction. If the underground part is not done well, such as pipe leakage or low heat transfer efficiency, the ground source heat pump won't work properly, and the overall effect of the combined system will be greatly reduced. 5. The Combined System Is a Good Choice, but Planning Must Be Done in Advance Overall, combining the PVT photovoltaic-thermal system with a ground source heat pump is indeed a good solution to the pain points of solar energy usage. It not only solves the issues of the PVT system being unable to provide continuous hot water and the power generation efficiency being affected by temperature, but also makes the ground source heat pump operate more efficiently and helps you save on electricity bills. From practical use, after adding the ground source heat pump, the system can produce more heat with the same electricity consumption, showing a significant energy-saving effect. Moreover, whether it's sunny or cloudy, day or night, the system can operate stably without the problem of lacking hot water or sudden drops in power generation. However, if you want to install this system, you need to carefully consider the issues I just mentioned in advance. For example, whether there is space at home to install the collector, whether the local geological conditions are suitable for installing a ground source heat pump, and what kind of thermal storage equipment to choose. Only by planning these well can the system truly function effectively, saving you trouble and money.