Let’s say we have a river able to generate 100 kW. In a 24 hour period, it produces 100 * 24 = 2,400 kWh. Let’s also say that we have a total daily demand of 2,400 KWH, but it is not evenly spread out: for 16 of the 24 hours, it averages 50 KWh, and for the remaining 8 hours it averages 200 KWh.
If we just throttle the turbine back (typical control method) to 50% of its capacity during the off-peak 16 hour period, we will have just dumped 800 KWh, and will then have to have some other source of energy (solar? wind? diesel?) to make up the extra 100 KWh during the 8 hour peak period. If the river is the ‘fuel’, we will have wasted a full third of it. My first obvious thought was to add enough battery capacity to store the excess during off-peak. But then the questions of cost, comparison between different storage technologies, balance between storage and generation, etc. arise.
Problem # 2
The sun shines and the wind blows unevenly throughout the day and throughout the year. (See distribution pattern). The peaks and valleys do not coincide with the usage peaks and valleys. The challenge is to find the most cost effective, environmentally benign, sustainable and efficient way to store the energy when the supply exceeds the demand, for use when the demand exceeds the supply. This storage can take many forms, and addresses both problems.
Each cluster of 8-10 homes will be grouped around a centrally located “Waste to Energy Center”, or ‘holon‘. Each holon will include electric generation capacity sized to supply 8-10 homes designed to use an average of 7 kWh/day, or 200 kWh/month.
The center consisting of a simple pole building with a sheet metal roof covered with solar panels and housing batteries, switch gear and a diesel generator.
Solar PV on roof
Central composter (a place to empty humanure and kitchen scraps from household toilets)
Walk-in cooler and freezer with lockers
Initially — until the hydroelectric system is brought online — energy sources will include only solar PV and diesel generators.
OMV Phase II construction will include the following:
All lighting will be CFL or LED. No incandescent lighting. (Low Cost Option: Select fixtures to take CFL or LED, initially install CFL, replace them over time as they fail with LED. With time costs come down, reliability goes up. Also use good lighting design, ambient and task lighting (e.g. focused under cabinet lighting, etc) for maximum effectiveness
. Circuit includes selected LED or CFL lighting, refrigerator (if efficient enough), computer, TV, etc.) See also this UPS comparison guide.
Install more efficient and more environment-friendly air conditioners. An air conditioner with VFD (variable frequency drive) condensing unit, uses R134a or R410a refrigerant which is more ozone friendly than R22. The condensing unit modulates to meet demand instead of on/off, so is more efficient. Replacing the Air-Pro units currently installed in Villas could have a possible 2 yr payback. Read more…
Note that these energy measures are not just additive, but multiplicative. Every watt of electricity consumed in the space (whether from appliances, computers, lighting, water heating or air movement) ultimately ends up as waste heat — which further adds to the AC load. More efficiency in each saves you twice. If done well enough, you can even save on capital costs — e.g. by eliminating the need for AC unit entirely. The more of these measures that are implemented, the higher the percentage of the total load that can be done with renewable energy. Getting to 100% is the definition of ‘sustainable’.
The farm is located near Costanera km 171. Owner is Tom Nigel. The stream appears to be smaller than SGEV Rio Aguila, but higher head is available – about 100 M vs 50 at SGEV. The upper 55 meters is … Continue reading →
The community will not be connected to the electric utility grid.
The property includes multiple potential sources of renewable energy including a river with significant hydroelectric potential, solar, biomass and wind. We are currently in the process of assessing each of these resources – both the amount of energy available from each, and the cost to develop it.
The current estimate, as of January 2013, is that the combined capacity of micro-hydro and solar PV alone will be able to supply 100% of the demand, at an average per household consumption of 6-7 KWH/day or 200 KWH/month. This is based on an assumed average of 2 KW of solar PV panels per household, plus 50 KW from the river. Hydro will dominate in the rainy season, solar in the dry season.
6-7 kWh/day is generally considered adequate to supply the basic needs of a well-designed, small, efficient home in the tropics. (To understand what this actually means, an online calculator is available at http://biorealis.com/SGEV. Users can plug in their own estimates of expected or desired daily use, and see how many panels would be required to supply the demand. The tool can also be used to estimate the percentage of the total demand supplied by each resource.
Various interconnection schemes are being evaluated, each with its pros & cons. The simplest and most straightforward off-grid system – but also the most costly and least efficient – would be for everyone to have their own stand-alone system with solar panels and batteries, and then be hooked up to the centralized system for supplementary battery charging. Estimated cost for this type of system is about $4-5 per watt, or $8-$10,000 for a nominal 2 KW system. (Estimate assumes quality components, professional installation and quantity purchase discounts. Market prices continue to change rapidly.)
A much better interconnection method would be an AC-coupled mini-grid, (as described in video at http://biorealis.com/OMV/deeptech/?p=1001). In this scheme, fewer panels and batteries would need to be purchased, and they would be installed in fewer, larger arrays, rather than on each house. This system can provide the same amount of power at lower cost because it has fewer parts, the panel arrays can be more optimally placed, and it allows more efficient use of the energy available. It can also be easily added onto as demand increases.
