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2.1 Review of related works
A renewable energy system, which was designed by some authors, is composed of some renewable sources, and targets a small area such as a village. The system supplies energy to rural area by using renewable sources. The system configuration of renewable energy system varies with site location. Because renewable energy are generally intermittent, it may happen that renewable power is not sufficient to meet the regional demand in some hours. Therefore, the proposed energy system is connected to the distribution grid, and buys electricity as backup whenever the renewable supply is insufficient. In contrast, excess electricity is sold to the electric utilities through the grid.
In their study, they have targeted a local village with a population of 9,000 in Iwate prefecture in northern part of Japan, examining the possibility of installation with four kinds of renewable sources, such as PV, wind electricity, biomass co-generation and geothermal heat pump. These renewable sources are combined with conventional energy systems in which electricity is supplied by the distribution grid, and heat is supplied with petroleum or gas. They have modeled a renewable energy system in rural area using several system modules. The network of the system is shown in figure 1. At the market node which is expressed in the shape of ellipse in figure 1, energy sources at end-users are decided based on the price of energy, and the selected energy is provided to the village. By this means, the most economical energy system will be configured and optimized.
The changes in the quantity of electricity supply are shown in figure. 2. During windy period, the wind generator is running well and the wind electricity constitutes a fairly large portion of total electricity which is supplied to the village. When wind electricity cannot provide enough power to meet the electricity demand, grid electricity will make up for a deficiency. Figure 3 represents the changes in the quantity of electricity supply during wind-less period. The portion of grid electricity is large in the figure, as the production of wind electricity is not sufficient.
The changes in the price of electricity are shown in figure 4. During the windy period, the price of wind electricity hovers around $4,000/MWh, and the price is much lower than that of other power generation. At the electricity market, the lowest price is preferred to supply electricity to consumers. Then the electricity market selects wind electricity as the lowest price, and most of the electricity is provided by wind turbines. However, during wind-less period, the production of wind power goes down and the price of wind electricity rises suddenly because of shortage of wind electricity. If the price of wind electricity becomes higher than that of other power generation, market selects other types of electricity to meet the demand at the village. In our study, alternative power means PV and grid electricity. According to figure 4, the price of PV hovers from 23,500 cents/MWh to 27,500 cents/MWh, while the electricity price of grid electricity shows 23,333 cents/MWh. Under this condition, the electricity market selects grid electricity among alternative electricity. Therefore, in case that wind electricity is in shortage and can’t meet all the electricity demand, grid electricity makes up for a deficiency
2.2 Heat supply
The changes in heat supply produced by different energy sources are shown in figure 5. Geothermal heat pump (GHP) and petroleum are main heat source. Figure 6 represents the changes in heat price. Because the power source of GHP is electricity, the price of heat by GHP is influenced by the electricity price. Compared with the fluctuation of the electricity price, price fluctuation of GHP heat goes along with fluctuation of the electricity price.
In the case of low electricity price, the price of GHP heat is also low. While in the case of high electricity price, the price of GHP heat is also high. During the lower heat price of GHP, the price hovers from 1,000 cents/MWh to 2,000 cents/MWh. Compared with the prices of other heat sources, the price of GHP is the lowest. As a consequence, heat produced by GHP is supplied to the village. On the contrary, when the price of GHP heat is high, the price hovers from 6,000 cents/MWh to 7,000 cents/MWh. Because the price of petrole um heat is 4,728 cents/MWh during that time, the price of GHP heat becomes higher than that of petroleum. Therefore, the heat market selects not GHP but petroleum as a heat source.
Because the prices of other heat sources are higher than petroleum, petroleum is selected as a substitution of GHP by priority. For these reasons, when wind electricity meets all the electricity demand in the village , heat is supplied by GHP, and when the production of wind electricity falls down, petroleum is selected as a heat source.
.2.3 Renewable Energy Development In Nigeria
The use of renewable energy is not new in the country. More than 150 years ago wood supplied most of our energy needs, which is the traditional method of consuming biomass resource.
