2022 Top Article – Solar PV and Thermal Energy Storage

Energy storage is an essential requirement as we transition to renewable energy sources. Thermal energy storage is very efficient, has a high energy density and a very low cost.

2022 Top Article – Solar PV and Thermal Energy Storage

Q&A with Mitch Hodges, Co-Founder and CEO | GreenPWR

Tell us about yourself and your role with GreenPWR.

Mitch Hodges – Co-Founder and CEO, GreenPWR. I am an electrical engineer with previous experience in mobile devices, IoT devices, smart lighting systems, and now in renewable energy devices.

I started GreenPWR after I left my previous mobile job and studied for a Masters in Sustainable and Renewable Energy at the University of Nottingham. During my studies, I met the Hockerton Housing Project team (currently one of our founders at GreenPWR) and started work on a renewable energy storage system using PV for hot water. After that short 3 month project timeframe, we had a working prototype. It was clear that this was a feasible product for the market and updated renewable hot water production, so we went ahead with bringing this product to market with a couple of additional co-founders.

Where are we with solar thermal energy? How technology has developed hot water production via photovoltaic over the past few years.

Innovations in solar thermal energy systems have reached a plateau. There are simple heat press systems with a rooftop tank, although the installation process is limited. Any temperate climate where freezing is possible will require a more complex closed loop system that has plumbing from the roof through the house, and a specialized hot water tank with heat exchanger and pump. These components have potential failures that are catastrophic for the solar thermal system. With any plumbing system, leaks can occur. Overheating is another concern if there is little water use or if the pump fails.

PV has seen a price drop over the years. This has allowed PV-based systems to become more viable. Some companies are starting to create products to support this particular use case, though this is still in its infancy.

What are the benefits of generating hot water by photovoltaic?

Hot water via photovoltaic brings many practical advantages over conventional solar thermal systems. The installation is much simpler. Wires are used to transmit power from the PV array to the inverter rather than heat transfer fluid through the plumbing.

With a PV system, there is no risk of overheating as the energy is collected by electricity. The overall installation system is optimized using ready-made components. Items required are the electric water tank on the immersion heater, photovoltaic panels, mixing value, quick shut off device and SunHopper-D. This greatly increases installation speed and keeps costs down.

The cost of photovoltaic panels has decreased over the years. This allows the SunHopper-D system to beat the cost of solar thermal systems and be much simpler to install, making this a modern method of generating domestic hot water via solar energy.

Additional rooftop space is actually required when PV is used instead of solar because the collector efficiency is lower. Although this is the case, the benefits of the system still outweigh this downside.

Tell us about your SunHopper-D and how heat energy is stored using a hot water tank indoors

Energy storage is an essential requirement as we transition to renewable energy sources. Thermal energy storage is very efficient, has a high energy density and a very low cost. By looking at the hot water heater as an energy storage device, we see that almost all homes have this energy storage facility to take advantage of.

The SunHopper-D uses a hot water tank as an energy storage device. The energy is not recovered as electricity, but as useful heat for domestic hot water. A backed panel arrangement consists of three to six panels of 60 or 72 cells, however typical installations require 4-6 PV panels. As a rough rule of thumb on an average year, one PV panel will produce between 7-12 gallons of hot water per day.

What is the SunHopper algorithm? What makes them useful and how are they key to pairing solar energy with low cost heat storage for later use?

Using hot water as a means of storing energy is not the same as a battery. The homeowner expects the water to be hot when needed. SunHopper’s patent pending algorithm monitors many aspects to ensure minimal energy consumption is used to ensure hot water. These include local weather forecasts, past water use, projected water use, shade conditions for the installation, time to use electricity rates, and the status of the thermostats inside the water tank. By using this set of inputs, SunHopper’s algorithm is able to maintain a balance between energy savings and hot water availability.

Where do you see SunHopper being installed? Share with us some of the possibilities and benefits.

SunHopper is designed to support as many installations as possible. This can be a complete off grid setup as only a dedicated PV pool is provided. The system can also be installed with a grate that can be used as a backup power source, or have a backup fossil fuel using natural gas or propane. In the case of a fossil fuel backup, this may entail the installation of two tanks where SunHopper can preheat water for the fossil fuel backup phase.

In the off-grid aggregate condition, the SunHopper will store as much energy as possible in the hot water tank. The AC input can be connected to a battery backup inverter if needed to help supplement power from a larger array, although this is optional. This can work for a small cabin, or for sinks in remote locations (such as bathrooms on a hiking trail).

Most common installations require some backup power to weather the vagaries of the weather. The average home will be able to reduce energy consumption by 60% to 80% on average for hot water production. The average single-family home uses 17% of its energy consumption to produce domestic hot water, so this is the second largest household energy consumer in which SunHopper-D can show significant energy savings.

Why does a mobile app function for monitoring and why did you feel it was so important to provide monitoring?

Our mobile app allows for remote monitoring, performance monitoring and system control in a convenient way. Our mobile app helps to show the power produced by the PV and the power consumed by the grid if an electric backup is used.

Control is also provided to optimize hot water production. Our algorithm has many settings, such as normal mode, eco mode, high demand mode, and vacation mode. Normal mode balances energy efficiency and hot water availability using past learned usage patterns. Eco mode is tougher to save energy, though the hot water supply may run low if there are deviations in usage. The high demand situation can be controlled when needed – eg if a family member is visiting and extra hot water is required. This will consume more standby power. Vacation mode disables backup power in the tank and only works on photovoltaic panels to reduce energy consumption. These settings help the user select the best plan and optimize the balance between energy savings and hot water availability.

Tell us about your vision for the future with energy storage and the path to future products.

GreenPWR focuses on the need to pair renewable energy sources with energy storage systems. Our next product will also use a domestic hot water tank but will use an existing PV installation and divert power to this in a smart way using our SunHopper algorithm. This allows a clean install for those who already have solar power to add energy storage without a very large battery. Existing products already in Europe complete this task, although our advantage with our algorithm will push the envelope.

Furthermore, we examine what other media within the home can be exploited as energy storage devices along with demand-side management to help level the home’s energy consumption. These following concepts expand and fill the existing void in connecting energy consuming devices with energy producing devices. These are exciting and interesting concepts with which we work to maximize self-consumption.


  1. US Energy Information Administration. Explain energy use. June 23, 2021. https://www.eia.gov/Explanation of energy / energy use /home. php
The content and opinions expressed in this article are those of the author and do not necessarily represent the opinions of AltEnergyMag

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