2022 Main article: Solar PV and thermal energy storage

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

2022 Main article: Solar PV and thermal energy storage

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

Tell us about yourself and your role at GreenPWR.

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

GreenPWR started after I left my previous job in mobile to study for my 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 co-founders at GreenPWR) and started working on a renewable energy storage system using PV for hot water. After that short project period of 3 months, we had a working prototype. It was clear that this was a feasible product to market and upgrade renewable hot water production, so we proceeded to bring it to market with our 2 additional co-founders.

Where are we with Solar Thermal? How has technology advanced PV hot water production over the last few years?

Innovations in solar thermal systems have reached a high level. Simple thermosyphon systems with a roof tank are available, although installation practicality is limited. Any temperate climate where freezing is possible will require a more sophisticated closed loop system with plumbing from the roof through the house, a specialized hot water tank with a heat exchanger and a pump. These components have potential failure events that are catastrophic for the solar thermal system. Any plumbing can leak. Overheating is another concern when little water is used or if the pump fails.

PV has seen prices drop over the years. This has allowed PV-based systems to become more viable. Some companies have started building products to support this specific use case, although this is still in its infancy.

What are the advantages of producing hot water with PV?

Hot water with PV offers several practical advantages over traditional solar thermal systems. Installation is much simpler. Wires are used to transfer power from the PV array to the inverter instead of a heat transfer fluid through the plumbing.

There is no risk of overheating with a PV system because the energy is collected through electricity. The overall system is optimized for installation using off-the-shelf components. An electric water tank for an existing immersion heater, PV panels, mix value, quick disconnect and SunHopper-D are must-haves. This dramatically increases installation speed and keeps costs down.

The cost of PV panels has come down over the years. This allows the SunHopper-D system to exceed the cost of solar thermal systems and is much simpler to install, making it an upgraded method of solar domestic hot water production.

Additional roof space is indeed required when using PV instead of solar thermal 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 product and how thermal energy storage is done inside the house with a hot water tank.

Energy conservation is a fundamental requirement as we transition to renewable energy sources. Thermal energy storage is very efficient, has high energy density and very low cost. Looking at the hot water heater as an energy storage device, we see that almost all homes have this means of energy storage.

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. Supported panel layouts are three to six 60 or 72 cell panels, but a typical installation will require 4-6 PV panels. As a rule of thumb averaged over the year, one PV panel produces 7-12 gallons of hot water per day.

What is the SunHopper algorithm? How is it beneficial and how is it the key to combining solar energy with low cost thermal storage for future use?

Using hot water as an energy storage medium is not the same as using a battery. The homeowner expects the water to be hot when needed. Our patent-pending SunHopper algorithm monitors several aspects to ensure that minimal energy consumption is used to ensure hot water is available. These include local weather forecasts, past water use, expected water use, installation shade conditions, timing of electricity use, and the condition of thermostats inside the water tank. Using this array of inputs, the SunHopper algorithm is able to maintain a balance between energy savings and hot water availability.

Where do you see SunHopper being installed? Share some features and benefits with us.

SunHopper is designed to provide as many deployments as possible. This can be a complete off-grid setup where only a dedicated PV array is provided. The system can also be installed with a grid connection that can be used as a backup power source, or have a fossil fuel backup using natural gas or propane. In the case of fossil fuel storage, this will result in the installation of 2 tanks where the SunHopper can pre-heat water for the fossil fuel storage phase.

In the general off-grid situation, 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 sinks in a small cabin or in remote locations (such as bathrooms on a hiking trail).

Most common installations will require some backup power source to cope with weather fluctuations. The average home will be able to reduce energy consumption by an average of 60% to 80% for hot water production. The average single-family home uses 17% of its energy consumption to produce domestic hot water¹, so this is the second largest consumer of energy in the home, which SunHopper-D can demonstrate great energy savings.

Why is the phone app feature for monitoring and why do you think it is so important to offer monitoring?

Our phone app allows remote monitoring, performance monitoring and system control in a convenient estate. Our phone app helps to show the energy produced by the PV and the energy consumed by the grid if you are using an electric backup.

Controls are also provided to optimize hot water production. Our algorithm has several settings: our normal mode, eco mode, high demand mode, and vacation mode. Normal Mode balances energy efficiency with hot water availability using previously learned usage patterns. Eco mode is more aggressive in saving energy, although the supply of hot water may be short-lived if there are fluctuations in use. High demand mode can be controlled when needed, for example if a family member is visiting and extra hot water is required. However, this will consume more storage power. The holiday mode turns off the storage power in the tank and only runs on the PV panels to reduce power consumption. These settings help the user choose the best plan and optimize the balance of energy savings and hot water availability.

Tell us about your future vision and future product path for energy storage.

GreenPWR focuses on the need to combine renewable sources with energy storage systems. Our next product will also use a domestic hot water tank, but will use an existing PV installation and intelligently direct energy to it using our SunHopper algorithm. This allows a clean install for those who already have solar to add energy storage without a very large battery. There are current products in Europe that end this problem, although our advantage with our algorithm will be pushing the envelope.

In addition, we are looking at what other measures can be used within the home as energy storage devices as well as demand side management to help with energy consumption levels in the home. These next concepts expand and fill the current void of connecting energy-consuming devices with energy-producing devices. These are interesting and exciting ideas that we are working on to maximize our own consumption.


  1. US Energy Information Administration. Energy usage explained. June 23, 2021: https://www.eia.gov/energy explained/energy use/homes.php:
The content and opinions of this article are those of the author and do not necessarily represent the views of AltEnergyMag.

Comments (0)

This post has no comments. Be the first to leave a comment below.

Post a comment

You must be logged in to post a comment. Log in now.

Recommended products

Canadian Solar - HiKuBlack - Black Back and Frame (Mono)

Canadian Solar – HiKuBlack – Black Back and Frame (Mono)

Aesthetic appearance of residential systems. with black plate and black frame, power range 380~405W, low power loss in cellular connection. Enhanced reliability. · Low temperature coefficient (Pmax). -0.34 % / °C, LID LeTID less than 2.0, Lower hot spot temperature, Better shade tolerance.


Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top