As the use of coal, petroleum, natural gas expanded and increased, Nigeria became less reliant on wood as an energy source. Today, we are looking again at renewable resources to find new ways of utilizing them to help us meet our domestic energy needs particularly in the electricity sector.(Enugu state Citizens’ , 2009)
Energy, and in particular, oil and gas, has continued to contribute over 70% of Nigeria’s Federal revenue. National development programmes, and security depend largely on these revenue earnings.
Energy, especially crude oil has over the past years contributed an average of about 25%nto Nigeria’s Gross Domestic Product (GPD), representing the highest contributor after crop production. The contribution of energy to GPD is expected to be higher when we take into account renewable energy utilization, which constitutes about 90% of the energy used by the rural population. (A.S Sambo, 2009)
The country is blessed with almost all the renewable energy resources especially solar energy with average sunshine of 5hrs daily(including the rainy season).There are opportunities for small hydro in most of the coastal areas in the southern region of the country.
Beyond the large hydropower capacity, the total contribution of renewable energy in Nigeria’s electricity industry is about 35MW, which consists of small hydropower and about 10MW solar PV representing about 0.12% of total electricity generating capacity in the country. There are still lots of hydro potentials that can be explored especially in the coastal region of the country.
The first independent Power Producer (IPP) in Nigeria was the Nigerian Electricity Supply Company (NESCO),a British-owned company supplying hydroelectricity power to the growing tin mining industry.in 1930,NESCO took over the 2MW hydroelectric power plant at Kwall falls in Plateau State from the Nigerian Power and Tin Fields that had earlier commissioned the plant in 1930.NESCO increased its generating plants to five hydro-electric and one diesel plant serving the tin industry and its environs. The Nigeria utility company, PHCN has taken over the supply to Jos and its environs while the hydroelectric power plant is not well maintained.
In Evboro II, village of Ovia South West Local Government Area in Edo State, a 3KW pico hydro scheme constructed under a culvert by an individual has been in existence. This scheme has for several years served 20 homes in the community.
This is a reference project that serves as call to the local and state government leaders to consider using micro power projects in the state to meet the energy needs of the rural communities and never to rely or wait on the Federal Government for power from the grid.
So far, little has been exploited from the abundant renewable energy resources in the country. Most of the projects carried out by the states are in the areas of solar street lights, solar pumping systems, solar hybrid systems, solar home systems and other solar applications such as refrigerators and solar lanterns. These technologies are deployed in rural communities.
Other technologies include; efficient wood stoves, small hydro schemes in Bauchi, Enugu and Edo state (locally constructed), pilot wind farms and pilot biogas digesters constructed in Sokoto Energy Research Centre of Usman Dan Fodio University of Sokoto State and Mayflower College, Ikene, Ogun state respectively.(Ebonyi State Citizens’ Handbook on Alternative Energy,2009)

Table 2.1: Available Renewable Energy Resources in the Country
S/N Resources Reserve
1 Small Hydro power (provisional) 734MW
2 Fuel Wood 13,071,464 hectares of forestland
3 Animal Waste 61 million tonnes/year (estimated)
4 Crop residue 83 million tonnes/year (estimated)
5 Wind 2- 4 m/s (average)
6 Solar irradiation 3.5-7.0kWh/m2 –day (average)

2.4 Renewable Electricity and Rural Electrification
As the country strives to increase power generation, it is obvious that conventional sources and grid extensions alone will not rapidly achieve the access and expansion targets desired, neither will it be cost-effective. A more reasonable approach would be accelerating rural electrification
coverage. This requires an aggressive deployment of various alternative energy sources to meet the household and commercial power demand in the communities.
The provisions of the Electric Power Sector Reform (EPSR) Act clearly state that the Federal Government will seek to meet national electricity access targets through the following strategies:
i. Grid-based extension for nearby areas;
ii. Independent mini-grids for remote areas with concentrated loads where grid service is not economic or will take many years to come;
iii. Solar Photovoltaic (PV) systems for remote areas with scattere