The primary gain in efficiency derives from being able to move electricity around the grid from where it is produced to where it is needed, as both supply and demand fluctuate. In the first scheme above, this isn’t possible. For example, on a house that the sun is shining on but where no one is home (maybe even for weeks or months?), any excess energy (after the batteries are fully charged) cannot be fed back into the grid. It will just be wasted.
Usage charges will be applied to cover operating and maintenance costs. As the system will be owned and operated by, and solely for the benefit of the community, usage charges will be set by actual cost of production. With solar and micro-hydro alone, these costs will be nominal, consisting primarily of labor cost to cover maintenance and repairs. If or when a diesel generator is added to the mix, there will also be fuel costs. Fuel crops have been planted on the property to offset these costs. (See http://biorealis.com/OMV/deeptech/?p=381 for details.)
It would be prohibitively expensive to build a system that could supply as much electricity as anyone ever wanted to use, so the supply to each home will be limited – both the instantaneous power draw (kW) and the total daily energy usage (kWh). A sophisticated metering system will be needed to regulate that usage. Appropriate products are being researched and evaluated (e.g. http://www.ekmmetering.com/).
Members will be required to provide their own power (e.g. onsite solar panels, wind turbine, small, low-decibel generator, etc.) to meet the demand for any usage above and beyond the capacity of the centralized system.
Efficiency is primary! Low wattage lighting (LED or CFL) and fans, low energy use refrigerators and gas stoves are mandatory. ”Tico” washing machines are encouraged, with clothes lines for drying clothes. Air conditioners will not be allowed to be connected to the mini-grid (nor are they considered necessary for a well-designed house at this altitude.) House plans are available that incorporate natural ventilation by way of cupola, roof monitor, or clerestory, interacting with well-placed operable windows and doors.
Clause 4 – Water Supply and Wastewater Collection
A potable water line will be plumbed to each home site.
Members are also encouraged to install onsite rainwater catchment systems – rain gutters, storage tank and filtration system. The goal is to not only supplement the centralized water system, but to provide redundancy and a measure of local self-reliance in keeping with the mission statement.
A centralized sewer system will not be provided. Each house will have either a standard Costa Rican ‘biodigestor’ (septic tank) or a composting toilet (recommended). It is also recommended that graywater be treated onsite to a quality suitable for reuse for secondary uses (e.g. irrigation). To learn more about the benefits of urine separation and dry composting toilets, see http://biorealis.com/OMV/deeptech/?p=1209. They conserve both water and valuable nutrients, in keeping with the mission statement.
Food Waste – All organic food waste will be composted or digested as part of the integrated food production system.
All Members must participate in the Recycling and Reclamation Program. Residents should have a composting bin for food waste and any other compostable materials, along with recycling bins for crushed metal cans, glass and plastic bottles and/or containers. Members must take recyclable materials to the designated recycled waste collection site located at the main reception/parking area.
“Toast, waffles, or pancakes: Off-grid living means not that we go without the energy that we need, but that we live more in tune with the natural rhythms around us.
“Living well on a small and finite amount of electricity is not mysterious or difficult. It starts with careful adherence to three basic principles:
Shift inappropriate loads to other forms of energy.
Reduce waste through efficiency, and increase conservation.
Use energy in proportion to the amount available.
“All forms of energy are not created equal. Electricity is a specialized, high-quality form that is not suited to all applications but great for some: lights, electronics, and motors, plus a few other specialized uses. By matching the best form of energy to its appropriate use, electricity consumption can be greatly reduced while enhancing comfort and convenience.
“Efficiency is always the first step in reducing consumption. Efficiency expert Amory Lovins of the Rocky Mountain Institute calls this “negawatts”—energy not consumed is energy that does not need to be produced. A good guideline is that for every dollar spent on upgrading efficiency, about $3 to $5 can be saved on PV system costs.
Update 6/12/2113 — thanks to Tim O’neill. Add links to freezer to refrigerator conversion how-to. Following up on the above quote that “…energy not consumed is energy that does not need to be produced.” here is a cool [no pun] idea for how to convert a chest type freezer to a refrigerator. It saves energy because (1) freezers are better insulated, and (2) the cold air doesn’t fall out of the top-opening box when the lid is opened. Simply plug it into a thermostat set at a higher internal temperature (lower delta tee) so it doesn’t run as often.
Two versions of urine separating toilets: One inexpensive, simple, DIY, the other more expensive (but still a heck of a lot cheaper than a flush toilet with conventional septic tank and leach field, etc.). This is more of a ‘finished’ product, maybe more acceptable to US tastes, and higher perceived value. Both involve a greater understanding and dealing with our own wastes…
An interesting very simple home batch digester design from Open Source Biotecture in Nepal: (One question: why is the truck inner tube in a barrel with water? What happens to the water when the bag fills and empties?