Overview

Scalability

Grid power is scalable and supplied in units of one thousand watt hours. Additional kilowatt hours (kWh) of electrical energy can be supplied at a decreasing cost. Mini-grid power is less scalable but can be a stepping stone towards grid power. Off-grid power is inherently unscalable and supplied in units of Watt hours (Wh - one thousandth of a kilowatt hour). More off-grid power costs as much per Watt hour as the initial small amount, which stunts development. A grid is like a pipeline while using batteries for off-grid power is like carrying buckets. Once you have a pipe you can just turn on the tap for longer to get more water, but until then if you want more water you have to carry more or heavier buckets and sometimes from further away.

Nevertheless until the pipes can be built, one still has to drink. When forced to use buckets while building a pipeline an important issue is how long they will be used for. If the pipeline will be completed soon, the buckets should either be of a  type that will remain useful for other purposes or should be as cheap as possible because they will be discarded soon.

Generally speaking solar panels will become useless when connection to the grid is established. So the investment or capital expenditure (capex) has to be amortized over that shorter period, not over longer lifetime of the panel.

Diesel generators will remain of some (reduced) value for standby power because the initial arrival of the grid may be unreliable (there are less redundant connections at the periphery of a grid so a single point of failure can still cut off power).

Smaller portable generators (usually petrol or kerosine) will not last as long as diesel or solar generators, but will lose less of their value when the grid arrives since they remain useful for portable tools etc as well as for standby power.

Even the smallest portable generator, say 300 W, used optimally, might be run for say 2 hours per day, producing 600 Wh per day. If the local effective demand is much less than that, it may be cheaper to use solar.

The exact threshold depends on many factors and requires careful calculation.

Unfortunately the most readily available calculators are provided by the advocates of "sustainable development" and mainly oriented towards reducing greenhouse gas emissions.

An extensive collection of Interactive Energy Calculators

is supplied by the US State of Texas (the oil state). The mentality involved is summarized in these excerpts:

Carbon Pollution Calculator	Each time you drive your car, hop on a plane, flick on a light, or consume energy in other ways, you may be contributing in a small way to global warming. This worksheet allows you to tally up your own personal "carbon production scorecard."
Electric Power Pollution Calculator	Generating electricity also results in the production of air pollution. Use this calculator to find out how much you pollute based on your electric power use and the type of fuel your utility burns.

 

Nevertheless, there may be valuable technical information on off-grid technologies among that collection.

NGOs often promote "sustainable development", ie development projects that will remain in existence for a long time and generate further requirements for consultancy work.

Aid agencies prefer to fund "replicable projects", ie projects which can be repeated at other places so that the overhead costs of the agency in sponsoring pilot projects that mainly benefit NGOs and a relatively small group of beneficiaries can be spread more widely and enable the operations of the Aid agency to scale and grow with the market for aiding underdevelopment.

For scalable development it is necessary to thoroughly understand the helpful advice given on how to maintain and replicate underdevelopment, critically assimilate the valuable data, and transform it into a new synthesis.

Battery technology is critical here. Portable batteries and chargers for filling them will still remain useful after the grid arrives. In areas with dispersed settlement patterns it will take much longer for the grid treach individual households (or for the households to move to more rational patterns of settlement) so batteries will still have to be used for transport of  electrical energy to homes even when the battery chargers are supplied by cheaper grid power at a local supply center such as a school within walking distance.

In urbanized areas with grid power, rechargeable batteries are used for portability and owned by the consumer together with a battery charger for charging overnight by simply plugging in to an AC power point. Optimal charging efficiency and battery life time is not critical to consumers because the costs are insignificant. Suppliers do not promote information about these issues because they have no interest in undermining the market for non-rechargeable dry cells marketed by the same "brands".

A different ownership model, possibly including metered charging of battery packs, may be applicable to transitional off-grid use of rechargeable batteries. Detailed models of the interactions between battery life cycle throughput, charging efficiency and generator maintenance and fuel costs depending on load factor will certainly be needed for planning installations.

Charger manufacturers have an interest in promoting more expensive chargers, that may also use the power supplied less efficiency (which doesn't matter when grid power is available). Some possibly valuable information on optimizing NiMH lifecycle battery throughput can be found in this user's manual for the Powerex MH-C 900 charger.

Homer

HOMER is a computer model that simplifies the task of evaluating design options for both off-grid and grid-connected power systems for remote, stand-alone, and distributed generation (DG) applications. HOMER's optimization and sensitivity analysis algorithms allow you to evaluate the economic and technical feasibility of a large number of technology options and to account for variation in technology costs and energy resource availability. HOMER models both conventional and renewable energy technologies:

Power sources: •  solar photovoltaic (PV) •  wind turbine •  run-of-river hydro power •  generator: diesel, gasoline, biogas, alternative and custom fuels, cofired •  electric utility grid •  microturbine •  fuel cell

Storage: •  battery bank •  hydrogen   Loads: •  daily profiles with seasonal variation •  deferrable (water pumping, refrigeration) •  thermal (space heating, crop drying) •  efficiency measures

 

Problem

1. This model assumes lead acid battery bank storage and does not provide analysis of capex and opex for small battery charging stations with multi-chtannel  charging of portable cells and battery packs (with or without supplementary lead acid storage) fo local transport of NiMH, LiFePO4 or small Sealed Lead Acid for households only able to afford White LED lighting and radio broadcasts etc or having to resort to pedal power.

 

2. Although freely available, software is closed source windows only and requires registration renewals. Need a transparent open source model with cross platform implementation in python that can also dump to spreadsheets and use an SQL alchemy backend database for parameters. Cross platform uses include web server, OLPC activity and Android cell phone (so use Jython compatible subset of cPython).

 

Multichannel Charger

OLPC has designed a flexible multi channel battery charger that works with either generator or solar with:

• Approximately 2 hours for complete charge
  • Maximum number of simultaneous charging channels
    • 15 Batteries on AC
    • 10 Batteries via 150W DC source
    • 8 Batteries via 2 60W solar blankets
    • 4 Batteries via 1 60W blanket

 Specifically for 22 Wh, 0.2 kg 6.7 V LiFePO4 batteries used by XO (2 x 3.3 V cells from BYD).

Page has links to tech specs of chips used in battery packs and charger and (forth) software that includes battery charging model. Also supports alternative XO battery packs (5 x NiMH 1.2  V). Discussion page also links to others involved.

OLPC people working on this should be a major source of valuable info (but obviously very busy).

Nepal

Lots more about batteries, solar lanterns, improved water mills etc is currently mislocated in subfolders under Nepal/Stakeholders. Lots more offline but no time to add at the moment. Check back.

Vipor

ViPOR

is an optimization model for designing village electrification systems. Given a map of a village and some information about load sizes and equipment costs, ViPOR decides which houses should be powered by isolated power systems (like solar home systems) and which should be included in a centralized distribution grid. The distribution grid is optimally designed with consideration of local terrain.

 Similar problems to Homer, with even more blatant bias towards renewables.

 Wiki

 A hopefully more accessible space has been provided for discussion at http://universalcommunication.wikispaces.com/