top of page


An experiment in using the combination of animal heat emission, a compost heat recovery system, and a photovoltaic direct powered thermal battery with thermal syphon to warm a greenhouse for extended growing season.

As a way of showing our appreciation, we are offering the following benefits. Contribute $50 or more and we will send you a copy of Spilling My Dirty Laundry While Meditating On Spin Cycle by Cassandra Lasdin (co-founder of Purple Raven Farm) It's a just-released book of poetry that you are sure to enjoy. Contributions of any amount will give you the option to join our mailing list for this project, where you can receive regular updates on our progress through construction as well as its success in use and any other exciting news that may develop through this project. We will include photos and videos showing what we've done so you can continue to be a part of this exciting project. Sign up here to receive your copy and to join the mailing list.

Again, Thank you from the bottom of our hearts for helping to make this project a reality.

The Project.

The "GREEN-BARN" is an experiment in northern, cold climate greenhouse heating. Our goal is to utilize a combination of sustainable greenhouse heating techniques that we can demonstrate to others in cold climate situations as a viable and attractive option while expanding our growing season and increasing our food production.

Access to healthy, sustainable, low carbon footprint, locally grown fresh food in an age of a changing climate, and less resilient, carbon-intensive large-scale farming practices, is ever more important now. Our long-term goal here at Purple Raven Farm is to produce healthy food in ways that remain resilient under growing climatic, resource and economic pressures so that we can continue to produce food for those in need as we move into this future. The success of the GREEN-BARN project will be a huge step in that direction. 

Proven technology.  Heating indoor spaces and/or water, with animals, compost or solar panels not only works but is efficient. Proof is important for an investment like this and we are taking it seriously. Our research into real-life examples of these different systems has provided us with the information needed to design and build with confidence. Although we haven't seen all three heating methods combined, we expect exciting results. Scaling up the GREEN-BARN in the future with potential grants or loans could be made possible through the success of this project.

We got this, but we really could use some help. Please consider making a one-time contribution to help us make our project deadline of this fall a reality. We will be sure to pass along your gift through the growing of food, to those who are in need.

Your generosity toward this project warms our hearts. Thank you!!!


Please continue reading for all the nitty gritty details.


What goes in? what comes out?


First, let's describe the thermal siphon and thermal battery system that both the compost heat recovery bin and solar PV hot water generator use.

A thermal siphon is a method of passive heat exchange, based on natural convection, which circulates a fluid without the necessity of a mechanical pump. Hot water goes up, cold water goes down. We heat water, and it naturally circulates through pipes laid out in our raised beds. As the heat in the water is absorbed by the thermal mass of the raised beds, it cools. When it cools it returns to the solar or compost heater and is heated again to keep the cycle going. As all this is happening, the raised beds in the greenhouse are warmed creating a thermal battery that in the case of the solar PV hot water generator, stores the heat produced during the day and releases it during the night keeping the greenhouse at a much warmer temperature even after the sun has set and outside temperatures drop.


Compost heat recovery bin.

Goats eat plants, then poop in the goat barn. We scoop up the poop, place it in the compost heat recovery bin and close the lid. As this breaks down it generates heat, we collect the heat and distribute it to the greenhouse beds through pipes using a thermal siphon and thermal battery system. Compost generates heat 24 hours a day because it is not dependent on sunlight. The finished composted manure is harvested from the bottom of the bin as we add more fresh manure to the top to keep things tidy in the goat barn. The finished composted manure is used to maintain healthy soil in our food gardens and in the greenhouse.


Solar PV hot water generator.

Solar PV panels produce electricity from the sun and are passed through a PWM MPPT 3kw heat charge controller for maximizing efficiency and allowing us to heat water with an electric hot water heating element without the need for electric batteries. A solar array of 10 panels and the use of this controller will produce enough electricity to heat water even in low-light situations like overcast days. We collect the heat and distribute it to the greenhouse beds through pipes using a thermal siphon and thermal battery system storing and releasing this heat into the greenhouse after the sun has gone down until the morning when the panels can begin producing electricity to heat the water and the process begins again.



Additionally, goats also produce metabolic heat (body heat). A full-size goat can emit between 2-3 hundred BTU per hour. For 6 goats that is a contribution of about a 500-watt space heater to the warmth of the GREEN-BARN.


Some important benefits of this system. No need for expensive batteries that need replacing as they age and require hazardous chemicals and mining practices. No waste from replacing greenhouse plastics ever. Goats produce half the CO2 of cows per kg and the composting of their manure not only adds to the health of soil but also sequesters carbon. The long life of all components and building materials requires minimal input to maintain the systems once it is set up. The solar panels can directly power, without the use of batteries other devices such as vent fans or water pumps during warmer seasons when heating is no longer needed. 


Things are already in the works.

We are hard at work milling lumber in preparation for the construction of the GREEN-BARN. We have sourced an amazing deal on double-glazed tempered glass for the greenhouse and we have already purchased the 10 panels for our solar PV array. We are making final drawings, and reviewing our notes, have our material list ready to go, and are getting very excited.

The barn itself will be constructed from locally harvested trees that we are currently milling ourselves. The metal roof panels and siding we will purchase from a local Amish business that we have had a good experience with and are the best prices around. They fold, rib and cut the metal without the use of electricity. Neat! We are using a combination of both rigid foam panels and earthen building materials we produce on-site to give the structure the insulative properties we need to retain the heat produced. We have a good lead on goats and have sourced some good goat fencing. We will start with a single acre of pasture this year to start us off. We have the land, tools and construction experience needed to make this a reality. 

We shop around, buy used, scavenge, fabricate ourselves, or do without where we can to get the best value where possible. 

Your support helps us purchase the materials we can't scavenge, but are critical to the success of this project. This allows us to focus on putting our labor into completing construction by our fall deadline. 

We hope we have inspired you to think about greenhouse food production in a new and interesting way. Our personal journey through learning and planning has been an exciting adventure and we are very pleased to be able to share it with you.



David and Cassandra

Co-founders of Purple Raven Farm.

bottom of page