The Greenhouse as it Stands:
The Greenhouse as it stands today was mainly the result of donor funding. Because of the way that the school goes through the process of development the team at LaFarm found the opportunity to get their greenhouse when they could. Lafayette currently uses Tolino’s Fuel Service to provide the propane for the heating system at LaFarm. Tolino’s charges different rates for different volumes of delivery. The LaFarm system uses a 500 gallon tank for its fuel storage and per safety regulations can only be filled to 80% capacity meaning the maximum it can be filled is 400 gallons. This only falls within two pricing ranges offered by the company; Under 350 gallons at $3.20 per gallon and over 350 gallons at $2.90 per gallon. The output of the current system is 186750 BTUH runs on propane and given the size and temperature the system needs to produce at least 32243200 BTU per month throughout the winter to keep temperatures adequate. With one gallon of propane containing 91,452 BTU it would take roughly 352 gallons a month to operate the heater (EIA 2022). LaFarm plans to use the greenhouse to grow seedlings from late December through February. Given the types of crops that the farmers plan to grow in the green house the average temperature required is 60 degrees (Davidson 1984). Given the low factor of heat loss from the twin wall polycarbonate panels around the greenhouse, heat loss is not a major factor in the cost of any system. With the heating requirement exceeding the limit for the better of Tolino’s rates with the tank being emptied the cost of operating the propane heater is $1,020.80 per month.
| Propane Facts | |
|---|---|
| Gallons per Month | 352 |
| BTU Consumed/month | 32243200 |
| $/Gallon | $2.90 |
| Monthly Cost | $1,020.80 |
Biomass Furnace:
Biomass furnaces can vary greatly in size but based on the temperature we need to keep and the size of the greenhouse the size we would need costs around $19,000 to purchase and install (NREL 2021). These heaters can be used to automatically regulate temperature as well as be manually operated. With the average price of the pellet fuel being $250 a ton and having a BTU content of over 8,000 per pound, that’s half of the minimum heat requirement already met. With the additional heat being provided from the geothermal supplement the cost will be around $250 a month (EIA 2022). With so little in expenses on the operation of this unit a payback analysis shows that savings will have the system paid back within 24 months. While it might take two tons of material to operate it will only cost between $250 and $500 dollars a month to operate. To further cut expenses in the unit, biomass pellets can easily be made at LaFarm. As an additional learning tool for renewable energy processes Lafayette could take steps to making its own fuel. There are also numerous ways to turn bio waste into the pellets for the system, potentially further reducing LaFarms carbon footprint and saving additional costs. As research into biomass continues fuel prices are expected to decrease further.
Geothermal Systems:
Geothermal heating systems are much more expensive than any other option to install but it has very low operating costs. The geothermal system does not require a fuel source like the other options meaning the only costs are electrical. The pump systems that these units use cost $200 a month to operate. These can live up to are expected to still be in operation after 50 years so with an average price of over $30,000 this unit is not small order but with savings of over $1,800 a month and the geothermal systems dual use as a heating and a cooling system it can pay back in around 3 years. Without any excess fuel requirements the power requirements could be easily covered by the solar panels which make up the final part of the alternative plan. The recovery from that cost comes from the constant use of the system’s heating and cooling ability. Without this constant use there’s no telling how long the recovery on this investment would take. Since the greenhouse is to be used as an events space when it’s out of season it should be recovered quickly.
Solar Panels:
Solar expenses have been hard to predict because there is no previous consumption data. The greenhouse has never been used so without knowing how much electricity will be used makes it difficult to make the comparison. Even so, installing solar panels runs an average cost of $16,000 depending on the needs of the system and this is the size that meets the estimations of the greenhouses energy consumption. Solar panels in Pennsylvania have been shown to cost $2.38 per kilowatt. Lafayette’s electric provider Met-Ed charges 10.5¢ per kWh. With the solar array generating 20000 kWh per year which is equivalent to a $2,100 electricity bill. The projected consumption would be 19500 kWh per year meaning that there is an excess of 500 kWh equal to a 52$ credit. This large gap makes the alternative attractive however there are concerns. Given that the greenhouse’s main season of concern is the winter, solar devices do not always perform well. In previous years farmers at LaFarm had difficulty with the consistency of a solar powered monitoring system out in the fields. Given the harsh Pennsylvania winters with lots of snow and heavy clouds, solar is not entirely flawless. The resulting lack of reliability in this case cost the workers at LaFarm a lot of work. To work around this, we could add a solar energy storage system to collect energy during the summer and store it year round. This will allow all the excess power generated during the summer to be turned into further savings through the winter. Typically these large solar batteries will cost $5,000 and store about 12kWh equivalent to about 18 hours of continuous power. Assuming more than one might be needed to ensure electricity never runs out the additional cost would double.
| Solar Analysis | ||||||
| Initial Costs (Array+Batteries) | Life | Electric Rate ($/kWh) | Excess Power (kWh) | Credit | Total Savings | Payback (Years) |
| $ 17,000.00 | 20 | 0.105 | 500 | $ 52.50 | $ 2,152.50 | 7.897793264 |
If the greenhouse does not want to be totally removed from the grid, it could still sell the solar energy back to the electric company through net metering. The standard net metering rate is 11¢ per kWh Depending on the company this could be a great deal considering the greenhouses’ very limited summertime application. This solar array with its additional batteries will take the school about 8 years to pay back.
Review:
| Alternative System | Initial Cost | Life | Operation costs (monthly) | expected savings (monthly) | depreciation | Payback Per (months) | Incentives |
| Geothermal | $30,000 | 30 | $200 (in electrical) | $820.80 | $1,000 | 36.55 | 30% Uncapped Tax Credit
($9,000) |
| Biomass | $19,000 | 25 | $250 (Pellets) | $770.80 | $1,200 | 24.65 | |
The system in place now is by no means a poor economic decision given the circumstances of development. The optimal long-term system would be the biomass heater. It has a moderate upfront cost but with such low operating and maintenance costs it can pay for itself within 5 years given its limited use. Using the existing frame, we could easily install an outdoor heater. If LaFarm begins to produce its own biomass it could cut costs even further. Geothermal is a huge forward looking technology. Having such a sustainable technology can serve as proof of feasibility for use across the campus to help with the climate action plan. The upfront cost while high is mitigated but the year round use potential of the greenhouse allows it to be economically viable as a test. Solar is very effective and has a few options to connect with the grid or make the greenhouse totally independent. The power requirements here are not expected to be great meaning that this might even be negligible unless the power is sold back to the grid.
To read the conclusion to this work, please follow the link here.